What do the number at end of model numbers mean? When i see thing on the internet about aircrafts it often has a number at the end of the model number such as B737-300, what does the number after the dash mean?

In the case of the 737, the first series produced was the 737-100.  Not many were made.

Then the 737-200 was built, which was very popular.

The third generation of the 737, known now as the "Classic", had three variants, the -300, the -400, and the -500.  All are very similar, the significant difference being the size.  The -300 has bigger (more powerful, as well as physically larger) engines than the older -200 did, and a longer cabin.  With its success, Boeing decided to lengthen the cabin further, resulting in the -400.  They also made a variant that was essentially the length of the shorter -200, and since it came along third it got the next designation, the -500.

The next generation of 737's, known as the "Next Generation", runs from the -600 through the -900, and this time Boeing decided to make the numbers correspond with the fuselage length, so the -600 is about as long as the -200 and -500 (roughly), the -700 is comparable to the -300, the -800 is longer as the -400 was, and the -900 is longer than anything before.

Now they're out of numbers, and so the NEXT generation of 737's, known as the Max, gets single digit numbers... the Max -7 (i.e. 737-7) corresponds roughly to the length of the -700, the Max -8 to the -800, the Max -9 to the -900, and so on.

The point of this long discussion is simply that the numbers following the dash represent different variants of the aircraft.  In some cases, it may be a new generation design; in other cases it may simply be a different fuselage length.

As the suggested-as-duplicate question discusses, HOW those numbers are chosen is sometimes driven more by marketing than it is by mathematical progression.  Often, though, the higher number indicates a later version, and often-but-not-always, a newer generation.  But you really have to know the particular aircraft line to know which it is.


How can the Pipistrel Apis land safely? I just saw a photo of the Pipistrel Apis motor-glider, and it got me wondering: How can it safely land with only 2 wheels total? To me it seems that falling to the side would be inevitable, and with wing fuel tanks, that could be terrible. In all the pictures, it's resting on (one of the) wingtips.

Are the wings/wingtips reinforced for landing & supporting the airplane on the ground?

Many modern gliders only have one wheel -- two is a great luxury!

In a glider the wing and flight controls remain effective until the aircraft is almost completely stopped - with a little training and practice it's possible to balance on the one (or two) wheels right up to the point where you're nearly stopped, at which point the glider will gently tip onto one of its wings as it comes to a halt.

As you've surmised the wingtip usually has some reinforcement or other provision (such as a skid plate or a small wheel) to prevent damage when it contacts the ground. The photo below is of one of these wingtip wheels.


What other circumstances may cause the autopilot to trip out? I recently watched Air Crash Investigation, Air France Flight 447.

The autopilot handed back control to the flight deck after the pitot tubes temporarily froze. The autopilot knew it was getting naff information and said: "We can't deal with faulty information so we are handing control back to the flight crew".

This got me thinking. What other instances, beside instrument error, if any, will the autopilot trip out, and hand control back to the crew?

An initial Google search was not helpful I am afraid. A pdf of the Airbus systems (350 pages long) was available, and a news source on everything the autopilot does, but nothing mentioning examples where all of a sudden the autopilot may switch off, even temporarily.

The reason I ask this is that if this is the only reason the autopilot may trip out, surely the crew of Flight 447 would have been aware that it was due to information that was not correct, and therefore to just remain as they were until the sensors came back to life again.

That is what I can not understand.

What other circumstances may cause the autopilot to trip out?

There are numerous circumstances, a few at random

pilot presses the autopilot disconnect pushbutton.
applying force to control-stick that contradicts autopilot.
entering a stall.
activation of high AoA protection.
descending below MDA on a non-ILS approach.
inconsistent data.

  will it not inform you of why it has tripped out?

Pilots check the ECAM for messages and suggested actions.

The AF447 accident report contains ECAM messages, note the ones at 02:12:44:

The Pilot in charge should assign which pilot handles ECAM messages, they should then have applied the ADR Check Procedure

  1.16.8.2 Case of speed display anomalies

  The philosophy for processing the anomaly is described in the “UNRELIABLE AIRSPEED INDICATION / ADR CHECK PROCEDURE” that is in Flight Manual (AFM) and transcribed in the Airbus FCOM and the Air France Operations Manual.

  Airbus

  The FCOM procedure indicates that:

  The crew identifies the loss of consistency in indicated airspeeds;
  And if the safety of the flight is affected by the indicated speed anomaly, and until the aeroplane reaches the safety altitude or the aerodrome circuit altitude, the crew first performs the  Memory items indicated in the “UNRELIABLE AIRSPEED INDICATION / ADR CHECK PROCEDURE” inset. The objective of these memory items is to maintain the aeroplane within a safe flight envelope and to stabilize the flight path to allow time to find, in the QRH, the tables giving the more precise pitch attitude and thrust values to be used for the flight:

Notice that the first two items are for the pilots to make sure the autopilot (AP) and autothrottle (A/THR) are OFF.

The pilots did not systematically work through ECAM messages and did not apply the ADR check procedure (one they would have memorised in training). They were confused and acted erratically. They stalled the aircraft, ignored the stall warnings and held the aircraft in the stall from above it's operational ceiling right down to sea level.

The sad truth is that the only action really necessary was to keep the wings roughly level for a few minutes. It is possible that if both pilots had folded their arms, tucked their legs back and taken a 5-minute nap, everyone on that plane would still be alive.

Glossary

- ADR = Air Data Reference
- AFM = Flight Manual
- ALT = Altitude
- AOA = Angle of Attack
- AP/FD = Autopilot / Flight Director
- A/THR = Autothrottle
- CLB = Climb (throttle setting)
- ECAM = Electronic Centralised Aircraft Monitor
- FCOM = Flight Crew Operating Manual
- ILS = Instrument Landing System
- L/G = Landing Gear
- MDA = Minimum Descent Altitude
- MSA = Minimum Safe Altitude
- NAV = Navigation
- PF = Pilot flying
- PIC = Pilot in command
- PROC = Procedure
- RED = Reduction (thrust reduction altitude - during climb after take off)
- SPD = Airspeed indicators
- TOGA = Take-Off / Go-Around (throttle setting)
- QRH = Quick Reference Handbook


What is the difference between Vno and Va What is the difference between the maximum structural cruising speed (Vno) and the manuevering speed (Va)?  Can you also please explain how these speeds are calculated?

I do understand that Va is set to where the wing will stall before the plane will go over its G limit but what does Vno mean?

Va limits G loads resulting from pilot input of maximum control deflection to limit load.  Vno limits G loads caused by vertical gusts over 30 ft/sec, without pilot input, to limit load.

In other words, Va protects you from bending the wings from pulling too hard, and Vno protects you from bending the wings from going too fast through bumps.


Is a biplane without dihedral more stable than a low wing monoplane without dihedral? I was wondering if a biplane's top mounted wing created the same stability effect as that of a high wing airplane?
Also, would the unstable effects of the low wing cancel the stability provided by the high wing and condition the biplane to behave like a mid wing airplane? If yes, is it one of the reasons why manufacturers make the top wing longer or is it just extra length provided to generate more lift and replace that lost due to wing interference?
This questions have been bugging me for some time now.
Someone pls clarify me.
Maybe I missed something...

Narrow answer: Yes, it is.

But no aircraft designer in his right mind would build an unswept low wing aircraft without dihedral. So this question is misleading.

Please look here why low wing aircraft need more dihedral.

Please read here why a low wing aircraft is just as stable as a high wing aircraft. The high wing does not entail more stability!


Which source to use when reporting the current altitude to ATC? While flying from KSNA to KVCB VFR at night, Norcal Approach asked for my current altitude.  I was somewhere between 12.0 and 12.5 depending on which reading I was going to use.  ATC had me confirm.  My GPS altitude was 12.5, my transponder was showing 12.3, and my altimeter indicated 12.0.  I am assuming, since altimeter settings are based on the barometric pressure on the ground, that the thinner air above 12,000 feet would make my altimeter the least reliable of the three and the GPS the most reliable.

When ATC asks, should I give them the altimeter indicated altitude?  Also, is the transponder altitude that I can see derived from secondary radar and isn't that what ATC is already seeing?

When asked for altitude, you report the altimeter reading, utilizing the correct barometric pressure entered into the Kollsman window.

ATC separates traffic based upon indicated altitude.  The indicated altitude may include errors, such as the pressure ATC provides, but all aircraft in the area will presumably be using the same barometric pressure, and will have similar errors.

GPS altitude, which some call an absolute altitude, is an altitude relative to a model, normally the WGS84 elipsoid, and has it's own set of errors.

By convention, indicated altitude, based upon local pressure, is used for aircraft separation.


What dictates the prop RPM used during cruise? I've seen on numerous different constant-speed propeller aircraft and different pilots using different RPMs during the cruise phase on a propeller aircraft. What dictates the RPM used during normal cruise operations, and why is that the case? Often there are multiple possible throttle/RPM combinations that deliver the same power, so where would you pick one or the other?

"Dictate" is the wrong word.  Within the ranges listed in the POH, the pilot may select rpm/MP settings as he pleases to meet other criteria.

Charles Lindbergh instructed many WWII pilots in a technique to extend range, by flying with low rpm and high manifold pressure.  This extended range by reducing the "pumping losses" required to maintain low manifold pressure.  Over long distances this technique did extend range considerably.

Secondly, lower rpm reduces noise - remember that the propeller is the largest contributor to a propeller-driven plane's noise signature.  This is important in the terminal environment where the noise can affect the ground, but it also affects in-cockpit noise regardless of altitude.

This answer does not contradict the former answer, but it extends it to point out that there are other important factors that the pilot should consider in selection of engine operation parameters.


What is this loose object above the flap fairing? During my flight, I noticed a loose object above one of the flap fairings. You can see it in this video: https://imgur.com/wCPSEem.

Is it normal or should I notify the airline?

People pointed out to a similar question, but A) I'm not sure it's the same rubber; B) it's a different airplane model, C) the behavior of that rubber (if my footage shows a rubber indeed) is not the same, D) the other question asked what that rubber is, whereas my question is specifically about it being loose. I'm no aviation expert nor an engineer, but it doesn't feel right to me that it's loose.

It’s a neoprene seal which may be a little loose there at the end like that and made to flutter by the flow of the boundary layer air around it.  That’s a common part used sometimes around the edges of enclosures eg flaps, landing gear fairing doors, etc. 1) to prevent scuffing or abrading parts during operation and 2) to seal out boundary layer flow, reducing drag.  You can notify the airline but the problem is benign and will not affect scheduled operations.


What happens if I activate VFR flight plan later than filed ETD? Let's say I filed a VFR flight plan with ETD (1500), en route (2 hours), ETA (1700)

If I depart and activate the plan at 1600, now the new ETA will be 1800 which is an hour later the the filed ETA. Is the ETA changed automatically on the system? or do I have to contact FSS and change to prevent initiation of the search and rescue?

Assuming that you've submitted a Delay Message in order to prevent your flightplan from being deleted you have to do nothing at all.

In your flightplan you only state your ETD (Expected Time of Departure) and ETE (Estimated Time Enroute). Your ETA (Estimated Time of Arrival) will be calculated and relayed to all stations in need of the ETA by AIS (Aeronautical Information Service).

To pick up your example:

Filed ETD: 1500
Filed ETE: 0200

AIS will relay ETA 1500+0200=1700 to your aerodrome of destination.

Let's say you've departed at 1554. Your aerodrome of departure will pass a departure message to AIS (so they know you are on your way) together with your ATD (actual time of departure) which would be 1554 in the example.

AIS will then calculate ATD+ETE => 1554+0200=1754 and relay the corrected ETA to your aerodrome of destination where the data in your flightstrip gets corrected.


Where can I find maintenance manuals for the A380? My friend recently acquired an external green light from an A380. They are the only details i have from him. I tried hunting the internet for maintenance manuals, technical details, schematics, basically anything i can think of. Apart from a couple scam websites selling Haynes manuals, i came up with nothing.
Does anyone know the power requirements for the lights or, ideally, a document that lists aircraft details and specifications. I imagined that maintenance details will be available, but nothing came up.

You’re going to be looking for the Airbus Illustrated Parts Catalog (IPC) for the A380 airplane.  It’s something I’m sure you can request from Airbus, but it’s gonna cost you.


What makes an airport "international"? What are the requirements for an airport to be designated as an international airport in the US? Is there a minimum runway size or required customs office?

There is no US regulation about whether an airport can be called "international." The Secretary of the Treasury designates the official list of international airports of entry. But not all airports on this list are even called international, and it does not include all airports with international flights. There are even some airports called "international" with no customs facilities or plans to have them in the near future. The airport name is determined by the airport owner.


What is the purpose of the little eyebrow windows on the Boeing 737? Anybody know what these windows were used for?

From Wikipedia: Boeing 737:

  Most 737 cockpits are equipped with "eyebrow windows" positioned above the main glareshield. Eyebrow windows were a feature of the original 707 and 727. They allowed for greater visibility in turns, and offered better sky views if navigating by stars. With modern avionics, they became redundant, and many pilots actually placed newspapers or other objects in them to block out sun glare. They were eliminated from the 737 cockpit design in 2004, although they are still installed at customer request. These windows are sometimes removed and plugged, usually during maintenance overhauls, and can be distinguished by the metal plug which differs from the smooth metal in later aircraft that were not originally fitted with the windows.

Boeing has also determined that removing the windows reduced the cockpit noise by about 3 decibels. The newer models have 10 vortex generators above the cockpit where the windows used to be. It also reduces maintenance costs.


Bright exhaust in afterburner vs no visible (bright) exhaust when not in afterburner? When a jet engine has its afterburner engaged, a bunch of fuel is dumped into the back of the engine for additional thrust.  This burning fuel causes the exhaust and inside the engine to glow brightly, which is quite visible even to the casual observer.  However, when the afterburner is not engaged, there is no visible light at all that I've seen coming from the engine's exhaust.  I would think that the fuel burning process of a normal jet would be visible out the back as well, just not as noticeable as afterburner exhaust, but that doesn't seem to be the case.

Is there visible light from the exhaust of a non-afterburner jet and I'm just not seeing it, or is the burning fuel inside the engine so much that it just doesn't get out.

It's because on a jet engine the flame in the burner can is carefully controlled and contained by airflow that is guided in from the sides to keep the flame in the center of the burner can so it doesn't touch metal (only maybe a 3rd to half of the airflow out of the compressor gets burned; the rest is for temperature control - which is why there is enough oxygen in the air leaving the turbine to support reheat).  The flame is supposed to be out before the gasses have left the burner can or else the turbine will overheat. The turbine itself is getting burned air that has been mixed with un-burned air to cool it off.

On most engines, if you see a light in the tailpipe of an engine not in reheat, it means there is a flame aft of the burner can in the turbine zone, which is very very bad, except when initially starting and some is briefly visible after lightup.

On some engines, if there is a direct visual path up the tail pipe, through the turbine and stator blades, into the center of the burner can, you may be able to make out a bit of bluish light (should be bluish; yellow light means too rich and the yellow is un-burned carbon fluorescing, like any yellow flame).


What is the critical altitude? What is the definition of critical altitude and why is important to know in Vmc graph? Also, is there any critical altitude in the Piper PA-44 Seminole?

Critical altitude is the maximum altitude where the engine turbochargers (or turbonormalizers) can maintain sea level standard pressure to the engines. Above the critical altitude the engines will produce less power, although still delivering more power than an normally aspirated engine at the same air density.


How do conventional and T-tails differ? What design considerations go into the decision between conventional tails and T-tails?  Functionally the horizontal stabilizer/stabilator are the same in both cases, providing negative lift, the elevator control and a method for pitch trim.  What are the differences though?

As far as I am aware the T-tails I have flown have T-tails for avoiding propwash (PA-44) or aft engine placement (EMB-145).  Are there other reasons for having a T-tail?  What are the aerodynamic consequences a pilot needs to be aware of with a T-tail (e.g. avoiding hard de-rotation on touchdown, issues at high AOA, etc)?

There is more to a T-tail than that:

Aerodynamics:

The placement on top of the vertical gives it more leverage,
especially with a swept tail.
Depending on wing location, it stays in undisturbed flow in a stall. Note: This is really depending on the details, the HFB-320 had a forward swept wing and a T-tail, which made a deep stall possible (and in one case fatal).
By designing the junction with the vertical well, the T-tail has less interference drag. It also helps to reduce wave drag, especially when using a well designed Küchemann body (the round, long, spiky thing on the tail junction of a Tu-154) by stretching the structure lengthwise.
It can help to increase the effectiveness of the vertical tail by keeping the   air on both sides of it separated. At the other end, the fuselage does this already, so moving the horizontal tail up does not hurt so much there. As a consequence, the tail can be built lower.

Structure:

The mass of the horizontal tail on a long lever arm (= the vertical tail) means that the torsional eigenfrequency of the fuselage will go down. This might be a problem in case of flutter.
As a consequence of the smaller vertical tail, a T-tail can be lighter. Note that the increased leverage means that the horizontal tail can be smaller as well. This reduces friction drag and is the main reason why most modern gliders have T-tails.

Control:

A T-tail produces a strong nose-down pitching moment in sideslip.

If it were not for the flutter and pitch-down, T-tails would be more widespread ...


I have a document referring to aircraft with maximum takeoff weight of 45000T. Is this an error? I got the attached document from http://www.aisthai.aviation.go.th/.

This document refers to aircraft with MTOW 45000T.

Is that 45000 tons? That's pretty heavy for me. Or am I interpreting the document incorrectly?

It stands for metric tons, as indicated in the "GEN 2.1 Measuring system, aircraft markings, holidays" section of the AIP that you linked to as one of the units for mass.

That being said, the number format appears to be wrong and they most likely intended 45.000 metric tons, which works out to about 99,000 lbs. and is a somewhat common point to use for aircraft classification in other countries.


How do you avoid power of 10 or order of magnitude errors when using an E6B calculator? I am currently working through Gleim's instructions for using their E6B calculator.
It says: "The numbers on the inner and outer scales represent multiple sof 10 of the values shown." And "EXAMPLE: The number "20" on either scale me represent 0.2, 2.0, 20, 200, or 2,000".
I've been working through the examples, and a recurring problem is getting the right value to multiply by 10, but not knowing what power of 10 to multiply it by. (To put it in math terms: right mantissa, wrong exponent).
What is the process or rules to make sure you get the right answer every time? Obviously, getting a flight calculation wrong by an order of magnitude is not a problem you want to have!

It's not a problem you'll ever have in practice, as it will always be obvious to you whether that "2" on your wizz wheel is 0.2, 2, 20 or 200. It is not a problem you'll have with time/endurance etc issues as the inner scale of time is unmistakable.
But lets take some practical examples:
Conversion Nautical to statute miles

Set 90 next to the "NAUT" marking
Read the value next to the "STAT" marking. it is somewhere about 10.5.
You know that nautical miles and statute miles are fairly similar
You therefore know this cannot be 10 Statute miles, nor 0.1 so must be around 100
The answer is 103.5

Calculate speed from distance and time

Distance is 26NM and time is 13 minutes
Set 13 on the inner scale opposite 26 on the outer scale
The rate arrow points at the speed. It says 12.
I'm flying a standard single engine prop. Can it fly at 12 Knots? Can it fly at 1200 Knots?
The answer can only possibly be 120Knots

Fuel burn rate

You took 32 gallons of fuel and flew 4 hours 20 minutes
Set 4:20 on the inner time scale against 32 on the outer scale
Rate arrow points at 74.
Did I burn 74 Gallons per hour? My Cessna only holds 40! Did I burn 0.74? That seems awfully low - with that my endurance would be measured in days when I know its roughly 4 hours.
The answer can clearly only ever be 7.2 Gals/hour burn rate

The thing with being out by a factor of 10, is that it is always obvious you're out by a factor of 10. 2x, 3x even 4x you might get confused. But I don't think you ever will with 10x
The even shorter answer is that once you've gained your PPL you'll only ever pull out your E6B to answer these such questions, and any other time you'll use modern, electronic tools to answer these questions. Slide rules; gone from the classroom in the 1970's but still used to teach people to fly.


Why can not two modes coincide perfectly for some cases in Flutter phenomena? I have a question about flutter phenomena. As you know, flutter occurs when two modes (for example, first mode and second mode) coincide (that is, after a specific velocity, the frequencies of two modes will be the same and equal) and the damping term will change into positive which causes failure.

However, for some cases, frequencies of two modes do not coincide perfectly (they are not equal) and damping parameter negative sign will change into positive, which mean flutter is happening.

Why is this happening? Why can't the frequencies of two modes coincide perfectly?

Flutter happens when the frequency of two modes coincide. These modes must be of different nature, so their frequencies can move in different directions. Typical examples are elastic modes (with eigenfrequencies independent of speed) and aerodynamic modes (with eigenfrequencies proportional to speed). When flight speed increases, the aerodynamic mode becomes faster (think of dynamic pressure as of the stiffness of the spring in a spring-mass system) while the elastic mode stays constant. At some point both have the same frequency, but flutter will already appear when they are close enough so each builds up the amplitude of the other. This will become more efficient when the frequencies are identical, but this is academic:  When flutter starts, it is a bad idea to accelerate further.

Example for an elastic mode: Wing bending. The first mode is just the tips moving up and down, the second mode is one tip up, the other down, which will rotate the fuselage, the third mode (or for pedants: The second symmetric mode) is again both tips up, but now with the midspan section moving down and so on. They are harmonics (like the oscillations of guitar strings), so their frequencies are at a fixed ratio, with the first mode having the lowest frequency. See below, from top to bottom.

Example for an aerodynamic mode: Aileron flutter, fast-period mode (especially when coupling to the bending mode in sweptback flying wings).

For me, your diagrams don't make sense. They should look more like that:

EDIT:

With Shellp's comments I realized that the answer above is too simple. The lines in the graph are for the static case of the elastic vibration. Once this wing moves through the air, it's movement will change the local aerodynamic forces, which will modify the flutter modes. The motion-induced aerodynamic forces counteract the elastic motion at slow speeds, adding damping (negative, because they reduce the motion). With damping, the frequency of the mode is reduced.

At higher speeds, delays in the buildup of pressures mean that now the aerodynamic forces lag behind the motion, and once this lag exceeds a quarter of a period, they produce positive damping (this is an unfortunate wording, so stay with me. The damping term is a negative number when it really damps the motion, but when the term becomes positive at higher speeds, it is still called damping, but now the motion is excited instead of damped in the common sense. So let's call positive damping "excitation" from now on).
This excitation now increases the flutter frequency, so in reality the two flutter phenomena now get locked together. The first graph in the question above shows the frequency going down with speed, which looks unusual to me. The second graph shows this locking-in with an increase in frequency over speed, but at very high frequencies (it must be a small structure). If you want, the excitation is pushing the elastic frequency up, so both lock together without converging completely. But that cannot last forever - at higher speeds they should diverge, but in reality the structure is overloaded way before that happens.


Why are the intakes of some fighters not attached to the fuselage? Look at the photo below. As you can see the intake isn't attached to the fuselage. Why? Other examples include the F-16, F-22, and F/A-18 Hornet.

(F/A-18E Super Hornet Walk Around)

That's called a 'fuselage boundary layer diverter channel', or splitter plate.

The air near the fuselage or wings is slowed down (thereby losing energy). Those plates ensure the jet engines get free stream air, which improves the engine performance. This free stream air will be undisturbed, allowing a more uniform intake of air.

You can also find it on the Concorde.

Related: What is the function of the holes in splitter plates?


Why would the digits fade out and blink in darkness on a KX-155? I have a radio installation with two KX-155 Nav-Comms.  These radios are equipped with a photocell to automatically dim the displays to match cabin lighting.  In dark lighting, the digits fade to the point of unreadability, with some segments being visible and some not.  I can brighten and read the displays by aiming a flashlight into the photocells.
It seems like there is a bias set incorrectly or an excitation voltage which is wrong.
Why might this be happening?

Yes, there is a trim pot on the display circuit board that adjusts the dimmer level.
The display intensity pot is R438. The red arrow points to it:

The dimmer pre-set should be marked on the outside cover, and is adjustable without removing the covers, but it only adjusts the max brightness.
It could also be the photo cell that is bad or dirty. When the display starts to loose it's brightness, that's usually a sign that it's about to go south. It can be readjusted with the pot a couple of times, then is only visible when the radio has warmed up, then finito. Try a new photocell, very easy to replace.
Be sure to observe all regulations concerning avionics maintenance!!
Source of info: http://www.337skymaster.com/messages/showthread.php?t=478


What would happen if an airplane flew through a tornado? I read a question which asked whether planes fly over hurricanes, so my question is what would happen if a low-flying commercial plane tried to fly through a tornado.

Assume that it's traveling at cruise speed.

It depends on the strength of the tornado and other variables, but in most cases, a plane Vs tornado will end very very badly for the aircraft and its occupants in a low altitude high speed scenario.
A good example would be the NLM CityHopper Flight 431, a Fokker F-28 that flew into a thunderstorm 8 minutes into takeoff and crashed after the wing was torn off. From the summary of accident report at aviationsafety.net:

At 17:12 the aircraft entered a tornado, which resulted in loads on the airframe increasing to +6.8 G and -3,2 G. The right wing was bent upwards followed by a severe downward sweep. This compromised the structural integrity of the wing, causing a large portion of the outer wing to separate in an upward and rearward motion. Control was lost and the aircraft impacted a railway bridge inverted.

Everyone abroad the aircraft perished. FAA is pretty blunt about flying near one:

Pilots should observe the following rules for any flight routed even potentially near actual or possible thunderstorm activity:
• Avoid all thunderstorms.

And also,

Although pilots have flown through limited state thunderstorms with little or no damage to the aircraft or passengers, these pilots should consider themselves extremely fortunate to be alive.

(emphasis original).
Note: I've used both thunderstorms and tornadoes here. weather.about.com defines them as:

Thunderstorm: A storm (produced by a cumulonimbus cloud) that includes rain showers, lightning, and thunder.
Tornado: A violently rotating column of air that extends down from the base of a thunderstorm to the ground.


Should head stay level or inclined in a bank? I just started to receive instructions to become a glider pilot, yay me! :)
I (and my instructor) have noticed that I have the tendency to keep the head level (eye-line parallel to horizon) in turns and my instructor says that wouldn't be a good idea, because at some point I won't be able to keep the head level anymore, so I should practice with keeping my head level to the lateral axis of the plane, i.e. inclined together with the bank and eye-line parallel with the wings.

What do professional or experienced glider pilots do? Is it maybe a matter of taste? Or should I let go of this tendency because at some point I just can't use horizon and gravity-sensation to orient myself (due to g-forces, spinning, etc.)?

I am not a glider pilot, but the principle holds for flying any fixed wing aircraft1: you should keep your head level with the aircraft, as you described, not the horizon.

As your instructor explained, there may come—or will come—a time when you are not able to keep your head level with the horizon due to the nature of a particular maneuver or orientation, and that is a practical matter to consider. It is certainly difficult to incline one's head 60° to the side in a steep turn.

From my perspective, however, the more important reason is that your frame of reference needs to be the aircraft. You are used to viewing the world with the ground as your frame of reference; down is down, up is up. As you learn to fly, however, you need to learn a new way to view three dimensional space, or—more specifically—the way you move through that space in the aircraft. It might sound cheesy, but you really need to learn to become one with the aircraft and hold the same perspective regardless of the aircraft's orientation.

Now, that being said, as you gain experience and develop your skills, you may come to realize that this perspective shift does not always require that your head remain rigidly perpendicular to your shoulders. Rather, it is a matter of perception which will eventually be independent of how your head is oriented relative to the aircraft. At my first flying job I spent much of my time in maneuvering flight and my head was rarely still—much less level with the aircraft. I spent a great deal of time with my head on a swivel, looking up and down, side to side, craning forward to clear into a turn, looking back into the cockpit, etc.

At this stage in your training, however, it is probably important to train to keep your head straight within the aircraft; certainly follow your instructor's instructions, and you should do well.

1This probably holds true for rotorcraft as well, or any aircraft for that matter. I am only sharing what I am familiar with.


How is pressure related to air density? This is confusing to me:

Since pressure increases with temperature (I don't know why), how can air density decrease with temperature. In a hot day then pressure would increase and air density decrease? How is that possible?

@casey @steve V. @StallSpin

The point is this: FAA writtten says:
The altimeter will indicate lower altitude than actually flown in a temp warmer than standard. I understand that this way: this an example

1) Indicated Altitude: 12.000ft
   True Altitude: 12.000ft
   Temperature: -9 Celsius (STD)

Then suddenly the air temperature changes from -9 to +20 (Example) and in a couple of minutes we have:

Indicated Altitude: 12.000ft
   True Altitude: 14.000ft
   (In warmer than stantard, pressure increases so the aneroid waffers in the altimeter will contract indicating lower altitude (lets say it indicated 10.000), then the pilot will climb "back" to 12.000 but in reality (true altitude) he is climbing to 14.000.

Am I getting this right?

2) Now another thing, temperature decreases with altitude, so aneroid waffers are expanded with altitude.

Does the aneroid waffers mesure density or pressure?

The atmosphere approximates an ideal gas, and as such you can relate pressure and density through the ideal gas equation.  The form we use in meteorology uses mass density and is given by:

$$p={\rho}RT$$

where $P$ is pressure in units of Pa, $\rho$ is density in units of kg m-3, $R$ is the gas constant for dry air (287 J kg-1 K-1) and $T$ is temperature in Kelvin.  This assumes a dry atmosphere and humidity will decrease density for a given pressure.  Consideration for water vapor is usually brought in by changing temperature into virtual temperature $T_V$ where $T_V=T(1+0.61q)$ and $q$ is the mixing ratio of water vapor (units $kg~ kg^{-1}$).

Pressure increases with temperature because the particles have more kinetic energy (which is proportional to $T$).  Imagine a box full of bouncing balls, if these balls start moving faster the balls will hit the walls of the box harder, imparting more force on the box.  Pressure is merely force per area, so if the force increases but the box stays the same size, the pressure has increased.

Air density can decrease with temperature if pressure is also decreasing.  If pressure is constant, this cannot happen (they would be inversely related).  Any time you specify a relation between any two of pressure, density or temperature you must hold the third constant or specify its behavior.

For example, hot air rises, but why then is it cold on top of a mountain.  The answer is that hot air is less dense than the cold air surrounding it for a constant pressure, and being less dense it rises.  With a mountain, the pressure is decreasing, and we likewise find in the atmosphere that temperature decreases with decreasing pressure.

On a hot day what tends to happen is that the surface, which is being warmed by the sun, heats the lowest level of the atmosphere, reducing its density (it is at the same pressure as its surroundings and its T rises).  This will eventually drive convection and mix this warmer air vertically.  Given enough time, this will reduce the mass in the column of air and therefore reduce the pressure at the surface.  These are called "heat lows" and you can see them forming in the desert areas and they play roles in sea breeze formation and the monsoons.

To address the expanded question:

The point in the FAA written is best understood by forgetting that we fly at constant altitudes -- we don't.  In level flight we fly on constant pressure surfaces which we then translate to an altitude.  In any given column of atmosphere, if it is warmer than standard a given pressure surface will be higher and when colder than standard the pressure surface will be lower.

To illustrate, let's consider you are flying at 3000 ft or roughly 900 mb.  Everywhere on this pressure surface will indicate 3000 ft on our altimeter for its current setting.  If we go somewhere hot, this pressure surface rises, and so we climb (though we think we are level) with this pressure surface but because the pressure has not changed, we still indicate 3000 ft.  However, we are higher than 3000 ft in reality.

This follows into your next question.  Aneroid wafers detect pressure changes and your altimeter displays an altitude not corrected for temperature.  This is why your true altitude can vary with temperature for a constant indicated altitude.  When you correct the altitude for temperature we call this "density altitude".

So back to my example above, your are flying along at 900 mb and indicating 3000 ft, and heading into warmer air.  The pressure surface starts to gently rise and as it does you are not yet following that rise and your altimeter will indicate a descent.  In true level flight you will begin to fly into higher pressure in this case as the 900 mb surface rises above you and the aneroid wafer in your altimeter will indicate a lower altitude and a descent.  You correct this and climb back up to the 900 mb pressure level so that your altimeter will once again indicate 3000', all the while actually gently climbing on this pressure surface.  You won't really be cognizant of this while flying however, and will just minimize vertical speed and maintain altitude blissfully unaware that you are really flying on a sloping constant pressure surface.

To better illustrate this, consider the following figure:

In this figure the reds signify a warmer than average column of air and the blues a cooler then average column.  The whitish area in the middle is a column at average temperatures.  The black solid lines are isobars (lines of constant pressure).  The dashed black line is a true altitude above the surface. Finally, the bold black line is the pressure level that corresponds to the true altitude of the dashed line at ISA conditions.

What you should notice is that the pressure levels in the warm column are spaced further apart because the air is less dense and more of it is needed to produce the same pressure (as pressure is just the weight of all the air above it).  Likewise in the cool column the pressure levels are spaced closer together because the air is more dense than standard.

To tie this into the discussions above, consider yourself in the standard column (white background) at the true altitude above ground represented by the dashed line.  Your altimeter does not sense this true altitude but instead senses the pressure outside of the airplane.  This will be roughly calibrated to your true altitude (uncorrected for temperature) but using the local altimeter setting.  Now as you fly either to the left or to the right and maintain a constant indicated altitude, you will track along the bold line, as this is the pressure that corresponds to your true altitude at standard temps.  As you fly toward a colder column you will in reality descend, and you will climb as you fly into the warmer column.


What exactly happens when power is reduced in trimmed, straight and level flight? I understand that trimming an aircraft at a particular airspeed e.g. 100kts will keep the aircraft flying at that airspeed (100kts) even if you were to e.g. Lower power. This is apparently accomplished by the pitching down of the trimmed aircraft.

But I am not too sure if I understand the rationale behind the pitching down. I hope to seek advice on whether what I understand is correct:

When you elevator trim to fly unaccelerated straight and level flight (all forces balanced) at e.g. 100kts, you are relieving the pressure needed to keep your aircraft in that angle of attack that produces enough lift to counter the weight, at that particular airspeed (because any increase or decrease in airspeed also will affect lift, so speed will affect the amount of lift that needs to be created by the AOA to counter the weight so as to stay level). So if your speed starts to drop, the amount of lift that your AOA must make = increased. But since you have trimmed elevator to that position means the AOA is fixed. So what happens is that the aircraft will pitch down (trade height which is potential energy for kinetic energy so your speed increase), then your speed will be back to what it used to be and your that trimmed AOA will continue to be able to supply that exact amount of lift, which together with the lift at that same airspeed is just right to counter the weight. So the aircraft will be back to level flight again.

Since power is lowered, I would expect the aircraft to continue to lose speed and the whole cycle of pitching down then back to straight and level will go on and on.

Does this make any sense?

This makes sense and is approximately what happens if you reduce thrust during trimmed straight and level flight. The aircraft will go though a series of damped oscillations, called 'phugoid' until it finds its new equilibrium state. The new state will be the original airspeed, but now in a constant descent.


Why do some helicopters have such complicated flight control mixers? Image source

Some helicopters have a very complicated set-up that mixes flight control inputs to many or all of the swashplate actuators, like in the picture above for the S-76.

Why are all the cross-couplings required, would the helicopter not be controllable without the flight control mixing action? We only need to cant the swashplate for cyclic control, lift it for collective, and connect the pedals to the tail rotor, right?

Flight dynamics of a helicopter are complicated indeed. Just to illustrate, consider a helicopter in a stable hover, with the pilot holding the collective, cyclic and pedals in the position that maintains attitude, altitude and heading.

They now want to gain altitude only, in a climbing hover. The sequence of events:

Pilot pulls on the collective, all rotor blades increase angle of attack and the rotor creates more lift. The helicopter climbs.
But because the AoA of the blades have changed, the engine must apply more torque to the rotor and the heading starts to change. So the pilot must apply pedal to change tail rotor thrust and compensate for the torque.
The increased thrust of the tail rotor causes lateral drift. So the pilot needs to input lateral cyclic in order to compensate.

To gain a pure vertical climb, the pilot needs to carry out simultaneous deflections of three flight controls! This collective-to-yaw and collective-to-lateral coupling not only occurs in the hover, but also in forward flight. When increasing speed, the pilot needs to:

deflect cyclic pitch forward;
increase collective for the additional required power;
deflect the pedal for the increase in rotor thrust - but at speed, the vertical fin and the tail rotor take over most or all of this;
deflect the cyclic to the side to compensate for the increased tail rotor thrust, or for the sideslip from the vertical tail stabilisation.

For small, simple and low cost helicopters, this is indeed the way they are flown. But for larger helicopters with a mission, some of the cross couplings are taken care of by the mechanical mixer: when increasing collective, a mechanical link automatically increases the inputs for the cross couplings. It does so in series with the flight controls, which do not move and retain their former selected position.

The drawing in the OP is of at the S-76, a medium sized helicopter, and we can find the following:

Collective/Roll mixer (lateral lead). Provides automatic rotor sideways deflection as a function of collective stick deflection.
Pitch bias actuator. Extends as a function of airspeed, so that the cyclic pitch stays near centre, for more comfort at high speed.
An unlabelled connection rod between collective and pedals.
Collective/Pitch mixer. This helicopter will start to pick up speed when collective is deflected, for a straight-up vertical speed, the pilot will need to deflect the stick backwards.

Also in the OP drawing: optional AFCS servos, which reduce control forces and provide the static stability that helicopter aerodynamics do not provide. Plus trim actuators, which change the neutral position of the feel springs or completely eliminates feel forces. And a yaw damper.

Very complicated indeed.


How does an aircraft maintain an orientation that was actually caused by a external disturbance? What is the difference between centre of pressure, aerodynamic centre and neutral point?

At this link, there is an image used to explain the answer, but not much has been spoken about it.

I understand that the disturbance was caused by either the CG moving too ahead or too rear, or the CP moving forward of the CG. I would like to know that in the given image, how did the aircraft hold the disturbed orientation ?
Was it perhaps by mechanically shifting the CP back again using some device ?
Thanks in advance.

Stability of the aircraft has nothing to do with control surfaces or moving CG to control the aircraft (that kind of aircrafts are very rare anyways). When researching or testing for aircraft's stability, control surfaces are either fixed to neutral position or they let alone to float freely, so control surfaces are not used to make aircraft more stable. That's of course true for conventional aircraft.
On the other hand you can produce an unstable or neutrally stable aircraft, however in that case you are required by regulations and nature to use some kind of control computers to keep aircraft in control all the time. MD-11 and Boeing 777 are two examples of this. Even though they are not unstable nor neutrally stable, they are definitely less stable than the requirements for the conventional aircrafts. To get away with that they have to have couple of flight control computers to keep the aircraft sane. However, even when the automation fails these aircrafts still have some positive static stability. How far you can go towards unstable side depends on design choices. You can further read Peter's post about why there is really less bang for buck when you further decrease the stability.
When statically stabil aircrafts are disturbed by any outside or inside forces (gusts, hitting control column etc) it  creates a restoring moment which returns aircraft to its initial position. That makes aircraft easier to fly.  Unstable aircrafts however tends continue to move in the direction of disturbance. So if a gust hits the aircraft and increases the AOA slightly, the aircraft continues to increase its AOA by itself and snap out of control eventually. That’s why you need flight control computers to stop any uncommanded movements.
The picture you show illustrates a neutrally stable aircraft, which means that it does not show any reaction to disturbances and maintains its disturbed position. Some aircrafts are designed that way to increase its maneuverability, reduce trim drag and increase fuel efficiency. Check out that link for a comparison of stable and unstable fighter aircrafts and how they behave during maneuvers. Some of these aircrafts are dubbed under different names such as relaxed static stability instead of calling them unstable or neutrally stable aircrafts in order not to freak out the masses.
Stability of aircraft is very closely related with CG position. As a general rule moving CG forward makes it more stable and moving aft makes it less stable and eventually unstable if gone out side of CG limits. Normally you won’t intentionally move CG out of limits but there are accidents which caused that. For example in this Boeing 747 accident at Bagram, payload got loose and moved aft of the aircraft uncontrollably during takeoff and aircraft become extremely unstable that no control input would be able to recover it.
These all are static stability. The dynamic one is another beast.


Where do countries under international sanctions find spare parts? Some countries are being touched by American or European sanctions. Such sanctions affects the possibility to import spare parts for American-made or European-made aircrafts (e.g. Iranian F14 and Venezuelan F16 or Puma). Yet these countries still have their aircraft flying.
Where do the sanctioned countries find their spare parts?
Do they still follow the required MRO process?

The consequence of sanctions on Arpartheid South Africa was a thriving military equipment sector with some remarkable products, including nuclear weapons. Simply put, other people are clever enough to find equivalent solutions to US engineered parts and only when a super expensive fab costing billions is needed will they need to downgrade their specs. But don't think that sanctions will in the long term keep other countries from owning fancy equipment: They will learn to build it themselves.


How can I combine flight training hours flown under various legislations in a single logbook? I am a European citizen and last year I went to the US to start flight training. I got my student license and did my FAA private written exam. I logged about 78 flight hours with a flight school.

I also flew several times with an FAA authorized instructor but I never logged those hours because I was flying part 141 and since my flight instructor was under part 61 I was afraid I could not log those hours. I do not have a private license because I had do go back to Europe.

Now I'm back in Europe but I have the chance to fly at Christmas with an instructor in the US (not a flight school). Could I log these hours on my logbook I had started in the US?

And how can I combine my US and European logbooks?

Based on what you've written, the main issue for you is TSA approval. As a foreigner, you can't receive initial flight training in the US from any school or instructor unless you have a TSA approval in advance. And you need one approval per school or instructor: if the TSA approved you for flight training at a 141 school, you can get training from that specific school only. To use another 141 school or a part 61 instructor, you would need a second, separate approval.

But, assuming that you do have (or can get) the TSA's approval then you can log the training time as usual. The instructor must endorse (sign) your logbook as described in 14 CFR 61.51(h):

  (h) Logging training time. (1) A person may log training time when
  that person receives training from an authorized instructor in an
  aircraft, flight simulator, or flight training device.

  (2) The training time must be logged in a logbook and must:

  (i) Be endorsed in a legible manner by the authorized instructor;

And your question about multiple logbooks has already been asked.


When is the autopilot engaged and disengaged? When does the pilot engage the autopilot during a flight? And when does he disengage it - e.g. at what height - during the descent?

I am a B777 pilot. On departure, we generally hand fly until about 10,000' to keep up our skills. If the departure procedure is complicated, we will ask for the AP on at 200' so there is no chance of messing up the departure procedure.

On approach I typically disconnect the Autopilot at about 1500' AGL once visual contact is assured and I am inside the Final Approach fix.

If there is any chance of a possible missed approach due to weather, or other conflicting aircraft, on the runway or elsewhere, I will leave the AP on until there is virtually no chance of a missed approach.

Most of the pilots I fly with tend to do the same.


What are the regulations for non-aircraft targets in airport movement area? In the movement area at a controlled airport, I would assume any airworthy aircraft is automatically eligible to make requests to enter into, exit from, transit through movement areas, for the purpose of aviation related activity.

What about the other ground vehicles and pedestrians? Do they need some  special permit, or can simply make requests like a crew member?

Ground vehicles are really problematic at an airport. The problem is not so much a matter of regulation as a problem that the people driving the vehicles sometimes are unfamiliar with flight processes so they create hazards without really understanding the danger they are creating. The "regulations" are that nobody is supposed to be on taxiways or runways without approval whatever that means, but since the FAA cannot revoke the license of somebody that does not have a license, it's a toothless rule. Also, the typical runway intruder does not even have a radio, so getting approval is problematic for them. Cops are the worst offenders. I have seen some very dangerous situations evolve from ignorant cops with no idea what they are doing just driving onto runways acting like they are god or something.

The main way the FAA interfaces to the ground control problem is to publish a lot of safety guidelines hoping that somebody will read them. Some airports have elaborate safety training for ground personnel, but the main risks usually come from untrained personnel at smaller airports where there is little or no training.

This is one of the main reasons why most airports work hard to get good fencing set up, so some bozo does not drive onto the runway.

In general, ground control takes care of authorizing vehicle movement and utility trucks are supposed to coordinate their actions with ground control. In untowered airports, utility trucks are supposed to call on CTAF to notify nearby pilots what they are doing, but unfortunately most do not have radios. Once I was landing and there was some truck on the side of the runway because the guy was removing a turtle or something. The truck had flashing lights so it was easy to see luckily.


Which type of control gives a more agile missile, tail or canard? I read somewhere (sorry don't remember where) that canards controls for missiles are more effective than tail controls.  Is this true, and if so, why?

Since the control unit sits at the tip of the missile, it is simply more practical to control it via canard deflections. The rear part can then be made as a simple pressure vessel with fixed fins and a nozzle.

If the rear fins would have to move, their actuators would either be in the way of the nozzle flow or would stick out on the outside - in both cases performance would suffer. Also, long cable runs along the side of the missile would need to be added.

By controlling the missile with the forward fins, any change of direction will be direct, whereas control via the rear fins means that the rear end of the missile would initially move away from the desired direction, until the change in attitude would move the missile towards its target. Thus, the canard will result in a more agile missile.


Should I log flight time as a passenger? If I only have a private pilot license, and am not the pilot in command, should I log my flight time?

If so, what are the limits of this? i.e. is that as true in the backseat as it is in the front seat? Must I have that type rating?

No, you should not*.

In my opinion, you should limit your logbook to records of your own flight experience. This would include any time spent training, as PIC, or as required crew.

The time you can log as PIC is that which you spend as the sole manipulator of the controls, the sole occupant, or as the pilot in command when the required crew is >1. Here's an article from an FAA FSDO describing the logging of PIC time in more detail. Rod Machado has some good coverage of this as well.

If you're just hanging out in the airplane, it doesn't matter if you're in the front seat or the back seat. If you're receiving instruction, you should get an entry and a logbook endorsement from the instructor you're flying with. Most General Aviation aircraft don't require a type rating, so I'm unsure what the context of your final question is.

* It's worth noting that you can technically put whatever you want in your logbook, though it's not a great idea; when it comes time to fill out an FAA 8710 form for later ratings, it can get confusing. In my opinion, you still shouldn't log any time, but if you're just wanting to record flights that you took with friends, that's fine. As an instructor who's had to slog through some weird logbooks, I'd really, really encourage you to track that elsewhere, though. Your logbook is exactly that - it's your logbook, for the logging of your flight time, and a record of your flight experience and training.


Should time in turbojet aircraft be logged as complex? I was having a discussion with a colleague about what aircraft qualify for logging complex time. We were discussing whether or not time flying transport-category turbojet aircraft qualified as complex according to the regulations. It's probably irrelevant at that point in a career, but my interpretation is that turbojet aircraft are not complex. 14 CFR 61.1 defines a complex aircraft as one having a retractable landing gear, flaps, and a controllable pitch propeller. It goes on to give some provisions for control computer or FADEC, but it still mentions propellor controls. In turbojet aircraft you just set the throttle, even if there are a lot of computer-controlled variables changing in the engine.

While it's not a jet, the Daher-Socata TBM 900 single-engine turboprop airplane has a single throttle quadrant and an automatically controlled propeller. It's still considered complex under the regulations even though there's no lever to adjust the prop and it's still complex. I give this example only because it has a single throttle lever and is still complex.

I'd love to get more interpretations on whether turbojet aircraft are technically complex according to the definitions of 14 CFR 61.

Complex ratings apply only to aircraft with propellers, so any kind of jet aircraft is by definition not complex.


What is the most 'environmentally friendly' way to learn to fly? As this question indicates, I've been thinking recently about the environmental impact of flying (since when automated cars are the only means of ground transport, aviation will be responsible for most greenhouse emissions).

So, as an amateur, novice pilot, I would like to know which is more environmentally friendly, learning in a glider or learning in a single engine prop (Piper Tomahawk, Cessna and the like)?

At first it seems obvious, the glider doesn't have an engine while the latter does. But if we assume the launch method of the glider is tow rope, this would be powered by a single engine prop, using more fuel than it would if it wasn't towing, plus the climb is the most fuel-expensive part of the flight anyway, leading me to think there might not actually be that much difference.

Clarification on this issue would be greatly appreciated.

Here are some options for flying in an environmentally friendly way:

Use an electric trainer: Since last year the all electric trainer aircraft Pipistrel Alpha Electro has FAA certification. Assuming the batteries are charged with renewable energy, this would mean no greenhouse gas emissions at all (excluding manufacturing). It will probably still take some time until larger all electric aircraft with higher ranges are available, but Airbus has already started research.
Use a glider with a winch: Assuming the winch is powered by renewable energy, this would also result in no greenhouse gas emissions. While winch launches are less common in the US, this might change in the future.

If you use a glider with tow plane, it will depend on how long you can fly with the glider. Assuming good thermals you could stay in the air for quite a while, which would easily be better for the environment than a single engine prop plane. But for training (where you would presumably want many takeoffs and landings), I agree with you that the tow plane would now use more fuel because it has to drag the glider along.


Why use an airplane with non-retractable landing gear for aerobatics? I'm watching footage from Red Bull Air Race 2017 in Kazan (one example is

            ) and clearly at least some of the airplanes used have non-retractable landing gear.

I was under impression that non-retractable landing gear increases drag and also makes the airplane larger which is hardly good for application where maneuverability and speed are important.

Why are planes with non-retractable landing gear used in such competitions?

As you mentioned, drag is one of the reasons why retractable landing gears are used in the first place. But in order to use it, there are way more considerations than just drag.

Scale: Size of the aircraft plays a big role here. Big aircraft have more room to keep the retracted landing gear. This is an issue as planes get smaller.
Weight: Retractable landing gears not only require more space, but they impose more weight
Cost: They add extra costs in installation and maintenance.
Application: High speed applications justify a retractable landing gear for a more aerodynamic shape. Does the present situation really need the application of a retractable landing gear?

These are some considerations that go into it, but not all of it. In the case of a high performance sports plane (like in the video above):

Scale: the planes are small. The retractable landing gear systems (system) need a lot of space. This is not what we want in a sports plane
Weight: A high percentage of the overall weight is taken by the system. This in turn increases the inertial forces* and decreases the overall maneuverability.
Cost: It is expensive to install. And it may cost even more due to the low volume requirements.
Application: More than high speed, high maneuverability is needed.

* Inertia is the tendency of a body to stay in the existing state of rest or motion. So inertial force is the force that keeps the body in its existing state of rest or motion.

[EDIT]
Based on a very good response below (from @Devil07), I am adding this important point here (just for a better overview of all important aspects):

Complexity: Retractable landing gears are complex piston mechanisms. Eventually it adds to the cost of installation and maintenance of the system.


What suits best for lateral controllability at high Angle of Attacks- a vortex generator or wing slots? At high angle of attacks, the prominent problem is the separation of airflow. And if this airflow separation is near ailerons, we lose lateral controllability.
And the solution is making the flow turbulent.
By adding slots in a wing at correct positions, we are capable of re-energising the flow. It is the same thing a vortex generator does (I presume).
But what device is best suited for the current case?
From an unknown source, I found:

At high angles of attack, the airflow over the ailerons can be separated from the surface. Vortex generators, positioned just forward of the ailerons, are designed to re-energise the boundary layer and help to prevent this separation. This makes the ailerons more effective at high angles of attack

(I do not how effective this reason is.)
And therefore, please consider the case of Leading Edge Slats (which creates a slot) too. At a high angle of attack, a LE slat helps by re-energising too. And If we have a turbulent flow (by employing LE slats) in the early stage, (I think) it is better than the case where we put vortex generators near ailerons, which may encounter an already separated flow.
Edit: The aspect of lateral controllability dictates the conditions where one wing can be at higher AOA than the other. Will Slats not fail to provide the desired effect due to its symmetrical effect (increasing CLmax simultaneously for both and stalling one of the wings and making into a spin)?
Does the "symmetrical effect" apply to VG and slots near the aileron too?

Vortex generators can be used at the leading edge to energize flow and delay separation.  They are widely used as an add-on device to improve low speed behaviour of a range of light aircraft, and in that usage they have a similar effect to a slot or slat in that they both increase stalling AOA and improve aileron response in the stall. I call them "poor man's slats".
However, slats are able to energize the boundary layer to significantly higher angles than leading edge vortex generators.  As an add-on, VGs are great, but if your objective was to maximize AOA at stall, you would go with a slot or slat.  A VG might raise stalling AOA from 15 to 19 or 20 degrees, whereas a slat/slot is good to the mid 20s.  Similarly, a VG can increase a wing's Clmax by maybe .3 to .5, whereas a slat/slot adds about 1.
To answer the question specifically, for maximum benefit for lateral controllabilty at the highest AOA possible, you would use a slot/slat. VGs would be a second choice, unless your objectives were more modest, in which case if they do the job, they would be a much cheaper and simpler solution.
There was a period back in the 40s when leading edge slots in front of the ailerons were popular as a way to maintain aileron authority through the stall (Globe Swift, Stinson, etc). Later, designers just included sufficient wing washout to achieve the same goal without the manufacturing hassle and drag, and fixed slots disappeared.
Modern transport airplanes and specialty STOL airplanes will use slats across the full span to increase stalling AOA and maximum lift the wing can make, as opposed to just improving aileron control.  Same with leading edge VGs, although the benefit is only about half.  On light twin engine airplanes, VGs have miraculous benefits for single engine performance.


Is it better to have the engines center or apart on a plane? Are there any advantages or disadvantages to having the engines closer or farther to the center of the plane?

How is the ideal engine spacing determined length or span wise for performance?

Related: How is the center of mass controlled in planes with multiple tail engines?

the further apart the engines are, the worse becomes the yaw in an engine-out situation. but spacing them (and their fuel tanks) further apart along the span of a wing allows more even distribution of load stresses.


Is reducing V1 a viable option for pilots when the ASDA is shorter than the ASDR? Let's say you were planning to ferry some passengers and cargo in a jet but after some calculations found out the ASDR (Accelerate-Stop Distance Required) was greater than ASDA (Accelerate-Stop Distance Available) of the only runway available in the airport. Can you address this situation by lowering V1 speed for the flight and thus shortening the ASDR?

This question has a context. People discuss the effect of a runway length on V1 on this post and seem to agree a runway length has no bearing on V1. In other words, however long runway you may have for your takeoff roll, if an engine fails after V1, you should continue the roll and take off, not the least because you never know you might be able to make a full stop without a runway excursion.

Granted what they say is true, is it as well not permitted to plan a reduced V1 speed for the runway whose ASDA is shorter than the ASDA for a maximum takeoff weight flight of the day?

Yes it's a viable option, but it must be approved by the manufacturer.

Lowering V1 requires lowering the thrust as well. Because high thrust at a slow V1 means the rudder won't have enough control to counter the thrust asymmetry when an engine fails. Low thrust equals low Vmcg, which can be the lower-limiting factor for the V1.

This reduced thrust setting (derate) can't be overridden in case an engine quits.

It works for short runways and contaminated runways and may allow higher MTOW, see here:

https://aviation.stackexchange.com/a/36068/14897
https://aviation.stackexchange.com/a/32290/14897

Another trick is the opposite: to increase the V-speeds (again, must be approved). It's called "improved climb". This only works if the limiting weight is the climb limit (not the field limit).

By increasing the V-speeds you get a better climb gradient for the same flap and thrust setting, i.e., there can be two sets of V-speeds for one flap setting, e.g., Flap 15, and Flap 15 Improved.

(Boeing)

RE: Is it really the case that a runway length does not affect V1?

Runway length affects V1 only indirectly and not always. In the takeoff performance calculation there isn't a graph or table to lookup that links length to V1. Headwind, cold weather, and high ambient pressure are some of the factors that make a runway longer than it actually is (performance wise).

The first step in performance planning is calculating the corrected length. From there there are three limiting weights: field, climb, and obstacle clearing. The lowest of the three will be the limiting weight of the day.

If the takeoff weight will be lighter than the lowest, then reduced thrust can be used to save on engine wear, for example.

Once the weight is known, then the V-speeds are checked. If the weight is between the climb and field limits, then the aforementioned improved climb calculation can be used (if approved). Likewise for the field limit and using derate.

In other words, the corrected length only affects one of the three weights: the field limit weight. Which may not be the limiting factor. If it is the limiting weight, then yes length affects V1, but it usually isn't for the big transport planes.


Why do reciprocating aircraft engines have more than one spark plug? Most reciprocating aircraft engines have two spark plugs per cylinder. What are the reasons for this?

Bold Method has a great post today about why aircraft engines have more than one spark plug per cylinder. There are a few basic reasons.

Reliability

Having two sparks plugs is more reliable. If one spark plug becomes inoperative for some reason, there's a second to provide the spark for the power stroke.

It should also be noted that the spark plugs are usually powered by dual, independent magnetos or, in some cases, an electronic capacitor discharge ignition. The redundancy of the ignition system adds to the reliability.

More Power

Having two spark plugs means the flame ignites from two points leading to more power per power stroke. This point is demonstrated during run-up. When the magneto check is done the engine RPMs drop when running on a single mag and set of spark plugs.

Even Combustion

Two sparks plugs and a two flame front leads to a more even burn of the fuel air mixture for a smoother running engine.

Prevent Fouling

Aircraft engines burn leaded fuel which can lead to getting lead deposits on the spark plugs. Having dual plugs leads to a more complete burn which can prevent the deposits from forming.


How can I correct an expected climb rate for density altitude? If a flight manual (for a naturally aspirated piston engine plane) gives a figure for a best climb rate at standard temperature and pressure, is there a way to adjust that figure for a different density altitude?

(I'm thinking there must be, but I can't find such a formula anywhere. Assume the same speed, weight, etc.)

That depends on what the POH for your specific aircraft includes. For example the POH for the PA-28 Warrior has a correction chart for calculating just that. In this case you need to use pressure altitude and local temperature (which combine to density altitude anyway).

Its important to use the POH for the specific aircraft as things like engine modifications, installed propellors and other changes to the airframe can greatly affect the numbers. These changes may only be reflected in the POH for the airframe its self and a copy found elsewhere may be inaccurate. Correction charts and your POH may also include pertinent information about operational limitations during a climb as well.


Why can’t we perform CONFIG 1+F Takeoff in the following conditions as per the MEL? I was reading in one of my company notices that we can’t perform  config 1+f takeoff on the Airbus A320 if we have the following faults.

SFCC SLAT CHANNEL FAULT
ADR 2 FAULT
IR 2 INOPERATIVE

Could someone explain the reasoning behind this?

First of all SFCC1 regulates the engines idle, lo or hi, according to the Flaps/slats configuration, for instance to provide low idle at initial descent

Also SFCC1 uses the blue hydraulic circuit for Slats, in hydraulic emergency case, only blue might be available as being generated by the RAT
  therefore SFCC1 fault is a no go, SO I assume at takeoff SFCC1 is available

SFCC1 uses primary ADIRU1 so if ADIRU1 is also faulty we go into a no go condition

Now if ADIRU2 is faulty, SFCC1 should rely on a single airspeed data, therefore if the speed is incorrect premature automatic retraction of the flaps might occur at takeoff, that is going from 1+F to 1 automatically, so take off with configuration 1+F is prohibited with these faults at takeoff


Why does the static pressure inside the cockpit vary from outside static pressure? When the static ports are blocked, pilots use the alternative static soure and it measures the static pressure inside the cockpit. And it is said that the static pressure inside is lower than the outside static pressure. I wonder why does this happen? Because you know cockpit is blocked from outside and how does the venturi effect applied inside the cockpit and static pressure inside?

You're referring to this statement in the Pilots Handbook of Aeronautical Knowledge, Page 7-12:

  Some aircraft are equipped with an alternate static source in the
  flight deck. In the case of a blocked static source, opening the
  alternate static source introduces static pressure from the flight
  deck back into the system. Flight deck static pressure is lower than
  outside static pressure.

The reason for this error with alternate static source is that the air flowing around the airframe creates a slight vacuum inside the airframe, thereby lowering the barometric pressure and generating erroneous readings in the pitot-static system.


Why do airplanes lift up their nose to climb? Is it right that basically an airplane just needs to accelerate to climb?

Greater velocity of an airplane leads to greater lift - and since its weight remains constant (or even decreases) - a greater lift leads to a gain in altitude without the need to pitch. But why do airplanes climb by "pointing the nose up"? Is it to climb as fast as possible and to need less horizontal space?

A climbing aircraft needs less aerodynamic lift than in horizontal flight, not more.

Now I have your attention, I hope. The reason is quite simple:

Lift equals weight, and just because the pilot choses a different flight path angle, the weight of the aircraft does not change. The total of all lifting forces must still balance the weight, but in climb you get a small lifting contribution from the engine(s) because its (their) thrust will point upwards just like the rest of the airframe.

Don't let the many arrows and greek letters confuse you. To be in equilibrium, lift (L, dark blue), drag (D, red), thrust (T, green) and weight (m⋅g, black) must add up such that they can be combined into a closed run of vectors. I've done this with the lighter-colored vectors around the weight. Since the flight path points upwards, so does the thrust which now has a small vertical component. The lift vector can be a little shorter now.

Consider the extreme case of vertical climb: Now all thrust supports the weight, and aerodynamic lift is no longer needed.

There is a second, much more subtle effect: When you climb, air gets thinner and engine performance goes down proportionally. At the same indicated air speed, the aircraft will continually decrease its climb speed, and this deceleration frees up a tiny inertial force, which again adds to lift and counteracts weight.

Conversely, at the beginning of a climb phase the aircraft needs to create momentarily more lift to accelerate itself upward. Only then, when climb speed increases, lift must be bigger than weight to overcome the inertial effect which at this moment works downwards. For the supernerds: If you integrate the lift deficit over time of the aforementioned effect and the extra lift over time for climb acceleration, both cancel exactly.

To answer your question directly: To climb you need to increase excess energy, not speed. This is normally done by increasing engine power output, or by trimming the airplane at a lower speed where drag is less, so more power remains for climbing. This question contains more details on how to get an aircraft to climb. Note especially @SteveV.'s bucket analogy.

If you use the airplane's kinetic energy as its source of thrust, the same mechanism can be applied to instationary climbs, where speed is traded for altitude, like in gliders.

The nose-up attitude is simply the result of a different flight path. Since the required aerodynamic lift will be almost the same, the angle of attack will also be almost the same and the whole aircraft needs to fly nose-up. This is similar to a car which has the same attitude towards the road, but when you drive uphill, both car and road will be tilted upwards.

This analogy breaks down when you change speed - flying at lower speed needs more angle of attack to still create the same lift, and this nose-up change will be added to your attitude angle.


What should a pilot do to perform a successful emergency water landing? What should a pilot do to perform a successful emergency water landing, also known as ditching of a big commercial jet?
Is there any checklist, or best practices, like "elevate the nose" or "retract the landing gear", to make it safer?
Are commercial Jets buoyant?

ditching http://www.flightglobal.com/blogs/wp-content/uploads/mt/flightglobalweb/blogs//learmount/Ditching.jpg

What should a pilot do?

Follow the checklist?

  Is there any checklist?

There are many such checklists in the intertubes and whole books have been written on the subject

Here's the start of one for 737s

For comparison, here's one for a Cessna light aircraft

  Are commercial jets buoyant?

Yes, initially, if substantially in once piece. We know that because several intrepid pilots have tested this idea (obligatory hat-tip to Sullenberger).

It makes sense that the fuel tanks in the wings, especially once emptied of fuel, are buoyant. The wings are obviously capable of supporting the fuselage. The fuselage is a pressurised tube and should be buoyant too, until the passengers and crew start making large holes in it.


What happens if a commercial airplanes navigation system completely failed during a flight? What would happen if all of the the navigation systems (such as GPS & INS) in a commercial aircraft completely failed?

Could the aircraft land safely without all the navigation aids?

The possible answers to your question are for all practical purposes infinite depending on the details of the system failure, the weather, where you are, and crew experience, to name a few. However, as a thought exercise extremely unlikely to ever happen in reality, let's play with it a bit.

First, let's define the navigational systems failure to be such that we cannot determine our position by reference to instruments in the cockpit. What have we got left? If we can still communicate, others can work with us to determine our position and develop a course of action.

The simplest case would be if we were talking to ATC, were in an area of secondary radar coverage, and our transponder was still working. If that were the case, it would be a matter of getting radar vectors to wherever we wanted to go. If I were the captain, I would want to go to the nearest suitable airport since if I had had a failure of everything that could tell me in-cockpit where I was, I would be worried about possible further failures.

If talking to ATC and in an area of primary radar coverage only or you also had transponder failure, they could give us a series of turns to identify us (used to do that back in the 1960s occasionally).

If you were out of range of VHF communications with ATC, you could try getting a relay via another aircraft that was in VHF range of ATC. Two aircraft at altitude can talk to each other at far greater distances than an aircraft to a ground station. A simple call to any listening station or aircraft on 121.5 requesting assistance will almost always get a response.

If VHF communication is not possible, you could try getting a patch through to ATC on HF radio. My favorite back in the 1990s was Stockholm radio. These days, however, SATCOM is available. I don't know anything about it, but I imagine it provides the ability of an aircraft anyplace in the world to be patched through to an appropriate ATC facility.

So, if you're talking to ATC (by whatever means) but you're out of radar coverage, what then? Every captain would remember generally where he was prior to the failure. It could be as simple as someplace in the North Atlantic and eastbound. He could simply tell ATC that and that he will fly a westerly heading. ATC would clear the altitude he was at and look for him along the westerly limits of their radar coverage for when he inevitably would show up. Actually if it was the North Atlantic and it was nighttime, he could just follow any airplane in front of him. They're easy to see stacked out into the distance.

The general idea would be to get to where you could be seen by ATC, and go from there. Anymore, there aren't a lot of areas along regularly traveled airline routes over land in North America and Europe where above 30,000 ft an airline flight won't be seen. That was true back in the 1990s, more true now I am sure, and increasingly true through the world, especially if military radar can be utilized..

The more interesting problem becomes that there is a loss of communication as well as a loss of navigational ability. The possibilities here are limitless. A simplification would be to say that what you would do would be to take up a heading that you believe will get you to where you could visibly see a land mass with airports, and land at the first suitable airport you see. Most airline flights are along routes that the crew is very familiar with; they know what they've been flying over many times, and that would be a help.


Aerodynamics of Flight Control Surfaces From what it appears to me, flight control surfaces seem to be taken for granted. In terms of how they actually work and what kind of physical outputs they give in terms of forces and such.

Take for example the elevators of a Boeing 777, if the pilot wanted to pitch up, the elevators would move up. What are the physics behind this? Is it air being deflected thus a change in momentum occurring to pivot the aircraft's tail down or is the angle of attack changing due to the moving nature of the trailing edge? or both?

I am quite interested to know because I want to simulate Aerodynamical forces in a game I plan to make soon. Diagrams would also be useful but not required. Thanks in advance.

Thankfully, aerodynamics in the usual flight range is linear.

Therefore, there is a gradient of lift over angle of attack and another one over the flap deflection angle. Both are constant over a range of maybe ±15° and can be combined. The angle of attack is referenced to the fixed part of the flight surface and the deflection angle to the moving part relative to the fixed part.

Another parameter which influences lift is the camber of the flight surface. Positive camber produces more lift at the same angle of attack. Deflecting a flap changes this camber, and its effect can be linearly added to that of the angle of attack.

  Is it air being deflected thus a change in momentum occurring to pivot the aircraft's tail down?

Yes, when a flap moves, the angle of attack stays constant but the camber of the flight surface changes, thus producing a change in lift. In your example, a trailing-edge up deflection decreases camber, the surface produces less or negative lift which produces a moment around the center of gravity.

And yes, lift is produced by deflecting a stream of air.

Things get more complicated and interesting when the aircraft leaves the angle of attack range in which aerodynamics is linear.


Ventral masts- what are they? I have kids working on a model of a Boulton Paul Defiant, a WWII-era fighter plane. When we found images of this plane, it shows two rods sticking vertically down from the belly of the plane. Some of the images show them to be quite long-- the plane would have a hard time landing if they remained that length! After doing some searching, it seems like these are called "ventral masts". What are these for? Do they retract for landings? Thank you!

Normally, those masts are located on the upper fuselage and sometimes on the wings. They are used to string antennas between them and other airplane parts, or are antennas themselves.
In case of the Boulton-Paul Defiant, those antenna masts could not be located in the upper hemisphere in order to keep the field of fire of its gun turret free. Together with the Blackburn Roc and the Hawker Hotspur, those airplanes had a unique layout for a fighter with a single pilot and a gun turret placed behind the cockpit. How well this idea turned out in practice can be read in this answer.
In case of the Defiant, those antenna masts were made retractable to allow take-off and landing. The antennas were needed for communication and navigation.

The different antennas on a Grumman TBF Avenger (picture source).


Where are the flap track covers on this wing? I don't see it has covers for the flap tracks, so,where are the covers for the flap tracks?

Image taken from the English for Aviation book (Oxford).

The aircraft is a Vickers VC10

From the Vickers VC-10 repair manual:

General arrangement of VC-10 wing (picture source). Note the labelling of the Shock bodies as "flap rail fairings".

The flap tracks were inside the Küchemann bodies and the flaps were between them. This produced gaps between the five flap segments which made them less effective than the modern design of uninterrupted flaps with the flap tracks below them.


What is the effect of flow separation on lift, pressure distribution and drag? Consider an airfoil (a wing) in an airflow. When angle of attack increases, at some point the flow start to separate from trailing edge. By increasing the angle of attack more, this separation area increase toward the leading edge up to stall condition which must be avoided. We know that it will cause to reduce the lift and increase the drag suddenly.

But i don't remember what was the exact reason behind this. Whats the magnitude of pressure inside separated regions of flow (wakes)? is it higher or lower than normal flow patterns before separation occur?

I read (for example here) that separation increase 'Pressure Drag' as the pressure inside wakes are lower(?) and we get a more net back force comparing front side and back side of the airfoil:

  In aerodynamics, flow separation can often result in increased drag, particularly pressure drag which is caused by the pressure differential between the front and rear surfaces of the object as it travels through the fluid

But if this is true, then how could we say that this lower pressure in upside of the airfoil decrease the Lift? as the lift is produced from pressure difference of top and bottom of the airfoil.

Note: i can explain the reason using newton third law and change in flow directions. but not sure about exact pressure profiles.

You need to distinguish between boundary layer flow and outer flow.

Separation means that a parcel of low energy air moves with the wing (here the pressure is about -0.2, expressed as a pressure coefficient). For the outer flow, the contour of the airfoil changes to one of the original airfoil plus the parcel of separated flow. Since this is on the rear upper side of the airfoil, the airfoil "looks" thicker and longer, effectively presenting to the outer flow a body of less camber and angle of attack.

This in turn will reduce the suction in the region of attached flow right past the nose, where normally a high suction peak produces both lift and nose thrust. With a reduced suction peak, the airfoil produces more drag and less lift.

Viscous and inviscid pressure distribution at 12° AoA, calculated with XFOIL 5.4. The dashed lines show the inviscid pressure distribution where flow separation does not happen, while the solid lines show the viscous pressure distribution with separated flow over the last 20% of the upper side. The lines around the airfoil contour show the boundary between the boundary layer and the outer flow. Separation thickens the boundary layer, substantially altering the shape around which the outer flow streams.

The altered airfoil shape causes a reduction in the effective angle of attack, so both the suction on top and the pressure on the bottom are lower. This means that separation causes lift loss; once separation starts, the lift curve slope becomes flatter and can reverse (which indicates a full stall).

In the sample shown above, only on the last 12% of the upper side would separation cause pressure to be lower than in the inviscid case. Note that pressure on the bottom is also lower, so the difference between both (which causes lift) is quite unchanged by separation. Without separation, viscous and inviscid pressure distribution are quite similar, therefore the inviscid distribution is a valid first-order approximation of the viscous pressure distribution without separation.

The reduced suction peak at the nose and the higher suction on those last 12% is what causes more pressure drag. Note that the area around the suction peak points forward and that near the trailing edge points a little backward (especially at high angle of attack). This means that less of the nose thrust pulls the airfoil forward and also there is less pushing from the pressure near the trailing edge.

To estimate the drag increase due to separation of the full airplane configuration, assume a drag increase as if the lift would increase linearly, without separation taking place, including induced drag. Combine this drag with the "real" lift, including losses due to separation, and you will arrive at a surprisingly realistic lift-to-drag ratio of the aircraft between separation onset and stall.


Can we use ECI coordinates for an airplane? It is taught for navigation systems (like an airplane) on Earth we us ECEF (earth-centered, earth-fixed) and for space systems (like a satellite) we use ECI (earth-centered inertial). But why is ECEF exclusively used for navigation vehicles on Earth and ECI is exclusively used for satellites and spacecraft in space?  Why can't we use ECI for an airplane to observed another perspective?

The basic reason is the goal in navigation.  For an airplane it is to deliver the aircraft to a particular destination on the earth's surface, potentially also avoiding certain areas fixed to the earth's surface.

If you do all your navigation calculations in ECI, you then have to keep track of the earth's rotation to translate that to a point on the surface.  If you do all the navigation in ECEF, then that translation is unnecessary.

Both methods are mathematically valid (for ECEF, you have to have some method of removing or ignoring the non-inertial frame effects like Coriolis; for ECI, you have to keep track of earth rotation).  I don't have any direct evidence, but I suspect that since ECI was not an option historically, the current solutions are robust and no one is looking to create a radically different method for unknown benefit.


How do fighter jets communicate with an intercepted plane that's lost comms? RAF Typhoons were scrambled today to intercept an Antonov 26 that lost comms, triggering a sonic boom over London.

The flight was escorted to Stansted airport, and the answer at What's the point in escorting a threatened flight with two fighter jets?
 says they "guide" the rogue jet to the airport.

How do they actually do this? Once they've established the jet is not a threat, how do they communicate with the other pilots?

I have an image in my head of them writing ← 120° (etc.) on a little whiteboard :P

This is covered in the FAA's AIM, Chapter 5, Section 6. The UK has similar procedures.

First, the standard guard frequency is 121.5 or 243.0 MHz. If you aren't listening to this frequency and get intercepted, you should start listening.

Methods like LED signs or possibly as whiteboard as you suggested can also be used. Otherwise, they maneuver their aircraft to send standard signals. See the guides above for details on the signals sent by interceptors and how they should be acknowledged. Basically:

You have been intercepted, follow me

Interceptor: Rocks wings (and flashes lights irregularly at night)
Intercepted: Same

You may proceed

Interceptor: Breakaway, climbing turn away from aircraft
Intercepted: Rocking wings

Land here

Interceptor: Circling airport, lowering landing gear, overflying runway (landing lights on at night)
Intercepted: Lower gear, land

The intercepted aircraft can also send signals. The interceptor will respond with one of the signals above.

Designated airport is inadequate

Intercepted: Raise gear, flash landing lights

Cannot comply

Intercepted: Switching on and off all lights, but distinct from flashing lights

In distress

Intercepted: Irregular flashing of all lights

In the case of the Washington, DC Special Flight Rules Area (DC SFRA), there is a Visual Warning System (VWS) of red and green lights that will let the pilot know that they shouldn't be there. The pilot is supposed to turn directly away from the center of the SFRA. If they are in contact with ATC they must advise that they have been illuminated by the system, otherwise they should contact ATC on a guard frequency and identify themselves.

Of course, an interceptor can't force an intercepted aircraft follow instructions. It goes on to explain what will happen if you don't follow those rules, which probably apply in any situation where the risk is too high:

  Further noncompliance with interceptor aircraft or ATC may result in the use of force.


Is there any part of a flight where the pilot would pitch down? Would the pilot ever pitch down (even slightly) during a flight, or would he/she simply reduce power to reduce altitude?

This question is not similar to Why do airplanes lift up their nose to climb? (asked by Chris) for it the reasons aircraft pitch up. This question is looking for an answer that explains if and when a pilot pitches down during a flight to reduce altitude, the very opposite of the question of @Chris.

The most common case to pitch down is to speed up, not to reduce altitude, for example when transitioning from a climb (at climb speed) to level flight (accelerating to cruise speed). You can transition to level flight by reducing thrust, but that'll leave you level at climb speed, and is usually not what you want.

Changing configuration will usually require pitching changes to maintain stable flight. In particular during the approach-to-landing, extending the flaps will substantially increase the drag, and in order to maintain airspeed, you'll need to pitch the nose down. If you don't, you'll bleed off airspeed and potentially eventually stall unless you overpower the drag with thrust.

There are of course unusual circumstances that will require a pitch-down as well, obstacle avoidance for example (e.g. airplanes). As mentioned in the comments, to make a speedy descent you'll probably also want to pitch down (such as in case of pressurization problems or fire on board).