What is the step-by-step process to become a ground instructor in the US?

You may want to check out this document from the FAA also linked in that document is this document which may shed more light on the matter

  The general qualifications for an Instructor Rating require you have a
  combination of experience, knowledge and skill. Title 14 of the Code
  of Federal Regulations (14 CFR) part 61 requires that pilots must be
  able to read, write, speak, and understand the English language. If
  you cannot meet these requirements of English fluency, an airman
  certificate cannot be issued. For medical reasons, an appropriate
  limitation may be placed on the certificate.

  You must pass the Fundamentals of Instructing Knowledge Test and a Flight or Ground
  Instructor Knowledge Test specific to the instructor rating sought.
  You may take these tests on the same day, and you do not have to take
  them in any particular order. An instructor rating obtained by passing
  the Military Competence Instructor (MCI) exam does not require the
  candidate to take the Fundamentals of Instructing (FOI) exam.

  When
  applying for any additional instructor rating, you are not required to
  take the Fundamentals of Instructing Knowledge Test again. Once you
  have acquired a Flight Instructor Certificate, you are eligible to
  give ground instruction required for a Pilot or Instructor Certificate
  or rating, based on the ratings on your Flight Instructor Certificate.
  Because of this, it is not necessary to obtain a separate Ground
  Instructor Certificate since you would already have these privileges.

AskACFI breaks it down nicely here.


Is there a generic term for origin and destination seen from an airport point of view?

Perhaps the “remote” airport — that should work for both arrivals and departures.


Can pressurized aircraft be flown without pressurizing

Yes you simply fly with the pressurization system set to a mode that holds the outflow valve open so the air conditioning air being pumped in can't "inflate" the cabin; it all just goes overboard.  Most transport aircraft have a specific QRH procedure for "unpressurized flight", which among other things, limits the maximum altitude to 10000 ft, the altitude that most people can tolerate without any risk of becoming hypoxic.

Airlines will ferry airplanes from place to place unpressurized for maintenance.  An airliner may also be forced to descend due to a pressurization problem, and they will descend to 10000 ft and may even continue to destination at that altitude, weather permitting, as long as there aren't other problems present that dictate an immediate diversion.


Why is the trailing edge sweep angle smaller at the wing root?

There are two main reasons:

Swept wings suffer from interference at the center of the wing. If wing taper and sweep remain constant over the full span, the lift distribution will show a distinct drop at the center. This is called the "Mitteneffekt". The remedy is to locally increase the wing chord near the root and to decrease the wing's sweep angle. This, together with a change in airfoils and local incidence, "fills up" the dimple in the lift distribution and reduces induced drag.
Large aircraft need heavy wing spars, and increasing chord near the root gives the spar more height while the relative thickness of the airfoil can remain unchanged. A higher spar is structurally more efficient, so increasing its height at the root saves weight. Since the relative thickness determines the maximum operating Mach number, it cannot be increased locally without hurting the whole wing. The better alternative is to disproportionally increase wing chord at the root.

The unswept trailing edge near the root is a consequence of Boeing's flap track mechanism. Boeing Fowler flaps move perpendicular to the hinge line, and an unswept hinge line avoids lateral movement of the flap. Another consequence is a gap between the inner and outer flaps in order to allow both to move back without colliding. Boeing fills the gap with a high-speed aileron. Also, this gap avoids that the flaps protrude into the hot, turbulent exhaust stream of the jet engine.
Airbus flaps move in flight direction and leave the sweep angle of the trailing edge free. Also, they don't need a gap between the flap segments left and right of a sweep change of the hinge line.


Why do eastbound transpacific flights fly at lower latitudes than their westbound counterparts?

The different routes are due to the enroute winds created by the jet stream. The following map shows the current winds over the Pacific:

(map from skyvector.com)

You can see strong winds from the West in the central Pacific region of up to 150 knots (see here for a legend on how to read wind barbs). A flight from Hong Kong to Los Angeles benefits from these winds. A flight in the opposite direction would experience this as a headwind though and will therefore try to avoid the region. You can see that the winds are much weaker in the North.

In order to organize traffic in the Pacific, a track system has been established: Pacific Organised Track System (PACOTS).

  The Pacific Organised Track System (PACOTS) is a flexible set of aircraft route tracks that primarily link commercial air transport gateways of Japan and Southeast Asia and the gateways of Hawaii and the North American West Coast, as well as those in Texas.

(skybrary.aero)

The following map shows the current PACOTS tracks:

(map from skyvector.com)

The green tracks are for westbound flights and the blue ones for eastbound flights. Due to the changes in the jet stream, these tracks are re-defined twice a day:

  The tracks are developed twice daily by the Japanese Air Traffic Management Centre (ATMC) in coordination with Oakland ARTCC. Eastbound tracks are valid from between 0500Z and 1000Z (depending on origin) to 2100Z (with specified crossing time windows for 160E) and are given a numeric designator. The opposite direction westbound tracks are valid from 1900Z to 0800Z (with specified crossing time windows for 160E) and are designated alphabetically.

(skybrary.aero)


The reason for using glassfiber on radome coverings is simple: Electromagnetic transparency. Carbon fiber conducts electricity, so it will absorb much of what the antenna radiates away or "listens" for. Glassfibers are good insulators and transparent to radar waves.

The reason for glassfiber on forward-facing surfaces is impact tolerance. Compared to carbon fiber, glassfibers have a higher elongation at fracture and are a homogenous material. First to the elongation point:

Energy absorption is the integral under the stress-strain curve, and a higher elongation at fracture gives glassfiber better energy absorption qualities. The peak loads for carbon might be a bit higher, but carbon breaks at an elongation of less than 2% while glass stretches to 5% before rupture. Both, however, are inferior to most metals which have a phase of plastic deformation before rupture.

The second point is based in the anisotropic nature of carbon fiber:
When a carbon fiber is loaded in a direction away from its lengthwise axis, it will break easily. Glass, being an isotropic material, has the same strength in all directions, so a glassfiber composite is much better in taking arbitrary and impact loads.

Now that the question is much more general, here are the main differences:

Price must come first on this list. Glassfiber is dirt cheap compared to carbon fiber. If I look up the prices for woven material at Aircraft Spruce, a yard of 50" graphite cloth is about 30 USD while a comparable E-glass cloth runs at less than 10 USD.
Density is next: Carbon fiber weighs 1.7 g/mm³ but glassfiber 2.5 g/mm³. Both have similar strength, so a carbon structure will easily be lighter than a glassfiber structure.
Stiffness: Carbon fiber is about three times stiffer than glassfiber. Extreme varieties like pitch-based carbon fibers can be up to 10 times stiffer but offer few benefits. The higher stiffness produces less flex of a wing spar under the same load. Open class gliders need carbon fiber spar caps, or their wings would have too much dihedral in flight.
Fiber diameter: Glassfibers are much thicker than carbon fibers, which makes them better in compression loads. Finer fibers need better support from the epoxy matrix against buckling.

I mentioned conductivity already, but one funny consequence from the anisotropic nature of carbon fiber has not been mentioned yet: Along their fiber axis, carbon fibers have a negative coefficient of thermal expansion. When combined with the proper amount of epoxy resin, this allows to build structures which keep their length constant when temperature changes. Note that the structure will still expand perpendicular to the fiber axis when heated, though.

Another peculiarity is that transparency reverses in the optical spectrum of electromagnetic waves. Now glass is transparent and carbon is opaque. This made the designers of the first carbon fiber fuselage install a lightbulb in the tailboom, so the preflight inspection can be done in the same way as it is done in glassfiber gliders.


Is an approval required to fly from the right seat?

As Ron mentions in the comments here in the US it is not illegal by any specific regulations however...

Most GA aircraft (the smaller ones at least) only have a single set of instruments that reside in front of the left seat as you mention in the question. Lets say hypothetically you were flying right seat and something went wrong. Due to the angle of view you were not able to read an instrument and this lead to an accident. Lets say you lose your primary CDI/Glide Slope while flying an ILS approach and you need to use one on the far side of the cockpit. For some reason you are alone and in the right seat. If an accident did occur as a result of this you may be able to be held to

  §91.13   Careless or reckless operation.

  (a) Aircraft operations for
  the purpose of air navigation. No person may operate an aircraft in a
  careless or reckless manner so as to endanger the life or property of
  another.

Since the left seat was open and available for you. But other than that there is no regulation preventing such operation.

Ron  posted an excellent article in the comments below that has at least one quote worth mentioning

  Aircraft insurance policies and flying club rules often specify that
  all flying is to be done from the left seat unless the pilot holds a
  current flight instructor certificate or has specific authorization.

While this is not an FAA regulation insurance companies or the rental/flight club you get your plane from may stipulate left seat only flying.


Do the pilots have to recalculate the balance when 6 passengers show up last minute in a 737?

Loadsheets have a section called 'last minute changes'. As the name implies, pilots can record last minute changes here. If the changes are minimal, there is no need to recalculate the mass and balance, and trim settings.

What constitutes 'minimal' depends on many things, principally limits set by the operator or manufacturer. I can't verify this but think 400kg would fall within these limits, unless the aircraft was already at its performance limits.


In which cases the lift distribution is not elliptical? (i.e. e≠1)

When is the lift distribution not elliptical?

The distribution is non elliptical basically always, you have to struggle quite a lot to achieve an elliptical distribution.

As far as I know only the Spitfire managed to decently approximate the elliptical distribution, and even then, the unavoidable presence of the fuselage had its consequences.

  What are the physical or ideal causes?

Ideal? I think you are confusing what is ideal here. The ideal case is the elliptical distribution, since it gives you the minimal induced drag for equivalent lift.

As basic theory goes, you can have an elliptical distribution with an elliptical wing (is a consequence of the so-called lifting-line theory).


Where are the first structural damages after maximum speed is passed?

Q: Which link of a chain will fail first when you exceed the maximum design tension?

A: The weakest link.

It could be any link since none is designed as the weakest link.


Why would there be flight restrictions when the barometric pressure exceeds 31 inHg?

It is because standard altimeters are not adjustable beyond this range. The AIM 7-2-2 contains information on how to handle it:

  When the barometric pressure exceeds 31.00 inches Hg. The following procedures will be placed in effect by NOTAM defining the geographic area affected:

  (a) For all aircraft. Set 31.00 inches for en route operations below 18,000 feet MSL. Maintain this setting until beyond the affected area or until reaching final approach segment. At the beginning of the final approach segment, the current altimeter setting will be set, if possible. If not possible, 31.00 inches will remain set throughout the approach. Aircraft on departure or missed approach will set 31.00 inches prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower. (Air traffic control will issue actual altimeter settings and advise pilots to set 31.00 inches in their altimeters for en route operations below 18,000 feet MSL in affected areas.)

  (b) During preflight, barometric altimeters shall be checked for normal operation to the extent possible.

  (c) For aircraft with the capability of setting the current altimeter setting and operating into airports with the capability of measuring the current altimeter setting, no additional restrictions apply.

  (d) For aircraft operating VFR, there are no additional restrictions, however, extra diligence in flight planning and in operating in these conditions is essential.

  (e) Airports unable to accurately measure barometric pressures above 31.00 inches of Hg. will report the barometric pressure as "missing" or "in excess of 31.00 inches of Hg." Flight operations to and from those airports are restricted to VFR weather conditions.

  (f) For aircraft operating IFR and unable to set the current altimeter setting, the following restrictions apply:

     (1) To determine the suitability of departure alternate airports, destination airports, and destination alternate airports, increase ceiling requirements by 100 feet and visibility requirements by 1/4 statute mile for each 1/10 of an inch of Hg., or any portion thereof, over 31.00 inches. These adjusted values are then applied in accordance with the requirements of the applicable operating regulations and operations specifications.

  EXAMPLE-
  Destination altimeter is 31.28 inches, ILS DH 250 feet (200-1/2). When flight planning, add 300-3/4 to the weather requirements which would become 500-11/4.

     (2) On approach, 31.00 inches will remain set. Decision height (DH) or minimum descent altitude shall be deemed to have been reached when the published altitude is displayed on the altimeter.

  NOTE-
  Although visibility is normally the limiting factor on an approach, pilots should be aware that when reaching DH the aircraft will be higher than indicated. Using the example above the aircraft would be approximately 300 feet higher.

     (3) These restrictions do not apply to authorized Category II and III ILS operations nor do they apply to certificate holders using approved QFE altimetry systems.

  (g) The FAA Regional Flight Standards Division Manager of the affected area is authorized to approve temporary waivers to permit emergency resupply or emergency medical service operation.

  b. At or above 18,000 feet MSL. To 29.92 inches of mercury (standard setting). The lowest usable flight level is determined by the atmospheric pressure in the area of operation as shown in TBL 7-2-1.

So because most altimeters do not have this kind of range, the altitude readout will be inaccurate. This is especially problematic for IFR operations where you do not have visual reference to the ground.


What is the minimum distance between two civil airplanes parked in a hangar?

If you look at some civil-aircraft hangars, you will see that the planes are almost touching each other, as you can see here:

The planes are so close to each other to fit a maximum amount of planes into a hangar.

There are different types of hangars. Some are built just to store aircraft when they aren't used, some are built for aircraft-maintenance-operations and can even contain robots. Hangars can be simple buildings with a big and open space or they can be very complex facilities.

If you want more infos about aircraft hangars take a look here.

You can find the minimum separation distances between aircraft and minimum distances between the aircraft and other obstructions here

Take a look at this table from this document (page 30):

As you can see, the minimum distance between the wings from two parked aircraft is not always the same.

  Dimensions vary for different models and configurations of aircraft.

If you want to find out the min. distance of an A380, you need to take a look at the documents provided by Airbus.

No, there is no basic rule. The safe distance is determined by the aircraft-type, configuration and the hangar (owner).

If the airliners are stored in the hangar, they can be pretty close to each other. However, maintenance of a big airliners takes up a lot of space:


How strong must wind gusts be to prevent landings and takeoffs?

You have two questions here,

  I hope this is not as trivial as it sounds. Is there a wind gusts
  threshold based on which, at a given airport, incoming flights are
  diverted and outgoing ones are delayed?

As far as I know there is no specific threshold for which they will divert. You may want to read up on wind shear here as an airport may advise sever or unsafe wind shear and urge pilots to divert. There will be a point (often at single runway airports) where a landing in a particular type of aircraft becomes unsafe or even impossible as a result of wind but this will vary by plane.

  Also, I assume that aircraft are designed according to a specific max
  wind gust, so if there is any wind gusts threshold, I expect it to be
  less than the design threshold. Is this correct?

Yes, aircraft are designed with whats called a maximum demonstrated crosswind component. The key here is that this is a demonstrated limit not necessarily an airframe limitation. The number is published in the POH for the aircraft made after 1975 and provides a general guideline of the maximum cross wind the plane can be landed safely in however its more than possible to land it in higher wind situations.

Also it should be noted that some of this is up to the pilot in command. Just because a towered airport clears you to land does not mean it is safe for you to do so likewise just because a pilot diverts does not mean they were instructed to do so by the tower they may self elect based on their personal abilities.


Why don't airliners have any mirrors or cameras?

Aircraft rarely collide with any objects. Cameras would only be helpful if the extent of the damage is visible from the outside. Instruments, on the other hand, can be used to diagnostic the problem even if the system fails "internally".

E.g. Many hydraulic lines and cables run across the wing. If these is damage on the leading edge, is it the slats? A hydraulic leak on system A? system B? Is the de-ice working? You need instruments to get a better picture.

Some aircraft indeed come with cameras. The Boeing 777 has cameras on the bottom of the fuselage and the tail to aid pilots during taxi operations (the 777, especially the 777-300 variant, is really long...)

The Airbus A380 also has a tail mounted camera. Passengers can enjoy a spectacular view of the clouds, the high speed takeoffs and landings:

As for mirrors, pilots don't overtake other planes or back off like drivers do. There really is no need to know what is behind the aircraft. Pushback is accomplished by the tug on the ground, who has a much better view of the area than the pilots.


What are the hinged(?) structures in front of the F-4 Phantom's intakes?

From Wikipedia:

  A splitter plate is a component in some jet aircraft, used to control the airflow into the engine. Where the engine air intake is mounted partway back along the fuselage or under the wing, the splitter plate diverts the boundary layer away from the engine intake. It is a form of boundary layer control.

From Youtube: an F4


Can a plane be IFR certified, but not allowed in IMC?

Question: Can these planes be certified for IFR, despite the IMC limitation?

No

Refer to  FAA Order 8700.1:

  B.  Type Certificate Data. Appropriate type certificate data will
  indicate whether the aircraft meets the requirements for IFR
  operations.

  (1) Section 91.9(a)prohibits aircraft operations without compliance
  with the operating limitations for that aircraft prescribed by the
  certificating authority.

if no, can they be used for training for one's instrument rating and for the instrument rating checkride?

Yes, as per FAA Order 8700.1:

  9.  USE OF AIRCRAFT NOT APPROVED FOR IFR OPERATIONS UNDER ITS TYPE CERTIFICATE FOR INSTRUMENT TRAINING AND/OR AIRMAN CERTIFICATION
  TESTING.  The following paragraphs are intended to clarify the use of
  an aircraft not approved for IFR operations under its type certificate
  for instrument flight training and/or airman certification testing.

  A.  IFR Training in Visual Meteorological Conditions (VMC). Instrument
  flight training may be conducted during VMC in any aircraft that meets
  the equipment requirements of part 91, 91.109 , 91.205 , and, for an
  airplane operated in controlled airspace under the IFR system, 91.411
  and 91.413 . An aircraft may be operated on an IFR flight plan under
  IFR in VMC, provided the PIC is properly certificated to operate the
  aircraft under IFR. However, if the aircraft is not approved for IFR
  operations under its type certificate, or if the appropriate
  instruments and equipment are not installed or are not operative,
  operations in Instrument Meteorological Conditions (IMC) are
  prohibited. The PIC of such an aircraft must cancel the IFR flight
  plan in use and avoid flight into IMC.

For example, you can obtain an Instrument--Rotorcraft in an R44, even though its not legal in IMC.

  Although the R44 IFR Trainer was designed for instrument flight
  training, it is not approved for actual IFR operations. While student
  pilots are flying on instruments, the instructor must act as the
  safety pilot and operate only under VFR conditions.

if yes, then if one were to be flown into IMC, would be this be a legal violation or a warranty violation?

This would be a legal violation of 91.9(a)

  91.9(a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating
  limitations specified in the approved Airplane or Rotorcraft Flight
  Manual, markings, and placards, or as otherwise prescribed by the
  certificating authority of the country of registry.


Has anybody done gliding experiments with exact replicas of the birds or other real world flying creatures?

The closest I know of are several attempts to build models of pterosaurs.

Since the head with its long beak is ahead of their center of gravity, the configuration is statically unstable in yaw and needs continuous control corrections. On the other hand, this instability provides very quick responses. This YouTube movie contains footage of a Pterodactyl model made by Paul MacCready in flight. Note that Paul had attached a conventional tail for the first flights to statically stabilize the model in pitch and yaw. Later in the flights this tail was removed. The small skin area between the legs was most likely not sufficient for pitch stabilization, and small changes in wing sweep were used to stabilize the animals in pitch, just like modern birds still do.

Another branch, the Rhamphorhynchoidea, had a tail which provided additional lateral and longitudinal control. Palaeobiologists are still arguing, however, whether the tip of the tail was oriented horizontally or vertically in flight.


How attitude, speed, and altitude vary when increasing pitch?

The general answer goes something like this:
Level flight, at it's most basic involves a balance of 3 factors:

How fast are you going, relative to the wind?
What is the angle of attack (AOA) of your wings, relative to the wind?
How dense is the air that you are flying through, based on altitude, temperature, humidity, etc.?

Speed and AOA are variables that you indirectly control, via throttle (by increasing thrust) and yoke (by using elevator to alter pitch) respectively. The thing is, changing one variable (speed, AOA, or density) requires that one or both of the others change to maintain equilibrium. Want to stay in level cruise at a given density altitude after lowering throttle? AOA must increase. If the AOA stays the same, the aircraft will begin to sink because the current density cannot provide enough lift at that combination of AOA and speed.
That explains some of the "Why". Now let's consider your scenario. You have taken throttle out of the equation. Thrust is fixed and cannot be changed. This means that for any change to AOA, density must provide the equilibrium. Unless you are already at your stall speed, a slight increase in AOA without lowering throttle will begin a climb at slower forward speed because this new combination of AOA and speed are producing excess lift at the current air density. You have traded forward speed for extra lifting force. Because the throttle and new pitch are now fixed, the airplane will simply climb at it's new speed and AOA until altitude and temperature lower the outside air density to the new equilibrium point. At this point, the aircraft will once again be configured for level flight at the new density altitude. Also, because the density will change gradually, so too will the rate of climb decrease gradually. It will probably take a good while to fully level out.
ADDENDUM:
The "lift" topic always sparks arguments, because technically, lift can be generated in any direction, depending on the definition of lift you are considering. An aircraft moving through the air on its side, may still create some small amount of force laterally, which opposes gravity, even though the wings may be producing no force at all. A helicopter in hover is utilizing all of its accelerated airflow for to counteract gravity, but a change in rotor disc tilt divides that total force between lift (opposing gravity) and thrust (opposing drag). An aerobatic airplane hanging on its prop is utilizing accelerated airflow in much the same way. An aircraft flying upside down is creating lift that is simultaneously against the pull of gravity AND toward the bottom of the aircraft.
Additionally, Bernoulli's principles work equally well in any orientation. An asymmetrically cambered airfoil mounted vertically will still create an area of lower pressure on one side than on the other, and is still capable of altering angle of attack to adjust deflection. Is this lift? The simple physics definition would say "No" because it is not opposing gravity. An aerodynamic analysis of the airfoil would say "Yes", the airfoil is creating lift according to its orientation, which in this case, affects only yaw.
It would be nice if the entire world could agree that Lift is the sum of all forces that act in opposition to gravity, and Thrust is the sum of all forces that counteract drag - regardless of whether these forces are provided by airfoil or prop (which is still an array of airfoils!). Unfortunately, for now, clarification is often required when discussing this problem in polite company.
In closing, I would like you to consider this: in your scenario, the reason that your airplane slows down is because, much like the helicopter, your prop disc is being tilted, dividing its power between lifting and thrusting. The drag on the airplane remains, so the added burden of lift is what leeches away the speed. The wings, on the other hand, no longer bear the full burden of opposing gravity, so the lift that they are producing DOES become less, but only because they are now sharing that load with the prop.


What is the real impact of biofuels on aviation?

The "real" (or at least ideal) impact of biofuels in aviation is a reduction in CO2 emissions. When they burn, they produce exactly the same amount of CO2 as fossil fuels, but, all this CO2 came from CO2 that was already in the atmosphere. So it's only putting back what was already there:

  From the standpoint of human-released carbon dioxide, other greenhouse gas emissions, and contributions to climate change biofuels have one large advantage over gasoline, diesel and other fossil fuels: The feedstocks for biofuels are part of the above-ground carbon cycle. Unlike petroleum or coal, the soybeans, corn, switchgrass and other biological materials that are made into biofuels are not dug up from underground, nor do they release long-stored carbon as carbon dioxide into the atmosphere when burned. Instead, when biofuels are burned, carbon dioxide they recently captured is release back into the atmosphere.

This is sometimes claimed to mean biofuels are carbon neutral. For example, it's claimed here a 95% reduction occurs. But it's a bit more complex than that:

  Producing biofuel with crops like corn often requires converting land from food to fuel production or destroying natural ecosystems that provide valuable services, including carbon sequestration. Crops also require fertilizers, pesticides and large amounts of water, as well as machinery for planting, growing, harvesting, transporting and processing. If forests are cleared for fuel crops and if the entire lifecycle of the fuels is taken into account, biofuels don't always reduce overall greenhouse gas emissions. Palm oil, used for biodiesel, is especially bad, because valuable carbon sinks like peat bogs and rain forests are often destroyed to grow palms.


Are there any aids (like a padded "belt") that can ease hip discomfort during aerobatics?

You can try out a padded harness which may help, a variety of places mention the stuff offered by Hooker Harnesses and may be what you are looking for.

(source)

If you currently only have a lap belt installed in the aircraft in question you may want to consider 5 point harnesses as they can help by moving some of the load to your shoulders.


Why do most propeller-powered planes not have an autothrottle?

Because each jet engine only has one lever; each piston engine has three.
Jet engine's throttle is pretty straight forward - move forward, more power. The computer automatically manages fuel flow to prevent surge, flameout and N1 overshoot.
On a piston engine you have three - a mixture lever, a propeller lever and a throttle lever. Granted, I don't think auto-mixture would be too hard to implement. Now, do I want a high-speed climb or high-power climb? And remember, the prop and throttle must be managed together. You cannot go beyond a certain power range with the props set for low rpm, otherwise you'll damage the engine.
It's like a car's automatic transmission, except it has one more dimension.
Power affects pitch
When you change power you must change the aircraft's pitch altogether. Autopilots on modern airlines have quite a number of vertical modes: ALT, V/S, G/S, VNAV, FLCH, TO/GA, CLB etc. None of those have the concept of gear ratio, which is required for propeller management.
Can you design an autopilot system such that it functions on propeller engines? Absolutely. But it is going to be complicated. Not only the usual operations, but the failure modes, have to be engineered and learnt by the pilots. How do you deal with an auto-mixture failure? RPM mismatch? Such training would add unnecessary cost to an otherwise simple aircraft operation. If your airplane does not have a variable pitch propeller, it is probably too simplistic for this kind of autopilot anyway.
Jets have another property which makes auto throttle a logical choice - the faster you fly, the more powerful the engines. Thus, on a jet, you would have to make continuous throttle adjustment if you change your airspeed. So an auto throttle would be helpful. Pistons do not behave like that.
Turboprops
One of the main reasons for choosing piston aircraft is - it is simple. It just fly. No fancy stuff. No lengthy preflight checks. No computers. I just want to get flying. This thinking also extends to turboprops.
It's worthy to note that the ATR does not have auto throttle as well. The ATR 42 has power management (but not speed management), where activating it will simply move a bug on the torque gauge; the pilots have to manually move the levers to follow it. The ATR 72 has a notch for the pilots to place the throttle levers, but still, no motor to move the levers automatically. I can't think of any reason behind this design philosophy besides simplicity and cost.


What is the most 'environmentally friendly' way to learn to fly?

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

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

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


How has CAD influenced aircraft design in the last few decades?

We used CATIA extensively in the design of the F-22.  It helped all the supporting "ilities" also in their tasks.  Great tool.


What are the requirements for a 'complex' airplane?

For the FAA, a "complex aeroplane" must have:

A retractable gear (not necessary for a seaplane);
In-flight adjustable flaps; and
A controllable pitch propeller.

The FAA's definition is given in 14 CFR 61.1:

  Complex airplane means an airplane that has a retractable landing
  gear, flaps, and a controllable pitch propeller, including airplanes
  equipped with an engine control system consisting of a digital
  computer and associated accessories for controlling the engine and
  propeller, such as a full authority digital engine control; or, in the
  case of a seaplane, flaps and a controllable pitch propeller,
  including seaplanes equipped with an engine control system consisting
  of a digital computer and associated accessories for controlling the
  engine and propeller, such as a full authority digital engine control.

However, the EASA has a different definition of a "complex motor-powered aircraft" that is an airplane, which is considerably more "complex":

  an aeroplane:

  with a maximum certificated take-off mass exceeding 5 700 kg, or
  certificated for a maximum passenger seating configuration of more than nineteen, or
  certificated for operation with a minimum crew of at least two pilots, or
  equipped with (a) turbojet engine(s) or more than one turboprop engine

Note that 5700kg is about 12567 pounds.


Airliner speed when descending through 10,000 feet

Note that the speed you saw would have been ground speed not air speed. But in any case, you generally descend with the autopilot in a mode that pitches to hold an airspeed, called "Speed Mode" or something similar.  The other option is to descend in a mode that pitches to a vertical speed, called "VS" mode.  Speed  Mode is used most of the time.  You set the target speed the AP will maintain with a dial on the autopilot panel that moves a bug on the speed tape.

When you start a descent you will usually dial the speed you want to descend at, engage speed mode, then pull the thrust to idle, and over you go. Say you are descending with the bug at 290, which means the bug is set to 290 on the tape and the airplane will nose up or down as required to hold that speed, and in this case you are in some kind of dive.

As 10000 ft approaches, say passing through 12000, you just dial the bug down the speed tape to 250.  The airplane will pitch up a bit and start decelerating, then start pitching down again to maintain 250.  You try to time it so you are hitting 250 just as you are passing 10000.

ATC doesn't know your indicated airspeed, only your ground speed, so a controller has to estimate your airspeed based on the wind and ground speed.  This means being a few knots over the limit won't get you busted.

If you screw it up and are still too fast by more than say 10-20kt passing 10000 (or maybe because of some other imperative), then you'll dump some speed brakes to slow down faster.  But like I said, 10kts too fast passing 10 is not a big deal.


Where does the air enter the passenger cabin?

It looks to me in your top image that the air vent is right there at the center of the ceiling.

It looks like a linear slot diffuser running the length of the cabin.  Similar to this


Why does lower atmospheric pressure produce higher EPR (thrust)?

You can also notice that for one atmospheric pressure, the EPR remains constant until it starts to get really hot.

That's a flat rated engine (or an engine that is not easily temperature limited).

The three limits for a jet engine are: pressure limit, temperature limit, and N1 RPM limit.

How can a lower atmospheric pressure produce higher thrust when temperature is constant?

Cold weather—high EPR is as you said is straight forward.

Normally a decrease in pressure would decrease the EPR. However, engine manufacturers are willing to push the pressure limit when the ambient pressure decreases (altitude rises).

This allows more thrust for a takeoff from a high airport, which otherwise would significantly limit the engine/airplane. This increased tolerance comes at the cost of more frequent checks for the engine, i.e., more money.

  We are frequently asked why this is the case. The engine manufacturers,
  recognizing that good takeoff performance may be critically important on the more challenging
  routes, allow some increase in the pressure-limited takeoff thrust setting at altitudes above sea
  level.

  Jet Transport Performance Methods - Chapter 15


Is there a central database for all airline reservation information?

The simplest answer is that United and Thai have a codeshare arrangement, so United booked a ticket on all 4 segments using its own reservation system. United's reservation system communicated with Thai's to reserve your place, and the ticket was issued by United.

that being said, there are a number of GDSs (Global Distribution Systems), which are multi-airline reservation systems, all of which communicate with each other. Complete information on GDSs can be found in Wikipedia.


Which are typical rpm values for aeronautical turbines?

First of all: There is not one single speed on many aircraft engines. Big propeller engines have a reduction gearbox so the propeller runs at a lower speed than the core engine, and multi-spool turbines have an inner, high-pressure section with higher rotational speeds than the outer, low-pressure parts of both the compressor and the turbine. Take the Progress D-27 turboprop for example: It has three spools and a reduction gear, so its components run at four different speeds.

Generally: The bigger the diameter, the lower the typical speed. Fan and propeller blades should run at a high dynamic pressure, but still at subsonic speeds to avoid the higher losses involved with supersonic flow. Since the tip will be the part with the highest speed, and propellers have bigger diameters than fans, propellers run at lower speeds. Also, their bigger diameter makes propellers more efficient. The more air mass is involved in thrust creation, the higher the propulsive efficiency will be. Propellers on slow-flying electric or human-powered airplanes run at only hundreds of RPM, well below speeds where their tips would approach Mach 1, in order to convert as much of the limited power to thrust as possible.

If flow speed allows, core engine parts run at the highest RPM possible, because the faster a turbine or a piston engine runs, the more power it will produce for a given size. Therefore, core engines of the same size run at the same speed, regardless of their type, their bypass ratios or their use. Only stationary gas turbines for power generation might run a bit slower than their aircraft-mounted siblings to increase their life.

The high pressure compressor and turbines of an airliner engine will run at above ten thousand RPM, while the propeller of a large turboprop engine wants to run at about 1700 to 2200 RPM, and in case of the NK-12 of the  Tu-95 the propellers run at only 750 RPM. Both the fan and the propeller are powered by separate low pressure turbines. The fan and low-pressure compressor of a big airliner engine run at between 2500 and 4000 RPM, and the turbine of the PT-6, a classical turboprop engine, at 30.000 RPM. Since power is torque times RPM, a faster running shaft will be lighter than one running at low speed, so the speed is only reduced directly at the propeller mount.

A fan's optimum speed is between that of the compressor and the propeller and would ideally also need a gearbox, but here the transmitted power is so high that a compact gearbox will be hard to design. Even if it runs at 98% efficiency, it will produce waste heat in the order of several hundred kilowatts in case of a big airliner engine. Some small engines with just a single turbine use gearboxes already (e.g. the Lycoming ALF507), and now the next generation of efficient fan engines are also introducing gearboxes. But so far, most engine designs have preferred to run the fan faster than what would be ideal. Note that the tip speed of a modern, ungeared fan is already well above Mach 1.


How did aircraft communicate during early air travel?

Radio was not widely used until the 1930s, before that, mostly light signals were used. Early ground support aircraft in WW I could drop little notes which were pencilled by the observer, stuffed in a small capsule to which a streamer was fitted, and that was dropped as closely as possible to the troops which should get that message. This method was still used in WW II, when most aircraft had radio, because only specially equipped ground troops had compatible receivers.

The first regular flights by night were 1921 for the air mail connection between Omaha and Chicago, and electric flood lights were positioned along the flight path.
When Lufthansa opened the first night connection between the Reich and East Prussia in 1926, they posted burning oil drums along the way to mark where the pilot had to fly. Communication the other way (air to ground) was not possible on those flights.

The first air-to-ground radio communication used morse signals, and this is the origin for these strange three-letter names for things like local air pressure at the ground (QFE) or pressure corrected to sea level conditions (QNH). There was a whole lot more of those, including some to order coffee before landing, but they are no longer necessary. Read all about it here.


Is there any legitimate reason for adding momentary power when descending at idle with full carburettor heat on?

straight out of the Airplane Flying Handbook, pp 9-4

  Operating the engine at idle speed for any prolonged period
  during the glide may result in excessive engine cooling, spark
  plug fouling, or carburetor ice. To assist in avoiding these
  issues, the throttle should be periodically advanced to normal
  cruise power and sustained for a few seconds.

This procedure is common during emergency descents or steep spirals to prevent the engine from cooling off too much.  If the engine mixture is excessively rich, spark plug fouling can occur.  Fouling can be cleaned off the plugs by running the engine at Cruise power settings with a properly leaned mixture in about 10 or so seconds.


Was a six-engine 747 ever seriously considered by Boeing?

The "fifth engine mount" option on the 747 is not designed to handle a running engine. It was an option used only by Qantas as a means of ferrying spare engines to remote locations, where flying a plane for a long distance to a maintenance facility on three engines was not possible. Only four of the Qantas fleet of 747s (totalling more than 60 aircraft) had this fifth engine option.

The mount for the fifth engine was not designed to transmit any thrust the engine would have delivered if it was running, and it fact the engine is partially disassembled by removing the fan to reduce drag (which reduced the loads on the 5th engine mount, as well as drag on the plane as a whole).

Some pictures and videos here: https://www.flightradar24.com/blog/how-qantas-ferried-an-engine-on-the-wing-of-a-747/

To convert this into "a 5 or 6 engined plane" would require a lot more than just "a few pipes and wires". The wing structure would have to be redesigned to handle an extra 50,000 pounds (or more) thrust from each extra engine, plus the extra weight of a proper pylon and nacelle structure. Considering the aerodynamic wing flutter problems with the initial 747 design, sticking another two engines on the wing would most likely have required a complete redesign of the wing.


What is the cost savings of using electronic motors to taxi?

Jet engines are not very efficient at low power and speeds, so using an alternative method of propulsion is a good opportunity to save fuel.

An aircraft the size of an A320 will probably burn about 200 kg of fuel during taxi (based on this and this). Assuming fuel costs \$3 per gallon, this is about \$200 per flight.

The cost of the added weight from the electric motor will vary based on flight length, but assuming \$0.05 per pound, the extra cost would be \$16.50. Of course you are saving 200 kg of fuel, so this also helps to offset the weight. The electric motor is powered by the APU which uses much less fuel than the engines.

As KeithS points out, this adds up quickly. Even if United Airlines only equips its 150 A320 series planes with this equipment (which would certainly be a large upfront cost), and those planes make 5 flights each per day, that adds up to \$150,000 in savings every day. This will of course depend on fuel prices, which are actually well under $3/gal at the moment.

A simple way to save some fuel while taxiing is to only use 1 engine (or 2, for four engine planes) to taxi. This doesn't save as much fuel as the electric option, but also has much less upfront cost.


How do I do these VOR time and distance calculations?

Here is the formula you are looking for:
(You can use this formula to answer your first question. I'm not entirely clear on what the second question means.)

Here is a nice discussion of the time/distance check from the Flight Learnings website: time/distance to station


If the airport reported BKN002, would that prevent performing a DH 259' approach?

Since you ask about ICAO, I have checked ICAO's PANS-OPS and Manual of All-Weather Operations.

"Ceiling Required" is not an ICAO term.

Since you tagged one of the plates SBAO (a Brazilian FIR; Atlantico ACC), I found a blog post from 2017, Brazil drops Ceiling requirement. From which, only 10 countries use that term, and ICAO hasn't used it since 1979 when PANS-OPS (8168) was released. My only guess is that your Jeppesen screenshot predates this 2017 change (the copyright says 2016).

You need to refer to the local AIP if this term is used locally.


What does the letter D on the underside of the wing stand for?

It stands for Deutschland. And the 366 is the remainder of the registration. The 'D' is the prefix to aircraft registered in Germany, think of it as an international license plate. The pre-1928 allocation was D-nnnn (max four digits).

Registration prefixes do not always have a clear meaning though.

For the placement, see here: Are the size and location of the registration number regulated?


Where can I find Air Traffic Control information material suitable for beginners and students?

Another good reference would be the training materials for VATUSA. This is part of an online system called VATSIM where people both fly and provide ATC virtually.

Although some of it does not apply to real operations (and of course none of it should be actual operations), it still covers real procedures based on the actual rules.

The basic guides do a good job of providing an introduction to the basic concepts, but the more advanced stuff is less helpful.

Other regions have their own VATSIM organizations, if you prefer a region other than the US.

In addition to the materials available, participation is also great for learning. Through VATSIM you can get training on the materials and then get hands-on experience working with (virtual) traffic.


Why does the rotor thrust decrease at smaller tip clearance for shrouded rotor?

This is the reason why a jet engine needs a shroud around its core: to reduce blade tip loss. When you decrease the wingtip clearance, you are curbing the wingtip vortices or the wingtip pressure bleed, and in doing so you are making each blade more and more effective at approximating its ideal i.e. infinite span high-low pressure spatial distribution under and above it, and this more ideal pressure difference accelerates the airflow better, which results in more inflow, which reduces the angle of attack of each blade a little, but increases the overall thrust produced. Think of the shroud as a big end plate for each and every blade. Think of this setup as the fan in a high bypass ratio turbofan: less fan tip clearance = more thrust.

EDIT: I'm not sure the author understood it as I do in his paper. He never clearly explained it in his writing. Plus, just why is there so much lift distributed at the wingtip? I've never seen anyone design a propeller with so much bending moment. He is making a propeller much heavier than it really is because the propeller could be less rigid and lighter and still providing the same thrust. If you really want an efficient prop, put the majority of lift near the midsection, and let the lift taper when approaching the tip.

EDIT: See how shroud works on a bona fide jet engine compressor:


Does full nose up trim yield best glide in Cessna 172/152 for a given load?

That ground instructor is giving you bad information. You can not make a blanket statement like "full nose up trim" and expect it to be valid for any and all situations.

You are correct that the best L/D speed will yield the best glide ratio and that the speed will vary with weight.

The best trim position is the one that will maintain the best glide speed hands off. Any other trim position will require an additional control input to fight the trim and that input will cause additional drag.

So no, full nose up trim will not yield the best glide unless by some remarkable coincidence that is also the trim position for hands off best glide speed.


What is the airplane with the best flying characteristics?

First, let's get a little perspective
Stick and Rudder was written in the early days of aviation. To a modern reader, things were really weird back in the early days of aviation.

For a while, air traffic control was a guy sitting in lawn chair next to the runway waving a big flag that said "GO".
Parts on the plane just failed.  Planes would crash on their way back from bombing Hitler, a truck full of mechanics would come out to bolt on some (hopefully) new parts, and then they'd take back off in the crashed airplane to go bomb Hitler some more.
One time, the Allies bombed Switzerland by mistake. This was a world where more than one airplane could miss not only a target, but the entire country.

The kinds of things that went on in those days as a matter of routine would send any modern-day NTSB investigator into full-blown panic attacks.
What I'm getting at here is that it's a mistake to judge Stick and Rudder by modern standards.  This is not the equivalent of brain surgery.  You have to think of this as a surgeon just trying to get other surgeons to wash their hands with soap before they operate.
Now on to your questions

Have aircraft flying characteristics improved?

Yes. One example out of many:  Cuffed wings.

How much have they improved?

Enough that Wolfgang didn't need to write a second book.

And what airplanes have we built that have the best flying characteristics (which are the "best-behaved")?

An Airbus flying in Normal Law.
There's a section in Stick and Rudder (page 160 in some editions) where Wolfgang says that a "foolproof" airplane is one in which the controls have been restricted so that the pilot is mechanically incapable of pulling the airplane to an angle of attack which will result in a stall.  Guess what?  A pilot flying in normal law can yank on elevator all day long and not stall that Airbus.
An Airbus in normal law automatically trims itself.
An Airbus in normal law automatically increases power on the engines if a pilot pulls the airplane into a high angle of attack.
Some people might hesitate to put words in a dead man's mouth, but he's not here, so I'll go for it:  The best behaved airplane according to Wolfgang would be a modern-day Airbus airliner.


How to calculate minimum flying speed in distributed propulsion?

The better way to look at predicting the performance of a distributed propulsion wing (specifically the NASA X-57 wing concept) is to think of the propellers along the span as a high-lift device that augments the lift of the wing through interaction with the trailing-edge flaps, rather than as headwind-generators. In other words, the propellers increase wing C_L, allowing you to have a smaller wing for the same landing and takeoff distances.

With many small propellers, you get performance that starts to resemble a jet flap or externally blown flap, but without the complexity of internal ducting or non-uniformity due to a small number of engines.

Optimistic rule of thumb from thin airfoil theory is that, for a 2D section
$c_\ell = \frac{\partial c_\ell}{\partial\alpha}\alpha + \frac{\partial c_\ell}{\partial\delta_F}\delta_F$

$\frac{\partial c_\ell}{\partial\alpha} = 2\pi(1+0.151\sqrt{c_J}+0.219c_J)$

$\frac{\partial c_\ell}{\partial\delta_F} = 2\sqrt{\pi c_J}\left(1+0.151\sqrt{c_J}+0.139c_J\right)^{\frac{1}{2}}$

where $c_J = 2\frac{h_J}{c}\frac{V_J}{V_\infty}$

$V_J$ can be calculated from propeller momentum theory based on disk area, input power, and assumed efficiency.

Bear in mind this is for section $c_L$, and will need 3D corrections for the whole vehicle based on percentage of span with propellers, induced flow, etc. It is also reasonable only in the limit of small flap deflections and angles of attack. Wind tunnel data or flight test reports might be a better place to get a first-pass estimate.

https://www.researchgate.net/publication/299641308_Comparison_of_CFD_and_Experimental_Results_of_the_LEAPTech_Distributed_Electric_Propulsion_Blown_Wing

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740003719.pdf

https://arc.aiaa.org/doi/abs/10.2514/6.2019-3170


How should these translated takeoff and climb settings be interpreted?

12 degrees nose up

Since it says this comes after the ground roll, it sounds like this is the pitch you rotate to when you reach rotation speed. You then hold this pitch for the initial climb out.

  1500 feet; decrease power/reduce engine thrust power

In English, generally "power" is used on propeller aircraft, and "thrust" used on jet aircraft. Other languages might not translate exactly. On a turboprop airplane, you would have power levers, which you use to select a power setting. At this point, you would decrease the power setting to a climb/continuous setting.

  climb speed

This just means you will fly whatever speed you plan in climbing at. This would depend on the aircraft, and the flight. Especially larger, higher performance aircraft will have some standard "climb speed" that is used during climb, to balance ground speed and rate of climb. "Cruise climb" may be used to describe a slower climb where emphasis is placed on a higher ground speed. In smaller aircraft there may be less performance margin. This wording may also be leaving it open, as on some flights you may want best rate/angle of climb, others would use a regular climb speed.


Does temperature affect dynamic pressure?

Yes, temperature affects dynamic pressure by affecting air density: it reduces with increasing temperature.

Dynamic pressure q $ = ½ \cdot \rho \cdot V^2 $

The molar form of the ideal gas law: pressure p = $\rho \cdot R \cdot T$, with R = gas constant and T in degree K

$$\rho = \frac{p}{R \cdot T} \tag{1}$$

Eliminate $\rho$ from dynamic pressure:

$$q = \frac{p}{2R \cdot T} \cdot V^2 \tag{2}$$

From (2) we can see that if temperature increases, dynamic pressure decreases linearly. In a deleted answer @xxavier mentions correctly that Indicated Air Speed is a measure of dynamic pressure, so let’s compare the two situations. 5°C = 292K, 40°C = 327K, TO true airspeed on a cold day = $V_c$, on a hot day = $V_h$

$$ \frac{p}{2R \cdot 292} \cdot V_c^2 = \frac{p}{2R \cdot 327} \cdot V_h^2$$

$$ V_h^2 = \frac{327}{292} \cdot V_c^2 => V_h = \sqrt{\frac{327}{292}} \cdot V_c  $$

$$ V_h = 1.058 V_c \tag{3}$$

So to reach the same IAS, TAS must be 6% higher. But there are more ways that dynamic pressure affects time to reach rotation IAS:

The propeller thrust is proportional to air density: simple momentum theory models thrust as $T = C_T \cdot ½ \rho A \cdot (\Omega R)^2$. Again density $\rho$ which decreases linearly with temperature according to (1). Propeller thrust reduces with factor (292/327), integrated over time until $V_h$ is reached. 11% less thrust to reach a 6% higher velocity.
The engine has less dense air to operate with. From this site:

  When your engine is not equipped with a turbo- or supercharger it will also suffer from the less dense air. Each intake stroke (which is by volume) will contain less air molecules and thus less power can be developed by the engine (due to the fixed fuel / air ratio).

So yes, dynamic pressure plays a role, but the real underlying cause is the less dense air everywhere. Also in the dynamic pressure.

Notes:

All above comparisons at equal static pressure $p$.
$V_c$ and $V_h$ are actual true airspeeds, not indicated speeds.


What percentage of professional pilots end their career early for medical reasons?

(US-based answer)

The problem with answering your question is that it isn't all clear what "losing a medical" actually means. If a pilot is denied a medical, the FAA will obviously know and you could probably get that data from them somehow, even if it takes an FOIA request. But what if you just decide not to renew because you know you'd fail? For all the FAA knows, you might have retired, changed career or even died.

If we assume you do mean "denied" then the only specific number I could (quickly) find for denials was from 1978:

  The annual denial rate based on airman applicants is 7.9 per 1,000
  airmen. By class of certificate applied for, the annual denial rate
  per 1,000 applicants is 4.5 for the first class, 6.0 for second
  class, and 10.2 for third class.

You could apply those rates to the number of airmen certified each year to get an estimate of the absolute numbers, but obviously using a 40 year-old report may not be accurate today. And determining how medicals 'map' to pilots may not be easy.

If you want a better answer, you'll have to define exactly what you're asking. To get an accurate number (whatever that means for your purposes) you might have to look for some specialized actuarial or medical research on this.


Why do VTOL aircraft (F-35 or Harrier) have only one engine?

VTOL aircraft can have more than one engine. It is just that the design process of the Harrier and F-35 led to a situation where only one engine was required.

The main challenge in any VTOL aircraft is to have the engine produce thrust in two different phases of flight: during cruise and during takeoff/landing. This basically requires the powerplant on the aircraft to have two different characteristics at those two phases, because

The direction of the thrust vector is different in TO/Landing and cruise
Amount of thrust required is different; for vertical TO, the thrust should be more than the weight while in cruise, the required thrust is (comparatively) pretty low.

A number of approaches have been tried to solve this problem:

Takeoff the aircraft vertically (aka the tail sitter), like Ryan X-13 Vertijet, and then transition to horizontal flight. However, one major problem is the pilot has severe disorientation problems during transition
Put extra fans, like the Ryan XV-5 Vertifan. The problem was the large (wing) area taken up by the fan and weight penalties. Ironically, a similar concept has been used in F-35
Put extra engines specifically for vertical lift (aka the 'Rolls Royce Concept'), used in Dassault Mirage Balzac. Though this offered (theoretically) better safety, the weight penalty was too much.
Optimise the main engine for cruise and deflect the thrust for takeoff and augment with (small) lift engines (aka the tiltjet concept), like the German EWR VJ 101. This reduced the weight penalty and complexity, but reduced safety in the event of an engine failure.

In order to avoid the weight penalty, the best approach is to have no extra engines at all, with the thrust deflected down at take off and landing. This was called 'vectored thrust' (a term attributed to Theodore Von Karman). This concept was tested in the Bell X-14, which had fixed eingines and thrust vectoring vanes that deflected the exhaust to achieve vertical lift.

Source: history.nasa.gov

In case of the Harrier, the engine, the Bristol Siddeley Pegasus was first developed (as BE.53) and the Hawker aircraft decided to develop an aircraft around it.

During the design proces, the aircraft was redesigned around the Hawker modified BE 53 which the rear jet was split into two, like the Hawker Sea Hawk, which had a similar arrangement. This lead to the 'four poster' thrust vectoring system in the  Harrier.

Source: www.aerospaceweb.org

This is the reason, the Harrier had a single engine.

The case of F-35 is different. The F-35 was designed to replace aircraft operated by a number of US services, and as such had conflicting design requirements. At one end, the USAF wanted a conventional fighter while the USMC wanted a VTOL aircraft. The USN requirements were somewhere in the middle.

Lockheed designers decided that the best way to meet these requirements is to have a separate fan for lifting the aircraft in VTOL, which can simply be eliminated in the USAF and USN variants. This led to the lift fan arrangement (eerily similar to the Vertifan arrangement).

"F-35B Joint Strike Fighter (thrust vectoring nozzle and lift fan)" by Tosaka - Own work. Licensed under CC BY 3.0 via Commons.

So, in case of F-35 the use of a single engine was the best way to meet the requirements. The engine used, the Pratt & Whitney F135 is the most powerful fighter jet engine in service, which helps in making F-35 the first supersonic VTOL aircraft.


Do F-4 Phantom II pilots actually fold the wings?

As several of the comments have mentioned, the F-4 have the option of folding the outermost section of their wings, as shown in the picture below.

The main purpose of this was simply to save precious space on aircraft carriers, it had no use when flying. There have been some incidents where wings have either started to fold during flight or where the pilot forgot to unfold before takeoff, but it was not designed for this. Many other naval aircraft have the option of folding their wings in a similar manner, such as the F/A-18.

The F-14 Tomcat uses a completely different mechanism to adjust the wing sweep while flying, and although it had a special "parking setting" for the sweep, it was used to adjust the wing sweep according to the speed of the aircraft.

The A-7 Corsair II and the F-8 Crusader also had wing folding, but in addition they could also adjust the attitude of the wing while flying, primarily to improve visibility for the pilot when landing as seen below.


What to do as an international student without a driving license that is needed for PPL Training in Germany?

You do not need a driving license to request information from the German Register of Driver Fitness.

The Kraftfahrt-Bundesamt has a website in English with information on how to request your information free of charge: https://www.kba.de/EN/ZentraleRegister_en/FAER_en/Auskunft_en/faer_auskunft_inhalt_en.html?nn=642934


What is the most overlooked item during preflight inspection?

This FAA article is about using electronic checklists for airline flights (it concludes that they're better than paper ones) and includes this quote:

  They found the crews averaged 3.2 checklist errors per flight (one of
  the observed flights had 14.) The most-common checklist error involved
  the omission or deferral of an item, which was later forgotten.

NASA commissioned a general study into checklists in 1990, but it doesn't identify specific items that are commonly overlooked. It does say that as the number of items on a checklist increases, the chances of overlooking any individual one does too:

  Swain and Guttman (1983), in their study of nuclear power plant
  operations “recognized the fact that as the list of items grows, there
  may be a higher probability of overlooking any given item” (chap. 15,
  p. 13)

The final section of the paper has recommendations for checklist design, which could be considered the "best practices" you mentioned, but of course it's a very general list, e.g.

  The most critical items on the task-checklist should be listed as
  close as possible to the beginning of the task-checklist, in order to
  increase the likelihood of completing the item before interruptions may occur

AOPA's Flight Training magazine has an article on "frequently forgotten" checks that is more specific and most of the checks seem to apply to most (light) aircraft, but it doesn't provide any authoritative sources. They also have a "how to preflight" article that gives more information and includes this interesting observation:

  As an experiment, I held a preflight contest with a "bugged" trainer.
  I reversed the rigging on the ailerons so their movement was contrary
  to control inputs. Every one of the contestants checked control
  movement and freedom, but no one caught the problem.

Putting all that together suggests - only to me, and I'm not an expert - that it's less important to think about specific items that you might forget, and more important to ensure that you complete the checklist fully and really verify the results of each check. If you consider some checklist items to be 'more important' than others then it could also lead to mistakes because you overlook the 'less important' ones.


What factors contributed to enable Rickenbacher to be found?

Actually it was during WW2 and it was the Pacific:

  One of Rickenbacker's most famous near-death experiences occurred in October 1942 [...] The bomber strayed hundreds of miles off course while on its way to a refueling stop on Canton Island and was forced to ditch in a remote and little-traveled part of the Central Pacific Ocean.

I am not familiar with the episode, and this source is currently not working for me, but from the little information that the wiki reports, I have the impression that the main factor has been pure luck.


Will an airliner with a quieter cabin have a quieter cargo hold?

The cargo hold will probably be quieter if the cabin is quieter, but there are multiple variables that can affect this. As Peter Kämpf commented, the noise source will depend on the position in the airplane. The two main sources of noise are the air moving past the airplane, and the engines. The two main noise concerns of manufacturers and operators are cabin noise and community noise.

Reducing the noise at the source is one option. Engines are the main sources of noise and receive special treatment to reduce noise as much as possible. This can reduce cabin noise and/or community noise, and should help both the passenger and cargo decks. Newer aircraft like the A380 will tend to have quieter engine installations than older aircraft like the 747-400.

In the case of the cabin, noise can also be controlled with insulation. Insulation in the cabin will help with both noise and temperature control. Both are less important in the cargo hold, but do have some importance since it is only separated from the passenger area by the floor. Cargo hold insulation will provide protection for structure from fire or accidental damage, and some degree of temperature protection. So it is possible that the cabin receives added protection from these features that the cargo area does not benefit from.


How can you fly your own military jet in terms of altitude and acrobatics?

But practically can you fly it?

Sure.

I mean how high can you climb?

As high as you want, assuming you have an oxygen delivery system (14 CFR 91.211, note that "civil aircraft" means "any aircraft not a public aircraft" means "any aircraft not owned by the government," so you can't get out of it that way) and assuming both you and the plane are certified for IFR flight (14 CFR 91.135).

How fast can you go (I know no supersonic flights are allowed above land, but what about sea)?

Below 10,000 MSL no faster than 250 KT, and below a Bravo shelf or near a Charlie/Delta airport no faster than 200 KT, unless the minimum safe airspeed for the aircraft is higher than that (14 CFR 91.117). For supersonic flight see 14 CFR 91.817, 91.819, 91.821.

Can you do barrel rolls and pull Gs?

Assuming the aircraft is certified for aerobatic flight (or perhaps if it has an experimental certification), yes, as long as you comply with the restrictions in 14 CFR 91.303; or failing that, submit an application for a waiver of Part 91 rules (FAA Form 7711-2) (see also) and get such a waiver.

Also, can you use it to fly internationally (assuming that you can attach external fuel tanks in the first place)?

Yes, if you comply with each country's respective airspace/border entry rules.

Can you actually have fun with it lol? Assume that money is no issue.

Depends what you think is fun.
Basically there are no special rules for ex-military aircraft; if you can legally get your hands on one, and if you can legally fly it, you can do whatever any other aircraft is allowed to do as long as you follow the rules any other aircraft has to follow.


Are sun's UV rays more harmful on an airplane at high altitude?

Hmmm, opening the window at 30.000ft, where the air temperature is about -40°C/-40°F, air speed is extreme, you can't survive without oxygen, and you want to put your arm outside???

Well, if you really do, you'll get a sunburn quite fast. I got a sun burn within an hour in an altitude of 3500m / 12000ft, though I was tanned due to two weeks at the beach.

The ozone did already absorb a large fraction of the UV-C radiation, but as most of the air mass is already below you, the rest of the sun light will not have been filtered so much.

So, let's close the window.

To my knowledge, side windows and canopies are made of some kind of polycarbonate like or Plexiglass.

CERN measured the transmission of light through a 2mm sheet of plexigas and came to the result that no light below ~350nm, passes this sheet. Depending on source, the UV region starts below 380-400nm.

Source: https://cds.cern.ch

Keep in mind that the windows are usually thicker, which makes this step in the diagram much steeper.

So, there isn't much UV left which can cause a sun burn, but let's take the data from rredc.nrel.gov to calculate how much light you get and compare it to the light at ground. I found a function describing the data from CERN quite well, and applied it to the sun spectrum data (without atmosphere) twice, to get a Plexiglass window of 4mm thickness. So, this is the worst-case, with no air above the aircraft pre-filtering the sunlight.

Here is the result, which shows that sunlight is much more intense, and its color is heavily shifted to blue. But the intensity drops to zero, just where the UV-A range starts. Even, if you put the beginning of the UV-A range to 400nm, the intensity is still lower than at the ground.

Wind shields of larger aircraft are usually a quite thick composite material of glass and some plastics, which should absorb UV the same way as polycarbonate does, if not better.

So, I don't see any evidence that you get more UV light in an aircraft than on ground.

However, you should not underestimate cosmic radiation, which is absorbed by our atmosphere quite well on the ground, but not at high altitude. A transatlantic flight is equal to an X-ray photography of your chest. Flying staff is an occupation group exposed to much higher radiation doses than any other group and it's dose usually is supervised.

EDIT:

As @PeterKämpf pointed out, Plexiglass is only one material used, and it is not a polycarbonate, which I didn't notice. But polycarbonates don't differ much concerning UV transmission, as the following diagram shows. However, I also read that polycarbonates - in contrast to plexiglass - are not UV hard and need an UV blocking coating when used outside.

Source: www.plasticgenius.com


How is bleed air used to start a jet engine?

(Source) Image shows how the shaft is connected to the gearbox.
The engine shaft is connected to an accessory gearbox. The spinning shaft spins the gearbox, which drives the generator, the engine-driven fuel pump, and other accessories.
The same gearbox can be spun using high-pressure air—from the APU or a start-cart. This high-pressure air spins a turbine (air turbine starter), which drives the gearbox.
(Source) Air start location.
Once the shaft is spinning fast enough to bring in compressed air that would guarantee a successful and sustainable burn, the fuel is introduced, and the engine starts and speeds up further. The turbine then disconnects. Just like how a Bendix drive1 in most car engines disengages the starter motor once the engine is started.
In a twin-spool (two-shaft) jet engine, the gearbox is usually connected to the high-pressure shaft—the same shaft for the compressor/turbine stages closest to the burners.
What can go wrong?
Apart from starter- or gearbox-related malfunctions, not enough air pressure to spin the shaft—which would be an issue with the APU, start-cart, or piping.
If the jet engine is sitting in fast-enough tailwind entering from the rear (the jet pipe), the engine will be windmilling in the wrong direction, it could result in too much force for the gearbox to overcome. In this scenario, the pilot would select the engine reversers—by opening the reverse doors / engaging the buckets, less wind will be allowed to spin the shaft the wrong direction.

An exceptionally strong tailwind (in excess of approximately 20 knots) may prevent positive N1 rotation at a max motoring RPM of 15% to 20% N2. In this condition the Captain should do one of the following:

Have the aircraft towed into a position (headwind or crosswind) in which the N1 rotation stops or is in the correct direction.

Have the ground crew verify that both engines are clear of personnel and equipment, then deploy both engine reversers. After approximately two minutes, have the ground crew verify zero N1 rotation. Prior to starting an engine, verify the reverser is stowed and latched.

(MD-80 manual)

(Source) Reverse buckets.

1 Same Bendix we know, that's how he made his initial fortune.


Do pilots have to stop at the hold position of the takeoff runway?

No, there is no mandatory stop. Typical clearances given before departure are:

BigAir 123, hold short of runway 36.
BigAir 123, line up and wait runway 36.

Former phraseology in the US was "position and hold".

BigAir 123, behind landing A320, line up and wait runway 36, behind.

Note the word "behind" being repeated at the end of the clearance.
The interesting ones:

BigAir 123, are you ready for immediate departure?

It will be asked by the tower controller to assess if they can squeeze BigAir 123's departure between two landings, for example.

BigAir 123, cleared for takeoff runway 36.

It can be given to an aircraft still on the taxiway. In such case, BigAir 123, who will have proceeded through checklists and briefings while taxiing, will turn into the runway and takeoff, without having to stop at any point.
It is possible that the crew actually needs to stop, to finish their preparations. In such case, they will normally report not ready for departure, if asked. The tower controller doesn't want aircraft making unexpected stops on the runway, especially in a single-runway airport, this can result in the following landing having to go-around.
Also note that the word "takeoff" is used only in the context of an actual takeoff clearance or its cancellation. Otherwise the word "departure" is used, e.g., are you ready for departure? Also see the Tenerife disaster.


If the Concorde had an engine fail at cruise altitude, would they enter the coffin corner?

The Concorde doesn't need reheat to cruise supersonically, just to get there (the range would be pretty short if it did).  If it loses an engine it's not going to put the other 3 into reheat to hold altitude and speed (fuel burn) and it will do what just about all airliners have to do when at they lose an engine, descend to whatever its engine-out service ceiling is.  This is done at some speed near minimum drag that gives the flattest descent, called "driftdown" speed, whatever it is, and it will just pitch down as required to maintain that speed with the available military rating (non-afterburner) thrust. Obviously, it will come out of mach as it does so.

Also I should point out that being a supersonic aircraft, it doesn't really have a "coffin corner" in the normal sense.  That applies to subsonic airplanes that are limited to a speed just shy of Mach, and when they get so high they become hemmed in by stall speed on one side and trans-sonic related issues on the other.  The upper limit of a supersonic airplane's speed is aerodynamic heating related and is a function of the airframe material's ability to run at high temperature, which limits aluminum structures to below Mach 3.  This is why the SR71 is titanium.


Is there a minimum distance that a pilot is required to fly?

There is no rule that says that a flight needs to be at least x miles long. Most training flights don't even leave the vicinity of the airport, and they still count.

The only thing stopping your hypothetical scenario would be that the pilot taking off from the uncontrolled airport needs to obtain an airspace  clearance before taking off. If the bigger airport is busy this could be denied, in which case the pilot would be stuck!


What are the US flight planning regulations for an alternate airport?

It is important to point out that what follows only applies to flying under §91. Operations under §135 have a different set of requirements for alternates than those specified here in §91.169. Your question includes the general-aviation tag, which is poorly defined (at no fault of your own); the tag description given on this site includes all civil aviation other than §121 airline flights, but many definitions exclude charter, or even all §135 flying. In what follows I will assume flight operations conducted exclusively under §91.

Q1:
Yes, that is correct. An alternate is always required on the flight plan unless—among other things—the first airport of intended landing has an instrument approach prescribed under §97 or otherwise authorized.
Weather conditions also determine that exception.

Q2:
This is mostly true, but needs some corrections and clarifications.

There is no requirement for the airport to have weather reporting or forecast based at or provided specifically for that airport. The regulation merely requires "appropriate weather reports or weather forecasts". This could include weather information such as Area Forecasts or even TAFs or METARS for nearby airports.

Yes, this is accurate.

Yes, this is true when understood within the programing–type flowchart logic you use. However, just to be clear, lack of an IAP alone does not disqualify the airport as an alternate—see #2 and §91.169(c)(2).

No, not necessarily. AIM 1-1-18(b)(5)(c) clarifies that operators with non-WAAS equipped GPS systems can plan to use a GPS approach at either their destination or the alternate, but not both:

(c) For flight planning purposes, TSOC129() and TSOC196()-equipped users (GPS users) whose navigation systems have fault detection and exclusion (FDE) capability, who perform a preflight RAIM prediction for the approach integrity at the airport where the RNAV (GPS) approach will be flown, and have proper knowledge and any required training and/or approval to conduct a GPS-based IAP, may file based on a GPS-based IAP at either the destination or the alternate airport, but not at both locations. At the alternate airport, pilots may plan for:
(1) Lateral navigation (LNAV) or circling minimum descent altitude (MDA);
(2) LNAV/vertical navigation (LNAV/VNAV) DA, if equipped with and using approved barometric vertical navigation (baroVNAV) equipment;
(3) RNP 0.3 DA on an RNAV (RNP) IAP, if they are specifically authorized users using approved baroVNAV equipment and the pilot has verified required navigation performance (RNP) availability through an approved prediction program.

Note: TSOC129 and TSOC196 are the non-WAAS TSOs (as opposed to the WAAS TSOs: TSO-C145 and TSO-C146)

Yes, this is seen in AIM 1-1-18(b)(3)(b):

Ground-based facilities necessary for these routes must be operational.

Yes, this is true.

Yes, though I would say equal to or greater.

Q3:
Yes, the filed alternate—and the approach used to qualify it—are for legal filing purposes. In the actual flight, another appropriate approach, deviation airport, or approach at the deviation airport can be selected as needed.


Is it possible to reach an A340's fuselage from the ground?

Yes, the refuel/defuel service panel can be reached from a person standing on the ground.

From the Airbus A340-200/-300 Aircraft Characteristics - Airport and Maintenance Planning document, the height of the panel in question is just under 2 meters from the ground:

The panel is located on the lower area of the wing/body interface fairing as seen here (item 13):


Is there a limit to a subsonic ramjet's pressure ratio?

Yes, they have a limit at around 2. And this can only be achieved at Mach 1, as Peter Kampf points out. Increasing the inlet to diffuser area ratio to extreme values will just lead to your engine being filled with slow moving air. The mass and volume of air in your engine will increase, but neither the pressure nor the rate of airflow will increase appreciably


What is the difference between ARINC 429 labels 025 and 102 for Selected Altitude?

According to A429, the difference is the type of data coding. Label 025 is BCD. Label 102 is BNR.

Label 025 by being a Binary Coded Decimal codes each character of the altitude value in binary. With a range of 0 to 50000 feet, the first digit uses 3 bits and the remaining use 4 bits each for total of 19 data bits.

Label 102 is a Binary number. The range is 0 to 65535. There are 16 data bits (2^16 = 65536).

Both are transmitted. Receivers will use the version most appropriate for the application.  BCD is normally used for display. BNR is normally used in computations.


Can accelerations be used to calculate load factors?

It sure can; in fact, they are equivalent (with an offset of 1G).

In the body frame, the vertical equation of motion is:

$$Z+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$

Accelerometers can't measure inertial or gravitational forces, so vertical acceleration as measured is $N_z=Z/m$.


How do I keep coordinated on a windy day?

Don't chase the ball.  Heck if you're VFR/VMC, you should barely be glancing at the ball or any of your instruments and should have eyes outside.  Remember flying a little uncoordinated alone is not going to force a spin.

Stall + Yaw = Spin

So how do we mitigate this during gusty approaches?  We fly a little bit faster.  I like to use 1/2 the gust factor and add that to my final approach speed.

I'm not saying accept being uncoordinated, but when it's gusty out you don't chase airspeed, so why chase the ball?


On average, how many overhauls will thrust reversers have in their lifetime?

The answer varies from aircraft to aircraft. The newer varities such as the A380 go for a overhaul in about 1200-1500 hours, whereas the B777's go once in 1600-2000 hours of service.When an aircraft goes to overhaul, only then the thrust reversers go to overhaul, because they are an important component of the engine of modern day aircrafts. Though we do not know when will an aircraft retire, so it i difficult to come at a concrete result. But, talking about B747, many airlines are retiring them at the age of 40 years. So, 40 years = 350400 hours. 350400/2000 = 175(Approx.) So, for a B747 the answer should be like 175, and this does not necessarily implies to other aircrafts as well.


Can a commercial pilot decide where to make their turn after departure?

The short answer is yes, a commercial pilot can make a decision when to turn.

To clarify a few points though, there really isn't such a thing as a "published vector".  If a departure procedure with heading were to be published it would then become a Standard Instrument Departure, or SID.  True, some SIDs will specify radar vectors, but this simple tells pilots that they should expect ATC to assign headings that will vary depending on traffic, not which heading they can expect to actually fly.

Next, "commercial" pilots don't do anything different than private pilots, airline transport pilots, or military pilots.  When and where you turn during departure depends primarily on whether you are operating under IFR or VFR.  Secondarily, decisions on when to turn will be based on terrain, noise abatement, company policy, and lastly personal preference.

So, considering my answer in light of the above, there is a big difference between a 737 operating IFR on a SID, and a commercial pilot in a 172 towing a banner under VFR out of a non-towered airfield.  If you have a specific scenario you are wondering about you might get a better answer if you can narrow down the question.


Where does the 35 feet screen height come from?

The best explanation I've seen for the logic behind the 35 foot crossing height requirement can be found in the FAA Instrument Procedures Handbook (IPH). It's available from the FAA website at this link: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/instrument_procedures_handbook/
In Chapter 1, Departure Procedures, under Design Criteria on page 1-16: "The aircraft climb path assumption provides a minimum of 35 feet of additional obstacle clearance above the required obstacle clearance (ROC), from the DER outward, to absorb variations ranging from the distance of the static source to the landing gear, to differences in establishing the minimum 200 FPNM climb gradient, etc."
So, the 35 feet is in place to account for a multitude of variables. The phrase "differences in establishing the minimum 200 FPNM (Feet Per Nautical Mile) climb gradient" covers a whole host of potential errors such as variations in individual aircraft performance, early rotation, late rotation, under rotation, over rotation, poor airspeed control, etc. This error proofing is important since the 35 foot requirement is used when building all performance data for go and no-go decisions. That performance data is all based on set assumptions. Reasonable deviations from the assumptions are mitigated (somewhat) by the 35 foot margin.
As with most safety margins, there isn't necessarily a precise reason for the size of the buffer. However, even increasing the crossing height a slight amount, say to 50 feet can have significant effect on performance calculations. At a minimum climb gradient of 200 FPNM, the difference between a screen height of 35 feet and 50 feet is just over 450 feet of required horizontal distance. In a tight performance situation such as high pressure elevation or short runways, a 50 foot crossing height could be too much for some large commercial aircraft.
Of note, the regulation that created the 35 foot crossing height, SR422, came about in the late 50s during the beginning of jet-powered commercial aviation. The aircraft being designed and fielded back then, the Boeing 707 for example, would have had a hard time making a higher restriction. That likely had influence on the required crossing height.


Why did my phone's GPS receiver stop working when the plane was descending to land?

A GPS needs a line of sight to (at least) 4 satellites in order to compute a position. Given that you were able to get a position during the cruise, I assume that you were close to a window and had a clear view of a part of the sky.

During the cruise, the aircraft trajectory was close to a straight line (or changing slowly), so your receiver was able to keep a line of sight to the same set of satellites. But during the approach, the trajectory was much more dynamic (lots of turns), so your receiver didn't had a constant line of sight toward the same set of satellites and "lost" them. It takes time for a receiver to "lock" on the signal of a given satellite, so the receiver it couldn't compute a position from other satellites because they were not in sight long enough.


What does runaway failure mean (position difference between APPU and FPPU) on A320?

A runaway failure of an actuator is a situation where the actuator deflects maximally into one of its stops and stays there. Particularly hydraulic actuators can be subject to these: if the servo valve cannot close due to for instance dirt being stuck in the valve, oil flow will cause this type of failure. Electrical actuators commanded by a servo loop can fail in this mode as well.


why are there no production canard GA aircraft?

Why would you fly with a deployed spoiler when you can have a clean aircraft? Sure, there are many canard kit plane designs, but when you look closer at their performance, its is not improved by the location of the elevator. Burt Rutan would always choose a higher wing loading than required to fulfill the FAR part 23 requirements for low speed, so his designs could cruise faster. When asked about this, his usual response was "**ck the FAA!".

When you look closely, canards will give you:

With natural pitch stability a higher lift coefficient on the forward wing which also needs to have some margin for control surface deflections. Consequently, the big, rear wing is operating at a fraction of its potential when the aircraft stalls.
The vorticity from the front wing creates a downwash at the mid section of the rear wing and an upwash at the outer sections. The strength of these induced speeds varies with speed, so the main wing can produce an elliptic circulation at only one angle of attack. At other angles, its induced drag is higher than what is possible with a conventional configuration.
The center of gravity is ahead of the main wing, so the landing gear needs to retract into the fuselage, taking space away from the cockpit. To move the wing center section forward, so it can accommodate the landing gear, the wing needs to be swept (which creates a host of problems of its own).
There is no good position to put a vertical surface, so again sweep is used to shift some part of the airframe backwards and combine the vertical with winglets. Those need to point upwards, so they do not hit the ground during take-off and landing when the better winglet would point downwards.

Canards start to make sense when they are unstable, but this is not a good approach for a GA aircraft.


At least three of the "fallback systems" I know of are looking out the window, being familiar with the airport and its markings (as well as associated hotspots, as airport diagrams may indicate), and also paying attention to the radio, if you're equipped.  Of course, no one of these methods is foolproof, so it takes a combination of alertness and prudence to avoid incursions.  I was taught to look both ways before intersections, or to look both ways before entering a runway, just to make sure I didn't miss anything.  Also, using lighting on your aircraft appropriately helps make you more visible.

Other planes may not have a radio, so you may not hear a radio call of someone else in the pattern.  Also, at a complex intersection in a new airport, it may be confusing where you are, or what hold short lines you're about to cross -- so being aware of your surroundings is important here.

There are some technologies the FAA has been implementing to reduce the risk of runway incursions, such as Elevated Runway Guard Lights and stop bar lights, plus ground radar technologies (for ATC) to assist (see ASDE-X and AMASS).  Note that your A/FD entry may list, for example, that not all taxiways are visible from the tower -- which is a good reason to stay extra alert.

Other sources:

Runway Incursion Avoidance
Wikipedia

An additional FAA training video:

Airport Signs, Markings, and Procedures: Your Guide to Avoiding Runway Incursions (Because John and Martha King.... and Harrison Ford!)


Can a passenger plane stand still in the air, or hover at a fixed location above a ground?

NO, at least not during landing. And especially not an Airbus.

Two reasons:

While up in the jet stream a 150 knot wind is normal, wind over 100 knots (185 km/h, 115 mph) near the ground only occurs in hurricanes (and tornadoes) and would be so turbulent that landing it it would be most likely out of question.
When landing in strong head wind the pilots will use higher air speed. This is because strong winds have a nasty habit of changing in strength or direction quickly and if the head wind reduced suddenly, the plane would loose lift and crash. So the pilots maintain some minimum ground speed to have a safety margin for that case.

Airbus even has a minimum ground speed warning exactly to keep the pilots out of this risky flight regime and that would be blaring in cockpit if the A330 in the video really almost stopped in midair. There must be something wrong with it (the linked article does not link to a video, only a screencap and one can't tell from screencap what is going on).


Are return springs on a carburetor throttle mandatory or not?

The FAA doesn't require it, but some carburettor manufacturers may have them. You can get return springs for Rotax engines, but only for non-certified aircraft and then again only to prevent throttle creep


Which standard is applicable to the electric power system in civilian US aircraft?

The answer is not straightforward.  Power supplies used in commercial aircraft LRUs are required to meet RTCA DO-160G, sections: 16 Power Input, 17 Voltage Spike, and 18 Audio Frequency Conducted Susceptibility - Power Inputs.

The issue is this is what the consumers of aircraft power have to deal with.  It doesn't actually specify what the aircraft power distribution system has to provide. Though by inference, the power generation system must deliver power within the bounds of what the consumers can accept.

In my experience, aircraft OEMs design their power distribution system and then levy specific requirements on the power supply design of all consumers on the aircraft. While DO-160 covers the majority of the need, the OEM requirements will include additional requirements deemed necessary by their design and analysis. As a Boeing engineer explained to me, "The requirements are not to protect your power supply.  They're there to protect my power bus."

The reality is aircraft power is a small dynamic system and it is impacted by everything on the bus.  It has to be designed as a system unique to each aircraft. Since it's part of the aircraft, the aircraft rules come into play.  For air transport aircraft, that means 14 CFR Part 25. The applicable portions include 14 CFR 25.1310 and the Electrical Systems and Equipment subject section.

Additional guidance is available in Advisory Circular AC 25.1353-1a ELECTRICAL EQUIPMENT
AND INSTALLATIONS.


Can thrust vectoring be used to enable the use of flaps on tailless delta-winged aircraft?

No, for several reasons

What you want is to compensate for the additional lift from downward deflected flaps at the back of a flying wing with vectored thrust. As @Sean points out this will not bring a noticeable net benefit if the lengthwise location of both forces is similar.

But that is not all.

Besides the force equilibrium around the flying wing you also need to consider how it behaves when flight parameters change, say by gusts. Will it return to the old state? How will the dynamic behavior be?

More camber means that the zero lift angle of attack becomes more negative. A deflected flap adds camber near the trailing edge. If the wing now assumes a higher angle of attack due to a gust, the change in local lift over chord will make the wing pitch up more. The forward region of the airfoil will add more lift relative to the initial state than the rear region because the zero lift angle of attack has been shifted downwards, adding a pitch-up moment. The whole aircraft will become unstable from the added camber of the flap.

Flying wings don't need computer control. All the Hortens and Fauvels of this world flew just fine with a human pilot and mechanical controls. That is because they use reflex airfoils and wing twist so the rear part of the wing creates less lift relative to its area. This is the condition for static stability and it gets removed with a positive flap deflection.

Adding that flap will add so much instability that computer control would have a hard time to keep the aircraft stable. If the flap produces substantial additional lift, the thrust vector control would need to effect large changes in pitching moment. Now consider you fly into an airport along the glide slope, with the engine close to idle. Where would the required pitching moment come from? Thrust is insufficient and reducing your flap setting will stall the aircraft. The best solution is to not deflect the flap in the first place and to add more wing area relative to a conventional aircraft.


What is the aerodynamic reason military parachutes are square?

The top pic is the new T-11 canopy adopted by the US Army.  Has a significantly lower descent rate and less opening shock compared to the old T-10.