Why is "dragging it in" considered bad in small aircraft, but fine in larger aircraft?

For the GA fleet, there is some historical precedent operating here.  Years ago, engines were much less reliable than they are today.  Dragging it in generally means that you cannot glide it in if you have a complete power failure.  This translates to saying in the event of an engine failure, you are landing off airport with limited selection of landing sites (your altitude is low as you are now below pattern altitude).  So if you are flying behind an old Curtis OX-5 in your Jenny, a gliding approach to landing was recommended back in the day.

Engines are much more reliable today.  After an analysis of landing accidents, the FAA determined that a stabilized approach to landing is less likely to result in an accident, and they changed their guidance accordingly. Stabilized approaches are partial power-on landings.  Some old timers and some old time CFIs reject the FAA's statistical analysis and still teach/fly glide-it-in landings.  Properly executed, both approaches to landing are safe.  It is just that the FAA thinks that stabilized approaches are safer given engines commonly in use today.

It is also true that virtually all airlines require stabilized approaches in their operating specs, and that a go around is mandatory if the approach is not stabilized.  With this in mind, flight schools that aspire to send their graduates to the majors will all teach stabilized approaches.


What is the current state of regulation regarding VTOL aircraft in the LSA category?

The FAA term for VTOL [other than helicopters and lighter-than-air craft] is "Powered Lift". Also of note, gyroplanes by nature may be able to land vertical but cannot takeoff vertical so are not VTOL.

LSA excludes powered lift. Not much more to it, unless maybe it launches from a catapult and lands with a parachute.

title 14 CFR section 1.1 "General definitions":

  Light-sport aircraft means an aircraft, other than a helicopter or
  powered-lift that, since its original certification, has continued to
  meet the following:

  (1) A maximum takeoff weight of not more than—

  (i) 1,320 pounds (600 kilograms) for aircraft not intended for
  operation on water; or

  (ii) 1,430 pounds (650 kilograms) for an aircraft intended for
  operation on water.

  (2) A maximum airspeed in level flight with maximum continuous power
  (VH) of not more than 120 knots CAS under standard atmospheric
  conditions at sea level.

  (3) A maximum never-exceed speed (VNE) of not more than 120 knots CAS
  for a glider.

  (4) A maximum stalling speed or minimum steady flight speed without
  the use of lift-enhancing devices (VS1) of not more than 45 knots CAS
  at the aircraft's maximum certificated takeoff weight and most
  critical center of gravity.

  (5) A maximum seating capacity of no more than two persons, including
  the pilot.

  (6) A single, reciprocating engine, if powered.

  (7) A fixed or ground-adjustable propeller if a powered aircraft other
  than a powered glider.

  (8) A fixed or feathering propeller system if a powered glider.

  (9) A fixed-pitch, semi-rigid, teetering, two-blade rotor system, if a
  gyroplane.

  (10) A nonpressurized cabin, if equipped with a cabin.

  (11) Fixed landing gear, except for an aircraft intended for operation
  on water or a glider.

  (12) Fixed or retractable landing gear, or a hull, for an aircraft
  intended for operation on water.

  (13) Fixed or retractable landing gear for a glider.


Would mechanical indicators have helped in the Air France 447 incident?

Unfortunately, if there had been a jazz band in the cockpit singing "The plane is stalling" it wouldn't have helped. If Moses had been in there carrying a stone tablet newly-carved by God himself inscribed "Pitch down" with a host of angels to help announce it, that would have made no difference.

The unrecoverable problems were in the pilots' brains and in the communication between them, not in the aircraft or the technology.

Once in that state, only a fresh perspective (for example stepping back from the problem, bringing in a fresh person to look at it, using a checklist) is likely to snap those trapped in it out of their spiral: of alarming events, inappropriate reaction, unexpected result of the new inputs, and mounting panic.

It's a common experience in many crafts and disciplines, though in some - like computer programming - it's easier to find the new perspective than in others, such as piloting or surgery.

Anyone who has found themselves in that spiral will be able to tell you that adding more data or new sources of data to the mix rarely help.

It seems reasonable to think that a clear, simple and apparently unarguable piece of evidence would be the way out of such a situation. Unfortunately, in practice, it rarely if ever is, and there is nothing to suggest that in this case it would have been any different - despite compelling intuitions to the contrary.


Why wasn't Saint-Exupéry able to cover more distance before his 1935 desert crash?

This site has more details on why it took so long to get to Libya
https://www.thisdayinaviation.com/30-december-1935-wind-sand-stars/

After taking off at Paris, Saint Exupéry followed the Seine to the valley of the Loire and continued south, crossing the southern coast of France near Marseilles. The fliers had been over the Mediterranean Sea for a short while when they saw fuel leaking from the left wing. Prévot calculated that they had lost 20 gallons (76 liters) of fuel. They turned back and landed at Marignane to repair the leak and refuel before continuing.  Saint Exupéry wrote, “I drank a cup of coffee while the time lost hurt like an open wound.”
Once again heading across the Mediterranean toward Tunis, they encountered low clouds and heavy rain which forced them down to just 60 feet (18 meters) over the water. They flew along the coast of Sardinia as the weather improved.
F-ANRY crossed the coast of Africa at Bizerte, Tunisia, and about fifteen minutes later landed to refuel. With two hours of daylight remaining, Saint Exupéry and Prévot took off again, now heading toward Benghazi, Libya. They landed there at 11:00 p.m., local time, and in just twenty minutes the airplane had been refueled and once more, they were airborne.
Flying east after moonset, Saint Exupéry and Prévot were in total darkness. After three hours a faint glow of his navigation lights on the airplane’s wingtips told Saint Exupéry that he had flown into clouds, with visibility measured in just feet.
At a time when there were no navigation aids, pilots had to navigate by their compass, airspeed indicator and clock. Though Saint Exupéry had met with meteorologists to plan his flight, there was no way to update the weather information after takeoff. He had no way of knowing whether an expected tailwind had held, or if it had changed; was his speed across the ground faster or slower than planned? Had the wind blown him right or left of course? Had the atmospheric pressure changed, causing his altimeter to read higher or lower than the airplane actually was? Flying across the emptiness of the  Sahara Desert with no landmarks, in total darkness and now just a few feet of visibility, he and Prévot could only guess at their position.
4 hours, 15 minutes after taking off from Benghazi, the C.630 crashed into gently rising terrain at 170 miles per hour (274 kilometers per hour).

More on the plane:

The Société des Avions Caudron C.630 Simoun was a four-place, single-engine, low-wing monoplane with fixed landing gear. It was built of wood, with the surface of the wings and fuselage covered in plywood sheet then covered with doped fabric. Carefully curved aluminum sheet metal covered the top and bottom of the fuselage. The C.630 was 8,70 meters (28 feet, 6½ inches) long with a wingspan of 10,40 meters (34 feet, 1½ inches) and height of 2,25 meters (7 feet, 4½ inches). The airplane’s gross weight was 1,230 kilograms (2,712 pounds).
The engine was an air-cooled, normally-aspirated 9.500 liter (579.736 cubic-inch-displacement) Renault Bengali 6Pri inverted inline six-cylinder overhead-valve (OHV) engine rated at 180 cheval vapeur (177.5 horsepower). The left-hand-tractor, direct-drive engine turned a two-bladed, metal Ratier variable-pitch propeller. The propeller could be set to coarse pitch by a mechanic prior to takeoff, then an air bladder mechanism could change it to fine pitch for cruise flight.
The C.630 had a maximum speed of 310 kilometers per hour (193 miles per hour). The service ceiling was 7,500 meters (24,606 feet) and normal range was 1,260 kilometers (783 miles). Twenty C.630s were built before production changed to the slightly improved C.631.

Not a lot different than my Cessna Cardinal, which is a little wider (35'6"), 4 seats, fixed gear, and 180 HP Lycoming engine with constant speed (variable pitch) prop totally controlled from within the cockpit. Service ceiling only 14,600 feet (altitude where climb rate drops to under 100 ft/min). Gross weight 2,500 lbs. Max speed (never exceed speed) is 192 mph, with max cruising speed of 158mph (speed not to exceed except in smooth air). Cardinal carries less fuel most likely, just 50 gallons, my best range at 10,000 ft is 615 miles.  I think our longest flight has been about 4 hours, can only listen to ATC for so long!


Are taxiing aircraft to hold short of taxiway hold short markings if not instructed by ATC to do so?

This is one biggest pet-peeves of mine that even old, experienced pilots have missed after years of flying.

Taxi instructions are just that: Instructions, not clearances. Mind you there are some clearances when on the ground aswell, crossing a runway, entering a runway, backtracking, maybe some others.. mostly involving the runway. But a general text like ‘Taxi to holding point Charlie via Golf’ is an instruction.

Ok, so the difference is just pedantic but there is one big caveat: when you are cleared to land, cross, enter on a runway you are guaranteed the runway is, well, Clear and will continue to be so for the ammount of time you need it to land/take-off.

This is not true for taxi instructions. You are instructed on what path to take on the ground, but the taxiways and route to your runway is most definitelly not cleared of other aircraft (unless we are talking about low visibiliy ops, but just bear with me for now). When taxing you are still supposed to look out for other trafic and try to avoid hitting other airplanes taxing around as much as you can.

You might be instructed to go via one taxi path and then later told to give way to another aircraft comming from your left. See how the path has not been ‘cleared’? It is not a clearance.

All this talk to sum up: entering/crossing a runway is a clearance. Crossing a (non-mandatory) taxiway holding point is not. Is the answer slowly building up ?

Crossing a runway hold short makrking (two dased lines and two solid lines) you need clearance.

Crossing a taxiway holding marking (or intermediate holding position, or cat 2/3 holding when not in low-vis) does not require one.


What are the data elements shown on the GE235 flight data recorder (FDR) plot?

From top to bottom:

  main gear : whether there is weight-on-wheel not [scale on the left, in blue: "air/gnd"] (thanks to DeltaLima for pointing this out)
  VHF1 : probably if there was communication of that radio channel (speculation on my side) [no scale]
  Master warning : if the MW signal for engine flame out was active or not [scale on the right, in green : "fault/-"]
  CLA : Conditioner Lever Angle [scale on the right, in green : "fuel SO/no FSO"]
  Beta : usually is used to indicate aircraft sideslip, in this case is referring to the propeller blades, 90 degrees signal feathering. [scale on the left, in green : "90//10"]
  Bleed valve : whether it was open or closed (as labeled on the right) [scale on the right, in green : "open/closed"]
  PLA : power lever angle, aka throttle lever position [scale on the left, in green : "80//30"]
  ITT : inter turbine temperature [scale on the right, in green : "700//100"]
  NP : propeller RPMs as % of max RPMs [scale on the left, in green : "100//0"]
  Fuel flow [scale on the right, in green: "2000//0"]
  Objective TQ: objective torque (*) [scale on the right, in green : "100//80"]
  TQ : torque [scale on the right, in green : "200//0"]
  NL : low pressure shaft RPMs [scale on the left, in green : "100//0"]
  NH : high pressure shaft RPMs [scale on the right, in green : "100//0"]
  Oil pressure [scale on the right, in green : "100//0"]
  Barometric corrected altitude [scale on the left, in cyan: "2000//0"]

*: from page 2 of that link:


Why is the battery turned off for checking the voltage on the A320?

The voltage varies with what is connected to the bus.

Adding load will, for every electric source, reduce the voltage. And you wouldn't know how much is still OK without also knowing what is powered.
When the battery is charging (e.g. from ground power), you'll see the charging voltage even if the battery is empty.

With battery off you remove this variability, so they can give you exact number that signifies the battery is sufficiently charged.
(IIRC there are few things on the hot bus that are always connected, but their power consumption is known, so you check the battery under well defined conditions)


What altitude restrictions are there in Class C airspace?

Absent an explicit instruction to the contrary, VFR traffic can do whatever it wants in class C/D/E airspace. ATC is not supposed to give you both lateral and vertical control instructions at the same time because that could interfere with your ability to maintain VFR cloud clearance requirements. Class B has different cloud clearance, so you will almost always get both, and you should "unable" them if complying is not legal.
If ATC has told you to "advise any altitude changes", then do so—before starting up or down. If they told you "altitude your discretion", then they don't care. If they said neither, it's recommended to advise by default unless you're doing something where an altitude change is obvious, such as entering the pattern. They key is to not surprise them.


How dangerous would it be to start a jet engine with coins inside?

As you say "it depends". Modern jet engine front turbines are designed to reject foreign object debris outside the core, which is where the damage would really matter. Jets suck up hard foreign object debris like pebbles often enough and it will ding things a but but hardly cause catastrophic damage. I'm sure coin throwing has gone unnoticed, and it made no difference in the end.

Really, it's not a big risk for the most part, modern high-bypass turbofans have a large bypass duct, when coins are thrown into an engine which is not running they will drop to the bottom of the bypass duct and get blown harmlessly out the back when it's started. However, there's just enough risk that a coin could find its way into the compressors and cause enough damage to need expensive repairs, and that is why they will take the airplane out of service.

Of course it depends on the coin, if you threw this bad boy in it would be a different story:


Why is KLAX and KSEA depicted class D in IFR low enroute chart?

Your question is interesting but the answer is not fully obvious without a bit of research.  In looking at the KSEA IFR Enroute chart (L01 IFR enroute chart -third image below) it does indeed show that a portion of the the Seattle International Airport is within Class D airspace.
The second image below shows an excerpt from FAA Order 7400.11E describing the Class D airspace as it relates to KSEA.
The third image is from the L01 IFR Enroute Chart for Seattle.
The fourth image below shows part of the legend for an IFR Enroute Low Altitude chart.
So, although some general information relating to the OP's question may be addressed by looking at the link shown above by @randomhead as it applies to LAX, the OP is asking a reasonable question which is fundamentally different (from the question addressed in the link mentioned above) and probably should be left open.
Further, it is a fairly unusual circumstance to have Class D areas attached to the primary airport upon which the Class B airspace is predicated, so a discussion relating to identifying the affected areas that are Class D versus Class B may be very informative.
Likely, the Seattle Class D airspace (dimensions shown above), is to handle go-arounds, (that turn and enter a downwind to return to the airport as opposed to returning to the TRACON to be vectored out for another full [longer] approach), helicopter traffic, traffic watch aircraft, etc. (being on or staying on the Control Tower's frequency, for example) .
If you do the research for KLAX, it's the same principle (but different dimensions for the Class D).


What is the minimum stopping distance for a 747-400?

Interesting question. I think it could be done in the right conditions if you are willing to accept some damage and depending on the runway.

Is the runway level or uphill/downhill? If you could land uphill in a high wind that was almost all headwind, I believe you could either do it or would overrun the runway at a low speed. Airplanes slow down really quickly going uphill.

A stripped 747-400 probably weighs about the same as a 747-400 freighter, maybe a little less because the freighter has the equipment for loading and securing pallets. If you're using Firefox or Chrome (IE won't work), click on any aircraft at 747.terryliittschwager.com and you'll see the empty weight is around 362,000 lbs (you can change the weight unit to kilos there if you wish).

I used to land at Tel Aviv with only 15,000 lbs of fuel in 747-200s. The -400 burn rate may be a little higher, but let's use that. You would have to be comfortable with being totally committed to landing, with the possibility of only one quick go-around. Maybe you could even cut the 15,000 down to 10,000 with no go-around possibility?

Let's use 375,000. Vref for a -200 at 400,000 (lowest figure in the table I have) is 118 kts. In that area Vref decreases 3 kts for every 20,000 drop in weight, so we can take that 118 down to 115. I forget whether Vref is 1.2 or 1.3 times stall. Let's use 1.2, which would put the stall at 96. I would imagine a -400 is comparable insofar as these speeds are concerned, but I don't know.

How about one-time-use arresting gear of some sort on the last 400 meters of runway?

You could drop some more weight by taking out one engine. 747s regularly do 3-engine ferries. It's no big deal. However, I'm not sure if the weight loss would be worth losing the reverse thrust of the engine being taken out. There is a lateral imbalance consideration there, but 747s used to carry a spare engine in a pylon under the wing, so if you removed an inboard engine, I'm guessing you could live with the imbalance.

Speaking of reverse thrust, it used to be for the 747-200 that the published figures for minimum landing distance were brakes only, no use of reverse thrust. If that's the case for the chart shown in the previous answer, the figures there can be reduced, and you would want to use FULL reverse immediately. Don't worry about compressor stalls, after all, I'm guessing you're not going to use the engines again.

Also, I'm sure there are performance figures for the effect of runway slope and headwind.

It would be a challenging situation, one of those things some crazy Aussie might try!  lol


How does an A330 detect stall without airspeed?

Stalls occur based on a wing's angle of attack rather than the aircraft's airspeed.  (In fact, one of the basic facts that all pilots learn in their initial training is that an airplane can stall at any airspeed).  The A330 measures angle of attack using vanes mounted on the fuselage:

However, below 60 knots, these vanes become ineffective.  During the AF447 accident, the stall warning only engaged intermittently because the computers detected that the airspeed readings from the blocked pitot tubes were invalid, and therefore silenced the stall warning system.

Furthermore, because of the lack of valid airspeed data, AF447 was no longer in normal law (and therefore had no automated angle-of-attack protection), a fact which the pilots may not have been aware of.  By the time the deicing equipment had cleared the pitot tubes, the aircraft was at such an extreme pitch that airspeed indications were still considered invalid, and the stall warning system did not activate.  The computers only activated the stall warning system when the crew pitched down, which brought valid airspeed data back into the cockpit.

An Airbus press release suggests that this may have contributed to the accident:

  We also note that the aircraft, or more specifically the design of the stalling warning system, misled the pilots: each time they reacted appropriately, the alarm triggered inside the cockpit, as though they were reacting wrongly. Conversely, each time the pilots pitched up the plane, the alarm shut off, preventing a proper diagnosis of the situation.

(Emphasis mine)


Why didn't the Concorde have flaps or slats?

Why no flaps?

Flaps change the pitching moment of a wing. After all, they add lift over the full chord, so the sum of the increased lift attacks at about mid-chord, which is a quarter chord aft of the regular lift. If there is no separate tail surface to compensate for the pitching moment caused by that extra lift, the aircraft will quickly pitch nose-down and crash.

Next, flaps change camber and, therefore, are destabilizing the wing. Without a stabilizing tail, a cambered delta configuration will become unstable. The only camber which is helpful for delta wings is at the leading edge and must be compensated by a little trailing-edge up deflection of the control surfaces. Positive camber near the trailing edge is destabilizing and can only be tolerated on a flying wing with artificial stability augmentation.

Why no slats?

Slats are helpful for delaying flow separation to higher angles of attack and allow a wing to create more lift. To understand their effect, it is not enough to consider what they do to the flow around the wing, but also the effect of the wing on the slat needs to be understood. A slat is like a small wing flying just ahead, and therefore in the upwash, of the main wing. The wing will induce a very high lift on the slat and in turn see its suction peak around the leading edge greatly reduced, which helps in keeping the flow downstream attached. The comparison plot below should illustrate this effect nicely:

Figure 36 from A. M. O. Smith's paper "High Lift Aerodynamics"

But a delta wing at high angle of attack does not have attached flow on its upper side. It makes use of flow separation at the leading edge which creates a powerful vortex over the upper wing. This is called vortex lift. So for take-off and landing, deploying leading edge devices would help Concorde only a little - they are most helpful in the region just before vortex lift kicks in. This would be for subsonic cruise, for which the original Concorde wing was completely unsuitable. Adding camber at the leading edge would had increased subsonic L/D a lot, so the subsonic cruise segments (like all flight above land) and flight in holding patterns would had been much more efficient. That was not considered initially, and the lower complexity of an un-slatted wing was preferred.

With Concorde B, a span increase and the addition of variable leading edge droop (no slats!) were proposed. The picture below is taken from the original web site which has been the source for the site you linked to in your question.

Concorde B aerodynamic improvements (picture source)

If you now look how the L/D would had been improved by this, it becomes obvious were the leading edge devices helped most. The L/D improvement at take-off and landing, by the way, can be mostly attributed to the span increase.

Concorde A and B aerodynamic efficiency comparison (picture source)

This information is missing from the site you linked to, but is essential for understanding why Concorde B had variable droop added: It should help to extend range beyond the Paris-New York connection and allow more efficient subsonic flight (especially the hold at 250 kts).


Is the ATC of the lower and upper areas of the Netherlands combined or segregated?

Note that the Netherlands is a bit of a special case.

Below FL245, Air Traffic Control is provided by Luchtverkeersleiding Nederland (LNVL, the Dutch Air Traffic Control) and Dutch Mil (Dutch military ATC). Until one year ago, the Dutch military  operated from their dedicated air traffic control centre in Nieuw Milligen. Since January 2018, they are colocated with LVNL at Amsterdam Airport Schiphol and largely use the same systems as LVNL.

On the lower area map (below FL195), all sectors marked as Amsterdam Radar are controlled by LVNL. The  sectors marked as Dutch Mil  are controlled by the military, and despite some of the sectors are still named NW Milligen, they are controlled from the same room as Amsterdam Radar at Schiphol. As you can see on the upper area map, all sectors are marked Amsterdam Radar.

Their systems are partly combined, but military sectors and civil sectors are never combined. So if a lower sector is controlled by Dutch Mil, the upper sector will be controlled by a different controller.

When both the lower and the upper sector are controlled by LVNL, they can be combined during hours of low traffic. In that case there may be a single controlled controlling flights in the lower airspace and in the upper airspace. Combination is possibly also with adjacent sectors.

But wait, that's not all. Note that the map mentions that the Upper Area is between FL195 and FL245. The upper airspace mentioned so far in this answer, has a ceiling of merely 24500 feet.

Above FL245, ATC is provided by EUROCONTROL's Maastricht Upper Area Control (MUAC). They are located in Maastricht, far away from Amsterdam. They use the same radars, but their control system is totally different. Sectors of Amsterdam and Maastricht can thus not be combined.

Within MUAC's airspace, there is horizontal and vertical sector splitting. Especially the Delta sector is a busy one, with lots of transit traffic to/from UK/Atlantic and with climbing/descending traffic from/to London, Frankfurt, Cologne/Bonn, Brussels, Amsterdam and many more airports.


Why do gusts change the airspeed during landing, but turning (which changes where the wind is coming from) does not?

Before I get into the question about the turning fighter jet, a few words about airplanes' being extremely sensitive to gusts during final stages of landing. If this was actually true, I'd be dead by now. Seriously. Airplanes are sensitive to gusts during landing, I'll give you that, but I think it's exaggerating beyond reason to say it is extreme.

Now, back to one of the most persistent myths in aviation:

The myth of the downwind turn

The jet in your question does not make a full turn from headwind to downwind, but it does not matter, the physics are the same as in the myth of the downwind turn.

As you stated the plane is moving along with the airmass. So, for the plane, aerodynamically there is no head-, side-, or downwind. Only us on the ground can feel it, as we are locked into to the coordinate system of the earth with our feet.

The airplane is locked into the coordinate system of the airmass, and as long as the airmass itself does not experience acceleration, the airplane flying in it can turn in whichever way, and it will not notice any change in the wind direction.

The direction of the wind is locked into the coordinate system of the earth, so in your example there is no change in wind direction. Not for the jet aerodynamically speaking, and not in the sense of navigation (relative wind changes, but you use the same formulas for the calculations anyway). What does change is the groundspeed of the aircraft, and this is the reason wind (and gusts especially) causes some concerns for landing planes. Takeoff is also affected, but not quite as much as landing.


Is white/brown-out effect hazardous during the landing roll out?

From a partial accident list on Wikipedia, the issue seems to affect only helicopters.

A fixed wing rolling out should have no issue. As the dust/snow cloud will be behind the windshield. A plane landing in sequence should wait until the dust/snow settles.

Also an approach in poor visibility caused by a sandstorm would be no different than an approach in fog. An instrument approach will be carried out.


Is a vertical stabiliser needed for straight line flight in a glider?

The stabilizer is meant to keep the nose pointing into the wind.

Any asymmetry in he wings/fuselage will create a tendency to yaw, you will need to compensate for that. The easiest is a fixed vertical stabilizer at the rear.


What kind of cameras are onboard high altitude UAVs that aid in its control?

The Bottom Line Up Front

Infrared and visual video cameras aid in navigation of larger class UAVs and are helpful for safety but do not satisfy the legal requirements for unmanned aircraft to operate in US/international airspace. Instead, the use of onboard navigation systems like GPS, combined with air traffic control services and common flight safety rules allow safe navigation of high and medium altitude UAVs.

What UAVs Operate at High Altitude?

Northrop Grumman's "RQ-4" variants (e.g. USAF RQ-4B Global Hawk, US Navy MQ-4C Triton, NATO RQ-4D Phoenix) are the only widely recognized UAVs flown at high altitudes (FL500-600). The RQ-4 is also the largest UAV with a wingspan greater than a Boeing 757.  All other UAVs, including the MQ-9 Reaper, operate at medium or low altitudes.

How Does the RQ-4 Navigate?

The RQ-4 has sophisticated, GPS & gyro-enabled navigation computers that ensure it always knows where it is and where it is going. To avoid airborne hazards like other aircraft or bad weather, it follows the same instrument flight 'rules of the road' that manned aircraft rely on when flying at night or in the clouds. Specifically, air traffic controllers use radar to track aircraft from the ground and alert the pilots if they see an unsafe situation on their radar screens. These instances are rare, however, because everyone follows their flight plan and obeys air traffic controllers' instructions in order to remain safely separated in the air--even remotely piloted aircraft.

Does the RQ-4 Have Any Cameras Used to Aid in its Control?

Yes. As a backup to air traffic control clearances to taxi, takeoff, and land, the RQ-4 has a forward-facing infrared video camera on the nose of the airplane.  Although it is not legally required to have this camera, it is used only as a backup for the pilot to ensure the runway is clear of obstacles during taxi and prior to landing on the runway. Radio transmission of the video camera signal is via line-of-sight antennas only (not over satellites), so therefore it is limited only to the airfield/runway environment where the ground control station is located and is not used while away from the airfield during climb, cruise, or descent.

Note there are two small windows in the pressurized camera compartment: One upper window for the video camera lens and the lower window used to display the pressure dial for the camera compartment.

What About Medium/Low Altitude UAVs?

Medium altitude UAVs like the MQ-9 predator carry a variety of infrared (day/night) and electro-optical (day only) full motion video cameras used primarily for their mission rather than for navigation. Unlike the high-altitude RQ-4, they operate at the same altitude levels as commercial air traffic.  They can follow the same instrument flight 'rules of the road' that manned aircraft do when flying at night or in the clouds. Often, their mission requires them to fly in areas where following these rules aren't required by all aircraft. In this type of airspace, pilots of smaller aircraft like gliders and crop-dusters don't have the radios to communicate to air traffic control and count on other aircraft to 'see-and-avoid' them instead. The MQ-9 does not have a pilot onboard to look out the window and avoid these 'visual flight only' aircraft, so it needs other solutions to ensure safe navigation.

The MQ-9 does have a powerful ball-mounted, full-motion video camera onboard. However, the USA's Federal Aviation Administration and the worldwide International Civil Aviation Organization has not deemed the use of this camera as a sufficient substitute for the see-and-avoid requirement. Therefore, despite the MQ-9's robust visual/infrared camera system, it must rely on other methods of deconfliction like temporary/military restricted airspace, special clearances, and even chase airplanes, in order to conduct its training in the US and its missions overseas.  The same challenges exist with smaller, low-altitude military unmanned aerial systems and commercially operated drones.

Are Cameras Any Good For Long Range Navigation?

That depends on what you consider long range. Navigation using cameras, especially to avoid other aircraft, requires low-latency. It does little good to see a rogue aircraft filling your windscreen if, by the time you see it on the screen, the plane has already crashed into your UAV. This usually isn't a problem for FPV hobbyists because they have a line of sight video signal, directly from the RC aircraft, that feels instantaneous to the pilot wearing FPV goggles. On the other hand, truly long ranges require operation beyond line of sight, relying on satellites to pass information to/from the aircraft. This extra architecture causes video latency, sometimes up to multiple seconds, making it nearly impossible to visually react to a time-critical safety event.

A Better Alternative to Cameras

In addition to the video latency problem, video cameras on medium/high altitude UAVs are specialized to focus on small targets at long range--not scanning the skies for unidentified aircraft. Imagine trying to spot a fly buzzing around you while looking through a toilet paper tube. An additional, wide-angle navigation camera/lens could be carried on the aircraft but it would not be worth the additional cost, weight, space, and power consumption. Instead, long-range aircraft like the RQ-4 and MQ-9 rely on a framework of aircraft regulations, ground-based air traffic control, and segregated airspace to safely navigate.

Note: This response was drafted from scratch, solely to answer Rajath's question about cameras on high altitude UAVs. Thanks in advance for your feedback.


The French word for hail is grêle which is abbreviated GR.  METAR is an international standard so you will see some non-English words included in the METAR.


Why do flight attendants on the 787 lock the dimmable windows at different phases of the flight?

On long-haul flights, most passengers will want to sleep, often including when the aircraft is flying through daylight. It's especially common on East-West long-haul flights for lots of people to want to sleep when it's daylight outside the aircraft, since the aircraft will often be crossing many time zones (and, during the summer months, also often flying through regions where it's daylight all day or nearly all day.)

Even on aircraft without dimmable windows, the cabin crew will normally tell passengers to keep window shades closed after the first meal service when the cabin lights are turned out for that reason. On the 787, the crew will dim and lock all of the windows centrally instead of telling the individual passengers to do it and this also prevents a passenger from undimming it and waking everyone up. Unfortunately, that does happen from time to time on aircraft with normal window shades where the crew can't prevent it and it is really annoying when you're trying to sleep if you don't have an eyemask on.

Here are some common examples of the types of long-haul flights where many or most passengers will be trying to sleep during hours where the aircraft is flying through daylight:

Flights from East Asia to the U.S., even though they're typically at least nominally "overnight" flights, will actually spend much of the time flying through daylight. The actual darkness outside will only last a fraction of its usual time, since the aircraft is flying in the same direction as the Earth's rotation at a pretty significant fraction of Earth's rotational velocity.
Flights from Europe to North American typically occur entirely during daylight. While it's 'daytime' on these flights, these days are often (quite literally) long days for travelers, so many will want to try to nap during the middle of the flight.
Late flights from North America to Europe often leave North America within an hour or two of midnight and land in Europe around midday, even though it's only 6-8 hours later. The latter half of the flight takes place in daylight, but passengers will still be trying to sleep.
Summertime flights from North America to East Asia will typically experience midnight sun. Even though these flights often occur almost entirely during 'overnight' hours, their flight paths frequently take them well into the Arctic Circle — sometimes even near the North Pole — where it will be daylight outside, even though it may be near midnight local time. This typically occurs around the middle of the flight, when nearly everyone will be trying to sleep. As most readers of this site will know, the reason these flights fly so far North is because that's actually the shortest path, since Earth is a spheroid. For example, this map shows the shortest-distance path from New York's Kennedy Airport (JFK/KJFK) to Shanghai's Pudong Airport (PVG/ZSPD):

Shortest path from JFK to PVG, generated on gcmap.com


Wingtip landing light lenses are hazed - what can I do to make them clear again?

The hazing is a collection of very small scratches on the acrylic, and the way to remove them is to actually remove a thin layer of the acrylic - the trick is to make sure you use something that won't damage any of the paint/metal around the cover.

A mild acrylic polish is your best bet, although any mild abrasive will work (including non-"sensitive" toothpaste and a paper towel... although it might take a while!). There are plenty of "Perspex cleaner" style products for a reasonable price to do it.

Use a small amount (multiple small applications are better for controlling the spread) and try to use a thicker "paste" type of abrasive rather than a runnier one, for the same reason. Apply a small amount and some fairly firm pressure with a cloth, as per the instructions of the cleaner, removing any excess regularly.

If you think there are deeper scratches than just a very fine "hazing" on the lens, you can use a fine sandpaper (eg 1600 grit) to sand the acrylic first before using the polish


What airframe design is best for stormy weather?

In observing the configuration of the current aircraft used for weather study, it's important to also note that those planes were originally built for different missions that allowed modifications for such a special purpose.

The P-3 was built as a maritime patrol plane, which is a role not all that different from weather observation. It requires good range and endurance to allow the plane to fly out to sea and remain there long enough to accomplish its mission. The primary mission is using sensors, either onboard or deployed from the aircraft. The plane must also be able to withstand more time spent at lower altitudes and in more turbulence than typical aircraft.

The C-130 was built as a transport plane. This requires good range and payload capacity, both in weight and volume. These attributes have allowed it to serve in many roles, such as attack, special operations transport, and electronic warfare. As both aircraft were originally built for the military, they are built to withstand higher loading than typical civilian aircraft, which is useful when flying to bad weather.

4 engines are less efficient but provide redundancy - Both aircraft have 4 engines, as this is a good compromise between size of engine and propeller for this size of aircraft, at the time at which they were designed (around 1960). This primarily provides redundancy. The plane is required to be able to fly with one engine failed, and controllable with two on the same wing failed.

Turboprops are efficient at moderate speed - Both aircraft are also powered by turboprops. The primary roles for the aircraft do not require high speeds or altitudes, which is where turbofans have an advantage. Turboprops provide good power and efficiency at moderate speeds and altitudes, which is acceptable for shorter cargo missions and maritime patrols as well as weather observation. It's worth noting that the US Navy is replacing the P-3 with the P-8, which is a twin engine jet aircraft. A large part of this is likely due to the availability of an existing aircraft design, not being worth the cost of designing an entirely new plane. Although two engines provide less redundancy, they can still provide a similar level of reliability. Japan designed an entirely new maritime patrol plane, and opted for 4 turbofans. Although turbofans may require more fuel, they do allow higher speeds which allows the aircraft to reach its station faster.

Low wing may be a more versatile configuration - The high wing of the C-130 is mainly to allow easy loading and unloading of cargo by keeping the fuselage closer to the ground. This is less important for a weather observation role, though it does allow better downward visibility from the cabin. The P-3 sits higher above the ground, which allowed for a radar to be mounted underneath. Mounting sensors on top is certainly an option but may require modifications to retain stability. One might conclude that a low wing offers more versatility in this regard.

Moderate aspect ratio with sweep to match speed - The wing design will depend on the speeds for which the aircraft is designed. Low aspect ratios and high sweep or delta wings are good for reducing drag at higher speeds. There is no need for very high speeds in a weather observation aircraft, so these would seem to be poor choices. High aspect ratio and low sweep are good for reducing drag at lower speeds, which can maximize endurance. Though endurance is important for weather observation, these designs also have higher wing bending and generally lower top speeds. Both the C-130 and P-8 have moderate aspect ratios and low sweep, which offers a good compromise for strength and efficiency. Jet aircraft fly faster and generally use moderate sweep and aspect ratio.

Conventional tails can be more robust - T-tails have some issues with control and stability, and this prevents them from being used in most cases. The T-tail is mainly useful when the normal position of the horizontal stabilizer is taken up by engines or cargo doors, or would place it too close to wash the engines, or if efficiency is a high priority. Control and stability are particularly important when flying in adverse weather conditions, so if there is no other reason for having a T-tail, a conventional tail works better. All of the aircraft mentioned above have conventional tails.


What is the aerodynamic purpose of an Acorn?

It's doing one or both of two things:

Fairing in some kind of projection as Ron said, may be an antenna or a mass balance.
Fixing an airflow disturbance at the T intersection.  Bullet fairings are a common band aid for that sort of thing.

Russian designs seem to be big on bullet fairings.


In order to become a pilot, should an individual have an above average mathematical ability?

In short, no.

To quote Patrick Smith, veteran pilot and author of Cockpit Confidential and the blog  "Ask the Pilot,"

  There's a lingering assumption that airline pilots are required to demonstrate some sort of Newtonian genius before every takeoff- a vestige, maybe, from the days when airmen carried slide rules and practiced celestial navigation...
  The basics are what pilots encounter. Routine arrival assignments require some quickie mental arithmetic.

So basically, it doesn't involve super complex math. You need to be able to do some moderate arithmetic and geometry, but nothing so complex that it can't be done, as Smith says, on

  my $6.95 calculator from CVS- the one flight-bag accessory more indispensable than an emergency checklist, aircraft deicing guide, or a bag of ramen noodles.


What are the equation linking static air temperature with true airspeed & altitude?

Provided that your calculations take place for a standard day, below 11 km altitude the Outside Air Temperature is simply a linear function of altitude. From the wikipedia article for Standard Atmosphere:

So OAT = 15 - 1.98 * Altitude, with OAT in °C and Altitude in 1,000 ft. Airspeed data is superfluous.


How many private jets land at Heathrow airport per day?

None!

January 2018 movements, source: CAA

Related: Where does an A-lister land when they waft in from paradise? Yes, Luton

To try to explain why this absence of business planes at a large airport, its important to understand that private aviation in Americas and in Europe are not seen the same way.

In Americas private planes are very common, this is not the case in Europe, where you must be lucky to know someone in your neighboring who is a pilot. As a consequence airliners and other planes have separate lives with different fees paid.

For example, I live in Paris: Business planes use Le Bourget aerodrome (the one which hosts the Paris Air Show -- btw nobody here knows what is the Paris Air Show, as everyone calls it Le Salon du Bourget since it exists... --, while airliners use CDG or Orly airports (and now the remote/low cost Beauvais). This is the same in UK.


Are there any autopilots that are capable of landing a damaged aircraft better than any human?

Reconfigurable flight control systems have been a topic of research in military aircraft for decades. The science is existing and mature, but not an easy one: damage cannot be predefined, and therefore cannot be explicitly programmed in.

Classical re-configurable flight control systems attempt to re-program on the fly: the transfer function between input and expected aircraft response is constantly monitored, and if actual response differs from expected response, the gains in the loop are reset on the fly in order to get closer to a stable, matching response with neutral trim.

From this paper, which is almost 20 years old:

  The goal of control reconfiguration is to maintain handling qualities in the presence of a large universe of damage and failure modes. In contrast to robust control design methods of the past, the emphasis in control reconfiguration involves a combination of on-line parameter identification control redesign and/or adaptation for a degraded mode of flight.

Neural networks are now being implemented in reconfigurable flight control systems. These work as the synapses in our brain: there are a lot of possible connections, which are defined in our childhood as a result of positive and negative experiences. The system is self learning, from a multitude of outcomes that are labeled either "desirable" or "not desirable". Neural networking is what makes Google Translate possible; translating a language by programming is just not possible because of all of the different inflictions and double meanings in a language.

So in military aircraft an auto-damage-pilot is very well possible. Civil airliners are a different matter, not because of technology but because of certification. Safety is of the highest importance, and how can we prove that our re-configuration is actually helpful?


Why do some fighter jets have two pilots while others have only one?

All fighter aircraft have one pilot, though some have two crew members.

The backseat crew member is not a pilot, but often either a Radar Intercept Officer (US Navy), Navigator/Weapon Systems Officer (USAF, IDF), or Flight instructor.

Though not fighter aircraft, I believe that the SR-71 backseat crewmember operated the reconnaissance equipment as the single crewmember on the U2 was often overloaded with keeping the thing in the coffin corner and operating the reconnaissance equipment. Jan and Habu mention in the comments that the SR-71 backseat crew member was also the navigator and operated the ECM equipment. Additional comments mention that the B-1B consists of four crew members: two pilots, an OSO (offensive systems operator), and a DSO (defensive systems operator). The B2  has two crew members, both pilots, and while one is flying the other can rest, navigate, or operate the weapons system. Thanks to Jan, Habu, and Joel for comments and clarifications!


Yes, Telluride RWY 9, as can be seen clearly in this video.
Screenshot from video:


How do I calculate the normal component of the velocity at the midpoint of a source straight panel?

You can find a mathematical derivation of the $\lambda_i/2$ result in Katz and Plotkin, chapter 10. In this PDF, the result you are looking for is on page 234 (250 of the file itself). Anderson approaches things a bit differently, but you should be able to see at a high level how the approaches are analogous. The math gets a bit complicated and it's really not necessary to comprehend every step in detail to understand the application to aerodynamics. However, a good exercise if you really want to dive into the math is to translate Katz and Plotkin's approach into Anderson's notation, or vice versa. For me, though, it's good enough to see that it can be done and move on with the more interesting applications.


Are there ground stations at the waypoints a pilot may fly to?

Ground based radio navigation (VOR, VORTAC, LORAN, NDB) by necessity have ground stations to handle generation, amplification and broadcasting the signals used for navigation.  Here is an example of what a VOR station looks like:

"Table Rock VOR" by ZabMilenko - Own work. Licensed under CC BY 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Table_Rock_VOR.jpg#/media/File:Table_Rock_VOR.jpg

Waypoints that represent these stations will have ground facilities underneath them, but they are the minority of waypoints.  Most waypoints are defined as a distance along a radial from one of these stations, so there will be no ground station below them.  Other waypoints are lat/lon fixes provided by GPS, so there are no stations below them.

Keep in mind, no matter if there is a ground station or not below a waypoint, their presence is not important to how navigation is performed.  Waypoint passage will be noted by needles, to/from indicators, DME mileage changing, or by a points along a magenta line on a map display.

VOR stations are often named by their location e.g. the VORTAC in San Antonio, TX is named "San Antonio (SAT)".  Others are named for regional things, e.g. "Ranger (FUZ)", "Cowboy (CVE)" and "Maverick (TTT)" all located in Dallas, TX named after their major sports teams (baseball, football and basketball respectively)


Why do some airplanes have vertical strakes?

The vertical tail surface is like a wing, maybe with a smaller aspect ratio, but it works much the same over sideslip as a wing works over angle of attack. The fuselage, however, is a slender body with a much smaller lift curve slope, but a much higher "stall" angle. In fact, its lift curve slope is nonlinear and tends to increase with higher angles of attack and angles of sideslip. If you want to know more how the lift curve slope varies with aspect ratio, please read this.

This means that at some sideslip (around 15° for most configurations) the vertical tail stalls and its stabilizing side force decreases with further increase in the sideslip angle, whereas the destabilizing influence of the fuselage increases further. The aircraft becomes laterally unstable pretty soon.

To buy a little more stability around the point where the vertical tail stalls, these strakes have been added. They have a high leading edge sweep, so they will produce vortex lift just like a highly swept delta wing, only sideways. The suction force of this vortex will act on the root of the vertical, just were it has the biggest chord. In fact, this helps to keep most of the vertical active, because now it becomes part of that delta wing ahead of it.

The strakes in the upper picture have a different purpose on top, however. They limit flow separation on the rear fuselage in high speed flight by preventing crossflow. Actually, they are an embarrassment for the aerodynamicist, because they show that the lower fuselage suffers from flow separation just when it hurts most.

Most military cargo aircraft have them, because in order to keep the ramp short and to provide enough clearance for rotation, their tailcones are steeper than what the airflow can manage. Among modern military transporters, only the Lockheed C-5 (thanks to @dotancohen for the hint!) and the Antonov-70 can do without them. This was a definite source of pride for the chief aerodynamicist of the Antonov Design Bureau, Oleg Bogdanov.

The lower fin in the second picture was added to compensate the destabilizing influence of the two floats, which will destabilize the aircraft in much the same way as the fuselage does.

Extending the vertical downwards also helps to improve handling qualities and should be done as much as tail strike clearance allows.


What is the procedure if both pilots are incapacitated?

To put it short: no.

Unfortunately it might even take a while for anyone to notice both pilots are out. Most likely the first would be an air traffic controller since he/she couldn't reach the pilots on radio.
If the cabin attendants find both pilots incapacitated, they would most likely

try to find a doctor or nurse to help recover a pilot
try to find if any of the passengers was a pilot


How could a 45 years old DC10 be still in service with one of the largest cargo airline?

The DC-10’s have all been converted from DC-10’s to MD-10’s. The last conversion was in 2007, I believe. The entire aircraft wiring was replaced, the avionics package converted to glass cockpit and other structural work was also performed. As a result, the airframe was “zero houred” upon completion of the conversion.

Although they’re getting older, they’re still warhorses and their reliability is still good.

Also, cargo operators don’t put nearly as many cycles on their aircraft as passenger carriers. As a result, there is a lot less wear and tear on the aircraft.


Induced drag is caused by the downward deflection of the air streaming around the wing. The resulting aerodynamic force is tilted backwards by half the deflection angle, and the air flows off the wing with an added vertical speed component, producing downwash. Increasing the downwash angle means increasing both lift and the backward tilt, so the induced drag goes up with the square of the lift produced.

If you want to minimize induced drag for a given lift, this quadratic dependence means the optimum is reached when the downwash angle is constant over span.

  How is the induced drag calculated for a wing with elliptical planform?

The elliptical, untwisted wing has the same angle of attack and the same lift coefficient over span, and produces the desired constant downwash angle.  To simplify things, let's assume the wing is just acting on the air with the density $\rho$ flowing with the speed $v$ through a circle with a diameter equal to the span $b$ of the wing. If we just look at this stream tube, the mass flow is $$\frac{dm}{dt} = \frac{b^2}{4}\cdot\pi\cdot\rho\cdot v$$

Lift $L$ is then the impulse change which is caused by the wing. With the downward air speed $v_z$ imparted by the wing, lift is: $$L = \frac{b^2}{4}\cdot\pi\cdot\rho\cdot v\cdot v_z = S\cdot c_L\cdot\frac{v^2}{2}\cdot\rho$$

$S$ is the wing area and $c_L$ the overall lift coefficient. If we now solve for the vertical air speed, we get $$v_z = \frac{S\cdot c_L\cdot\frac{v^2}{2}\cdot\rho}{\frac{b^2}{4}\cdot\pi\cdot\rho\cdot v} = \frac{2\cdot c_L\cdot v}{\pi\cdot AR}$$
with $AR = \frac{b^2}{S}$ the aspect ratio of the wing. Now we can divide the vertical speed by the air speed to calculate the angle by which the air has been deflected by the wing. Let's call it $\alpha_w$: $$\alpha_w = arctan\left(\frac{v_z}{v}\right) = arctan \left(\frac{2\cdot c_L}{\pi\cdot AR}\right)$$

The deflection happens gradually along the wing chord, so the mean local flow angle along the chord is just $\alpha_w / 2$. Lift acts perpendicularly to this local flow, thus is tilted backwards by $\alpha_w / 2$. In coefficients, lift is $c_L$, and the backwards component is $\alpha_w / 2 \cdot c_L$. Let's call this component $c_{Di}$: $$c_{Di} = arctan \left(\frac{c_L}{\pi\cdot AR}\right)\cdot c_L$$

For small $\alpha_w$s the arcus tangens can be neglected, and we get this familiar looking equation for the backwards-pointing component of the reaction force: $$c_{Di} = \frac{c_L^2}{\pi\cdot AR}$$

If the circulation over span has an elliptic distribution, the local change in circulation times the local amount of circulation is constant, and the induced drag $c_{Di}$ is at it's minimum. If this would be different, a higher local $v_z$ causes a quadratic increase in local induced drag, so the whole wing will create it's lift less efficiently.

  Is this wing shape the most efficient ?

Only if you ask an aerodynamicist would the answer be yes. An elliptic wing will give you the best ratio of lift to drag, which clearly is one way to express efficiency.

In reality, the wing has to lift itself plus a payload, but only lifting the payload should be considered when formulating efficiency. Therefore, pure lift/drag optimization is too narrow. What should count is the best ratio of lift minus wing weight relative to drag. R. T. Jones wrote a NACA Technical Note back in 1950 in which he looked at this problem analytically. Wing weight goes up when much lift is created near the tips, because this lift will cause a disproportional root bending moment, and the wing spar which has to carry this bending moment is a significant part of the wing structure. Therefore, reducing lift at the tips and adding more lift at the root will create a lighter wing for a modest drag increase, resulting in an overall optimum for an almost triangular lift distribution. When compared to an elliptical wing planform, the total wing span of such an optimized wing is bigger for the same overall drag, but this wing will weigh less.

Spanwise loading comparison for wings of the same fixed lift, from NACA Technical Note 2249.

But this is too easy. Scaling laws must be considered in addition. You know that elephants have much more massive legs relative to their body size than antelopes (or even ants, for an even more drastic comparison), since body mass scales with the cube of linear dimension while structural strength scales only with the square of linear dimension. This means that wing spar weight will be proportionally higher for larger aircraft.

As a consequence, insects have more elliptic wings than albatrosses, and model aircraft have optimum wings which are much more elliptic than the optimum wing of an airliner. The optimum shifts from an elliptic load distribution at very small scales to an almost triangular distribution at large scales.


Is the size of hail on the ground any indication of the winds and updrafts of a thunderstorm?

The October 2018 issue of AOPA's "Flight Training" magazine provided the following illustration and comments.

A 24mph updraft will form ~1/4" hail, while a 98mph updraft will form
4" hail.
Down drafts are usually about 1/2 the speed of the updraft
(due to a larger outer core area).
When a pilot encounters a
downdraft, expect an updraft twice the speed to soon follow.
The change will be a quick dramatic shear.
Only about 10% of thunderstorms produce hail.


For how long after the last A380 delivery does Airbus have to provide spare parts for it?

When a company decides to terminate the construction of a specific airplane, then this company needs to follow some conditions. In the contracts between Airbus and airline companies, there are many conditions concerning multiple aspects.

There are conditions for example about:

spare-parts availability
transfer knowledge about specific features of the airplane
training (not for all the occasions)
and more (we are not in a position to know them all and in detail)

These conditions are discussed in the beginning, before the signing of the contract. Of course, conditions may differ from one contract to the other, but I think you got the point behind this idea.

So there is no way that someone will tell you what will happen between Airbus and their clients because this information is confidential. As soon as, the clients of Airbus do not sue them, then their contracts are including mechanisms about this.

Lastly, these contracts most of the time are including basically conditions about safety or financial sections. There is coming the role of ICAO, IATA, EASA, FAA and more. These organizations are responsible for managing properly also the sector of safety/security. The fact that spare-parts availability is playing vital reason in the safety of the passengers among the world, then it is 100% sure that they also know about it and they know how to handle it.

Hope that I helped.


What are the main differences between scimitar and regular propellers?

Primarily the curved sweep of the blade's leading edge, allowing for better efficiency at higher engine speeds.


How can pilots lacking instruments interpret vectors given by ATC?

14 CFR Part 25 describes the requirements for an airliner like the 737 to be certified by the FAA.

§25.1303   Flight and navigation instruments.
(a) The following flight and navigation instruments must be installed so that the instrument is visible from each pilot station:
...
(3) A direction indicator (nonstabilized magnetic compass).

Indeed the 737 has a magnetic compass, centrally located above the windshield. It's just hard to see in the picture you have, as it's hidden behind the overhead console controls. This is a very typical location for the compass in many large aircraft (but not all), as it's centrally located, allows both pilots to see it, and will have less interference from other instruments.

Even the newest version, the 737 MAX, has a compass.

Images Source


What is the purposes of grid-like pattern route for small aircraft?

These are most likely photography flights for cartography. Due to the COVID crisis, there are many flights like these lately because it is now easy to obtain permission from Air Traffic Control for these patterns.


What is the material that is used for turbine blades that has the highest melting point?

Gases temperature on the turbine blades can reach 1700-1800K. There is no material which can withstand such a temperature in conjunction with enormous centrifugal forces.

That's why blades are not only made of nickel superalloys, coated with ceramics, but also are "film-cooled".

They have radial micro-passages where compressed air from high pressure compressor is fed. Most advanced designs also have micro-holes along that passages on the leading and trailing edge of the blade, which are the hottest points on the blade. This enables cooling blades down with air (air from HP compressor heats up to 400-500K, while blades work at 600-700K) and also creates a film of protective air over blade's surface, which prevents direct contact of blade and exhaust gases. That's because most of the heat transfer occurs by thermal conductivity at direct contact, and much less - by heat radiation.


What’s the setting range altimeters can handle?

There are actually multiple different answers depending on the specific type of altimeter system and what standard applies.

The stand-alone altimeters in older aircraft and small GA aircraft (panel mounted "steam gauge") are certificated to SAE AS392C, Altimeter, Pressure Actuated Sensitive Type. The specified scale range is "at least 28.1 - 30.99 inches of Hg (946 - 1049 millibars)".

This standard was updated in 2016 to require compliance with SAE AS8009C, Pressure Altitude Systems. Altimeters built to this standard have a specified range of 27.50 - 31.50 inches of Hg (931.3 to 1066.7 mb).

Aircraft with "glass cockpits" use Air Data Computers certificated to SAE AS8002A, AIR DATA COMPUTER - MINIMUM PERFORMANCE STANDARD. Barometric corrected altitude correction is covered by Table 2, which defines a range of 22.00 - 30.98 inches of Hg or 745 - 1049 millibars.


What are these markings on the runway at Haneda Airport?

I dug around for a while but couldn't find any official documentation on this (I suspect someone whose Japanese is better than mine will have to do that.)

But!  I did find the markings on all of the Haneda Airport runways and I noticed they were roughly halfway along the length of the entire physical runway.  A little bit of measuring confirmed my suspicion, it appears the marks show you exactly where the halfway point is on that particular runway.

I also looked at other Japanese airports and took measurements of the same markings at Narita, Osaka and Kobe.  All airports turned up the same results.  (You can use the measure tool on Google Maps to confirm if you'd like to)

I also find out that not all airports in Japan have these markings.  Neither Nagasaki nor Osaka seem to have markings like the ones mentioned above...

Not sure why they mark the halfway point...someone with better Japanese than me will have to look into the history of that decision.

Edit:  mins found some documentation and posted it in the comments (thanks mins!):

This is an English translation of a report done by the Japan Transport Safety Board regarding a runway overrun.  They mention the meaning of the markings (in passing) on page 2.

Here's a capture mins created of the relevant part of the report:

So, there we go, more than just circumstantial evidence we have the aviation authority of Japan saying it's true.  It's the halfway mark for the runway.


Is it allowed to use an ex-military aircraft overseas?

If it has an N-number and an airworthiness certificate that allows the operations you want to perform with the aircraft, it doesn't matter what it did in a past life, you can operate wherever the country that controls the airspace will allow you to do so. As was mentioned before, the regulations of the country in which you wish to operate the aircraft are more relevant to what you want to do.

If on other other hand you have an ex-military aircraft that has an N-number but an exhibition-only experimental airworthiness certificate for a warbird, to pick an example, or some other type of restricted certificate, you're likely to be required to notify the FAA where and when you intend to fly it, and that may trigger additional oversight and possibly a denial of the permission to do so in a foreign country. The operating limitations document of the airworthiness certificate may also limit you to specific airspace within the US. Check the aircraft documentation and see if the FAA already put limits on the helo's operations.

That's where you will find the answer from the FAA point of view.


How much does a Hundred Dollar Hamburger actually cost?

The flight school I fly out of rents a 152 at 86USD an hour wet. Assuming you need some cash for the burger lets say you save the remaining 14 dollars for that you are right at your 100. With the 152 cruising at just about 95 Kts you need to keep the distance (both ways) under 95nm to say in our budget.

KDYL → Sky Manner (N40) is a 15nm hop and Sky Manner has a nice little restaurant.

If you want to put some actual time on the plane

KDYL → KRDG is a 39nm hop and there is a restaurant there.

Both of these hops keeps the hobbs at under or right at an hour of flying which keeps you under your total of 100USD for the flight and the burger.

That being said, there are bigger, faster, more expensive planes you can fly much farther to get food. I was chatting with a guy who flew his PC-12 from PA to Martha's Vineyard for lunch with some clients... I assume that was far more than 100$.


Will a Secondary Surveillance Radar be affected by a 300m high wind turbine?

No they won't, since secondary surveillance radar (SSR), as you point out, does not rely on reflecting electronic pulses, but rather on digital communication with an aircraft transponder.

Transponder signals do still travel in a straight line (line of sight), so obviously putting a very large obstacle (such as a mountain) close to an SSR will limit the radar coverage in the area behind the obstacle.


Why is dropping off passengers on the ramp by bus not more common?

The use of a jet bridge has several major advantages over loading passengers from the ramp via portable staircases or built-in "air stairs", among them:

Boarding of handicapped passengers
Not all passengers can use stairs: a jet bridge allows passengers with limited mobility, particularly those confined to wheelchairs, to board and disembark from the same level as the passenger deck.
Accommodating these passengers from the ramp would require some kind of lift mechanism to raise them to the passenger deck of the aircraft - this is typically accomplished elsewhere in the terminal when a jet bridge is used, e.g. via passenger elevators in the ticketing area, or in the type of design shown in your question, via an elevator in each "mini-terminal".
Passenger shelter
Boarding from the ramp may work well on a beautiful spring day, but in less favorable conditions (rain, snow, temperature extremes) most passengers would not find the experience to be enjoyable. The jet bridge provides an enclosed and relatively climate-controlled route from the terminal to the aircraft.
Passenger Safety
Airport ramps are inherently dangerous places: Aircraft are starting their engines, being pushed back for departure, etc. and ground support vehicles are moving at all times carrying luggage, cargo, catering supplies, etc. to and from the aircraft. In addition to the ongoing movement there is a great deal of noise from these operations.
Bringing passengers into this environment represents an inherent liability risk: Someone could be struck by a support vehicle, or injured by jet blast. A jet bridge is an enclosed area away from these dangers, providing an improvement in passenger safety.
Airport Security
A great deal of effort goes into ensuring that unauthorized persons do not have access to the airside facilities at an airport. Bringing passengers into this area represents a security risk, as even a ticketed passenger could be intent on causing disruption or damage once airside.
A passenger wandering off on the ramp would represent both a safety hazard (as the passenger could be injured) and a security hazard (as the passenger could perform any number of malicious acts before they are located).


What aircraft are these, and why are these engine sizes so different?

(Left), (Right)

On the left is the Pratt & Whitney J75 (JT4A) on a DC-8, with ram air inlets1.

On the right is an RR RB211, possibly on an L-1011. The EPR probe (I think) can be seen protruding from the inner lip at the 12 o'clock position, plus the snubber2 holding the blades together.

The former is a turbojet, that's why it's narrow. The latter is a high-bypass turbofan, that's why the big fan.

We can't directly compare both engines. The RB211 is 14 years younger, and much more powerful, suited for big planes unlike the narrow-body DC-8. The RB211 wouldn't fit under the wings of the DC-8. Different planes, roles, and engine requirements.

(Source) DC-8 with the high-bypass CFM56.

The DC-8 was later retrofitted with high-bypass because it's better for fuel economy and noise—the CFM56 to be precise—without the DC-8 getting the retrofit, the CFM56 would not have become as ubiquitous as it is now. The project needed civilian customers to survive3.

First run years: J57 (1955), RB211 (1969), CFM56 (1974).

L-1011 (top) and DC-8 (bottom). Eyeballed the scale.

1 Accessories on the Pratt and Whitney engines are mounted beneath the high-pressure compressor casing. Two drum-type oil coolers are provided, each fed with air from individual ram intakes in the lower part of the nacelle.— Flight
2 A snubber (or clapper) is a damper used to prevent blade flutter on narrow-chord fan blades, at the cost of reduced efficiency. Hollow wide-chord blades are more stable and do not need snubbers.
3 The CFM56 featured article on Wikipedia is a must read.


Is true altitude vertical separation between airplanes dependent on temperature?

Yes, the vertical geometric separation is temperature dependent.

If it cooler than ICAO Standard Atmosphere (ISA) conditions, the geometric vertical separation is lower than the pressure altitude separation. If the temperature is above ISA temperature then the geometric separation is higher.

The ICAO atmosphere assumes a sea level temperature of 15 degrees Celsius and a lapse rate of -6.5 degrees per 1000 geopotential meters altitude. At FL250, according to the model, the temperature is
-34.5° Celsius, at FL260 it would be -36.5°C.

Because the ISA is based on geopotential height, the geometric separation between FL250 and FL260 under standard temperature conditions would be slightly over 1000 feet. In fact it would be 1002.1 feet, because gravity is about 0.2% lower at that altitude.

If we would take the same mathematical model as in ISA, but would offset the temperature by -20° Celsius (-5°C temperature at sea level), the geometric difference between FL250 and FL260 would be only 932.7 feet.

If we offset the temperature by +20°C, the difference would be 1072.7 feet between FL250 and FL260.

This can be approximated by looking at the ratio of temperatures expressed in Kelvin. The average temperature between FL250 and FL260 is -35.5° C or 237.7 Kelvin. For 20 degrees below ISA temperature a rough estimate would yield:

$\frac{237.7 - 20}{237.7}×1000$ft = 915 feet.

For separation between aircraft and terrain, temperature effects are taken into account by adjusting the minimum safe altitude.

For vertical separation between aircraft no adjustments are made by ATC, but the effect is taken into account in safety cases.


What are the off-airfield rules for private helicopters in New Zealand?

I believe the relevant rules around helicopter landings are covered by CAA Part 91 section 91.127 Use of aerodromes.

You are permitted to land a helicopter off-airfield. Land owner approval is required (except in the case of emergency), just like any other use of land.


Do fighter jet pilots ever use autopilot?

I'm not in the military, so you could say I'm talking out my rear end here, but based on my experience as a pilot: yes, military pilots use the autopilot all the time.

Here's my reasoning, in order of most to least convincing evidence:

Punching the autopilot off takes about a fifth of a second.  The button is right there on the yoke, for crying out loud.  The time it takes to turn it off is not a good reason not to have it on.
The autopilot is a labor-saving device.  When you're in an aircraft (and particularly when you're solo in one) there are times when you'd rather be paying attention to your chart or setting up the FMS or stretching or eating a candy bar instead of actually flying the plane. Also, when Air Force pilots fly long repositoning flights, the autopilot reduces fatigue between in-flight refuelings (the Navy uses carriers).
Times when you might have to leave the designated path for a mission happen a lot less than you think.  Again, not in the military, I'm just basing this on the realities of fuel and the number of military aircraft out there.  Maybe if you're flying close air support for teams on the ground or something, but remember that the military is first and foremost a logistics organization - it's a machine for moving people and things from one place to another.  Most of the time, military aircraft aren't on a hair-trigger moment's notice ready-to-engage posture, they're going from one airfield to another for training or maintenance or something.
In most aircraft, you can override the autopilot if you need to anyway.  Again, never flown a military fighter aircraft, but based on what I know about flying in general, even if you're chilling in your F-22 (with the autopilot on) if you grab the stick and yank, the airplane will move.  (I would be interested to know whether this is true of Airbus aircraft. EDIT: Question answered after 4 years!)


No. A (pure) glider cannot make a go-around in the way a powered machine can. The glide path can be influenced by airbrakes, flaps,  chutes or slipping, but mostly those are for reducing your L/D, i.e., steepening the approach (you win again, gravity!).
Gaining height without updraft is only possible by converting kinetic energy (speed), and that gain is limited by the stall speed. So while you can rise a few meters when you pull up from landing airspeed, you will find yourself way too high above the runway at minimum speed and hoping for the best.
The highly enjoyable* spectacle of a low fly-by of a glider is achieved by starting with really high (unlandable) speed which is then converted into height and shortly followed by the inevitable landing**. For some older (mostly wooden) gliders, even this is not a very good idea because they combine a lower VNE with lower L/D ratios,  leaving you low and slow after pulling up from redline speeds.
In a glider, you get one chance for a smooth landing (freak thermals excluding). But a properly trained pilot gets used to this very quickly. A proper landing procedure together with brakes, flaps, etc. will bring you down safely.
*but not necessarily safe or recommended
** unless you catch a proper thermal or dynamic updraft.


If an elliptically-shaped aerofoil gives the optimum lift distribution, why aren't propeller blades designed around this ideal?

If an elliptically-shaped aerofoil gives the optimum lift distribution …

I interpret this as an elliptically shaped wing, because only then the question makes sense.
Propellers are similar, but not identical to wings.

Dynamic pressure varies along blade span. The outer sections needs less chord for the same lift compared to inner sections.
Propeller blades operate at the start of a helical wake, so induced speeds are different than those on straight wings.

What is required is not an elliptic lift distribution, but minimum induced losses. Albert Betz showed in 1919 that the optimum induced speed is constant over the propeller disk, just like downwash is ideally constant over span for minimum induced losses. Based on this, Larrabee found an efficient computation method and practical propellers have to find a compromise between theory and practical constraints. The most important are

Compressibility effects near the tips (which force thinner airfoil and lower lift coefficients than what the ideal prescribes). An extreme case is the Junkers VS-9 propeller used on the Ta-152.
Structural limits at the root (which force the use of much thicker airfoils).

Betz' theory is meant for lightly loaded props. Once disk loading goes up and the propeller diameter cannot grow proportionally, propeller chord and blade count grows and the main concern shifts to converting all available power to thrust. Concerning fancy blade shapes: They have more to do with marketing or unscientific voodoo beliefs by some hobbyists. Generally, a straight shape works best.


What would have been the other stops of Amelia Earhart's ill fated last voyage?

This table from Wikipedia shows the final two planned legs of her flight being:

  July 3, 1937 Howland Island   to  Honolulu, Hawaii     1900 NM  Planned
  leg

  July 4, 1937  Honolulu, Hawaii to Oakland, California  2400 NM  Planned
  leg


How are multi vs single engine helicopters categorized?

For the FAA, rotorcraft powered by more than one powerplant are not separately classified.

A random N-number search for a random twin-engine helicopter—AgustaWestland AW109—using the FAA registry yielded the type as: Rotorcraft.

However for a Boeing 707, the type came back as: Fixed Wing Multi-Engine.

I couldn't find a place where the different classes are listed on the FAA website, whether for fixed-wing or rotorcraft.


Which are some planes shaped like an inverted wing?

Your intuitive feeling that the fuselage could be used to create additional lift is correct. Indeed, some aircraft are specifically shaped such that fuselage could provide substantial lift (and that's excluding any 'flying wing' design where fuselage is completely blended with the wing).

However, these are generally supersonic fighter aircraft. At supersonic speeds, even the 'normal' tubular fuselage will create significant lift, given a decent angle of attack. Moreover, the engine air intakes, if properly designed, will create even more lift.

In GA aircraft, on the other hand, the effect must be negligible, and structural considerations (yes, including high/low wing) are much more important.

The primary aerodynamic consideration for the fuselage is, generally, minimising its drag and reducing interference with other parts, primarily the wing. In this regard, by the way, C172 (or any high-wing aircraft) is more 'lift-friendly'. High-wing design has less negative wing/fuselage interference; in fact, it can be even positive. In simple terms, the part of the wing above the fuselage still creates lift, and probably more of it than the whole fuselage (although I have no numbers at hand).

I also must duly note that the principle of lift generation has little to do with the geometric length of the upper and lower surfaces. It is a popular misconception. The air indeed moves faster over the upper surface, but this is due to entirely different reasons. There are several good explanations of lift on this site.


How does wing shape impact shock structure?

Is the shock seen in the side view (airfoil shock structure) related to the one seen in the top view?

No, not at all. The first picture (side view airfoil) shows an unswept wing in supersonic flow and is not very precise. The shock angles of the LE shock and the TE shock should be identical.
The second picture (top view wing) shows a swept wing at bit above the speed of sound (almost half the speed in the first picture). Here, the flow pattern around the airfoil is fully subsonic (that's why the wing is swept!) and only its most forward tip will cause a shock which is almost straight because flow speed is only a bit higher than the speed of sound.

How would the shock structure change if the airfoil is kept the same but the wing is swept more? (If you can show some 3D plots for the shock structure, it would really be helpful!)

That depends on the ratio between speed and sweep angle. As long as the sweep angle exceeds the shock angle, flow around the airfoil behaves like in the  subsonic case with a stagnation line, flow around the round leading edge and no bow shock or expansion fans. When the shock angle is greater, the airfoil will show a flow pattern like in the top picture. Sorry, no fancy 3D plots!

Can you explain what determines the shock angles in this picture (is it sweep or airfoil shape or both - and which is more dominant)?

The first and foremost factor for the shock angle is speed. Mach 1 will cause a straight shock and higher speeds will bend the shock backwards into an oblique shock with a shock angle $\varphi$ according to the equation $$\varphi = arccos\left(\frac{1}{Ma}\right)$$
This angle will become smaller with increasing bluntness of the body causing it.

Shock angle diagram (from Wikipedia, source). The caption is: This chart shows the oblique shock angle, β, as a function of the corner angle, θ, for a few constant M1 lines. The red line separates the strong and weak solutions. The blue line represents the point when the downstream Mach number becomes sonic. The chart […] is valid for an ideal diatomic gas.
Explanation: M1 = Mach number ahead of the shock, M2 = Mach number past the shock. β is the half cone angle such that β + $\varphi$ = 90°.
Consequently, the angle of the shocks emanating from that T-38 show that it flies at around Mach 1.09. In Schlieren images like this darker areas indicate higher density and lighter ones lower density. The two dark lines coming from the fuselage tip and engine exhausts are the two compression shocks which are audible as a double boom when a supersonic aircraft passes overhead.


"short parking" seems to be an informal European term for "short-term parking".  So it's referring to the time a vehicle is parked, not the distance.

If I heard it about the location of an airliner, I'd think they meant that the gate areas were full and it had to be put somewhere temporary (and inconvenient) this time.


How did they solve the compressor stall issue of the F-14A in the B?

Grumman changed the F-14 powerplant from the Pratt and Whitney TF-30 engine to the General Electric F-110 engine when the F-14B was developed.  This not only provided the airframe with an extra 16,000 lbs of thrust compared with the old TF-30 engines but also a much more stable, reliable gas core as compared with the P&W design.  I don’t know if they have managed to wring out the issues in the F119 and F135 engines, but Pratt and Whitney engines have been notoriously finicky and prone to compressor stalls if not petted nicely.  GE engines, particularly military aircraft engines, are some of the most robust and reliable jet engines out there.


As you make a symmetrical airfoil thicker, in which direction does the lift force increase?

Lift is defined as the vector component of the total aerodynamic force perpendicular to the freestream velocity vector. Wikipedia about lift

By definition lift can not contribute to thrust or drag, so the direction is fixed.

The sense of the lift vector is opposite to the flow deflection caused by the angle of attack, so the lift increases in that sense.

For your project you might be interested in looking at the lift/drag profile, rather than just at lift.


Spanwise flow and wingtip vortices in forward-swept wings

There is no magical switch that gets flipped once you cross a specific sweep angle. Things are gradually changing with the cosine of the local sweep angle. Now let's look at your questions one by one:

  What happens to the wingtip wake on a forward-swept wing?

Nothing special. It is part of the full wake system and behaves like in any other aircraft of comparable aspect ratio and lift distribution over span. For high sweep angles and high lift, the wing torsion will increase local loading towards the tips, making the tip vortex relatively stronger.

  Does sweeping wings forward completely eliminate it, and if it depends on sweep angle?

Why should it? No, the tip wake of the wing with more forward sweep will be stronger for comparable wings with different sweep, for aeroelastic reasons as explained above.

  How to estimate sweep angle, at which the spanwise flow starts to flow to the root?

See here for the reasons for spanwise flow. As soon as forward sweep results in a lateral local speed component, spanwise flow will happen.

  Considering a tapered wing with only trailing edges swept forward, is it enough to get wing characteristics (primarily spanwise flow) like (or close to) forward-swept one?

With a straight leading edge, flow will not exhibit any sweep effect. With a large taper ratio, forward sweep can still become significant towards the trailing edge, but most flow acceleration happens around the nose, so overall sweep effects will still be small.


Flight tests of new aircraft are covered under Part 21 Subpart B—Type Certificates §21.35 Flight tests.

There is no provision for the carrying of 'passengers' during any test flights, but then, there is no limit on the number of 'flight crew' either. FAA regulations does not explicitly prohibit the carrying of any passengers as such; however, it places onus on the applicant for ensuring the safety of anyone abroad during test flights:

  (d) Each applicant must show for each flight test (except in a glider or a manned free balloon) that adequate provision is made for the flight test crew for emergency egress and the use of parachutes.

This places severe restriction on carrying of anyone during test flights. However, before certification, the manufacturer can carry passengers as long as it is not for commercial purposes. Actually, Airbus did this during the test flights of A350 XWB:

  Another important aspect of A380 and A350 XWB testing was the Early Long Flights (ELF) programmes, which went above and beyond certification requirements. For these evaluations, a cabin-equipped flight-test aircraft was operated on simulated commercial services with real “passengers” – comprised of Airbus employees – and actual airline flight crews to evaluate cabin systems in typical operating conditions.

Unless the flight testing is at an advanced stage or the manufacturer is extremely confident of the design, I don't see any non-essential flight crew being allowed in test flights, for obvious reasons.

In case of test flights after maintenance or alteration, CFR § 91.407 - Operation after maintenance, preventive maintenance, rebuilding, or alteration says almost the same thing:

  (b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.


Can active flight plan be sent for the aircraft in the air?

Your question is short on details, but in general, yes this is possible. A flight could be coming from anywhere, for example:

Another jurisdiction (FIR)
Uncontrolled airspace
A beach somewhere

In these sorts of cases, you may see the first FPL message after the aircraft has departed. The departure aerodrome, if known, may appear in the ADEP field (field 13a), or it may be ZZZZ for an unknown aerodrome, or it may be AFIL for an "air filed" flight plan.


How does the reusable holdback bar work?

Source: YouTube

The bar is placed between a tong-like (two hooks) device on the aircraft, and when released, the body of the holdback bar envelops the hooks (note the disappearing red paint on the tips of the hooks) forming a collet.

On the inside, as the plane pulls on the bar (1), the walls (2) compress a chamber filled with hydraulic fluid (3). The fluid pushes into a channel and pushes against a sphere (4). At the right pulling force, the sphere is pushed which allows the fluid to fire the piston (5) freeing the inserted hooks from the bar.

Source: YouTube

Reference: Repeatable release holdback bar, US Navy patent US4101099A


What does it mean when the controller uses the word "request"?

In civil aviation the ICAO standard phraseology should be used. This phraseology is described in ICAO document 9432.
The standard ICAO phraseology is to use the word report in the first case.
According to the definitions it means: "Pass me the following information ..."

  [callsign] report heading

The second phrase is even stranger. QNE is the standard pressure altimetry setting of 1013.25 Hectopascal (29.92 inches of mercury in the US). When an altimeter is set to standard pressure, the normal way of reporting the altitude is in Flight Levels. So in this case the standard phraseology should have been

  [callsign] report Flight Level.


Are there some minimum criteria for a field to be registered with the FAA as an airstrip?

Good question.

14 CFR Part 139 requires FAA to issue airport operating certificates to airports that:

Serve scheduled and unscheduled air carrier aircraft with more than 30 seats;
Serve scheduled air carrier operations in aircraft with more than 9 seats but less than 31 seats.

Also:

  VFR charts depict airport's hard and soft surface runways. Enroute charts depict airports having hard surface runways of at least 3000-foot in length. If your airport meets those criteria, you may contact the local Federal Aviation Administration, Airports District Office or Aeronautical Information Management, AJV-21, at 1-(866) 295-8236 to have your airport charted.

That means for a private airstrip, it's your call as the owner to have it placed on a chart. Pretty cool.

More: https://www.faa.gov/licenses_certificates/airport_certification/


Why can't sonic booms be heard at air shows?

Just for a bit of flavour, I recall an article from Air Progress from the late 70s about Darryl Greenamyer setting the low altitude absolute speed record, in his "homebuilt" F-104, of Mach 1.3 (mentioned in this article) in 1977.

For the run he had to cross very low over timing trigger devices at the start and end of the speed course at the dry lake bed at Edwards, which were set up with cars parked beside them.

I remember the description of the event by the writer who witnessed it from somewhere along the middle of the course, a safe distance away with other observers.  The F-104 passed over the car at the 1st speed trap at 60 ft AGL and passed the writer in absolute silence, and it wasn't until a second or so had passed that a sound like a dynamite explosion a couple hundred feet away went off.  All the glass of the cars at the speed traps blew out and their trunks popped open.  The writer was warned in no uncertain terms that if he didn't protect his ears he'd get hearing damage, and not to be fooled by the initially silent passage of the jet itself into taking his fingers out of his ears.

Imagine that happening at an airshow.


What structural design methods were used for early turbojets?

Going back further to the early 40's to the de Havilland Goblin turbojet:
There is an in-depth article from Flight from February 21st, 1946. The first page is here, but you'll need to download the rest of the pages from the navigator on the left. It even comes with this diagram showing the forces on the different parts.

Materials
Reading through the article, the biggest unknown back then was the materials to choose for the hot sections.

Plenty of theoretical information was available on blade form, but little was known about the operating temperatures likely to be experienced. Chief properties required of the selected materials were a high resistance to creep, corrosion and scaling.

They got their hands on the strongest materials, and with the aid of heat-sensitive paint, they scaled back the requirements.

On the first few engines, turbine discs were made of austenitic steel, but later, with the aid of heat-sensitive paint, it was found that ferritic steels with their greater strength, around the working temperature of 750 deg. C. and a lower coefficient of expansion, would prove satisfactory.

Vibrations
For vibrations, what I gather is it's not that big of a deal for turbojets compared to turboprops of that era, but here's the relevant part:

[...] subsequent measurements of vibration for the whole power unit have shown that the vertical oscillation is less than ± 0.001 inch.

Trial-and-error
There is also the test-to-destruction method (not really):

[...] troubles experienced included weaknesses in the welding of combustion chambers, and in the construction of the intake ducts and the tail pipe.

So, there was a fair share of trial-and-error.
Forces
Regarding the forces, and that's a guess here, we find:

Any thrust loading is taken by the front bearing which is located on a stub or pivot shaft between the air intake ducts in front of the impeller.

Post-examination of the bearings may yield information.
For gas-load calculations, back then they've already made very powerful turbocharged engines, so they've had the knowledge. As the article suggests, the chief issue was the materials.


How does a non US pilot buy a N reg plane?

The ownership requirements for registering an N-reg aircraft are discussed in this question. The current FAA information says that the only options open to a non-resident foreigner are:

  A corporation or association:

  organized under the laws of the U.S. or a State, the District of Columbia, or a U.S. territory or possession,
  of which the president and at least two-thirds of the board of directors and other managing officers are U.S citizens, and
  in which at least 75% of the voting interest is owned or controlled by persons that are U.S. citizens,

  A non-U.S. citizen corporation organized and doing business under the laws of the U.S. or one of the States as long as the aircraft is
  based and primarily used in the U.S. (60% of all flight hours must be
  from flights starting and ending within the U.S.)

So you either need a corporation that's majority controlled by US citizens, in which case there are no restrictions on flight activities; or, you can use a non-US citizen corporation but then most of the flight hours have to be in (or to/from) the US.

The ideal way to go about this would be to find someone near you who's already done it. Many flight schools and individuals outside the US operate N-registered aircraft so you might be able to find someone who can tell you how they did it. You'll need to do this research anyway, because if you're basing an N-reg aircraft outside the US then you'll need to find an FAA mechanic near you who can legally perform maintenance on it. If your country has some kind of GA or pilot's association then you could ask them too.

You can also look for companies (usually law firms) who specialize in doing this and get their advice and/or retain them to actually set up the ownership structure that you need. That's going to cost some money - and many firms are focused on business jets, not light singles - but it could be a minor cost compared to the aircraft and maintenance, depending on what you plan to buy. I found a few by Googling but a personal reference from someone near you would be a lot more useful.


Is there a reason Germania aircraft cabins have blue lights?

Bergische Universität Wuppertal has done some research that chronobiologically-adapted LED lighting can enhance passengers well being and they can sleep better during a flight.

This article details about this research:

  Adaptive solid-state lighting (SSL) scenarios in which the color and
  brightness of lighting is varied during long-distance overnight
  flights results in passengers that sleep better and are more alert
  upon arrival.

  ... at the start of an overnight flight that warm-white light helps to
  stimulate melatonin production and increases passenger relaxation ...
  blue-rich cold light in the morning increased alertness

There have been studies showing benefits of biologically effective lighting for more relaxed flights.