Is there a limit to the possible altitude for electric jets?

That electric propulsion needs no oxygen is of little help for flying high. The composition of the atmosphere does not change too much with altitude, so it is the low atmospheric density which limits maximum altitude. We had this discussion before, and indeed solar-electric propulsion helped to reach record altitudes: The AeroVironment Helios set a record at 29,524 m which will be hard to break.

Supersonic speed helps to fly high - while subsonic designs run into the coffin corner, supersonic flight helps to maintain high dynamic pressure even at altitude. However, the energy requirements for doing so will require an energy density of the batteries which is several magnitudes above what is currently possible. If you only want to go fast, the current limit with electrical propulsion and already rather generous assumptions is somewhere around Mach 2.

Flying higher does not reduce the thrust requirement since the same lift has to be generated. The best lift to drag ratio is achieved in subsonic flight. Going supersonic means crossing a drag peak, but beyond that the maximum possible lift to drag ratio is well below that at subsonic speed and decreases again with increasing Mach number.

Mr. Musk is clearly out of his competence when he claims that supersonic electric airplanes are viable, even with the progress in battery technology to be expected in the next few decades.


Calculating the horizontal distance the payload would travel with a parachute (horizontal drift)?

The first thing to figure out is how fast your parachute will fall. From https://www.pcprg.com/rounddes.htm you can compute the falling velocity:
$$ V = \sqrt{\frac{2 W}{\rho C S}} $$
Where

$C$ is the parachute drag coefficient which is approx 0.75 for a parachute without holes or slits cut in the fabric; same value in both Metric and English unit systems

$S$ is the total surface area of the fabric used to build the parachute, plus the areas of the holes and vents cut in the fabric if present. The units of S are in square feet (English) or square meters (Metric). This definition is such that when vents are cut in the fabric, the value of $S$ remains the same but the value of $C$ becomes smaller.

$\rho$ is the air density

near sea level its value is given by
0.00237 sl/ft^3 (English units) and 1.225 Kg/m^3 (Metric)
near 4000 ft or 1219 m above sea level its value is
0.00211 sl/ft^3 (English units) and approx. 1.07 Kg/m^3 (Metric)

$W$ is the weight of the parachute + load, in pounds (English) or Newtons (Metric)

$V$ is the vertical descent velocity, here expressed in ft/sec (English) or m/sec (Metric)

You can either assume a constant speed all the way down, or make it a function of $\rho$.
With starting altitude and speed you can find the time it will take to fall.
Then you add the wind contribution. Multiply the wind speed by the descent time and you get the maximum range the parachute can reach.
The calculations will get a little mode tricky if you have a rho profile by altitude and wind speed profile by altitude.


Is a single engine failure on the HondaJet recoverable?

There would not be much point in having two engines if a single engine failure would be unrecoverable.  In fact, that would make the plane twice as likely to have an unrecoverable event!

If one engine has a 1/1million chance of failure, then the chance of failure of at least one of 2 engines is 2-in-a-million.(technically, slightly less than 2-in-a-million... but close enough)  And if either engine failure is catastrophic, then you've doubled your chances of losing the plane.

I don't know about the HondaJet in particular, but by logic and statistics, I can say that a single engine failure must be recoverable.


What are these autonomous, shape-shifting indoor neutral-density craft I read about?

The comment by @Andy suggesting they were Festo Air Rays almost nailed it.
They were Festo Air Penguins!

They can be seen maneuvering in these videos:

The article http://www.robaid.com/bionics/airpenguin-flying-robot-penguins-whats-next.htm describes the mechanism:

A strut to which the two wings are attached passes through the helium-filled balloon. This new type of wing design can produce either forward or reverse thrust. Each wing is controlled by two actuators: a flapping actuator for the up-and-down movement of the wings, and a further unit that displaces the wing strut to alter the pressure point of the wings. There is also a central rotational actuator for the two flapping wings that direct their thrust upwards or downwards, thus making the AirPenguins rise or descend.
The wing strut, which is supported at the pivot point of the torso, can be moved either towards the front or rear edge of the wing. Displacing the strut towards the front, for example, causes the wing’s pressure point to migrate forwards. The air-stream pressure bends the cross-section of the wing in such a way as to produce a profile that generates forward thrust. If the wing strut is moved towards the rear edge of the wing, the pressure point is likewise moved to the rear and the AirPenguin flies backwards. With this design a self-regulating, wing pressure-controlled, passively twisting adaptive wing has been realized for the first time.
The AirPenguins are also equipped with complex navigation and communication facilities that allow them to explore the space they float in on their own initiative, either autonomously or in accordance with fixed rules.

While they can be autonomous, and fly in formation, they can also maintain a "ground link."

By means of XBee, based on ZigBee, large volumes of data can be transmitted between the penguins and the transmitting stations by 2.4-GHz band radio. The penguins recognize each other on the basis of their distances to the transmitting stations. The rapid, precise control allows the AirPenguins to fly in a group without colliding, while also mastering height control and positional stability. As an alternative, they can act synchronously as a group. A comprehensive central surveillance system provides security in case of sensor failure. When AirPenguins are on low energy supply it prompts the penguins to return to the charging station.
The ongoing development of sensor and control technology is thus also being promoted along the road to decentralized, autonomously self-controlling and self-organizing systems thanks to the inspiration from nature.

While searching for information I found this even more advanced, articulated light (but not neutral buoyant) craft, the BoiniCopter, also http://www.robaid.com/bionics/festo-bionicopter-robot-dragonfly.htm which states a mass of 175 grams and wingspan of 70cm :

note: I have no affiliation with these sites or companies. This answer is a bit long I know, but the material is a bit unique. I felt that in this particular case the extra background may be helpful.


What are the aircraft requirements to legally offer commercial sightseeing flights in a C-172?

It needs to be airworthy, as per 91.403, which is defined to include compliance with all ADs:

  (c) No person may operate an aircraft for which a manufacturer's
  maintenance manual or instructions for continued airworthiness has
  been issued that contains an airworthiness limitations section unless
  the mandatory replacement times, inspection intervals, and related
  procedures specified in that section or alternative inspection
  intervals and related procedures set forth in an operations
  specification approved by the Administrator under part 121 or 135 of
  this chapter or in accordance with an inspection program approved
  under § 91.409(e) have been complied with.

It needs a 100-hour, as per 91.409:

  (b) Except as provided in paragraph (c) of this section, no person may
  operate an aircraft carrying any person (other than a crewmember) for
  hire ... unless within the preceding 100
  hours of time in service the aircraft has received an annual or
  100-hour inspection and been approved for return to service in
  accordance with part 43 of this chapter or has received an inspection
  for the issuance of an airworthiness certificate in accordance with
  part 21 of this chapter. The 100-hour limitation may be exceeded by
  not more than 10 hours while en route to reach a place where the
  inspection can be done. The excess time used to reach a place where
  the inspection can be done must be included in computing the next 100
  hours of time in service.
  (source: 14 CFR Part 91.409).

Part 43 Appendix D specifies the items which need to be checked in the 100-hour inspection.

And it needs to have all the other necessary mechanic's inspections, including ELT, transponder/pitot static system, etc., and pilot checks, like VOR accuracy.


Substitute Suitable RNAV system for Inop Radar on approach “requiring” Radar

Since "radar" means "ATC radar", I'm not sure how a pilot could substitute anything for it. The issue isn't that the pilot needs radar to navigate the approach; it's that's ATC needs radar in order to allow the approach in the first place.

Per this answer, ATC can only clear aircraft for an RNAV approach without an IAF if radar monitoring is available. I don't think we've found out why that's the case, but it's what the ATC orders say (4-8-1(h)). Since the approach above has no IAF, that means ATC can only clear you for it if they have radar monitoring.

4-8-1(g) also instructs controllers not to let pilots choose their approach if there's no radar available:

  g. Where instrument approaches require radar monitoring and radar
  services are not available, do not use the phraseology “cleared
  approach,” which allows the pilot his/her choice of instrument
  approaches.

In other words, ATC has to make sure that they clear pilots for approaches only if their own requirements are met.

But as it happens, ATC does have a possible substitution for radar. The ATC orders 5-5-4 say:

  The use of ADS-B only information may be used to support all radar
  requirements associated with any published instrument procedure that
  is annotated “Radar Required”.

I assume that means that - at least theoretically - if ATC lost radar but could still receive ADS-B, they could clear you for the approach. But that would be ATC substituting equipment, not the pilot :-)


How dangerous can it be if something falls from a flying aircraft?

The standard operating procedures state that before every flight, a thorough pre-flight inspection should be performed. Depending on the aircraft, minute and tiny details are not even omitted.

Things do not normally and occasionally fall off from a flying airplane, the same way as different objects do not fall from a driving car, although the pre-drive inspection of a car is no where nearly as comprehensive as the pre-flight inspection. Yet, how many times we have seen a bumper, guard, muffler or rear-view mirrors falling off?

How dangerous it would be when it happens? This depends on the part which has fallen. Some parts are not noticeable until landing or next inspection and some can cause disasters.

Baltimore Sun reports this:

  No deaths or injuries have been reported in such incidents, but the
  Federal Aviation Administration is not even 100 percent certain of
  that.

The proper term for this incident is Things Falling Off Aircraft (TFOA). The pilot must then submit a hazardous material report within 24 hours in case the material can cause further harm.

This site has listed some TFOA incidents:

  In August 2000, a KLM Royal Dutch Airlines Boeing 747 was forced to make an emergency landing when some engine pieces plummeted to the
  ground and landed on a crowded Los Angeles beach
  On March 10, 2005, a couple taking a stroll through woodlands near Gatwick airport had a lucky escape when a door from a passing British
  Airways jet, crashed to earth. A part of the 70-pound door from a
  Boeing 777 had become dislodged just after take off and missed the
  couple by only 20 feet!
  On August 11, 2006, a door fell off from a TAM Fokker 100 from Sao Paulo to Rio de Janeiro. It dropped off 18 minutes after departure but
  the plane was able to return to Sao Paulo without incident. Nobody was
  injured.
  An engine exploded on a Japan Airlines flight bound for Tokyo with pieces of the engine falling on a neighborhood in Jakarta. The falling
  debris hurt no one but 16 homes were damaged.
  The right wheel of a Blue Panorama Airlines Boeing 737 fell off after it departed from an airport in Spain and was forced to make an
  unscheduled landing amid emergency in Rome.
  A similar incident happened near Los Angeles where an American Airlines Boeing 757 lost its right nose gear but managed to land
  safely with 105 passengers on board.
  A landing gear door fell off a Delta Airlines Boeing 727 shortly after the plane took off from Boston*s Logan International Airport.
  The 30-pound metal door crashed into an empty street in a quiet
  residential neighborhood.


What is the cheapest plane one can buy to fly above Mach 1 and be able to pull 8g plus?

Ignoring the various practical limitations that 99.9999991% of people would encounter....

The answer more has to do with what is available than what would be optimal. There are not a whole lot of air frames that fit such a criteria and there are even fewer that are for sale to/in the public hands, when talking about things that exist in the single digit realm for-sale quantity is a real factor.

This McDonnell Douglass F-4 is currently listed for 3,950,000 USD and perhaps gives a good basis for what such a plane would cost. The F-4 carries 3335 gallons of Jet fuel, at my local field where fuel is a reasonable 4.50 a gallon its going to cost you 15000 USD to top off the tanks. Fuel burn depends on how you run the aircraft, if you are slamming it at super sonic speeds all the time your hourly burn rate is going to be high.

Maintenance is harder to pin down. These jets were generally operated by the military so you are going to need to find a mechanic out in the world that is willing to deal with it. You may get lucky and find someone who has some military experience to do the work but if you cant you are going to need to hunt down all the maintenance manuals and related documentation for the aircraft which may be harder to come by than you think. On top of that you need to keep two J79 in working order that may already have a lot of time on them.

If you want to hop to the other side of the pond design wise this MIG-29 is listed for 4.60 Million USD and will get you into the super sonic spectrum and allow you to pull some G's.

So for ~4.5 Million and some non determinant maintenance costs, lets say conservatively 500,000 a year for fuel, oil, incidentals, maintenance, some new tires, avionics and other odds and ends you can have all the fun in the sky you want.


How much does a Black Box Underwater Locator Beacon (ULB) cost?

There is one listed here on Ebay for $750. Some of the makers like L-3 list contact info for getting pricing, all of the other sales sites I am finding look like you need to submit for a price quote.


Would solar panels on the wing of an aircraft increase drag?

No, assuming the wing geometry and the coefficient of friction of the material on the surface of the wing do not change. So, swapping a section of aluminum or carbon fiber skin on the wing for a section of Plexiglas or silicate glass under which you place the solar cells will, all other things being equal, have a negligible effect on drag.

However, doing something like this, all other things are not necessarily equal. First off, the border between the normal skin material and the solar cell cannot be a perfectly smooth transition; at some level of magnification, there will be a noticeable seam which will reflect as an increase in the surface "roughness" of the with with solar cells compared to the one without. While nonzero, it's likely negligible if the parts of the wing are well-fitted.

Second, there will likely be a change in mass when removing a thin layer of aluminum, carbon fiber or polymer sheathing, and replacing that with Plexiglas with solar cells underneath (plus the power wiring, converters and other additional components that otherwise wouldn't need to exist). Classically, that has no effect on drag, but it will change momentum calculations which affect how much the drag matters, and also as was stated, heavier masses require higher angles of attack to increase lift and counter weight, which increases induced drag as the effective shape of the airfoil slicing through the air changes to present a larger cross-section. Wing stress moments will also be affected as the weight distribution of the plane between fuselage and wings has changed, and this can change the amount of effective dihedral due to wing loading under various conditions.

Lastly, there will be a nonzero difference in surface roughness between the majority of the skin or sheathing and the solar cells. For instance, a matte finish as some aircraft have is rough by definition to provide different reflective planes to scatter light. You want a highly polished surface on the solar cells to minimize energy loss through the outer layer. Even if most of the aircraft is finely polished, there's a difference in how fine a polish various materials can take; the harder the surface, the easier it is to take a fine polish.


Yes, it's still done today, at least in military aviation.

It's to ensure that the undercarriage does not excede the number of landings it has to endure before being checked/overhauled/replaced. Landing an aircraft can typically be the most stressful regime of flight in terms of loading of certain bits of the aircraft, so it is pertinent to log how many times it happens per flight.


Which aircraft type flies the most annual passenger-miles?

Some heavies (747, 777, A380) fly short- to medium-haul in Asia and the Middle East. You could say they're stealing jobs from 737's and A320's.

Anyway, what I could find was for the US only.

Checking the Revenue Passenger Miles Total by Aircraft Type for 2016 on transtats.bts.gov we find—

All 737 variants: 153.2 billion
All 777 variants: 38.3 billion

Expanded:

Boeing 737-100/200         18,374,213
Boeing 737-200C                58,536
Boeing 737-300          6,609,070,471
Boeing 737-300LR              574,860
Boeing 737-400          1,484,593,783
Boeing 737-500            324,819,083
Boeing 737-700         44,485,736,725
Boeing 737-800         69,014,076,197
Boeing 737-900         18,203,949,655
Boeing 737-900ER       13,058,102,746
Boeing 777-200-        32,808,990,997
Boeing 777-300-         5,466,846,693

Top types with at least 10 billion pax miles:

Boeing 737-800                  69,014,076,197
Airbus Industrie A320-100/200   48,907,277,978
Boeing 737-700/700LR            44,485,736,725
Boeing 777-200ER/200LR/233LR    32,808,990,997
Airbus Industrie A321           28,492,821,887
Boeing 757-200                  26,182,350,221
Boeing 767-300/300ER            24,176,619,545
Airbus Industrie A319           22,087,734,671
Boeing 737-900                  18,203,949,655
DC9 Super 80/MD81/82/83/88      15,379,739,818
Boeing 737-900ER                13,058,102,746
Airbus Industrie A330-200       10,556,831,804

From this top list:

Single-aisle: 285.8 billion
Widebody: 67.5 billion

(Narrow- vs. widebody above is just in case you are wondering. Arbitrarily selecting top-x won't reveal much.)

Boeing's outlook for the future based on past- and current-trends sees the single-aisle market outgrowing the widebody.

I've tried to dig deeper, but it seems some 260 governments don't openly share those statistics, we'd need to hire an analyst firm for a worldwide view.


What does ATC mean when they say "no longer a factor"?

This one is usually replied in relation to other air traffic around a particular flight which at one point may have posed a collision risk but is no longer in a position to do so.  Example
ATC: “United 2410, traffic is two miles at your ten o’clock at 5,700.  Cessna.  Report them in sight.”
If it appears the other aircraft will no longer cross paths with the aircraft being directed, the controller may say something like:
ATC: “United 2410, the Cessna traffic no longer a factor.  Turn right heading 340.  Descend and maintain 3,800, slow to 160 knots.”


Why don't airports have weigh stations to prevent overweight takeoffs?

Aircraft are heavy.

Really, quite heavy.

An Airbus A340, depending on type, has a maximum takeoff weight (MTOW) of up to 380,000 kg.

A Boeing 747, again depending on type, can have a maximum takeoff weight of a shade under 447,700 kg.

Measuring that kind of weight accurately is certainly not impossible, but it's not exactly easy either.

A bigger issue is that it's not as simple as saying that if the aircraft weighs more than some number of kilograms, then it's overweight, and if it weighs less, then all is fine. The distribution of that weight within the aircraft – precisely that "weight and balance calculation" which you mention – matters, sometimes a great deal. The aircraft could be putting an acceptable weight on the wheels, but if the weight is too far forward or too far aft, may still be outside of its controllability limits once it lifts off the ground.

Simply putting the aircraft on a scale and providing the pilots (somehow) with a weight-on-wheels readout as they taxi will catch the situation where the pilot can't add (as in, mathematically add up the weight components that make up the total aircraft weight), but it won't necessarily catch the situation where the load is improperly balanced.

So you'd be adding another fair bit of complexity (which can fail in various ways) to a currently relatively simple part of aviation (the taxiways or apron), possibly giving the pilots a false sense of security, and not solve the problem. Someone would still need to do a weight and balance calculation, at which point the weight-on-wheels reading can, at best, provide a rough sanity check on the weight part of the weight and balance.

Seems easier to just try to figure out ways to make the weight and balance calculations easier to perform, and make random spot checks on weight and balance calculations done (and schedule followup training if the pilots, or ground crew, or whoever else, need it).


High performance endorsement in airplane modified by STC

No.  All that’s required is that you received ground and flight instruction in an aircraft which meets the requirements for a high performance airplane in 14 CFR §§61.31 (f) and received an high performance endorsement from an authorized instructor in their logbook.  If the approved STC makes alteration to the engine such that the power out is now rated to exceed 200 bhp per the terms of the STC, then the airplane would be considered high performance under §§61.31.


Why are heavy flaps better than just a bigger wing?

When flaps are retracted they do nothing, which is the whole point. The byproduct of lift is drag, a larger wing will create more lift, but more drag as well. More drag equals a slower cruising speed, or bigger engines to power past the drag along with higher fuel consumption. Flaps let airplanes cruise faster by getting out of the way.


Will depression from 20 years ago prevent me from being an airline pilot?

It does not sound like a dealbreaker, however I'm not an aviation medical examiner. I do not think that depression diagnosed when you were a minor would prevent you from becoming a commercial pilot now, I do not even know if you would be required to declare it to an airline on an application. The biggest hurdle you would have is the medical I would expect. You might need to have a psychiatric evaluation, or it might be far back enough that isn't necessary. It likely depends on the severity of the depression you were diagnosed with on the DSM (diagnostic and statistical model of mental disorders, a tool used by professionals to assess and diagnose mental conditions) scale.

My recommendation would be to talk to an aviation medical examiner. Many pilots deal with, or have dealt with depression, sometimes severe, so it should not be hard to answer. You lose nothing by trying.


What is the concept behind being able to continuously pour iced tea while rolling an airplane?

The maneuver Bob Hoover is performing is a specific kind of roll called a barrel roll.  If you look at the path traced by this maneuver it is a corkscrew rather than a linear path that you might be imagining.  Because the airplane is rotating about a longitudinal axis as it translates forward there is centripetal acceleration toward the axis of rotation, or "up" in the reference frame of the person in the airplane.

To the observer in the reference frame of the airplane (e.g. the pilot or a passenger), the centripetal acceleration is interpreted as the fictitious centrifugal force.  This is exactly the same mechanism that you experience when driving around tight curves, though the force is in a different direction.  The end result in the airplane is that for a properly executed barrel roll, the centripetal acceleration causes the net force you experience inside the airplane to remain constant throughout the roll (in your reference frame, with the net force pointed "down").

If you were to close your eyes you would not know the plane rolled.  Likewise, the iced tea does not "know" it is upside down.  For a less dramatic demonstration, next time you are on a commercial airplane pay attention to when the plane is banking and turning and note that a cup of water on the tray doesn't notice the turn.  The cup stays in place and the fluid remains level (with reference to the airplane).

You can also demonstrate this with a small bucket and some rope.  Put some water in the bucket, tie the rope to the bucket and swing it in a circle vertically (be careful).  The water stays in the bucket if you swing it fast enough, and this is the same mechanism you see in Bob Hoover's video except it is the whole airplane being swung around in a circle like the bucket.


What are the benefits of a non-orthogonal (scissor) tail-rotor?

(Source)
The comments and answers already say it's for noise reduction. What's more intriguing is the how:
The blades are not coplanar (image).
The tail-rotor of the Apache rotates clockwise (video) when viewed from the port side. The nearest blades (nearest plane) to the viewer are the leading blades of each group. A group is two close blades regardless of plane, e.g., 1 and 2 as labelled above are a group, 1 is leading.
The thrust of the tail-rotor is being directed away from the viewer (port to starboard), which means the viewer is looking at the pressure side of the rotor.
Below on the left is what it looks like from behind the Apache. This arrangement allows the trailing blades (2 and 4) to miss the wake from the ones ahead of- (and closest to-) them.
(Own work) Left: Apache; Right: coplanar normal spacing. View is from behind and thrust is left to right.
This L scissor configuration, as it is known, where the lower blade is leading yields more thrust due to the better interaction.

Based on extrapolation of the test results and calculations, the increase in thrust over a conventional four-bladed rotor of the same dimensions is about 10%. Rozhdestvensky attributes Bell's failure to come to similar conclusions to their use of a very small model.

And quieter, too
Noise measurements during flyovers were made with a Havoc having the four-bladed scissors tail rotor and the three-bladed tail rotor from the Hind. The two rotors made about the same noise at low speed but at high speed the scissors rotor was quieter. The primary reduction was in the "broad-band" frequency range from 600 Hz to 2000 Hz. Much of the noise at these frequencies is due to the effects of the tail rotor working in the confused wake of the main rotor. The scissors rotor apparently acts more like a two-bladed rotor in this situation.
(Helicopter Aerodynamics Volume II, p. 72.)


Can one make an electric-sailplane from transparent carbon fiber?

As long as there are load-bearing structures beneath the fiber (I don't know how strong that fiber is so I will assume it is fabric-like), it will most likely fly if designed properly. If the fiber is smooth, it shouldn't be much different than regular fabric or other composite skins.

And yes, there are plenty of sailplanes that self launch with electric or gas motors. You would just have to take into account the weight and position of the motor when you add it in. This could mean that you need to lengthen the tail section for more tail down force, move the seats further back, place the engine in a more neutral CG position above the fuselage on a pylon, or any number of other methods. You might then also need to increase the wing surface area a bit, to lift the extra weight. Also take into account the weight and position of the batteries. The design effects and considerations are pretty straightforward, but dealing with them may or may not be complicated.

The Soviets tried in the 1930's to make an invisible spy plane (an AIR-6 I believe) by replacing the cloth skin with a cellophane-like material so that its entire was transparent. At just a few thousand feet the engine could be heard but the plane was almost completely invisible. Unfortunately the cellophane-like material would rapidly degrade after a few flights or several days out in the sun. It seems like your idea would be the modern version of that endeavor.


How many fuel pumps does a Katana DA20 have?

There are 2 fuel pumps on the Diamond DA20. One is electric and is controlled by the pilot and one is mechanically driven by the engine and is constantly running while the engine is running.

After take off, you switch the electric one off and the mechanical one keeps supplying the engine with fuel.


What is the procedure to obtain an FAA ATP while in the United States for a holder of a CPL from Pakistan?

There are many things that need to be accomplished.

Get a letter of authenticity from the FAA validating your license is valid and from an ICAO contracting country.
Study and pass the ATP multi-engine written test.  You may have to get a graduation certificate from a school offering the CTP course.
Apply for and receive TSA clearance.
https://www.flightschoolcandidates.gov/afsp2/?acct_type=c&section=WN
Take the FAA ATP practical test in an A320 airplane or FFS simulator.  It is best to contact a training center on what is required.


Regarding the 1902 Wright glider. Why is the airspeed, Va, calculated adding the ground speed, Vg, and wind speed, Vw?

The gliders had no instruments of any kind, let alone an airspeed indicator. Thus the only way to measure airspeed was to measure the windspeed and add that to the speed over the ground, itself calculated from distance flown and time aloft for each flight.


What is the accuracy of distance and position calculation?

The aviation industry is in the process of moving to Performance Based Navigation (PBN) within Required Navigation Performance (RNP) airspace.  Using this structure the primary performance is measured by the Total System Error (TSE) which must be less than 2 times the RNP value 95% of the time. Example: In RNP 1 airspace the aircraft must maintain positional accuracy within 2.0 NM of its desired path 95% of the time. The standard for navigational equipment (FMS) is defined in RTCA document DO-283B, Minimum Operational Performance Standards for Required Navigation Performance for Area Navigation.

The TSE for an aircraft is broken down into three components; path definition error (PDE), position estimation error (PEE), and path steering error (PSE).  Your question directly relates to PDE.  The accuracy of PDE depends on several components, the primary one being the accuracy of the positional (fix) information published by the regulatory agency (FAA in the US) contained within the navigational database. For enroute and terminal airspace, the accuracy of fix information is less than 0.01 minutes of latitude and longitude or about 17 meters.

Using the data from the database and the WGS84 earth model, the FMS will compute lateral path data.  Lateral paths are computed as a geodesic on the surface of the WGS84 ellipsoid.

DO-283 specifies the following data (among other) resolutions for display and entry:

Distance:  0.1 NM for values <10 NM, 1 NM for values >=10 NM
Fix latitude/longitude: 0.01 min
RNP:  0.01 NM for values <1.0 NM, 0.1 NM for values >=1.0, and <10 NM, 1 NM  for values >=10 NM
EPU: 0.01 NM for values <1.0 NM, 0.1 NM for values >=1.0, and <10 NM, 1 NM for values >=10 NM
Present Position latitude/longitude: 0.1 min

DO-283 also states rounding of displayed data is desired.  For that reason internal FMS computations normally are performed to 1 decimal place more than the displayed resolution and then rounded.

From the above you can see that the displayed distance of a leg should be within 0.1 NM for distances less than 10 NM and 1 NM for longer distances.

As for your 3-D question, lateral (LNAV) and vertical (VNAV) navigation are computed separately.  VNAV is still predominately barometric based except for precision (GBAS) and near precision (SBAS) approaches which use WGS84 geometric height.

For positional data, along with the present position, the system must calculate an estimated positional uncertainty (EPU) as shown in the table.  The EPU calculation is quite complex and varies based on the source of the positional data (GPS, IRS, etc.)  This value when added to the PSE (cross-track deviation + errors) should be held within the RNP value.  As you can see form the structure of the EPU requirement, it is the most significant component of the system error.

Summary:

Calculating a geodesic path is required by the MOPS. Great circle is not acceptable.

Paths are calculated using lat/lon and baro altitude coordinates.  Distances are output in nautical miles; not feet, meters, or km.  Internally, the systems can use what ever they want.  Altitude is in feet or meters, depending on airspace rules.  The 3-D path is used to predict time of arrival at each fix along the route.

Positional accuracy (EPU) is calculated based on the selected nav sensor(s) using a number of statistical methods including Kalmann filters.


Who can perform different maintenance checks?

Airlines are free to conduct the tests wherever they prefer as long as they meet the required FAA standards.

An extract from American Airlines' Procedures:

"PS" Daily Checks

Each aircraft is checked every 2-3 days in its "PS" (Periodic Service) check. The aircraft is visually inspected and its maintenance log book is checked for entries and maintenance needs. The "PS" check can be performed overnight or during downtime during the flight day. It averages approximately two manhours.

"A" Checks

The "A" check is more detailed than the "PS" check. "A" checks are performed every 7- 9 days (approximately 80 - 100 flight hours). The "A" check is performed at one of 40 stations around American’s system. It averages 10 - 20 man-hours.

"B" Checks

The "B" check is an even more thorough maintenance check. The "B" check is accomplished approximately every two months (roughly 500 - 600 flight hours). Besides specific service performed on the aircraft, a detailed series of systems and operational checks are performed. American always performs "B" checks inside one of its hangars at seven different cities around its system. A "B" check requires approximately 100 man-hours on narrowbody aircraft (those with only one aisle) and approximately 200 - 300 man-hours on widebody aircraft (those with two aisles).

"C" Checks

The "C" check is the most thorough type of maintenance work performed by American. The airframe - virtually the entire aircraft - goes through an exhaustive series of checks, inspections and overhaul work. It is performed at either of American’s heavy maintenance and engineering centers in Tulsa, Oklahoma or the Alliance Maintenance Facility in Fort Worth, Texas. There are different levels of "C" checks depending on the type of aircraft.

Jet Engine Overhauls

Modern jet engines are among the most reliable devices in aviation. American does not replace and overhaul jet engines at a specific number of hours. Instead, American uses a 24- hour-a-day "condition monitoring" process that scientifically tracks the condition of every engine on every aircraft. Besides visual inspection, technicians monitor the internal condition of every engine, using such procedures as boroscope inspections and oil sample spectographs. The goal is to replace and overhaul an engine before a problem can occur. Engine overhauls are performed at the Tulsa and Alliance-Fort Worth Maintenance and Engineering facilities. The engine replacement is usually performed at one of the six "B" check hangar locations around the country.

To answer your question on the qualifications required to perform these checks, we'd have to go to FARs Part 65 which lists the privileges and limitations of a Mechanic Certificate.

In addition to the basic Mechanic Certificate, FAA allows two different ratings.

The first one is the Airframe Rating which, under §65.85, states:

  A mechanic who holds an airframe rating may approve and return to
  service an airframe, an appliance, or any related part after he or she
  has performed, supervised, or inspected minor repairs or alterations.
  He or she may also perform the maintenance actions required for a
  major repair or alteration, and should initiate the appropriate form
  (FAA Form 337, Major Repair and Alteration) associated with that work.
  However, the return to service action must be accomplished by a
  certificated A & P technician holding an Inspection Authorization
  (IA). (Refer to 14 CFR §65.95.)

After that comes the Powerplant Rating under §65.87 which states:

  Similarly, a mechanic holding a powerplant rating has the same
  limitations imposed regarding the powerplant and propeller as the
  airframe technician has on the airframe rating. He or she may perform
  and return to service minor repairs or alterations. He or she may also
  accomplish the work activities required for a major repair or
  alteration, but the work must be signed off for return to service by
  an IA.

That said, after all the checks have been performed, a person with Inspection Authorization (under §65.91) is responsible to approve the aircraft for return to service.

Source: American Airlines Aircraft Maintenance Procedures Fact Sheet


What is a two- or three-mile base exactly?

They basically ask you to report it as a "memory jogger" for themselves so that they can do something when you call in (like clear you to land).

A standard airport traffic pattern is described in Chapter 7 of the Airplane Flying Handbook as:

  The downwind leg is a course flown parallel to the landing runway, but
  in a direction opposite to the intended landing direction. This leg
  should be approximately 1/2 to 1 mile out from the landing runway, and
  at the specified traffic pattern altitude. During this leg, the before
  landing check should be completed and the landing gear extended if
  retractable. Pattern altitude should be maintained until abeam the
  approach end of the landing runway. At this point, power should be
  reduced and a descent begun. The downwind leg continues past a point
  abeam the approach end of the runway to a point approximately 45° from
  the approach end of the runway, and a medium bank turn is made onto
  the base leg.

It looks like this:

When the tower asks you to fly a two mile pattern, they want you to fly a pattern that has the downwind leg 2 miles out from the runway instead of the 1/2 to 1 mile that is normal.  The base leg would still be turned when 45° from the approach end of the runway.

In this case, you are either:

Doing pattern work in which case you fly the two mile wide pattern and should report turning base, or
Approaching the airport and the controller would like you to enter the two mile wide pattern on the base leg.  You should report the point where you would have normally turned onto the base leg if you were flying the entire pattern (45° to the runway).  This would actually be both of your last two scenarios above:  Established on the base leg, two miles prior to intercepting a two mile final (which for fun would actually be 2.83 miles from the runway).


How is Calculated TakeOff Time (CTOT) calculated?

I do not know the exact algorithm used for calculating CTOT's, but I can give you some background information about what information is used, and how pilots and air traffic controllers use CTOT's.

A CTOT, or calculated takeoff time, is a tool used within European air traffic flow and capacity management (ATFCM) to regulate the flow of air traffic through individual enroute sectors or airports.

The overall purpose of ATFCM is to prevent overload and ensure that capacity is utilised to the maximum extent possible and subsequently to ensure a fair distribution of delay.

Every area control sector and airport in Europe has a declared capacity, expressed as a maximum number of flight per hour. For enroute sectors, the capacity is determined by factors such as size of the sector, complexity of the route structure and military areas. For airports, the capacity depends on the runway and aerodrome layout, available approach types, weather etc.

For every IFR flight taking place within Europe, at least 3 hours before departure, a flightplan has to be submitted to the Integrated Initial Flight Plan Processing System  (IFPS), which is based in Brussels and Paris. The system will check that the flightplan is in correct format, and that it complies with any restrictions that may have been published, affecting the flight (for example, a certain route may only be available in a certain range of levels due to military activity).

The IFPS will process all these flightplans, and based on this information calculate the number of flights in any given sector or any given airport in Europe. If the number of planned flights (demand) exceeds the declared capacity, IFPS will start issuing CTOT's. A CTOT is a precise departure time, at which the affected flight must depart in order to ensure that, when the flight reaches the overloaded sector or airport, the demand does not exceed the capacity. This has the advantage that flights will spend their inevitable delay on the ground at their departure airport, instead of in airborne holdings. The IFPS will distribute delay fairly between flights. If an airport can handle 44 flights per hour, and there are 46 flights planned during some hour, the system will issue small delays to many flights, instead of just giving large delays to two flights. In case CTOT's are issued to flights as a result of an overload during a single one hour period, CTOT's will also be issued to flights planned in one hour before and one hour after that time, to avoid simply pushing the problem forward one hour.

In order to calculate these CTOT's, the IFPS must have access to up to date information about all flights. When submitting a flightplan, the aircraft operator includes an estimated off block time (EOBT), which is the time at which the aircraft is planned to leave the gate at its departure airport. If a flight is ready to leave its gate more than 15 minutes before the original EOBT, or is delayed more than 15 minutes, the airline must submit a new EOBT to the system, since the new departure time might result in an overload somewhere along the route. This may or may not result in the issuance of a CTOT time. Similarily, if a flight has been given a CTOT, but is unable to depart within the CTOT tolerance, which is -5/+10 minutes, the airline or air traffic control must submit a delay message to the IFPS, and a new CTOT will be issued. Obviously, IFPS must also be informed of any cancelled flights.

IFPS must also be provided with information about average taxi time at airports. The taxi time is the time it takes from the aircraft leaves the gate (EOBT) until it is ready for takeoff at the runway. During winter time especially, where de-icing operations at airports may reuslt in a very long taxi time, updating the taxi time in IFPS is very important. This is done by ATC. IFPS must know the taxi time because for each flight is only knows the EOBT time. Obviously, the system should not issue CTOT's that are earlier than EOBT+taxi time, since the aircraft would not be ready for takeoff at that time.

Air traffic controllers must depart any flights that have received a CTOT within a tolerance windon of -5/+10 minutes. If a flight is ready to depart before its CTOT, ATC must either have the aircraft wait on its gate, or some other place at the airport. At many airports, aircraft cannot be allowed to wait at the gate, because other arriving aircraft need to use the gate. It is then up to ATC to figure out what to do with the CTOT restricted flights until they can depart.
If a flight misses its CTOT, ATC is not allowed to issue a takeoff clearance. A new CTOT must be requested through IFPS, and the flight will potentially be delayed.

When a flight has received a CTOT, it is not set in stone. IFPS may send a slot revision message (SRM) if, for some reason or the other, the system has calculated a new CTOT. This can be both a better (earlier) or worse (later) CTOT. IFPS may also send a slot cancellation message (SLC), in which case the flight may depart without delay. Flights that are ready to depart within a short period of time, but are subject to a CTOT delay, can ask ATC to send a ready message, indicating to IFPS that if an earlier CTOT becomes available, the flight will be ready for it. In addition, an airline can request to swap CTOT's between two of their own flights, if the airline finds it more important than one flight arrives on time compared to another.

Finally, some flights are exempted from ATFCM restrictions, meaning that no CTOT delays will be issued. Examples of such flights are ambulance, fire fighting and search and rescue flights, and flights carrying heads of state. Flights departing outside of Europe will not receive CTOT's either, because no global ATFM system exists (yet) - but of course IFPS still has information about these flights, and they will be included in the calculations.

I hope the above gives you a better understanding of how air traffic flow and capacity management works in Europe. See this related question for information about ATFM in the USA.


Legal requirements for electronic flight bags like Foreflight or SkyDemon

you actually have two questions here

  ...for primary flight planning

EFB's with up to date charts are legal for planning and reference as covered in this question.

Many EFB's (well at least foreflight that I know of) here in the US allow you to file flight plans, and receive briefs from a weather briefer right in the system.

  ...and navigation

EFB's are legal for navigation as you would use a map but they are not legal replacements for GPS/AHARS units despite the features they have. Simply put they are not TSO'ed and not legal navigation instruments.

This is also spelled out in the regs directly

  The EFB system does not replace any system or equipment (e.g.
  navigation, communication, or surveillance system) that is required by
  14 CFR part 91.


would a dimpled heat shield reduce heat transfer during reentry?

Near as I know, the key to designing good re-entry vehicles or shielding is large flat plates, primarily because the design ensures the energy transfer from kinetic and potential energy of the craft to thermal energy  occurs mostly in heating the air flowing around the shape rather than the craft itself.  It sounds kind of counter intuitive, but doing this ensures the spacecraft remains as cool as possible and the least risk to structural damage from heating exists.  Therefore reducing drag is these applications is not a top priority.


Why did the design of the Boeing 247's cockpit windows change for some models?

From the Boeing 247 article (emphasis mine):

The cockpit windshield of the first 247s was angled forward, instead of the conventional aft sweep. This was the design solution (similar to that adopted by other contemporary aircraft that used a forward-raked windscreen) to the problem of lighted control panel instruments reflecting off the windshield at night, but it turned out that the forward-sloping windshield would reflect ground lights instead, especially during landings and it also increased drag slightly.[13][14] By the introduction of the 247D, the windshield was sloped aft in the usual way, and the night-glare problem was resolved by installing an extension (the glarescreen) over the control panel.[15]


Who decides what measurement units are used for altitude, and why is there no standard?

Unfortunately, countries tend to want to decide themselves how stuff is supposed to work once you're within their borders. That's why we have different rules and laws, and when you go somewhere else in the world, you might need to know some of the differences.

In England they drive on the wrong side of the road, imagine that! :)

In order to have things run smoothly in something so utterly international as aviation, the organization called ICAO (International Civil Aviation Organization) where most countries of the world are members, dictates the rules, (I believe they are) called the ICAO drafts recommendations which the member states should incorporate into their respective laws and regulations. If they choose not to, they need to inform the ICAO of such deviation, don't know exactly what happens then, but I believe the idea is to at least let everybody know there's a discrepancy.

The ICAO Annex 5 specifies units to use, including units for altitude and actually specifying meters as the primary unit, with feet being accepted as non-SI alternative. Why on earth you'd want to go against the majority on this I don't know, perhaps due to the fact that it's an SI unit and they want to be as much SI as they can. So it's basically up to each country how they want to play it. Most countries stuck with feet.


I have bad eyesight, can I still be a commercial pilot in Malaysia?

According to the Civil Aviation Authority of Malaysia's medical standards:

  (c) Distant visual acuity, with or without correction, shall be:
  (1)
  in the case of Class 1 medical certificates, 6/9 (0,7) or better in
  each eye separately and visual acuity with both eyes shall be 6/6
  (1,0) or better;
  (2) in the case of Class 2 medical certificates, 6/12
  (0,5) or better in each eye separately and visual acuity with both
  eyes shall be 6/9 (0,7) or better. An applicant with substandard
  vision in one eye may be assessed as fit in consultation with the DCA
  subject to satisfactory ophthalmic assessment;
  (3) applicants for an
  initial Class 1 medical certificate with substandard vision in one eye
  shall be assessed as unfit. At revalidation, applicants with acquired
  substandard vision in one eye shall be referred to the DCA and may be
  assessed as fit if it is unlikely to interfere with safe exercise of
  the license held.

The key words appear to be "with or without correction", i.e. it's completely fine if you wear glasses to correct your vision. That seems to be standard around the world, e.g. the US standards also allow correction.


What causes this surface texture, and how does it affect flight characteristics?

I believe this is buckling of the fuselage, due to heavy compression loading.
Buckling is the process of out-of-stress-plane movement which happens under compression. The below image shows it well.

Source

More info on buckling here.

Here's another picture, possibly of the same (type of) aircraft, with the description saying:

  It appears that the fuselage contains a very heavy cargo, the weight of
  which is reacted by significant overall shear loading at the axial
  station of the landing gear. The overall shear loading is absorbed by
  the skin of the fuselage, which has developed significant
  post-local-buckling diagonal tension between internal ribs and
  stringers.

This seems plausible to me, it could be that upon a rough landing, there was excessive compressional loading exerted by the landing gear, which caused the buckling.

I'm not an expert on airworthiness, but usually buckling indicates that a part is loaded more than it's supposed to be.

Source

Other aircraft have it too, see  this question with a further explanation about buckling.


How are military aircraft type certificated?

In the US, the military is not required to obtain FAA type certificates for their aircraft; the FAA is not the authority certifying a military-registered plane's airworthiness. They have the option of accepting an FAA type certificate (which they tend to do on aircraft based on civilian ones), but they run their own certification agencies for airworthiness, which are all that matters if the plane is in the military registration system. Here's an Air Force policy on the matter, here's a Lockheed powerpoint on the option to use FAA certification on commercial derivatives.


Martin-Baker tests their seats in an actual aircraft. They have, for some time now, used a Gloster Meteor to test their designs as discussed in this question. They also have a high speed sled at their facility for such tests.. 0-0 tests are easier to pull off since there is no moving component.

Individual components like explosive bolts or handles are likely tested like any other engineering component, in a test facility.


Mathematical function in performance diagrams

If you have a good set of well-spaced points, a best-fit polynomial in $x^2$ or $x^3$ is usually good enough. It's true that high-degree polynomials oscillate, and are therefore unreliable, but you're safe with squares and cubes...
This site is free and quite good: MyCurveFit.


How to increase your chances of survival in a plane crash?

« Some of the survival game involves factors passengers largely can't
  control, like the weather, flight crew skills, the design of airline
  seats and the construction, maintenance and age of the plane. But
  passengers themselves can do a lot to improve their chances of
  survival simply by making smart choices and being informed. »⁴

Things you can do:

Preventive Measures

Book the safest seat.
Avoid unsafe airlines.
Fly during daytime (as statistically it slightly increases chances of survival and some kind of incidents are far more common at night).

Preparatory Measures

Bring helpful items on board.
Clothes – what you choose to wear can help or hinder your escape:

Opt for flat, sturdy shoes. Flip-flops and high heels won't help you make it to the emergency exit.²
In case of a fire or glass and metal debris, long-sleeved shirts and heavy cotton trousers will offer more protection than shorts and a T-shirt.²
Form fitting clothes are less prone to catch fire.
Polyester and other synthetic fabrics will melt to your skin.³

Before Take-Off

Pay attention to safety advice. It can save your life. Read the safety card (in the seatback in front of you) as planes do differ.
Memorize the emergency exit locations before take-off. Plan and visualize your escape route. Count the rows (armrests⁴) to your nearest exit (in front of and behind you in case one direction is blocked!). That way, in the event of smoke filling the cabin or if emergency lighting fails and it’s very dark, you will know the number of seat rows and can feel your way to an exit.¹ Many passengers survive the initial impact but are killed by the ensuing fire, smoke and sometimes water. 90 seconds should be used as a time frame for escaping.⁴
Memorize where your nearest cabin crew are, because their help and instructions will make a huge difference.²
Be aware that at 35000ft you have just 30-60 seconds to don the oxygen mask and tug on the line to get the flow going. After that, you lose consciousness.²

In-Flight

Don't drink alcohol.
Seatbelt:

Keep your seatbelt on whenever seated (also prevents turbulence deaths).
Fasten it tightly - every inch of slack increase the potential g-forces you could be subjected to during an impact.²
Wear it across your pelvis, which will handle impact better than your stomach².
Practice opening and closing it:

  After interviewing 1,900 survivors and 155 cabin-crew members,
  Professor Galea made an interesting discovery: Most passengers lose
  valuable time because they struggle to undo their seatbelts. “People
  tend to try and press a button on the seatbelt, because in this
  emergency situation they revert to normal behaviour [learned from] car
  seatbelts [with] a push-button system.”²

During Take-Off and Landing (when ~80% of accidents occur²):

Don't sleep/nap wearing eye mask and earphones.²
Stay alert and aware of your surroundings.²
Keep your shoes on.²

When a Crash is Imminent

Brace for impact:

Put your feet flat on the floor, farther back than your knees ("aft position").²
Consider placing hand luggage under the seat in front of you to act as a cushion (to prevent your feet from hitting the seat, I assume). That way you are less likely to suffer broken ankles that will hinder your escape.²

Escape and Aftermath

After the initial impact it's common for fire to break out. Just a few breaths of toxic smoke can cause you to pass out. In the event of smoke/fire:

Cover your mouth and nose with a wet cloth (e.g. wet the seat back headrest).²
Stay low. (That doesn't necessarily mean crawl on your hands and knees. Although there will be less smoke at floor level, you could be crushed or suffocated under luggage and other passengers.) Instead, keep your head down.²

Don't retrieve your luggage.¹
Don't inflate your life jacket inside the plane. It hinders your escape.²
Move fast but resist the urge to push and shove. It's likely to make matters worse and cause others to lash out.²
Once on the ground get away as fast and as far as you can.²

sources: 1, 2, 3, 4


Is it legal to board a plane dressed like a flight crew member if you are not a crew member?

Without a precedent, there is no answer about legality. The French law about military uniforms (and by extension postal workers if they are government employees) is based on the Geneva Convention based on precedents and war crimes.

Disguised as a postal worker, René Veuve acquired and transmitted information about crucial enemy infrastructure, such as Le Bourget airport, an oil refinery and an underground rocket factory.

In this case René was a hero, now imagine the opposite happening from the Axis powers.

For this question, no one on the internet can/should say whether it's legal or not for a civilian to wear a generic* pilot's uniform and board a flight.
The precedents we have show that those who did it, did it for illegal reasons, not for fashion.
* For the non-generic uniforms as in this case, a man was charged in the U.S. with falsely impersonating persons privately employed. But I'd say from a distance you can't tell the difference, and so a prosecutor may ask for the same charge (only one way to know).
Security
The airport security may stop the good-looking person for questioning and they will be searched. Because that's one way to try to get contraband in/out of a country.

Man Carrying Cocaine Pretends to Be Delta Pilot at JFK Airport

If flying internationally, the border control officer may have a question or two to the non-pilot in uniform.
For the U.S., pilots in uniform are required to show two IDs:

(...) one from their company and one from the government, to be checked against a secure flight crew database.

It may be seen as a way to skip the security lines.
Airline / flight crew
The airline personnel may object and deny boarding because it may be taken as an impersonator with a malicious intent to gain access to the cockpit.

Frenchman impersonating pilot caught in cockpit of US Airways plane

Passengers don't know better, and the airline may not like it for their passengers to think their pilot is sleeping (see story below), or worse, drunk (or will they deny drinks?).

Pilot caught napping in business class while trainee flew the plane

Airline passenger accused of impersonating a pilot is rumbled

Man was wearing a Cathay Pacific uniform and claimed he was off-duty. Flight attendants grew suspicious and soon learned he was not a pilot.

Note: Not all airlines allow their staff to wear uniform when off-duty.
In other news, a drunk pilot in uniform may cause panic and stress to passengers, what if that civilian is also intoxicated?

Common sense says to avoid that.
I don't think we will find an aviation regulation for that, it will be a local matter fit for Law.SE, i.e., if you were denied boarding, do you have the legal grounds to sue the airport/airline?
Once someone tries it, sues the airline/airport, and the court passes a sentence, then we'll know (for one jurisdiction at least).


What are the reasons for an installed engine to produce less thrust than an uninstalled engine?

No, these losses are well known and are called installation losses.

Their reasons are:

Intake losses. In a ground test the engine will be fitted with a screen to avoid foreign object damage, but none of the long intake tubes which are common especially in supersonic aircraft.
Generator loads: The engine drives generators to supply the aircraft with electricity. This can be simulated in a ground run, but often the generator load is higher in flight.
Bleed air: Some of the compressed air inside the engine is piped to a heat exchanger and then into the cabin for pressurization and heating, or used for leading edge de-icing. Again, this can be simulated in the static test but sometimes bleed air losses are higher in flight.

Interference between fuselage and power plant is only to be expected with fuselage-mounted engines. This can be both beneficial (as in the precompression at high angle of attack and speed on the Rafale or the F-16), or it can distort the flow when side-mounted intakes are operated at a high sideslip angle.


Would it help airlines, if they knew passenger weight before hand?

Despite of the "delay" during the check in procedures, it would be safer than the average companies usually use.
For instance, the latest FAA guidelines on aircraft weight and balance control set individual passenger weight averages at 190-195 pounds for adults and 82 pounds for kids, depending on whether it's summer or winter. (Based on the assumption people wear heavier clothing in winter.)
I have read an article, and there are more pieces of information.

Airline begins weighing passengers for 'safety'


Is this opinion on personal computer flight simulators too strict or is it actually true?

It isn't true, not as an indictment of the simulator software community as a whole anyway. It may be that your pilot friend doesn't have experience with modern simulators, let's take X-Plane for example...

X-Plane has a "professional use" version, which is simply the regular X-Plane with a commercial license and a few extra features. The underlying software is still the same. X-Plane "for professional use" can be FAA certified as a training device.

This means that the aircraft behaves exactly as would be found in the real world. In fact, X-Plane is sometimes used to verify flight models before more expensive methods are used, and they are relatively accurate. NASA has even written research tools to utilize X-Plane. X-Plane's Garmin G-1000 is incredibly realistic, and X-Plane "for professional use" can drive G-1000 simulator devices.

You can buy other "professional level" simulators for home use like the Redbird Jay which runs the same FAA approved software as the certified simulators. The same is true with Elite Simulator.


Why force the nose of 737 Max down in the first place?

The main thing to avoid in aeroplane stability & control, is an aerodynamic nose up moment that is not commanded by the pilot. The uncommanded nose-up moment would not auto-stabilise, but rapidly get progressively larger with increasing angle of attack, and run away to a stalled aeroplane.

During certification of a passenger aeroplane, many tests are carried out to check if the airframe does not start to have a mind of its own.

If the pilot does not provide a control input, the airframe must return to the trimmed position.
Forces and inputs to move the aeroplane away from trimmed position must be such that there is an ever increasing force required to achieve an ever increasing nose-up position. The nose-up position must always be commanded by the flight control surfaces, elevator and stabiliser, in a predictable way.

One of the tests to be performed during certification is stick-force-per-g. Bank the aeroplane and start turning while pulling the stick back in order to maintain altitude. Then bank more and pull back more, in ever tightening turns. It must be progressively harder to pull back on the stick to maintain altitude, never easier.

It was during this wind-up turn that due to the engine configuration of the MAX an aerodynamic nose-up moment appeared, which would cause the pitch stick force to suddenly become less than expected. Not as bad as a runaway pitch, but still an undesirable situation when the pilot is still straining to maintain the manoeuvre. This is the situation that MCAS was originally designed for, to auto-compensate for this situation only. The aeroplane should always stabilise itself and manner of control must be predictable and within the reaction times of humans.

More info in the links in this question, very interesting articles which illustrate how MCAS design bloated from the original scope, under time pressure.


I suspect there is no such rule. I looked at a few online sources - none mention the word apology (or variants).

ATC communication is expected to be short and follow a standard set of stock phrase forms.

Anything outside that is discouraged unless necessary to clarify instructions etc.

FAA

An FAA document "Radio Communications Phraseology and Techniques" says

  Brevity is important, and contacts should be kept as brief as possible,

So any communication that doesn't follow one of the standard patterns is discouraged. It continues.

  but controllers must know what you want to do before they can properly carry out their control duties. And you, the pilot, must know exactly what the controller wants you to do. Since concise phraseology may not always be adequate, use whatever words are necessary to get your message across.

ICAO

An ICAO document "ICAO Standard Phraseology A Quick Reference Guide for Commercial Air Transport Pilots" says

  Phraseology has evolved over time and has been carefully developed to provide
  maximum clarity and brevity in communications while ensuring that phrases are
  unambiguous.

Again the emphasis is on brevity and standard phraseology. It also continues ina similar way to the FAA document.

  However, while standard phraseology is available to cover most
  routine situations, not every conceivable scenario will be catered for and RTF
  users should be prepared to use plain language when necessary following the
  principle of keeping phrases clear and concise.

Other

For non-pilot rubberneckers like me, a good intro to pilot-ATC communication is a "Say Again" blog post or Two by Don Brown.

  I remember one time when I was a young controller and working a slow, high-altitude sector. I was bored so I got into a conversation with a pilot about something or other. All of a sudden I noticed this F-15 was in a big turn.

 "Peach two one, Atlanta Center, where you goin'?"
 "Atlanta Center, Peach two one is declaring an emergency,
        we've lost an engine and are returning to Dobbins."

  He couldn't get on the frequency because I was having a conversation.


In what ways do air traffic controllers communicate with pilots in class A airspace?

Methods

VHF radio is one method. HF is used in oceanic areas, but it is in decline.

Data comms are also used, it's called CPDLC (Controller–pilot data link communications). The ATC sends a digital message to the pilot, and they respond the same way.

Too Much Static Noise (HF)

On long flights, the controller can grab the crew's attention by poking them using SELCAL. Too much static noise for a long time is tiring to listen to.

Chatter

Most of the chatter is handing off the plane from one controller to another.

If there's bad weather en-route, the pilot will ask to deviate. That's another type of chatter.

Also climb, step-climb, and descent instructions.

Changes to route are also relayed.

When flying over areas not covered by radar, position reports are also provided by the crew and confirmed by the controllers.

PIREP's—or pilot reports—often include information like "watch out there's icing, tell the folks behind me."

Traffic separation instructions and traffic advisory information are also quite common.


What is the difference between variable and transient bleed valves?

Turbofan engines have two or three distinct spools made of some turbine stages driving compressor stages using a shaft. The turbine stages collect the energy from the fuel combustion hot gases and drive the compressor stages which feed the combustion chamber with air.

When the fuel rate changes due to throttle position being changed, a delay is needed for this spool system to adapt, the time their rotational speeds adjust for a new equilibrium. However a turbine engine compressor is a tricky system in which the compressor must never stop producing air for the fuel combustion, and indeed must never allow hot gases from the combustion chamber to return forward, else the air pump is drained, the turbine stops producing power to turn the compressor, and the compressor itself stops compressing air.

The role of the VBV and TBV, as well as other elements (variable stator vanes, active turbine blade clearance system...) is to maintain the engine in conditions which prevent it to stop. The position of all these mechanisms is determined by the engine controller, which today is electronic and digital, and comprised of the FADEC, the EEC/ECU and the HMU.

While the VBV deal with more general equilibrium, the TBV deals which very quick transient states found in engine accelerations. In both cases the device reroutes a given quantity of air in the core to another location.

Source

Shared characteristics:

On a CFM56, the Variable Bleed Valves (VBV) and the Transient Bleed Valve (TBV):

Are both part of the engine control.
Are actuated by the HMU under the control of the ECU (EEC).
Are used to maintain the compressor pressure within the optimal compression region when the rotational speed of the compressors (low and hight pressure spools) changes and a new equilibrium between spool speeds needs to be achieved.
Prevent stall.

The VBV:

12 VBV located between the booster and the HPC (within the fan frame).
One or two "master valves" which drive the other.
Reduce water and foreign object ingestion.
Open when the engine decelerates or at low speed.
Close when the engine accelerates or at high speed.
When open, air from the hot flow is discharged in the bypass flow.

Source

Source

TBV:

Single valve located between the HPC stage 9 (bleed air tap) and the LPT stage 1.
Is aimed to quickly react after transient HPC pressure changes.
Improve HPC stall margin during engine start and acceleration.
When open, air from the HPC is discharged in the cavity before the LP turbine.

Source

CFM56-7B, Source

More on this site:

What is the transient bleed valve in a gas turbine engine?
Why does the CF6/CFM56 Turbofan Fan Frame contain 12 circular holes between the primary and secondary flow?
How does the FADEC prevent compressor stall during rapidly increasing thrust demand?


Do Boeing and Airbus learn from each other?

Yes Airbus and Boeing learn from each other: they compete with each other. Both are implementing successful features of the competitor, and when the A320 came to market it required differentiating features to gain market share. The competing design from Boeing, the 737Classic, was completely re-designed in the 90s because of the lower specific fuel consumption of the A320. The other Boeing product competing in this class, the B757, is out of production. The resulting 737NG has outstanding fuel economy as well, partly achieved by the blended winglet which Boeing pioneered for this class of aircraft.

Where the two companies differ is in the design philosophy for interaction of the pilot with the aircraft. The A320 is actually the oldest design of Airbus that is still produced - the type was certified in 1988, while the 737 and the 747 type certificates were issued two decades earlier. The 737 MAX still has a common type rating with the original B737-100 and this poses a limit on the introduction of new flight crew ergonomics. The A320 could completely re-design all known features in cockpit control and implement new ones from military aircraft, such as the side stick which made the F-16 such a successful air superiority fighter.

The OP focuses on accidents and incidents which happened with the planes, due to incorrect pilot action. This is a subject where everybody learns from everybody, to continue to make air travel safer:

Every accident is thoroughly analysed in order to find the cause and prevent it from happening again in the future. This is done by independent government organisation who only focus on the cause of the accident, nothing else. The NTSB in the USA, the BEA in France.
As a result of this, there may be improvements imposed by the overseeing regulatory aviation organisations: FAA in the USA, EASA in Europe. They may write directives for aircraft manufacturers to implement changes in the design of the aircraft if that is where the incident cause was, or in the training procedures of pilots if pilot error was found to be a factor.

The ultimate proof of the pudding is in safety, and both Boeing and Airbus have excellent and very similar safety records for their aeroplanes. There are many ways that lead to Rome - everybody learns from everybody, and continues to improve their design which will always differ to an extent from the competition.


Are there take-over requests from autopilots?

I assume in your question the autopilot is engaged. When the auto-flight system reaches the limits of its capabilities it simply disconnects. On Boeing aircraft you get a
> AUTOPILOT DISC

Warning Message on the EICAS and the siren sounds. Now it is all manual flying for the pilots.
An example would be turbulence exceeding the auto-flight system capabilities to maintain the intended trajectory.
After the question was clarified:
The big difference between flying and driving are

system redundancy - in an aircraft, everything important is available two times, the very important stuff even three times. If there is a technical problem system performance normally degrades accompanied with appropriate annunciations to the pilots.
the environment you are operating in - in the air there is no road to follow or you fall off a cliff. There are mountains, yes, but in cruise flight (similar to driving on the highway) where your vigilance is lower the mountains are below you. In the end, the airway is an imaginary thing. An imaginary line drawn between two waypoints. You won't crash (immediately) if you deviate from it. Even your surrounding traffic is miles away laterally. When the margin for error gets smaller pilots are way more vigilant. During departure/arrival/landing, even when flying fully automated, the concentration is fully on the aircraft. So deviations from the intended trajectory are noticed early and can be acted upon quickly. This even goes so far that with most commercial operators there is a sterile cockpit rule below 10,000 ft where there is no communication in the cockpit which is not relevant to the current situation.
the system sophistication - the feat car manufacturers are trying to accomplish is way bigger than an auto flight system for an airliner. The margins for error are way smaller, yet the precision needs to be way higher. In aircraft the autopilot is basically a glorified feedback loop. And even if the autopilot system fails spontaneously due to technical problems the aircraft initially keeps flying without any intervention and only slowly deviates from its current trajectory as aircraft are designed to be aerodynamically stable.
training of the operator (pilot/driver) - commercial pilots train for abnormal situations in full flight simulators every six months. Drivers, well, don't. Their last training was most probably when making their drivers license many years ago. Another thing is vigilance and planning ahead. Pilots are trained to anticipate what is coming next. You try to get a mental picture of the traffic around you and where conflicts may arise. And as your aircraft is moving typically pretty fast and there are no brakes you can slam you are flying in a rather defensive way.

And I even have a real world example where the auto flight system performed flawlessly yet human intervention was required:

What you see here is a blurry photo of the incorrect turn construction of a departure. The departure trajectory is supposed to be a left turn to the next waypoint (white star). The flight management system constructed a right 270° turn (magenta line) to match all the constraints of the waypoints (flyover, etc) where a 70° left turn would have been the correct behavior. The aircraft was flown manually to adhere to the departure procedure.
In this case no system degradation or warnings were present. You can see that the Flight Director (FD) on the PFD on the right commands a right turn (vertical magenta line). The autopilot simply follows FD commands and would therefore fly this (wrong) turn.


Why is the gear handle shaped the way it is?

It's required by law, at least in the US. 14 CFR 23.781, Cockpit control knob shape specifies these shapes for the flap and gear controls on smaller aircraft:

For larger (transport category) aircraft, 25.781 specifies the same thing:

As for why those shapes are specified, it's for at least two reasons:

The shape resembles the thing it controls, so it's an obvious memory aid
The controls are all shaped differently, therefore you can distinguish them by touch alone, without needing to look at them

As others have noted, there have been accidents in the past caused by pilots using the wrong controls, and this is one reason why the FAA decided to do something to standardize them. Parts 23 and 25 also state where the controls should be placed, for the same reason.

The FAA's Airplane Handbook says:

  There have been many cases of the pilot mistakenly grasping the wrong
  handle and retracting the landing gear, instead of the flaps, due to
  improper division of attention while the airplane was moving.

They recommend - and I was taught - leaving the flaps alone after landing until clear of the runway (unless you have a good reason for retracting them earlier, like a short-field landing), then check and retract them with the statement "flaps identified and retracted". "Identified" in this case simply means that you're sure you have the right control in your hand. Some instructors even avoid touch-and-goes in complex aircraft (i.e. with retractable gear) because they feel the risk of retracting the gear rather than the flaps during the maneuver is too high; they stop and go instead, even if that means taxiing back for takeoff.


Is precession a problem for two-bladed propellers?

Wind turbines suffer not from precession per se, but from precession 'wobbling', when the gyroscopic force varies dramatically over a revolution. Normally, a 3-bladed prop would be heavier than a 2-bladed one, and will have greater gyroscopic effect (at the same RPM). However, it will be better balanced across a revolution. The closer to a solid disk, the better.

(In fact, a 3-bladed prop appears to be perfectly balanced in extreme positions. Considering blades slender rods or length $r$, the moment of inertia (MOI) of the propeller disk for turning across the spin axis (e.g. yawing) will be $1/3\cdot mr^2 + 2\times 1/3\cdot m(r\cos60°)^2 = 1/2\cdot mr^2$ in one extreme position (like −<), and $2\times 1/3\cdot m(r\cos30°)^2 = 1/2\cdot mr^2$ in the Y position. Compare this with variation from almost 0 to $2\times 1/3\cdot mr^2$ for a 2-bladed prop).

For a 2-bladed prop, this wobbling occurs at double the frequency of rotation. For wind turbines with their ~20 RPM this is < 1 Hz, a frequency that can interfere with normal yawing and even damage the structure. But aircraft props turn at much higher speed; a typical 2400 RPM will give you an 80 Hz hum. May be unpleasant, but far away from the natural frequencies of manoeuvring and of the airframe.

Also important to note that there are two effects at play here: precession (gyroscopic effect) exerts a force perpendicular to the applied rotation, but there is also simply a moment of inertia of the prop/rotor across its spin axis (as calculated above) that needs to be overcome. This latter one applies even if the rotor is stopped, but both wobble when it spins. Now, for airplanes with their fast spinning but relatively small props, the gyroscopic effect may be noticeable (see below), but just MOI is totally negligible (the mass of the blades is nothing compared to the rest). Yet for wind turbines the opposite must be true: the rotor mass/MOI is (probably) the dominant mass of the whole thing.

As for precession itself, i.e. the tendency to turn perpendicular to where you want to turn, most aircraft don't 'suffer' from it either. Aircraft simply don't turn (manoeuvre) too fast for it to be a problem, and the aerodynamic forces outweigh the gyroscopic ones by orders of magnitude. On normal propeller aircraft, only if you want to notice it, you might notice it when doing a manoeuvre.

In some circumstances, however, precession can be quite significant. This involves the cases when angular velocities are high (aerobatics), the aerodynamic forces are low or very finely balanced (hovercraft), or both (spin).


Why don't airlines have in-flight video recordings like buses do?

Many airlines do in fact have inflight camera feeds for Cabin surveillance so I do not think the question is relevant to most major airlines anymore.

For a specific example, Emirates Airline employs the Cabin Video Monitoring Systems (CVMS) across its fleet of Airbus A380 aircraft. These Cabin cameras can be accessed by Cockpit crew through the System Display or the Cabin crew through the FAP (Flight Attendant Panel) and for any abnormal situation such as a hijacking/hostage situation on ground, the CVMS can be accessed on a laptop via the GSP (Ground Service Panel). Additionally, as mentioned above, they have landscape cameras installed for an external video feed but that is more of a feature for passengers.

The advantages of a CVMS in a hijacking/hostage situation such as positioning, identity, body language and weapons of the hijackers plus general operational advantages such as issues during boarding/offloading and other emergency situations such as an evacuation are great and not to be discounted.


Is the total lift of a quadcopter the sum of the lift from each propeller?

Yes.  490 + 490 + 490 + 490 = 1960.  For practical purposes, the thrusts from individual rotors do not interfere constructively or destructively:  they neither cancel each other out, nor do they help each other.  This case is pretty much the same as multiple propellers mounted on a fixed wing.

The situation becomes more complicated only if some rotors overlap, or are coaxial.


How much distance do I need between quadcopter propellers to avoid issues?

Well, you gotta keep in mind that the airflow is mainly down, but there will always be a little flow side to side, (thus frames, also used for safer collisions,) so you should put them roughly 1/3 of the diameter of the rotors themselves away from each other. This provides enough space to keep your interference down, as the interference spreads  out to about 1/4 of the radius of the rotor. I have not seen that the number of blades matters much, as long as you follow the 1/3 diameter rule. You want to avoid the counter- airflow that can make your craft less efficient or jack the blades. Note also that raising two of the blades would cause serious problems with your efficiency, because two rotors blowing downwards in a cone, unless very effectively controlled, will kill the stability, creating unnecessary strain, or in bad cases, frame torque. The two above would create interference for the lower. This could, however, be avoidable if the top two were about 3/4  rotor diameter away, and no higher than 1/4 a rotor diameter. But then you'd be flying a very odd and somewhat unbalanced copter.


The pressurization relief valves are on the left side of the fuselage and are used to provide protection (for the aircraft) against excessive differential pressures. In this case, they are set to open at a differential pressure of 63.8 KPa (with 66.9 KPa) as a backup. From ATSB Investigation Report on the depressurization of Boeing 747 VH-OJK:

  The relief valves provided protection to the aircraft against excessive differential pressures, with the external latching doors providing a positive indication of valve operation. Aircraft systems documentation
  specified that the valves open at a differential pressure of 63.8 kPa (9.25 psi) to vent the fuselage interior to the ambient atmosphere. An additional relief setting of 66.9 kPa (9.7 psi) acts as a backup.

The same report shows the external blowout doors of the (both) relief valves open, as shown below.

In a related note, there is a negative pressure relief valve to prevent vacuum damage to aircraft during a rapid descent. Usually, this is a spring loaded valve that opens inwards at negative pressure differential.


When can I descend on a feeder route if instructed “maintain ... until established”

Is this something that you have experienced yourself? If so an example would be helpful. Approaching a feeder route and hearing "Maintain... until established" imply two separate situations, to my ear.
From a controller's standpoint, if you are operating on an unpublished route (radar vectors or direct the IAF or similar), we follow the 7110.65 4–8–1b:

b. For aircraft operating on unpublished routes, issue the approach clearance only after the aircraft is:
1. Established on a segment of a published route or instrument approach procedure, or
2. Assigned an altitude to maintain until the aircraft is established on a segment of a published route or instrument approach procedure.

So if you are flying toward the airport but not on any airway or feeder route, you will receive vectors to final, or to an initial fix. Then in accordance with b2 we can say "Maintain 2000 until established on final approach course, cleared VOR runway 18 approach." You descend and maintain 2000, and do not descend any more until you (as PIC) deem yourself established on the published approach segment. (The procedure is slightly different if you are with a Terminal Arrival Area designated for an RNAV approach and above the minimum altitude for that TAA; then we can just say "Cleared RNAV runway 18 approach.")
If, however, you are operating on a published route, such as an airway leading to a feeder route, all we have to say is "Cleared VOR runway 18 approach." You are currently at a safe altitude on the airway, and the approach is specifically designed to give you all the information you need to get from that airway altitude down to 0AGL without running into any terrain. If this involves the use of a feeder route, you are expected to use the feeder route and any altitude restrictions for it.

Essentially: I don't think you would be told "Maintain 2000 until established, cleared approach." Perhaps you would be told "Maintain 2000 until FIXXX, cleared approach" where FIXXX is the beginning of a feeder route and you will intercept FIXXX at an angle of 90º or less; you are then assumed to be established on a published approach segment once you cross FIXXX. Once you are established (i.e. after FIXXX) you may descend in accordance with the published approach procedure.


BasicMed does not completely do away with SI's so your buddy may still need one if he has never had one and has one of the 4 qualifying issues.

To directly answer your question the insurance company may deny a claim on these grounds as they are somewhat free to deny claims as they see fit. There is some more info from the FAA related to SSRI's here. Remember that basic med is about considering yourself fit to fly and being self conscious of your current state it does not set any protections for you that once you deem yourself fit to fly you actual are. Its a fairly new rule so only time will tell how cases play out in the future relating to issues.


Is this statistic about the fatal accident rate correct?

The passage you're asking about is a paraphrase of something Boeing spokeswoman Julie O'Donnell said. If you follow the citation in the article, you can see exactly what she said, and when she said it.

  "During the 1950s and 1960s, fatal accidents occurred about once every 200,000 flights," says Julie O’Donnell, a spokeswoman for Boeing. "Today, the worldwide safety record is more than 10 times better, with fatal accidents occurring less than once in every two million flights." [Emphasis added.]

O'Donnell is being quoted in 2014. According to the latest IATA safety fact sheet (published January 1, 2018), IATA measured a fatal accident rate of about one per 2.36 million flights in 2012, and one per 2.58 million flights in 2013. If I were rounding that down for a reporter in 2014, "less than once in every two million flights" is exactly what I'd say.

IATA counted 15 and 14 fatal accidents in 2012 and 2013, respectively. That's an average of one fatal accident every 25 days or so—just like you estimated. As @fooot pointed out in their answer, we've seen fewer fatal accidents in more recent years: an average of one every 30 days, 90 days, 40 days, and 60 days or so in 2014, 2015, 2016, and 2017, respectively.

Statistical postscript

I agree with your gut feeling that, if fatal aircraft accidents were happening at an average rate of one every 20 days, I'd be very surprised to see no fatal accidents at all last year. If fatal accidents were Poisson distributed in time, with a rate of one per 20 days, your chances of seeing no accidents in a year would be less than one in 80 million!

On the other hand, a year with no fatal large commercial passenger jet accidents is totally plausible, given the accident rate of one per 16 million flights that @fooot quotes. In 2017, that comes out to an average accident rate of less than one every 140 days—maybe a lot less, if large commercial passenger jet flights make up only a small fraction of all flights. If fatal accidents were Poisson distributed, with a rate of 1 per 140 days, your chances of seeing no fatal accidents in a year would be better than one in 14.


Airspeed Calibration alternate static source, what is this for?

This table is included because of the fact that the Alternate Static Port on 172s is inside the cabin. Thus, changes in cabin pressure (even really small ones) can have an impact on the static pressure that the system is using and hence on the indicated airspeed.

The things the table mentions like windows and heat vents all influence the pressure in the cabin, and hence the airspeed. In reality, if you have to use the alt static port you aren't going to be pulling out the POH to correct the speed as it is likely very similar.


Why was the Sukhoi Su-47 Berkut never adopted for service?

I do not have inside knowledge, but think it is easy to explain why the Su-47 did not progress beyond the prototype stage:

Sukhoi enjoyed great export success with the Su-27 and its derivatives in the 1990s, and this helped to advance work on the Su-47. Mikoyan was in less favorable financial shape during this time, which explains the delay in getting the 1.44 ready.
There was no credible threat that required Russia to procure a modern fighter design during the last two decades. The existing fleet was simply good enough.
The forward-swept configuration is optimised for close-range air combat, while the cost of modern combat aircraft dictates that they need to fulfil multiple roles. Note that the PAK-FA will replace both the MiG-29 and the Su-27 and their derivatives, so even Russia will not support two frontline fighters in the future.
Much has been learned in the meantime about stealth, so the Su-47 was already outdated by the turn of the century.

I have to admit that when I first saw the Su-47, I was scratching my head and wondered what the Sukhoi engineers were thinking when they proposed this design. But I had similar reactions when the Boeing X-32 was unveiled …

Edit: Now it seems the engineers at Sukhoi put what they learnt on the Berkut to good practice when designing the SR-10 two-seat trainer. The reason for the forward sweep is excellent handling at high angle of attack - however, this bleeds energy quickly and can only be used in few corner cases in air combat. But it certainly helps for pilot training if the possible angle of attack regime is large.


What is the form of information stored in black box?

There are 2 different black boxes.

The cockpit voice recorder. This holds audio from several different sources, including the microphone for each pilot, the radio and a general cockpit microphone.
The flight data recorder holds at least 88 different parameters including attitude of the craft, engine performance, autopilot setting, pilot input one the controls, etc.


Are commercial aircraft required to have the model number painted on them?

Every aircraft I have flown had a data plate mounted somewhere in the outside, showing the make, model, serial number, and the year of manufacture. You probably can't see it unless you're 3 feet away, but it's there.
The relevant regulation in the US is:

§ 45.11 Marking of products.
(a) Aircraft. A manufacturer of aircraft
covered under § 21.182 of this chapter must mark each aircraft by
attaching a fireproof identification plate that—
(1) Includes the
information specified in § 45.13 using an approved method of fireproof
marking;
(2) Must be secured in such a manner that it will not likely
be defaced or removed during normal service, or lost or destroyed in
an accident; and
(3) Except as provided in paragraphs (d) through (h)
of this section, must be secured to the aircraft fuselage exterior so
that it is legible to a person on the ground, and must be either
adjacent to and aft of the rear-most entrance door or on the fuselage
surface near the tail surfaces.

and

§ 45.13 Identification data.
(a) The identification required by § 45.11 (a) through (c) must
include the following information:
(1) Builder's name.
(2) Model designation.
(3) Builder's serial number.
(4) Type certificate number, if any.
(5) Production certificate number, if any.

Here's an example from a Stinson 108:


Why is the angle of the horizontal stabilizer marked on the fuselage?

I don't have the reference but it's showing the trim setting.  The picture looks like is an Embraer 170 on which the entire horizontal stabilizer moves.  The gauge gives a quick visual setting to confirm the the trim set in the cockpit matches the actual trim.


What are these thermal spots on this infrared image of an F-16?

In this picture from Wikipedia it can be clearly seen that the two along the bottom of the fuselage are both heated air data probes, as Federico pointed out. The probes are heated to prevent ice from forming and blocking air flow to the sensors. The forward one is a pitot probe, and the aft one is a total temperature probe. The AOA sensor can also be seen as a much smaller hot spot above the forward pitot probe.

I agree with Ron Beyer that the top area is probably the sun reflecting off of the canopy. The lower area is probably a sun reflection as well, off of the external fuel tank. You can see in the video that these areas are not always visible, and move as the F-16 flies past, consistent with a reflection.


What do the various A340 configurations (clean, 1, 1+F, etc.) mean?

A clean configuration is a configuration where landing gear, flaps, slats, spoilers etc. are retracted.

1, 1+F, 2, 3 and FULL refer to the level at which the flaps are currently deployed:


Do military pilots use amphetamines or other stimulants?

The U.S. Air Force (and Navy) still uses, and has used off and on since WWII,  what are commonly referred to as "Go Pills" for instances when pilots need to be up for long periods of time - in wartime, sometimes longer than the crew rest regulation. (These pills can also be used for altering sleep cycles, along with "no-go" pills; for example, when changing from day to night).

The most common go pill is Dexedrine, which is an amphetamine. You can find some more information in this article.


ADS-C is used in oceanic environments, for example over the Atlantic and the Pacific.

FL350 to FL390 on the North Atlantic Track System is restricted to ADS-C equipped aircraft. Non ADS-C aircraft have to fly either below or above those levels (crossing through those levels is permitted)

The text below is a part of today's Norht Atantic Track message issued by Shanwick Center (EGGX):

  222021 EGGXZOZX

  (NAT-2/2 TRACKS FLS 310/390 INCLUSIVE

  MAR 23/1130Z TO MAR 23/1900Z

  PART TWO OF TWO PARTS-

  E MALOT 53/20 53/30 53/40 53/50 RIKAL

  EAST LVLS NIL

  WEST LVLS 310 320 330 340 350 360 370 380 390

  EUR RTS WEST NIL

  NAR NIL-

  F LIMRI 52/20 52/30 52/40 52/50 TUDEP

  EAST LVLS NIL

  WEST LVLS 310 320 330 340 350 360 370 380 390

  EUR RTS WEST NIL

  NAR NIL-

  REMARKS.

  TMI IS 082 AND OPERATORS ARE REMINDED TO INCLUDE THE

  TMI NUMBER AS PART OF THE OCEANIC CLEARANCE READ BACK.

  2. ADS-C AND CPDLC MANDATED OTS ARE AS FOLLOWS

  TRACK A 350 360 370 380 390

  TRACK B 350 360 370 380 390

  TRACK C 350 360 370 380 390

  TRACK D 350 360 370 380 390

  TRACK E 350 360 370 380 390

  TRACK F 350 360 370 380 390

  END OF ADS-C AND CPDLC MANDATED OTS