PPL Theory

• Flight Planning & Performance (FPP)
• Meteorology (MET)
• Human Performance & Limitations (HPL)
• Law and Operational Procedures (LAW)
• Communication (COM)
• Navigation (NAV)
• Principles of Flight (POF)
• Aircraft General Knowledge (AGK)

Flight Planning & Performance (FPP)

Introduction to Flight Planning and Performance (FPP) (1)

Before we step into an airplane we are required to know the aircraft performance in our particular situation. We can ask ourselves questions like:

• How much runway distance do we need for take-off and landing?
• How long does our climb phase take to our cruising altitude?
• What will our cruising speed?
• What will be our fuel usage?
• What will be our gliding distance?

Now these are not questions we will guess or something but we carefully calculate using numbers and graphs from the pilot operating handbook (POH) of our particular plane type.

In this module we will dive deeper in these questions and look at how we can make these calculations.

Air density

The air density is a unit of how much air molecules a certain part of the air contains. We will pronounce this as kg/m³. In the International Standard Atmosphere which is the baseline reference for our pilots, the definition of this is at mean sea level that one cubical meter air (1000 liters) weighs 1,225 kilograms. So 1,225 kg/m³.

Air density is determined by a few factors like air pressure and temperature and derives from the general gas equation:

• Air Pressure (P): the air pressure in Pa (hPa x 100)
• Gas constant (R): this is a ratio between pressure, density and temperature. We mostly use the number 287 for this, the ratio for dry air.
• Air temperature (T): the air temperature at your airfield or cruising altitude in Kelvin, which is degrees celsius + 273.

Density (ρ) = P / (R x T)

An example calculation using todays numbers:

• Pressure: 1010 hPa x 100 = 101000 Pa
• Gas constant: 287
• Air temperature: 18 degrees celcius + 273 = 291

101000 : (287 x 291) = 1,209 kg/m³

This tells us that today the air is less dense than ISA, meaning we can expect worse aircraft performance. A result of the less density is the higher temperature (18 degrees instead of 15 according to ISA).

Density Altitude

To make this calculation somewhat easier for pilots to make, we have something called the Density Altitude. This is an altitude indication of how your aircraft will perform according to ISA. This makes these calculations much easier as we talk in altitudes instead of density like 1,225kg/m³. For example, if the density altitude is 3000ft we can expect performance as we are on 3000ft. This doesn’t mean we are actually on that altitude but is the altitude corrected for the actual air density.

Every 1c degree deviation of ISA temperature, we take 120ft as rule of thumb. If the air is colder than ISA this is a negative number, resulting in a lower altitude as the air is more dense. To calculate the density altitude we use the following formula:

Pressure altitude + (ISA DEV x 120) =

In the Netherlands, this density altitude often doesn’t make huge differences, but in countries with high elevations this can make huge differences in flight performance. Especially if you don’t take it into account. Let’s make up an example of Sedona Airport in the USA, the training airport when playing Microsoft Flight Simulator.

As this airport has an elevation of 4825 ft, we are a huge portion away from sea level. The airport also is in the rocky mountains range making the temperatures huge.

To calculate density altitude, we need the pressure altitude first. This is the “ISA” altitude corrected for active air pressure. This is 4825 - 150ft = 4675 ft. As we have 5 hPa higher air pressure than ISA this is a little win. Now the density altitude.

37 degrees - 15 = 22 degrees of ISA deviation.

4675 + (22 x 120) = 7.315 ft Density altitude, which is almost 3.000ft higher

Mass and Balance (2)

https://flighttools.justinverstijnen.nl/unitcalculator https://flighttools.justinverstijnen.nl/unitcalculator https://flighttools.justinverstijnen.nl/unitcalculator https://flighttools.justinverstijnen.nl/unitcalculator

The weight of an aircraft is a key factor to determine the flying performances. With the weight, we can calculate almost every V speed and the distance required for climb, take-off and landing. An aircraft is designed to operate in a specific weight range because exceeding this would result in unflyable planes with performance and controls not working as intended.

The key point here are:

• Mass: The weight force, at 1G this is equal to the weight but increases or decreases if G forces do
• Balance: The center of gravity point which must lie within limits

Why calculating Mass and Balance is being so important is partly described in this video, where the center of gravity of the plane shifted fatally to the aft part of the plane: https://www.youtube.com/watch?v=hvZEr3IkLJI

As mass and weight are mostly the same (if not talking about G forces), I continue to use the word weight.

Weight limits

We have two primary reasons why planes have maximum weights where they are certified for:

• Structural limits: An increase of weight means the planes’ stressing factor is also increased, like the design-load.
• Performance limits: The performance of planes are heavily dependent on the weight, like take-off and landing distances but also the V speeds like stall speed, best climb speed, glide speed etc.

Aircraft manufacturers use these terms to indicate the limits of weight for their aircrafts:

Exceeding these weights will result in the plane being classified as un-airworthy.

When performing fuel and weight calculations and realising that we cannot take-off from a runway with a certain mass, you must re-do your calculations in terms of weight and fuel. To lower the amount of runway needed, you need to decrease the weight.

Determining the weight

To determine an aircrafts weight, we have to calculate the actual weight of an aircraft. This is basically a sum of all known weights.

The sum of all those weights give us the actual of gross weight and will decrease during flight as the fuel is being consumed.

Fuel weight

We calculate the weight of the fuel in our plane by picking default numbers based on the fuel we use. This is based on fuel density where we calculate the volume multiplied by density:

• Density of AVGAS/MOGAS/Car gasoline - 0,72kg/liter or 6lg/USG
• Density of Jet-A1: 0,84kg/liter or 7lb/USG

And we can use these numbers for conversion:

• 1 Pound (lb): 0,4536 kg
• 1 US gallon: 3,785 liter
• 1 Imperial gallon: 4,546 liter
• 1 quart (qt) = 0,95 liter (a quarter gallon)

Tip: use my Unit conversion tool https://flighttools.justinverstijnen.nl/unitcalculator

Fuel terms

To calculate fuel, we have different categories where we use different parts of fuel. We must have enough fuel on board for the complete flight, possible diversion and even more than that. As fuel calculations are very important we determine the amount using these terms:

We base the forseen fuel consumption on the numbers of the pilot operating handbook.

Center of Gravity

The center of gravity (CG) is the central point of the gravity force. This point must be between the boundaries of the plane, as this has effect on the aircrafts performance. This center of gravity in general aviation aircraft is often determined in numbers of inches from a reference point. This reference point is called the “datum”. The reference point are mostly:

• The firewall (wall between engine and cockpit)
• Forward point of the fuselage/propellor
• Wing leading edge

The pilot operating handbook will describe what the datum of your particular plane is. This point must be the same for that same aircraft at all flights.

Here I created a mass and balance sheet for a Cessna 172 in my second flight lesson, fully within the technical limits of the aircraft.

• Normal category flights must stay within the red lines
• Utility/aerobatic flights must stay within the grey dotted lines

This states what the forward and after limits of the plane are in terms of center of gravity and how much weight we may carry. The whole flight, your weight and balance must be within the performance envelopes. This is the red area on the graph above.

To calculate the mass and balance, note all weights like done in the picture above and lookup the CG locations of your plane in the POH. Then its simply a multiply-sum where the weight must be multiplied by the CG location which gives the moment-number -> the resulting turning effect. Always use a method with a table and graphic to be sure about your aircrafts limits.

Weight, Arm and Moment

To determine the center of gravity the moments are very important. We will talk about this three terms here:

• Weight: The force applied by an object due to its mass and gravity
• Arm: The distance from the reference point or pivot point to the line of action of the force
• Moment: The resulting turning effect produced by a force acting at a distance from a reference point or pivot point

Arm and moment in picture.

During the flight, the center of gravity always will shift somewhat because of thefuel consumption. This effect can be bigger when the tanks are further away from the center of gravity. When having wingtanks, this effect is small but be aware to stay within the envelope of the mass and balance scheme. This is also the reason we always calculate the zero fuel weight.

Take-off and landing performances (3)

Calculating take-off and landing performances is crucial to us pilots as we want to know if we can land on a particular airport and runway with particular circumstances. To overcome shortage of runway, we calculate the distance we need according to the numbers in the POH. As the weather is never completely the same, we use the International Standard Atmosphere as reference point.

Take-off distances

The take-off consists of 2 different phases:

• Take-off run/Ground roll: The first part where we power the engines to create enough speed and lift to get of the ground.
• Initial climb: The first climbing phase where we need to clear an altitude above the ground (AGL) of 50 ft or 15 meters.

In the middle of the whole take-off we have Vr speed which we start rotating to get in the air. This is the aircrafts’ designed speed when taking-off is possible. We also know a Vlof speed which is the speed the plane comes loose of the ground, which is mostly close to Vr speed. We use this speed often in soft field take-offs to quickly get off the ground and win speed using ground effect.

Available take-off runway lengths

Determining the take-off performance is part of flight preparation. The needed distances must fit within the available distances at that time. We use three different terms to indicate the available runway length:

• Take-off run available (TORA): The distance available for the the take-off run.
• Take-off distance available (TODA): The distance available for the take-off run and climb to 50ft.
• Accelerate-stop distance available (ASDA): The distance available for a rejected take-off.

In the most simple cases, these three values are exactly the same, but this is not always the case.

Stopway and Clearway

Much airports around the world have additions to the runways for safety and ease of use. The 2 categories are:

• Stopway : A paved (verhard) addition to the runway only used for rejected take-offs (ASDA)

  • Sometimes on bigger airports this contains EMAS.
  • TORA + Stopway = ASDA

• Clearway : A clear-of-objects addition to the runway which can only be used for the climb to 50ft (TODA). This can also be sand or even water.

Sometimes, the stopway and clearway are combined as the image below states.

Landing distances

We devide the landing phase into two phases:

• Airborne distance: This starts at a distance of 50ft above the runway till touchdown
• Landing ground roll: Begining from touchdown all the way till the plane has come to a complete stop

The landing distance is therefore calculated starting from that 50ft point all the way till the end of the ground roll. The landing distance available (LDA) is the distance from runway threshold till the end of the runway which can be found in the AIP. Some airports have a displaced threshold where the runway doesnt start at the beginning of the runway material.

The part before the threshold can be used for the take-off but not for landing. This does also count for a stopway and clearway.

Take-off and landing distance factors

https://flightblog.justinverstijnen.nl/ppl-theory-fpp/#density-altitude

There are multiple factors influencing the take-off and landing distances which are:

• Weight (Take-off weight)
• Wind
• Density altitude (density of the air, Dense = more lift)
• Approach-speed (landings)
• Runway state (Dry, Damp, Wet or Contaminated)
• Runway slope
• Flaperons (Flaps)

Weight (Take-off weight)

An increase of weight requires us to make more speed, therefore increasing the take-off distance. As the weight factor increases, we also need to produce more lift and also requiring in a higher speed (Vlof). You can find the impact of weight on the take-off distances in the POH.

A rule of thumb we can use in general aviation aircraft is: an increase of 10% weight extends the required distance with 20%.

When landing, the weight will also increase our landing distance. More weight means a longer distance to stop that kinectic energy. More weight sometimes results in a higher approach speed. When landing after a flight, we have less fuel so also less weight. This lowers the gross weight. A good best practice is to use the take-off weight for your landing calculation, so you calculate with the numbers from the start.

Wind

The wind also is a major factor in take-off distances. As an aircraft uses air masses to fly through, we get more of that air by flying into the wind, having Headwind. Therefore increasing our TAS and decreasing ground speed, resulting in needing less take-off distance.

• Headwind -> less ground speed: Decreases take-off and landing distances
• Tailwind -> more ground speed: Increases take-off and landing distances

To give an indication of the differences check out the picture below, altough with headwind we will be able to reach a much steeper climb:

Density altitude

The density of the air is also an important factor of the take-off and landing distance required. As we know, the density of the air is a factor in the lift formula:

• Lift = 1/2 ρ V² CL S

The Rho (ρ) describes the density of the air. Altough the Rho and Airspeed are somewhat related as they both are in this formula:

• If density (ρ) decreases, Airspeed (V) must increase
• If density (ρ) increases, Airspeed (V) can decrease

Factors which influence the Density altitude and so our distances, which can obviously be a combined factor:

• High temperatures, warm air expands having less room for air molecules per m³
• Low air pressures due to high elevation or low pressure areas

In general aviation aircraft, the pressure altitude is enough as the tables and graphics in POH’s already contain this correction for temperature.

Approach Speed

The approach speed is often referred as the stall-speed multiplied by 1,3. In some cases we need a higher approach speed than normal, like when having more weight, flapless landing or weather conditions like gusting winds.

Runway state

The state of the runway is also an important factor for our required distances. The state is determined by three parameters:

• Runway material: Paved, Grass, Sand etc.
• Runway contamination: Dry, Damp, Wet and Contaminated
• Runway action: Number between 1 and 6 where pilots determine the brake-action score

As the surface of course is also a factor on our total needed distance for take-off and landing. A grass runway has a longer ground-roll than a asphalt runway for example.

Slope

A slope in the runway, especially in mountain-rich area’s is also a major factor in take-off and landing performance. This slope is described in a percentage. This percentage is based on the difference between elevation of the threshold and end, divided by the runway length multiplied by 100. If this is a difference of more than 2 percent, this will be mentioned on the airport-charts and AIP.

Taking off while going up on the slope results in a slower take-off needing more of the distance. Taking off downslope results in a shorter distance as gravity will help us gaining speed.

Flaperons (Flaps)

When performing short-field or soft field take-offs, flaps are recommended to use. Flaps increase lift, needing less runway for lifting off. This also decreases our ground roll, but increases some drag on our plane. This will result in a less steep climb-out and slower climb speed. We mostly retract them at around 200ft AGL.

Track and Crosswind components

Winds can be divided into two different components when flying an aircraft:

• Track wind component: The wind directly on your track (wind is determined from the source)
• Crosswind component: The wind that comes from the sides, setting you on a different track

Sine and Cosine

The sine and cosine are trigonometric functions to calculate a value of an angle.

• Cosine (X) represents the horizontal side of the angle divided by the hypotenuse
• Sine (Y) represents the vertical side of the angle divided by the hypotenuse

In aviation we mostly use the much easier version described above, but now you have seen the theory about these two functions.

Calculating Take-off and landing distances based on tables

To calculate and determine our take-off and landing distances, we need the numbers from the pilot operating handbook (POH) of the plane. Hiere all numbers are described in the two phases of take-offs and landings:

• Ground roll
• 50ft off the runway before landing or while climbing

For all of those calculations the numbers in the POH are the base numbers, or minimum required in best conditions based on the actual pressure altitude according to ISA and a selected temperature. On top of those numbers we add factors like described, which can look like these:

Take-off

This prevents discovering at 45 knots that the runway is too short. Worst‑case thinking is essential.

Landing

As we can see, much factors can determine the distances and basic required is almost never possible. However, these are summed up easily and including all factors while POH’s will offer you tables like these:

Calculating take-off distances based on graphs

A skill we need to posess is calculating take-off distances using these graphs. An example can be found here:

The variables used are:

• Runway temperature: 25°C
• Airfield elevation: 2500 ft
  • Pressure altitude: 2041 ft
  • Density altitude: 3731 ft
• QNH: 1030 hPa
• Headwind: 5 KT
• Take-off weight: 2150 lb
• Flaps: 25 degrees

We start at the left, co-relating the temperature to the pressure altitude. This corrects the pressure altitude to the actual outside temperature (hey the Density altitude). Then we shift from there in a straight line to the weight coloumn. We pick the first line there and follow that to the actual weight. Then from that weight we set a straight line to the wind component. As we have 5 knots headwind, our take-off distance will be decreased so the line has to go down. We join the first downward line to take some margin into account, leaving us with a total take-off distance of 1640ft which is 500 meters.

You can also parralel the lines but this approach gives us some extra margin.

Performance during cruise (4)

During the cruise phase, which means we are flying horizontal and level flight with constant speed, all forces of flight are in balance:

• Lift equals weight (L=W)
• Thrust equals drag (T=D)

Added to these forces is the first law of Newton, stating that an item which contains no net force, will be still or in a one-pairing movement.

Lift and weight have different application points. Lift on the pressure point of the wings and weight on the center of gravity. However, lift and weight are a pair of forces, causing the plane to be nose-heavy. This pair is compensated by the tail-heavy pair thrust and drag. The sum of the force-pair must be 0, which results in a horizontal and level flight. However in practice, there is not a complete balance between the forces. The remaining pair is compensated by the horizontal stabilizer.

Flight performances

To determine flight performances we have multiple definitions available which all have their own meaning:

• Endurance: The time which a plane can be in the air with the available fuel (duration), meaning we fly at the lowest fuel usage per hour and at low RPM
  • To fly for max endurance, fly V max endurance
• Range: The distance which a plane can fly with the avialble fuel (distance), meaning we fly at the lowest fuel usage per kilometer/mile.
  • To fly for max range, fly V max range
• Radius of action (Actieradius): The distance the plane can fly with the fuel and also return back to the starting point

Cruising performance factors

The cruising performance of an aircraft is determined by factors like:

• Wind
• Flaps
• Weight and Balance
• Altitude
• Outside Air Temperature

Wind

The wind will only affect the range, not the duration of the flight. As we know the E6B flight computer by now, we now that when wind comes from behind, the wind helps us get to the destination faster and headwind will slow us down:

• Ground speed = TAS + tailwind (lower Vmax range)
• Ground speed = TAS - headwind (higher Vmax range)

If we want to fly max range, we must fly with tailwind. This brings us further on the chart. If flying both A–B and B–A routes, the negative effect of headwind is greater than the positive effect of tailwind.

Flaps

Flaps increase the parasite drag and require more engine RPM, decreasing the range and endurance. We mostly will not use flaps in cruising conditions.

Weight and Balance

The weight and balance will influence the endurance and range in their own ways:

• More weight means needing more lift, also needing a higher AoA but this will also increase induced drag and ultimately needs more thrust to counter-act
• A frontal center of gravity must be compensated by the horizontal stabilizer by a downward lift-force. This must be counter-acted by more lift on the wings, increasing drag, increasing thrust
• A AFT center of gravity will result in less drag and needing less thrust

Air density

At higher altitudes, we have less air density. However, we need more engine RPM to fly with less air density. Less air density also means less air molecules hitting your wings and less lifting force. We must have more true airspeed (TAS) to compensate for this and this will cost more engine RPM.

Performance calculations

To make a navigation-plan we must calculate the needed fuel consumption including cruise speeds in TAS. In the POH of the aircraft you can find tables, telling you exactly the fuel consumption in different scenarios which you can use for the calculation.

The biggest factors are:

• Density altitude (pressure altitude + temperature factor)
• Engine RPM setting
• Manifold pressure in constant speed propellor planes

Then we reference the tables in the POH for the actual numbers. Some general rules and guidelines to use these tables for your calculations:

1. Pick numbers between altitudes/temperatures if actual numbers are not available
2. Expect worse than needed
3. Round off to the worse side rather than to the best side
4. The BHP is the gross crank-shaft power

Fixed Pitch propellor

For Fixed-pitch propellor planes like the Cessna 172, this table looks like this:

Let’s dive deeper into how to use this table for your fuel caulculation:

Constant speed propellor

For Constant speed propellor planes like the Cessna 208 Grand Caravan, this table looks like this:

Let’s dive deeper into how to use this table for your fuel caulculation:

You see, sometimes we must interpolate the numbers on the scale or pick the worse numbers for the overview.

Performance during climb and glide (5)

During a straight climbing flight with a constant speed, we have a balance in forces. The weight of the plane is always vertically pointed to the middle point of the earth. The lift-force always points perpendicular to the incoming air flow and up into the air. Higher pitch also means a tilted lift force.

In climbing flights we have a split into two weight components:

• L=G1
• T=D+G2

During climb the lift is smaller than the weight, because G1 is less than G. This lift shortage is compensated due to the thrust is slightly upward, adding a vertical component. This added upward component results in needing some less lift.

The thrust factor must not only compensate the drag but also a part of the weight. The weight also go a component on the longitudal axis in the same direction of the drag force.

Climb performance

The performance must be determined according to two criteria:

• Climb angle: This is the angle in degrees of how steep the plane climbs (on digital cockpits like the Garmin G1000 this are the lines on the screen)
• The climb speed in feet per minute (ft/min)

The climbing angle can be calculated with this formula:

sin = thrust - drag : weight

The climb angle is so the difference between thrust/drag and the weight. We also can determine the angle of climb in two different ways:

• Climb angle : The angle of climb relative to the incoming airflow
• Flight path angle : The angle relative to the ground

With no winds these two numbers are equal, but with a lot of headwind, the flight path angle becomes smaller meaning a steeper flight path. With tailwind, this angle will be more flattened.

The climb gradient is the transition of the climb seen over a certain distance, like over a nautical mile. If we climb 1000ft per nautical mile (6076ft), we climbed 16% of a nautical mile in a minute. (1000 ft / 6076 ft × 100 = 16,46%)

The climbing speed/rate of climb is the vertical speed of a plane. This means as this is 1000ft, we will be 1000ft higher if maintaining that vertical speed for a minute.

Green: Vx speedRed: Vy speed

Climb performance factors

The climb angle and rate of climb doesnt have static values but are determined by these factors:

• Air density
• Weight
• Flaps
• Extended/Retracted landing gear
• Wind
• Bank angle

Let’s describe them all.

Air density

The air density is determined by air pressure and temperature, as we already know by now.

• High air density means high air pressure and good aircraft climb performance
• Low air density means low air pressure and worse aircraft climb performance

The engine and propellor will perform worse with lower air pressure, as there are less air molecules to move and use to fly through. We also generate less lift, needing a higher AoA to maintain a certain amount of lift. Just enough to counteract our weight.

When climbing, we eventually hit a upper altitude limit of the plane. At that point, we climbed so much that the aircraft structure cannot generate more lift and thrust to get higher. For a Cessna 172 this is around 13.000ft. We know two certain limits:

• Theoretical ceiling: 0ft per minute (0 ft/min) (fpm)
• Practical ceiling: 100ft per minute (100 ft/min) (fpm)

These numbers are the result you can read on the vertical speed indicator when close to the limits. As we can almost never hit the actual ceiling, the practical ceiling is also the service ceiling described in the POH of the aircraft.

Weight

As we also already know, more weight means we need to generate more lift which therefore means more induced drag. This results in a lower rate of climb. When the plane becomes lighter after burning some fuel, the climb performance will be better.

Flaps and landing gear

Flaps and an extended landing gear will increase the parasite drag of the plane, which then will result in a slower rate of climb and a higher engine RPM.

Wind

Winds will influence the flight path angle and the climb gradient:

• Headwind: Less groundspeed and higher climb gradient
• Tailwind: More groundspeed and lower climb gradient

The wind only does change the speed opposing the ground, and as we can travel more or less distance to the ground, the gradient will be different.

Bank angle

As we bank, the lift vector will also tilt, needing more lift. In turns we will use some back pressure on the yoke to counteract this. In turns with a constant speed, you will notice a speed drop as result of extra drag. In climbing turns we use a limit of 15 degrees which is a nice compromise between climb speed, loss of some lift and turn speed.

Forces while descending

The forces of flight while descending are somewhat similar to climbing but then reversed. The gravity (G2) force gets a little thrust component and helping us to gain speed. This is why we descend with almost no power. During descends, the lift force ia slo a lot smaller because the negative AoA.

Forces while gliding

The forces while gliding, so with zero engine power, are slightly the same as descending, but we don’t have a small thrust power left. We have only some thrust left in the form of weight. This is why we sometimes call:

• Altitude : Potential energy (more altitude can be converted into speed because of this)
• Speed : Kinectic energy

Glide performace

During gliding flights, in most cases during an engine failure, we have two parameters to measure the gliding performance:

• Glide angle
• Glide gradient

In practice, we must immediately pitch to gain and maintain our best glide speed: Vbg. In a Cessna 172 this is around 65-68 knots. The point of minimum drag and most lift, the bottom part of the total drag curve. We want to keep as much options possible and therefore increasing the gliding distance is crucial for the options to land our aircraft. Maintaining the Vbg speed means that we have the smallest gliding angle opposing the ground.

Glide performance factors

The factors which can influence our glide flight are:

• Indicated Airspeed (IAS)
• Wind
• Flaps/Landing Gear
• Weight

Wind

Winds are very important when aiming for the highest gliding distance. We want to get tailwind, so we take advantage of the wind gaining more distance. When we actually want to land, then headwind is more favorable.

• Headwind: Decreases glide distance

• Tailwind: Increases glide distance

Flaps/Landing gear

Flaps and the landing gear will increase the parasite drag of the plane. Keeping those extended will therefore decrease our gliding distance significantly. We need to keep these retracted as long as possible.

Weight

The smallest gliding angle will be reached while maintaining one certain AoA, the one with the maximum L/D ratio. The angle however says nothing about the speed. More weight means an increase in the Vbg (best glide speed). A heavier plane therefore keeps a higher airspeed, meaning in reaching the surface faster.

End of the page 🎉

You have reached the end of the page. You can navigate through other blog posts as well, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog homepage

If you find this page and blog very useful and you want to leave a donation, you can use the button below to buy me a beer. Hosting and maintaining a website takes a lot of time and money. Thank you in advance and cheers :)

The terms and conditions apply to this post.

Meteorology (MET)

The atmosphere (1)

The atmosphere is the layer around the earth, which is around 100 to 200km from the ground up. Worldwide, we use the International Standard Atmosphere which is a mean set of conditions which will be somewhat different depending on the weather conditions, location etc. This is a mean of the conditions at 45 degrees north latitude.

In the standard atmosphere, we use these characteristics:

1. 0ft is at the mean sea level
2. The air density is 1,225 kilograms per cubical meter
3. The air pressure is 1013,25 hPa (millibar) or 29.92 inches of mercury (inHg)
4. The temperature at sea level is 15 degrees celsius
5. In the troposphere, the temperature decreases with 2 degrees celsius for every 1000ft up (2 degrees per 300 meters)
6. The tropopause is at 36.000ft (11km) and the temperature is -56,5 degrees celsius
7. The troposphere and stratosphere contains 78% carbon dioxide (co2) and 21% oxygen

This is a set of conditions, but some numbers can defer in the real world, due to the location or different seasons. Now, lets take a look at the different layers in our atmosphere:

Let’s take a further look into every layer in depth:

Thermosphere

The thermosphere is the first layer of the atmosphere and the one with the hisgest temperatures due to solar radiation. This layer also contains aurora’s and are the best visible from the (magnetic) north pole and south pole.

Mesosphere

The mesosphere is the layer above the Stratosphere and is the layer where the ozone layer resides. This layer is the part of the atmosphere where most meteors will burn up heated from the thermosphere, the layer above the Mesosphere.

Stratosphere

The stratosphere is the layer above the troposphere and starts very cold, but at the height it is around 0 degrees celcius. This is also the layer where the Concorde used to fly to achieve supersonic speeds, due to the low air density. The layer contains some jet streams.

Troposphere

In the troposphere, the lowest layer that spans from ground to around 36.000ft up is where all weather takes place. Here are the most winds, clouds and storms. When going from the ground up into the air in the troposphere layer, the temperature will decrease by 2 degrees celsius for every 1000ft you ascend. At around 36.000ft, the temperature is around -56,5 degrees celcius.

The temperature loss happens because of the loss of radiation coming from the earth. The sun warms up the earth, and earth radiates that heat back up into the air.

Ionosphere

We also have an additional layer called the Ionosphere. This is a layer where gasses will be ionized by the high level of solar radiation. The result of this is a somewhat conductive layer of electrons and ions where HF frequencies profit from. These will follow the curvature of the earth because of this Ionosphere, where normal frequencies follow a straight line colliding to the earth after around 300km. Also GPS can get some propagation errors because of the radiation in the Ionosphere.

This collective layer lays over the upper part of the mesosphere and thermosphere, residing between 60km and 500km altitude. However, its not classified as layer in our atmosphere but one with an important goal.

The balloon in the stratosphere is obviously an AI error. :)

Air Pressure

Air pressure is a result of the mass/weight of the air. Because there is so much air above the earth which compresses close to the ground, areas with a lot of air molecues will be created. You can see this as a tower of jenga you played before. The weight of all the bricks pushes on the lower layers of bricks.

On earth we have several high pressure areas and low pressure areas which are an result of temperature differences. High pressure areas always wants to go to low pressure areas, just like when you pump up a tire and let go the vent. The air from the high pressure area inside the tyre will go to the outside, low pressure area.

• In high pressure areas: cold air falls to earths surface, and cold air has more air molecules
• In low pressure areas: warm air from the surface rises, and warm air has less air molecules

So air pressure actually indicates the volume of air molecules in the area. The higher the pressure, the higher the volume of air molecules.

High pressure (H) and low pressure (L) areas are not absolute numbers, but relative to each other. For example:

• 979hPa (L) vs. 1013hPa (H)
• 1013hPa (L) vs. 1035hPa (H)

Air Pressure when elevating

When going up into the air, the air pressure will decrease like seen in the graphic below:

For reference, we will use this numbers:

• Every 30 feet up in the air represents an hPa loss in air pressure
  • Example: 1013 hPa on sea level (0ft AMSL) means a mean pressure of 1000 hPa at 390ft altitude

As this is an exponential relationship, this will guide you through the first 10.000ft (3,048km) in altitude, after that this trick does not longer work correctly of course. Some good rules of thumb:

• 5.000ft altitude: 75% (3/4) from ground pressure
• 18.000ft altitude: 50% (2/4) from ground pressure
• 34.000ft altitude: 25% (1/4) from ground pressure

For more information about Pressure and Density altitude, check out: https://justinverstijnen.nl/ppl-theory-nav/

Warmth and temperature (3)

The sun is the engine of Earth’s weather systems. Because the sun radiates its heat onto the Eart, we have nice temperatures. Without the sun, we would live in a mean temperature of around -200 degrees celsius.

The sun radiates its warmth to the earths surface and that will warm up the air above it. This is the main reason why temperature decreases with an altitude increase (going up is going cooler).

For transport of warmth in Earths atmosphere we have different terms:

• Radiation
• Convection
• Turbulence
• Advection
• Conduction

Let’s take a look at them all:

Radiation

Radiation is the transport of warmth using electromagnetic waves. This is mostly sunlight that reaches the earths and uses infrared and UV radiation. Objects and air which absorb radiation will increase in temperature.

Convection

Convection is the vertical transport of warm air caused by the differences in air density. An result of convection is (thermal) updraft, the component of how gliders can stay in the sky.

Convection happens when the layer of air above the earths surface warms up greatly, and this warmer air will rise because of the lower density. Hot air balloons fly because of the principle of convection.

Turbulence

Turbulence contains unorganized horizontal and vertical airmass movements. These are caused by several inconsistences:

• The wind blowing at a certain speed while hitting non-flat objects like buildings and mountains
• Windshears
• Thermal instability
• Fronts
• Jetstreams

Also warm air can move around the atmosphere by turbulence, but the main difference is that in this case, the air density is not the main reason of transport.

Advection

Advection sounds really like turbulence, but then organized and on great scale. Advection is a result of horizontal movement of air by the wind and air pressure differences. Wind and air mass is advection.

Conduction

Conduction is the transport of warmth by using physical contact. A warm object will conduct its warmth to a colder object using conduction. Because air is not a great warmth conductor, this happens the least of all transports but in combination with Convection its measurable.

To summarize all these forms of transport:

Greenhouse effect (Broeikas effect)

The greenhouse effect is an effect caused by sunlight going through the ozonelayer, which is a layer in the Stratosphere containing water vapor, and heating up the ozone layer.

Moisture in the Atmosphere (4)

In the atmosphere, there is a very small percentage of moisture. This is around 0 to 5% of all the air, mostly a result of water vapor of surface water. The moisture in the atmosphere is the cause of all weather types, like clouds, thunder, fog, mist and thunderstorms.

Water exists in the atmosphere in 3 types:

1. Ice
2. Water
3. Water Vapor

The picture below shows all the phase transitions from ice, to water and or to steam:

These terms will mean:

• Freezing: a simple one, water (liquid) going to ice (solid) is called freezing
  • Dutch translation: Bevriezen
• Melting: another simple one, ice (solid) going to water (liquid) is called melting
  • Dutch translation: Smelten
• Condendation: Gas (steam) going to water (liquid) is called condensation. An example is a cold beer just from the fridge which becomes wet at the outside of the bottle
  • Dutch translation: Condenseren
• Evaporation: Water (liquid) going to Gas (steam) is called evaporation. An example is a wet t-shirt on a line in sunlight. The water will use the energy of the sun to evaporate.
  • Dutch translation: Verdampen
• Sublimation: Ice (solid) going directly to Gas (steam) is called sublimation. An example is a brick of (dry) ice where smoke (steam) will appear from
  • Dutch translation: Sublimeren
• Deposition: Gas directly going from its steam form to ice (solid). Examples are ice on your car or plane or the white layer on grass and trees in winter days (rijp)
  • Dutch translation: Verrijpen

Easy to remember the terms:

• Freezing happens below 0°C
• Melting happens above 0°C
• Condensation happens when air temperature equals dew point
• Deposition happens below 0°C when air is saturated
• Sublimation happens below 0°C in dry air
• Evaporation happens at any temperature when air is not saturated

Relative Humidity and Dew Point

Warmer air can hold more amounts of moisture. This is because the warmer air expands and is less dense, so more room for moisture. To measure the amount of moisture in the air, we can use 2 methods:

• Relative humidity
• Dew point

Relative humidity

The relative humidity is a percentage that states how much percentage moisture is in the air based on the air temperature. While this is a percentage, it doesnt tell us something clear. This is because:

• 75% relative humidity at 30 degrees celsius will feel very humid and wet
• 75% relative humidity at 3 degrees celsius will feel very dry

This is because the mass of air is filled with 75% of moisture, but a higher temperature means a bigger storage of moisture. A low temperature will hold much less because its more dense. As we actually want to have numbers that tells us everything about the state outside, we have invented the Dew point.

The relative humidity is mostly the highest at night/early morning and lowest at 4 o’clock at noon.

Dew point

The dew point is an second temperature that is determined at the temperature and humidity. IIt tells us the amount of moisture in the air, by a sort of calculation from the actual temperature with an humidity percentage calculated up to 100% where the air is fully saturated by moisture. For example:

• Air temperature 25 degrees celcius
• Humidity is 50%
• At those conditions, the relative humidity is 100% at about 13 to 14 degrees celcius
• 13 to 14 degrees celcius is your dew point

So the dew point tells us much more about the current air condition, and can be used to predict the height of cloud layers. Here I have a table that tells more about air temperatures and humidity and how it will actually feel:

Vapor pressure (dampspanning)

Vapor pressure is the pressure by vapor created by molecules in the air when evaporated. This is indicated in hPa. This is also one of the conditions used to calculate the relative humidity.

Vapor pressure is calculated from air temperature and relative humidity. For example:

1. Air temperature: 20 °C
2. At this temperature the saturated vapor pressure is about 23 hPa.
3. The actual vapor pressure is 16 hPa.
4. To calculate the relative humidity: (16/23)×100= ~70%
5. Relative humidity = ~70%

Rule of thumb cloud base with Dew Point

We have a rough rule of thumb used in aviation to estimate the cloud base:

Temperature - dewpoint / 2.5 = answer ×1.000 is the cloud base in ft above ground level (AGL)

For example, the air temperature is 25 degrees and the dew point is 7 degrees.

25 - 7= 18 / 2.5 = 7,2 x 1.000 = 7200ft AGL

Vertical balance in the atmosphere (5)

So we have horizontal movements of air masses called the wind, but we also have vertical movements. Vertical movements have also a great impact on the weather. The stability of the atmosphere decides if vertical movements happen or they are suppressed.

Stability

Stability means how the atmosphere reacts when air is pushed up or down vertically. We can have an unstable or stable atmosphere:

• Unstable atmosphere: Air that is lifted keeps rising on its own, which can lead to clouds, showers, or thunderstorms. As long as the air is warmer than its surrounding air, the warm air will rise
  • Cloud types: Cumuliform
• Stable atmosphere: Air that is lifted tends to sink back to its original level. Vertical motion is suppressed, so clouds and storms are less likely.
  • Cloud types: Stratiform

Adiabatic processes

When a package of air rises, it will flow to an environment with a lower air pressure. The package of air will then expand, which costs a little energy. This energy source is the temperature. Cooling using temperature is called adiabatic cooling.

An adiabatic process is a change in the temperature of air without any heat exchange with the surrounding environment. You can see this as a temperature change within this air package:

• Air that sinks → is compressed → warms (adiabatic warming)
  • This will cause the molecules to move faster and results in a temperature rise
• Air that rises → expands → cools (adiabatic cooling)
  • This will cause the molecules to move slower and results in a temperature decrease

As long as the air will not be saturated by water vapor, then this will be called a dry-adiabatic cooling. When the air is saturated by moisture, then this will be logically called wet-adiabatic cooling.

• When dry the temperature decrease for every 1000ft in the air will be around 3 degrees celcius.
• When wet the temperature decrease for every 1000ft in the air will be around 1,8 degrees celcius

At the moment the air hits the dew point, the air becomes saturated with moist, condenses and a cloud has been born. The cooling rate will also decrease because of the condensing process releases warmth. Check out this moist lifecycle. You can calculate the dew point height with this formula.

Temperature gradient

The temperature gradient is a bit different as ISA describes, because of these adiabatic processes. It can also be that the temperature rises a bit and then decreases every X ft up. This is why we always speak about mean decreases.

To visualize this exactly, we have something called the “State curve”, the graph of the actual representation of the temperature gradient.

This state curve can present 4 types of stability in the air:

1. Absolute instability
2. Absolute stability
3. Conditional instability
4. Indifferential

Absolute instability

When we speak of absolute instability, then the temperature decrease is faster than a dry-adiabatic process. This is as we discussed earlier, more than 3 degrees celcius per 1000ft (1c per 100m). In this situation, the rising air package is warmer than its surroundings, so will continuously rise because of its lighter mass.

This is also a recipe for thunderstorms if the air is saturated enough. Air will continue to rise all the way to the Stratosphere creating cumulonimbus clouds.

Absolute stability

When we speak of stability, the temperature of the atmosphere will cool down slower than a wet-adiabatic process. Here the atmosphere is stable and there is not much air rising. A possible rising package of air will cool down to its environment and will stay in its vicinity.

Conditional instability

In a conditional instable atmosphere, the temperature gradient is between wet and dry adiabatic. Here the air is stable to call it a stable atmosphere but instable enough for a wet-adiabatic process. In the real world, this is the most happening situation.

Processes that influence stability of the atmosphere

We have some processes in the atmosphere that influence the stability, mostly processes that cause warming and cooling.

Radiation inversions

The radiation inversion is when the sun heats up earths surface and the directly layered air. In the evening, the air cools down at earths surface but the air above the surface stays a bit warmer. This causes instability and is the reason fog starts at the ground in the winter/spring mornings. Basically a temperature increase in the temperature gradient, after the inversion, the temperature will decrease per ISA conditions.

Right above an inversion, the wind speeds can drastically change, as the atmosphere is a bit more unstable above the inversion.

Advection

Advection, which is horizontal transport of air, alters the stability of the atmosphere. This will do it in these ways:

The main causes of this are that a cold surface will cool the air above it. With a warm surface, the air in the lower areas will warm up, and warm air will tend to rise. This creates convection and if the air contains enough moist, clouds and precipitation.

General circulation and pressure systems (6)

The movements in the atmosphere are primarily caused by pressure differences, which are caused by temperaturedifferences. In the tropical region, there is a lot of sun during the year and gets a lot more sun than the artic regions. This creates a static pattern of air movements which is called the general circulation.

At the equator, the strong sun radiation will cause rising air, and the pressure at the ground decreases. In this ring of low pressure, called the intertropical convergention zone (ITCZ), warm moist air will rise and flows at great altitude to the north and south. After cooling and becoming dry, this dry air falls back to earth at the subtropicals, which are around 30 degrees north and south latitude. This is the line of the Saharas, canaries.

On every half of the glode, there are 3 vertical cells as seen in the picture above. We also call them circulation patterns. These patterns are there all the time, all year.

Air pressure systems

The air pressure at all places around the world is measured by weather stations. Some offices will link all those fields to each other to create a pressure map of the world. Because all weather stations have a different elevation to the mean sea level (in ISA 1013 hPa), this pressure will be calculated to this mean sea level, based on the current conditions. This gives us a new Q-code, the QFF.

• QFF: Actual atmospheric pressure calculated back from ground to sea level
• QNH: Sea level pressure using ISA, where on sea level the altitude should be “0”.
• QNE: QNE is when we set 1013 on our altimeter. Basically the pressure altitude, which we use to fly Flight Levels
• QFE: Actual pressure on the field, being 1000ft above ground level means actually 1000ft in the air

As we can see on the map, the world contains a lot of low and high pressure areas. The “H” or “L” is pointed at the center, or the highest or lowest pressure point of the area.

The curved lines you see are Isobars, which are lines with matching air pressure. The dutch KNMI will use an interval of 5hPa for these lines.

High pressure area outline

A High pressure area always have a ridge (rug) which is a extension of the high pressure area and looks like this:

Low pressure area outline

A low pressure area has a trough (trog) and means the extension of the low pressure area, again where the center of the areas at the “L” represents the area of lowest pressure:

Cols

A col (zadelgebied) is an area that is surrounded by multiple high or low pressure area’s. In this area’s the pressure differences are small. In the chart below, we could see some cols :

• Argentina
• Around Los Angeles
• South Africa
• Japan

Being in a col, you can expect light and variable winds, as the air of the pressure area’s want to go to the lowest pressure area.

Low pressure areas defined

A low pressure area is an area with closed isobars where at the center is the area of the lowest air pressure. A low pressure area can occur where in the higher atmospheric layers divergence takes place. This means that the air compensates and starts a vertical airflow from the ground up to the tropopause. This will cause the pressure at the ground to lower as the air molecules rise up. The rising air cools down and condensation will happen what causes clouds and precipitation.

A result of the lower air pressure is, because high pressure areas will always flow to low pressure (bicycle tire), that at the ground the air will move to the center of the low pressure area. This process is called convergence.

Other words for low pressure area’s are:

• L
• Depression
• Cyclone
• Minimum

At the globe, the movement of air in a low pressure area can defer:

• At the Northern Hemisphere (0 to 90 degrees north latitude), the air will move counter clockwise
• At the Southern Hemisphere (0 to 90 degrees south latitude), the air will move clockwise

This circulation is called cyclonal, as it rotates the same way of a cyclone (which rotates counter clockwise at the northern hemiphere)

The cause of this difference is the Corioliseffect, a result of the globe which rotates. Air wants to go in a straight line from H to L, but as the earth rotates, these paths are curved. This is also visible at the chart above.

High pressure areas defined

In an high pressure area the pressure at ground level is higher than in the direct area. High pressure areas occur in the general circulation like the Azores islands (West to Spain). High pressure areas can also occur above a cold ground mass. This is called a thermal high pressure area. As the atmosphere cools down, the colomn of air will shrink and air will converge at high altitude. This makes the mass of air heavier and the result of this is the mass of air falling down (subsidence) to the ground. A high pressure area is now born.

During subsidence, the falling air will heat up and will clear out clouds. Generally there is better weather in a high pressure area than there is in a low pressure area, but this is no warranty.

Subsidence can also cause an inversion, which happens a lot. The inversion will stabalize the atmosphere, stopping the vertical movement of air. The result is that water vapor, dust, sand or other air-pollution can not go anywhere and hangs at low altitude. A great example is haze or smog in big cities with warm weather during a high pressure area:

At the globe, the movement of air in a high pressure area can defer:

• At the Northern Hemisphere (0 to 90 degrees north latitude), the air will move clockwise
• At the Southern Hemisphere (0 to 90 degrees south latitude), the air will move counter clockwise

This circulation is called anti-cyclonal, as it rotates the opposite way of a cyclone (which rotates counter clockwise at the northern hemiphere)

Winds (7)

Wind is the horizontal movement of air, caused by air pressure differences around the globe. We get air pressure differences because of temperature differences, where warm air expands and cold air contracts. Warm air causes the air pressure to become less as there are less air molecules per cubical meter and cold air causes the air pressure to become higher as more molecules will be there.

The wind is always measured in the direction where the wind comes from. In aviation we use a degrees measurement, where the number is always rounded to the closest interval of 10.

• A northern wind means the wind blows from north to south, and the wind will come from 360 degrees (we don’t count “0”.)
• A south western wind means the wind blows from the south west to the north east and wind will come from 230 degrees

The windspeed is measured in knots which represents the amount of nautical mile per hour. The wind measured is a mean wind direction over a period of 10 minutes. With small winds, 3 knots or even lower, this could be indicated as “variable”. Gusts are momentary and more powerful forces of the wind and are indicated at the METAR if 10 knots or more above the mean windspeed.

We also have wind power indications, which are based on the beaufort scale but is not used in aviation as its not linear and not precise enough as you can see here:

You could ask yourself why we measure and indicate the wind like this. If the wind blows to the north, it would be easier to say northern wind. In aviation we want to take-off and land our aircraft from a certain runway and favorite a runway with headwind (not with tailwind). This runway has a number corresponding to the magnetic course/direction it points at. By indicating the wind like this, the number is liked pretty much to the wind direction.

For example:

• If we have runway 18/36, and the wind comes from 310 -> Our favorite direction is 360 (RWY 36)
• If we have runway 09/27, and the wind comes from 330 -> Our favorite direction is 270 (RWY 27)

Taking off and landing with headwind (tegen de wind in) increases our true airspeed and decreases our ground speed, making those maneuvers a lot easier as we have less speed according to the ground.

Wind can do veering and backing, which both have a certain definition:

• Veering: The wind direction changes clockwise (ruimen)
• Backing: The wind direction changes counter clockwise (krimpen)

This will actually say nothing about the wind speed, only the direction.

Coriolis-effect

The coriolis effect is a result of curvy winds as result of the rotation of the earth. This effect has the most presence at the poles and the less at the equator. This happens as air travels to the poles, but the turning speed there is much slower than on the equator.

• Cause: The Coriolis force is caused by the rotation of the Earth. Moving air appears to be deflected because the Earth rotates beneath it.
• Direction of deflection
• Northern Hemisphere → deflection to the right
• Southern Hemisphere → deflection to the left
• What it affects The Coriolis force does not start motion, it only changes the direction of moving air.
• It acts perpendicular to the direction of motion and increases with wind speed and latitude (stronger near the poles, zero at the equator).

Winds in High Pressure areas vs Low pressure areas

In this illustration, we can see several different details here about winds and high/low pressure areas. We will look at all details applying to the northern hemisphere. In the southern hemisphere, all details are reversed.

This tool is called Windy.

• Winds in a high pressure ares rotate clockwise from the center out
• Winds in a low pressure area rotate counter clockwise to the center
• Winds blow parralel to the isobars at altitude, on ground this will back (krimpen)

One fact applying to the whole earth is that areas with isobars close to each other represents areas of high wind speeds. Just look at cyclones which are a low pressure area (the L south west of Iceland):

Massive wind patterns

Around the earth, we have various wind patterns that are happening on recurrence. We know art least three of them:

• Mistral: Powerful, cold and dry wind happening with cold polar air
• Sirocco: Southern wind, wet and warm mostly during the spring months
• Bora: Powerful cold and dry wind, mostly in the winter months

Fun fact, now you know where car brand Volkswagen got their names from :)

Small circulation patterns

We also have some small circulation patterns of the wind because of small geographical situations. Think of these situations:

• Sea and land-wind circulations
• Mountain and valleywind
• Fohn
• Mountain waves
• Venturi-effect

We will now describe them all and look at their characteristics

Sea and land-winds

Seawind circulations occurs when a big temperature difference exists between sea water and land. The sun will heat up land way faster than sea water and the temperature above land will increase faster. Above land, the air will rise (Convection) and results in a thermal low air pressure area, because of the air expanding due to the heat.

As the air pressure at sea becomes a bit higher and on land, a small wind will now occur. As we already know that air from a high pressure area will always flow to a low pressure area, sea wind is now created. The barrier between the cold sea-air and warm land air is called the seawind front.

Sea wind circulation mostly happens in the spring, where the sea water is relatively cool and the sun radiation is strong enough to heat up the land, creating the temperature and resulting air pressure differences. Also these winds are also affected by the coriolis effect. The winds of the sea can reach several kilometers into land (up to 50km, based on the ground resistance).

These seawinds can cause some turbulence and wind shears and on the sea, some cumulus clouds can form. Sometimes with precipitation (neerslag).

Mountain and valley winds

In the mountains and valleys, we have huge sun radioation and resulting temperature differences which cause a lot of thermal high and low pressure areas.

We have 2 definitions to know here:

• Anabatic winds: Rising winds up to the tops (blue)
  • Also called the Windward side (loefzijde)
• Katabatic wind: Descending winds from the tops to valleys (warm)
  • Also called the Leeward side (lijzijde)

At the Canary Islands, most islands have this as primary climate where at the north the clouds and precipitation comes to the islands but are held back by the mountains. At the south side of the islands, the weather is a lot better and more dry. To describe the full process:

1. Air full of moist will flow to the mountain side
2. The air rises, expands and cools down, called the adiabatic cooling
3. The air will reach the dew point
4. Water vapor will condensate and will result in clouds and precipitation
5. The clouds are pushed to the mountains and want to go up because of the Fohn effect
6. At the top, most of the water vapor is rained down and the air contains a lot less water vapor
7. Over the top, the air will fall down because of gravity
8. Descending air will be compressed and heated as result of the compression, called the adiabatic heating
9. Warm air can contain a lot more water vapor, causing the humidity to lower
10. Because of this, clouds will dissappear and we can enjoy the sun

Fohn effect

The fohn is a name for the dry katabatic wind that flows down from the mountain top down to the valleys. The fohn name is mostly used in the Alps to name the warm winds from the Mediterranean Sea but the effect/result is the same.

Because of this air flow, this can cause mild to severe turbulence above those mountains.

Mountain waves

Mountain waves will occur when the flow of air is pushed over a mountain ridge (bergrug). If a stable layer of air is present, the passage will back down. This causes a golf pattern which can be measured even several hunderd kilometers after the mountain ridge. Mountain waves will be caused in these conditions:

• The angle between wind and mountain ridge must be around 90 degrees
• A wind speed of 20 knots or more
• A stable layer of air of thousands of feets around the mountain-tops

Rotor and rotorclouds

Under the mountain waves, behind the mountain ridge and somewaht under the tops, a rotor will occur. Just like what happens at a plane-wing creating lift and stalling somewhat.

This mass of air rotates under a horizontal axis and wind speeds can be massive. Upward and downward speeds can be thousands of feet per minute and causes a lot of turbulence.

In dry air, this rotor is not visible, but with humid air they can cause rotary clouds. They look innocent but can blow with a lot of winds and cause severe turbulence. They look a bit like lenses of a camera.

Venturi effect

The venturi effect is wind that is forced to flow through a narrow space, causing the wind speed to increase and the air pressure to decrease. This seems not very important, but if flying there, the altimeter can indicate a lot higher altitude than you are actually flying. This difference can be hundreds of feets.

Valley inversion

A valley inversion is just like a normal inversion, but then in mountain-rich areas. The can occur in these conditions:

• When the air above a mountain ridge cools down, a downward flow of cool air will occur (katabatic wind) and will form a reservoir at the bottom of the valley
• As result of advection of warm air in higher layers of air

Valley inversions have several dangers for aviation which other inversions also have, like poor visibility, thick layers of clouds and high wind speeds at the upper side with windshears and turbulence. Taking into account you are flying in a mountain-rich area can cause huge accidents which pilots must be aware of.

Wind shears

Wind shears are rapidly changes of wind speeds and directions. Wind shears can be horizontal and vertical and will affect the way the plane flies. As we need air speed, including winds, to fly we need a flow of air. But if that flow of air is interrupted instantly, our speed and or altitude can result in a major decrease. We don’t want this when taking off or landing.

• Vertical windshear is the differences of wind in vertical scale. As we descend, we will getting less winds eventually resulting in a loss of airspeed and life. Our plane will descend even faster
• Horizontal windshear is when the cross winds are changing rapidly, which can cause us to get of track for landing. Buildings are the most important cause of this happening. As ground resistance rises but then catching some of the winds, we can go off track
• Updrafts and downdrafts are a result of convection and will have vertical winds, pulling you up or pushing you down. This mostly happens in the vicinity of thunderstorms

The 5 most important causes of wind shears are:

1. Front passing by
2. Thunderstorms
3. Ground resistance (wrijving) in the form of buildings, forests or obstacles
4. Inversions
5. At the top of a layer of friction (wrijving)

Results of wind shears

Wind shears can occur at every altitude, but are the most dangerous above the ground like in take-off and landing.

You know, planes fly because they have a speed in the mass of air they are flying into. This is called the True Airspeed (TAS). If we have a ground speed of 70 knots and a headwind of 30 knots, the resulting TAS is 100 knots. If that headwind suddenly changes from 30 to 0 knots, our speed will decrease 30 knots. This causes our plane to create a lot less lift, resulting in a sudden descend. You can imagine as this happens feets from the runway, this can cause severe incidents.

We speak of a low level windshear if this happends 1600ft AGL (500m) or lower.

Turbulence

The wind never flows from A to B in a horizontal line with a constant speed. By buildings, forests, obstacles, heating and instability (all called ground resistance) or different layers of air, the wind will get an unorganized flow. This is called turbulence.

Turbulence has several causes:

• Thermal turbulence: Heating of earths surface with rising air causing mild turbulence (thermiek/convectie)
• Mechanical turbulence: Caused by winds flowing to buildings, forests or altered by ground resistance (present in ground to 3000ft AGL)
• Orographic turbulence: Turbulence caused by mountains, rotorwaves and mountain waves and can reach above the actual mountains in the area
• Clear air turbulence: Turbulence caused by clear and cloudless area’s. This is caused by jet streams and mountain waves

We classify turbulence into 3 categories:

• Mild turbulence
• Moderate turbulence
• Severe turbulence

As every type of plane is built different, so is the level of what you feel. An Boeing 737 is less likely to feel turbulence than a Cessna 172.

Types of air (8)

An air mass is a collection of air with equal temperature and humidity spanning several hundred kilometers. An air type has a area of source which is a great area with similar elevation. The mass must be long enough to stay in that area. Examples are:

• Oceans
• Deserts
• Snow plains

The source of the air mass is deciding the results of the air type. If this is moving, the properties will change. This process is called transforming and the properties will change from the source of air to its transfomed state.

The area’s of source which decide the weather in the Netherlands (and the rest of Europe) are:

• Atlantic ocean
• Siberia
• North Africa

Definitions of air types

We have some definitions for different air types which we call in a certain abbreviation:

• The geographic source of air
  • Maritime (Air comes from water)
  • Continental (Air comes from land)
• The thermodynamic layout of the air
  • Arctic air (AL)
  • Polar air (PL)
  • Tropical air (TL)

An combination of these is used when we say the cold eastern wind in the Netherlands is cPL. Continental, polar air.

A full table of all possibilities and definitions:

CM = cold mass WM = warm mass *Abbreviations in Dutch

Air masses

Because of cold mass will be heated and warm mass will be colled down, this can have some consequences for the vertical stability in the atmosphere. They can result in precipitation, clouds and fog.

• If a mass of air on 1,5 meters is colder than on the ground, we speak of a cold mass
• If a mass of air on 1,5 meters is warmer than on the ground, we speak of a warm mass

Clouds and precipitation (9)

Clouds will occur when warm rising air is cooled down by adiabatic processes. By cooling down air, the water vapor will condensate to water which is the cloud itself and can be in the form of rain. Because warm air can hold more moist, all of this moist is colled down and a cloud is born.

The condensation process

Condensation occurs when air is saturated with water vapor, so cooling to the dew point. In clean air, this happens far beyond the dew point. The proces will goes much faster if there are condensation nuclei (condensatiekernen) in the air. Types of those condensation nuclei are:

• Dust parts
• Sand
• Soot particles
• Salt crystals

Clouds appear in rising air which is cooled down by adiabatc processes, and then saturated with water vapor. If the air has condensation nuclei, this goes faster into liquid water.

Rising air movements

There are multiple causes of why air masses will rise into the air. Lets take a look at them:

• Convection (thermiek): Local heating of the surface by the sun causing a part of warm air to rise and then cool doen. With enough cooling, clouds will form if the water vapor is condensating to small droplets of water. Convection happens the most at sunny summer days without clouds where the ground can warm up easily, like above sand and mountains and during the afternoon.
• Forced lifting: When in a mountain-rich terrain or close to mountain waves
• Low pressure areas that cause rising air movements, first converging air and then rising into the air

Influence on stability

The type of clouds generated is dependent on the stability of the atmosphere.

• In an unstable atmosphere with much vertical movements this will cause cumuliform (stacking) clouds
• In an stable atmosphere with much vertical movements this will cause stratiform (layered) clouds

Condensation level: with decreasing air pressure when going up, the dew point will also decrease. This decrease is about 0,6 degrees celcius every 1000ft.

Every 400ft up, the temperature and dew point will come together by 1 degree celcius.

Fundaments of clouds

As result of condensation of water vapor, there will be a lot water droplets (0,01 to 0,1 mm). These droplets will stay liquid if they stay above 0 degrees. Under 0, they can freeze but will most likely not be directly. Most water dropleys will freeze after being -12 degrees celcius, after being undercooled water. This is water that is under the freezing point, but not freezing because of moving or not enough oxygen.

There are clouds like the cirrus which only are made of ice crystals because of the altitude where they reside. Water droplets and crystals are called cloud elements.

Clouds that are completely made of liquid water are called water-clouds. If clouds are partly made of water and ice, they are called merged clouds. For ice clouds, they are logically made up of ice.

Categorization of clouds

Clouds are categorized into 3 levels based on their altitude and they partly get the name from the height and then a suffix of the cloud type.

Here I have generated a nice legenda which contains the most occuring types of clouds and their altitudes to better map them and give a better understanding than a table:

A good rule of thumb is that Cumulus clouds are formed by convection (unstable atmosphere), and Stratus type clouds formed by stable atmosphere

Cloud types (own pictures)

To train my eye a bit better, I went through my picture gallery and searched if I could find the cloud types in my pictures which was really fun to do. I always liked to take pictures of clouds and sunsets because they can sometimes be a piece of art.

Cumulus (Cu)

Here I have a picture full of cumulus (stacked in Latin) clouds, everybody seen them a lot during summer days:

Immediately gives away why they are called “cumulus”. They are stacked/cumulative clouds.

Nimbostratus (Ns)

Very boring rain clouds, which everybody seen a lot in their lives:

Nimbostratus clouds can be present on any layer, but from the ground we see the lower part only. These are clouds which drop water and can be present in a warm-front.

Stratus (St)

These clouds are called “stratus”. This is latin for “layered”.

This is a clear and big layer of the same level clouds in the low altitude region.

Altostratus (As)

The altostratos is a combination of “alto” which means high altitude and “stratus” which means layered in Latin. This gives us high-layered clouds:

Altostratus clouds are mostly present when a warm-front is near and coming.

Altocumulus (Ac)

The altocumulus clouds are a combination of “alto” which means High and “cumulus” which means stacked in Latin. They look like this:

There are multiple types of clouds in this picture, but the most are altocumulus. These are the small clouds in groups. They can indicate some instability on medium height but are not a direct danger for flying VFR.

Cirrus (Ci)

Cirrus means “hair” in Latin, and are the thin and high level clouds you see often during the summer. They are mostly ice crystals because of their high altitude.

The so-called “chemtrails,” like seen in the picture above which are actually frozen water vapor resulting from aircraft burning fuel, are part of cirrus clouds.

Cumulonimbus (Cb)

The mother of all clouds, present in all 3 layers and the most dangerous clouds for the ground and aviation are cumulonimbus clouds. These can span from around 1.000ft up to the end of the troposphere and are clouds containing thunder, heavy rain, heavy winds(shear) and hail.

Here we have a big one, photographed from a plane at 37.000ft above Portugal in rain season. Not knowing about the dangers of this cloud type back then but thought it was really cool.

This second one is from a summer evening with predicted thunderstorms within an hour, but no full view of the cloud like in the first picture. Such a pretty side view of the high cloud.

In aviation, the general guideline is to stay away at least 15-20 NM from these type of clouds, even with a Airbus A380.

Precipitation and occurence

Precipitation means neerslag in Dutch and is everything that falls out of the clouds onto the ground. Think of:

• Drizzle (motregen)
• Rain
• Snow
• Snow grains (motsneeuw)
• Snow pellets (Korrelsneeuw)
• Hail (hagel)

Precipitation occurs when the cloud elements expand due to several reasons into bigger precipitation elements, which will be heavy enough to fall down due to gravity. A cloud always contains water vapor, but only when this vapor is combined into bigger water droplets, they will reach the ground.

Precipitation and cloud types

To further clarify which precipitation we could expect from a certain cloud, let’s take a look at this table:

Disappearing of clouds

Clouds can disappear in various ways and reasons. This is comparable to the disappearance of fog/mist.

• Raining out: The cloud can simply rain out, losing all of its precipitation components. If no condensation will happen simultaneously, the cloud will lose all its water and dissolve.
• Merging: A cloud can merge with dry air and can cause cloud elements to evaporate. This proces happens continuously because outside of a cloud, the air is not saturated. The outside of a cloud is always more dry and stopping the condensation process can help dissolving the cloud.
• Heating: A cloud can also dissolve due to heating up. This helps lower the relative humidity in the cloud, and mostly will happen due to sunlight heating up the earth, and that warm air rising. This happens mostly for low-level clouds. Clouds in a high pressure area can also dissolve due to subsidy, causing adiabatic heating to dissolve the cloud.

Cloud base and coverage area

For describing the cloud base in aviation, we use 3 terms:

• Type of clouds
• Coverage
• Cloud base altitude (AGL)

Cloud coverage

We use a coverage called in octa’s, where a visual viewer/system will look into the air and divides it into 8 parts. Then it determines how many parts are filled with clouds and makes a representation:

Cloud base

The cloud base is the altitude above ground level (AGL), mentioned in feet (ft). This will be the lowest cloud layer.

The cloud ceiling is the altitude (below 20.000ft)which covers more than half of the sky, so broken clouds (BKN) or overcast (OVC).

If the sky cannot be seen due to fog or mist, there will be a vertical visibility mentioned in feet. This can be measured or estimated.

Cloud types

In the METAR of an airport, the cloud types itself will only be mentioned if significat, like a Cumulonimbus (Cb). The cloud types are used in meteorological messages like in the Dutch general aviation weather bulletin: https://www.knmi.nl/nederland-nu/luchtvaart/weerbulletin-kleine-luchtvaart

Thunderstorms

Thunderstorms is a phenomenon that brings huge dangers for aviation. Thunderstorms only exists in cumulonimbus clouds which bring huge rising and descending winds, turbulence and heavy rain or hail with it. The biggest threat is a thunder strike into the plane, where risks of fire or blindness can occur.

The Netherlands knows around 25 thunderstorm days per year, espexcially over land.

Cumulonimbus clouds are built upon cumulus clouds in a unstable atmosphere which can continue to grow up. We have a towering cumulus cloud type, this is a beginning stage of a cumulonimbus (Cb) which can also be seen as altocumulus castellanus (Acc), which happens with instability on mid-level. This looks like this:

You will see in an nutshell where this name comes from, a castle wall.

Thunder is a electric load from a cumulonimbus cloud. This phenomenon happens when the mass will hit the ground resulting in a flash and a very loud and sharp sound.

Layout of thunderstorms

The layout of a thunderstorm is like how the air movements will be started:

• Frontal thunder: When air passes a front and is forced to rise, thunderstorms can occur if the air is humid enough and the atmosphere is unstable. This can occur in a cold or warm front
• Orographic thunder: Orographic thunder occurs from the forced rise of air over a mountain
• Air mass thunder: Air mass thunders are thunderstorms that are not caused by front passages. During the summer, the high levels of convection in a unstable atmosphere this type can occur. Especially above area’s of high levels of heating like sand grounds. This type is a great example of the heavy storms at the end of a warm and sunny day.

Developement stages of a thunderstorm

A thunderstorm knows 3 stages:

• Cumulus stage (beginfase): Here the cumulus cloud will be expanded due to the rising air. This is only a water-cloud. If this reaches a great altitude, this will be mentioned in the weather reports as towering cumulus. A begin stage of a thunderstorm, with lots of updrafts (convection)
• Mature stage: At the mature stage, the cloud will pass over the 0 degrees celcius point up in the air and the cloud has merged. In this stage, you can expect heavy rain, hail and thunderstroms, and the cloud is a passage for heavy winds from up in the air which is called updrafts/downdrafts
• Dissipating stage: At this stage, the downdrafts will be the boss and because of this, updrafts will be suppressed. This stops the vertical flow of warm humid air and this is the beginning of the end of the thunderstorm. The cloud will rain out till the water is depleted, but the top of the cloud (anvil) can exists for several hours after this, as this is a cirrus cloud, containing ice crystals

The weather during thunderstorms

As the thunderstorms will occur during a unstable atmosphere, you could predict that the weather itself can also be a bit unpredictable.

During thunderstorms, you can expect these types of weather:

• Heavy amounts of precipitation
• High winds and turbulence, with windshears and a high frequency of gusts
• Variable winds as big as 360 degrees difference
• Lots of downdrafts and downbursts of thousands of feet per minutes (a Cessna 172 climbs normally between 700/1000 feet per minute, to give a scale)
• Squalls, which are heavily increased winds minutes before a thunderstorm reaches you

Visibility and fog (10)

In VFR flights where we fly inder Visual Flight Rules, pilots must remain direct sight on ground and water. This is dependent on how many visibility we have in the cockpit, as we have to avoid other traffic. In aviation we can use different terms to describe the visibility:

• Flying visibility (vliegzicht): The visibility from the cockpit
• Ground visibility: The visibility as seen from the ground/tower
• Runway visibility (RVR): On bigger aerodromes, the RVR will be reported under 2000 meters

Visibility direction

The visibility is not always exactly the same in various directions, due to fog or other phenomenons. This can also be reported in different terms to give the pilots a better understanding to avoid assumptions leading to accidents:

• Prevailing visibility (overheersend zicht):This is the value of visibility over at least 50% of the horizon
• Minimum visibility: This is a visibility measurement where the direction of sight is added to, for example 1800SW: this means 1800 meters in south-western direction

Measurements and instruments

To save a lot of time for airport-associates, most measurements are done automatically by instruments. Runway visibility is measured by transmissometers next to the runway, where the visibility can be seen live within seconds. However, intrepretation of automatic systems must be considered if we want to believe this 100%.

Flying visibility

The regulatory visibility for VFR is described in the rules of air space classes. The visibility for VFR that is very important is the slant visual range. This is the line of sight in front of our plane, where we look to the ground. However, when some haze, mist/fog or brume exists, this can decrease drastically.

Mist and Brume occurs

Mist and brume occurs by colling air without any vertical movement. Mist/fog will be categorized into the origin of cooling:

• Cooling at cool surface
• Merging
• Evaporation

Radiation fog

In clear nights, the surface of the earth will cool down by heat-radiation. The air above will also cool down, sometimes even lower than the dew point. This results in condensed water vapor and this is called radiation mist. This can beup to 1000ft high, but also around 2 meters high. Then it will be called ground fog.

Advective fog

Cooling at a cold surface can happen when warm humid air will flow to an aera with cold underground. This fog will be advected. This mostly happens during winter, after a period with frost ends by a new flow of air with relative warm and humid air. This is the warm mass.

Above the sea, this type of mist is called sea mist.

Fog by merging

Merged air can also cause mist

Evaporation fog

Fog can also occur by evaporation of rain. The rain increases the humidity in cold air and this results in rain-mist.

Dissolving mist

The dissolving process of mist is exactly the same as with clouds, they can dissolve in three ways:

• Heating and therefore evaporating the moist
• Merging with dry air, lowering the dew temperature
• Rain out

Mist vs Fog vs Brume

Mist, Fog and Brume are all terms that sounds like they mean the same, but we consider them partly different:

Fronts (11)

Fronts are different weather systems that collide with each other. On a location where two different masses (with different temperatures) of air will collide, there will be a transition zone which is called a “front”. A front is often referred to a zone with clouds and precipitation and therefore relevant for aviation. The weather conditions in a front are dependent on the temperature differences between the air masses, where we have some terms for:

• Active fronts: these fronts consists of huge temperature differences
• Inactive fronts: these fronts constst of low temperature differences

Here active fronts will let you know that they are there with lots of rain and maybe thunder where inactive fronts often go by unnoticed.

Types of fronts:

We can have multiple types of fronts, as illustrated below. The most important types are:

• Warm front
• Cold front
• Occluded front
• Stationary front

Fronts mostly consists of these components:

• Surface front: This is the separation layer, the line between multiple fronts
• Ground front: This is the separation layer, but then on the ground directly under the surface front
• Frontal zone: This is the zone of a front as this can be up to 100km in size

Fronts in meteorologic charts

On charts, fronts will be indicated as lines with different symbols on them, mostly as seen in the picture above about fronts them selves.

Note: the high level/upper air symbols will not be filled, so the middle should be white.

Layout of a warm front

Warm air is lighter than cold air. The warm air mass will flow above the cold layer. This flowing warm air will merge with the cold air and will pull up the air, till the cold air dissappeared. This merge with the forced rise of warm air causes cooling and condensation and can cause clouds and precipitation.

As the rising movement of warm air to the surface front, this will cause condensation. This is the reason why the whole front contains closed clouds:

Source: pilotinstitute.com

Details:

• Precipitation with poor visibility (drizzle)
• Haze
• Pressure rises at arrival, and decreases after passage
• In summer this can cause cumulonimbus
• Wind veeres and increases after passage
• Low turbulence

Such warm front which is stable is a package of cirrus clouds, followed by cirrostratus, then altostratus and then nimbostratus, containing rain. This can also contain a hidden Cumulonimbus, which we call embedded Cb’s.

If the warm front arrives, you will start seeing some cirrus clouds, then some rain and visibility and air pressure will decrease. The winds will increase.

A warm front is slow and therefore is a period with some days of no VFR flying.

Layout of a cold front

Cold air is more dense and heavier than warm air, which causes cold air to displace warm air first at the ground. Just like the warm front, the cold front will move in the direction of the cold air.

Source: pilotinstitute.com

Details:

• Pressure decreases at arrival, increases after passage
• Wind increases and veeres after passage
• Good visibility (when no precipitation)
• Moderate to heavy turbulence and wind shears

The slope of the cold front is much steeper than the warm front. A cold front is also much faster than a warm front, passing by at a higher speed. However, cold fronts can be more dangerous as the warm air causes clouds to rise, causing towering cumulus clouds which can evantually grow into the dangerous cumulonimbus clouds.

A cold front tends to stay at ground level, pushing the warm and moist air up. This creates instability and causes the air to reach its dew point and condensate.

If a cold front arrived, the air pressure will drop, the wind will increase. Then the clouds will increase too.

Stationary fronts

Stationary fronts will stay at a certain position or will move very slowy. Sometimes even slower than 5 knots. There will be no movements, only parralel to the front. This can cause long periods of bad weather, due to the slow speed.

Source: pilotinstitute.com

A stationary front contains weather conditions of both warm and cold fronts and can take up several hours to days.

Winds mostly blow the way the front lies. Not from cold to warm or reverse.

Occlusions

Occluded actually means “hidden”.

Occlusion is where a cold front catches up with a warm front. The warm air is forced to rise off the ground, and the system becomes dominated by cooler air at the surface. This often leads to widespread cloud, steady rain, and sometimes stronger winds near the low-pressure center.

A classic example is a mid-latitude cyclone over northwestern Europe. For instance, when an Atlantic low moves toward the UK or the North Sea, the faster-moving cold front can overtake the warm front. As the occlusion forms, people often experience a long period of thick cloud, persistent rainfall, falling visibility, and a noticeable wind shift.

Then we can have cold front cllusions and warm front occlusions:

• Warm front occlusions: Looks like a line with open red hemispheres on one side and closed red hemispheres on the other side
• Cold front occlusions: Looks like a line with open blue hemispheres on one side and closed blue hemispheres on the other side

Upper-air fronts

We speak of a upper air front if the front-surface is only at high levels and not on the ground. This can occur when a front at the ground dissolves and turbulence merging different masses of air. This can also happen in mountain-rich areas.

Polar fronts

Weather in Europe will be dependent on two big masses of air, polar air from Greenland and tropical air from the Azores islands and north Africa. The transition layer of these two masses is the polar front, just where West europe is. In the summer, this front can be found at latitude 60 north, where Iceland and Sweden are and in the winter at 50 degrees, the line of Netherlands and England.

Frontal depressions

A frontal depression forms when cold polar air meets warmer air along the polar front. A disturbance creates a wave in the front, causing surface pressure to fall and a low-pressure area to develop. The system then forms a warm front and a cold front. Warm air is forced to rise over cold air, producing clouds, precipitation, and wind. As the depression intensifies, the cold front eventually catches the warm front, forming an occlusion, after which the system usually weakens.

The weather we can expect in a frontal depression is a warm front followed by a cold front.

Thermal depressions

A thermal depression is a low-pressure area caused mainly by strong surface heating. When the ground heats up quickly, the air above it warms, expands, and rises. This creates lower pressure at the surface and can draw in surrounding air.

A common example is a heat low over a hot desert or inland plateau during summer. In the afternoon, intense sunshine heats the land strongly, the air rises, and a shallow low-pressure area forms. This can help trigger local winds, dust lifting, or thunderstorms if enough moisture is present.

Ice build-up (12)

Ice build-up can happen on the ground and during flight. Ice on the plane is a huge risk for aircraft, as this causes the following problems:

• Lift will be decreased
• Weight will be increased
• Ailerons and trim can freeze solid
• Ice on propellors decrease thrust
• Ice on propellors can cause huge vibrations
• Ice on the windshield can decrease visibility
• Ice can cause vibrations on antenna’s, potentially breaking them

Let’s take a look at what weather conditions this can happen.

Ice build-up formation

Ice build-up will happen if the temperature is under 0 degrees, and the air contains enough undercooled water. The most chance on undercooled water is between 0 and minus 12 degrees celcius. Mostly, ice build up will happen when precipitation, coulds, brume, fog or mist is in the air or flying into.

The outside temperature of the plane material can also be 0 degrees celcius or lower, causing any moist to freeze on contact. Especially when going from cold air into warmer and humid air.

Types of ice build up

The types of ice build up are:

• Hoar frost (rijp): Freezing water vaporfrom clear unsaturated air under 0 degrees. This will be a thin layer just like on your car in winter-mornings
• Rime ice (ruige rijp): Undercooled water that freezes instantly at contact on your planes’ surface, which looks like coarse (grof) ice
• Freezing rain (ijzel): Undercooled water that is made of big droplets, that freeze instantly upon contact

Ice build-up in fronts:

When in a front precipitation from warm air comes into the cold air, this will then be undercooled water. This frontal investion will cause a ice triangle. In this ice triangle, undercooled water will fall in the form of freezing rain or drizzle which causes a lot of ice build up.

Because of the small slope of the front surface, the warm front is bigger than a cold front.

Ice build up in carburetor

In the carburetor, fuel is mixed with air si the engine always have a optimal mix of both. The engine will suck outside air into a narrow space, called a venturi and then in the carburetor. In this narrow space, there will be a lower air pressure (Bernoulli’s law) and the sprinkler will get fuel, which is combined into brume with the air.

The combination of the air pressure decrease and evaporating fuel, the themperature in the carburetor will decrease with temperatures up to 40 degrees celcius. This cooling can condense the water from the air, and can evantually lead to a solid freeze. This causes the engine to run inconsistent or even turn off, which we don’t want in flight.

The most chance of carburetor ice is in these conditions:

• High humidity: 60% or higher
• Low engine RPM

Always turn on the carburetor heat (CVV) in conditions where you have a lower RPM, sometimes in cruise, but this leads to a drop in RPM.

Meteorologic information sources (13)

Before we are going to lift of in our beautiful aircraft, we must first as part of our flight preparation, look at the weather in our area. The weather can often be predicted pretty well, but in some circumstances this can be very unpredictable.

We can use the following sources to get a good understanding of the weather during the flight:

Significant Weather Charts

Significant Weather Charts are published by the World Area Forecast Center in London or Washington and contain charts with detailed information. This information is encoded with different icons and have their own meaning.

Significant weather charts are meant for a great overview-forecast, especially when planning international flights. These show the flight levels FL100 to FL450

Graphic Low Level Forecast

The graphic low level forecast (GLLFC) is a combinaton of the low level significant weather chart for a Flight Information Region and winds/temperatures from ground to FL100.

All the flags are windbarbs which show the wind direction and speed. It does it in this way:

The max is three of the same filled symbol, with winds above 150 knots you should ask yourself if you even want to be outside.You can see this as a weather station with a banner, it always points to the direction of wind source.

• SIGWX: Significant weather
• VIS: Visibility
• CLD: Cloud base, octa’s, type of clouds and altitude of cloud tops

There are some other abbreviations used in this type of charts:

• COT: Coastal
• LCA: Local
• MAR: Maritime
• MON: Mountain
• VAL: Valley
• LAN: Above land
• MTW: Mountain waves
• WS: Wind shear
• MOD: Moderate
• SEV: Severe

Aerodrome routine meteorological report (METAR)

On controlled airfields, for the full 24 hours on a day there will be done measurements of the actual weather and published every 30 minutes. This looks like a code to new people, but still resides from older ACARS and teletext solutions used in the past.

METAR EHAM 211125Z 05009KT 020V080 9999 FEW008 07/04 Q1019 NOSIG

This actually means this:

• EHAM Amsterdam Schiphol Airport.
• 211125Z Observation on the 21st at 11:25 UTC.
• 05009KT Wind from 050° at 9 knots
• 020V080 Wind direction varying between 020° and 080°
• 9999 Visibility 10 km or more
• FEW008 Few clouds at 800 feet
• 07/04 Temperature 7°C, dew point 4°C
• Q1019 Pressure 1019 hPa
• NOSIG No significant changes expected in the near future.

That states a lot more; meaning a cold spring day with this weather:

Source: AMS Live on Youtube

CAVOK means “Ceiling and Visibilty OK” and is only mentioned by ATIS/METARs if the following criteria are all met:

• Horizontal visibility of 10.000 meters or more
• Cloud ceiling 5000ft or higher
• No significant weather like cumulonimbusses, towering cumulonimbusses
• No thunderstorms
• No ground fog/haze/brume
• Measurement is not done automatically (otherwise it will be NCD meaning No clouds detected)

If one of the above criteria are not met, NSW or NSC will be used:

• NSC (No Significant Cloud): no clouds below 5000 ft and no CB/TCU present.
• NSW (No Significant Weather): indicates that no significant weather phenomena (e.g., rain, snow, thunderstorms) are occurring or expected. Mainly used in TAF trend forecasts.

In America we have another option: CLR

• CLR (Clear): no clouds detected below 12,000 ft (primarily used in North America).

If the METAR contains any slahes ////, then the information is not measured, giving no 100% warranty on the information:

METAR EHAM 211125Z ////KT 020V080 9999 BKN008/// 07/04 Q1019 NOSIG

Here the wind and type of clouds is unknown, meaning that any cumulonimbus could be hiding.

METAR is actual measured weather with a trend and TAF is a forecast for the coming 24-30 hours. When departing from a controlled airfield, you are required to listen to the ATIS containing this METAR information which will be coded with a increasing letter (like Delta). When asking for the flight clearance, you have to pass on this letter as acknowledgement that you have listened the ATIS. When a new METAR is released in the meanwhile, you need to monitor the ATIS again.

A SPECI is actually a intermediate METAR, published if any significant change was measured. On military fields, this color code is being used.

TAFs

An airport with weather station also has something called a Terminal Aerodrome Forecast. This is a text-based forecast of the weather in reach (5 nautical mile range) of the airport in de coming 30 hours. We use this to plan flights more that 6 hours ahead. A metar is only valid for 30 minutes.

• If needing weather information within 2-3 hours of landing at an aerodrome, use the trend of the airport
• If needing weather information longer than 3 hours, use the TAF

VOLMET

A VOLMET is weather information for planes en-route. This is broadcasted on VHF frequencies which you can listen out, and are totally meant for international commercial traffic. “En vol” in French means for flight, this is the source of this name.

The VOLMET is really like an ATIS but then on route and an example is this:

“Amsterdam VOLMET weather at 1125 UTC on the 21st. Wind 050 degrees at 9 knots, varying between 020 and 080 degrees. Visibility 10 kilometres or more. Few clouds at 800 feet. Temperature 7, dew point 4. QNH 1019. No significant change expected.”

SIGMET and AIRMET

Aside from the given sources of weather information, two separate messages can be published:

• AIRMET: Advises of less severe weather, but still important for flight operations. Typically affects smaller aircraft or general aviation. Examples: moderate turbulence, moderate icing, mountain obscuration, widespread IFR conditions.
• SIGMET: Advises of severe or hazardous weather that can affect all aircraft. Higher priority than AIRMET. Examples: severe icing, severe or extreme turbulence, volcanic ash, sandstorms, severe thunderstorms.

In simple terms:

• AIRMET = caution (important weather)
• SIGMET = danger (serious weather hazard)

These messages can be received from your preparation, ATC or flight information services or your VFR navigation app like SkyDemon.

Weather radars

We also have weather radars, both on the ground and installed on some planes. Weather radars will send radio frequencies in the 6GHz band into the air, and can detect any reflections. This 6GHz band can receive precipitation elements pretty good and therefore can make a good forecast of the weather ahead. It basically sends a radio pulse into the air, and those precipitation elements like rain and snow reflects it back.

Sometimes, this causes clutter, which are false positives received by other devices or buildings on the ground but will be filtered for the greatest part.

A weather radar as a reach of around 200 to 250km, which makes it possible for the KNMI residing in de Bilt to scan the whole country and great parts around it.

Thunderstorms can also be detected as they are being measured using a different set of electromagnetic radiation detectors.

Satellite images

We can also use satallite images from the Europen Metrosat satellite. This satellite makes pictures every 15 minutes in two different types:

• Visible light (VIS)
• Infrared (IR)

These can be used to cross check to view which type of clouds are present and which protions are visible.

Visible light images give a great overview of the clouds. Thick clouds are lighter than thin clouds, but no difference can be seen within low and high clouds.

Infrared images will show the temperature of the clouds, where warm surfaces are darker and cold surfaces are lighter. Low clouds therefore are grey and high clouds are white.

Left: Infrared Right: Visible light

Thunderstorms are not visible on these satellite images because they look like high clouds. Satelitte images can only detect the highest point of the clouds, so we can use them but this is not our primary source.

To use satellite images, visit this website: https://eumetview.eumetsat.int/static-images/latestImages.html

GAFOR

In some countries, we have the GAFOR, called the general aviation forecast. This is a code which is valid for 6 hours, looking like a METAR but has some different coding:

GAFOR: Route A – X-RAY Validity: 21 March 2026, 1200–1500 UTC Weather: Broken cloud layers, local rain showers, moderate visibility reduction in precipitation Cloud base: 1,500–2,000 ft AGL Visibility: 5–8 km, locally 3 km in showers Wind: 220/15 kt, gusting 25 kt over higher terrain Freezing level: 6,000 ft Turbulence: Light to moderate below 4,000 ft Icing: Nil below freezing level

The types/codes are given:

O – Open: Conditions are suitable for VFR along the route D – Difficult: VFR is possible, but conditions are difficult M – Marginal: Conditions are marginal for VFR X – Closed: The route is closed for VFR due to weather conditions

In the Netherlands, you can use the Weather Bulletin for General Aviation from the KNMI which gives a better understanding but bigger countries work with the GAFOR, mostly bigger countries.

That was it for Meteorology.

To do

• Review fronts, transitions and results
• Adiabatic processes
• Anabatic/katabatic processes
• Coriolis effect and forces
• Frontmist is caused by warm fronts and its precipitation

End of the page 🎉

You have reached the end of the page. You can navigate through other blog posts as well, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog homepage

If you find this page and blog very useful and you want to leave a donation, you can use the button below to buy me a beer. Hosting and maintaining a website takes a lot of time and money. Thank you in advance and cheers :)

The terms and conditions apply to this post.

Human Performance & Limitations (HPL)

Breath and effect of low blood pressure (1)

In aviation, we are mostly in environments of low air pressure. As we go further up in the air, the pressure goes down. This will have some effects on humans, where we could have hypoxia and barotrauma.

Hyperventilation and carbon dioxide-poisoning will play together with breathing and the effect on blood gasses. We will take a look into them all.

The air in the troposphere

In the Troposphere (0-36.000ft), we have an air mass that consists of the following components:

Air pressure

As we already discussed this topic thoroughly in Meteorology, please take a look at there if you want to know more about air pressure: https://justinverstijnen.nl/ppl-theory-met/#air-pressure

The art of breathing

Organs and vessels in your body need energy to function properly. This energy will be generated by burning nutrients (voedingsstoffen). The process of burning nutrients is called oxidation. In this process, oxygen is used and as a result carbon dioxide which we breathe out. So the goal of breathing is to get energy.

Breathing conists of 3 phases which are in a never-ending circle:

1. External respiration is the process of gas exchange between the lungs and blood
2. The transport of oxygen and carbon dioxide from and to organs and body tissues
3. Internal respiration is the gas exchange between the blood and the body tissues

The functions of why we breathe are:

1. Transport of gasses between blood and lungs
2. Cel-breathing between body cells
3. Transport of carbon dioxide between vessels and organs and the lungs
4. Transport of oxygen to organs and vessels

Because we need to actually be able to inhale and exhale air, the oxygen pressure in the lungs is lower than in the atmosphere. This is because breathing requires air to move in and out of the lungs. For that airflow to happen, the oxygen pressure inside the lungs must be lower than in the atmosphere.

The most important factor of breathing regulation is the carbon dioxide pressure in the blood.

Ventilation

Ventilation is the process where due to the movements of the breast carcass air is transported from and to the lungs. The capacity of a adult is around 6 litres. The vital capacity, usable capacity and actually filled part is around 4,5 litres.

• At rest, the breath frequency is around 15 per minute
• Every time, around 0,5 litres of air is inhaled, called the breathvolume

When breathing, the lungs fill up with air and the air will go through the small bronchi and bronchioles in the lungbladders. These lungbladders are called the Aleovi.

Alveoli and external respiration

The alveoli is responsable for the transport of gasses. Oxygen and other gasses in the air will go through the thin wall between lung bladders and blood. Simultaneously, carbon dioxide will flow through the blood back into the lung bladders, which is actually the external respiration. The blood rich of oxygen is then pumped from the lungs to the heart and other organs through the body.

The frequency and depth of breathing is primarily controlled by the carbon dioxide concentration in the blood.

Transport of oxygen in blood and internal respiration

Oxygen in blood will be transported by a special transport-protein called hemoglobin (Hemoglobine). This is a ron-containing protein which is located in the red bloodcells. This stuff is the cause of the red color blood has.

In the exchange of gasses in the alveoli, the hemoglobin will be almost fully (97%) saturated with oxygen. This oxygen-rich blood will be pumped through the body and body tissues. In the meanwhile, the body tissues will give back the carbon dioxide back to the blood. This is a description of the internal respiration.

When hemoglobin absorbs oxygen-molecules, the color will change:

• Oxygen rich blood is clearly red
• Oxygen-low blood is dark red

In cases where a person has less oxygen than needed, the skin will color blue. This process is called cyanosis (cyanose). This will be visible at the fingers or lips first.

Hemoglobin and its properties

The link between oxygen and hemoglobin depends on the amount of available oxygen in the alveoli. The higher the O₂ pressure, the higher the concentration of oxygen in the hemoglobin. This link can be seen in the graphic below:

If you increase your flying altitude, the oxygen pressure will decrease. This will go slowly in the beginning of the graphic, but from around 70%, this will go very fast at the steep side of the curve. The curve can result in very fast change of symptoms.

Hypoxia

Hypoxia is a condition where a body gets too less oxygen. When exposed for the first time to an environment with low concentration of oxygen, you will not really feel a difference, because oxygen saved in the blood and body tissues can be used for a few minutes. After the oxygen supply is depleted, you will start feeling some really big differences:

1. Impaired judgment and visual (especially at night)
2. Reduced concentration
3. Euphoria and or Overconfidence
4. Headache
5. Dizziness
6. Fatigue
7. Shortness of breath

The chance of getting hypoxia is different for every person, but some critera:

• Oxygen pressure (PaO₂) as stated in the graphic above
• Exposure time to less oxygen
• Oxygen usage of the body, this is linked to physical extertion (lichamelijke inspanning)
• Personal condition
  • Better when not tired
  • Better when not drinking
  • Better when not smoking
  • Better when not having a too high BMI

Because of night visuals are affected first, the maximum altitude without supplemental oxygen is 5.000ft instead of 10.000ft in daylight.

Fun fact: Hypo is a definition of: “Too less”, xy is a shortened version of Oxygen.

*Based on the pressure altitude

A rule of thumb is to remember the 5.000ft at night and 10.000ft at day as lines to not cross without forms of oxygen. Above 10.000 feet, you must have supplemental oxygen for everyone on board for 30 minutes or longer. From 13.000 feet and above, supplemental oxygen is mandatory.

Other causes of hypoxia

There are some other, way less occurring causes of hypoxia:

• Hypoxic: The oxygen pressure is too low
• Anemic Hypoxia: This is caused by a too low capacity of oxygen transportation in blood, due to blood loss, blood donation, exposure to carbon monoxide or Anemia (bloedarmoede).
• Ischemic Hypoxia: This is caused by a decrease of blood transportation to body tissues. Mostly occurring when exposed to G-forces. More on G-forces later

Carbon monoxide (CO)

Carbon monoxide is a highly poisonous gas without color or smell which arises when hydrocarbons not fully burn. Types of hydrocarbons (koolwaterstoffen) are:

• Oil products
• Gas
• Exhaust gasses (small percentage)
• Cigarette smoke (small percentage)

Carbon monoxide is highly poisonous because it wants to merge with hemoglobin. This affinity is around 200 times stronger than the affinity with oxygen. You’ll get the idea. Because of this a small percentage is needed to disrupt the flow of oxygen and unconciousness comes within minutes.

Sources of carbon monoxide

Exhaust gasses contain a small percentage of carbon monoxide. In planes and helicopters with a leak in the exhaust-system can also leak carbon monoxide. This can also leak through the cabin heating system to the cabin itself.

Symptoms of carbon monoxide poisoning

The following symptoms will happen when being in a carbon monoxide poisining:

• Light headache
• Hyperventilation
• Sleepy feeling
• Degraded decision making
• Short-breathing
• Tunnel vision
• Seeing blurry

And every second exposed to carbon monoxide, these symptoms will increase till you die. If exposed to air with 0,1% of carbon monoxide, you could die just within 30 minutes when doing nothing.

This is why we pilots have CO/carbon monoxide detectors on board:

This is a passive detector, which only colors. If feeling one of the symphoms, look at the dot. If its dark, then open the windows and land as soon as possible. There are also active detectors available just like in your home.

Important things about Carbon monoxide and flying

• Be alert when feeling light symptoms
• Be alert on exhaust gasses in the cockpit
• Have a CO detector, recommended is an active that makes noise if it detects something

When having symptoms or an alert that goes off, do these things:

• Turn off the cabin heating
• Ensure fresh air goes into the cockpit, for example by opening an window
• Use supplemental oxygen if on board
• Land as soon as possible, or do a precautionary landing
• Call a doctor
• Investigate the aircraft by a certified organization after landing

By breathing fresh air, the elimination of carbon monoxide from the body can speed up.

Hyperventilation

Hyperventilation is usually caused by stress or anxiety, leading to excessive breathing that lowers carbon dioxide (koolzuurgas/koolstofdioxide) levels in the blood, which then produces the characteristic symptoms:

• Dizzyness or light headed
• Short breathing
• Feeling tingling in hands, legs or around the mouth
• Muscle cramps or decrease in muscle power

To solve an ongoing hyperventilation, let the person breathe into a small waste bag. This will breathe in some carbon dioxide (CO₂), and will increase the CO₂, which solves the symptoms.

Hyperventilations can also happen fysiologic when fitnessing or working out. The human body will then on purpose have less O₂ in its blood and will increase the breathing rate to compensate for it. This is normal behaviour.

Expansion of closed gasses

In the human body, there are some cavities which are filled by air or gasses. With an increase of altitude, this atmospheric pressure will increase and those gasses will expand.

Complaints caused by expansion of those gasses can occur in several organs like the middle ear, paranasal sinus (neusbijholtes), the gastrointestinal tract (maagdarmkanaal) and teeth. Symptoms can be feeling little to severe pain.

Middle ear

The middle ear is linked up by the eustachian tube (buis van Eustachius) with the nasopharynx (neuskeelholte). This helps having the air pressure on the eardrum equal.

If the nasopharynx swells up by a sinus infection or hay fever, the eustachian tube can be constipated. When increasing or decreasing in altitude, this leads to a pressure difference between the middle ear and the atmosphere. This can cause the eardrum to bend in or outside.

This is why it’s not a great idea to fly if having a sinus infection because it can permanently damage your hearing.

When having this, you can get pain in your ears, pressing feeling or even cracks in the eardrums. This is called barotitis.

The eustachian tube is designed that air can easily escape through the middle ear. When climbing in a plane, most people doesnt have that much problems. The most problems are when descending, where the pressure will increase rapidly.

Barodontalgia

Barodontalgia is where teeth give a lot of pain because of the pressure difference. This pressure pushes on the teethnerves causing this pain. This goes away in time, as the pressure equals.

The circulatory system (2)

The circulatory system (de bloedsomloop) is the transportation of blood throughout the body. Blood transports oxygen and nutrients to organs and body tissues and collects garbage in the form of carbon dioxide (CO₂) and other garbage. The engine of this circulation is the human heart.

The heart is a specialized muscle which is a double pump:

• The left half pumps blood around the body which is called the big circulation
• The right half pumps blood to the lungs which is called the small circulation

The heart pumps around 60 to 80 times per minute at rest.

Regulation of heart rate

The heart rate will be controlled primarily by the sinus node (sinusknoop), which is a nerve node (zenuwknoop) in the heart itself. The speed where the node will fire signals is influenced by hormons like adrenaline.

Blood vessels

Blood vessels are tube-like structures in the human body where blood flows through. There are 3 types of blood vessels:

1. Arteries (slagaders): These carry oxygen-rich blood away from the heart through the human body. The aorta is the big body arterie that comes directly from the heart
2. Veins (aders): These carry blood back to the heart after the oxygen and other stuff is depleted from that blood
3. Capillaries (haarvaten): These are called this because those are the thinnest blood vessels. They ensure blood reaches the body tissues in cells and waste products are moved back in the blood

The coronary artery (kransslagader) is the road of blood to the heart itself.

Blood pressure

Blood pressure is the pressure of the blood vessels in the big circulation. This pressure is a result of the heart pumping in a certain speed. Blood pressure is measured in the two stages, and gives a double number. For a normal adult, the healthy blood pressure is 120/80 (mmHg or inches of mercury).

• Systolic pressure (overpressure): This is at the moment of contraction (samentrekking) of the heart and reaches about 120 mmHg
• Diastolic pressure (underpressure): This is the moment of underpressure between contractions where the pressure decreases to about 80 mmHg

This gives us the 120/80 healthy condition which can defer for every person.

Regulation of blood pressure

Most organs can survive some time without blood supply, but the human brain is very sensitive at variation of blood supply. This is why the human body consists of baroreceptors. These are pressure-sensors which are in the aorta and arteries which will measure the blood pressure. A low blood pressure is then corrected by increasing the heart rate or increasing the force of pumping.

Cardiovascular diseases

Cardiovascular diseases (hart en vaatziekten) are the primairy cause of death in the western world. One because its a broad term and 2 because we are not living very healthy. Incidents that could be categorized as cardiovascular diseases are:

• Heart attack
• Angina pectoris
• Cerebral infarction (herseninfarct)

These diseases are caused by atherosclerosis, which means that the veins are full of calcic (kalk). This will then also cause bloodstols which is called thrombosis.

An heart attack and angina pectoris are coronal heart diseases. This is when the coronal veins/coronary arteries (kransslagaders) are affected. If one of the coronary arteries slits up by atheroscerosis, a part of the heart muscle will die because of a oxygen deficiency (zuurstoftekort). This is the definition of a heart attack. A cerebral infarction for the brains is the same principle.

High blood pressure

At a high blood pressure, also called a hypertension the diastolic pressure is higher than 90 mmHg and the systolic is higher than 140 mmHg. A mild increase of the blood pressure will not give symptoms, but is one of the critical causes of atherosclerose and with this other cardiovascular diseases. When having a blood pressure of 160mmHg/95mmHg or higher, you will not pass the medical certification (class 2) you need for a PPL license.

The causes of hypertension can variate between such different items:

• High body weight (BMI above 25)
• Unhealthy food
• Not enough physical exercise (less than 150 minutes per week)
• Genetic factors

Accelerations during maneuvers

During normal conditions with normal gravity, a human is exposed to around 9,8 m/s of gravity. During maneuvers, this can increase where the power on a body can heavily increase. We will call this G-forces or gravity-force. This number states the force and is a factor of how heavy you feel opposing the gravity.

• Positive G (+G): Blood is pushed toward the feet. This can reduce blood flow to the brain and may cause blackout or tunnel vision, like as we learned, the brain needs oxygen to function and we disrupt this
• Negative G (−G): Blood is pushed toward the head. This increases pressure in the eyes and head and can cause a red-out, where vision turns reddish

Humans usually tolerate positive G better than negative G because the blood vessels in the head are more sensitive to increased pressure. In both cases, its heavily recommended to stop your maneuver and keep the plane level.

• The human brain has a oxygen storage of about 5 seconds

In fighter jets, the pilots have a special suit (g-suit) which is very tightly around the stomach and contains pressured air. This helps the flow of blood and stops it from going to the feet. They are also specially trained with breathing techniques where they can be exposed to 9G for a small time, where normal people will pass out at around 4-5g for some seconds.

The eyes (3)

Eyes of a human person are built from glass-like material, which is a clear and jelly like liquid. The inside of the eye is for the biggest part the light-sensitive retina (netvlies). At the front of the eyeball, there is a lens and iris, which is the rainbow-membrane and the diaphragm of the eye. The pupil is the central opening in the iris.

From retina to view

The eyes work realy similar to how a camera works. Light will be projected by the lens onto the retina which consists of light-sensitive cells. The signals of those cells will be transported by the eye-nerve to the brain. In the brain is the view converted to real pictures the human can see.

The iris is really similar to the apperture of a camera. In low-light area’s, it will become bigger to cach more light where it becomes smaller in light-rich area’s to compensate for the heavy amounts of light.

Cones and rods

In the human eye, we have 2 components which helps getting a good view:

• Cones (kegeltjes): Are used for seeing sharp and details, but not for light. They are connected all to a single cell -> parralel
  • Kegeltjes -> Kleur + detail
• Rods (staafjes): Are used seeing in the dark, their light-sensitivity is 10.000 times higher than rods. Cones are less great for seeing sharply as they are all connected to some cells -> serial
  • Staafjes -> Nachtzicht

Area of view

The area of view a human person can see is circle-formed and is around 90 degrees long to 60 degrees up.

Central viewing part

The rods are concentrated on the yellow part, called the macula lutea. The center of the yellow spot is called the fovea and only consists of cones, without any blood vessels between. There is a very small area where you can see very sharp, of around 5 degrees up and width. This is the text you are now looking at.

Peripheral visual field

In the part of the retina outside of the yellow spot, we have the peripheral visual field (perifere gezichtsveld). This part only consists of rods and you will not see very sharp in this part, but its great for seeing better in the dark. Our eyes are a combination of both things, making it all round. This part only has 10% of the sharpness of the central viewing part.

Blind spot (Optic disc)

At the part of the retina where the nerves converge and transition into the eye-nerve, we dont have light-sensitive cells. This is the blind spot, called the Optic Disk. This sits around 15 degrees outside of the view of every eye.

To test your blind spot:

• Cover your left eye and stare at the cross with your right eye
• Now slowly move towards the computer screen while still staring at the cross with your right eye
• At somewhere around 30 centimeters inches from the computer screen, the black circle will disappear. This is the blind spot of your eye

Viewing sharpness

The visus is the rate of detail which we can see. The visus of the eye is always linked to the central viewing area. An eye with normal sharpness can separate details with the size of one arc minute (boogminuut). This is equal to:

• A line of 1,75 mm thick at 6 meters distance

This is called visus 6/6, 20/20 or 100%. Young children can have even more than 6/6 or 100%.

The sharpnmess is dependent on several factors:

• The amount of light, too much or less light means no sharpness
• The contrast of the object
• The refraction status, which is weaker in two conditions: nearsighted and farsightedness

Accomodate

Accomodating means setting your eye sharp. The lens of the eye can make itself ball or flat, respectively for seeing close by or far away. This proces is a lot harder from 40 years old where this completely stops around 65 years old. This is called presbyopia.

Refractive errors

Some people have a different shape eyeball, which means no sharp vision can be projecten onto the retina. The most occurring types are:

• Myopia: Nearsightedness. You can see nearby objects clearly, but distant objects look blurry. (Bijziendheid)
• Hypermetropia: Farsightedness. You can see distant objects more easily, while nearby objects may look blurry. (Verziendheid)
• Astigmatism: A common vision condition where the eye is not perfectly curved, causing blurred or distorted vision at different distances.

Having such errors can speed up the presbyopia process when becoming older.

Depth-perception

To estimate distances between objects as person, we need to see sharply in the distance. The brain will use both binocular as monocular reference points to convert visual information to a three-dimensional vision.

• Binocular: using both eyes
• Monocular: using one eye

Stereopsis

Stereopsis is the process your brain takes to combine two slightly equal visions into one big vision. Its making a panorama-picture realtime, the whole day long.

Night vision

For seeing properly in low light environments, we use the rods in our eyes. The cones are barely adding something to this in low level environments.

The rods are outside of the yellow spot, thus the central vision, which is the reason you sometimes have to look about 5 to 10 degrees away from an object in the dark to actually see it.

Dark-adaption

For the most effective night vision, the rods have to adapt themselves to the darkness. This can take up to 30 minutes and will make a human eye about 1 million times more light sensitive. This is the reason when flying in the dark, the lights on board are also dimmed greatly. In case of emergencies, we dont have to adapt our eyes to the darker environment outside of the plane.

In the first 10 minutes, the cones will be more sentitive but the rods will take over after that. The speed depends on the first and second environment. How bigger the difference is, how longer the adaption takes.

Light-adaption

Light adaptation is much faster than dark adaptation because the eyes are adjusting to light that is already available. At night flights, the cockpit and cabin lights are mostly red to not expose too much blue light. Blue light makes the light/dark adaption proces longer.

Eye defects

We have some bugs that people can have with their eyes:

• Cataract (Staar): A defect where the lens of the eye becomes cloudy, causing blurred or dimmed vision (mostly happening above 45 years old)
• Glaucoma: A group of eye diseases that damage the optic nerve, often linked to high pressure in the eye, and can lead to vision loss

The hearing (4)

The hearing organ consists of 3 parts

• The outside ear
• The middle ear
• The inside ear

Lets take a look at this picture:

Outside ear

The outside ear is the outside part containing the ear-auricle (schelp), the ear canal and the eardrum. The auricle catches sound and will lead that into the ear canal. This will cause the eardrum to vibrate and convert the signals to the brain.

Middle ear

The middle ear is a air-filled hollow pipe connected to the Eustachain tube and this tube is connected to the nasopharynx (neuskeelholte). With this connection, the pressure can be similar in both the inside and outside ear.

The cochlea is the actual hearing organ, which is filled with moist. The vibrations of the eardrum will transported to the cochlea using some small bones. In the cochlea, some vibration-sensitive hairs are available which move with the sound and this transfers to the ear-nerve to the brain.

We also have the vestibule, which is the organ of equilibrium (evenwichtsorgaan).

Inside ear

The inside ear consists of the Cochlea and the Vestibule and can witness turning increases, linear increases and sound.

Sound waves

Sound is fast air pressure changes which the hearing organ can witness. These air pressure changes are called sound waves and are indicated in Hertz (Hz). 1 Hertz means one vibration per second, where human speaking sits from 500Hz to 3000Hz

The amplitude of the sound means how loud the sound is, measured in Decibel (dB). The decibel ratio is exponential, where every 3dB increase means twice the amplitude.

Ear defects

The ears and soudn transported to the brain can decrease over time. We have multiple types of defects:

• Conductive hearing loss (geleidingsverlies): This means when the cause sits in the ear canal, ear drum or middle ear
• Perceptive hearing loss (perceptief gehoorverlies): This means when the cause sits in the cochlea or ear-nerve. This is mostly permanent and contains noise induced (NILH) and elderly loss of hearing (presbyacusis)

When exposed to high levels of sound, the sound will increase the hearing threshold. This means you temporarily perceive this louder sound somewhat more quiet, indicating that your ears will start hearing loss.

Wearing a headset in a single engine plane prevents you from having hearing defects and will make you communicate much better than shouting.

Balance and air sickness (5)

In the inside ear are 2 organs located:

• Cochlea: already discussed, organ which processes your hearing and sounds
• Vestibule: the balance organ

The vestibule itself also consists of 3 parts:

• Utriculus: a bladder filled with moist and otoliths
• Sacculus: also a bladder filled with moist and otoliths
• Semi circular canals: These are three canals filled with moist, 1 is horizontally and 2 vertically

Otoliths

The otolith organs consists of 2 groups of hair cells which will be covered by a gelatined layer. At the outside, there are some calcium carbonate crystal which are the actual otoliths itself.

These two groups each have their weaknesses:

• The horizontal otolith is sensitive for horizontal speed changes (left, right, front, back)
• The vertical otolith is sensitive for vertical speed changes (up, down)

These organs detect linear speed increases. The otoliths have a higher density than the moist around, they will glow a little bit behind. The hair cells will move similarly and this gives us the feeling of moving.

Semi-circular canals

The semi circular canals are the three “half-circles” you see at the ear schematic. These canals are filled with fluids where one lays horizontally and the other two vertically. These canals detect angle speed increases as they both make an angle of 90 degrees and can detect rotations around all three axis:

• Roll
• Pitch
• Yaw

When the head rotaties, the fluid will have a short latency because of mass-slowness. The movement of the fluid will be picked up by the small vibration hairs. If the rotation speed will stay the same, the feeling will disappear after a while when the fluid is stabilized.

Both the Otolith and semi-circular calans have a perception threshold, which must make a speed increase to notice. If the fluids don’t move at all, we can get illusions, like we don’t percept movements at all. The balance-setting will be applied when no speed increases are being percepted.

The balance-organ is not designed to feel a difference in gravity and centrifugal force.

Semi circular canals are sensitive for angular accelerations (hoekversnellingen/draaiversnellingen).

Air sickness (also called travel sickness)

Air sickness is a movement sickness which is really similar to car sickness. It is primairily caused by contradictory information from seeing and feeling in your body. Flying with people that cannot see the horizon can also cause this.

Symptoms of air sickness are:

• Nausea (misselijkheid)
• Throwing up
• White-face
• Transpiring (cold sweat)
• Heart-poundings
• Hyperventilation
• Sleepyness

Air sickness can hugely decrease the normal functions of a human person. Good to know as pilot.

Air sickness is less common for people like pilots as they control the plane and are in sync of what they see, do and feel. Focussing on controlling a plane also helps getting enough cognitive effort.

One way to manipulate the body of passengers who are getting air sick easily is to give them some tasks, like making pictures of buildings, looking out for certain points of interests on the ground or help to look out for other traffic. This doesnt have to be al real task you need, only to keep them busy.

After a person is exposed multiple times to certain plane movements, the sickness will go away as the person adapts to the movements. Also avoid turning your head in situations with turbulence or heavy winds, as this also manipulates the semi-circular canals.

Perception and orientation (6)

A human is continiously aware of the state of the body against the environment around it. This capacity of aerial orientation is the result of 3 components:

• Vestibilar device: delivers information about the direction of gravity and speed changes
• Proprioception: This exists of nerve-endings in the human skin, muscles and joints. Basically everyting you feel including intuition
• The eyes: The eyes deliver the visual image. This is 80% of the full orientation-process

The combined information of these 3 systems will enable us to do handlings and coordinate movements. When one of those three will stop functioning or delivers wrong information, most all-day tasks are becoming very hard to impossible.

Because of all these instruments our human body has, there is a very important rule to note:

• Disregard your feelings when controlling a plane

In a plane you will move around and fly horizontally just because your eyes see a straight horizon. When flying without any sights and on feeling, you will end up losing control over the aircraft within 60 seconds and even faster when banking.

Desorientation

Desorientation happens when the perception and orientation stops working. Your human body who was designed to feel and coordinate on the ground is tricked into things that do not happen actually. This is called an illusion, which is basically an incorrect perception.

Examples of illusions are:

• Leans: A pilot may feel that the aircraft is banking even when it is actually level, or feel level after returning from a real bank. This can lead to incorrect control inputs as the pilot tries to “correct” a false sensation.
• Coriolis Illusion: This happens when the head is moved during a prolonged turn, creating a powerful sensation of tumbling or spinning on a different axis. The result can be severe disorientation and an inappropriate attempt to recover from a motion that is not actually happening.
• Somatogravic Illusion: Rapid acceleration can create the false sensation that the aircraft is pitching up, while deceleration can feel like pitching down. This may cause the pilot to push or pull the controls incorrectly, especially during takeoff or go-around.
• G-Effect: High or changing G-forces can distort a pilot’s sense of pitch and attitude. This can result in a false perception of the aircraft’s position and lead to dangerous control errors.

The Leans illusion is the most happening illusion and can be very dangerous if not treated correctly.

Visual illusions

We also have visual illusions, where we percept things differently than they are really.

• Approach and Landing Illusions: Visual cues during approach can make the runway appear higher, lower, closer, or farther away than it really is. This can lead to an unstable approach and an incorrect glide path. This is especially important at runways with a slope angle.
• Strong Lights and Contrasts: Bright lights, dark surroundings, or sharp visual contrasts can distort depth perception and distance judgment. As a result, the pilot may misinterpret altitude, alignment, or rate of descent.
• Autokinesis: A small stationary light in darkness may appear to move when stared at for several seconds. This can cause the pilot to mistake the light for another aircraft or to follow a false visual reference.
• False Horizon: Sloping cloud formations, shoreline lights, or ground patterns can be mistaken for the true horizon. This may cause the pilot to align the aircraft with a misleading reference and enter an unsafe attitude.

To avoid desorientations, the most important rule is to not do VFR in Instrument Meteorological Conditions (IMC). Stay alert and keep your situational awareness and use the IM SAFE checklist.

Looking out

In VFR flights, we mostly fly with the see-and-avoid principle, where we constantly look out for other traffic and avoid them as much as possible by sterring to the right. ATC does only completely separate VFR traffic in Class B airspace (Also in A, but we are generally not welcome there as VFR).

To look out for other traffic, we use a method called scanning, where we will keep a good picture of the fromt 180 degrees viewing field in front of the plane. We can switch for around 10 degrees and at least one second to actually separate the details/clouds from real threats in the air.

Some limitations of this principle aire:

• Human facturs
• Fast movers
• RAM-course, where other traffic keeps a constant relative bearing from our plane
• Hear is see

This is why we would always sign into Traffic Information Services, have our Transponder enabled and TCAS if built in.

Flying and healthiness (7)

Flying in a wrong condition is prohibited by the dutch “Wet luchtvaart”. Before even thinking of touching a plane, we must first run through this IM SAFE checklist:

• Illness
• Medication
• Stress
• Alcohol
• Fatigue
• Eating

Illnessses/sickness

Someone who is really sick will not feel like flying. If not functioning properly in day to day tasks, you wouldn’t be flying either. We can have several idderent types of sicknesses:

• Sinus infection
• Hay fever
• Gastrointestinal disorders (Maagdarmaandoeningen)
• Infections

If flying with a sinus infection or hay fever, the chance of these two symptoms is greatly increased:

• Pressure vertigo
• Pain in the frontal sinuses and paranasal sinuses

Medicines

When a pilot uses medicines, there are some things to look after:

• Possible side effects
• If the results are enough for flying an aircraft

If you are using medicines to suppress pain or other things, you must ask yourself if fit-to-fly. Some regulatory rules that forbids flying in these certain conditions are:

• Using medicines which can disrupt safe flight execution
• Be aware of possible decrease of medical condition
• Pilots are required to ask for advice if having any chronical sickness or medicines

Coughing medicines

There are some medicines against coughing, which work by supressing the cough reflexes in the brain. They also give some feeling of sleepyness.

Ephedrine and other dangerous medicines

In some countries, we could buy cocktails of different medical cpmponents like:

• Antihistamines
• Adrenal cortex hormones (bijnierschorshormonen)
• Ephedrine
• Pseudoephedrine

They all are forbidden in the Netherlands because of the great side effects like sleepyness and seeing blurry.

Sleep and calming medicines

Medicines that cause sleepyness are considered one of the most dangerous types of medicines for aircraft pilots. Those medicines can cause effects up to 72 hours like:

• Sleepyness
• Less capacity for stressful situations
• Less concentration
• More vulnerable for illusions

The general guideline is when taking medicines that cause sleepyness, wait at least 24 hours before controlling a plane.

Alcohol

Flying under influence of alcohol is forbidden, just like driving. In aviation, the rules are more strict because of possible damages. The general rule is that someone drinking any alcohol must wait to 10 hours before controlling an aircraft. In reality, people can have a decreased functioning even after these 10 hours.

A person is punishable when having more than 0,2 promille, which is 90 (µg/l) micrograms per liter. This counts for everyone doing flight preparations, executions and such.

Obesity

Obesity or being overweight causes more diseases and people are a lot more sensitive to hypoxia and G-forces.

Smoking

Smoking has both short-term and long-term effects on the human body. The long term effects are primarily in diseases, but some short term effects are applicable to flying an aircraft.

• Smoking causes hypoxia around 4.000ft to 5.000ft earlier than normal people (dangerous in night flying)
• Smoking causes a light form of anemia (bloedarmoede)
• Smoking people ar emore vulnerable to carbon monoxide poisoning
• Smoking causes the overall blood flow to have less oxygen

The circadian rythm

The circadian rythm is an internal clock of the human body where the internal temperature rises when we should be awake, and drops when we should be at sleep. This temperature range is about 1 degree celcius.

At night flying during the window of circadian low, this brings extra risks, like a decreased capacity of decision making and little less reaction-time. This is why pilots are not allowed to fly more than 10 hours per 24 hours.

Types of tiredness

We speak of two types of tirednesses:

• Acute tiredness: After speeling not well, effort or mental effort you can be exhausted and tired for a day
• Chronical tiredness: You can be exhausted over a longer period by work, stress or other exhausting activities

One way to eliminate tiredness is to do power naps during the day. This is researched and can have a positive effect on the functioning of a person.

Psychoactive stuff

ICAO defines certain stuff as psychoactive:

• Alcohol
• Opiates
• Cannabis
• Calming stuff
• Cocaine

Therefore all countries forbid the use of these stuff in combination with aviation. The only exceptions of this are coffee and tea.

Eating and dehydration

A human that has eaten too less have a low blood glucose level. This is also called “hypoglycemia”. Being hungry can cause light sickness like dizzyness, tiredness and nausea (misselijkheid).

When being dehydrated, we mean that you have drank too less. Symptoms of dehydration are:

• Dry mouth
• Headache
• Dizzyness

After ignoring those initial symptoms, more can arrive.

Information processing (8)

A human persion catches information by it senses. These senses are:

• Sight
• Hearing
• Smell
• Taste
• Touch
• Balance

The senses are more of less sensors (to talk in IT terms) which continously register information and pass it to the brain. The human brain will select and combine the needed information and how to interpret this.

The first step in the process of information processing is perception (waarneming). This is a subconscious process where the information will be saved in your memory. We cloud also call this the sensory memory. Signals will only saved for several seconds here before being overwritten by new information.

Short-term memory

After we will set our concentration on several infoemation, this will be saved into your short-term memory. This is where something we see will be converted into decisions and doing actions. However, this memory has a limited capacity of around 3 to 7 items with information, but we can prolong this items by continuously repeating it. Information in the short-term memory will reside there for a minute at max.

Some disruptions of short-term memory are

• Sensitive for external disruptions
• Parts of a clearance can be forgotten if out of time/items

For the most part, if things are in your short memory and you need them to remember for flight safety, the best thing is to write them down. This helps extending the remembrance period plus you have it written down.

Long-term memory

The long-term memory differs from the short-term memory by terms of capacity and retention-time. This part has an unlimited capacity and can save information for years.

This memory contains different categories of information:

• Implicit memory: memory without conscious effort; habits and automatic responses
• Declarative memory: memory for facts and events you can state
• Explicit memory: consciously recalled memory; largely the same as declarative memory
• Procedural memory: memory for skills and actions, like cycling or typing; a type of implicit memory

However, the capacity is unlimited of the long-term memory, but very specific information can be lost very easily. Like “hey, how did I do this 3 weeks ago”. This is why making documentation andwriting things down can really help you. Exactly the reason I started my website.

Prospective memory

The prospective memory is a small part where you think of tasks you have to do in the future. They could be forgotten if we don’t have a certain trigger (cue) for it. Like setting the altimeter on 1013hPa at the transition altitude or at work, doing something for your collegue, but simply forgot about it because no cue was given.

Exactly why we use checklist in the cockpit.

Perception

The vision that is projected onto the retina is a direct view of reality. You should think that everything will reach our brain without changes and thus is objective. However, this is called a bottom-up in the perception process.

In reality, everything we see is percepted by the brain. Depending on your activity, we expect certain things to happen, like our Cessna lifting of at 55 knots on the runway.

Human perception is not always 100% in sync with reality, and experience and exceptancy will also play their role in this:

• Selective processes: the brain focuses on some information and filters out other information; in aviation this can make a pilot miss important cues
• Subjective processes: information is influenced by personal interpretation, feelings, and past experience; this can affect judgment and decision-making
• Expectancy: the tendency to see or hear what you expect instead of what is actually there; in aviation this can lead to wrong assumptions
• Probability: how likely something is to happen; in aviation it helps assess risk and choose the safest action

This is the reason several people can have a completely different view of the same situation. An example is when flying IFR with an inexperienced pilot. The experienced pilot will carefully follow the instruments where the more inexperienced pilot will fly on perception. The experienced pilot will do this better.

Visual illusions

In an earlier module, we already described some sense-illusions but we also have some visual illusions we must know and defend ourselves against.

Illusions sometimes can be very tough to “un-see” but being with two pilots can help a lot. The most important is the context of where the illusion is in and this will depends on how we see and then percept it.

Attention

Attention is assigning thinking processes to certain tasks. Selecting is essential as we have a limited capacity and only want to focus on the essential parts which can be processed in our short-term memory. This is called selective attention.

A human person can delegate attention into what is called divided attention where more people, like 2 pilots, will delegate tasks to each other. This is where the principal of Pilot flying and Pilot monitoring comes from.

We also have attentional tunneling which everybody knows; thinking too long about one job and completely forget about the rest.

Vigilance

Vigilance (waakzaamheid) is the process where a person will actively be aware of the attention is spent on the right and essential things. This is important, as some repetitive tasks can lower our vigilance due to the repeating cause. This can cause adecreased level of vigilance, called hypovigilance.

Some causes for hypovigilance are:

• Sleepyness or being tired
• Eating -> after diner dip
• Monotonic sounds like engines of servers
• High temperature
• Stress and pressure
• Fast irritance and bad communication

Limiting information processing

The proces of human information processing knows some built-in limitations where we have to be aware of.

• Confirmation bias: This is a state where we expect something based on knowledge or events and we will keep searching for clues that confirm our initial bias, even when those are not even related that close

A great example of confirmation bias ending up fatal is:

A well-known aviation accident that is often used to discuss confirmation bias is Eastern Air Lines Flight 401, which crashed into the Florida Everglades on December 29, 1972. The crew became focused on a landing gear indicator light that seemed to suggest the nose gear had not locked properly. Because they were convinced the main problem was the landing gear, they directed most of their attention toward confirming and solving that issue, while failing to notice that the aircraft had begun to descend. The autopilot had been altered unintentionally, and the plane gradually lost altitude until it crashed. The U.S. investigation found that the crew’s attention was distracted from monitoring the flight instruments, allowing the descent to go unnoticed.

Automating tasks in the cockpit

Automating tasks in the cockpit can drastcally reduce workload and with that stress and such in the cockpit. Navigating with charts are replaced with tablets with GPS, autopilot for climbing and descending/cruise and other systems. However all these cool things, there are some cons about automating tasks:

• Automation complacency: where pilots trust too much on their automations, unseeing critical errors like other traffic
• Autopilot which deactivates itself after having a minor error and not hearing the beeps, causing the plane to descend from itself

Decision making and errors (9)

Decision making is a comprehensive cognitive process where a person needs to make choices. This process will start with perception and information processing, like described in the earlier modules.

In decision making, there will come a lot of human factors into play:

• Knowledge
• Skills
• Experience
• Attitude
• Motivation
• Fysiologic condition
• Psychologic condition
• Incluences from the outside like group-pressure or passenger pressure

Decision-making process

Normally, making decisions will happen in these steps:

1. Observe the problem (waarneming)
2. Attention on the details (aandacht)
3. Think of what is needed to cause this issue (interpretatie)
4. Execute a certain checklist or action (besluitvorming)

Situational awareness

To make safe and correct decisions, it is good to have a good situational awareness. This states that you exactly know what you are doing, what problem you need to solve and what things will help doing this. Also knowing where you fly is great. Without a good situational awareness you are sensitive for making errors which can lead in disasterous outcomes.

Situational awareness happens at three levels:

1. Perception: catching relevant information from the environment
2. Understand: based on knowledge or skills you will create a good overview of the real situation
3. Forecasting: prioritizing and anticipate on what is going to happen

If this situational awareness is decreased, your own reality does not match with the actual realtity. This will improve the chance of any wrong decision (garbage in, garbage out)

Factors that decrease situational awareness:

• Bad attention spanning
• Bad communication
• Stress
• Vermoeidheid
• Too high or low workload

We can prevent and restore situational awareness by doing those things:

• Keeping the golden rule of aviation, in this order:
  • 1 Aviate
  • 2 Navigate
  • 3 Communicate
• Admit and tell: if any doubts or uncertainties occur, speak up and just tell the situation
• Keep workload and stress levels low and prioritize
• Take your time to think and analyze and don’t do actions speedy

Good flight preparation and communication in briefings before a flight is a great way to enhance situational awareness.

Decisions and execution

To make a decision, you need to follow several steps. In the first place you need to assess the risks and the situation. Then all different options must be viewed and analyzed and the right option must be chosen which will overall give the best result.

Risk assessment and consideration of alternatives will differ from person to person. Also the pilot, plane, environment and 3rd party influence will all count towards this.

Personality and attitude

Decision making is not a objective process. Different persons will make different decisions based on the same situations. This all syncs with the personality and attitude of a person. Some persons are really fast at understanding a problem and will take a immediate decision, where other people need to write all different options down and (over)think them.

Some attitude exists, but must be prevented at all times:

Decision making in groups

Decision making in groups can have positive and negative effects.

• Positive effects are more knowledge, awareness and more eyes
• Negative effects is that you can exeed your personal limits and try things to look thougher than you actually are

Human error

We will call a human error such if a human decision does not stroke to the intention, leading to a unwanted result. Causes leading to human errors are liked described in earlier modules.

Human errors are for example:

• Flying into a TMA without clearance
• Forgetting carberateur heat on final

Actively violate rules are not human errors but violations with possible law-outcomes.

Learning from errors

In a human life, it is really critical to learn from errors we make or that other people make that can happen to you also. This is why every aircraft incident is thoroughly researched and the local authorities will create a final report with their recommendations described. They will fill the report with at least these information:

• Cause of the incident
• Analyzing the factors of the cause
• Report of how the incident happened
• Recommendations on how the industry can learn extensively from the errors or decisions made

The root purpose of this report is to learn from errors, not to point fingers at different orianizations and such. However, it is possible that certain organizations or individuals may be prosecuted (berecht) by law for negligence (nalatigheid) or for knowingly taking the wrong actions.

Safety culture

To learn from everyones errors, it is also important to note errors that does not lead directly to incidents. Pilots will only report their own faults if the company culture is open, and good. If the company is very toxic or closed with lots of punishments available, they will severely less open to speak about their own faults.

Therefore, in any company with pilots, there need to be a culture called “just culture”. Errors by pilots must not be directly leasding to the loss of license or work but into extra simulator training or personal training to actually become a better pilot. Only punishing and whining about errors resulting in lots of paperwork doesn’t make anyone a better pilot. Just culture must know what has gone wrong, not specifically what person did this.

It must be noted that actively violating rules and laws on purpose is a completely different story.

Stress (10)

The human body consists of mechanisms which adapts to the physical and physich threats (stressors) in its environment. The reaction of the human body is called stress, which we know 3 causes of:

1. Environmental stress: temperatures, noise, lights, vibrations, turbulence, air pollution or hypoxia
2. Psychological stress: Conflicts, great happenings in human life like marriage, divorce diseases, deaths, fired, changing jobs or high workload in the cockpit or fear of flying
3. Physiological stress: Sickness, bad food, tiredness or alcoholusage

Note that 2 and 3 are different, altough the word might look the same.

Acute stress

Some events can cause the human body to build specific hormones, like adrenaline. This can also happen in the cockpit, where the human body will go in the primitive fighting mode. The hearts pounds faster, breathing goes faster and muscles will get more blood. This also can cause hyperventilation.

Stress has a lot of causes for a person to function, where it decreases its function level:

• Clammy hands
• Transpitating
• Vibrating hands and lips
• Dry mouth
• Hyperventilation
• Heart poundings
• Headache
• Dizzyness
• Stomach pain

Stress can therefore work against you, when in a degraded level of functioning where also having less concentration on the situation. It can also cause you to decline recently learned tactics, and do regression, where you pick up older methods you are more familiar with.

During acute stress, our body will flow through these phases:

1. Alerting phase
2. Resistance phase
3. Exhaustion phase

Stress vs Performance

Its no suprise that stress is a primary cause of how we perform. To further clarify that, there is a graphic from Yerkes and Dodson, clearly stating how those two are related:

The best levels of performance are in the middle, where we have some pressure to do things the right way and at the level we need. Low stress can cause some boredom and disinterest, where high levels causes anxiety and the things already described.

Stress is also cumulative, were every waterdrop helps overflowing a glass of water.

Dealing with stress

Every person will act different under similar conditions. One person will totally overflow and freak out where the other laughs a bit and solves the situation. It all is dependent on personality and perception.

Decreasing stress levels by specific strategies s called coping, and strategies that work are different for every person:

• Stay current, deal in the current conditions
• Good flight preparation and think of what to do when and why and brief them to your co-pilot
• State personal limits, like 10 knots crosswinds or not under 5000 meters of visibility.
• Prioritize, remeber: aviate, navigate, communicate
• Dont be distracted by minor errors, fly the aircraft
• Stay calm and take your time

One final sentence to think about:

• Its better to be on the ground, wishing to fly than being in the air wishing to be on the ground

Extra information

Henry’s law

Henry’s Law states that the amount of gas dissolved in a liquid is directly proportional to the pressure of that gas above the liquid. In simple terms: the higher the pressure, the more gas dissolves in the liquid. When the pressure decreases, the gas comes out of the liquid again.

A simple example is a soda bottle: when the bottle is closed, carbon dioxide stays dissolved because of the high pressure. When you open it, the pressure drops and bubbles form.

A real life scenario of this phenomenon is decompression sickness.

Decompression sickness

Decompression sickness happens when pressure decreases too quickly, causing gas bubbles to form in the blood and tissues. It is commonly known as:

• Bends and creeps where skin itching or a crawling sensation
• Chokes where serious breathing difficulty caused by bubbles affecting the lungs
• Double vision in your eyes

Pressure vertigo

A more specific medical term is alternobaric vertigo, which means vertigo caused by a pressure difference between the two middle ears. This can happen when flying with a sinus infection.

Raw notes Theory course

HPL (Human Performance & Limitations)

Oxygen and circulation

• Arteries carry oxygen-rich blood.
• The pulmonary artery carries oxygen-poor blood (only exception).
• Blood pressure and temperature are regulated via the central nervous system.
• Normal blood pressure: 120/80 mmHg (baroreceptors).
• Composition of blood:
  • Red blood cells: hemoglobin.
  • White blood cells: immune defense.
  • Platelets: clotting.

G-forces

• Pulling the yoke = positive G-force.
• Pushing the yoke = negative G-force.
• Increased G-force can cause loss of consciousness (less blood to the brain).
• Negative G-force is more dangerous.

Hypoxia and breathing

• Hypoxia = oxygen deficiency due to insufficient oxygen/blood supply.
• At night: maximum 5,000 ft without supplemental oxygen.
• Dark adaptation is lost faster than visual acuity.
• Carbon monoxide cannot be smelled (CO itself is odorless).
• Flushed cheeks.
• Exhaust gases contain carbon monoxide.
• Hypo = too low.

Physiological vs non-physiological responses

• Physiological: due to physical exertion.
• Non-physiological: due to anxiety/stress.
• Yawning is associated with tingling in the fingers.
  • No tingling.
  • Tingling present.

Barotrauma and pressure

• Barotrauma = pain caused by pressure differences.
• Pain during descent → stop descending.
• The eardrum is airtight.
• “Popping” ears → descend or climb more slowly.
• Frontal sinus.
• Gases and pressure differences with altitude changes.
• Teeth: toothache due to pressure differences.
• Eustachian tube.

Vision and perception

• The eye is remarkable.
• The eye is a light-sensitive organ.
• The iris works like a camera lens.
• Eyes accommodate by adjusting focus.
• Fovea (yellow spot).
• Light-sensitive cells (rods and cones).
• Saccadic movements → processing pause.
• Visual illusions and perceptual loss → noise/deafness.
• Semicircular canals (balance).
• Otolith organs (acceleration).
• Airspace.
• Motion sickness → focus on horizon.
• Passengers.
• Symptoms: quiet.
• Rapid changes → flying is a bad idea.
• Perception threshold.

Importance of vision

• Eyes are very important (±80% of information).
• Vestibular system = balance → integration.
• Proprioception = body position.
• Disorientation Type I = unrecognized.
• Disorientation Type II = recognized.
• Fluid in balance organ causes sensation of turning.
  • After some time it feels stationary.
  • 2 seconds or after-image up to 48 hours.
• The Leans → sensation of banking.
• Coriolis illusion → semicircular canals.
• Somatogravic illusion → linear acceleration (e.g. during takeoff).
• Approach illusion is dangerous → PAPI helps with glide path.
• Runway shape.
• Flicker vertigo (e.g. helicopter) → light flicker effect.
• Scanning is important.
• Peripheral vision is important.

Fatigue and substances

• Fatigue:
  • Poor vision.
  • Alcohol use.
  • Stress or high workload.
  • Hay fever and colds.
• IM SAFE checklist.
• Sleeping pill: 24 hours.
• Long-term medication: 7 days.
• Alcohol: ±90 mg threshold.
• Would you fly under the above conditions?
• Smokers operate at a higher “physiological altitude” (less oxygen).
• Coffee: max 3 (in moderation).
• Attention is not always primary.
• Vigilance = sustained alertness → short-term attention.
• Hypovigilance = too low attention level.
• Task importance.

Situation awareness

• Perceive.
• Understand.
• Predict.

Human performance (Rasmussen model)

• Skill-based → routine.
• Rule-based.
• Knowledge-based → confirmation bias.
• Order is important.

Personality = genetics and environment. Non-punitive vs Just Culture → no punishment approach.

End of the page 🎉

You have reached the end of the page. You can navigate through other blog posts as well, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog homepage

If you find this page and blog very useful and you want to leave a donation, you can use the button below to buy me a beer. Hosting and maintaining a website takes a lot of time and money. Thank you in advance and cheers :)

The terms and conditions apply to this post.

Law and Operational Procedures (LAW)

Aviation rules and laws in the Netherlands (1)

Because the whole world uses aviation to get from A to B, the world needed an organization that will monitor, review and publishes rules for aviation. This is the International Civil Aviation Organization (ICAO), founded in Chicago in 1944. The primary rule was to standardize aviation around the world.

In the Netherlands we have the so called “Wet Luchtvaart” (Aviation Law) and contains all the basics of ICAO themselves, changed for this country. This contains mostly some minor changes from the EU laws.

Treaty of Chicago and ICAO (2)

From the 1944 conference, ICAO was founded and almost all countries around the world are member of this. ICAO publishes guidelines and advisories for countries to adopt to ensure safety but countries are not required to do so. EASA in Europe is an other story, that are laws that all European countries must follow.

• ICAO publishes advisories and recommendations
• EASA publishes laws that are required to follow by the pilot in command

The goal of this conference was to found an organization, ICAO, that creates standardized rules which all pilot in commands around the world must adhere to. From this conference there was signed the Treaty of Chicago which contains a huge load of rules in Annexes, which are attachments to the treaty:

Ground area and sovereign countries

The treaty explains that every country has full control over their own ground area and the air above the ground. It also explains that the water around countries are member of that country, at least within 12 nautical miles (22km) from the coast. Within those 12 nautical miles, the country is responsible for closing the airspace and control it by monitoring and giving clearances.

Access to airspaces

The treaty explains that the participating countries will permit access for uncontrolled flights like from private pilots without landing in the country. This is called the freedom of the air, which gives you the right to cross airspace from another country, with a possibility to make a diversion or emergency landing. This also gives commercial freedom, like transferring passengers or goods to another country.

However, the country where you land can determine if your cargo must be checked or forbid certain goods to ship into the country. Here the country where you land has the lead, because of the sovereignity. They can also forbid, or lead you to a different route in case of emergencies or international emergencies (like war).

A country can also force you to land in their country if they want to check your passengers or cargo. This is called a Safety Assessment of Foreign Aircraft (SAFA) check.

Uniformity of aviation rules

All participants of aviation of the treaty are required to comply with as much rules as possible of the treaty. These rules are described in Annex 2. The best thing is that the whole world uses the same rules, but some countries are more strict than other countries, especially the USA as a result of the 9/11 attacks.

Customs and immigration

A plane can be used to transfer cargo and passengers, so the customs of a departing and landing country must use an airfield with customs, which will check if everything is following the rules. You may only plan to fly an international flight when departing from an international airfield.

The treaty of Chicago states that aircraft can be allowed in a country without paying customs or other costs for fuel, oil, spare parts and extra stuff. This would make it impossible as every country has their own rules for taxes and importing goods.

It can also be required for international flights to submit a General Declaration. This requirement is mostly when flying outside of the Schengen-zone, incoming or outgoing.

Required documents on board

On every flight it is required to have these documents on board:

• Certificate of Airworthiness
• Pilot License / Certificate of the pilots given by country (or EU) of aircraft registration (ICAO-confirmed, RPL and LAPL not included)
• Journal

Radios and technology

The board devices of the plane must comply with the minimum requirements of the country where the plane is registered. When using the devices, the rules of the country below the plane apply.

For the radio’s, only qualified personnel that have a RT certificate may send over the radio.

Cameras

Countries can forbid you to use cameras on board of aircraft. In most countries, there are restrictions on making pictures of military facilities. In the Netherlands, there was a very restricting law that forbid most of the pictures from the air, but was suspended in 2013.

Aircraft (3)

All aircraft must be registered in the national aviation register and will receive a registration number. This number must be short, but with the most combinations possible.

In the Netherlands, this is done by the “Inspectie Leefomgeving en Transport” (ILT).

Registration numbers will be made up in two parts:

• Country/Nationality code - Registration mark

Some examples will be:

• PH-JSV
• OE-HWN
• PH-1234

Every country has it’s own code, which you can find here: https://www.avcodes.co.uk/regprefixcur.asp

Here is an example of the registration numbers and method in the Netherlands:

Some sensitive combinations are not included, and may not start with “Q”.

The registration number is like a license plate for a car. A unique number, instead of “A red or yellow plane”. There are some requirements for this number to be visible:

• Both sides on the wing or tail (visible from Air)
• Both sides at the underside of the wings (visible from ground)

There are some specific guidelines for visibility

• Registration number must be 50 centimeters high on the fuselage
• Registration number must be 30 centimeters on the vertical stabilizer
• It must be clear and readable from several hundred meters distance

Aviation Traffic Rules (4)

Most of the rules in the EU about aviation are described in the Standardised European Rules of the Air (SERA), or called No 923/2012 which can be found here: https://eur-lex.europa.eu/eli/reg_impl/2012/923/oj/eng

Countries can deviate from these rules but must align with the rules described in the SERA as baseline.

In an aircraft, the Pilot in Command is responsable for a flight following the rules. Violation of rules is only permitted in emergency situations.

Flight Rules Collections

For types of flights, we have 2 collections of rules:

• Visual Flight Rules (VFR): Flying on visual checkpoints and POI’s
• Instrument Flight Rules (IFR): Flying on instruments/navigational waypoints

Commercial flights will always fly on IFR to reduce the workload of the captains. Also, they very often have to fly through cloud layers where flying visually is not possible.

General flying guidelines

We have some general guidelines for flying in the air. These rules are based on:

• Corrections on earlier mistakes/incidents/crashes
• Safety
• Minimizing pilot input

1. Throwing items from the plane is not permitted
2. Simulating IFR in a not IFR ready environment
3. Avoid collisions. Formation flights only permitted when its a controlled flight
4. Priority rules, traffic from the right has priority
5. Two planes that fly right head on must deviate to the right to avoid collision
6. Overtaking must be done over the right side, under a 70 degrees angle of the overtaken plane

There are some special events that could happen:

1. Gliders must avoid hot air balloons
2. Planes must avoid hot air balloons and gliders (they are the one that have the most control)

General ground guidelines

1. Pedestrians and cars must give way for (towed) aircraft
2. Emergency vehicles have priority to every other traffic on the ground
3. Starting aircraft have priority over taxing aircraft
4. Taxiing aircraft must steer to the right to pass each other without collisions (pilot is on the left)
5. Crossing roads gives priority to right traffic
6. Use as much space as possible when overtaking aircraft on the ground

General Circuit guidelines

When flying a circuit around an aerodrome or airport, these rules apply:

1. Injecting the circuit must happen on the signal aera (or else when permitted by ATC)
2. The circuit must be followed, stay within the borders
3. Go arounds must be done safely
4. Exiting the circuit must be done at the given position and under an angle of 45 degrees
5. Follow deviations in circuit procedures (always check published procedures by AD/airport)
6. Controlled airfields has a complete circuit at 1000ft, uncontrolled mostly on 700ft (or else published)

VMC minima

To fly VFR, flight conditions must be at least the rules below:

• 10.000ft/FL100+: 8000 meters or better visibility and 1500 meters horizontal and 1000ft vertical from clouds
• 3000 to 10.000ft: 5000 meters or better visibility and 1500 meters horizontal and 1000ft vertical from clouds
• On or below 3000ft: 5000 meters or better visibility, clear from clouds and view on ground or water

In airspace classes F and G, its allowed to reduce the required visibility below 3000ft. In these special conditions, you may fly with 1500 meters visibility:

• 140 knots or less speed
• Very small chance of meeting other traffic

Flying VFR in CTRs

When flying VFR in CTRs, you must follow these rules:

• The cloud ceiling is 1500ft or higher, or less than 4/8 octas (SCT)
• Ground visibility is 5000 meters or higher

VFR limitations

When flying VFR, you have the following limitations:

• Flying in airspace class A without clearance
• Above FL 195 (19500ft pressure altitude)
• At night without Night VFR rating
• Faster than 530 knots GS
• In airspace classes C to G below FL100 and faster than 250 knots IAS

Flying VFR at night

When you want to fly VFR at night, you must comply with these rules:

• Cloud ceiling must be higher than 1500ft or lower than 4/8 ctas (SCT)
• Visibility in airspace classes F and G on or below 3000ft is at least 5000 meters
• On or below 3000ft AMSL (or 1000AGL if higher) there must be visual on the ground in all airspace classes
• In mountain rich areas, VFR minima will be more strictly than written down here

Day and night period

To define hen its day and night, we have the following rules:

• Its night between the end of civil twilight and the start of morning dusk
• Its civil twilight and dusk when the sun is less than 6 degrees under the horizon, which is around 30-45 minutes after sunrise/sunset

Some countries, like the Netherlands, have a defined “Uniform Daylight Period” (UDP), which defines the start of sunrise and end of sunset on average for the whole country. This is published in the AIP.

Minimum VFR altitude

When flying VFR, you must comply with these altitude rules:

• Above cities or buildings with an altitude to not bother people, but high enough to make an emergency landing (1000ft above the highest building)
• At night: 1000ft above the highest building in a vicinity of 8000 meters or 2000ft in mountain rich areas

You may only defer from these VFR minimums when performing these actions:

• Take-off and landing
• Picking or delivering towing operations
• If any special clearance is given, for example to practice forced landings

Signals

Distress situations

Of course we hope to never need this part of information, but it’s crucial to know. What to do in distress situations, which are the most dangerous, where life is on the gamble.

When an aircraft is in immediate danger, the following steps must be done as pilot in command:

• Transmitting, on the frequency the aircraft is, MAYDAY,MAYDAY,MAYDAY followed by a message that states the callsign current position, heading, altitude, type of disaster and intentions
• Setting the transponder to 7700 (seven, going to heaven).
• Shooting red flares into the air

An aircraft that is in danger is allowed to do everything just to get attention. If this includes a low fly by or calling the LVNL (in the Netherlands) by phone, this is allowed.

The number of the LVNL which could be called in case of emergencies is: 020 406 3999 (source: https://www.lvnl.nl/contact#anchor-d1e22f2a46cf4e81b142c96f01eb99ce).

Emergency situations

In the case of an emergency situation, which is where an aircraft needs priority but not immediate landing, instead of MAYDAY we use the phrase PAN PAN, PAN PAN, PAN PAN. Stating that we need priority caused by an error on board, smoke of strange smell or a person getting sick or incapacitated.

• Just like the distress, start transmitting PAN PAN, PAN PAN, PAN PAN followed by a message that states the callsign current position, heading, altitude, type of disaster and intentions
• When the radio is not working of your aircraft, you can just go through with your flight and try to call the LVNL emergencies number. Also first transmit your message twice when stating “TRANSMITTING BLIND DUE TO RECEIVER FAILURE *message*” like stated here: https://justinverstijnen.nl/flight-rt-course-notes/#frequencies-and-radio-explained

Dangerous or restricted area

When flying into a danger zone or restricted area, its possible that you get some radio calls to defer your course. Its also possible that flares in red and green colors (every 10 seconds) are shooting into the sky where people on the ground warn you about the possible danger you are to encounter. You as pilot in command should always leave the area as quickly as possible. If this takes a 180 turn, do that.

Signals at aerodromes (visual messages)

Its possible if the aerodrome thinks your radio isnt working, that you get visual messages when in the circuit. This can be confirmed if you don’t hear anything on the radio like a response to your message.

The visual messages are also stated in the COM course, and therefore a link to that section:

• https://justinverstijnen.nl/ppl-theory-com/#visual-messages

Some clear notes to remember them good:

• White means clear to land or return to starting point
• Steady green is a clearance to take-off or land
• Steady red means stay where you are or keep circling
• Flashing green means cleared to taxt or return for landing
• Flashing red means expedite, vacate runway or aerodrome unsafe, do not land

To confirm messages given visually, you need to make clear that you saw, understand and performing them. This can be done:

• In daylight, swinging your wings left and right
• In daylight on the ground, moving your rudder full left and full right
• At night or dawn: flash your landing light 2 times or if not possible do other lights like strobe or navigation.

Ground signals

If any radio failure occurs on an aerodrome or aircraft, the aerodrome will put some ground signs at a certain place. This can be at the runway itself.

Here is an overview of the different signs you could encounter. They are also described on the back of the VFR chart.

These signals are physically on a large banner which the aerodrome has to put at a certain place in case of emergencies. Physical and visual does always work.

Marshalling signs

At an airport, there is a chance that a marshal will give you instructions about what to do. This will mostly only happen at controlled airfields.

Some additions to the signs that can be given by marshalls:

• Stopping and turning signs are given with his arms. The faster his gesture, the faster you must stop or turn.
• Braking is gestured by the marshall making a fist. Stop braking is the complete opposite gesture.
• Start engine: The marshall will point at the engine that can be started. In most cases with VFR flying, this is only one engine.

Unlawful Interference

In case of unlawful interference, we mean that the aircraft is interfered. This can be a hijack or weaponized aircraft where people in or outside of the aircraft can be in danger. You as pilot in command are asked to do the following actions (if possible of course):

• Notify local aera by radio
• Set 7500 on transponder (five, man with a knife)
• Land as soon as practical at the nearest airfield or keep your current altitude and heading
• Make a emergency notification at the international emergency frequency: 121.500 MHz and keep notifying about heading/altitude differences.

Intercepting civil aircraft (by military)

If an aircraft does not comply with rules, for example flying in a restricted area, the aircraft can be identified, call out or intercepted by the military. In the worst case scenario, there will be a fighter jet flying next to you to check what you are up to.

In this situations, do the following steps:

• Notify your current frequency about this happening
• Set transponder 7700 or other code when asked
• Set radio to 121.500 MHz to communicate with a possible fighter jet next to you
• You have to do everything you are told at this point
• If not possible to communicate because of an language barrier, the following ICAO phrases will be used

Based on the situation, its possible to answer the actions:

The fighter jet can also give some visual instructions:

Air Traffic Control (5)

Air Traffic Control (ATC) is for the highest safety possible when flying an aircraft. Because ATC has an overview of all aircraft, their task is to make it safe for everyone by separating aircraft from each other, leading them to certain points etc.

The full list of tasks of ATC:

• Prevnting collisions between aircraft
• Prevention collisions with obstacles
• Enhancing traffic flow
• Giving advices for an safe and efficient flow
• Notifying responsible organizations and helping them

There are 3 types of air traffic service:

• Air Traffic Control for airspaces A, B, C
• Flight Information Services, like Dutch Mil Info or Amsterdam Info
• Alerting service for avoiding possible collisions

The structure of services and their responsibilities is shown on page 44. ¥

Flight Information Regions (FIR)

All airspace parts are together managed by a Flight Information Region (FIR). This is separated for horizontal areas, like the Netherlands is member of the Amsterdam FIR. Belgium is member of the Brussels FIR and so on.

A FIR is a region where all three types of air traffic services take place. Bigger countries like France and Germany have multiple FIRs (4 to 5) to separate the workload.

Air Space Partitions

On page 44 is described that there are multiple manners of separating airspace next to A to G. This must be researched. ¥

Dutch Airspace (as example)

On page 45 there is also a vertical view of the Schiphol (EHAM) CTR, please review thoroughly. ¥

Some simple rules apply for the Dutch airspace:

• From ground to 1500ft, airspace is always G with the exception of CTRs
• A CTR for civil airports is always airspace class C
• A CTR for military airports is always airspace class D
• CTRs in the Netherlands start from the ground and stop at 3000ft AMSL
• Above and outside CTRs we have TMA area’s which are Terminal Maneuvering Areas. This can be seen as approach traffic. Their airspace class defers based on the goal and application.
• Amsterdam has a CTA above the TMA. VFR flights are not permitted in this area and is from FL95 to FL195.
• Amsterdam has a Upper Control Area which spans from FL195 to the ceiling, but good luck getting a Cessna 172 above 19.500ft :)

This is all page 45.

Air Traffic Control areas

Air Traffic Control areas are as the name suggests, areas where ATC provides control to your aircraft. This happens mostly with IFR flight rules.

Air Traffic Control areaa are:

• Area Control Center (ACC) (for example: Amsterdam Center) - Leads aircraft in their region from A to B
• Approach Control Unit (APP) (for example: Schiphol Approach) - Leads traffic to the destinated approach path for inbound aircraft
• Aerodrome Control Tower (TWR) (for example: Schiphol Tower) - Leads aircraft to a runway and gives landing clearance

Airspace classes

Same explaination as already done, search for the complete table for a copy. ¥ (Page 47).

Airspace classes can also be temporary active. Always refer to the NOTAMs when planning a flight to be sure you are allowed and flying in the airspace you are supposed to be.

VFR rules and Air Traffic Control

VFR flights are mostly uncontrolled, but in some cases they will be leaded by Air Traffic Control:

• VFR flights in air space classes A, B, C and D.
• Special VFR flights
• VFR flights departing or landing at controlled airfields

A highly advisable note: being controlled by the tower doesnt nessecarily mean that you are being separated from other IFR or VFR traffic. Please refer to the air space classes definitions. (Page 49).

Flight Information Services

In uncontrolled airspace, like E to G, its highly advisable to sign into the Flight Information Services. These will give you important information like:

• Meteorological information like significant or unforecasted weather (SIGMET/AIRMET) or at your destination airport
• Regional QNH, to have all planes in the region flying on the same pressure altitude. This may not be the actual pressure but is an average for the whole region
• Information about navigation tools
• Information about aerodromes (busy or landing not possible)
• Traffic information to avoid collisions (best effort of FIS)
• VFR-unwanted weather reports
• Military operations (like a NAVO Top)
• Other important information for helping you having a great flight

In the Netherlands, we have two Flight Information Services:

1. Amsterdam Info for randstad: 124.300 MHz
2. Dutch Mil Info for the rest of the Netherlands: 132.350 MHz

You always have to sign in to FIS by describing your flight:

1. Dutch Mil Info, PH-JSV
2. PH-JSV
3. Overhead Apeldoorn
4. 1500ft
5. VFR to Eelde
6. Request flight information services

They will respond with a message to maintain your flight, important information and a regional QNH which you must set. Sometimes they give you a special Transponder code.

Aerodromes (6)

In the Dutch LAW, we have two separate laws for aerodromes:

• Besluit Burgerluchthavens (2009)
• Regeling Veilig gebruik luchthavens en andere terreinen (2009)

Its required to always use airports for take-off and landing. The only exception is when in a distress/emergency situation and you have to do a forced landing.

Gliders and hot air balloons are allowed to take-off and land from any land that is applicable. The same applies for police or emergency choppers.

Civil aviation is forbidden to use military airports, except if they have a special clearance.

Position of an aerodrome

The podition of an aerodrome is fixed by a clear GPS point, called the Aerodrome Reference Point (ARP) and is mostly the geometric center of the aerodrome. This will never change in normal situations, but an aerodrome can expand so a new ARP has to be assigned. This ARP is mentioned in the AIP.

Available runway lengths

Already described somewhere, look that up and adjust. ¥

Taxiway markings

Described on page 59, good to review further.

Aircraft Detection Lighting System (ADLS)

Page 66

Air Traffic Control in-depth (7)

In this part we will describe all rules about working with Air Traffic Control.

VFR Flight Plan rules

For VFR flights, it is required to submit a flight plan. This flight plan contains some general information of your planned flight, like:

• Waypoints
• Speed (TAS)
• IFR/VFR rules
• ETA
• Departure
• Arrival airport
• Contact information
• Number of passengers on board

We have to submit this at least 30 minutes but preferrably 60 minutes (maximum of 5 days ahead) before starting. Your flight plan can be transferred between ATC units so everybody knows exactly what your intentions are.

However you may sumbit a flight plan for every flight you do, it is only required by law in the following circumstances:

1. Flights that cross international FIR stations, unless otherwise described in AIP of the states
2. Flights that fly through controlled airspace, so airspace class A, B, C or D.
3. Flights to or through areas assigned by authorities, like the North Sea Area Amsterdam (NSAA)
4. Flights at night leaving the vicinity of an aerodrome (further than 5 NM)

VFR Flight Plan submitting methods

We can submit a flight plan by using the following methods:

1. Via Amsterdam Integrated Briefing (homebriefing.nl)
2. By radio in-flight

Submitting a flight plan by radio has its own rules to comply with:

• Flight plan only applies to a section of the flight
• Flight plan must be received at least 10 minutes before flying in a controlled airspace
• CTR Schiphol is forbidden
• Flight is in airspace A, B of C or above FL195

Flight without flight plan

You can also do a flight without a flight plan, but is only permitted when following these rules:

• Flying from and to an uncontrolled aerodrome
• Flying exclusively in airspace classes E and G

Submitting a flight plan can have a huge advantage for search and rescue missions, as they know your intentions.

Change of flight plan

Sometimes a change of flight plan is needed. Maybe the destination or alternate has changed or the number of passengers.

A change in flight plan has to be submitted at least 30 minutes before departing. If the delay is more than 30 minutes, you are required to cancel the flight plan and submit a new one.

In flight, you must follow your flight plan, and if your speed does defer 5% or more you have to notify the flight information services or ATC.

Closing your flight plan

When your flight is completed, your flight plan must be closed. This means the towers and ATC knows your flight is over and all processes stops. It is possible that if you forget to do this a search and rescue mission will be started, which you have to pay.

To close a flight plan, do one of the following options:

1. Land at your destination which must be a controlled aerodrome, they automatically close it
2. Notify the ARO of your area

When closing your flight plan, you must notify the following information:

• Registration number
• Departure Aerodrome
• Time of arrival
• Alternate airport (if diverted)
• Arrival airport

Diverting

If landing is not possible at your planned destination, we have to divert to our alternate aerodrome or make a forced landing. In this case, we have to notify our planned destination by phone. This can be the control tower or ARO.

Altimeter settings procedures

In our plane we have the altimeter which actually measures pressure based on a reference point. This reference point is the QNH, the actual, mean pressure on sea level.

Because in some areas planes must be on the same page, we have regional QNHs, so multiple planes are flying on the same reference point and collisions can be avoided.

When flying above the decided transition altitude, we switch our QNH to 1013 and we fly on flight levels, ending on 5. FL55, FL65, FL75 etc. IFR flights will take the rounded levels like FL60, FL70 or FL80.

In the netherlands, the transition altitude is mostly around 3500ft. The transition level is 1000ft higher. For avoiding collisions, its not permitted to cruise between the transition altitude and level, as this is for corrections of multiple, different built altimeters or pilot errors.

When descending, we will asap set the local QNH to make sure we fly at the correct setting and having the ground at the planned distance.

Semi circular altitude system

For deciding our flying altitude, we use the semi circular altitude system. This means we pick our altitude based on magnetic ground course. VFR flights pick flight levels ending on 5, IFR picks flight levels ending on 0.

• 000 - 179 degrees: Odd (FL55, FL75, FL95)
• 180 - 359 degrees: Even (FL65, FL85, FL105)

Great dutch way to remember: Oost = oneven.

Altimeter setting options

Because our altitude meter doesnt measure exact altitude above ground but the pressure difference from a reference point, we can select multiple reference points.

• QNH: This is the locally measured pressure, calculated back to mean sea level
• QFE (Aerodrome elevation/AGL): This is where you set the altimeter to 0ft on the ground so you measure the altitude above the ground, based on the aerodrome.
• ISA/Standard: This is always 1013 and is mostly used above the transition level.

The altitude meter may defer a bit but not more than these values:

• 60ft difference to actual for altimeters to 30.000ft
• 80ft difference to actual for altimeters to 50.000ft

page 83

Pilot licenses (8)

Medical class 2 is EASA approved and valid for this periods

• Till 42 years old: 60 months/ 5 year
• Till 51 years old: 24 months/ 2 year
• 50 years and older: 12 months/ 1 year

Flight Preparation and execution (9)

In this module, we will go deep into the rules for preparing a flight and then executing it according to your plan.

The 3 most important subjects in this module are:

1. Aviation intelligence
2. Flight preparation
3. Instruments and gear

All rules in this module are according to ICAO Annex 6, called the Operation of Aircraft - International General Aviation). For Europe we have the Air regulations 965/2012 where for PPL pilots, the Non Complex Operations part applies.

Aviation intelligence

The pilot in command of an plane must ensure every flight is prepared. This minimizes the chance of mistakes or worse things from happening.

The information a pilot must gather before performing a flight is:

• The Aeronautical Information Publication (AIP)
• The Notice to Airmens (NOTAMs)
• Aeronautical Information Circular (AIC)
• Aviation Charts (like the VFR Netherlands chart)

Aeronautical Information Publication (AIP)

The Aeronautical Information Publication is required by each country to host and publish where all rules will be described. Therefore this has to be publicly accessible. The AIP contains all information that is relevant for flight preparation and safety for people in and outside the plane.

The AIP always looks like this:

1. General (GEN)
   • Gen 1: National regulations and requirements
   • Gen 2: Tabels and codes
   • Gen 3: Services
   • Gen 4: Charges for aerodromes and services
2. En-Route (ENR)
   • Enr 1: General rules and procedures
   • Enr 2: Air traffic services airspace
   • Enr 3: ATS routes
   • Enr 4: Radio navigation aids/services
   • Enr 5: Navigation warnings
   • Enr 6: En route charts
3. Aerodromes (AD)
   • AD 1: Aerodromes/heliports introduction
   • AD 2: Aerodromes
   • AD 3: Heliports

Here are 2 examples of AIPs of different countries:

The Netherlands:

Norway:

You see that the format and information separation is the same for both AIPs. A list of AIPs for all countries can be found here: https://wiki.ivao.aero/en/home/operations/Global-AIP

The AIP can change in two ways:

• Amendments: Permanent changes
• Supplements: Temporary changes (shorter than 3 months)

The AIP will change in a cyclus of 28 days, this is not every month. The effective dates are worldwide described:

The AIP of the netherlands has changed every 28 days in the last months.

The new admendment changes has to be released 42 days before becoming effective so everyone has time to implement.

Notice to Airmen (NOTAMs)

NOTAMs are pieces of information that are important for day to day flight preparation. They are recognized as essential information before taking off.

NOTAMs are not published in the AIP, because this has two reasons:

1. The information is temporary
2. The information will be effective shortly

NOTAMs are effective information for pilots to know. Some examples of NOTAMs caused are:

1. Danger areas effective at a specific day
2. Restricted area effective
3. Obstacle anti collision light not working
4. Temporary changes at aerodrome (like a temporary displaced threshold at the runway)
5. High obstacle (crane) in the vicinity of the aerodrome

NOTAMs will be separated into 4 different classes:

• A-series: International traffic and en-route traffic
• B-series: National and international traffic
• M-series: Military based notams which also must be read and obeyed by civil aviation
• S-series: Special, snow, SNOWTAM

There also exists a ASHTAM, which is a very special and rare NOTAM which announces volcanic ash in the area. In the Netherlands, we don’t have volcanoes, only dykes. :)

Dutch pilots can view NOTAMs on the website https://homebriefing.nl, which is the International NOTAM office (NOF) of the Netherlands. Also NOTAMs from adjecent countries are announced in the Homebriefing website. This is part of the Aeronautical Fixed Service (AFS).

NOTAM code

NOTAMs are pronounced as partly coded information and some abbreviations. An example of a NOTAM effective at the day of writing this:

(A0116/26 NOTAMN
Q)EHAA/QOBCE/IV/M/A/000/999/5227N00531E005
A)EHLE B)2601120600 C)2604122200EST
E)MOBILE CRANE BTN PSN 522654.4N 0053040.1E AND 522656.6N
0053044.1E, BTN 553M AND 655M BEYOND THR RWY 05 AND 235M RIGHT FROM
RCL. 160FT AMSL, MARKED AND LGTD.)

I will break this NOTAM down:

As you can see, such NOTAM is very specific and contains safety messages. In this case we are warned for a crane possibly in our path, in case of making a emergency landing or go around.

There is also a type of NOTAM described:

• NOTAMR = Replacement
• NOTAMN = New
• NOTAMC = Cancellation

Let’s do another NOTAM break down:

(B1293/25 NOTAMR B0960/25
Q)EHAA/QPIAU/I/NBO/A/000/999/5215N00603E005
A)EHTE B)2512300950 C)2603301200EST
E)IFR APPROACH PROCEDURE RNP RWY 26 NOT AVBL.)

In NOTAMs there will be used some abbreviations of general subjects that are used often:

Aeronautical Information Circulars (AIC)

Some information is crucial to pilots but are not mentioned in the AIP or NOTAMs. Some practical messages. These will be distributed through the AIP but in his own tab:

Some practical things which could be mentioned there:

• Warning for the increased use of laser pointers on the ground
• Implementation of 5G, high usage of specific frequencies
• An area with multiple unknown transmissions
• Drone warnings

These AIC notifications are mentioned in 2 categories:

1. AIC-A: which are general or technical notifications for national and international aviation (only in English)
2. AIC-B: which are general or technical notifications for national aviation (in English and Dutch)

You see, same strategy as the NOTAMs.

Aviation maps

For VFR flights, some different maps are published through the LVNL website (or other website for different countries).

1. Aeronautical chart - ICAO 1:500.000: this is a general VFR map for the whole country Netherlands which can be found here: https://www.lvnl.nl/diensten/aip/downloads
2. Visual Approach Chart: which is specific to each aerodrome on how to fly the approach and landing
3. Aerodrome Charts: which is specific to each aerodrome and contains taxiways, aprons and parking.

Each pilot is required to have the charts on board for the departure and destination aerodrome and execute the flight according to these charts.

Flight Preparation

Pilot in Command rules

Here we have all rules according to flight preparations which are effective to the pilot in command (PiC).

• Each flight must have the pilot in command assigned and on board
• The pilot in command is responsible for the safety for people in and outside of the plane
• The pilot in command is responsible for a safe execution of the flight
• The PiC must know all rules and follow them, except for distress situations (but leads to a huge process of debriefing)
• The PiC must brief its passengers for safety informations, processes and brief other safety information of the plane
• The passengers are required to follow all instructions the PiC gives

Pilot in Command responsibilities

The pilot in command is responsible for the following actions:

• The aerodrome, facilities on the ground, communication tools and navigation tools are compatible with the planned flight
• The plane is airworthy, which can be decided at the final time in the take-off roll
• Maintenance is done correctly and checked by the pilot in command before executing the flight
• All instruments crucial for a safe flight are working, checked according to the checklist and working before take-off
• All required documents are on board
• The mass and balance calculation is done and within limits
• The pilot in command is not sick or in a bad healthy condition or drank alcohol in the 24 hours before the flight

Weather information

The Pilot in Command is required to study the weather forecast of the departure, arrival, alternate (1, 2, 3) and en-route circumstances. This can be done though METARs of airports, TAFs or simple methods like buienradar.nl (don’t use it as your main source).

Mandatory notifications

At some point in flights, the pilot in command is required to notify the autheorities of some possible things happening. He can do this himself or give this to the “pilot-monitoring”, but the PIC is responsible for the execution of all tasks.

• Writing defects in the technical logbook of the plane
• Dangerous/significant weather must be notified to the flight information services or ATC
• In the case of a (possible) hijack, this must be reported to the authority (in Netherlands, the LVNL)
• The pilot in command notifies the authorities after accidents with injuries or fatalities or with damage to properties or the plane

Flight Planning

Alternate airport(s)

The Pilot in Command is required to select an alternate airport in case a flight cannot be proceeded to the planned destination. It must have a alternate airport selected in the planning stage but is allowed to change this during the flight in case of technical failures, bad visibility or other problems.

Fuel and oil

The Pilot in Command is required to have enough fuel/energy on board to complete a flight, with enough space to also reach the altername without using the final reserve fuel (30-45 minutes).

By calculating the fuel, take the following things into account:

• Weather
• Your cruising altitude
• Factors that effect plane performance
• Possible delays or diversions in-flight (having to avoid a cumulonimbus cloud)
• All unforseen circumstances in-flight

Final Reserve Fuel (FRF) requirements

The final reserve fuel is the last 30 (day) to 45 (night) minutes of fuel you have on board of your plane. In normal circumstances this may never be used. The PIC is responsible for having enough fuel/energy on board to ensure a safe landing.

• At day we must have at least 30 minutes of final reserve fuel based on a holding pattern on 1500ft
• At night we must have at least 45 minutes of final reserve fuel based on a holding pattern on 1500ft

If the holding usage is not known, you can use the best range speed. This is around 65-75 knots in a Cessna 172).

Fuel Management

The PiC is required to calculate the fuel usage and to prepare this into blocks. It must be known exactly what the final reserve fuel is, so in-flight this is clear.

If the final reserve fuel is used in flight the pilot must announce an emergency and land as soon as possible. This comes with a lot of debriefing processes and possible fines or penalties as result.

If landing on a controlled airfield, the pilot in command must notify ATC about minimum fuel. This is done by adding the words “MINIMUM FUEL” to the initial message, and possibly repeat this one or 2 times.

Tanking with passengers

When tanking with a flight of passengers, the following rules apply:

• Passengers may never have the seatbelt on during taking
• The ground cable must be connected at all times
• The best is to board passengers after tanking is complete

Oxygen and pressure altitude

The plane must have enough oxygen and tools on board, especially in these situations:

• Flying higher than 10.000ft AMSL for longer than 30 minutes
• Flying higher than 13.000ft pressure altitude at all times

Ice

The plane may only start the take-off roll when no sign of ice is detected. Ice will negatively decrease lift and controlability of the plane.

If this happens in the air, the PiC must ASAP descend to an altitude the ice melts or even do a emergency landing.

Medical problems

The pilot in command will never proceed the flight if he is not medically able to complete a flight. This can result in a emergency landing.

Required instruments and tools

In Annex 6 of the Chicago treaty, there is described a minimum of instruments and tools on board before allowed to take-off. These are:

The instruments and tools are not related.

Seats and seatbelts

• Planes must have seats or lying places for people above 24 months
• All seats must have 2-way seatbelts
• Pilot seatbelts must have a shoulder harness (to avoid bumping head into dashboard)
• All people on board must have their seatbelt on during take-off and landing
• Pilots must wear their seatbelt at all times

Flying above water

Single engine planes which fly above water outside of glide distance to land (for a Cessna 172, 1.5NM per 1000ft altitude in good conditions), must have life jackets for every people on board. This must be within arms reach so it can be put on while having the seatbelt on.

Long flights (more than 50NM or 30 minutes) above water must have an additional risk assessment by the pilot in command (pic) like:

• Distance to ground (no sea)
• Sea conditions
• Dinghies
• Signalling stuff like flares or fireworks
• Survival tools like first aid kits and food

Flights over uninhabited areas

Sometimes we need to fly above areas where there is no-one in the vicinity. In this case the plane needs to have:

• Signalling tools like flares or fireworks
• Survival tools like first aid kits and food

Mandatory documents on board

When flying a plane, the following documents (of every pilot) needs to be on board before even starting an aircraft (Page 131):

• Flight crew license
• Medical certificate
• ID
• Aircraft flight manual
• Certificate of registration
• Certificate of airworthiness
• Airworthiness review certificate (ARC)
• Noise certificate
• Radio station license
• Journey log/technical log
• Third party insurance certificate
• ATS flight plan
• Up-to-date aviation charts, departure airfield, arrival airfield and alternate airfields
• List of hijack procedures (page 40)
• Information about search and rescue facilities in the flying area
• International flights: Technical maintenance log
• ICAO attachment for flying in an aircraft registered in another country
• Other general information in the overflying or landing country

Now you definitely don’t want to take all those documents with you the whole time. You are allowed to have (digital) copies of the official documents in the plane while the official document is in the office. The only documents that needs to be the original:

• Flight crew license
• Airworthyness certificate
• Medical certificate

Also according to NPA 2024-02, you are always required to have the latest published checklist for your aircraft on board.

Communication and navigation

For controlled flights (A to D airspace), you are required to have a VHF installation which can do two-way communication in the 118.000 to 137.000 MHz range and has 8.33KHz channel separation.

Also planes needs to have a Emergency Locator Transmitter on board. They have to transmit on 121.5 MHZ and 406 MHz.

A plane is also required to have an transponder on board with mode S (Code/Pressure altitude/Ident).

Lights

All planes have to enable their anti collision lights (strobe) during the day, if it has them built in.

During night flights (after sunset), enabling landing/taxi lights is required.

Navigation lights must be enabled as the plane starts the take-off roll till the moment it stops the landing roll.

The lights layout of an plane is:

The navigation lights can be both static and flashing.

Operational procedures (10)

In aviation, there are some procedures that needs remembering for different scenarios. You always must know what to do in certain situations.

We will talk about:

• Bird strikes
• Emergency landings
• Precautionary landings
• Contaminated runways

Bird strikes

When a plane collides with a bird, the plane can be moderately or heavily damaged. A famous example of a succesfull landing after a bird strike is the Hudson miracle, where an Airbus A320 hits a fluck of birds after take off and loses both of its engines.

https://nl.wikipedia.org/wiki/US_Airways-vlucht_1549

So, if an Airbos A320 gets critical problems with birds, we certainly do with our Cessna.

The best thing is to try to avoid bird strikes at all times, however this may be impossible. The most chances of having to deal with birds in the Netherlands are:

• Waterrich areas like Zeeland or Flevoland
• Nature reservations
• Airports
• Garbage

On the VFR chart are some tips about high concentrations of birds measured and in the AIP under ENR 5.6 and ENR 6-5.3 there is actual reported information about bird migrations and riskfull areas.

Most bird strikes happen under 2500ft AGL. The highest chance is within the ground and 1000ft. The LVNL has some security measures because of this, it forbids flying over Zeeland and the Waddenzee below 1000ft AGL.

Sometimes high bird risks are mentioned in the NOTAMs, especially if they are reported to be around an aerodrome.

A forecast about bird migrations can be found here: https://www.flysafe-birdtam.eu/

On a controlled airport, tge ATC, ATIS or NOTAMs can also mention birds as possible risk. ATC can also cancel your take-off or landing clearance if birds are detected. This can also happen on Final, so a go around is mandatory.

Bird strikes are part of the notification requirements. (161)

Emergency Landings

An emergency landing is known as a landing where your plane doesnt have forward power, so no engine(s) and a landing must be done. This is in case of an engine failure, smoke or fire.

We call a emergency landing on water “ditching”.

The pilot in command is responsable for the plane, passengers and goods until the authorities took this over.

The pilot in command is also required to notify ASAP the Onderzoeksraad voor veiligheid (OVV) and the national aviation authority (LVNL in the Netherlands).

Precautionary landing

An precautionary landing is a landing with power where resuming the flight is not safe, and the aircraft must be land to avoid the problems to be worse. This can be things like:

• Engine stalls
• Electrical smell or light smoke
• Radio failure

Before doing a forced landing of this kind we need to do the following steps:

• Transmitting an urgency message using PAN PAN, PAN PAN, PAN PAN
• Search for a suitable spot
  • Against the wind
  • No obstacles
  • No animals
  • Not too close to houses or buildings
• Inspection run, low fly by to inspect the predetermined land
• Expect a short field or soft field landing, so execute it

Runway Contamination

Take-off and landing performance of a plane is very dependent on how the runway state is. Planes perform much better on a dry runway than on a wet or contaminated runway.

To brief pilots and ATC about runway states, we use 4 different states:

• Contaminated: A runway which is at least for 25% covered with contamination
• Wet: A runway where the surface can still be seen until 3mm of water
• Damp: A wet, shiny runway without floods of water
• Dry: A dry runway

Types of runway contamination:

• Water
• Frost
• Ice
• Wet ice
• Slush (melting snow)
• Dry snow
• Wet snow
• Compacted snow

For the states of runways in winter weather we have a SNOWTAM. These are spreaded using the same channels as normal NOTAMs. An example of a SNOWTAM:

Next to runway contamination states, we have also braking action. This is an index-number about how good the brakes work in a runway (higher is better)

The problem with these codes is more or less that these are relative. On the same runway, the one pilot may say braking action 4 where another pilot with a much heavier plane may report 2.

Sound Nuisance

Planes that are not checked and certified with a valid sound document are forbidden to fly. Only some older planes can get a sort of exclusion, a sound description.

Sound classes and measures

To class airplanes based on their sound production, we have 8 sound classes, where silent is class 8 and very loud is class 1. The actual number is the number of decibels and this decides the class itself.

Sometimes an airport takes some measures for not producing too much sound. It can take some runways as preference, select different departure or arrival routes. A plane may also not make a turn lower than 500ft. (148)

Search and Rescue (11)

In case of a plane or multiple planes in danger, the procedure “Search and Rescue” will be started. This starts with 3 emergency phases:

1. INCERFA -> Uncertainty phase: ATC has not heard of the plane for 30 minutes
2. ALERFA -> Alert phase: In case of hijack or technical problems
3. DESTRESFA -> Distress phase: In case of technical problems, no fuel and a landing/crash will be made or is already done

ATC (FIC,ACC,TWR) is responsible for the alerting and notification services. If an uncontrolled flight without flight plan was being performed, the aerodrome leader is responsible (tower or a specific person).

Alerting by local ATC (TWR)

If an airplane is transferred to tower and does not contact tower or radio contact is lost and the plane does not land within 5 mintes, TWR must contact the ACC or FIC about this incident.

Tower is responsible for notifying fire trucks and or rescue operations in case of these situations:

• Accidents on or in the vicinity of the airport
• When information is received about an unsafe situation on a plane
• When a plane itself requests this

The alerting messages will be transferred to the Rescue Coordination Center (RCC) and there the search and rescure procedure will be started. The official Joint Rescue Coordination Center JRCC in the netherlands is located in Den Helder, doing both maritime and aeronautical search and rescue operations.

The RCC itself is purely a coordination center and only notifies other parties like the Knoninklijke Marine, Luchtmacht, Douane or the police.

Notes to self for preparation

• The country of registration sets the instrument colors and limits
• In CTRs, the cloud-base must be at least 2500ft AMSL
• Ground visibility is measured by a transmissometer
• Aviation Services do flight information, alerting and traffic control
• Amsterdam FIR has Local, Approach and Tower
• If you have a radio errors before entering a CTR, land on the closest airport which is not in CTR
• If you have radio errors after entering CTR, proceed according to plan and look for visual signs
• EASA FCL is the Flight Crew Licensing part of law
• The OVV does research for accidents in the netherlands with netherlands plane, netherlands plane in other countries, other country plane in the netherlands and netherlands plane on the sea

End of the page 🎉

You have reached the end of the page. You can navigate through other blog posts as well, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog homepage

If you find this page and blog very useful and you want to leave a donation, you can use the button below to buy me a beer. Hosting and maintaining a website takes a lot of time and money. Thank you in advance and cheers :)

The terms and conditions apply to this post.

Communication (COM)

Introduction

This page contains only some theoretical additions to this page: https://justinverstijnen.nl/flight-rt-course-notes/

The International Aeronautical Telecommunication Service (IATS)

Clearances

When you want to cross a runway, you have to request this:

• Request cross runway XX

When a radio frequency must be silent due to emergencies, the following will be called:

• STOP TRANSMITTING MAYDAY
• And also make sure to not disturb any distress messages
• Always mention the altitude in distress messages

Also mention these items in a distress message (when possible):

• Mayday, Mayday, Mayday
• Callsign
• Type of emergency
• Position
• Heading
• Altitude
• Intention

When the hour of transmitting is known, we can skip that and only call out the minutes:

• 13:35 is then three - five

For the readability scale, review this table: https://justinverstijnen.nl/flight-rt-course-notes/#readability-scale

For the message types and order: https://justinverstijnen.nl/flight-rt-course-notes/#module-2-message-categories-and-priority

VHF frequencies will travel in a almost straight line, lower frequencies like VLF and LF will follow the ground course

When getting a objective to reset transponder, call out where XXXX is the code:

• Resetting XXXX

When getting the objective to hold position and cancel your take-off, call out:

• HOLDING POSITION CANCELLING TAKE-OFF

Make sure, air-ground is duplex and air-to-ground is simplex: https://justinverstijnen.nl/flight-rt-course-notes/#module-5-definitions-and-abbreviations

Few clouds is 1/8 or 2/8 octa’s, scattered clouds is 3/8 or 4/8, Broken clouds is 5/8, 6/8 or 7/8 octa’s, overcast is 8/8. https://justinverstijnen.nl/flight-rt-course-notes/#weather-types

Vacate will always be used to “leave a runway”. When leaving a circuit, we call out, leaving your circuit area.

When asking to stop squawk charlie, we have to disable the pressure altitude setting. This can be to set from ALT to Standby.

Non-spelled abbreviations

There are some abbreviations which we (aircrafts and ATC) don’t spell letter by letter because of the often use. These are:

Airspace classes

All around the world, we use 7 different airspace classes, devided into the letters A to G. To make it clear what every airspace is for, please refer to this table:

*VFR traffic only permitted with clearance from ATC.

When the chart doesnt define an airspace for an area, this always will be Class G (geen in Dutch).

Taxi instructions

On the ground, driving our aircraft to the ramp, hangar or runway is called taxing. We could get some different instructions which we have to read back to ensure the pilot and ATC are on the same page, or else some huge accidents could happen.

* Aircraft description could be something like a helicopter, a Boeing 737 or Cessna 172

Traffic information sentences

When signed in to the traffic information for a region with airspace classes D to G, we could get call outs to watch other traffic. As we don’t get instructions from information to fly certain headings, only information about other traffic we have to look out ourselves.

There are some phrases we could say when coming across other traffic, based on your action. As all planes in a region are required to sign into the same frequency, they will hear your action as well.

Distress calls

Distress calls are used when in immediate danger when an aircraft is in immediate danger, like an engine failure or electrical failure.

We must always include the following in a initial distress message, when possible of course. Remember: 1. Aviate, 2. Navigate and 3. Communicate

• Mayday Mayday Mayday
• Callsign
• Type/Cause of distress
• Intention
• Position
• Altitude and Heading

Radio communication in Emergency situations

An example of an distress call could be:

As it may be not possible to say this message out loud during emergency, at 2500ft we would have around 3,5 miles of glide distance with a Cessna 172 and with a speed of around 65 knots we would have only 200 seconds from the start of the failure to a possible emergency landing.

Scenario

• Aircraft: Cessna 172
• Altitude: 2500 ft AGL
• Airspeed: 65 KIAS (best glide)
• Assumptions: no wind, flaps up, propeller windmilling

Glide distance

Rule of thumb for a C172:

• ≈ 1.5 NM per 1000 ft

Calculation:

• (2500 / 1000) × 1.5 ≈ 3.75 NM
• ≈ 6.9 km

Time available

Approximate glide ratio: ~9:1

At 65 kt:

• Sink rate ≈ 730 ft/min

Time from 2500 ft:

• 2500 / 730 ≈ 3.4 minutes
• ≈ 200 seconds

Result

Time available: ~3–3.5 minutes (≈ 200 seconds)

Maximum glide distance: ~3.8 NM (≈ 7 km)

Watch me demonstrating the whole procedure succesfully on MSFS 2024 in a Cessna 172:

https://www.youtube.com/watch?v=5eUdD0nZgq8

1. Pitch for the best glide speed (Vg) which is 65 knots in the Cessna 172
2. Orientate for a spot to land and stay in the vicinity
3. Troubleshoot the problem
4. Crank the engine at max 3 times
5. Shutoff all fuel flows
6. Disable ignition
7. Extend flaps when inbound to land
8. Disable Master switch
9. Butter the landing

This is an great example of having aviate on the first position, then navigating and if we have time left, communicate.

Visual messages

When a tower assumes your radio communication doesnt work, they could give you visual messages by shining light to you. These lights could have different meanings.

Fixes and classes

When asking for a radio direction, we could given a heading/QDM with a specific class. This tells us how good the heading can be:

• Class A: around 2 degrees of possible deviation
• Class B: around 5 degrees of possible deviation
• Class C: around 10 degrees of possible deviation
• Class D: less accuracy then class C

This are the classes given by a ground direction finding station, but we can also get a fix when you combine multiple direction findings (QTF). The QTF is the QDR + variation.

Some ground stations have multiple stations which can directly give a fix, which will be made up by finding the direction from the multiple stations. These will give a fix with a specific class:

• Class A: Within 5 NM (9,3km)
• Class B: Within 20 NM (37km)
• Class C: Within 50 NM (92km)
• Class D: Less accuracy than Class C

To learn more about Q-codes, visit: https://wiki.ivao.aero/en/home/training/documentation/Q_code_definition

End of the page 🎉

You have reached the end of the page. You can navigate through other blog posts as well, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog homepage

If you find this page and blog very useful and you want to leave a donation, you can use the button below to buy me a beer. Hosting and maintaining a website takes a lot of time and money. Thank you in advance and cheers :)

The terms and conditions apply to this post.

Navigation (NAV)

Introduction to Navigation and Flight Planning

Navigation and Flight Planning is a very important part of preparing your flights and knowing where to go in the air. When a flight is not properly prepared you can get several different kind of issues. These are the most pilot-caused problems in the air:

• Incorrect fuel calculation
• Incorrect mass & balance calculation
• Fail to read and understand NOTAMs

When planning a flight, we always make a A to B flight with an alternate as C. The alternate is mostly an airport in the vicinity of B, but can also be A. As we might revert back to A, we need to have at least double the fuel as we need for getting from A to B.

Runways, Take-off and landing

Runways are straight pieces of grass, asphalt or bitonimous where a plane can take off or land on. They always have 2 numbers, like 04 and 22. This indicates the magnetic heading of the runway based on magnetic north. This is by design so you could land a plane without navigation and only with your magnetic compass.

Runways have some characteristics which we should take into account before taking off and landing to make sure we can succeed or reject a take-off and that the runway is long enough for our plane to actually land.

We have the following abbreviations:

• Take-off run available (TORA): this is the area we can run-up our plane to rotation speed, or where we actually lift off the ground
• Clearway: is is a piece of extra cleared area after the runway to lift off our aircraft to at least 50ft above the ground. This can also be water, if the elevation of the runway is higher than the water.
• Landing distance available (LDA): this is the area where can land the plane in normal conditions, without the stopway at the end.
• Stopway: this is a designated piece of extra runway to stop our aircraft if overshooting the normal runway
• Displaced threshold: this is the part at the start of the runway with the arrows, its meant to extend the runway for take off but not meant to used for landing, only in case of emergency.
• Accelerated stop distance available (ASDA): this is the area where we can take-off and reject our take off. ASDA includes the stopway and the displaced threshold.
• Take-off distance available (TODA): This is the sum of the displaced threshold, LDA and clearway. Also lnown as the area where we can start our take-off till we hit 50 feet.

When calculating your take-off and landing performances, numbers may never exceed those numbers above. You can find the actual numbers in the AIP.

International Standard Atmosphere (1)

Worldwide, we have the same default settings for our standard atmosphere on sea level:

• Temperature: 15 degrees celsius
• Air pressure: 1013 hpa (29.92 mmHg)
• Air density is 1,225 kg air per cubical meter (m3)
• Vertical air gradient is -2 degrees per 1000ft (-6 degrees per 1km or 0,65 degrees celsius per 100 meters)
• Nitrogen: 78% (stikstof)
• Oxygen: 21% (zuurstof)
• Carbon: 0,03%
• Gasses: 0,9%
• Humidity

On around 18.000ft the airpressure is half of sea level pressure (500hPa), and on 36.000 ft, the temperature is around 56,5 degrees celsius.

We have multiple layers in the air:

• Troposphere: ground to 36.000 ft
  • “Tropopauze at 36.000ft which can defer day to day”
• Stratosphere: 36.000ft to 160.000 ft

Pressure Altitude

Pressure altitude is the altitude corrected to the International Standard Atmosphere, namely 1013 hPa (which is also called QNE). For performing take-off calculations, we will want to know how our plane performs which can be different with different pressures. This is a live indicator of being above or below earth’s standard atmosphere.

In short:

• Higher pressures (Low altitiudes): Better engine performance, better propellor performance and more lift
  • More oxygen and more air molecules
• Lower pressures (High altitudes): Less engine performance, less propellor performance and less lift

Pressure altitude examples

In an airport which mostly is lower or higher than mean sea level, there will be a small correction needed. For example, our airport is at 17 feet above sea level, and the actual pressure is 1032 hPa on sea level at a day with nice weather, the pressure altitude is -489 ft. This means our take-off performance will be better as we have more air molecules which is better for our engine.

In the same example with a pressure of 968 hPa on sea level, we will have a pressure altitude of 1238ft. This means our aircraft will perform as it takes off at 1238ft above sea level, which will have some disadvantages. As there is less air, we will need a longer runway, our engine performance is less and our lift will be less as there is less air. However, flying in relative high pressure altitudes is good for having speed, as drag decreases in lower pressure.

As you can already see, this example gives two completely different scenario’s with around 1700ft difference. In countries like the USA where airstrips can be at 5000ft altitude, the pressure can be a huge difference which we must take into account.

Check out this tool to calculate and visiualize Pressure/Density altitude: https://flighttools.justinverstijnen.nl/pressuredensityaltitudecalculator

Density altitude

Now we know the pressure altitude, we need to correct it for Density altitude, because warmer air is thinner than colder air. This is because warmer air expands, just take a look at a hot air balloon. This means that on 5000ft pressure altitude and on a hot day of 35 degrees, the density altitude (also known as “performance altitude”) will be almost 9000ft. So we can expect our plane to behave as it is on 9000ft in normal ISA conditions.

Thinner air means less oxygen and less air molecules, denser air means more air for lift for both propellor and the wings. Less oxygen also means less engine performance but a higher true airspeed due of less resistance from air molecules.

To calculate the density altitude from pressure altude, you can use the E6B or the tool below:

Check out this tool to calculate and visiualize Pressure/Density altitude: https://flighttools.justinverstijnen.nl/pressuredensityaltitudecalculator

Tip: Use an E6B calculator for a quick and thorough calculation of Density altitude based on the outside air temperature (OAT) and pressure altitude.

GPS coordinates and Earth

GPS coordinates are made to navigate and pinpoint certain places in the world. In aviation, we mostly use these 2 possible notations;

• Decimal: 51,
• Degrees, minutes and seconds (DMS): 51 degrees, 30 minutes and 30 seconds

The equator and 0-meridian is the actual 0 point of earth. From there we look up the coordinates:

For reference, the Netherlands lies between 50 and 54 degrees North, and 4 and 7 degrees East.

In a degree goes 60 minutes, where each minute is around 1 nautical mile (zeemijl), and this is 1852 meters. This is measured on a meridian, not on the parralels.

Transponder communication and usability

The transponder on board of an airplane is used by Secundary Surveillance Radar (SSR) to identify the blips shown on the map. In the plane, a device called the Transponder is turned on and sending out signals in pulses at around 1090MHz. This pulse consists of 4 digits and the transponder has several modes:

• Mode A: Squawk code
• Mode C: Pressure altitude (not AGL/MSL!) but measured on the ISA pressure -> QNH 1013
• Mode S: “Selective” (identify code, TCAS, etc.)

Mode C also contains the code and mode S also contains the pro’s of mode C, this is cumulative.

ATC can ask for your transponder capability, you can say “Transponder capability Sierra” for Mode S transponders.

Map projections (15)

To project the globe which is a round object, we can use multiple different projections, each with their pro’s and cons.

* main property

This makes clear that poth projections are great in their own use:

• Mercator for whole world navigation -> like a complete map
• Lambert for small regional navigation -> like VFR charts

Then we have “Grootcirkels” and “Loxodromen” (Rhumb lines), which are different on both types of maps:

A loxodroom means that a line on a chart hits all medians under the same angle (same degrees). This is why a loxodroom is straight on the mercator chart and curved on the curved lambert chart.

Planes fly mostly loxodromische routes on one fixed heading, the magenta line on the Primary Flight Display.

In the Lambert Conformal Conic Projection, construction means that the parralels defer between the default parralels.

The shapes to remember:

• Lambert -> Loxodroom -> Hol Pool
• Mercator -> Grootcirkel -> Bol Pool

Planet earth (14)

Earth is no perfect ball but is a ellipsoid.

Earth has “Grootcirkels” and “Kleincirkels”

• Great circle is a circle which combines with the middle
• Small circle is a smaller circle which not combines with the middle

The equator devides earth into the north side and the south side. When the north side has summer, the other side has winter. We also have 2 extra parralels small circles above and below the equator:

• Tropic of cancer (Kreeftskeerkring) at 23.5 degrees north
• Tropic (Steenbokskeerkring) at 23.5 degrees south

And then we have 2 polar circles, which are a indication of the angle the sun as opposing the north/south axis of the earth (which causes the different seasons):

• North artic circle: 66.5 degrees north
• South artic circle: 66.5 degrees south

Parralels

There are parralels at each 10 degrees that horizontally divide earth

The equator is the only groot circle which also is a parralel

There are also some meridianen which goes from north to south only, and so look like half-groot cirkels. These are comparable to the timezones

Earth turns 15 degrees per hour (1 degree per 4 minutes) so 3 degrees on the chart is 12 minutes

180 degrees median is the date-line next to new sealand. The 0 median is the UTC line

Earth is 40.075 kilometers long measured on the equator parralel

Earth is 40.008 kilometers long measured on the 0 degree meridian

This is divided into 360 degrees medians

One minute on such median is 1.852 meters or exactly one nautical mile (NM). However, this is on average. At around 60 degrees north or south, one nautical mile is actually 2 minutes, cutting this in half.

One minute on a parralel is around 1856 meters, so more distance and longer time horizontally

True north vs. Magnetic north vs. Compass north (16)

In aviation we have different types of norths, called the True north, magnetic north and compass north. All three sounds the same but are different of course.

To calculate courses, deviation and variation, use this tool: https://flighttools.justinverstijnen.nl/coursecalculator

1. True north: This is the north that is displayed by charts, atlasses and small-scale globes. This is also the location where the icebears live.
2. Magnetic north: This is the north decided by earth’s magnetic field. This changes over the years, and lies now somewhere in the north side of Canada (around 1100km from the true north)
3. Compass north: This is the north displayed by your compass, which will be a minor correction to the magnetic north. The actual difference can be found on the calibration chart:

For the actual magnetic heading of 330 degrees, we have to steer 328 on the magnetic compass. This difference is mostly somewhere around 0 to 5 degrees.

Then we have multiple corrections we have to take into account:

• Deviation
  • Magnetic north and compass north
  • Afwijking of the compass in a plane due to correction and magnetic field of radio/electronics
  • Listed as +2 or minus 2 what means: the compass reads 2 degrees more or less than the magnetic north (Thisdeviation is caused by not using the compass/standing still of the plane and is measured every maintenance)
• Variation
  • Magnetic north and true north
  • Afwijking of the magnetic north
  • Example: VAR 2 W decreasing 7’ annually
• Correction (miswijzing)
  • The sum of deviation and variation summed up (or subtracted) gives you the correction of what to fly with your specific aircraft based on the magnetic compass

We can make multiple calculations with these numbers:

• True Heading - Variation = magnetic heading
• Magnetic Heading - Deviation = compass heading
• True Heading - Variation - Deviation = compass heading

This variates between west and east. We use the guideline: East = least (-) and West = best (+) but this only applies when going from magnetic to true/planned chart route.

For true/planned chart route back to magnetic is the calculation reversed, we have to subtract west and add east. This is due to the slight west position of the magnetic course.

1. Course: This is the direction you are planning to fly
2. Heading: This is the direction your nose of the plane is pointing at, which han change due to wind
3. Track: The actual line flown with the wind taken into account

Example:

• You plan to fly 90 degrees. This is your course planned on the chart (Course)
• The wind is coming from 360 degrees and blowing you to the south, you keep 100 degrees (Heading)
• Your True track is then 90 degrees as you correct your heading for the wind (true track)

Then we can base these courses on True North (charts), Magnetic North (on board) and Compass Heading (on board).

More information on how to actually calculate this can be found here.

Also, use this tool to visualise what is happening: https://flighttools.justinverstijnen.nl/coursecalculator

Distances (17)

For calculating units, use this tool: https://flighttools.justinverstijnen.nl/unitcalculator/index.html

In aviation, we will use these units:

• 1NM is 1852 meters
• 1NM is 6000 feet
• 1 feet is 0,3048 meter
• 1 NM is 1,15 statute mile (15%)
• 1 Statute mile is 1609 meter
• 1 Kts is 1 nautical mile per hour which is 0,5 meter per second
• One minute on a median is 1 nautical mile (NM)

Actieradius is both to and returning to your starting point (A - B and B - A)

Range is only A to B

Scale of a map is projected like this:

1:500.000 is 1 cm on the map is 500.000 cm in real life (or 5 kilometers)

Time (19)

The apparent solar time is the actual time based on 12 o clock noon -> highest sun point

1. Local time is regional time of the country, UTC is Greenwich time
2. Standard time is the time of a country (actual time)
3. Local Mean Time (LMT) is the actual sun time based on the setting of the sun -> linked to closest meridian

Time notation can be done in various ways:

• 1345
• 13:45
• 13:45 UTC
• 13:45 Z
• 13:45 LT (Local Time)

Calculate UTC from LMT

We can calculate the LMT from the actual time:

• 1 degree is 4 minutes
• 1 median minute is 4 seconds
• Pick the distance from your location to your actual time median and calculate the difference

Uniform Daylight period is the calibrated daylight time, + 15 minutes before sunrise and + 15 minutes after sunlight.

VFR Navigation (20)

Navigation in VFR is done based on visual references, track calculations and wind calculations. Because the wind is a mass of air where the plane flies in, we will arribe at our destination “together with the wind”. Which means we have to correct our track for the wind.

Before going into the deep explaination, let’s process all the different terms we must know:

• Gispositie: Your destination with the wind taken into account, but not entirely sure.
• True position/Fix: A fix where you cross referenced chart/GPS with what you see outside and confirmed
• Wind-triangle
  • Air vector (1 triangle)
  • Ground vector (2 triangles)
  • Wind vector (3 triangles)
• Ground course: This is the track to be flown relative to the ground
  • True track (TT) -> Track based on true north
  • Magnetic track (MT/MC) -> track based on magnetic north
• Intended track: This is the chart-based ground track to be flown
• Actual track: This is the actual track flown to correct the wind
• Track error: this is how much degrees you must steer to your intended track if deviated (100 degrees intended, 90 true heading is 10 degrees track error). This is also the difference between true track and actual track if there is no wind.
• Drift: This is the amount of degrees between the intended and actual track to correct for the wind (opposite of the wind correction angle WCA is 7 degrees right means drift is 7 degrees left)
• Heading (air course): Amount of degrees based on the north where the plane flies to in the air
• True heading: Course based on true north
• True track: the flying track based on true north, and so on your VFR map
• Magnetic heading: Course based on magnetic north
• Magnetic course: the glying track based on magnetic north
• Compass heading: Magnetic corse with compass error correction added/subtracted
• Wind correction angle (opstuurhoek): this is the angle between the intended ground heading and the true heading (what to correct)
• Isogonic line: A line on a chart that represents the local magnetic variation
• Agonic line: A line on a chart that represents a magnetic variation of 0 degrees

If there is no wind, the air track, intended track and actual track are all the same value.

The wind triangle

The movement of the plane relative to the ground is decided by three vectors:

1. The air vector -> Heading and True airspeed (TAS)
2. The ground vector -> Track and ground speed (GS)
3. The wind vector -> Wind direction and speed (260 at 8 knots)

The numbers correspond with the arrows/triangles in the drawings, but we calculate in the order 1, 3 and then 2.

Air vector

The air vector’s length is based on the true airspeed and course based on the true heading. The start position is called the true position.

Wind vector

The wind has a speed and track, but wind is pronounced where the wind comes from. This is the opposite of planes because it makes calculations easier.

Ground vector

Now we know those two values, we can make an airplot. This gives us the result of the track incl. wind correction, basically the ground vector.

Calculating Tailwind/Crosswind components

We can calculate the headwind and crosswind components with the sinus and cosinus to have a better understanding of the actual wind blowing against your plane:

Crosswind = sin(wind direction - ground course) x wind speed

Example: sin (270-285) x 12 = -3,1 knots

This means wind comes from the left with 3 knots blowing you to the right

Head/Tailwind = cos (wind direction - ground course) x wind speed

Example: cos (270-285) x 12 = 11,6 knots headwind

This means from the 12 knots wind, we get 11 knots onto head and 3 knots from cross.

You could also use these numbers to remember quickly (or take a E6-B on board)

Example: your heading is 180, wind comes with 15 knots from 223. Difference is 43 degrees, we pick 45:

15 knots x 0,7 = 10,9 knots crosswind

15 knots x 0,7 = 10,9 knots headwind

Track error correction by incorrect steering

If deviated from the original route, we must correct this by steering the opposite way. But how much, that is something we can calculate.

We can use the 1 on 60 rule: every degree off from the intended route will result 1 nautical mile (NM) on a distance of 60 nautical miles.

Example: After 20 NM you are 2 NM from track. We will calculate this to 60 miles, which is times 3: 6 NM deviation every 60 NM. This means also 6 degrees off track.

To correct the course, we must multiply this correction times 2 to get to the original track. This is called the track error (trekfout).

Best fuel consumption methods

• To fly to a far aerodrome, fly maximum range by leaning the mixture, with tailwind and minimize drag
• To maximize endurance, fly as low as possible with minimal RPM

Als keep in mind that the disadvantages of wind are greater than the advantages. For example:

• We fly from our starting point to the east (090) with 100 knots (IAS).
• We have a wind from west to east (270) with 25 knots.
• Our ground speed (GS) will be 125 knots
• This means we are 125 nautical miles from our starting point after 60 minutes
• If we turn around, we fly into the wind which will slow us down, because we don’t have tailwind anymore our speed is back at 100 knots. In fact we have to subtract those 25 knots of wind from our ground speed
• We fly back to the starting point with 75 knots of ground speed (GS)
• However, this will take 100 minutes (1h40m) (125 nautical miles / 75 knots * 60 is 100 minutes)

Automatic Direction Finding (25)

Automatic Direction Finders or ADF in short is a piece of hardware in the plane that can contact Non directional Beacons (NDB) beacons on the ground to find the correct direction to it. It is basically tuning the frequency when in range and then read the direction the signal comes from. The frequency of ADF works between 190 kHz and 1750 kHz (LF and MF). Most NBD beacons use a frequency between 250 kHz and 550 kHz.

The plane only contains a directional-sensitive receiving system, in these 3 parts:

• Antenna system
• Control panel to tune the frequencies
• Indicator

the ADF has three important buttons:

1. ADF: this turns the device on, and another press enables the ANT mode which is used for testing only.
2. BFO: Identify NDBs
3. FRQ: to switch between stand-by and active frequency

Your ADF system in the plane only connects to NBD beacons (sometimes reffered as locators) on the ground. It then shows a relative bearing to the beacon, based on the heading of the plane. It basically says, turn till the plane in the middle of the indicator and the line are aligned.

• Relative bearing: The angle to turn to exactly the beacon
• Compass heading: The actual compass heading
• Compass bearing: The solution of the sum Compass heading + Relative Bearing

Example: We fly at 173 degrees and our ADF indicator says “69”, we sum those up and that gives us 242 degrees. We have to fly 242 degrees on our compass to fly directly to the beacon. This because the ADF gives us a relative bearing, so the “langsas” of the plane is 0 degrees.

Bearing means “peiling” in Dutch.

Now we must make it harder, we can do a magnetic bearing to the NDB beacon. We take the outcome of the sum above the blue bar and put into a new sum.

Compass bearing + deviation = magnetic bearing. This magnetic bearing is the QDM, also called, the ground track to follow to reach the NDB. The reverse of the QDM is called the QDR, which is from beacon to the plan. We have to add 180 degrees to the QDM to get the QDR.

Example: our compass bearing is 242 degrees. Our deviation is 4 degrees west (indicates too much west) so we have to subtract it. The magnetic bearing is 238 degrees.

Now we could correct this number on top of all for the true north instead of magnetic north, which gives us the “true bearing”: Magnetic bearing + variation

Example variation east: Magnetic bearing 238 + variation (2,45 degrees east) = 240,45 degrees

Example variation west: Magnetic bearing 238 + variation (2,45 degrees west) = 235,15 degrees

Look at how the variation can change the headings, because we go from magnetic to true, we have to subtract west and add east. In the case of true/chart to magnetic this flip-flops.

ADF indicators

We have 2 types of ADF indicators:

• Relative Bearing Indicator (RBI) (Left)
• Radio magnetic indicator (RMI): This is a indicator that has a gyro in it and turns with the magnetic compass. This shows the actual QDM at any time. Ligher aircraft doesn’t have a RMI.

In the RMI, the green arrow is the QDM.

NDB beacons are the oldest type of beacons and are only used today as holding points. Today we have VOR/DME beacons and also the more user-friendly GPS.

NDB beacons have a range of about 10-25 NM

NDB beacons are “locators” and shows with a “L” on maps. SOmetimes they are used as approach locators.

En route beacons could have a range up to 200 NM.

Reliability

A NDB beacon is not always reliable. These are factors that plays when using NDB beacons:

• Transmit power of the transmitter
• Weather -> rain and thunderstorms
• Around 6 degrees correction
• LF/MF frequency so much affection by terrain
• Night effect -> skywaves (less range and interference)
• Coast-effect -> Curving radio waves due to sand and sea -> Rely on visual navigation in coastal areas
• Mountain effect -> curved lines/multi-path effect due to bouncing of signal
• Interference of other NDBs

VOR Navigation (26)

VOR beacons are the next evolution on top of ADF where most of the issues with ADF are fixed.

VOR stands for VHF Omnidirectional Range, and sends signals to every radial around it. It also works on VHF which makes the range and interference much better. The frequency range is 108.0 MHz to 117.975 MHz.

VORs are always based on magnetic north.

Its works basically like this: tune to the VOR frequency and your CDI will show an arrow to the beacon. On top of ADF you can select where to join the VOR radial and navigate to that. It also dhows course deviations with the needle. Also it shows if going to or from the beacon. With DME we could also measure the distance to the beacon where we will go dive in deeper in the next module.

VOR has the following advantages on top of ADF

• Less interference
• Less reliant on weather
• No strange side effects
• Better navigation as you select where to get to the VOR
• Selectable on navigation frequency
• Better precision

A VOR is an hexagon on the chart. If its outlined with a square, it also has DME.

VOR beacons push out 2 different signals:

• Reference signal: A signal which sends out signals for verification. This also contains a MORSE code to verify you are on the right VOR
• Variable signal: A lighthouse-like signal that varies over all the radials to send out a signal which planes can receive. Thus it knows where to navigate to

VOR navigates you to the magnetic north, so 0 degrees on the VOR radial is to the magnetic north. We also have to take the local variation of the beacon into account which also would be on the map.

The instrument to use with VOR beacons is the Omni Bearing Indicator (OBI), which contains the CDI (needle) and the selector (OBS) to set the desired radial of the beacon. It also shows “From” and “To”, to point out if you are flying to the beacon or flying away from it. Later more about that.

The horizontal needle represents the course/track to the beacon radial, where needle right means you are too much to the left. This is based on the view of the beacon itself. Each dot/stripe is 2 degrees off the selected radial (330 degrees in this case). The needle represents the track you must fly to get to the selected radial of the beacon.

You will select 330 degrees if you want to overfly the beacon with a heading of 330 degrees. Its as simple as that. The from region will then be 330 + and -90 degrees and the to region 330 - 180 = 150 degrees, 90 + or - that number.

• Radial: The line you are on (above screenshot: radial 150)
• Magnetic ground track (above screenshot: 330 degrees
• CDI: Course deviation Indicator/needle -> shows the correct track to steer to overfly the station at selected magnetic heading
• To/From: Shows if you are flying to or away from your selected radial - and + 90 degrees of your selected heading

To/From indicator

The to and from indicators are shown on the right side of the indicator and will tell you if you are flying the right way. We could fly heading 0 degrees and are north of the indicator. It will then show as if we are south and flying to it. The to/from indicator will then show “From” as we are currently flying away from it. The signal will be sent into the radial but otherwise there wont be a note to tell you if the direction is correct.

As we then select the 180 degrees radial, the indicator will switch “To”. We could also use the “from” course if we need to fly 240 degrees over the beacon and then for 10 miles further.

Using the VOR navigation equipment

In the cockpit we have a separate radio for navigation. We need to tune to the frequency to start using the beacon. The frequency is on your VFR map or app.

We can tune to the frequency and set it as active to make the OBI adjust to the beacon. You can also press the IDENT button to get the unique morse code which is also on the map.

Using multiple VORs can help you getting a “fix”, or a real position as you know where you are relative to a beacon. Useful when you are lost or lost your visual references.

The range of a VOR beacon is the same as with normal VHF radios and can be calculated with this formula:

1,23 * (√antenna elevation in ft) + (√plane altitude in ft)

Let’s say, the antenna height is 1000ft and our altitude is 13.400ft:

1,23 * (√1000)+(√13400)= 181,27 nautical miles (NM)

Horizontal Situation Indicator (HSI)

In newer planes, we will have a HSI instead of a CDI. This new variant doesnt use FROM/To but always shows the correct direction with an arrow. It always leads you to the correct heading and shows if on or off course to the beacon.

GPS errors

GPS is a great navigational system, but comes with different possible errors:

• Propagation errors can occur due to the ionosphere
• Geometry errors can occur due to close positioning of satallites
• Atomclocks in GPS satallites can be restored in the Master Control Station

A GPS satallite sends out 2 codes.

To get a two-dimensional (2D) fix from GPS (length and width), you need at least 3 satallies

To get a three-dimensional (3D) fix from GPS (length, width and altitude above ground), you need at least 4 satallites

1-in-60 rule

The 1 in 60 rule is a quick method to estimate how far off course you are without using trigonometry.

It is based on this practical approximation:

After traveling 60 units of distance, an error of 1 unit sideways equals an error of 1 degree.

This works because for small angles, the tangent of the angle is approximately equal to the angle itself (in degrees). It relies on small-angle approximation, which is why it is accurate for normal navigation errors.

You can use these simple calculations and I have some examples below:

• Miles off track * 60 / Miles flown = Track error in degrees (trekfout)
• Miles off track * 60 / Miles left = Correction angle (sluithoek)

When you only have the amount of degrees:

• Track error in degrees * miles flown / 60 = Track error in NM (reverse of the calculations above)
• Miles off track * 60 / Miles left = Correction angle (sluithoek)

For example:

• We plan to fly a route of 88NM in total
• After 63 NM, we find ourselves at 4 NM off track with 25 NM to go
• We do 4 * 60 / 63 which gets us 3,8 degrees off track in 60 minutes
• We do 4 * 60 / 25 which gives us 9,6 degrees which we have to correct
• This means we have to fly 3,8 degrees to correct our heading + we have to add 9,6 degrees to actually get at our destination. From the heading we have flown, subtract 13,4 degrees

Example 1 – Finding heading error

You planned to fly 60 nautical miles, but you end up 1 NM off course.

Calculation: 1 ÷ 60 × 60 = 1°

Result: Your heading was about 1 degree wrong.

Example 2 – Larger distance

You flew 120 NM and are 2 NM off course.

Calculation: 2 ÷ 120 × 60 = 1°

Result: Still about 1 degree heading error.

Example 3 – Correcting your heading

Route: 174 NM After: 112 NM Track error (drift): 6°

Using 1-in-60:

• Off-track (NM) ≈ Distance × Error(°) / 60
• Off-track ≈ 112×6/60=11.2112 × 6 / 60 = 11.2112×6/60=11.2 NM

Result: You’re about 11.2 NM off the intended track.

Calculations

Because navigation contains alot of different calculations, I will write them all down here:

Time to distance

58 NM in 40 minutes

Example: 58 / 40 minutes x 60 minutes = 87 knots

Distance to time

58 NM with a speed of 87 kts

Example: 60 minutes / 87 ground speed = 40 minutes to travel 58 NM with a constant speed of 87 kts

Speed to time

25 minutes with a speed of 110 kts is 45,8 nautical mile

Example: 110 knots / 60 minutes x 25 minutes = 45,8 nautical miles (nm)

Time to decimal

This formula shows how to calculate the decimal notation if you only have the time/DMS notation:

Formula: Degrees + (Minutes ÷ 60) + (Seconds ÷ 3600)

Example: 48° 51′ 24″ → ?

Step by step:

1. Degrees: 48
2. Minutes ÷ 60 = 51 ÷ 60 = 0.85
3. Seconds ÷ 3600 = 24 ÷ 3600 = 0.0067
4. Sum up everything: 48 + 0.85 + 0.0067 = 48.8567°

Solution is 48.8567° and we have to do this for both north/south and west/east

Decimal to time

This formula shows how to calculate the time/DMS notation if you only have decimals.

Formula:

Degrees + (Minutes x 60) + (Seconds × 60)

Example:

40.6892°

1. Degrees: 40
2. Minutes: 0,6892 x 60 = 41.352 rounded to 41
3. Seconds: 0.352 × 60 = 21,1 rounded to 21

Solution: 40 degrees, 41 minutes and 21 seconds, in short 40° 41′ 21"

ISA to temperature on altitude

To calculate from ISA (15 degrees celsius on 1013 hpa) to a certain ground temperature on a specific altitude, use this calculation.

Example 1: Ground temperature is 26 degrees and elevation is 1650ft. The QNH is 1013

1650ft / 1000ft * 2 degrees per 1000 feet is 3,3. This means it’s 3,3 degrees warmer than ISA which must be taken into account for density altitude calculations

Example 2: Outside air temperature (OAT) means on the altitude is -9 degrees and elevation is 6225ft. The QNH is 1002

1013-1002 = 11 * 30 ft hpa is 330ft difference. The pressure is lower than 1013 so we add this to the actual altitude to get the pressure altitude: 6555ft

6555 / 1000ft * 2 degrees per 1000 feet is 13.11 degrees.

ISA temp is 15 - our temp 13.11 is 1,89 degrees according to ISA. But the actual OAT is -9 so its -9-1,89 = -10,8 degrees colder than ISA.

This can now be dialed on the E6B to get the actual density altitude:

• Pressure altitude: 6555
• OAT: -10,8

Gets you the density altitude of around 5000 feet.

Example 3: Density Altitude is 12.000, OAT is +20 degrees, calculate pressure altitude

12 x -2 + 15 (ISA) = -9

20 - (-9) = 29 degrees on the ground

120 feet per degree is 120 x 29 = 3.480 feet to subtract from density altitude

12.000 feet DA - 3.480 is 8520ft pressure altitude

Speed and distance to time

115 knots

73 Nautical mile

distance : speed = time (decimal) * 60 is time in minutes

73 : 115 * 60 is 38 minutes

Distance and time to speed

320NM

2 hours and 23 minutes

Hours and minutes to decimal -> 143 minutes

Distance : time * 60 = Speed in knots

Speed, distance and fuel flow

Speed is 125 kts

Distance is 105 NM

Fuel flow is 2,5 GPH (US Gallons per hour)

105 : 125 = 0,84 hours -> 2,5 * 0,84 = 2,1 US Gallon (x 6 to LBS if fuel density is 0,72 kg/l)

True Track/Compass Heading questions

To calculate questions about certain headings with variation and deviation into place, we can use the following abbreviation:

• Cadbury - Compass heading
• Diary - Deviation
• Milk - Magnetic Heading
• Very - Variation
• Tasty - True Heading
• Dr(iving) - Drift (or WCA)
• TTrucks - True Track (ware kaartkoers)

Let’s say, we have a True Track of 352 degrees, and we want to know some of the other values. Let’s do this:

Now we can fill in the blanks step by step to get to the actual other values correctly and in the correct manner:

Left to right: Subtract (-) West and Add (+)East numbers (LR -W +E) Right to left: Subtract (-) East and Add (+) West numbers (RL +W -E)

Source: https://www.youtube.com/watch?v=FtBFgr61bW8

Use this tool to calculate this stuff: https://flighttools.justinverstijnen.nl/coursecalculator/index.html

Calculating the Total compass error (miswijzing)

The Total compass error is the sum between true heading and compass heading, exactly in this format. A positive digit will give you an east error and a negative digit will give you a west error.

Temperature and altitude correction

Vuistregel: 4 ft correctie per °C temperatuurafwijking (per 1000 ft hoogteverschil)

Dat betekent:

• Temperatuur 1°C kouder dan ISA → 4 ft extra fout per 1000 ft
• Temperatuur 10°C kouder dan ISA → 40 ft fout per 1000 ft
• Temperatuur 30°C kouder dan ISA → 120 ft fout per 1000 ft

Headings/courses extra

CH 098°; deviatie +2°; variatie -8°; drift 5° L. Bereken de TT.

Kompasluchtkoers (CH) 317°; deviatie +3°; variatie 5°W; drift 10°R. Bereken de ware grondkoers (TT).

TH 358°; MH 352°; deviatie +3°. Bereken de miswijzing.

CH 317°; deviatie +3°; variatie 5°W. Opstuurhoek 10°R; er is geen trekfout. Bereken de TT.

CH 054°; deviatie +3°; variatie 5°E. Bereken de TH.

CH 224°; deviatie -3°; variatie 4°W. Bereken de TH.

CH 098°; deviatie +2°; variatie -8°; drift 5° L. Bereken de TT.

Made a tool to exactly understand this topic: https://flighttools.justinverstijnen.nl/coursecalculator

Using the E6B Flight Computer

With the E6B flight computer, we can calculate a lot of different things. On the front side, we can calculate and convert units. The other side is used to calculate true heading based on true track and the wind component. Also we get an indication of what our speed will be.

1. Unit conversion
2. Calculating Density altitude from pressure altitude and temperature
3. Calculating true airspeed with altitude, Calibrated Airspeed (CAS) and temperature
4. Calculating drift and wind correction angle
5. True airspeed and wind to ground speed

Raw notes (exam preparation)

• Lambert chart (VFR Netherlands) is conform, which means angle-corrected (hoekgetrouw)
• Lambert chart has straight meridians
• Lambert chart has crossing meridians and parralels in 90 degrees angles
• DME always gives one decimal: so 2 nautical miles will be presented as 2.0
• A plane following a straight heading, also follows a loxodrome
• Meridians are both groot cirkels and loxodromes
• A grootcirkel is the shortest route and requires continious steering
• Meridian conversion is the angle of meridians and the 0 on the mercator-projection
• In the flight plan, you always mention the true airspeed (TAS).
• To get relative bearing, you do QDM - heading
• The wind vector can be determined by the air and true position (2 of the 3 of the triangle)
• WCA - track error is drift
• The wind-angle is the angle between wind and the true track
• Semi-circular altitude system will be determined based on magnetic ground course
  • East: odd flight levels ending with 5 (oost = oneven) (000-179)
  • West: Even flight levels ending with 5 (180-359)
• On the VFR chart, airports will be marked with elevation and then the runway length
• Time depends on the geographic length, every 15 degrees represents 1 hour, 1 degree per 4 minutes, 1 parralel minute per 4 seconds

To do examenvoorbereiding:

1. VOR Beacons
2. Trekfout
3. ADF/Relative bearings

End of the page 🎉

You have reached the end of the page. You can navigate through other blog posts as well, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog homepage

If you find this page and blog very useful and you want to leave a donation, you can use the button below to buy me a beer. Hosting and maintaining a website takes a lot of time and money. Thank you in advance and cheers :)

The terms and conditions apply to this post.

Principles of Flight (POF)

The atmosphere (1)

The atmosphere is the layer around the earth, which is around 100 to 200km from the ground up. Worldwide, we use the International Standard Atmosphere which is a mean set of conditions which will be somewhat different depending on the weather conditions, location etc. This is a mean of the conditions at 45 degrees north latitude.

In the standard atmosphere, we use these characteristics:

1. 0ft is at the mean sea level
2. The air density is 1,225 kilograms per cubical meter
3. The air pressure is 1013,25 hPa (millibar) or 29.92 inches of mercury (inHg)
4. The temperature at sea level is 15 degrees celsius
5. In the troposphere, the temperature decreases with 2 degrees celsius for every 1000ft up (2 degrees per 300 meters)
6. The tropopause is at 36.000ft (11km) and the temperature is -56,5 degrees celsius
7. The troposphere and stratosphere contains 78% carbon dioxide (co2) and 21% oxygen

This is a set of conditions, but some numbers can defer in the real world, due to the location or different seasons. Now, lets take a look at the different layers in our atmosphere:

This is a repeat of the information already learned in the Meteorology course. For more information, check out

Air Pressure

Air pressure is a result of the mass/weight of the air. Because there is so much air above the earth which compresses close to the ground, areas with a lot of air molecues will be created. You can see this as a tower of jenga you played before. The weight of all the bricks pushes on the lower layers of bricks.

On earth we have several high pressure areas and low pressure areas which are an result of temperature differences. High pressure areas always wants to go to low pressure areas, just like when you pump up a tire and let go the vent. The air from the high pressure area inside the tyre will go to the outside, low pressure area.

• In high pressure areas: cold air falls to earths surface, and cold air has more air molecules
• In low pressure areas: warm air from the surface rises, and warm air has less air molecules

So air pressure actually indicates the volume of air molecules in the area. The higher the pressure, the higher the volume of air molecules.

High pressure (H) and low pressure (L) areas are not absolute numbers, but relative to each other. For example:

• 979hPa (L) vs. 1013hPa (H)
• 1013hPa (L) vs. 1035hPa (H)

Air Pressure when elevating

When going up into the air, the air pressure will decrease like seen in the graphic below:

For reference, we will use this numbers:

• Every 30 feet up in the air represents an hPa loss in air pressure
  • Example: 1013 hPa on sea level (0ft AMSL) means a mean pressure of 1000 hPa at 390ft altitude

As this is an exponential relationship, this will guide you through the first 10.000ft (3,048km) in altitude, after that this trick does not longer work correctly of course. Some good rules of thumb:

• 5.000ft altitude: 75% (3/4) from ground pressure
• 18.000ft altitude: 50% (2/4) from ground pressure
• 34.000ft altitude: 25% (1/4) from ground pressure

For more information about Pressure and Density altitude, check out: https://flightblog.justinverstijnen.nl/ppl-theory-nav/

Pressure Altitude

Pressure altitude is the altitude corrected to the International Standard Atmosphere, namely 1013 hPa (which is also called QNE). For performing take-off calculations, we will want to know how our plane performs which can be different with different pressures. This is a live indicator of being above or below earth’s standard atmosphere.

In short:

• Higher pressures (Low altitiudes): Better engine performance, better propellor performance and more lift
  • More oxygen and more air molecules
• Lower pressures (High altitudes): Less engine performance, less propellor performance and less lift

Pressure altitude examples

In an airport which mostly is lower or higher than mean sea level, there will be a small correction needed. For example, our airport is at 17 feet above sea level, and the actual pressure is 1032 hPa on sea level at a day with nice weather, the pressure altitude is -489 ft. This means our take-off performance will be better as we have more air molecules which is better for our engine.

In the same example with a pressure of 968 hPa on sea level, we will have a pressure altitude of 1238ft. This means our aircraft will perform as it takes off at 1238ft above sea level, which will have some disadvantages. As there is less air, we will need a longer runway, our engine performance is less and our lift will be less as there is less air. However, flying in relative high pressure altitudes is good for having speed, as drag decreases in lower pressure.

As you can already see, this example gives two completely different scenario’s with around 1700ft difference. In countries like the USA where airstrips can be at 5000ft altitude, the pressure can be a huge difference which we must take into account.

Check out this tool to calculate and visiualize Pressure/Density altitude: https://flighttools.justinverstijnen.nl/pressuredensityaltitudecalculator

Density altitude

Now we know the pressure altitude, we need to correct it for Density altitude, because warmer air is thinner than colder air. This is because warmer air expands, just take a look at a hot air balloon. This means that on 5000ft pressure altitude and on a hot day of 35 degrees, the density altitude (also known as “performance altitude”) will be almost 9000ft. So we can expect our plane to behave as it is on 9000ft in normal ISA conditions.

Thinner air means less oxygen and less air molecules, denser air means more air for lift for both propellor and the wings. Less oxygen also means less engine performance but a higher true airspeed due of less resistance from air molecules.

To calculate the density altitude from pressure altude, you can use the E6B or the tool below:

Check out this tool to calculate and visiualize Pressure/Density altitude: https://flighttools.justinverstijnen.nl/pressuredensityaltitudecalculator

Tip: Use an E6B calculator for a quick and thorough calculation of Density altitude based on the outside air temperature (OAT) and pressure altitude.

Lift (2)

Lift (draagkracht in Dutch) is a component that keeps a plane in the air. This is the upward force that fights the gravity/weight of the plane. It works basically as the wind flows over and under the wing. As the air over the wing goes faster and under goes slower, it will combine at the end of the wing.

The two primary causes of lift are:

• Pressure differences: under the wings the air pressure increases, wanting to go to the low pressure area above the wing
• After the trailing edge of the wing, the air goes down, under the wing the air goes up

We can explain why an aircraft flies because of 2 elementary laws:

Both laws describe that a flow in a narrow area will go faster and has a lower pressure. This helps us better understand how an aircraft flies.

How an airplane generates lift

Lift works basically with these 4 components:

• Wind velocity: The more headwind (speed) you have, the more air and air molecules will hit your wing. This pushes the wing upward where the wind will then be directed to the ground and changes the velocity. Changing the direction and velocity of this wind has a reaction which is lift force.
• Angle of Attack: The angle of attack is the angle of the wing hitting the wind. By default, planes have a little angle of attack of a few degrees but we can increase this with the yoke (steer) of the plane
• Drag: The drag component is how much air resistance we have in a particular situation. The higher the angle of attack, the more drag and how harder the engine must work to compensate for it, which can evantually result in a stall
• Lift force: The lift force is the resultant of the wind velocity, drag and the angle of attack and states how much the wing is pushed up

Let’s take these 4 components into a simple drawing:

The black line represents the chord of the wing. This is the same with the outline of an wing:

We also have the resulting air-force, which is a line 90 degrees of the wing profile, based on the oncoming wind.

Static and Dynamic pressure

For the example of Static and Dynamic pressure, I will stick to the example of a garden hose, pinched. This results in two things:

• Static pressure (A): This is the air pressure in the hose which will decrease when narrow and will increase again after the narrow part is over
• Dynamic pressure (B): This is the pressure of the water, the speed of the water, and this increases at the cost of static pressure

Take a look at this drawing, which makes more sense:

This basically works the same as the pitot-static system of an airplane, the static port measuring the static air pressure, as the pitot probe measures dynamic pressure. Inside of the measurement systems, there will be calculated the results which are Indicated Airspeed (IAS), Altitude and Vertical Speed (VS).

Dynamic pressure is measured with this formula:

• “P = q = 1/2 ρ V²”

This means:

• P: Total pressure
• Q: Dynamic pressure
• 1/2 ρV²: Also dynamic pressure but explained granular

Bernoulli’s law states that for example water or air going into a narrow space at a certain speed, will also come out of that narrow space with that certain speed.

Air flow around a wing-profile

The air will flow around a wing-profile. Because of the leading edge of the wing, the incoming air will divert up and down, bringing the flow-lines closer together.

Just like the two laws already predicted, the airflow will increase and the static pressure will decrease. At the leading edge of the wing, the lines will be closer together. Here the pressure is relatively low. Near the trailing edge of the wing, the flow lines will be less close. The speed of the airflow decreases and the pressure increases.

Under the wing, the airflow will have to make a smaller angle and path, causing the air to move at a slower speed but at an higher pressure.

Upwash and Downwash

The upwash is an uplifting movement as result of the pressure differences. The leading edge of the wing needs to split the airflow. This point is called the “stagnation point”, the point of air coming to a small temporary stop and then leaded over or under the wing. In the picture below, you can see that the airspeed is 0 at the stagnation point.

The downwash is a descending movement of the airflow after it hit the wings. As Bernoulli’s law already stated, the dynamic pressure increases then the static pressure decreases, so the air above the wing goes at a faster speed.

Too see this all put into perspective, view this image:

• Airspeeds are a reference

An wing profile described

A wing profile has various parts, which we will describe now:

• Leading edge: The frontal part of the wing where the airflow first hit the wing
• Trailing edge: The aft-part of the wing where the airflow leaves the wing
• Chord: The imaginable line from leading edge to the trailing edge
• Camber line: The camber line which is the skeleton-line, is a line which is in the middle of the top and bottom
• Camber: The maximum distance between the camber line and the chord
• Thickness: The maximum distance between top and bottom. This will sometimes be referred as the “thickness-to-chord” ratio

Angle of incidence and Angle of attack

• The angle of incidence (AoI) (Instelhoek) is the angle between the longitudinal axis of the plane and the chord. This is how the aircraft is built and is by design, so the plane generates enough lift in straight and level flight.
• The angle of attack (AoA) (Invalshoek) is the angle between incoming airflow and the chord. This is the pitch angle you can set with the yoke, which controls the elevator.

The angle of attack will often be reffered as “α”. It also is an result of sum angle of incidence, the pitch angle and the glide angle.

Glide angle

The glide angle (baanhoek in Dutch) is the angle between horizontal and the flight path. The flight path is the path the center of gravity flies through the air.

The lift formula

The lift formula is an outline of the resulting airforce on a wing profile. Lift is dependent on these 3 things:

1. Dynamic pressure of the incoming airflow
2. The lift co-efficient
3. Wing surface

The formula goes like this:

• Lift = 1/2 ρ V² CL S

So all these components work somewhat together to produce lift. This means the result of all must be positive, where one value can be less or more than another at certain parts of a flight. We will take a deeper look into the Lift components.

Dynamic Pressure

The dynamic pressure is the pressure of the free airflow just before the wings. 1/2 ρ V² altogether is a sum of static and dynamic pressure, where V² means only the dynamic pressure. The V factor is equal to the True Airspeed. Headwind is also counted within this V factor, which means that the more headwind, the more lift.

Static pressure in this formula is also very important. This is directly dependent on the static air pressure in the air you fly in. The higher the static pressure, the more lift. This also means that if we climb with a plane to about 34.000ft where the air pressure is about 25% of the pressure on earths surface, you will need much more speed to retain a specific amount of lift.

Lift coefficient

The lift coefficient is a sum of the angle of attack, amount of lift and drag. In a graph, this looks like this:

• A fun fact is that because of the angle of incidence of a Cessna 172, a plane wil always have a higher angle of attack than 0.

This graph outlines that the more angle of attack we have, the more lift. However, there is a bount that this stops which is called the critical angle of attack. In a Cessna 172, this is around 15-16 degrees nose up. Pulling even more on the yoke causes the plane to stall and dip from the sky. This can be very dangerous at lower altitudes.

Stalls lesson

A high angle of attack results in the air not gluing anymore to the wing but to transform into rotor flows. To get a better view of what exactly happens:

Wing Surface

The wing surface is a factor that directly influences the lift of a plane. In the formula, this will be in the value square meters (m²).

How bigger a wings’ surface is, the more lift it can deliver. We can also do some things with our wings to produce even more lift as they increase the wing surface area. Think about:

1. Flaperons (flaps)
2. Slats (on airliners)

We set flaps on take-off to produce more lift at a lower speed. This means we need less runway to take-off from. When landing, we use more flaps to create more drag and decrease the speed. Flaps help us in these parts of the flight to have more time, see the runway a lot better and to descend in a much steeper line.

Indicated Airspeed and Lift coefficient

Then in straight and level flight, there is a great connection between the speed and the lift coefficient. The lift equals the weight of the plane and the speed is higher than the amount of drag. However, if the angle of attack increases -> the lift coefficient will also increase. If preventing that the lift increases, the airspeed must be decreased.

• A high speed needs a low angle of attack
• A low speed needs a high angle of attack

Symmetric and asymmetric wing profiles

• An Asymmetric wing profile is where the top of the wing has more camber, this is what most planes have
• A symmetric wing profile is where the top and bottom of the wing are the same, mostly in aerobatic planes

This also means something for the lift coefficient and the angle of attack performances. For example, a symmetric wing profile will start with 0 lift coefficient. This gives it somewhat less lift than an asymmetric profile, as shown in this graph:

• Red: Asymmetric
• Green: Symmetric

Here an asymmetric wing profiles will eventually reach a lift coefficient at a negative angle of attack.

Three-dimensional airflow over a wing

The airflow over the wings looks like this in three-dimensional setting:

On the left, the airflow underneath and above the wing is illustrated and on the right we have the difference in pressure (Up = low and under = high). This difference in pressure will tend to flow to the wingtips. This movement actually causes the wake turbulence to happen. This movement however induces a decrease of lift and an increase of drag, induced drag, to be pronounced correctly.

Wake turbulence

Wake turbulence (zogturbulentie) is caused by lift, and will show as two opposing turning rotors behind the wingtips. This is an excellent example of Newtons third law in action, which states that for every action in the universe there is an opposing reaction. The force of the lift creates an reaction in the form of wake turbulence.

The reaction of two opposing wings will cause this wake turbulence. The strength of the wake turbulence is affected by the amount of lift the plane generates. A Boeing 777 will generate lots of lift to fight its huge mass compared to a Cessna 172 and so generates more wake turbulence.

A good advice is if taking of behind an airliner, to wait for at least 3 minutes for the wake turbulence to completely dissipate. Heavy wake turbulence can cause huge problems as the airflow for light planes will be disrupted.

I found a great video explaining the effects of wake turbulence and wingtip vortices here.

Some other facts:

• The strength of the wingtip vortices are caused by the amount of ligt
• The strength of the wingtip vortices are also caused by the angle of attach, where a higher angle of attack will generate more wingtip vortices
• The wingtip vortices are the strongest during take-off and landing
• An aircraft in clean configuration produces the most wingtip vortices
• Wake turbulence will move the direction of the wind

The risks of wake turbulence

The greatest risks of wake-turbulence are:

• Rapid roll-movements which will be so powerful steering against it will not be possible
• Structural damage to the plane
• Loss of height
• Greatly reduced climb performance
• Not enough lift at take-off (if taking of after a HEAVY aircraft)

Wing shapes

The shape of an wing from the top view is called the wing shape. We have mostly two types of wing shapes:

• Straight wings
• Tapered wing

These wings also have some more properties:

• The wing-root is the part which is sticked to the fuselage
• The end part of the wing is called the wingtip
• The wing span is the total length of both wings from the wingtip of the left to the right wing

The distance of the wing leading edge to the trailing edge is called the chord as we already saw. Sometimes this chord is not a straight line. We then speak of a mean chord.

We can calculate the wing aspect-ratio using this formula:

Aspect ratio = Wingspan divided by (/) the mean chord.

Now the aspect ratio also helps producing lift. The higher this ratio, the more steep the lift-curve is. Take a look at this graph:

For reference, here a glider plane as a much steeper line than a fighter jet. This is like we already discussed, a result of the wingspan divided by the mean chord.

Wing surface

The wing surface is the total surface area of a wing. We calculate also the part above the fuselage, and is called the gross surface.

Drag (3)

Drag (weerstand) is the resistance of the air a plane flies through. Oncoming wind slams into the cockpit, leading edge wings and wheels and this partly slows us down. More information about this component will be discussed further in this module.

We can feel drag especially when on a bike and going really fast (25-30 km/h or higher). You feel alot of upcoming air which slows you down. This is the exact same on a plane.

To let an aircraft actually fly, the thrust component of the engine must be higher than the total drag at all times. In an horizontal flight, the amount of drag is equal to the amount of thrust, bringing you forward in a constant speed.

The drag formula

The drag formula is similar to the already discussed lift formula, and looks like this:

• Drag = 1/2 ρ V² CD S

The only difference is that we replace the lift coefficient with the drag coefficient. This drag coefficient is also dependent on the angle of attack (AoA). More angle of attack means more drag, as the leading surface of the plane increases a bit.

Types of drag

We have two types of drag, which we can separate into two categories:

• Induced drag (geinduceerde weerstand): Induced drag is caused by generating lift. When no lift is produced, no induced drag is produced either. We also can call this lift-dependent drag. This drag mostly happens at low speeds.
• Parasite drag (schadelijke weerstand): Parasite drag (schadelijke weerstand) is another type of drag, which increases as the speed increases. We also call this speed-dependent drag. This drag mostly happens at high speeds.

Here again we see the third law of Newton into place; where a specific force is reacted with another opposing force.

Induced drag

So induced drag is produced and a reaction of generating lift. This is caused by the fact that the air over a wing has a lower pressure than under the wing. Because of this pressure difference and high pressure wants to flow to low pressure, some lift will leak away which causes some extra drag.

Induced angle of attack (AoA)

This air can also flow away to the wingtips, which causes some downwash behind the wings. This causes the incoming airflow to get a descending motion and causes the aerodynamic force to tilt somewhat. This also increases the drag component.

We can also have an induced angle of attack where the induced drag is counted from our effective drag.

Induced drag and speed

The induced drag is dependent on the lift as we already stated. The angle of attack also directly impacts this type of drag, where high angles of attack result in more induced drag. The induced drag also increases at low speeds and decreases at high speeds.

• High TAS: low induced drag
• Low TAS: High induced drag

Other factors for Induced drag

Some other factors that can influence the induced drag are:

• Wing aspect ratio: The aspect ratio (ratio between wingspan and mean chord) has a great effect on the induced drag. A thin and long wing (glider) has a short tip and therefore less room for air leakage from under the wing to above the wing.
• Wingtip construction: The construction of the wingtips are also influencing the amount of induced drag. An example is the Beech Bonanza V35 which has somewhat thicker wingtips where some fuel tanks are attached. This reduces the induced drag.
• Ground effect: In the ground effect the aerodynamic properties of a wing will have a minor difference. As there is less air mass just above the ground (0 - 2 meters), there is less room for wing vortices and downwash. This has some profitable results for us: more lift and less drag.

Ground effect

Ground effect gives us more lift, and therefore also a steeper lift coefficient curve. Keep in mind that leaving the ground effect changes the profit back to normal. Ground effect is at its most at a half wingspan above the ground. At 10% of a wingspan, the induced drag will decrease with almost 50%.

We have to take this change in properties into account, especially with landing:

• More lift means a slower descend or even some climbing
• Because of the decreased drag the plane will glide for a longer distance
• The decreased downwash will also decrease the angle of attach of the vertical stabilizer, making the nose descend a little

When taking off, keep this properties into account:

• When climbing out of ground effect, drag increases and lift decreases making us dip a little
• You can rotate with a slightly lower speed but you need ground effect to win speed to get to Vx
• In soft field take-offs you can use the ground effect to eject early from the ground and then win speed in the ground effect

Parasite drag

Parasite drag (schadelijke weerstand) is another type of drag, which increases as the speed increases. This has nothing to do with producing lift.

Parasite drag can be divided into 3 categories:

• Form drag
• Friction-drag
• Interference drag

Form drag

Form drag is caused by the shape/design of the aircraft. As the air flows upon the leading edge, the air will be separated and a pressure difference occurs. By this separation the airflow gets disrupted, building up a new pressure opposing the movement direction. This is called wake.

A brief description is; the more streamlined an aircraft part is, the better the air will follow that part. This will cause less separation and less wake.

A great illustration of this in action:

This is the reason planes like the Cessna 172 have wheel-fairings.

Friction drag

When air flows over a fixed surface, air molecules will be braked due to this friction. These slower molecules then will also be slowed down by the molecules farther away from that surface. The further the molecules are away, the less this slowing force is.

Even though air feels light, it sticks slightly to the skin of the aircraft. This creates a thin layer of slowed-down air called the boundary layer. The smoother and cleaner the aircraft surface, the lower the friction drag. Rough surfaces, dirt, ice, rivets, or exposed parts can increase it.

In the cruising phase of a flight, the most drag you feel is an result of the friction drag.

Interference drag

Interference drag is caused by the close placement of all airplane parts close together. All those different parts have their own airflow which can (partly) disrupt each others airflow. This often happens where parts join together, such as the wing and fuselage, struts and wings, or landing gear and body. The airflow becomes more turbulent in these junction areas, which increases drag.

To minimize interference drag, aircraft manufacturers apply fairings to different parts, like from wing to struts.

Total drag

The total drag of that we experience during flights is a sum of induced drag + parasite drag. We can see an example of this put into a graph:

Here we have in the middle a point where we have the least drag, this is where both amounts of drag are exactly the same. This is the V minimum drag (Vmd) speed. Often very similar to our best glide (Vg) speed, used to glide the most distance over a certain amount of distance.

Speed stability of the total drag

We have a graph to get a better understanding of the two parts of drag and your airspeed.

• Red: Backside of the power curve, here is the plane not stable in terms of speed. A small decrease in speed means a increase in drag as the line is steeper. The speed will therefore decrease if not corrected with the throttle.
• Blue: Normal operating area, here the plane is more stable in terms of speed. Light corrections will be applied automatically due to the higher speed.

Stall and spin flight (4)

A stall means exceeding the critical angle of attack. Stalling will occur when the plane has such a high pitch up momentum that the airflow is disrupted. The wing will instantly stop producing lift and the drag will increase substantionally.

Stalling does not neccesarily apply when flying at low speeds. When flying at a low speed, you need to pitch up to retain your altitude. There is a moment that the wings are so high up, causing a wing drop, nose drop or a heavy decrease of altitude occurs. This is a stall. But a plane can also stall when at its top speed, just because the airflow is disrupted.

In aerodynamic terms, we determine the cause of a stalling wing the behaviour of the boundary layer of the wing.

Boundary layer

The boundary layer (grenslaag) is the small layer of air which hits the wing surface. At the surface of the wing, the flow of air will be slowed down as result of resistance. At the surface, the air will even be completely still (no-slip). From the surface the boundary layer will span up to where the flow of air is not disrupted anymore.

A good picture of this happening in both laminar and turbulent air, check out this picture:

Laminar vs Turbulent

Laminar and Turbulent are each others complete opposites. Laminar beans that the air is very clean (organized) without movement, laminating the air over and under the wings. Turbulent means that this air is very unorganized which can happen by convection (rise of warm air), clean air turbulence or wake turbulence.

When the air is laminar, the following properties are:

• All air molecules will move from left to right
• Nice and orderly
• In parralel lines from each other

Boundary layer separation

When flying at greater angles of attack, the boundary layer will eject from the wing. This separation will result in a loss of lift, and is caused by the pressure gradient from the leading edge of the wing over the top.

From the leading edge of the wing, the pressure drops to a minimum. The point where this minimum is reached is at the front of this wing. After the front the pressure will increase again where at the trailing edge of the wing, the pressure is equal to just before the wing.

After the point of minimum pressure, the boundary layer has to flow in the opposite way, which is not easy by nature. This will increase to happen if the angle of attack also is increases until the wing is in a complete stall. At this stalling point, the separation point has made all its way to the leading edge of the wing.

Effects of increasing AoA

The effects of increasing the Angle of Attack (AoA) are the following:

• Stagnation point will change to the leading edge -> alerting the artificial stall warning of the Cessna 172
• The static pressure on the top side of the wing decreases
• At a asymmetric wing profile, the rpessure point will change forward to the leading edge at first but at hitting the critical angle back to the trailing edge
• The lift coefficient increases and decreases rapidly after hitting the critical AoA
• The drag coefficient increases slowly but very fast after hitting the critical AoA
• The total drag decreases at a certain angle but increases at a higher AoA

Stall speed

When practicing stalls in a plane, we will close the throttle making the engine run stationary and keep our altitude. We do this because power-off stalls are less dangerous than power-on stalls. As we lose speed, we need to correct for it by increasing the angle of attack. All the way to the critical AoA. In the formula of lift coefficient, the lift-coefficient factor increases where the speed factor decreases.

Just for fun, here is the formula again:

• Lift = 1/2 ρ V² CL S

You can find the stall speed (Vs) in the pilot operating handbook (POH) of the plane. V speeds are always referenced at the Indicated Airspeed (IAS), which is what you see on your speed meter in the cockpit.

For more information about stalls and my stalls lessons, visit this page:

Stalls lessons

Stall speed factors

There are some factors that influence the stall speed of the plane. Because the speed is not a hard value, especially in the atmosphere which can change from time to time, they are all calculated using the following properties and are worst case scenarios:

• No flaps: Flaps help reducing the stall speed by around 5 knots on a Cessna 172
• Straight and level horizontal flight
• No engine power
• Center of gravity is in the front position
• The plane is at its maximum take-off weight (MTOW)

Weight

According to the lift formula, the lift factor must be equal to the weight factor to stay in the air. The lift factor must be higher if you want to climb. The POH always refers to the maximum take-off weight, so the worst case scenario here.

Womething which also is an option is to look at the ratio between weight and wing surface, which we call the wing loading:

• Weight/Surface = 1/2 ρ V² CL

How more the wing loading factor is, the more the stall speed.

Load factor

The load factor is the ratio between lift and weight. We will pronounce this in simple numbers: in straight and level flight, this ratio is 1. When manoeuvering, like turns or climbing this ratio will increase. At an angle of 60 degrees while climbing the load factor will be 2.

We can make this load factor visible with a little addition to the lift formula:

• Load factor x Weight = Lift = 1/2 ρ V² CL S

Here is described that the lift must not only be equal to the weight, but on the weight multiplied by the load factor. This makes clear that a change to the load factor has the same effect as on weight increase of difference.

For reference, here we have some numbers where we describe the load factor and increase of stall speeds in different turns:

Thrust

The thrust is the forward power the engine(s) and propellor(s) generates and will influence the stall speed in two ways:

• Thrust increases the vertical power/component
• Thrust increases the airspeed over the wings

At higher angles of attack, the thrust gets a upward component. The thrust reduces somewhat of the weight, where the lift decreases without stalling. The stall speed will get somewhat lower because of this when having full engine power.

Extra thrust on the propellor will also increase the flow of air over the inside - parts of the wings. The inside parts of the wings will get more air decreasing the stall factor there. This is great, as we keep control over the ailerons. However, when stalling, you must only steer with the rudder to avoid a spiral dive/spin.

Center of gravity

Another factor on the stall speed is the center of gravity. Ever tried to balance a straw on your finger? The point where the straw stays into plane without tilting to one of the sides is called the center of gravity.

In a plane we have also a center of gravity as we must be in balance. If the center of gravity is at the front section of the fuselage, the stall speed will increase. This is due to the extra correction the horizontal stabilizer needs to make to keep the plane level and this increases the stall speed. The POH refers to the most forward center of gravity possible while still inside of the Mass and Balance envelope as worst case scenario.

Turbulence

Turbulence is also a factor which can influence the stall speed. In turbulent weather, the wind speed and direction will constantly change. This results in a angle of attack which also changes in small differences. At low speeds with high angles of attack, a upward wind can pull the plane into the critical angle of attack, resulting in a stall.

Stalls in climbing or descending turns

When climbing or descending, the wings have both a different angle of attack. This difference occurs because the outside wing has a longer distance than the inside wing. Because both wings are vertically making the same distance, the flight path of the outside wing has a flattened curve.

In a climbing turn, the angle of attack of the outside wing is the highest. If the speed decreases, the outside wing will stall first. At a descending turn, the inside will stall first. This is the reason the turn from base to final in the circuit is the most dangerous turn, which is commonly flown with somewhat more speed and a less steep turn (around 20 degrees in a Cessna 172).

While climbing:

• Outside wing stalls first

While descending:

• Inside wing stalls first

Stall warning

When an aircraft is in a stall, the plane will lose altitude very fast and the plane can become uncontrollable. A stall warning is therefore very important, as this can (re)gain your attention. The stall warning sounds just before a real stall happens, giving you enough time to remediate the risk instead of fixing the stall.

We call it an approach to stall when a stall is around the corner but not fully developed. You can see this as the point in the lift coefficient curve where the line stops to increase.

Sympthoms of an approach to stall are:

• Stall warning horn rings
• Buffeting, this is an aerodynamic clue that the plane is about to stall where the drag of the separation layer takes over the lift making the aircraft shake somewhat
  • This effect is not that audible on a Cessna 172
  • It does on low-wing aircraft like Piper, Diamond Aircraft or Cirrus types
• Airspeed too low
• Controls becoming sloppy -> lower airspeed means lower air and less “grip”

We have two types of stall warnings on general aviation aircraft:

• Electrical flapper
• Underpressure horn

Both systems relatively work the same, where both will sound an alarm if the stagnation point will shift more to the underside of the leading edge because of the critical AoA. The electrical flapper works on electricity and is more or less a button which must be pressed up. Is the button pressed, then the alarm will sound. The underpressure horn is mechanical and works at all times, by sounding the alarm if air is sucked through it.

These alarms will sound in normal conditions, at around 5 to 10 knots prior to hitting the critical AoA. However, if dealing with ice build up on the wing, the wing will already stall before the alarm is sounded which makes this situation very dangerous. For more information about ice build-up, check out: the meteorology page.

Flight properties at a stall

A nearing stall has some downsides to the controls of the plane. If one of the wings will stall prior to the other, then this will result in a wing dip and also in a spral dive if not corrected. To help pilots with controlling a plane that is about to stall, aircraft manufacturers have some design improvements done to the wings.

• Washout: Sometimes a wing is somewhat twisted by design, where the angle of incidation at the root is bigger than on the tip. This causes the root to stall first leaving enough air to still control the aileron at the tip. This difference is mostly some degrees. This also creates that buffet effect on the stabilo where a pilot is alerted about a nearing stall without any electrical or mechincal parts working
• Stall strip: This is a metal strip on the leading edge of the wing which also causes the wing root to stall earlier than the tip.

Stall prevention and recovery

As we already discussed, a stall is caused by exceeding the critical AoA. To recover the stall, we need to minimize the AoA and so need to push the yoke forward.

An aircraft has also some features to recover itself aerodynamically:

• Backward movement of the pressure point
• Decreasing the AoA of the stabilo

The stabilo always has a smaller AoA than the wings. This is by design, so the pilot has elevator authority even at a stall of the wings. If the plane stops pitching up, the downwash of the wings will reduce also resulting in the stabilo to decrease its AoA.

Ice build up

Ice can build up on the plane on the ground and during flight, when the air is saturated enough and also under the freezing point. If having ice on the wings and you are still on the ground, do not take-off.

Ice will build up on mostly the leading edges of the wings, horizontal and vertical stabilizer and on smaller parts like the pitot tube and antennas. Even a small layer of ice can reduce lift by up to 50% and increasing drag by up to 100%. This because the friction drag is increases and this will influence the boundary layer.

In short, no flights if having ice on the plane.

Spins

During a stall the plane can roll. This roll movement can have different causes like propellor slipstream, turbulence or minor differences in the wings or plane shape.

Because of the roll movements the AoA of the descending wing will increase. As the wing is already stalled the lift will decrease with the result the roll movement will be enhanced and another decrease of lift. When in a stall, roll movements will not be silenced like in normal flight. This roll momement is called a wing dip.

A plane has some side-effects when controlling. If steering with the yoke to roll, some yaw is a side effect. If controlling the rudder to yaw, then rolling is a side effect because of the differences in drag and lift.

In a spin these movements will stay and this situation is called autorotation. The result of this is a downward spin flight or in short a spin.

Phases of a spin

The spin can be divided into three phases:

• Wing dip: One of the wings dip because of a stall
• Incipient spin: This is the first 1 to 3 rotations where the nose also dips and a spin is imminent if not corrected by the pilot
• Developed spin: Here the plane has all its momentum to keep spinning, the airspeed looks low that this phase but the descending speed is very high

Spin recovery procedures

We can recover from spins safely if we have the altitude:

Recovery from wing dip

• Opposite rudder to level off the plane
• Unload the wings by pushing the yoke forward
• Level off using the yoke

Recovery from fully developed spin

• Close the throttle to not be sucked into the spin, this decreases aerodynamic forces on the plane
• Ailerons neutral, keep them level
• Full opposite rudder as your spin direction
• Steer level
• If the spin has stopped stop rudder input and pull out of the dive

As we already saw in the flight lessons of stalls, we must never use ailerons to get out of a stall. This makes a difference in the AoA of the ailerons making the situation even worse.

Spiral dive

A spiral dive looks similar to a spin but in a spiral dive there is no stall active. In a spiral dive the AoA is small at a high and increasing speed.

The spiral dive can occur when making a steep turn of 45 degrees or more to correct for a low pitch by pulling on the yoke. The nose will hardly rise and the turn will be tighter causing the nose to drop even more. The speed will increase in this situation.

To recover from a spiral dive:

• Close the throttle to not be sucked into the spin, this decreases aerodynamic forces on the plane
• Level the plane with the ailerons -> because of the high airspeed you have a lot of aileron authority because of the loads of air
• Pull up from the dive

Aircraft Controls (5)

The movements of an aircraft can be defined using these three imaginary axis':

All these axis’ come together at the center of gravity of the plane. To put all effects and controls in a table including the dutch translations:

Primary Flight Controls

These effects and axis’ are primarily controlled by the primary flight controls:

• Roll: Ailerons
• Yaw: Rudder
• Pitch: Elevator

All of these controls work similar. They change the camber (welving) of the wing or elevator. One of those controls in downward position means an increase of lift, where a upward position means a decrease of lift. It just changes how the air flows around.

If we look at the ailerons, we can see that they also change the wing’s angle of attack. As a result, the chord line tilts slightly, causing the aircraft to roll. On most aircraft, the ailerons are located near the tips of the wings. This is related to the moment arm: the farther they are from the fuselage, the less control force is needed to produce the rolling motion.

Side effects

• Rolling is yawing
• Yawing is rolling

These controls are not completely separated from each other. For example, if we only steer with the rudder, the plane will also roll. This is because the outside wing will produce more lift as result of the higher speed. A rolling effect will be felt and seen.

The other way around, if we only steer using the ailerons, then we can feel also a yawing motion. This is an result of the lift which now works from an angle. The incoming airflow hits the horizontal stabilizer under an angle getting a side-aerodynamic force resulting in a yaw towards the low wing.

The plane wants to get the nose into the wind. This is what we call the weathercock effect.

Hook effect

During a rolling movement the aileron of the upward wing will move down to create more lift. This also results in more drag. This extra drag results in the plane to yaw in that direction which is called the hook effect.

To help reduce this hook effect, aircraft manufacturers apply these design-additions to the ailerons:

• Differential ailerons: Here the movements of the ailerons are not in sync. The upward aileron had a bigger movement than the downward aileron. This gives both wings an equal amount of drag suppressing this effect greatly.
• Frise ailerons: These are constructed so the leading edge of the aileron will get some incoming air under the wing. This also gives both wings an equal amount of drag suppressing this effect greatly.

The remaining effect can be adjusted by steering with your rudder. This is what we do in the cockpits.

Effects on controls and airspeed

When the control surfaces (roeren) have more airspeed, the effectiveness (which we call authority) increases. As more air passes by over the control surfaces, it has more to make their movements. This is the same reason as why on lower speeds you need to do bigger steering actions.

The elevator and rudders exist in the slipstream of the propellor, so the effectiveness of these tail controls are also dependent on the engine RPM. Not only the airspeed, as on higher RPMs the propellor rotates a lot faster.

Influence of Engine RPM on pitch

The engine RPM also has influence on the effectiveness of the stabilizer controls. More RPM means a faster slipstream and a increase in downwash behind the horizontal stabilizer. If you increase RPM, the horizontal stabilizer will be pushed downward which increases the nose pitch. Decreasing RPM does the complete opposite, lowering the nose and increasing the horizontal stabilizer.

This is a design requirement for all planes; the nose must be going down after decreasing engine RPM to hold a specific speed. This prevents a unpredicted stall.

Mass balancing

The construction of an aircraft has a good flexibility and can deflect some during aerodynamic forces. If a wing bends downward because of turbulence, the aileron will be somewhat behind because of mass slowness and results in the wing pushed even further downward.

In the process of mass balancing, sometimes there are placed some small parts of metal in various places on the plane to ensure both sites are of equal weight. This decreases things like flutter which is an aerodynamic unbalance and can break an aircraft in seconds. This is always done in the section before the Vne speed, which is the Never Exceed Speed (160+ knots on a Cessna 172).

Aerodynamic balancing

Any of the control surfaces will pick an attitude which is level with the incoming airflow. To actually steer an aircraft, the pilot must win this incoming airflow by putting more force into the controls. In the factory, aircraft manufacturers apply some tricks on the airplanes to keep the controls into balance. One of the things on a Cessna 172 to achieve this aerodynamic balance in the controls is a horn balance. This is this part of the elevator:

Aerodynamic balance can be seen as powered steering in cars. They make the steering process a bit better, decreasing the change of flutter.

Trim surfaces

A plane also has some trim surfaces which are mostly controlled using a trim wheel in the cockpit The movements of this wheel corresponds with the movement of the yoke.

These are two types of adjustable parts of control surfaces to further enhance flights:

• Adjustable trimming surfaces: These can be adjusted during flight to keep a plane straight and level
• Balancing trimming surfaces: These can only be adjusted on the ground and mostly by the aircraft manufacturer

Trimming surfaces are so small parts of moveable control surfaces at the end of that surface. These can be set in a specific way, so the pilot doesnt need to apply forces on the yoke at all times.

For example, the Cessna 172 has a adjustable trim surface on the elevator. With this surface, we have a small part of the big elevator which can be controlled to stay in a desired position. This only controls the pitch axis.

This small part changes the camber of the elevator, where the elevator surface controls the camber of the horizontal stabilizer itself. By setting the trim there will be some camber at the backside of the elevator. This small setting is enough to keep the elevator in a fixed position. All of this is done using aerodynamic forces, so that is the reason the position of this trim is completely the opposite of the elevator itself. At take-off we set this small surface level with the elevator.

This trim in a Cessna 172 is controlled using a trim wheel in the cockpit.

Ground adjustable trims

A plane sometimes also has some ground adjustable trims, like the bottom corner of the rudder. If the plane has a few grams offset, these can be bent to make them aerodynamically stable.

Some planes also have balance-surfaces which reduce the force needed to steer the aircraft. This is the complete opposite of the trim, where the balance surface does exactly what the elevator itself does, sometimes even with a bigger steering effect.

Flaps

Flaperons (kleppen) are meant to alter the flying properties at lower speeds. These are surfaces at the trailing edge of the wings. They work basically by changing the camber of the wing somewhat, where they increase lift and drag. This makes flying at lower speeds possible during take-offs and landings.

Flaps are often mechanically or electrically and are measured in how much degrees difference they offset from the angle of incidation of the wing.

Flaps have some pro’s in using them:

• The lift coefficient shift up and somewhat to the left, making the stall speed lower
• The critical AoA increases a little with flaps extended, this is because of the extra drag
• Flaps increase drag, and slows the aircraft down
• Flaps help to see the runway much better during landings as the AoA is lower
• The stagnation point of the wing shifts somewhat backwards

Types of flaps

Historically multiple types of flaps has been tested and the most used types are these:

• Plain flaps : Mostly used on weight reduced planes like bush planes and is a plain part that pushes downwards
• Split flaps : Old technique where the trailing edge of the wing actually splits. The legendary DC-3 has them for example
• Slotted flaps : Similar to a plain flap but incorporates a gap between the flap and the wing to force high pressure air from below the wing over the upper surface of the flap. Used on most general aviation aircraft like Cessna 172
• Fowler flaps : Extended out of the wing and pushed downward. Used the most on traffic jets (A320/A330/A350, B737, B777, B787)

Operational use of flaps

We generally use flaps in the take-off and landing phases of flight where these have advantages.

During take-offs

• Decrease of ground roll
• Increase in lift, slight increase of drag

After taking off, we set them very fast to 0 as because of the increased drag, we will achieve lower speeds.

During landings

• Decrease of stall speed
• Lower pitch attitude
• Steeper approach and better obstacle clearance
• Higher drag means a better round out above the runway

Leading edge flaps (Slats)

Slats have the exact same purpose as flaps, increasing the lift coefficient making lower speeds possible. They are installed on the leading edge of the wings instead of on the trailing edge. They are always combined with flaps settings to prevent any assymmetry from happening.

Slats also help increasing the critical AoA where flaps only decrease them but help to fly at lower speeds. Slats are mostly used on bigger commercial jets and bigger general aviation aircraft.

Turning

According to Newton’s first law, an object without any forces will move in a straight line with a certain speed. Making a turn thus needs a net force. The net force on an object is the sum of all forces acting on it.

“An object at rest stays at rest, and an object in motion stays in motion at a constant velocity, unless acted upon by a net external force.”

This force will work right onto the movement direction of an airplane and because every turn will be part of a circular movement, the required force will point to the middle of the circle. This force is called the centripetal force (middelpuntzoekende kracht).

This centripetal force is a result of the horizontal component of the lift which occurs when the plane banks into a turn.

Balance of force in turns

If a plane turns in an incorrect manner, there will occur a situation where there is no balance between the vertical forces. The gravity will stay in a straight line to the earths surface but the vertical component of the lift is tilted (to the turning side) because of the turn. This vertical lift component is now smaller than the gravity, making the plane go down. This is why a plane needs some back pressure on the yoke in turns, which increases some lift to compensate and recover the balance between lift and weight.

To get a better view of this occurence:

Rate of turns

The speed of how we fly a turn is called the “rate-of-turn”. This is measured in the amount of degrees change per second. The most important one is a Rate one turn which is 3 degrees per second and costs 2 minutes for a full circle. You can calculate the amount of degrees needed to bank with this formula:

• Bank angle for rate one = TAS in knots : 10 + 5

As we can see, the airspeed is a dependency on the bank angle. Let’s say, we fly at 135 knots and want to make a rate one turn:

• 135 : 10 + 5 = 18,5 degrees bank angle

Some other examples:

• Cessna 172: 95 : 10 + 5 = 14,5 degrees bank angle
• Airbus A320: 235 : 10 + 5 = 28,5 degrees bank angle

The fun fact is, the only two dependencies are the airspeed and the bank angle. If you want to fly a turn slower, decrease your airspeed. If you want to complete a full circle faster or in a more narrow area, increase the bank angle.

Turn coordination

During a turn there will be some yawing motion. The nose will also turn in the direction of bank. If the yaw-speed is correctly and in sync with the bank angle we speak of a coordinated turn. A situation where the incoming airflow is coming straight from the front, seen from the cockpit.

If this is not the case, we have two other options:

• Slipping turn: The nose falls behind when not enough rudder input is given
• Skidding turn: The nose is in front when giving too much rudder input

In the cockpit we have the turn coordinator which works with a gyro, telling us exactly how much rudder input the plane needs. The keyword here is: “Step on the ball”, meaning to press the pedal at the side of the ball just to keep it in the middle.

Load factor during maneuvers (6)

The construction of an aircraft needs to be solid enough to catch all forces, both on the ground and in the air. The aircraft parts need to be strong enough to carry its weight on the ground, especially at harder landings. In the air, the plane also needs to be strong enough to withstand some maneuvers like:

• Turns
• Turbulence
• Dive flights (aerobatics)

During the design of an aircraft, manufacturers takes the expected load factors into account. The load that an aerobatic plane gets is of course much higher than a Cessna 172. Under static strength of an aircraft we think of the force or load the construction can have once without breaking. If an aircraft is under load for multiple times there can happen some metal fatigue, permanently weaken the construction. During the walk around, this is one of the visually things to check on an aircraft:

• Cracks
• Wrinkled paint job

The maximum load factor which the plane must withstand is called the limit load. This possible load factor number is the force a plane with an undamaged construction can have. Under this number, some part smay temporarily bend like the wings but the flight properties may not be influenced.

Load factor numbers

The static strength of an aircraft is measured in G-force, where a plane on the ground is always 1G, or 1x the mass.

Again, here we have some numbers where we describe the load factor and increase of stall speeds in different turns:

Now we have some extra numbers for different category airplanes:

Always refer to your planes POH for the actual numbers, the numbers above are generally for aircraft categories. Different planes are certified for different amount of forces.

G force factors

Planes are mostly designed to carry positive lift, so the positive G force numbers are higher than the negative numbers. During negative G forces, all parts are loaded downward but planes are actually designed to fly upward.

The Load factor diagram

The load factor diagram shows at which speeds a specific aerodynamic load is pushed on the plane. The load factor as we already know is a ration between lift and weight so these numbers influence the load factor. To be careful enough we need to take both numbers into account.

At higher speeds we can produce more lift, so the lift number goes up at higher speeds. The Va speed is the maneuvering speed of an aircraft, which is around 103 knots in a Cessna 172. This is the speed where full inputs can be given to the plane without overstressing the plane. The Vne speed is the Never Exceed speed and is the red line on the airspeed indicator.

The non colored parts of the graph are outside the stall limits no are aerodynamically not reachable. As you can see is the most change of overloading the aircraft at higher speeds.

When a plane flies at 87 knots for example, a pull on the yoke will result in the plane first loaded to 2G and then in a stall as it comes outside of the green area. At an speed of 120 knots and higher with a Cessna 172 its possible to reach the limit load factor. But this can be reached earlier in the envelope if the plane has more weight. This is described by the second law of Newton: “The acceleration of an object depends on the net force acting on it and the mass of the object.”

Aerodynamics of propellors (7)

Obviously the job of the propellor is to convert engine power into thrust. Thrust is forward power of the plane which also can be helpful turing climbs. The propellor of the plane is directly connected to the crank-shaft (krukas) or indirectly with a gearbox.

Most planes in general aviation have 2 to 4 propellor blades and can contain up to 7 in some cases, but 2 to 4 are the most generic options. The blades are often made of aluminum or carbon fiber and meet each other at the hub, where the propellor is connected to the crank-shaft. The part on top of the propellor is called the spinner, which makes the propellor aerodynamically streamlined.

Propellors of a fixed pitch propellor plane are often twisted at the center. This is done to make the AoA of the propellor in the incoming air the same for the whole blade. The center part gets less air, so get a higher AoA. Exactly the same principle as the wing and the flaps as we already know. This is called propellor wrong.

The spinner is streamlined for better aerodynamic performance but also is used to steer air into the air-inlets to cool the engine. Very clever designing.

How a propellor works

The propellor works almost the same as a wing. They also have incoming air and the blades making an AoA relative to the incoming airflow. The propellor then causes a resulting air force. This force can be divided into:

• Thrust: Straight and forward power
• Drag: Drag of the propellor
• Resultant aerodynamic force: The two forces of forward and drag means a resulting force that is somewhere between those two axis, totally dependent on the pitch of the nose

Propellor blade angle

The blade angle of a propellor is the angle between rotation-axis and the chord of the blade.

The pitch of the propellor is the theoretical distance the propellor covers in one rotation:

• Small blade angle: Fine pitch -> Optimal for climbing
• Big blade angle: Coarse pitch -> Optimal for cruise

The blade angle of a propellor is similar to the angle of incidence on a wing.

Propellor Angle of attack

The angle of attach of a propellor blade is the angle between chord and incoming air. Just like a wing. A plane who is standing still on the ground, the AoA is equal to the blade angle as there is not that much incoming air. If the plane moves forward, more air will come in from the front. The angle of attack decreases in this case.

At an increasing forward movement speed the AoA will be 0 or even negative. The propellor doesn’t produce thrust anymore.

Propellor Wrong

The propellors of fixed pitch propellor planes like the Cessna 172 are slightly wronged. This means the root of the propellor has a bigger AoA than the tips. As the whole propellor rotates, the tip will cover a much bigger distance than the root of the propellor. This results in less air picked up. To compensate for that effect, the AoA is higher at the root of the propellor to span the thrust over the whole blade. If these are not wronged then the propellor will be working very inefficiently.

Fixed pitch propellor RPM

In fixed pitch propellor planes like the Cessna 172, the RPM of the engine is equal to the RPM of the propellor. The AoA of an propellor is the highest when standing still on the ground. At a high AoA, the drag is also much bigger making full throttle exercises not very dangerous for the engine.

When flying the propellor produces forward motion (thrust) the AoA will decrease. This also results in a lower drag making the propellor spin slightly higher. Theoretically you can’t exceed the engine rpm limits on the ground, only in the air because of this. This phenomenon is also to be seen during flights. When the pitch attitude is higher, the engine RPM will decrease. When descending, the RPM will decrease. During descends we also draw the power back. The much lower drag and the extra downward thrust you otherwise get can reach high speeds in seconds.

Propellor windmilling

When the forward speed increases, the AoA of the propellor will decrease. At a certain rotating speed the AoA becomes zero and no thrust will be produced by the propellor at that point. If the speed increases even more than that, the propellor AoA will be negative; the propellor produces drag instead of thrust.

The propellor stays rotating because of the incoming airflow, making it a flying windmill. At an engine failure, the propellor will also continue to rotate. This windmilling effect causes some more drag. This extra windmilling decreases the glide angle and so gives you less gliding distance.

Engine power to thrust conversion

The power a propellor gives is dependent of the forward speed. Power x speed. If a plane is standing still with a rotating propellor, trust is produced but the power is 0. At an increasing forward speed the power is also increasing, till the limit is reached. As we just learned that the AoA decreases at higher speeds, the thrust will eventually also be decreased.

If we make a relational graph with the power and speed, the curve will be increasing till the point where the AoA is zero. The power will then just like the lift coefficient drop very vast.

This is the case for a fixed pitch propellor which only produces optimal thrust during a certain speed, dependent on the construction of the propellor. It works good during or climb or cruising but never both.

• Small blade angle: Fine pitch -> Optimal for climbing
• Big blade angle: Coarse pitch -> Optimal for cruise

Constant speed propellor planes

Aircraft manufactures thought of a clever idea to make propellors where the pilot can set the blade angle based on the flight phase, where they can decrease the AoA in climbing phases and increase the AoA during cruise to get the most out of the engine at all times. These planes are called constant speed propellors -> the propellors always rotate at a constant speed.

This gives the pilot 3 handles instead of two. Next to a throttle and mixture they alsy get a blue for this cause. With that handle you can set a desired propellor RPM where you still control the fuel inlet pressure (manifold pressure) with the black throttle.

The graph shows that the line of a constant speed propellor is more flat and spanning the whole range. This means it can convert as much engine power to thrust as possible, and not only during climb or only during cruise.

You can see the constant speed propellor just like switching gears in a car. You can switch gears at all times to make the fuel efficiency better but also get higher speeds when you most need them.

Propellor side effects

The propellor is a great tool to produce straight forward motion called thrust. But the propellor also causes some aerodynamic side effects:

• Slipstream effect: The effect that turns around the plane and pushes against the rudder
• P-factor (assymmetric blade-effect): The assymmetric power the prop delivers at high angles of attack
• Torque effect: The effect of the plane wanting to counteract the propellor movement

Let’s dive deeper into these three effects and how to take them into account as pilot and ultimately counteract them.

Slipstream-effect

The slipstream effect on single engine planes is caused by the right-rotating prop (seen from the cockpit). This slipstream rotates around the longtitudinal axis of the plane and hits the vertical stabilizer and rudder. During climbing situations, this results in a yawing motion to the left as the right-turning air hits the vertical stabilizer on the left side.

Aircrafts are designed to somewhat suppress this effect by assymmetric stabilizers, setting this under a small angle or a small ground adjustable trim surface on the rudder.

If we set a lower RPM, the slipstream becomes way less and then aircraft designs tend to yaw right. This is why we learn in single engine planes to counteract this effect as following:

• High RPM: Right rudder
• Low RPM: Left rudder

Think of: Low is Left or Left is Low.

P-factor

The P-factor or assymmetric blade-effect with right rotating prop as seen from the cockpit is caused when a propellor that rotates is not perpendicular (loodrecht) to the flying direction. The downward blade produces more thrust than the upward blade. At high angles of attack, the downward blade moves in the flying direction but the upward blade moves opposite to the flying direction. The downward blade gets a higher AoA where the upward blade AoA decreases, and as we just learned that a higher AoA procudes more trust, we get asymmetrical thrust. The actual result is the nose of the plane wanting to go left.

This is the somewhat strange cause of why we need to give some right rudder in a left climbing turn.

Torque effect

The torque effect is exactly how it sounds, a rotating propellor produces a torque/rotating effect. We have to agree with mr. Newton again because this is an effect of his 3rd law; “For every action (force) in nature, there is an equal and opposite reaction”

The action is the propellor turning and the reaction is the fuselage of the plane wanting to roll left. This is mostly noticable during the take-off phase. The plane wants to roll left, resulting in more drag and force on the left wheel. The torque effect is therefore the same direction as the slipstream effect and increases the tendancy of the plane to go left.

During take-offs or touch and go’s, counteract by steering somewhat right with the rudder.

Source: Boldmethod.com

Stability (8)

An aircraft is continiously exposed to different attitude changes as result of wind, turbulence, convection or smaal yoke inputs. After being exposed to such change the forces and moments on the plane wordt not be balanced causing a huge workload for the pilot. Flying must be fun and easy to do, the easier it is, the safer.

An aircraft has great control-properties if its stabilityis good. With stability we mean that the plane must restore itself to the balance state after a small change, apart from if this change is intentional or not. Stability also has some downsides, when turning or maneuvering we are changing the attitude of the plane and makes this somewhat harder. Aircraft manufacturers seek to find the perfect balance between stability and maneuvering.

Types of stability

We can have three types of stability:

• Statically unstable
• Neutral (indifferential)
• Statically stable

Some examples of how this looks:

As we can think of the mass of the ball and the gravity working against themselves, in the statically stable situation, the ball would move around somewhat and then return to the before point when moving. This makes it statically stable.

The ball on the left would after moving never reach its stability point. The middle ball will constantly pick a new balancing point, but will need continuous corrections.

Dynamic stability

The dynamic stability describes the flow of the three situations above into the speed of returning to the balancing point and thus being stable. When a plane’s attitude is changed during cruise flight where all 4 flying forces are balanced, the plane must return to that balancing point as soon as possible. We can only achieve dynamic stability if the plane is statically stable.

Static stability

For a plane, the construction needs to be stable at all three axis':

Longitudinal stability

The longitudinal stability is the stability of the lateral axis, the pitch axis. An aircraft is longitudinal stable if the it restores the pitch to the state before interruption like minor inputs, wind or turbulence. Planes are designed that the center of gravity lies in front of the pressure point. Weight and lift cause a nose down moment.

To compensate for this moment and to make the plane longitudinal stable, we have the horizontal stabilizer at the tail of the plane.

When the center of gravity (CG) is in front of the pressure point, the horizontal stabilizer must do a negative force. Because of the distance between CG and horizontal stabilizer is much longer than between CG and pressure point, a small horizontal stabilizer moment is needed. This distance defines operationally how stable the plane is on the longitudinal axis, the more the CG is up front, the more stable the plane is. If this CG shifts backward, then the stability decreases.

Canard

A canard is a set of small wings at the nose of the plane. Some planes counteract the longitudinal stability by shifting the wings somewhat to the back. This creates a more frontal CG in combination with this added set of small wings. These canards always produce positive lift as the AoA is positive.

Center of Gravity boundaries

As the CG has a big impact on the stability of the plane, the allowed position of the center of gravity is strictly limited. This CG must be within a limited frontal and after CG. Exceeding this values can dramatically decrease stability and flight performances.

• Too Frontal CG : This makes the plane stable but requires bigger steering forces. This can also lead to being unable to perform a roundout during landing.
• Too Aft CG: If the CG is more to the tail of the plane, the longitudinal stability is relatively small. The pilot must continuously correct the pitch resulting in uncontrolled pitch up movements.

Horizontal Stabilizer AoA

To get enough longitudinal stability, the horizontal stabilizer has a smaller angle of incidence and so AoA. This is done so every pitch change has a bigger effect on the horizontal stabilizer than on the wings. This angle of AoA of the wings and the horizontal stabilizer is called the long-V angle.

This difference in AoA also causes the wings to stall first in high nose up situations, making the elevator still controllable to recover.

Directional stability

The directional stability is the stability around the vertical axis (yaw). If during a flight the air comes straight head-on, the flight will be coordinated. If because of a small yaw imput the air will not come front, a slip occurs. We call the angle between the incoming air and the longitudinal axis the slipping angle.

An aircraft is directionally stable if during a slip it wants to recover itself to be aligned with the incoming air again. This is mostly achieved by the use of the vertical stabilizer. This also gets a different angle during slips, which result in an aerodynamic force from the side making the slip undone.

Effect of Center of Gravity

The distance between the vertical stabilizer and the CG (the arm) determines the directional stability. A more aft-CG will decrease the arm of the vertical stabilizer and making it less effective and so less stable. A more frontal CG does the opposite, increasing the effectivity and stability.

Lateral stability

The lateral stability is the rolling-axis stability. An aircraft is roll-stable when it returns to wings-level state after rolling. Just as the directional stability, is the roll stability a result of a slipping movement. Because of this movement another force occurs which restores the balance.

At lighter planes, this stability is reached by placing the wings under an angle of the longitudinal axis like a Piper plane. This is called a dihedral. If the wingtips are lower than the wing-root, then it would be called anhedral.

Such dihedral is dependent of a slipping movement where the airflow comes at an angle. This can happen when a plane rolls, the AoA of the lower wing will increased and the higher wing decreased resulting in a recovery to wings level.

Dihedral effect

A high-winger like a Cessna 172 has a better rolling stability than a low-winger like a Piper. The cause of this is in the behaviour of the crosswind-flow when a rolling motion.

The crosswind-flow will be bent off by the fuselage. At a high-winger this results in a bigger AoA of the low wing. This results in more life, pushing the low wing up and be balanced again.

End of the page 🎉

You have reached the end of the page. You can navigate through other blog posts as well, share this post on X, LinkedIn and Reddit or return to the blog posts collection page. Thank you for visiting this post.

If you think something is wrong with this post or you want to know more, you can send me a message to one of my social profiles at: https://justinverstijnen.nl/about/

Go back to Blog homepage

If you find this page and blog very useful and you want to leave a donation, you can use the button below to buy me a beer. Hosting and maintaining a website takes a lot of time and money. Thank you in advance and cheers :)

The terms and conditions apply to this post.

Aircraft General Knowledge (AGK)

The airframe (1)

The frame of a plane consists of several parts, which all make flying and steering in the air possible by various actions. I will describe all parts in English and Dutch:

• Wing - Vleugel -> The horizontal part which makes flying an aircraft possible in the first place by generating lift
• Aileron - Rolroer -> These are the parts at the end of the wings, making roll-turns (banking) possible. They are at the end of the wing due to force x moment
• Elevator - Hoogteroer -> This part makes going up and down in an aircraft possible
• Rudder - Richtingsroer -> This part at the end of the tail can move to change direction in flight and is being used to make small corrections
• Flaps - Landingskleppen -> These are parts on the wing which can be used in take-off and landings to fly at lower speeds nearby the ground. They extend to induce more drag, which equals a lower speed and they generate some lift
• Vertical stabilizer - Kielvlak -> This is the standing part of the tail of an airplane, stabilizing the airflow and makes the plane fly into one single direction
• Horizontal stabilizer - Stabilo -> This is the horizontal part of the tail of an airplane, stabilizing the airplane in horizontal flight

Aircraft construction

The aircraft itself can be constructed in several different ways. The most important thing here is the type of aircraft. Bush planes are very light and will be less likely to use heavy stainless steel.

• Monocoque: A construction method where the external skin of the aircraft carries almost all of the loads. There is little or no internal framework. It’s lightweight but can be less tolerant to damage, since the skin itself is the main structure.
  • Outside supports all forces
  • Comparable with a can of coke
• Semi-monocoque: A more common design in modern aircraft. The external skin still carries loads, but it’s reinforced by an internal structure (frames, stringers, bulkheads). This makes the structure stronger, more damage-tolerant, and easier to repair than pure monocoque.
  • Inside supports half of the forces and outside half of the forces
• Truss contruction: This method will support all forces on the inside of the plane. Here the outside could be any material, like leather or vinyl.
  • Inside supports all of the forces

The wings

We could have two types of wings:

• Cessna 172 has the wings above the cockpit: high-wing (hoogdekker)
  • This needs support of the wings which we call: braced wings
• Piper PA-28 tas the wings below the cockpit: low-wing (laagdekker)
  • This doesnt need support of the wings which we call: cantilever wing

Both of this types of planes have their pro’s and cons. A Cessna doesnt need a fuel pump, as gravity does its thing. Als we cannot see traffic above us very good in a Cessna, but not very good under us with a cantilever wing.

There are also planes which have a V shaped tail with a rudder and elevator combined. These types of tails are called a ruddervator.

Tires

We can have 2 types of tyres on arplanes:

• Tube-type: This type has an inside and outside tyre, just like your bicycle
  • More warmth
  • Higher chance of tire blowout
  • Contain slipmark
• Tubeless: This only has an outside tyre

Tyres can slip over the rim during landings, this is the reason maintenance does a little slipmarker on the tyre and rim. This is mostly red.

Hydraulic systems

Hydraulic means litteraly transfer using liquids (hydro). We can transfer different forces using liquids using this formula:

• Force = Pressure x Surface

This means, the less surface and the more pressure, the higher the force.

Liquids are a great way to transfer force, as fluids can not be compressed unlike air.

Brakes

Brakes are systems built on the axes of the airplane to brake it, to lose power. This process converts the kinetic energy of the plane into energy in the brakes, which is warmth. Brakes are mostly powered using hydraulics.

Icing

As we don’t want ice on our plane or in parts of the plane, we have ice-preventing systems as we know two different categories:

• Anti-icing: Systems that prevent ice from happening like windshield anti ice, engine anti-ice or the pitot heat
• De-icing: Systems that remove already built up, like rudder boots on the trailing edge of the wing

Both systems are being used to battle ice during flights.

Fire and smoke in the plane

There are situations that fire and smoke can happen in the cockpit. Let’s dive into the different scenarios.

Engine fire during start

During starting the engine, engine fire can happen. This is mostly because of overpriming the engine, having way too much excess fuel that ignites instantly. Also priming with the throttle which pumps fuel into the carberator, increases the chance of engine fire.

The actual procedure to follow during this situation is specific to your aircraft but the base is something like this:

• Continue cranking for 5–10 seconds to try to suck the flames into the engine

If engine starts:

• Parking brake set
• 1700 RPM
• Prepare seatbelts, doors, fire extinguisher
• Wait max. 2 minutes/120 seconds
• If fire continues:
  • Mixture cut‑off
  • Throttle full open
  • Fuel selector OFF
  • Ignition OFF
  • Master switch OFF

If engine does not start:

• Mixture cut‑off
• Throttle full open
• Continue cranking briefly
• Ignition OFF
• Master switch OFF
• Fuel selector OFF (if possible)
• Extinguish fire using any possible method

Smoke in the cockpit

Smoke can happen in the cockpit due to several causes:

• Short-circuit in the electrical system
  • Disable the complete electrical system and turn off electrical components one by one with the circuit breakers till you found the problem
• Engine fire
  • Mixture lean, disable fuel selector. If fire doesnt extinguish, then make a dive in the hope the fire will be put out because of the high airflow and disable Cabin Heat to prevent transition to cockpit
• Other parts on fire

To correctly battle these situations, we must first know what to do exactly in each situation. These are described in the POH of your aircraft.

Fire types and extinguishers

Maintaining a fire is done by having these three components:

• Fuel (flammable material)
• Oxygen
• High temperature

By taking away only one of these three components, the fire will extinguish. We have four types of fire with possible extinguish methods:

• A = All that can burn, wood, paper, textile, plastic etc
  • All types of extinguishers
• B = “Benzine” or oil
  • All types of extinguishers
• C = Gas
  • CO2 and Halon
• D = Metals, aluminum or magnesium
  • Halon
• F = Fat

Water based extinguishers are not that practical for electrical and type B fires. Water is heavier than fuel. Also, Halon extinguishers are very poisonous so good ventilation is needed when using these. This also counts for CO2 type extinguishers, which are generally not for closed environments.

The piston engine (2)

In planes, the most used engine type is a four-stroke (viertakt) gasoline engine. Four strokes means that the engine uses 4 strokes to complete the fuel burn process. The engine is obviously the most important part of getting the propellor to turn.

The engine has the following parts:

• Carberateur: A part of the engine which mixes fuel and air for the correct burn-mix.
• Inlaat: The part where a mix of fuel and air is going into the cilinder
• Inlaatklep: A gate which closes and opens momentarily between the verbrandingsruimte and the Inlaat,
• Uitlaat: The part where the burnt fuel rests are deported out of the engine and is connected to the main exhaust
• Uitlaatklep: A gate which closes and opens momentarily between the verbrandingsruimte and the Uitlaat
• Bougie: The part which makes the mix of air and fuel burn by using electrical sparks
• Nokkenas: This part is connected with gears to the Krukas and decides when the Inlaatklep and Uitlaatklep are being opened and closed. In a four-stroke engine, this happens at half the speed of the Krukas.
• Cilinder: This is a name for the whole burn-part of the cilinder
• Verbrandingsruimte: This is where the actual mix of fuel and air is happening
• Zuigerveren: Attached to the Zuiger and it’s purpose is to isolate the Verbrandingsruimte from the rest of the cilinder
• Zuiger: This is a part which is connected to the Krukas that does the actual motion for the Krukas to be turned.
• Drijfstang: This is the part connected to the Krukas and the Zuiger.
• Krukas: The krukas is a part there all dynamic force of the engine is linked with and at the end of this as, we have the propellor. In a car, here are the wheels connected.
• Carter:
• Krukkast: This is the central part of the engine, and is where the krukas and Nokkenas are located. At the underside of the Krukkast, we have a Carterpan which contains oil and “lagering” for the Krukas

Burning fuel in a 4 stroke engine is completed in 4 phases:

1. Inlaatslag (Intake)
2. Compressieslag (Compression
3. Arbeidsslag (Power)
4. Uitlaatslag (Exhaust)

Engine shapes

There are multiple types of motorshapes. In planes, the most used shapes are:

• Line engines
• Boxer engines (horizontally exposed)

Engine power units

The units which can be used to measure engine power are mostly indicated in Horse Power (HP/pk). This is a worldwide standard, but sometimes the actual measurement method is described. Sometimes BHP % is used in the POHs of the aircraft. The method to measure is a special installation connected to the crankshaft, and measuring the force needed.

We also have an indication of how long you may use full engine power. The indicator for maximum continious power is the maximum power you can use unlimited. Engine power is mostly indicated using Revolutions per Minute (RPM). In the cockpit we cannot read the actual power it delivers, only the RPM of the crank-shaft. The part which the engine powers and is connected to the propellor in front.

At bigger heights, like from 3000ft, we need to pull somewhat on the mixture handle to reduce the amount of fuel going into the engine. At bigger altitude, the process is more inefficient when putting too much fuel into the engine.

• Manifold pressure: Inlet pressure
• Brake horse power: The power the brakes of the plane can withstand.

The power of a piston engine depends on the air density. This is depending on the pressure, temperature and humidity. At a low air density

Turbo-engines are in 2 types:

• Altitude boosted: This type, the turbo always runs till big altitude to help the engine when horse power decreases
• Ground boosted: This is the most existing type of turbo engine and the turbo always runs to increase engine RPM. This works till the critical altitude.

How a turbo system works

A turbo system is basically a turbine and a compressor. The turbine is driven by the exhaust gasses and is connected through an axis with the compressor which is placed in the air inlet system. The compressor will increase the pressure of the air inlet, resulting in an increase in intake speed. This increases the motor-power. Turbine compressors rotate at a very high RPM, around 80.000 RPM to 100.000 RPM in some cases.

The schematic drawing of a turbine-compressor combination.

As a result of the compressed intake and the flow of hot exhaust gasses, the temperatures of a turbo will increase very high. Turbo’s can even be glowing red. Turbo engines therefore often have a intercooler, where inlet air is compressed and colled. This is similar to a radiator. Turbo engines also need some minutes of stationary running before shutting down to completely cool down.

A waste gate is a extra portion at the exhaust part where waste air can flow through in cases of having enough air. Some engines have a automatic waste gate function, in these type planes you can use full power on sea level.

Fuel System (3)

The fuel system and parts of aircraft are categorized into two categories:

• The fuel tanks with the fuel lines to the engine
• The induction system to merge the fuel with air where two types are possible

The fuel system can consist of the following possible parts:

• One or more fuel tanks conistsing tap-points with air vents amd cross-lines
• A fuel selector valve to select a specfiic tank or to open both or close both
• Fuel pumps
• Primer system

Fuel tanks are very often located in the wings, but can also be in the wingtips or fuselage parts.

The goal of the fuelsystem is to drive fuel to the carberator, where the fuel and air mixture is created before being ignited in the cylinders. If fuel tanks are located above the carberator, like on the Cessna 172, the fuel will flow due to gravity feed. We do not need fuel pomps in this case, which saves us some maintenance and another important part which can be broken.

On planes where the fuel tanks are on the same level or lower than the carberator, the fuel needs a pump to do the work. This pump is mostly driven mechanically by the engine. For backup purposes, in most cases we also have a electronic fuel pump which is often called a stand-by pump or auxillary fuel pump.

The fuel output point in the fuel tank is in most cases at the lowest point of the tank. However, we lose some part of the fuel making the difference between all fuel and unusable fuel. On the Cessna 172, we lose around 1,5 USG because of this. The pro of this is that possible dirt and other contamination is sinking to the bottom and not injected into the fuel system.

Fuel venting system

To prevent some underpressure while descending, fuel tanks consists of a venting system. This helps to maintain the atmospheric pressure in the fuel tank and is very critical at high-wing planes to ensure fuel always flows to the engine due to gravity. This does it by maintaining the outside atmospheric pressure so no vacuum can occur. Types of venting are:

• Venting pipes in the tank itself
• Special tank caps

Fuel tanks also have a drain at the bottom side, which can be used if any contamination or water is in the fuel and the color can be checked. Here we also have a strainer where water and contamination can be removed from the tank.

Vapour lock

Vapour lock is a phenomenon where bells of air occur in the fuel lines, making the fuel flow very hard or sometimes even impossible. This is caused by long terms of stationary running while on a very hot, warmed by the sun, platform. To solve vapour lock, turn on the electrical fuel pump and or enhance engine cooling. Using Mogas fuel increases the chance of vapour lock.

Fuel selectors

Fuel selector valves are being used to select where the fuel comes from. By setting this switch, you actually turn a mechanical valve to decide the flow of fuel. In most cases, we set this on both (if applicable) but in some cases to check or to balance the fuel in both tanks we select one of the two tanks only.

Carburation

To let a piston engine work, the mixture of fuel and air must be optimal before being delivered to the cylinders. This mixture can be made using two different systems:

• Carburator system
• Injection system

In the carburator, air and fuel are mixed into a optimal ratio and then will be delivered to the engine cylinders. The carburetor consists of a pipe with a narrowing, the venturi, and a throttle valve which you control with the throttle handle in the cockpit. In the venturi is a sprinkler which is connected to the float-chamber. This system is also called a updraft carburetor

Fuel to air ratio

Chemically, combustion is a reaction of a particle with oxygen. To start a combustion, fuel must be combined with air in a specific ratio. When one of both is too less, no combustion can happen, so the combustion area of an engine is within a certain area.

To ignite 1 grams of fuel, we need 14,7 grams of air. This makes a ratio of fuel 1:14,7 air, or the mixture containing 6,4% fuel.

• Rich mixture: 1:8 or 11,1% fuel
• Lean mixture: 1:20 or 4,8% fuel

In engine descriptions, the version with the ratio is almost always used as where the percentage does make more sense. We need to control the mixture because we can fly in air with a lot of air molecules close to the ground but also in air high up with way less molecules. We need to keep the ratio on about 1:14,7 which we can do by decreasing the amount of fuel. However, in situations where we use full engine power during climbing, we always use a richer mixture, as excess fuel is also used to cool cylinder heads.

Additional carburetor parts

The carburetor contains some additional parts to make it work as expected:

• Idle sprinkler (nullastsproeier): This part ensures enough fuel is sprinkled during idle power, otherwise the engine will stop working
• Acceleration pump : When the throttle value is opened up quickly during acceleration, the sprinkler will start somewhat slower making the engine not run optimal. Some carburetors are equipped with a accelerationpump, pumping extra fuel into the carburetor, solving this problem
• Mixture-handle: The mixture handle itself controls the amount of fuel that is mixed with the air. As you push it forward towards Rich, you get a rich mixture, meaning much fuel per air molecule. By pulling the mixture, this amount will be decreased
• Idle cut-off valve: The plane also has a mixture handle that can be fully pulled to idle cut-off. This means the idle spinkler and carburetor are both disconnected from the fuel, and the engine to lose fuel resulting in a shutdown of the engine. This is the common way to turn off a planes’ engine in general aviation
• Power enrichment system: This system ensures in throttle full-scenario’s, the fuel is somewhat more rich to help the engine cool more efficiently. Excess fuel is used to cool the cylinders

Air inlet system

Air normally reaches the carburetor through the engine air inlet system. This inlet is located at the front of the aircraft, just below the propeller. Before the air reaches the carburetor, it passes through an air filter. This inlet or filter can become blocked by debris, grass, snow, ice, or other contamination, which is why inspecting the air inlet and filter area is part of the preflight inspection.

On carbureted Cessna 172 models, an alternate source of air is provided through the carburetor heat system. When the carb heat control is pulled in the cockpit, a valve in the carburetor air box changes position. Instead of using the normal filtered outside air, the engine draws warmer, unfiltered air from around the exhaust heat muff.

This warm alternate air helps prevent or remove carburetor ice. It can also allow the engine to keep running if the normal air inlet or air filter becomes blocked. However, because the air is warmer and less dense, using carb heat usually causes a drop (~10%) in engine power and RPM. Therefore, carb heat should be used according to the aircraft checklist and operating procedures.

• Carb heat off: Filtered air from outside
• Carb heat on: unfiltered air from the exhaust

Icing in carburetors

The moisture in the air can freeze in the carburetor if the temperature there is below 0 degrees. The temperature in the carburetor is always lower than the outside air temperature, because of the following reasons:

• Vaporizing of fuel: Vaporizing fuel costs energy and this is picked from the air, causing the temperature of the air to drop
• Lower pressure in the venturi: Lower pressure means a decrease in temperature

This is the reason we turn on carburetor heat in every situation in the plane where we don’t use full power or cruise power. In my flight lessons, at every moment (ground excluded) where we need less than 2000RPM:

• In the full circuit
• During landing
• During descending
• During gliding

Carb icing can happen at any outside air temperature, even on hot and sweaty days:

• High humidity: The more moist in the air, the more can be frozen
• Low engine RPM: less heat is more ice

We check for carb ice during the before take-off checklist by setting an RPM of around 1700, and then enabling carb heat. We can check for carb ice in these two ways:

• Set Carb Heat to on: ice melts and RPM increases
• Set Carb Heat to off: RPM increases to above the initial RPM and slowly runs back

During the flight, we can recognize carb icing due to these causes:

• Reduce in Engine RPM
• Reduce in manifold pressure (constant speed propellor planes only)
• Very inconsistent running engine

Other rules about the Carb heating system are:

• Disable it (OFF) mostly on the ground, due to unfiltered air
• Disable it during climbs and go-arounds to get the best engine performance
• Enable or disable Carb Heat, no in between settings
• Carb Heat on means higher fuel usage

Fuel injection

Carburetors have two important downsides:

• Icing in the venturi, possibly causing dangerous situations if not handled properly
• Fuel/air mixture distribution over cylinders is not equal

These problems can be solved by using fuel injection. This system, which is available in modern aircrafts, has an injection in every cylinder controlled by a fuel control unit in between.

Just like the older carburation system we have a throttle valve, controlling how much fuel is pushed to the engine. This fuel now reaches the fuel control unit which equally distributes the available fuel onto the cylinders using the fuel divider. Most gasoline-based engine will inject the fuel continuously, not only when busy in the intake stage.

Fuel injection systems are always equipped with two possible ways of pumping fuel, which can be mechanical, using gravity or electrical. In the fuel manifold the fuel flow is measured, just like described in the disgram above.

Fuel injection systems are more complex and more expensive than carburetor systems, but we don’t need to bother about that carb heat again.

Aircraft fuel types

In aviation we know three types of fuel, each for their own cause.

An important parameter of fuel for planes is the knock resistance (klopvastheid). Fuel with a low knock resistance can burn under high pressure and normal operating temperature, leading to detonation. This is called detonation and results in a rough running engine.

Most planes can, some with some revisions, run on both AVGAS and MOGAS. The primary reason to use one of the two is the price. At this moment, the prices in the Netherlands are around:

• AVGAS: 3,94 per liter
• Mogas: 2,63 per liter

Fluids themselve cannot burn. They first have to vaporize and the vapor needs to have a specific mixture with air to actually burn.

Static electricity and Fuel

Resistance of two substances can produce a separation of electrical load. If the contact is broken, the two substances keep their electrical load. A plane can be loaded statically by precipitation, dust or sand in the air. This can also happen due to the flow of fuel in the tank installation. A passing thunderstorm can also cause a plane to be statically loaded.

Static energy can also cause interference in radio or navigation systems. To unload the plane from static energy, the plane has some static wicks, paths of low resistance with the air to unload itself which are mostly attached to the elevator and ailerons.

When the plane and tank installation have a different static load, a spark can transfer electrical load between the two objects when they are connected. To prevent this from happening and to send the electrical load directly into the ground, we always connect a plane using the ground wire during tanking operations. This is a wire we connect to a conductive part of the plane, like the nose wheel axis.

Fuel contamination

Aircraft fuel must be free of dust, water and other particles. When fuel is in the tanks, fuel can be contaminated. This is the main reson to check the fuel for any contamination with a dip stick and the drain. Water is the most occuring contamination and can leak in due to vapor, leakage and during rain. Water and fuel will not merge, and water is more heavy that fuel, so water will drop down and fuel will float on top of that.

Diesel engines

Diesel engines are very similar to gasoline engines. An important difference is that the diesel engine doesn’t have a ignition system. The compression ratio of a diesel engine is much better and works by pushing diesel in an area of high pressure and high temperature causing the diesel to ignite. Diesel engines need a better and stronger construction because of this.

Diesel engines also don’t have a throttle value, but a constant flow is delivered to the engine, results in a better power to fuel ratio.

Diesel engines have two engine-driven fuel pumps:

• Low pressure pump: Pumps fuel to the high pressure pump
• High pressure pump: Pumps fuel to the injection system with an overflow system, which excess diesel will flow back to the fuel tank

Diesel engines also don’t have mixture handles, but are electronically controlled using FADEC.

The ignition system (4)

After we have discussed the carburetion and injection system of engines, we will now take a closer look at the ignition system of general aviation aircraft. Ignition of the fuel/air mixture is what our propellor causing to turn and giving us thrust.

With gasoline engines, fuel/air mixture is ignited using a spark which is produced by a spark plug using high voltage. This voltage is around 20.000 volts and this voltage is produced by the magneto’s. The goal of the ignition system is to generate high voltage so the spark plugs will spark at the right moment to ignite the fuel/air mixture.

Parts of the ignition system are:

• Magneto’s
• Voltage distribution system to distribute the voltage over the spark plugs
• Spark plug cables : to conduct the voltage from the distributor to the spark plugs
• Spark plugs which generates a spark and ultimately ignites the fuel/air mixture in the ignition phase of the cylinder

Magneto ignition

In aircraft the engines use magnet-based systems to generate high voltage. This magnets are typically the dynamo’s where aircraft engines have two of, the left and right magneto. These magnets will spin around very fast. As long as the engine runs, the magneto’s will turn, making them completely separate from the electrical system which you control with the Master switches and alternator. Also we have some redundancy in if there is a problem in the L magneto circuit, we can run on R and still land the aircraft safe and sound. However, using one of two magnetos will result in a ~10% performance loss.

The magnetos are connected with gears to the crank shaft, the main shaft of the engine that rotates and is connected to the propellor, and they rotate within a coil. A rotating or moving magnet inside a coil produces electrical current, which is delivered to the spark plugs.

The produced voltage is dependent of the turning speed of the magnet. How faster the engine runs, the more voltage is produced. When starting, this system needs a impulse, mostly installed on the left magneto, which delivers more voltage in a short while and igniting just later to start the engine smoothly.

Start vibration

An alternative solution to the impulse link is an electrical start vibration system. The starting vibration will give the left magneto a pulsing voltage. This will result in a serie of sparks, but can only be used if having enough battery power.

Ignition moment

The ignition must happen on the right moment to be effective. If the fuel/air mixture is not ignited at the right moment, this will work against you instead of helping you further.

• Pre ignition: This is when the mixture is ignited too early
• Detonation: This happens when the pressure builds up in the cylinders and igniting at the wrong moment, leading to engine damage.

Some causes of detonation are:

• High engine temperature and too less cooling
• Too lean mixture
• Hot spots in the engine, like a hot spark plug
• Fuel with too low knock resistance or too low octane number
• Pre ignition

Spark plug contamination

A spark plug that has the right working temperature, will clean itself and will be free of carbon or lead. With running stationary for a long time, the optimal temperature will not be reached and can result in the engine running too rough. This is the reason we set the engine for around 1000 rpm during taxi and stationary, which is higher than the complete idle RPM, which is around 600-650RPM.

Diesel engines and ignition

Diesel engines doesn’t have spark plugs. Diesel engines will suck air and compress this. At the end of the compression stage the diesel will be injected into the cylinder, causing it to ignite due to the high pressure and temperature. Mostly similar to gasoline-driven engines but doesn’t have spark plugs.

Ignition switch

General aviation planes have a ignition switch where we control the ignition system with. This mostly have 5 different modes:

• OFF : Here the magnets are connected to the ground of the plane and disconnected from any source of power. No sparks will be produced in this setting, during normal situations
• R : Only the right magneto works in this setting
• L : Only the left magneto works in this setting
• Both : Both magnetos are working in this setting
• Start : The starting engine is powered in this setting and only the left magneto as impulse

During the before take-off checklist, we test the magneto’s on working and stability. If one of the two is not working properly, we will confronted with this at this moment. If the engine is running on one of the two magnetos, we should get a ~10% RPM drop. If one of the two is defective or inoperative, the RPM will not drop during the switch to R or L, and then can result in the engine turning off as we set a defective and non-voltage generating magneto.

A magneto can also be defective due to a grounding problem. During the run up, we will not see an RPM drop on one of the two separate settings. This can make the plane dangerous, and we may not park this plane without a good indication mark, as the magneto’s will be still powered. Rotating the prop results in a engine start. This will be minimized by disabling the engine using the mixture to idle, where no fuel is left in the cylinders and nothing to burn.

Engine cooling (5)

When burning fuel, a huge amount of heat is produced. As this will increase at higher RPMs and higher throttle settings, the engine needs to be cooled. Proper engine cooling extends the lifetime of an engine. At the best working temperature, the engine runs optimally which we want. We then get the most out of the engine. Other cons of high engine temperatures are thin or burnt oil, defective pistons, spark plugs and such.

In general aviation aircraft, these types of engine cooling is being used:

• Air cooling
• Liquid cooling

Most aircraft use air cooling or a combination of both. Liquid cooling is often used for cylinder heads and with diesel engines.

Apart from the cooling system, excess warmth is also dispatched through oil and oil coolers. Fuel also helps cooling the engine. Using a more rich mixture will cool the engine as this evaporates. This evaporation will help to cool the cylinder heads.

Air cooling

The cooling with air is very easy on airplanes. As air will flow through the openings at the front when flying this already has a major impact. The propellor also blows some air into the inlets at the front. Inside, most parts are equipped with big metal parts which pickup most of this air to cool and conduct the heat out. Most parts have cooling fins, making the contact-surface bigger and better cooling. Inside the engine compartment, some baffles (leiplaten) are added to redirect the airflow for optimal cooling.

Optimal cooling of the engine is reached during the cruise phase, as this redirects the most air at the highest speed into the air intakes. During climbs or running stationary the cooling will be worse.

Cowl flaps

Cowl flaps are used to redirect the airflow in a sucking motion, enhancing engine cooling and performance. These are often used in turbo-compressor engines. These are mostly open during taxi, take-off and climb and closed on cruise. Then re-opened at landing. If a plane has any problems with cooling in cruise, they can be re-opened.

Liquid cooling

An engine can also be cooled with liquid. Liquid can reach places with tubing where air cannot flow through. However, this is another extra reservoir, radiator and pump which can be defective. Liquid cooling is also more stable, and the radiator will only be opened when the cooling liquid reaches around 80-85 degrees celcius. Also the liquid will expand when being warm and contract when its cold, so an expansion reservoir is also installed.

Engine lubrication (6)

An engine needs to be lubricated using oil. The oil has these primary functions:

• Decreasing friction between parts
• Decreasing temperature and wear
• Cooling by conducting due to friction and burning which is called internal cooling
• Transporting small parts of wear and burnt carbon particles
• Securing metal surfaces from corrosion and from burnt fuel
• Closing the gap between cylinder wall and piston

We can use oil in two separate ways to get oil at the right places where engines can use both simultaneously:

• Pressure lubrication: Primary way, uses pressure built up by a pump to flow the oil around the circuit, reaching the crank shaft, bearings and camshaft.
• Splash lubrication: Uses splashing to cool and lubricate the bottom of the pistons and cylinders and bottom of the crank shaft

Oil circulation systems

In airplane engines, we can use two different oil circulation systems:

• Wet sump : In a wet sump system, oil is stored in the oil cump (carterpan), installed at the bottom side of the engine. The oil pump will pump this oil from the sump to the oil filter and then through the systems. From the engine, every droplet of oil that leaks is redirected back to this sump. This system is cheap and light and therefore used in much smaller airplanes
• Dry sump : In a dry sump system, oil is stored in a separate tank. The engine has a small carter to catch oil which drops back from the engine after doing its job. A separate scavenge pump will pump the oil which reached the carter to the oil reservoir. A dry sump system needs therefore two pumps, one for the system and one to pump oil back to the reservoir. This system is mostly used in aerobatic planes, where the engine is inverted so you can fly at inverted positions without an engine that turns off.

Oil cooling

To cool the oil and regulate the temperature of the oil we have a oil cooling system, equipped after the oil pump, before the oil is pumped into the engine. This cooler is a thermostatic temperature regulator which is cooled by the cooling air which flows in the engine compartment. This also works with a bypass system, redirecting directly or via the cooling compartment. If the oil pressure is high, this will also open to always have oil in the engine.

The oil filter is a paper filter in a metal case, around the size of a can of soda and is replaced every 50 flight hours.

Engine oil types

Oil consists of hydrocarbons and needs additives to lubricate the engine in a broad working temperature range. A cold engine needs to have the same lubrication as a warm engine. Oil has the following properties:

• Viscocity : The viscocity of the oil states how syrupy the oil is. The higher the number, the thicker, and the more resistance of flowing, also dependent of the temperature of the oil

In plane engines, we use both single grade and multigrade oil types. Single grade has big difference in temperature ranges and multigrade is “graded” for multiple temperature ranges. In the summer, we need to use thinner oil.

The indication is:

• Single grade oil : oil 80 or 100
• Multi grade oil : 15W50

Multigrade has the gradation in the name. During cold operations, the first number states the viscocity and at high temperatures the second number. Due to different additives the oil becomes more thick with a higher viscocity. In this number, the W stands for “Winter”, so Viscocity 15 during Winter (cold start) and 50 during engine operating temperature.

Oil pressure

In the oil system, the oil pressure is regulated by the oil pump which is directly driven by the engine. The oil pump delivers pressure at a very low temperature. To prevent the pressure exceeds the limits during high RPM situations, the engine contains a pressure relief valve. Via the pressure relief valve the oil will be pumped back to the carter. This flap will open at a certain pressure and stabilizes the oil pressure.

The most important indicator of the oil system is the oil pressure meter. A minimum pressure is needed to take care of having enough oil in the engine and enough cooling and lubrication.

• Low oil pressures: Lead to bigger wear, high temperatures and in worst case engine failure
• High oil pressures: Lead to leakage, damaged oil filter or damaged oil cooler

The normal and allowed ranges and limits are described in the POH. On the indicator, we get a good view of what is normal, too high or too low.

Too low and too high oil pressure can have similar causes, so let’s sum them up in a table:

A high oil pressure can happen if the engine is just started and cold. The oil is too thick and will be pumped hardly into the engine. When the engine has warmed up the viscocity will lower and the oil pressure will be within normal operating ranges. An engine takes around 10-20 minutes to fully warm up every component.

Oil temperature

Next to the oil pressure, the second most important indicator of the engine health is the temperature. The temperature will decide the viscocity and the lubricating properties of the oil. High engine temperatures can be caused by:

• Too much heat production in the engine, high environmental temperature
• Flying at high RPM too long
• Lean mixture
• Too less cooling in the engine, possibly during climb
• Too low engine oil-value
• Defective or dirty oil cooler
• Defective indicator

The oil temperature is dependent of the operating temperature in the engine. If this temperature is too high, then we can take some steps to try and resolve this high temperature by picking less RPM, flying faster for more and better airflow, riching the mixture or to open the cowl flaps.

High oil temperatures often happen with low pressure. By the high pressure, the pressure drops as the oil gets thinner. If the engine cooling is enhanced, the temperature and pressure will be normalized.

Oil usage

Every engine will use oil but the amount of oil is dependent on several factors. The oil usage will be dependent on:

• Type of oil
• Condition of cylinders
• Condition of pistons
• Condition of piston springs

A new engine which doesnt have already lubricated piston springs uses more oil. The same counts for older engines with much wear to the piston springs.

Constant Speed Propellors (7)

Constant Speed Propellors or variable pitch propellors are propellors where the angle of the propellor blades can be adjusted based on the phase of flight. Planes with this feature often have more blades than 2 on each propellor and are equipped with a blue Prop RPM handle in the cockpit, next to the black throttle and red mixture. Pro’s of planes with this feature is that they are much more efficient, generating more thrust with less engine RPM. With the black handle, we control fuel inlet pressure which is called Manifold pressure and with the blue handle we control the speed of the propellor, the RPM and indirectly the blade angle.

Planes equipped with constant speed propellors are also equipped with a governor. This is a part in the plane that actually sets the correct propellor blade based on the handle setting.

• When taking off and climbing: blades are set to full fine ( High RPM )
• When cruising : blades are set to coarse blade angle ( Low RPM )

As the propellor will always rotate at the same RPM, the angle of attack and drag can reduce when in horizontal flight as we go at a faster airspeed. This makes the plane setting a more coarse blade angle to increase this, making the engine run on lower RPMs than with fixed pitch propellors and having more control + efficient use of engine power.

Most blade-change systems are hydraulic, but some are also powered electrically. Hydraulic systems make use of the oil pressure to control the mechanism, so this also uses engine oil.

How this system works:

1. When setting the handle to Low RPM which is fully backward, the spring on the governor (the vertical pipe and part of the constant speed unit) will push on the fly weights which are those two balloons, making them fly outwards. They rotate at the crank shaft speed as a gear connects the governor to this crank shaft
2. The fly weights are engine RPM sensitive, making them fly outwards due to high RPM and fly inwards at low RPM due to centrifugal force
3. The fly weights are connected to the pilot valve, which is a valve that can complete the oil circuit to the propellor, in Low RPM settings this valve will open, at High RPM the valve will close
4. The propellor hub is hydraulically powered by the high pressure oil pump pushing the blade to a bigger angle.

Overloading the engine

When a high manifold pressure is combined with a low engine RPM the engine can fill up the cylinders too much, causing extreme pressure and temperature in the ignition space and can overload the pistons and crank shaft. This also increases the chance of detonation. Refer to the POH of the plane for recommended setting combinations.

Pre-flight check

During the pre-flight check, we will check the governor operation. This can be done when the engine is running and when it is in normal operation temperature. We will set the handle over the full range for a few times and check if the RPM changes value. Doing this multiple times will ensure the warm engine oil reaches the system and guarantee fully operation.

Single acting variable pitch propellor

Smaller planes are often equipped with single acting variable pitch propellors, where the blade angle is controlled one-way with oil pressure. The oil pressure ensures a coarse blade angle where centrifugal forces will ensure a fine pitch angle.

Loss of oil pressure

As we already discussed, when powered hydraulically, the system uses the engine oil to function. The pitch of the blades is mechanically limited to help us in failures. When oil pressure is lost, the propellor blades will set by spring force to the fine pitch setting (high RPM) making it a fixed pitch propellor and us able to land safely. This also needs a limited airspeed and limited engine RPM setting as the engine RPM can now be exceeded by the low propellor drag.