Could I hold both an EASA license and a UK CAA license?

You may need to wait until the dust settles to see exactly what the regulations end up being but if the rest of the world is an indicator then yes you can hold licenses from various places at once. Licenses can in some cases be issued simply by applying and proving your currently issued one is valid (from somewhere) as is the case with the FAA but this will likely vary by jurisdiction.


For an airport to be designated as an IFR alternate, does it have to have a TAF?

tl;dr You don’t need to have a TAF at the alternate and can use other sources of weather.

Keep in mind that there are two reasons that an alternate is required. First is to assure that the pilot has evaluated the weather at the destination and considered what to do if the destination is unavailable. Second is to let ATC know what the pilot intends to do if they lose communication. In the modern ATC system, with near universal radar coverage, that isn’t as much an issue as when the regulations were written.

In the US, the destination and alternates must comply with 91.169. It specifically says that there must be weather reports or weather forecasts for the airport. Normally when you flight plan you would rely on the Terminal Area Forecast to determine whether the weather one hour before and one hour after the estimated time of arrival at your destination is above the minimums. If that is not the case then an alternate is required. And again you would rely on the TAF for the forecast.

However, TAFs are not the only way to get a forecast. NOAA publishes Graphical Forecasts for Aviation and if the weather for the area is above minimums, you could use that as a means of satisfying the requirement.

Here is an example where the coastal forecast is below minimums but the airports inland will be VFR.

Or you could look at airports around the alternate and if they are above minimums, then your alternate would be as well. In the TAFs below, there are lots of airports that inland that do not have TAFs but that you can surmise that they will be VFR.

In practice, picking an airport with a TAF as an alternate is much easier. There is no requirement that you actually go to the alternate if you can’t make the destination. And with ADSB-In, you can monitor the weather while you fly, so you have a much better idea of what the weather is doing at your destination. You can divert to an alternate at any time it doesn’t look like the weather at your destination is below your personal minimums.

§91.169   IFR flight plan: Information required.

  2) Appropriate weather reports or weather forecasts, or a combination
  of them, indicate the following:

  (i) For aircraft other than helicopters. For at least 1 hour before
  and for 1 hour after the estimated time of arrival, the ceiling will
  be at least 2,000 feet above the airport elevation and the visibility
  will be at least 3 statute miles.

  (c) IFR alternate airport weather minima. Unless otherwise authorized
  by the Administrator, no person may include an alternate airport in an
  IFR flight plan unless appropriate weather reports or weather
  forecasts, or a combination of them, indicate that, at the estimated
  time of arrival at the alternate airport, the ceiling and visibility
  at that airport will be at or above the following weather minima:

  (1)
  If an instrument approach procedure has been published in part 97 of
  this chapter, or a special instrument approach procedure has been
  issued by the Administrator to the operator, for that airport, the
  following minima:

  (i) For aircraft other than helicopters: The
  alternate airport minima specified in that procedure, or if none are
  specified the following standard approach minima:

  (A) For a precision
  approach procedure. Ceiling 600 feet and visibility 2 statute miles.

  (B) For a nonprecision approach procedure. Ceiling 800 feet and
  visibility 2 statute miles.


What is the most simple plane lift equation that gives realistic solutions?

First, you need to add the effect of density $\rho$: Air density changes with altitude, and this affects both lift and drag (at least if you model airbreathing engines).

For lift $L$, use $$L = c_L\cdot\rho\cdot\frac{v_h^2+v_v^2}{2}\cdot S$$

For drag $D$, you should only simplify the equation as much as possible. Your equation is simpler still and doesn't model the increase in drag with more lift. The simplest practical equation will look like this: $$D = \left(c_{D0} + \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)\cdot\rho\cdot\frac{v_h^2+v_v^2}{2}\cdot S$$

More lift will need more thrust and will limit the upward acceleration. Climbing higher will reduce thrust in proportion with density and limit the possible speed range.

Nomenclature:
    $c_L \:\:\:$ lift coefficient (normally between 0 and 1.5)
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing (ratio of span to mean chord)
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor (use 0.8 when in doubt)
    $c_{D0} \:$  zero-lift drag coefficient (use 0.02 when in doubt)


What aerodynamic data exists for the Yak-130?

The Yak-130 has a maximum g-loading of +8g to -3g and is capable of executing the flight manoeuvres specific to current operational and developmental combat aircraft, including Su-30, MiG-29, Mirage, F-15, F-16, Eurofighter, F-22 and F-35. This aircraft is of classical swept-wing and empennage monoplane design and light alloy construction with carbon-fibre control surfaces. Kevlar armour protection is fitted to the engines, cockpit and avionics compartment.
Flight angles of attack < 40°.
Speeds:
– level flight, maximum   1 050 km/h
– takeoff (full fuel load)    200 km/h
– landing 195 km/h

Side lift and flight envelope is kind of hard to come by, but I got this information from https://thaimilitaryandasianregion.wordpress.com/2015/10/25/yakovlev-yak-130/.
I would also recommend http://www.airforce-technology.com/projects/yak_130/ as another source to look through. Hopefully I was of any help to you in writing your essay.


Was destruction of SR-71-related tools really extraordinary?

was there any legitimate reason for it?

Unused tools, the tools for making a plane which isn't made anymore, are most probably put somewhere in storage, since the factory floor is best used for actual production.

While an aircraft plant for making top-notch, spyplanes is generally quite secure, any storage facility is probably less secured. Maintaining a high-security level for a storage facility seems like spending good money for a not awfully good purpose.

So in order to prevent the tools for the secret planes being stolen from a run-of-the-mill storage facility, it is much more secure to have them dismantled.

Note, that the SR-71 was produced in a time, where 24/7 surveilance was not as common as it is today. I suspect, that setting up a high-security storage facility would involve a lot of guards guarding basically junk-metal. Guarding scrap metal also doesn't seem to be an awfully motivating task for the guards.


What is the technical term for ARINC 429 data injected into a heartbeat stream going to an LRU?

ARINC 429 is both an electrical bus standard and a data standard.

The electrical standard defines a unidirectional, one to many (Tx to Rx) serial data bus that is transmitted using bipolar Return to Zero (RtZ). This makes the signal self clocking. If no data is being transmitted, the line stays at 0 VDC (Null) which consequently removes the clock as well.

Since there is only one transmitter on a line, there isn't any "injection" of data onto the bus by another source.

The ARINC 429 Data standard uses the serial bus to transmit packets of information, called labels. These labels are 4 bytes (32 bits) long.

An ARINC 429 receiver is designed to expect a constant stream of labels to update the receiver's internal data within a certain time limit. If a label isn't received within the specified period it is considered stale and is left to the receiving LRU to decide how to handle stale data.


Are warnings generally "source-focused" or "effect-focused"?

They are source focused. They display precisely the condition that exists, not the follow-on effects.
WARNING indications that could be dangerous if not acted on right away are Red.  Indications that must be taken into account with some action but are not an immediate danger are called CAUTIONS, and are Yellow.  Indications that just indicate a status condition, like a loss of redundancy which does not degrade function but needs to be addressed on the ground, are Status messages, and are White.
Most indications are just exceedances of some parameter above or below a limit, like an idiot light on your car.
Examples:
"GEAR BAY OVERHEAT" would be a red WARNING that tells you that the temperature in the landing gear bay exceeded a certain temperature.  Not necessarily that there is a fire.
"L ENG LOW OIL PRESS" would be a red WARNING that tells you the oil pressure dropped below x psi.  Not that the engine is about to blow up from lack of lubrication.
"R SCAVENGE EJECTOR" would be a yellow CAUTION indicating that the output pressure of the scavenge pump in the right fuel tank is below X psi. As a Caution, it needs to be acted on in some way, but it's not a danger right now.
The protocol is, a message tells the pilot exactly what condition was exceeded or what failed.  What to do about it is found in the Quick Reference Handbook that is usually stowed at the base of the center console where both pilots can reach it.  It's a binder with a tall narrow page format, with all of the  Caution and Warning messages cataloged by system, and a logic flow chart presentation for each with a procedure for each CAUTION and WARNING that is to be followed, that is meant to be easy to follow in a dark cockpit while under stress.
Only a small number of WARNING conditions expect the pilot to deal with the condition from memory.  These are called "Memory Items" or "Immediate Action Items", and you're expected to be proficient and doing steps A B C D immediately from memory.  The QRH is consulted later to perform an expanded procedure when safe to do so. There might be half a dozen or a dozen WARNINGs that have memory items that need to be performed as soon as the warning appears, and you have to have nailed down in your mind so your hands just fly around automatically when they happen.
For example, an engine fire on takeoff has a series of Memory Items, done as a standardized drill: thrust lever to idle (with a protocol where each crew cross checks and confirms the actions), thrust lever to fuel shutoff, Fuel and Hydraulic Shutoff button push, Fuel boost pump off, Fire Extinguisher Push if the fire indication hasn't gone out, and so on.  For  that sort of thing, you drill those sequences until you're blue in the face and can perform the steps without having to think about them, while under intense pressure and distraction.
Another one would be a depressurization event.  After the crew gets their masks on and establishes communication with each other through the mask mics, you declare "emergency descent", slam the thrust levers to idle, pop flight spoilers fully out, dial the autopilot altitude select to 10000 ft, engage autopilot speed mode, causing the plane to pitch over to maintain the speed with the thrust removed, and dial the speed setting to maximum operating speed (Vmo).  Those are the memory items. Once settled down in the descent with the autopilot holding the airplane in a shallow dive at redline speed (if you think something structurally is compromised after a "big bang", company procedures may advise staying at current airspeed in the dive instead of accelerating to Vmo), the non-flying pilot gets out the QRH and you go through the expanded depressurization procedure together.
Messages will generally be prioritized when multiple messages appear, and lesser importance ones filtered out when a lot of conditions are set. And a lot of messages are inhibited during the takeoff process because they can wait.
WARNING messages will often be accompanied by CAUTIONS, but multiple WARNINGS are unusual.  Getting multiple WARNINGS in a situation where you are already surprised by seemingly nonsensical activity (like trim wheels spinning madly for no apparent reason) can push you toward brain lock unless you've trained yourself, or have the right instincts. Boeing thought that the trim wheel spinning madly for no reason could be dealt with using the Stab Trim Runaway procedure, but stab trim runaways don't generally include the trim running wildly, then stopping, then starting again, then stopping again.
At some point you have to just ignore all the data and just fly the plane.  But that's pretty tough when the plane is trying to dive itself into the ground seemly possessed by a demon, in addition to all the garbage being presented as messages.  It's not hard to imagine anybody going into brain lock with that kind of data explosion combined with bizarre behaviour.


Where can I find the transition altitude in different countries/regions?

Asia

Hong Kong: 9,000 feet

Africa

South Africa: fixed and to be at least 1000 ft above the highest ground within 25nm radius of an airfield (AIC 20.2)

Europe

Belgium: 4,500 feet (AIP Part 2,, ENR 1.7.2)
Netherlands: 3,000 feet (IFR) / 3,500 feet (VFR) (AIP Part 2, ENR 1.7.1.1)

Oceania

Australia: 10,000 feet MSL (AIP ENR 1.7 (2.1.1))
New Zealand: 13,000 feet AMSL (CAA CAR 91.425)

North America

Canada: 18,000 feet (SOR/96-433 602.34)
United States: 18,000 feet MSL (14 CFR §91.121)

South America

Argentina: Depends on terminal airspace
Brasil: Depends on terminal airspace
Chile: Depends on terminal airspace
Colombia: 18,000 ft (SAM/IG/12-NE/23)
Ecuador: Depends on terminal airspace
Paraguay: 3000 ft (SAM/IG/12-NE/23)
Perú: Depends on terminal airspace
Uruguay: 3000 ft (SAM/IG/12-NE/23)
Venezuela: Depends on terminal airspace


What does the indication "ATC" in some Take-Off Minimums mean?

I believe I have found the answer to my own question, while examining the records of a meeting held by FAA concerning this subject ( source ). It clearly states:

  [ AERONAUTICAL CHARTING FORUM Instrument Procedures
  GroupMeeting 17- 02 –October 24, 2017 ]
  When ATC crossing altitude restrictions require a climb gradient on a SID, it is proposed to establish a single climb gradient that would allow compliance with all ATC restrictions. These climb gradients would be
  identified on the chart as ATC climb gradients. Rich explained how the aircrew should treat each climb gradient differently. An obstacle climb gradient should be treated as a plane that the aircraft cannot ever penetrate from above, that is, the aircraft must always remain above the climb gradient’s surface. Conversely, an ATC climb gradient only represents the average gradient needed to meet the crossing restriction at the fix where it’s established. In this case, the aircraft’s altitude between the point where the climb starts and the point where the altitude restriction is established is not that important, provided the crossing is made at the fix at (or above) the minimum charted altitude. The purpose of the ATC climb gradient is to inform the pilot of the necessary performance needed to comply with the altitude restriction. The working group suggested that a SID should be limited to one obstacle climb gradient, and if necessary, one ATC climb gradient. Further, an ATC climb gradient and the associated crossing restrictions should be eligible for cancellation by ATC when not needed or when aircraft performance is limited.


Is there any regulation to ensure that life jackets and safety cards are on-board?

The FAA has a similar requirement (commercially under part 121)

  (a) Except as provided in paragraph (b) of this section, no person may
  operate an airplane in any overwater operation unless it is equipped
  with life preservers in accordance with §121.339(a)(1) or with an
  approved flotation means for each occupant. This means must be within
  easy reach of each seated occupant and must be readily removable from
  the airplane.

  (b) Upon application by the air carrier or commercial operator, the
  Administrator may approve the operation of an airplane over water
  without the life preservers or flotation means required by paragraph
  (a) of this section, if the air carrier or commercial operator shows
  that the water over which the airplane is to be operated is not of
  such size and depth that life preservers or flotation means would be
  required for the survival of its occupants in the event the flight
  terminates in that water.

In other words they are only actually required (per FAA regulations) when operating over water so not every plane (route provided) technically needs them. However many airplane seat bottoms may double as a personal flotation device so many planes are equipped with them by the nature of their construction.


How is the FPA (flight-path-angle) computed?

The flight path is a path defined with respect to the ground. Therefore, the flight path angle must be computed with the ground speed:

The flight path angle $\alpha$ is calculated by the on-board computers with:

$$ \alpha = \text{arctan} \left( \frac{V/S}{\text{GS}} \right) $$

The source of the ground speed would in general be aircraft dependent, but for an airliner this would come from the Air Data Inertial Reference System (ADIRS). See also How is the actual ground speed of an airliner measured?

Some non-precision approach charts will also have a table with required vertical speeds for various ground speeds to maintain the target flight path angle. This is particularly helpful if your aircraft cannot fly a given FPA itself. This is an example from Amsterdam Schiphol (EHAM) VOR Approach for runway 09:

If you e.g. fly with a ground speed of 150kt on this approach, you would just dial in 800ft/min and you would get the desired 3° FPA.


From Aerodynamic view, what is the advantage/disadvantage of the Akagi Kaman K-Max Helicopter?

It's a twin rotor design, counter-rotating: no resulting torque on the airframe and no tail rotor needing to be powered. The twin rotors do not share a common shaft, with all of the extremely complicated control mechanisms that these require.

From J. Gordon Leishman, Principles of Helicopter Aerodynamics, section 2.15:

  The design advantage of a twin rotor is that all power can be devoted to providing useful vertical lift and performance. However, the two rotors and their wakes interact with one another, producing a somewhat more complicated flow field than is found with a single rotor, and this interacting flow incurs a loss of net rotor system aerodynamic efficiency.


Why aren't bird radars placed on the front of commercial aircraft?

There really is no such thing as "bird radar".  Radar comes in a few frequency bands that have certain advantages depending on the distance, resolution and attenuation you need out of it.  The band isn't the only factor here as the band will dictate what size dish you need and your aircraft nosecone will but a distinct upper limit on that.  Weather radar is geared toward detecting rain drops and anything bigger than rain (hail, bugs, birds, etc) with reasonable distance and attenuation features (you want to penetrate into a storm).  Birds will show up on this radar, though depending on smoothing and processing algorithms you may need a flock of them before they get drawn on the radar, at which point they'll look like some rain.  A radar optimized to detect bird sized objects would probably use a wavelength that did not let you see things as small as rain drops and small hail.
Some other things to keep in mind are that the radar is not always on, and it should be off on the ground except during takeoff when needed.  The reason for this is that you do not want to be putting radar energy into people, and they tend to be in the way on the ground.  We only turned the radar on for takeoff when there was significant weather around the field and wanted to be prepared for requesting diversions.  Aircraft radar tilt can also be adjusted, so we wouldn't be looking at birds in front of us, but clouds above and in front of us.
Wit that said, our SOP on fields with known heavy bird activity was to takeoff with the radar on and pointed forward because someone had the idea that the birds didn't like being in the radar beam.  I have no sources to back that idea up, but it was written into our FOM.
Now assume you can takeoff and see a flock of birds on the radar.  Do you have enough time to do anything about it?  If so, what do you do, some maneuver away from them or do you turn into them in hops they take the evasive action?
Now back to the title question: Why aren't bird radars in the nose cone?

The weather radar can see birds, it would be redundant.
A bird radar (optimized for birds) would not be good at seeing weather, so where would the weather radar be placed?
In a real situation, what would a bird radar enable you to do with a positive detection with the time you have to react to it?  Probably not much.
Weather is a much more common threat than flocks of birds, so if you can only have 1 radar system, you want the weather radar.


Why do some companies perform their freight flights only during the night?

As the previous answers have stated, their schedules are determined by what best suits their needs. However, those schedules can be complicated by contractual and curfew requirements.

A contractual example: Thousands of expatriate Brits live in the south of Spain. They want their morning London papers. We would depart Stansted (just north of London) as soon as possible. We were contractually committed to have the load to Barcelona by 07:00 local, with huge penalties if we failed (the papers were worthless by noon), and then on to Palma de Mallorca. Hopefully by now, they transmit the papers electronically and print them locally.

A curfew example: A cargo flight departing Hong Kong bound for Chitose, Japan (refuel there then on to Anchorage). The old Kai Tak airport at Hong Kong had a 23:00 local curfew; Chitose had a curfew until 06:00 local. The solution to that was to depart Hong Kong just before the curfew, land at Taipei and park for a couple of hours (I forget the exact time), and then continue to Chitose to arrive just after 06:00 local.

All Japan airports at the time had a curfew from 23:00 local to 06:00. You could go out to the south end of the airport just before 06:00 local, and set your watch by the first arrival of what was tens of aircraft, both passenger and cargo, whose departure time was determined by the need to arrive as soon as possible after the airport opened


Do icing limits exist for parked aircraft?

I'm not aware of any limits every being published on transport airplanes.  On large aircraft, it's not too big a deal structurally because the bending loads imposed by a snow cover are not significant, since bending load applied by a couple of feet of snow (which weighs about 40lb/sqft) on such a large structure, designed to support 100+ lbs/sqft, is relatively mild.
On little airplanes, this can be a problem however.  Let 2 feet of snow, or 40 lbs/sqft, accumulate on a light aircraft or ultralight with large wings, designed to support maybe 5-15 lbs/sqft of negative load, and you will likely find the wing outboard of the strut is permanently bent down or has collapsed when you want to go flying.  Nature's just done a static load test on your wings and got carried away.
On a metal airplane, you at least take comfort in the fact that if the wing is not permanently bent down after you remove the snow, you're good to go.
On an airplane with wood spars, this is more of a gamble, because wood structures that are overloaded beyond the compression limit of the side in compression (the spar below the strut attachment bolt in the case of snow load) without overloading beyond the tension limit of the side in tension (above the strut attachment bolt, where it just breaks), can suffer from a dormant compression failure in the wood itself.
Compression failures are where the cellular structure of the wood fibres partially collapses.  This can leave the wood apparently undamaged (unless you can inspect the area to detect the tell-tale fine line across the grain), but weaken the wood in tension.  So when you go flying, and the wood below the spar attachment is loaded in tension again and has lost some fraction of its ultimate tensile strength, and you hit a bump that applies some extra G, whoops!
Anyway, if you own a light aircraft with wood spars you need to be aware of this and be extra vigilant about preventing large snow loads on the wings.  I'm not really keen on wood spars on light planes for this reason.  It's a reason you never buy a used Classic with wood spars that's had a wing tip repair (from the tip hitting the ground during a groundloop).  A friend bought an Aeronca Champ once and found his right wing had a wood compression failure above the spar bolt, caused by a wing tip strike, when he took it apart to recover it, after flying it about a year.  He was lucky; any significant negative G in that condition would have been fatal.
You could work out a limit for yourself if you know the wing loading and structural G limit for your own airplane. So if your wing loading at gross is 10 lb/sqft, and it's good for negative 2 Gs in flight, you can estimate that the wing can tolerate 20 lbs/sqft of snow accumulation, or about 1 foot thick and wouldn't want too much more than that to accumulate.


What is the takeoff thrust of a CFM56 engine?

Developing 21,600 to 33,000 pounds of takeoff thrust, the CFM56-5B is the only engine that can power every model in the Airbus A320ceo family.

Safran Aircraft Engines


What’s that weird sound during spool up on some aircraft?

That noise is almost exclusive to turbo fan engines.  If the air is right, turbo shaft engines can do it.
  On sudden and high power changes the big fan on the front is spinning at a different speed than the motor compressor.  Since the front fan is also the first couple of stages of the engine compressor, the air doesn't move cleanly between the two when they are not at the same speed, and make that sound.
The Navy S-3 made the same sound on power changes so it got the nickname Hoover.
@Rob,if you are close enough to it you can feel it.


Why do modern fighter aircraft still use transparent canopies instead of cameras feeding imagery to screens?

There is no major problem to be solved by moving the cockpit inside.

The canopy adds minimal drag, considering how much drag the whole of a fighter's airframe produces. It also offers the highest quality of vision.

To expand on the latter, let's define a few items that go into visual quality:

Field of view
Acuity, including in motion
Noise
Dynamic range
Reaction speed

The canopy's field of view is about half the sphere, while cameras can cover most of the sphere. A win for synthetic vision.

Good human vision (healthy young pilot) offers enough acuity to distinguish high-contrast objects down to about 0.1 milliradian in size. The best commercial video camera heads offer 4.5K*2K to 8K*4K resolution. To cover 12.6 steradian with 6 cameras, restricting each camera to a ~2:1 rectangle, somewhat correctable with an anamorphic lens... It's a textbook math problem, but we have the advantage of knowing it's not solved in a mathematically optimal way in real fighters using it.

For a "cube with overlaps" solution, which is viable for a fighter, the FOV of each camera needs to be about 1.6 radian vertically. This results in a best-achievable instantaneous resolution of 0.5-0.7 milliradian for Arri sensors or 0.4 for the RED (which has other drawbacks). These are commercial cameras that are miles ahead of the F-35's DAS, but indicative of what could be used in a fighter designed today and meant to fly in the 2040s.

This can be improved, 6 cameras are not some hard limit, but you're looking at 100+ to fully match the acuity of the human eye (a more accurate term than resolution, since the eye doesn't perceive the whole FOV simultaneously). At that point the system won't be reasonably compact and easy to add anymore.

At their maximum resolution, all cameras produce significant amounts of noise.  So does the human vision, but its noise is filtered out very well by the brain and almost eliminated in the macula. For small megapixel-chasing cameras, the noise is so heavy that their effective resolution is reduced several times. Above we assume professional cameras with full-format sensors. At any rate, camera+eye give more noise than just the eye.

The dynamic range of human vision, at 20 stops, is better than the best cameras at 15-16 stops, and much better than LCD at 10-12 stops (20 for OLED). But this is acceptable in daytime, and will mostly matter at night, where a fighter can rely on IR systems instead. The night-time performance of IR cameras, even though they lose a lot in resolution, gives synthetic vision a win on this.

For reaction speed, at their open gate resolution, cameras offer a best-case framerate of just 60. I won't copy the full math, but combined with a 60 fps display, this results in a minimum lag of ~40 milliseconds. This sounds acceptable at first. The real pain comes when you consider the motion resolution resulting from this low framerate.

To explain motion resolution, see how a moving picture looks on a display. This can be better demonstrated with a few illusions. Unless the motion is very slow, your motion resolution can drop from the camera's 8Kx4K to only 100-600 lines depending on the rate. In practical terms, you're going from discerning objects at 0.4 milliradian all the way to 2-10.

This won't matter much in level flight, but the moment a pilot with synthetic vision begins to maneuver, they will suffer major degradation of their vision. Video gamers learn to compensate by turning instantly and returning to a slow-moving image that can be seen at sub-1000 fps, but a plane doesn't do things instantly. Whether the ability to see while spinning will make a difference, losing it can affect pilot behavior just by trying to avoid that motion-induced blindness.

All in all, you've reduced the pilot's visual acuity, added noise, and greatly compromised their motion resolution - for what? We're not chasing Mach 3 anymore; it won't help against Mach 8 SAM. We've learned to make canopies stealthy through shaping and RF-reflective metal coating, so there's no need to shy away from one. We've learned to project images onto a transparent visor, so we can get the benefits of night vision and extra FOV without losing natural vision.

Most importantly, in the last 10 years we've also learned to protect data with authenticated encryption and send it fast over vast distances. So if things like best possible acuity, motion resolution, reaction speed, or tolerance to avionics damage don't matter much, there's no reason for the pilot to be inside the aircraft at all.


Is there a reason that commercial jets do not have a “dead man’s switch”?

Very intriguing question. I do wonder what it actually solves, though. Does it only solve the mystery of whether the very rare instance of incapacitation of the flight crew occurred? The Cockpit Voice Recorder does that if it is recovered. In the rare event that the CVR is unrecoverable, the dead man’s switch would only answer if pilot input occurred prior to a crash. How would it save lives? The pilot should already be in periodic verbal communication with Air Traffic Control.
On the other hand, a global monitoring system of the aircraft would make more sense. Each commercial aircraft already has transponders. In the US, each aircraft has ADS-b. This gives a nearly real-time position of each aircraft that can be tracked and archived. This would give searchers a better idea of where to search for survivors. Incorporating a 406 MHz PLB-style beacon into the Flight Data Recorder and the CVR would be even more advantageous in solving the mystery of what happened. Even an automated system that alerts ATC of when contact is lost with the transponder or ADS-b, or when the CVR or FDR 406 beacons were activated, or when the aircraft deviated too far off its filed flight plan, would be better than a dead man’s switch.
After all, in today’s era of modern telemetry and aviation security, would scrambling fighters be of any benefit to the passengers and crew on board while the aircraft is in flight? They would have no way of intervening to prevent a crash.
It’s only benefit would be to alert ATC of a terrorist highjacking in the event that the target were close to the airport. And, the overtaking of the cockpit happened in the last phases of flight. Now, the security of modern cockpits and heightened alertness makes the notification of ATC of a more likely.


A short(ish) version: for a tabletop computer or a laptop with Windows, any of the Microsoft Flight Simulator series will be fine. They are easy to use, and as you get better, you can add more and more realism.

If you want good graphics, these kind of games typically require quite a powerful computer, but a basic setup will get you started.

If I recall correctly, from MS FS 2004 onwards, you even get other planes flying around, and there is air traffic control you can communicate with via preset phrases.

MS should release a new version in the coming months, but I would remommend an older version, as one can probably find the a ta fraction of the price of the coming version(Amazon.co.uk less than 10£).

You should make sure the version you are about to buy is compatible with your Windows version. MS FS 2004 for example should run fine with Windows 10.

There is also X-Plane, I tried one years and years ago, but I recall it being not as easy to use. Flying I guess was pretty much the same: close enough for the real thing.


How do I calculate the total cruise power from the propellers accounting for the losses?

The flow leaving the propeller:

Contracts, as a function of distance behind the propeller. The impulse theory gives a contraction factor - for an idealised homogeneous outflow field. The contracted wake has a higher velocity than free stream.
Has a whirl component due to the drag of the blades.
Has propeller tip vortices in a contracting corkscrew field.

So if the aft propellers are far enough behind the forward ones, the aft propeller tips are unaffected by the wake of the forward ones.

If the aft prop counter-rotates, the whirl component from the front props will be removed. Optimal blade angle of the aft prop is different from that of the fwd prop, but the tips would remain relatively unaffected.

Picture above is from Leishman, which has a whole chapter devoted to rotor wake. There has been quite some research done on co-axial rotors for helicopters. There is some info and a link in this answer as well.

But I reckon you'll be in the right order of magnitude if you just compute required power as you would in an undisturbed flow, especially if you use ducted propellers which reduce the tip vortices.


Is it possible to determine a rotation speed (Vr) using other known V-Speeds?

From FAR 23.51 that covers normal, utility, acrobatic, and commuter category airplanes:

  For multiengine landplanes, VR,
  must not be less than the greater of
  1.05 VMC; or 1.10 VS1

So 110% of the Vs of a particular configuration works. (Do not use for flight.)

Note from @Pondlife: 23.51 has been superseded with 23.2115 and the quoted definition is no longer there.
Related: What makes V1 one or two knots less than Vr on this performance table?


Does the auto thrust at takeoff compensate for asymmetric engine characteristics?

@JuanJimenez's comments are correct. N1 (and the accuracy of EPR) are not indicators of a precise thrust force.

So to answer the title question, generally no, moreover the acceleration of each engine may be different, and that is why the pilots go through a stabilization step, where they apply some thrust, make sure they're responding in a sufficiently similar manner, then they proceed with takeoff thrust. The pilots will correct any yaw with the rudder, and any remaining effect could be similar to a very light crosswind.

Also see: How is thrust of engines on the two sides of an airplane kept exactly equal to prevent yawing? The same phenomenon due to wear and tear is discussed. It is trivial for the most part since there is a rudder.

Of course this affects fuel consumption in-flight as there will be a tiny yaw as well that needs to be trimmed out.

But don't take it from me, check the Airbus article, Engine Thrust Management - Thrust Setting at Takeoff.

  Every engine has its own performance level due to manufacturing tolerances. In addition, engine performance evolves with time due to wear and ageing. As a consequence, the acceleration profiles may slightly differ from one engine to another on an aircraft (fig.3), even if fitted with new engines.

  Similarly, the idle thrust can slightly differ from one engine to the other, moving the acceleration profile to the left on the graph (fig.4).

Earlier I said generally no, because there are always exceptions (never say never on the internet). The articles notes that the Trent engines of the A330 and A380 automatically manage the stabilization step.

RE notice: On old aircraft before FADEC pilots were manually adjusting the thrusts to be equal (...)

It's because before FADEC the link between each lever and engine was a cable, and each cable depending on its age and environmental factors, acted differently – different stretching, friction, set torque, etc.

With FADEC, this is no longer a problem. The same electronic command is sent. And depending on the target, e.g., x N1, this is what the engines aim for, regardless of each engine's age and the fact that exact N1 values don't mean the same thrust force. Pilots pre-FADEC, like pilots with FADEC, don't know the thrust that is being applied in lbf/kN.


Does an active pilot based outside the US require a flight review to maintain FAA currency?

FAR part 61.56 ( [U.S.]Flight Review ) requires a U.S.flight review (or authorized alternative - see below), for anyone operating an "N" numbered airplane within the U.S. (when using a U.S. certificate/or U.S. certificate based on a foreign certificate), even if that person is current in another country for which he/she also holds a certificate.

See also, FAR 61.75 (Private pilot certificate issued on the basis of a foreign pilot license.)

See also this FAA Legal Interpretation which relates to your question:
need for Flight Review for holder of U.S. cert based on foreign cert in accordance with FAR 61.75

NOTE: In accordance with FAR 61.56 there are various types of  pilot proficiency checks or practical tests, etc. that may be substituted for a flight review (i.e. see FAR 61.56(d)-(f))


Does the FlightRadar24 pose a risk to aviation security?

The data FlightRadar uses is provided by volunteers using commercially available ADS-B receivers. All it does is save the terrorist a couple of bucks buying an ADS-B receiver.


What is the maximum theoretical lift of a plane as a function of engine power and surface of the wings?

Your thrust equation is only valid for the static case (initial speed at infinite distance from the propeller is zero), and neglects the propeller's efficiency. For the flight case, I recommend to make a bold assumption for propeller efficiency and to assume that most power will be converted to thrust:

$$T = \frac{P}{v}\cdot\eta_{Prop}$$

A large, slowly turning propeller will have an efficiency approaching 90%, while a small, fast-spinning one will only reach 70%. If operated outside of its design speed, efficiency might even become negative. If you look for an upper boundary of thrust, the equation above sans efficiency will do nicely.

For the maximum lift answer you should expand your drag coefficient a little, as recommended already in this answer. $$c_D = c_{D0} + \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$

Now you can equate drag and thrust to get: $$P\cdot\eta_{Prop} = \left(c_{D0} + \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)\cdot S\cdot\frac{\rho}{2}\cdot v^3$$

and solve for lift: $$L = c_L\cdot S\cdot\frac{\rho}{2}\cdot v^2 = \sqrt{\pi\cdot AR\cdot\epsilon\cdot\left(\frac{P}{v}\cdot\eta_{Prop} - c_{D0}\cdot S\cdot\frac{\rho}{2}\cdot v^2\right)}\cdot\sqrt{S\cdot\frac{\rho}{2}\cdot v^2}$$

The minimum power is consumed when the ratio $\frac{c_L^3}{c_D^2}$ reaches its maximum. Expressed differently, this means that $$c_L = \sqrt{3\cdot\pi\cdot AR\cdot\epsilon\cdot c_{D0}}$$

Plugging that back into the lift equation I leave as an exercise to the reader.

As you can see, the answer really depends on the aerodynamic quality of your airfoil. The best you can reach with regular airfoils is a $c_L$ between 1.5 and 1.8, depending on Reynolds number. With slotted flaps this can be doubled, but $c_{D0}$ will go up substantially, so the best ratio $\frac{c_L^3}{c_D^2}$ can be gained with a clean airfoil.

Nomenclature:
    $c_L \:\:\:$ lift coefficient (normally between 0 and 1.5)
    $S \:\:\:\:\:$ Wing surface area
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing (ratio of span to mean chord)
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor (use 0.8 when in doubt)
    $c_{D0} \:$  zero-lift drag coefficient (use 0.02 when in doubt and 0.03 with a fixed gear)


Is an RT license required for EASA PPL holders?

EASA itself does not require a RT license (RT is usually legislated on national level), however, it gives the state issuing your license the possibility to include RT privileges as part of your license (item XIII in the license).

This is also the most common case, ie, your PPL will most likely include RT privileges, so you will not need an RT license in addition to this.

What EASA state are you planning to have your PPL issued in?


Is ultrasonic noise from small turbines painful to pets?

This answer lists a number of RPM values for different aircraft engines. A typical small turboprop engine, the PT6, runs its core at 45,000 RPM and the power turbine at 30,000 RPM, which should produce sounds in the ultrasonic region.

The picture below shows a cutaway of a PT6 (source); if you count the blades and take the result times 3 (the cutaway spans 120°), the high pressure turbine disc shows 54 blades and the power turbine 42 blades.

Each time one of those blades runs through the wake of a stator blade ahead of it, it will create a pressure change with a frequency of 30,000·42/60 = 21 kHz and 45,000·54/60 = 40.5 kHz. At idle power, the speed is a bit lower, but not by much.

So, yes, the dog might very well have heard a noise inaudible to humans.


Why would there be airflow from the back of a TAT probe?

This is a so called aspirated TAT sensor, optional on the Airbus. Air is being drawn through aspirated TAT sensors to ensure that they correctly indicate the temperature even when the aircraft is not moving.

Normal TAT sensors develop a bias when the aircraft is static.

This video gives a nice explanation.


Is it possible to change/repair an aircraft tire while in flight?

Accessing hydraulic lines & resevoirs is perfectly straightforward in plenty of aircraft -- the C-130 as one example.  With crew chiefs & their tools & spare parts on board, a temp repair on a hydraulic line would be possible. Highly unusual, but possible. Spare fluid is common enough to have on-board to replenish the resevoirs.

However, access to the tires... Nope.  I can't think of anything where you could do that, and it would have to be a designed-in capability. Typically, crew-accessible areas are pressurized, but where the wheels retract, aren't.  You have things like access to unpressurized bomb bays, and in unpressurized aircraft that's not a barrier, but still... If there are designs where the crew can access the tires in flight, I'm not picturing them.

As noted elsewhere, landing with a flat tire isn't typically a big deal.


Does the FAA have a best practice for highlighting memory items on a checklist?

The short answer is to use color in some way.

I couldn't find anything very detailed on this: there's plenty of general checklist information out there from the FAA, NASA, universities and so on, but nothing that goes into specific details on how to use colors, fonts or the other things that you mentioned.

There is an FAA report called The Use and Design of Flightcrew Checklists and Manuals that was part of the response to the Northwest 255 crash. Unfortunately it's from 1991 so some content is already dated, and it's aimed at part 121 and 135 operators with multiple crew members, but it's an interesting report anyway.

Their main recommendation on memory items was simply to reduce them as much as possible because memory is very unreliable compared to checklists, but again that's in the context of multi-member crews. As for design, layout, formatting etc., they did make some specific recommendations (see section 4.1 and Appendix A) and the most applicable one to your question seems to be the use of color-coding. They strongly recommended the use of color as a general method, e.g. headings in yellow for "abnormal" items and in red for "emergency" items.

Interestingly, the report says that at that time (1991) airlines resisted using color because of the costs of printing, but today it seems to be the generally accepted way to highlight critical checklists and items. However, each checklist provider has their own approach to coloring headers, text, blocks or even entire pages.

I don't think there's any such thing as a standard 'style guide' for checklists, so if you're making your own then you can obviously do whatever you want that works for you. But the 1991 report noted that most checklist problems were caused by missing or inaccurate items, so make sure you get the content right before you break out your paintbrushes :-)


What is meant by the term "Code on request"?

Yes, I think you're correct although the phrasing is unusual. The usual phrase is "clearance on request", which is used for IFR departures as explained nicely in this AOPA article:

  Experienced instrument pilots know that when they call to request
  their clearance, the controller may not yet have received it.
  "Clearance on request" is ATC's way of politely saying "I don't have
  it - I've requested it - you'll be the first to know when I get it!"

The only FAA reference for the phrase that I could find is buried in the glossary of the Pilot's Handbook of Aeronautical Knowledge:

  Clearance on request.  An IFR clearance not yet received  after filing a flight plan.

But as RalphJ commented, if this is a VFR scenario and you needed a class B clearance and transponder code then I assume that the controller said "code on request" to let you know that he was waiting for a transponder code for you, as you assumed.

It wasn't an instruction as such so you could just acknowledge it with "Roger" or whatever. See this question for more information on that.


Do any airbridges move vertically to match arrival/departure halls?

JFK's Terminal 7 (British Airways Terminal) had (no more) some gates with this feature. The terminal-side of the bridge moved vertically down for disembarkation, and up for boarding. You can see a photo in this post on flyertalk.com. Below is a comparison for the old/new systems:


What material is the B737 wing skin made out of?

Aluminum alloy 7178 on the upper skin
Aluminum alloy 7055 on the lower skin
Here is some technical information


Are there statistics showing the relationship between safety and the age of aircraft?

I could not find statistics, so I parsed the data available on https://aviation-safety.net/database. This site does have a statistics page, but it does not have an answer to your question.

I'm not a statistician so I'm sure there are much better ways to crunch and graph this data, but the raw data I found was:

The data includes 5075 crashes from the years 1919 - 2019.
The mean aircraft age is 15.58 years. This age is the age of the particular aircraft involved in the crash, not the "age" of the aircraft's type.

I did not normalize the data in any way, so take it with a grain of salt and except some skews and outliers (for example, a 75 years old DC-3 crashed earlier this year - https://aviation-safety.net/database/record.php?id=20190121-0). On the other hand, crashes in the early years will naturally skew the data, as every aircraft that crashed was new at the time of the crash.


What kind of failover system do Airbuses with side sticks have?

In case of a total electrical failure, the aircraft can still be controlled using rudder pedals and manual pitch trim.

The airbus EFCS (Electronic flight control systems) are configured as below:

Airbus EFCS; Image from smartcockpit.com

From Airbus Flight Control Laws:

  MECHANICAL BACKUP

  In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode.

  Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel.
  Lateral control is accomplished using the rudder pedals.
  Both controls require hydraulic power.

The A340 also seems to have a similar system. From the A340 Flight Deck and Systems Briefing for Pilots:

  Mechanical back-up

  • To sustain the aircraft during a temporary complete loss of electrical power.

  • Longitudinal control of  the aircraft  through trim  wheel. Elevators kept at  zero deflection.

  • Lateral control from pedals. Roll damping is provided by the Back up Yaw Damper Unit (BYDU).

A340 mechanical Backup system; image from A340 Flight Deck and Systems Briefing for Pilots

Note that this is given only as a temporary measure. Also, See How are fly-by-wire airliners controlled in case of complete electrical failure? and How does the Airbus flight computer's voting system work?


How different is ADFX/ARINC 664 router from normal Router?

The point of ADFX/ARINC 664 is that it is real time. That means the switch guarantees each type of message will be delivered in specified time according to its priority and allocated bandwidth.
For example the control computers probably need to know the inertial reference (attitude and speed) readings every 10 ms, so the switch can be configured to deliver one message from each inertial reference unit every 10 ms with at most, say, 2 ms delay (based on number of packet types with higher priority). And the switch guarantees that barring hardware failure it will deliver the messages within that delay always. That is a lot of logic on top of normal ethernet that just delivers packets on a best effort basis.
Additionally the logic also has to guarantee that if one of the units goes haywire and starts sending the packets faster than the allocated bandwidth, or starts sending jumbled packets, these errors won't interrupt any other communication going through the switch. If one inertial reference packet should be delivered every 10 ms, only one will be delivered even if the unit sends hundred of them.
And last there has to be a lot of integrity checking of the switch itself so if hardware does fail, the communication fails over to the backup network.
Since it is ethernet on the physical and data link layers, you can use plain ethernet switch for testing a component. But not for production and not for system test where you have to verify the traffic policing is set up correctly.


Is there a regulation that requires manufacturers to cover AD's for the life of the equipment?

The answer is basically no for aircraft not under warranty, but...

I've participated in numerous AD related activities on the OEM side, and I've never seen an AD with a commercial policy incorporated into it that dictated who pays for compliance, kits, or labor.

So strictly speaking, the aircraft operator is on the hook once an aircraft is out of warranty, but the OEM will normally have an internal commercial policy in place that its program office, customer support organization and spares organization uses as guidance on charges.

There is usually a Service Bulletin with a kit that has to be incorporated to terminate an AD and the OEM will decide whether to make the SB and kit available free of charge for some period of time when it's required to comply with an AD, for reasons of morality, politics and marketing. The commercial terms will be included in the Service Bulletin.

That is probably typical, but if an OEM is in a financially tight position and an AD's compliance is really expensive, the OEM may decide to make the operators pay for the SB and kit, or the costs related to a repetitive inspection, and take the heat by getting yelled at during operator conferences.

And sometimes, as in your case, if labor is significant, the OEM may also include a labor charge-back policy that will refund labor costs based on the estimated man-hours quoted in the Service Bulletin.

Sometimes operators include out-of-warranty "AD clauses" in their purchase contracts to avoid getting burned. And sometimes operators, especially those that may be looking for more aircraft, cut their own deals on the side.

Another factor is that, in order to get less onerous compliance terms or limitations in the AD itself (as I suspect in your case), the OEM may convince the regulator that they plan to proactively "campaign" a mod free of charge including labor charge backs, with a campaign completion date, and which may even include sending out dedicated teams to do the work (as with the Cardinal stabilator slot mod).  Sometimes this is enough to avoid an AD being issued at all if the regulator is satisfied that every affected aircraft will be fixed by a certain date.


What is the advantage of the two-part rudder and how does it work?

This is called Split Rudder and it provides redundancy. They run on different systems so if one fails, the other one can be used.

Here is a picture of a split rudder:

Split rudders also provide a finer high speed control, in that only the lower one moves at high speed, reducing the exposed surface area and therefore the control effect.

Very importantly, there is a structural benefit. When we use the rudder it imposes a twisting load on the vertical fin. By only using the lower rudder, when the aircraft is at high speed, we reduce the twisting moment and transfer that load to a bigger, stronger, part of the airframe. The principle is the same as why the outboard ailerons are disabled at high speed.

The patent information is here.


Will helicopter control inputs be reversed because of precession if the fuselage starts a rapid spin?

Short answer: no.

What are your flight control inputs?

Collective Pitch.
Cyclic adjustments to pitch and roll
Yaw / anti torque from the pedals, which control the tail rotor.

Let's take them in order.

Collective.  If the control inputs were reversed for collective pitch, you'd not be able to get the torque off by lowering collective (which is the usual response to a loss of tail rotor and the attendant upset it causes by loss of the anti torque function of the tail rotor being lost).  If the helicopter design reverses what the collective does, in terms of pitch increase or decrease, dependent upon the state of your tail rotor, nobody in their right mind will fly it.

Once again for emphasis: if you lose the tail rotor, you reduce collective pitch to reduce the torque, and thus the requirement for anti-torque (which is why the tail rotor is there in the first place).  Check the flight manual for your model of helicopter for further details on that in-flight malfunction / emergency.
Cyclic.  The control linkage between the cyclic and the means of tilting the rotor do not change if your tail rotor fails.  They apply their changes to the "tilt of the disc" as long as they are connected when you move the cyclic.

What happens as the fuselage beings to rotate (particularly if the rate of rotation increases) is that the pilot is at risk of being disoriented by the rotation and making control inputs that make the situation worse.  (See above: first, reduce pitch, and find a place to put the aircraft down per the flight manual).  The rotation of the fuselage does not change control linkages, it changes the OODA loop for the pilot:  Orient/Observe/Decide/Act is a continuous process (loop) when flying such that you make a control input to make the aircraft do something based on your perceiving a need to change.

The problem with a control input made when you involved with the uncommanded rotation of the fuselage is that the pilot's aim point keeps changing.  That isn't a problem of precession, that's a problem of "getting behind the aircraft."  It's a cognitive, not a mechanical, problem to overcome so that this doesn't end in tears.
Yaw Pedals.  Per your problem statement, they don't work, so reversing control inputs isn't an issue.  Your feet are along for the ride.  Your brain and your hands get you to the ground safely, or not.  The way to deal with yaw is via the torque reaction to main rotor pitch: with power on and no tail rotor, changing collective pitch will tend to make the nose move one way or the other.  (Your flight condition: In cruise flight, in a hover, or in one of the many between states that a helicopter can be in will influence that).

The problem with the uncommanded rotation of the fuselage isn't some change in precession, it's the disorientation of the pilot whose reference line keeps changing as the helicopter rotates.  The whole point of being the pilot is to control the aircraft.  The pilot's objective in this case is to reduce the disorienting rotation by reducing collective pitch and flying the aircraft (lacking your anti-torque inputs) as you normally would.  You won't get increased precession (vis a vis the cyclic inputs) due to the anti torque control being lost.  Your rotor system has enough inertia if you keep it at flight rpm where at least that isn't your problem.  Your problem is in lag, and making control inputs that are out of synch with the (constantly changing) orientation of the helicopter.

Depending upon aircraft type and the situation, you will likely need to secure the engine(s) before final landing so that you don't create a rotating situation right before touchdown if you need to add collective while you still don't have the anti torque from your tail rotor.

Check your model's flight manual for the detailed procedures to handle a loss of tail rotor.


Cold air accelerated backwards provides forward thrust by reaction. What really matters is the amount of mass accelerated backwards. Its temperature is not important...

Concerning the 'percent of air sucked', it depends on the design. A pure turbojet doesn't produce 'bypass air', and a turbofan may reach a ratio of 10:1, that ratio being the relation between the mass of 'cold' air pushed backwards by the fan in a given time and the mass of air that passes through the combustion chamber...


Which aircraft/powerplant manufacturers use metric hardware?

All use metric dimensions, only the numbers look sometimes rather odd.

This statement is more serious than it might look, in some places you order parts in metric dimensions and they come as 3.175 mm or 12.7 mm.

All Russian (and, by extension, all former East Bloc country) engines use metric dimensions. You only see fewer of them.

I am less sure about French engines like the CFM-56 which uses a GE-designed hot section, but the fully French-designed engines use metric, too.

In the GA world the modern Diesel engines are all metric.


How do commercial airlines prepare for pilots falling sick during the flight?

do they fly in a pilot (like mid-air refuel)?

No, that isn't really feasible!

See answers to Can a passenger jet be towed to safety if it breaks down in midair?

  do they leave it to the co-pilot to take care of such situations?

Yes. In both normal and emergency situations, the co-pilot is able to fly the aircraft, navigate to a nearby airport and land the aircraft without the assistance of the senior pilot.

From Skybrary

  Here are some lines of defense:

  The remaining pilot must assume or maintain control
  Establish a safe flight profile and engage the autopilot; use all possible automation
  Obtain cabin crew assistance
  Inform ATC
  If on an extended-range twin-engine operations (ETOPS)
  flight, the remaining pilot or PIC must assess whether to continue
  the flight, return to the departure airport or divert. The decision
  is based on:

  Weather conditions at the destination or alternate
  Reduction of flight time if diverting
  Workload involved in single-pilot operation
  Familiarity with the alternate
  Condition of the incapacitated pilot
  Availability of medical assistance
  Overall safety of the flight

  Arrange medical assistance upon arrival
  Brief a cabin crew member to assist if required
  Complete the approach and landing using the autopilot as much as possible
  A partially incapacitated pilot should not be allowed to participate in the    subsequent operation of the aircraft, as
  judgment may be impaired
  After landing, seek immediate medical assistance

See also IFALPA - Pilot Incapacitation

  The remaining pilot must first assume command and maintain control of the aircraft. Furthermore the position of essential controls
  and switches should be checked, and in nearly all cases, use of the autopilot should be made and an emergency be declared.
  Use of the autopilot and priority of air traffic service are two obvious and effective ways of maintaining a tolerable level of workload.

  The second step is to take care of the incapacitated flight crew member. The grounds for this are not entirely humanitarian; if left unattended an incapacitated pilot can become a major problem and in any case is a major distraction to the remaining crew. Thus
  the incapacitated pilot must be moved out of the range of flight controls. In all cases, the advisability of removing a pilot (perhaps unconscious) from the seat must be dictated by consideration of the phase of the flight, the crew available, and the contours of the
  flight deck.

  Note: Consideration of the restraint and care of an incapacitated pilot dictates that cabin attendants are at least familiar with the
  operation of harness and seat controls

  Finally, and after the incapacitated flight crew member has been taken care of, the remaining flight crew should re-organise the cockpit work and prepare for landing. Details will depend on many variables including such considerations as the type of aircraft being flown, phase of flight, en route and terminal weather, and many others.

  How does commercial airlines prepare themselves for these kind of situations.

I imagine that it involves the usual measures

make pilots take regular medical tests.
make pilots responsible for reporting own or crew illness, fatigue etc.
prevent pilots eating the same meals in-flight.
write procedures for pilot incapacitation in-flight.
train flight crew to perform those procedures
review and revise the above based on experience of relevant events.

From what I've read, non-pilot flight-crew are often given very basic training so that they understand the basics of flight. For example Transport Canada requires flight attendants initial training to include a pilot-incapacitation drill, an understanding of aircraft parts including rudder, ailerons etc, principles of flight, etc etc.

  Do they specifically check if there are any pilots in the passenger manifest

I believe the airline staff would often be aware of any airline pilots onboard (e.g. dead-heading crew) but not of GA or military pilots flying as normal passengers.


How do commercial pilots keep situational awareness of their current call sign?

Some modern airliners have a place where the flight number can be displayed on the cockpit displays. This information can be entered off the dispatch paperwork when setting up the flight plan, and is displayed throughout the flight for easy reference.

For example, you can make out "DLH463" on the screen at the bottom right of this Lufthansa A380 cockpit photo, corresponding to Lufthansa flight 463.

The Boeing 787 has a similar feature:

  The two outboard displays are a fixed format that provides primary
  flight display information combined with an “auxiliary” display that
  consolidates frequently referenced information for the crew, such as
  flight number, each pilot’s microphone-selected radio and its
  frequency, and transponder code.

You can see this on this 787 cockpit photo at the top of the leftmost monitor: "FLT -> BAW787"

(Photos not embedded due to licensing restrictions.)


Is there an analytical description of the NACA 642-015A profile?

This report seems to include a reference to an analytical description of 6-series airfoils

On your second question: found this reference in Synthesis Of Subsonic Airplane Design by E. Torenbeek:

  A modification to the standard series is the A-series in which the sharp trailing edge angle is replaced by a larger one, resulting from straight contours which run from 80% chord backwards.

The paragraph contains a reference to "Theoretical and experimental data for a number of NACA 64-series airfoil sections" which turns out to be NACA LM R6J01


Velocity induced by a straight vortex filament

You need to think in 3D. A vortex will induce a flow speed everywhere.

That is the point  lies in the plane containing the flow induced by the vortex at

Why would you think that vorticity induces a speed only in one plane? You start from the wrong presupposition.
Now consider the rings around the vortex filament in your first drawing. All around those rings a flow speed is induced. Its magnitude drops with the inverse of the radius of one particular ring but is constant along the circumference of that ring. Actually, that ring is only a section through an infinitesimal tube, just as infinitesimal as that vortex filament.

Irrotational vortex. © Silver Spoon, picture source.
Also, the symbol for vortex strength is a capital Greek letter Gamma ($\Gamma$), not $T$.


Is there a list of part 121 and/or 135 operators?

I have not found a list, but you can search for an airline here.

There is a link on the page to definitions of the terms. Basically, "domestic" and "flag" are FAR 121 operations, and "commuter" is FAR 135 operations.

There is also an unofficial database here that will tell you which FAR an airline operates under.


What is the distance from an airport from which an airliner climbs above 550 m?

For the landing is quite easy.

Airliners usually approach an airport descending along $3^\circ$ slopes. This means that they will be 300m AGL approximately 5.7km before the runway threshold, and they will be at 550m AGL about 10.5km before the same point.

For the take-off the situation is a bit more complicated, as each aircraft will have a different performance. Taking a value of about 1000ft/min for the vertical velocity and 200Kts for the forward velocity (in aviation we use the imperial system, for a bit of background see here) we get similar distances to the above (it is a $2.8^\circ$ slope)

Note that these paths are more or less a straight continuation of the runway, particularly on the landing side (less so on the take off side).

Each airport has approach and departure procedures, you could try to have a look at those. They are usually published by Jeppesen.


How can I calculate the force on the nose gear at landing?

Calculating the loads on the nose and main landing gear isn't really different. The answer you linked is a highly simplified approach you should be able to use for the nose landing gear too, but I will provide a "less simplified" approach to calculate the vertical forces. The braking force is already greatly described there.

A simplified approach

First you need to know the impact speed and the spring and damping characteristic of your landing gear.

At touch down there are three possible cases:

Main landing gear touches the ground first. Then the airplane rotates down with an angular speed $\omega_L$. The impact speed of you nose landing gear is therefore $$V_{Impact} = \omega_L \cdot d $$ $d$: distance between the
main and the nose landing gear.
Nose landing gear touches the ground first. (For now empty, if I get time I'll write about it later)
Both landing gears touch the ground at the same time. For a glide angle $\gamma$ the impact speed will be: $$V_{Impact} = V\cdot \sin(\gamma)$$ $V$: airplane speed

The stiffness ($k$) and damping characteristic ($c$) of the landing gear depend mainly on the suspension and the tires used. Tires inflated with a wrong pressure can be really dangerous as they can increase the load on the landing gear.

Putting this data together into a mass spring damper model like in the image

gives you an equation for the nose landing gear movement: $$m\cdot \ddot{x}+c\cdot \dot{x}+k\cdot x = -m\cdot g$$
For the reduced mass $m$ in the model use the mass carried by the nose landing gear.
$$m = LM \cdot \frac{d-d_{CG}}{d}$$
$d_{CG}$: distance from the nose landing gear to the center of gravity

$LM$: aircraft landing mass

$g$: gravity constant

The initial condition for the differential equation is: $$\dot{x}(t=0) = -V_{Impact}$$
The impact occurs at $t=0$.

To calculate the force on the nose landing gear you just have tofind the maximum acceleration and add the static and dynamic loads: $$F_{max}=-m\cdot g -m\cdot \ddot{x}_{max}$$

Real world problems

While the calculations above works for really stiff wings, in reality the loads on the landing gear will be (probably) higher. This is due to the inertial forces of the oscillating aircraft structure.

If you don't understand where this forces come from try moving your arms up and down while standing: you will feel small forces on your feet. Now repeat the experiment with two 60t heavy wings as in the A380 and you'll see that the forces are not neglectable. And were do the oscillations come from? The same as with a guitar string: after a small excitation (plucking the strings/ landing impact) the structure (guitar string/ aircraft wings) begins to oscillate.

What other things doesn't this model take into account? Coupling between nose and main landing gear, rotation inertia, nonlinear tire characteristics,...


Why doesn't the US have a flag carrier airline?

The definition of a "Flag Carrier", although somewhat vague and frequently disputed, is generally accepted to mean: an air carrier that is owned by, or subsidized by, the government of the country of registration, especially for the purposes of flying international routes.

Wikipedia:

  A flag carrier is a transportation company, such as an airline or
  shipping company, that, being locally registered in a given state,
  enjoys preferential rights or privileges accorded by the government
  for international operations. The term also refers to any carrier
  that is or was owned by a government, even long after their
  privatization when preferential rights or privileges continue.

Business Dictionary:

  Airline ... registered under the laws of a country whose government gives it partial or total monopoly over international routes.

The US has no carriers in this category. All subsidizing of major domestic and international routes ended with the Airline Deregulation Act of 1978. (Note: there are still some small airlines and routes that are subsidized to serve very small communities... If you want to read more about this program, it's called Essential Air Service.)


At the point where the structural rigidity needed to overcome the vibration of a single enormous pulse train becomes so heavy that the aircraft can't fly anymore, replace the single large pulsejet with several smaller ones, whose individual pulses are smaller.

Conversely, imagine replacing a car's V8 engine with a single-cylinder engine of the same power.  It would need much stronger engine mounts, flywheel, clutch, transmission, etc.  (Single-cylinder car engines weren't that rare a century ago; good luck finding one today.)

But the main reason that large pulse jets are rare is their low fuel efficiency.  The bigger the engine, the more that matters.

See also: What are the pros and cons of a pulsejet?


Can two aircraft be allowed to stay on the same runway at the same time?

There is another scenario other than "line up and wait" that the other two answers cover...

A "flight" of more than one aircraft may be cleared as a group to take-off. This can consist of many aircraft sharing the runway during take-off (and even landing).

So you can have multiple aircraft on the runway when:

A "line up and wait" order is issued to line up on the runway after another aircraft takes-off or lands. This is usually done so that the departing aircraft can get prepared while waiting for wake-turbulence to clear.
ATC clears multiple aircraft as a "flight". The aircraft must be part of a coordinated group and a single aircraft is the "lead" aircraft for the flight that receives/coordinates with ATC for clearances. The entire flight group will enter the runway and take off in a pre-coordinated fashion.

There are specialized scenarios as well, for example during Airventure Oshkosh. Aircraft will be required to "land on the dot" and multiple aircraft may be on the runway for take-off at the same time, although ATC coordinates them so that they don't depart at the same time, they are asked to line up "on a dot" (a colored circle on the runway) and will then be cleared to depart from there.

As an extreme example:

116 aircraft lined up on the runway and cleared for take-off at the same time.


How much air does a 777-300ER's pressure cabin hold?

I once read it's about 1 metric ton (1000 kg) of air for a large widebody.

Here's a ballpark calculation to verify this.

The 777's cabin altitude is 2430 meter (8000 ft) when it's cruising at max altitude.

Wolfram Alpha tells us that a cubic meter of air weighs 0.96 kg at that pressure.

DimensionInfo shows that the 300ER is 73.9 m long and 5.86 m wide.

For simplicity, consider the 777 to be a perfect hollow cylinder.  The volume of the cylinder is:

$$\pi \cdot \left(\frac{5.86}{2}\right) ^ 2 \cdot 73.9 = 1993\: m^3 $$

So that's about 1900 kg of air for the cylinder.
You have to subtract a large amount for the air lost to non-pressurized volume, tapering of the cylinder, non-circularity of the fuselage, and volume not occupied by air (structures, furniture, insulation, wiring, luggage, passengers).

I'd guess it's somewhere between 1000 and 1500 kg.

Whether people are on board or not has very little influence.  People float or sink in water depending on having air in the lungs or not.  So the density of a human is around that of water: 1000 kg per cubic meter.  [In other words: you could fit 10 people weighing 100 kg in a cubic meter if you pressed them hard enough].  So the density of air is a thousand times lower than that of the passengers.  Three hundred people - weighing 30000 kg combined - displace less than 30 kg of air.


From what I have studied at my instrumentation course, it rotates and reads the angle between the current position and the reference position.

You then have several (3-4) of them around the fuselage because a roll maneuver (for example) will alter the measurements asymmetrically and in this way you can compensate for this effect.


What is the maximum taxi speed and who defines it?

And here, a Reference from Boeing's 737 FCTM (pdf). Ch2 for ground operations.


Do aircraft manufacturers produce their own black boxes?

There's seldom a reason for manufacturers to design and build their own black boxes. It's expensive to run a production line to design, build a test a few. It's just cheaper to get an agreement with a company to make them for you. The second photo below shows a popular recurring model from Honeywell, which appears to have been used on the A330, B737 and B777.

Opening the black box can be a sensitive operation, especially if there's the fear that the chips might have been damaged. It's better to send it to somebody who's done it before rather than trying to master it on the first attempt, especially if you don't have the resources. Airplanes accidents don't happen very often.

Note that the case you're referring to, the Aircraft also appears to have been built by Airbus in Hamburg, and hence the German Accident Board automatically gets involved as well, much like how the NTSB gets involved in all Boeing crashes.

(source: naij.com)

A smashed up flight data recorder.

(source: dailymail.co.uk)

A photo from the NTSB with the Asiana flight 214 recorders

Another reason for this is if there might be political motives behind the crash, it's preferred to send it to a third party for analysis which is less susceptible to bias or interference.

If I gather correctly, data on the flight data recorder won't be encrypted at all- it will be fed out as serial data, but you will need the devices and software to understand this information, and if the outside connection is broken, you'll need to work your way to the chips themselves.

(source: com.au)

Photo showing apparently how black box are 'read'.

Furthermore, sending it to the company is not always a good idea- they might have motives to change the truth, especially if it was caused by dodgy maintenance or bad training, nor to the manufacturer, if it was production error. The accident investigation board is the best people for this matter.


How soon can I start my turn after reaching the missed approach point, when missed approach procedure calls for a climbing turn?

Based on your question and the circumstances you indicate:

On an approach that takes you down to 200' HAT (height above touchdown) and specifies a climbing turn without a "climb straight ahead to [some altitude] then climbing right turn," you should climb to 400 feet AGL and then start your right climbing turn along the missed approach course track.

From FAA Order 8260.3C, Section 2-8 Missed Approach, paragraph 2-8-6 [pertinent portion]:

  "2-8-6. Turning Missed Approach Area. If a turn of more than 15 degrees from the FAC is required, a turning or combination straight
  and turning missed approach area must be constructed.

  Note: If the HAT or HAA value associated with the DA/MDA is less than 400 feet, construct a combination straight and turning missed
  approach (see paragraph 2-8-8) to accommodate climb to 400 feet above
  TDZE/airport elevation prior to turn."

========================================================================


What are the effects of the Boeing 787's very flexible wings?

From here:

  The amount of flex is really a product of the material. The wing requires a specified ultimate strength; with metal, that translates into a given amount of flex. This can be varied within limits, but it is really the material, its stiffness to yield point ratio, and its fatigue properties, that control how much flex you are going to end up with. CFRP is a very different material, and has much less stiffness for the same yield point, and has essentially no fatigue problems. This is beneficial in that it provides a smoother ride in turbulence; the wing acting essentially like a giant leaf spring. There is some lift lost due to the nature of the curvature, though. However, this is relatively small.


What is this tube connected to a 757 for?

What Mike said is correct, but I thought I'd add a little more.

The hose is technically called the "PCA Hose" which stands for Pre-Conditioned Air Hose. The hose supplies pre-conditioned air to the aircraft from a ground based unit, that is typically electrically powered and is usually mounted on to each jetbridge. The air can be cold or hot, depending on the needs of the day. The aircraft has a connection that feeds directly into the aircraft's air distribution mix manifold, which is where recirculating air is mixed with fresh pack air before being sent back to the cabin. The ground port connector port has an exterior door and an internal check valve to prevent pressured air from escaping in flight (the 757 actually has two internal check valves that are in series).

When the pre-conditioned air is connected to the aircraft, a small amount of it is sent directly to the cockpit and is 100% fresh (at least on Boeing aircraft), while the remaining PCA air is sent to the mix manifold where it mixed with recirculated cabin air before being released into the cabin.

The main reason to use pre-conditioned air is that it allows the crew to shut off the APU (and air conditioning packs) at the gate, which reduces fuel burn, emissions, noise and maintenance cost. When fuel costs went up dramatically in the mid '00s, there was a major push at airlines to eliminate APU run times, because it is much cheaper to run a ground based, electric air conditioner than running the mini-jet engine to produce bleed air. At the same time, there was also a push to ensure that aircraft were connected to ground electrical power as well, for the same reason.

There are some downsides of using PCA air. First, the hoses get a ton of debris in them and the hoses themselves breakdown internally. All of this debris gets blown back into the aircraft and clogs up the ducts and gaspers. This drives a lot of extra maintenance cost on the air distribution system, which didn't used to require much maintenance. Screens help some, but don't fully fix the problem. Second, ground crew tend to always use the max flow setting on the ground unit, and this can over pressurize ducts on narrowbody aircraft, leading to their failure (especially when the ducts are clogged).

Third, many crews/airports think that on a "hot day" you still have to run the APU, this is false and actually counter productive the cold ground air blows directly on the mix manifold's temperature sensor, so the airplane thinks the air is too cold and starts adding "trim air" from the APU to heat up the mixed air. So running the APU actually makes the cabin hotter, but then the ground crew thinks "since the aircraft is hot with the ground air and APU, imagine how hot it'd be with just the ground air!" I've seen this a lot more at airports where 85F is considered a hot day, as opposed to airports where 105F is considered hot.

Finally, there is a lot of infrastructure and maintenance that goes into all the ground equipment and at some airports, the ground units are actually diesel powered. So at the end of the day, using PCA air and ground power probably save some money, but it definitely isn't "free."

Edit: As to the reason the PCA hose pictured is coming from the ramp instead of the jetbridge, this has to with the infrastructure setup at each airport. There are many systems that can route the PCA air underground. I assume that most of these systems use a centralized plant loop with chilled water/steam pumped throughout the terminal, then use a heat exchanger at each gate. Take a look at the recent setup at SEA for more information: SEA PCA Centralization Project. This Cavotec brochure has some interesting information and graphics as well: Cavotec Brochure (PDF)


How can the Antonov AN 225 only have 2 nose wheels?

The reason An 225 has only two nose landing gears (for a total of four wheels) is that it was developed from An 124 Ruslan, which had pretty much the same arrangement. This works during normal operations as the MLG take up most of the load.

However, for loading/unloading, the wheels are not loaded- the nose landing gear is folded, while a support strut comes out, which provides the necessary support and load carrying capacity, as shown below (thanks to @Federico for finding the image).

Image from airliners.net

In this image, you can clearly see that the NLG is folded and the weight is supported by the struts.

Image from news.yahoo.com


Is there any disadvantage to having the de-icing system on?

The wikipedia article already linked in the question says:

  The system uses power from the engines, thus reducing their maximum performance. With the anti-ice system on, the highest altitude at which the overloaded aircraft could fly – without stalling – was reduced to 31,900 feet (9,700 m).

The de-icing system on most turbine aircraft (including MD-82 involved in that accident) uses bleed air from the engines, that is it extracts some air from behind the (low pressure stage of the) compressor. This air is therefore not ejected from the nozzle and not producing thrust, so the thrust is reduced. Or fuel flow rate increased if thrust levers are advanced to compensate, provided the engines are still below their maximum permitted thrust setting. Either way fuel consumption per mile increases.

Compressing air increases it's temperature, so this pressurized air is simply blown through tubes under the critical surfaces. There are other uses of bleed air, mainly pressurization and air-conditioning, but turning on deicing increases it's consumption significantly.

And note that this switching de-icing off and on was part of the accident sequence. It was only because they turned de-icing off that they were able to climb to FL330 in the first place.

It is also often not allowed to use de-icing when outside temperature is higher than some value because the heated surfaces could overheat.


Why an external RAT on this early propeller plane at Charlotte?

Many older aircraft could be equipped with an optional external air driven generator, including, for example, the Luscombe 8A. Some air driven generator models were granted a Supplemental Type Certificate (STC) allowing them to be added to specific aircraft, such as the venerable J-3 Cub. The reason these were used is that, as you surmise, the engine is not equipped with any mechanism to drive an alternator or generator, i.e., there is no pulley, no gear mechanism, etc. Examples of those engines, still in use today, are the A-65, A-75 and original C-85. Newer designs of air driven generators are still available today, such as the BPE14 TURBO STAND-BY ALTERNATOR. The disadvantages include increased drag and exposure to ground obstacles, debris and of course, birds and bugs!


What is an out-of-trim condition and how is it detected?

The trim system on an aircraft relieves the control pressures so that the aircraft maintains an attitude without pressure on the control system.

When hand-flying this is very noticeable in that you constantly have to be pushing, pulling, or turning (in the event you have aileron trim) to maintain an attitude. Notice how I don't say "straight and level", you can trim an aircraft to maintain a climb/descent or other attitude as long as the trim tabs have enough authority.

Autopilots detect an out-of-trim condition the same way you do. They sense that there is pressure on the controls to maintain the desired attitude, and if this is over some threshold it will display a warning light for an out-of-trim condition. Some autopilots have a trim-up or trim-down light to help the pilot determine which way to trim the aircraft.

Here is a diagram from a S-Tec System 50 Autopilot found in many GA aircraft:

The "out of trim" condition lights are two yellow indicators on the right side of the auto-pilot instrument.

Why is this important? Mostly for the longevity of the equipment. The autopilot works by either physically moving the cables or actuating the hydraulic system. It uses power to run motors which cause the motors to heat up and use electrical power. By trimming the aircraft, you can reduce these forces required by the autopilot so that it isn't working so hard to control the aircraft.

Another good reason is that you don't want the aircraft to do something unexpected when you hit the autopilot "off" or "disconnect" switches. This is especially dangerous in IMC when you don't have a visual reference to anything. There are also conditions which can cause the autopilot to disconnect automatically, and it takes a few precious seconds to figure out what is going on before the pilot gets positive control.


Would a pure flying wing in straight and level flight have zero wing bending stress?

Net wing loading (weight per unit lifting area) can't be zero in level flight.  Lift must equal weight, else the aircraft will accelerate in the direction of the net force.

The loading distribution on the Helios is designed to reduce flexing moment along the span, which is an entirely different thing.  As you note, that optimization wasn't perfect, although pitch oscillation wasn't necessarily related to the wing flex that shows in the video.


Would the solid material inside an airship displace air and be counted towards lift?

It would, but it is so little it is not noticeable
Duraluminium has a density of 2780 kg/m3, plain air has a density 1.3 kg/m3. So the buoyancy is in the order of 0.05%. The dry weight of the Hindenburg for example was 100 tons, meaning that the buoyancy of the solid material is about 50 kg.
This is so little that other effects on lift — i.e. changes in temperature, internal gas pressure, external atmospheric pressure, dynamic lift from relative wind speed, ballasting, spending fuel, and more — will completely drown out this effect.


There are multiple ways to fly and control Unmanned Aerial Vehicles (UAV), or drones, for e.g. the Predator.

Source: science.howstuffworks.com

Some UAVs (like the Global Hawk) can perform the entire mission (from takeoff to landing) autonomously, negating the need for a pilot.
Most of the UAVs, like Predator can perform (i.e. fly in) some simple missions (like reconnaissance) autonomously.
In case a geostationary satellite is used for communication with the UAV, the latency is around 300 ms (The electromagnetic waves have to travel ~70000 km). In case of other delays (like equipment etc.) this will not be greater than 500 ms or around half a second. This is not significant in case of slow moving systems like Predator (they are not dog-fighting, after all) and the 'pilot' can effectively control the aircraft.
The only situation where this is a problem is when the UAV is taking off/landing and in this case, the control is handed over to local LoS operators.

The Predator is reported to have a 'latency' of around two seconds, which causes problems during takeoff/landing. According to the telegraph,

  But the two-second delay between a pilot moving a joystick in Nevada and an aircraft responding in Afghanistan is enough to cause a crash during take-off and landing. Crews in Afghanistan control 'launch and recovery’ through direct contact with antennae on the aircraft. Half an hour after take-off, control of the Reaper is handed to a crew in Nevada; half an hour before landing, it returns to the crews on the ground in Kandahar.

Note that the RAF also does things the same way. According to the report on formation of 'drone' squadron' at RAF Waddington,

  Although the personnel will be permanently based at RAF Waddington, some will go to Afghanistan to control the take-off and landing of the drones locally.


Did Solar Impulse flight in commercial airspace and have kind of type 23 certification?

To answer the question presented in the title, I looked to Wikipedia for details on the flight(s) of Solar Impulse. According to Wikipedia, Solar Impulse 2 (HB-SIB) circumnavigated the Earth’s Northern Hemisphere in 17 legs/flights. Of those 17 legs, 14 legs had maximum altitudes above 18,000 feet MSL. In the U.S., Class A airspace is between 18,000 and 60,000 feet MSL. It is not considered “commercial” airspace. It is accessible to any aircraft with a Mode C transponder and ADS-b, including experimental aircraft. And, even this requirement can be waived with prior approval.

  91.135 Operations in Class A airspace.

  Except as provided in paragraph (d) of this section, each person operating an aircraft in Class A airspace must conduct that operation under instrument flight rules (IFR) and in compliance with the following:

  (a) Clearance. Operations may be conducted only under an ATC clearance received prior to entering the airspace.

  (b) Communications. Unless otherwise authorized by ATC, each aircraft operating in Class A airspace must be equipped with a two-way radio capable of communicating with ATC on a frequency assigned by ATC. Each pilot must maintain two-way radio communications with ATC while operating in Class A airspace.

  (c) Equipment requirements. Unless otherwise authorized by ATC, no person may operate an aircraft within Class A airspace unless that aircraft is equipped with the applicable equipment specified in §91.215, and after January 1, 2020, §91.225.

  (d) ATC authorizations. An operator may deviate from any provision of this section under the provisions of an ATC authorization issued by the ATC facility having jurisdiction of the airspace concerned. In the case of an inoperative transponder, ATC may immediately approve an operation within a Class A airspace area allowing flight to continue, if desired, to the airport of ultimate destination, including any intermediate stops, or to proceed to a place where suitable repairs can be made, or both. Requests for deviation from any provision of this section must be submitted in writing, at least 4 days before the proposed operation. ATC may authorize a deviation on a continuing basis or for an individual flight.

For further details about the aircraft, it’s custom autopilot and flight controls, and the actual flight Itself, visit https://aroundtheworld.solarimpulse.com/adventure .


What is the material composition of aircraft compressor blades?

Have found a reference to "high grade steel" and to titanium. According to the (paper format) book, the parameter that dimensions the compressor is the perimeter speed (tip speed) of the blades $u_2$.

For steel: maximum $u_2$ = 450 m/s. With a total inlet entry temperature of 300 K, pressure ratio is 4.2
For titanium which has a higher strength/mass ratio: $u_2$ can be up to 500 m/s, leading to a pressure ratio of 6.

The book was written at the time of the B757/767 engines so there may be more modern materials around.

Also refer to this answer.

Update

A more recent reference is provided by this presentation for the Trent 1000 engine:

Fan and LP compressor blades are made from titanium alloy, containing small amounts of Fe, V, O, and Al.
IP compressor: 8 stages of titanium blades.
HP compressor: 6 stages of titanium blades.

The reason titanium is selected is that up to a certain temperature, titanium has the highest specific strength (strength/weight ratio), and in the compressor the temperatures stay below the transition temperature for nickel alloys:


What is the difference between a glider and a sailplane?

The sailplane article is focused around sport and recreational planes. The aircraft article describes a wide variety of aircraft, not simply planes, like hang gliding and paragliding.

Which makes sense - one is about aircraft, so it has the aircraft moniker. The other is specifically about planes, which are a subset of aircraft, and thus have the sailplane moniker.

There was an idea of merging them in 2011, but it failed.


Aircraft tires are indeed standardized by size and specification and with applications across models.

There is certainly a long list of available sizes and variations, just as with automotive tires. When needed for a new aircraft type design, these existing tire models are available to be incorporated into that design.

There are certainly many aircraft types that have necessitated special tire specifications through the history of aviation development, especially with the more esoteric military aircraft. Of course, this is how that extensive list of available tires came to be.

Aircraft tires are dimensioned by several measurements (as depicted in the images below):

Outside Diameter (A),
Cross Sectional Width (B),
and Inner (Rim) Diameter (C).

These dimensions will be noted as AxB-C. In some cases the A is left out for a B-C notation (see examples in the table of "Type III Nylon Tube Type Tires" below).

Image Source

Image Source

Air Hawk tires are one brand that I handle frequently; their tire products give a good representation of the generic sizes and specifications available. Follow the above link for examples from their online catalog.

See also this excerpt from their Aircraft Tires Specifications sheet showing examples of common dimensions and plys:

Goodyear has an exhaustive databook covering technical specifications for their commercial and military aircraft tires.

See that here: The Aircraft Tire DataBook

  Specific data on the proper tire sizes for different aircraft main and
  auxiliary/nose gear, speed ratings, nominal inflation pressures,
  dimensions, and other data needed by users to obtain the maximum
  service from their aircraft tires are presented in this booklet.


Why would a runway friction measurement improve over time?

There could be a number of reasons. Temperature affects asphalt significantly or calibration could be off.

But if higher friction is measured in the touchdown area after significant use I would look to rubber deposited by landing aircraft tires, which is stickier than asphalt. Dragsters do burnouts before their runs to put rubber on their lane. It is just like glue.


Is it possible for the sensors which determine when an aircraft has landed in water to become damaged?

Yes, the component in question is called the Underwater Locator Beacon.

They are not foolproof. To disable them manually you need physical access to the black boxes, which are located in the tail section of the plane.