Can large airliners such as a 747 maneuver without electricity?

Flight controls are pretty hard to break

For the 747 (at least through the -400) specifically, the controls are entirely hydromechanical, so yes, they will work without electrical power.  In general, all non-FBW airliners are this way.

FBW airliners vary, though.  All FBW Boeings and the first generation FBW Airbii (A320 family, A330/340) have hydromechanical backups to the FBW system.  The second generation Airbus FBW system, found in the A380 and A350, has abandoned hydromechanical backup controls in favor of independently powered electrical backup systems.

In addition, the chances of total electrical failure are extremely remote -- a failed engine will likely be windmilling (spinning from airflow through it) and thus turning its generator to provide some power, the APU has a generator on it in case all the engines seize up, and there is also a generator that is directly or indirectly powered by the Ram Air Turbine on airliners that use one (all non-reversion twins have one, and so do the A380 and the 747-8 -- earlier 747s don't, relying on windmilling engines for electrical and hydraulic power instead).  Finally, the aircraft has batteries that can provide a limited power reserve if all these other systems fail.  (FBW aircraft add to this with dedicated batteries for at least some parts of the FBW system.)

However, power loss is still a serious emergency

The main hazard posed by a severe electrical power failure, though, is trying to fly around in the clouds with one -- it can render you effectively "no-gyro", especially on older/smaller types that don't have a standby gyroscopic instrument with a dedicated power supply/internal batteries.  There have been cases where small airliners have gone down due to power failures -- while the flight controls were working fine, without power or a visible horizon, the pilots became spatially disoriented, and you can guess the rest.


Can a PPL holder fly family and friends aboard an A380?

Yes. But you will still need instrument rating and ATPL theory as this is multi crew aircraft. The amount of learning will be the same as to get CPL. Maybe fees for the license will be lower but who cares if you buy an A380?


Why did the Bede Bd5 have strakes on the horizontal tail?

They work like large vortex generators to delay flow separation on the underside when the stabilator is at high (leading edge down) angles at low speed.  IIRC, the BD-5 had stabilator stalling issues during development.  That's one way of doing it.  Another way is to put VGs along the underside leading edge.

The Cessna Cardinal had a similar problem when it first entered service and Cessna's fix was to put LE slots in (a famous Service Bulletin known as the Cardinal Rule, with a comprehensive fleet mod campaign for the initial 500 or so aircraft), more or less for the same effect.


Is it very rare to be a senior pilot with no emergency occurrence in history?

In the airlines, the number of flights where an emergency has been declared is about 1 in 600. In general aviation, it could be as low as 1 in 40 or as high as 1 in 6,000, but it's not "most".
In the airlines:
Poking around Google gives this USA Today story: Medical emergencies occur on 1 of every 604 flights, which references an article in the New England Journal of Medicine.
An answer on a different question on this site provides the following anecdote:

had occasion about a year ago to ask our airline safety department
what the most common cause was for declared emergencies in our
operation, and was told that far & away, sick passengers (medical
emergencies) were #1 by a huge margin, and everything else (which
includes all the aircraft-related events) was far down in the weeds in
comparison.

(emphasis added)
We'll assume that Ralph J's answer is correct and that medical emergencies are the lion's share of total emergencies. That being the case, the 1 in 600 number is probably accurate within an order of magnitude.
In general aviation:
Since 2001, the NTSB aviation accident database has been remarkably consistent in terms of the number of reports they get:

About 4,000 reports per two-year span (until 2013, when it dropped to a little under 3,500)
Between 60-90 reports containing the phrase "declared an emergency" within that span

As airline travel continues to be outrageously, shockingly safe, let's run with the assumption that most accidents in the database are non-airline accidents. That being the case, one in 30-40 of accident airplanes (not all airplanes) declared an emergency in a way that managed to make it into the accident report.
That doesn't fit with a fact I found in an AOPA handout though, which says that air traffic controllers provide more than one flight assist per day.  "More than" one could be anything, but let's be super generous and say there are 1,000 flight assists per year. Another FAA source says that there were 24 million GA flight hours in 2015. Figure a GA aircraft holds about 4 hours of fuel, then there were around 6 million GA flights in 2015, or one flight assist per 6,000 flights. That throws a wrench into our other estimate, but it also goes against the "very rare" statement of the inspector in the original question.
From personal experience
Anecdotally, I've flown a few thousand hours and I would say that I've heard aircraft on the radio requesting emergency services less than a dozen times. If I had to guess, I would put the number closer to the 6,000 side than the 40 side, but even if 1 in 40 was correct, 39 pilots out of 40 not having declared an emergency seems to contradict the statement of the inspector.
Conclusions
The TC inspector could be suffering from selection bias. If she or he deals with emergencies all day, it seems less likely that she would come into contact with the (seeming) majority of pilots that haven't declared.


How is it possible for supersonic aircraft to push air out of the way?

The idea that force can only be transferred/propagated at the speed of sound is a simplification.  It's a very reasonable simplification, which works in a very wide array of cases, but it's a simplification.

A fundamental concept in gas mechanics is the "mean free path length."  This is how far a molecule can travel on average before it collides with another.  This is on the order of hundreds of nanometers for pressures you'd see at reasonable altitudes (68 nm at STP).  If you are looking at processes that occur at scales much larger than this, it is very reasonable to model their behaviors as transmitting things at the speed of sound, because these statistical effects lead to a very natural expected speed of propagation.  It can be seen as a result of the central limit theorem applied to a very large number of molecular collisions where the drift velocity (average movement of particles) is relatively smooth.

As you push things, this nice model breaks down.  As you approach the sound barrier, you get pressure gradients that get shorter and shorter.  Near the speed of sound, these gradients start to get into the single-digit-multiples of this mean path length.  At this point, we can no longer assume that we can just model everything with the nice clean statistical models we had earlier.

What actually ends up happening in most situations is that you get a "shock."  Far from the flying body, the air transmits force at the speed of sound with respect to the unmoving air (or slowly moving, if there's a wind).  Right up against the flying body, the air transmits force at the speed of sound with respect to the flying body.  At "reasonable" speeds, there's a smooth shift from one to the other, where the pressure gradients aren't so steep that we can't call them pressure gradients.

At supersonic speeds, that smooths shift doesn't happen.  Instead, we end up with a thin shock region (on the order of 1 μm or thinner) where it's not reasonable to model the air as having a "pressure."  It acts more like a bunch of billiard balls being flung along.  This region, a few mean free path lengths wide, is where the usual rules we're used to, break down enough to resolve the physics.  On each side of the shock, "normal" speed-of-sound behaviors occur.  Inside the shock, it's messy.


How can investigators trust flight instrumentation from aviation accidents?

Investigators have experience in inspecting damaged equipment. Over the years they develop an understanding of what kind of damage comes from crashes. Based on this experience they can determine whether the damage is consistent with a crash or just typical operation.

As raptortech97 commented, the gyro from Copa 201 had a wire nearly severed. This is exactly the kind of normal damage that could happen to a gyro in operation, but not the kind of damage that would happen inside a gyro during a crash.

Of course there are many instances where investigators are unable to determine whether equipment was damaged before the crash. Items may be too badly damaged to determine this.

The comment about USAir 427 is also relevant. See also British Airways 38. Some failure modes leave no evidence behind, and thus are difficult to diagnose afterwards.

The investigation will take all of these factors into account along with all other evidence they have. They will not claim a definitive answer based on uncertain test results alone. In the case of Copa 201, the data from the FDR matched the behavior of a gyro with a loose connection, which matched the circumstances of the crash. In the case of the 737 PCU (USAir 427) and RR FOHE (British Airways 38), once the failure mode was tracked down, it was tested in the lab to confirm that such a failure was possible and could cause the expected effects, and to determine the best method to prevent it in the future.


How often does an airline pilot use the rudder pedals during flight?

Transport category aircraft have a yaw damper that will maintain coordinated flight when the aircraft is in the air unless the flying pilot overrides it with the rudder. It operates even if the autopilot is not in use. The usual procedure is that you take your feet off the rudder pedals as soon as you have lifted off and don't put them back on the rudder pedals until on short final.

The pilot will possibly use the rudder shortly before or going into the landing flare to slip into a crosswind and/or to align the aircraft with the runway if they were flying a crabbed final. However, with most if not all transport category there's nothing wrong with touching down in a crab correctly being flown to correct for a crosswind if desired.

So whether a short range light or a long haul flight, the amount of time in the air that the pilot needs their feet on the rudder pedals is minimal and is in seconds, at most a minute or so.

An exception, of course, is if there is an engine failure, in which case the pilot will use the rudder to counteract the adverse yaw from the asymmetrical thrust.


Why is the DC10/MD11 center engine placed where it is?

There are a few ways the aircraft engines can be mounted on the centerline, each with its advantages and disadvantages.

Image from Stanford University.

One way is to mount them as in DC10, with engine above the fuselage; another one is to use a 'S' shaped inlet and put the engine at the aft of the fuselage like Dassault Falcon 7X.

The main advantage of mounting the engine as in DC10 is that the inlet distortion is minimized and there is no need to cut a hole through the fuselage for putting engine. The main disadvantages are that it increases drag (slightly) and engine maintenance is a mess.

Apparently,the DC10 engineers tried to put all three engines in the wing during design, but were not successful.

Engines mounted in high thrust line like DC10 and Piper PA47 are highly stabilizing as increase in engine thrust causes a pitch down motion as the thrust is increased. This is usually disconcerting to the pilots, who expect the aircraft to pitch up while engine power is increased.

Finally they ended up adding design changes to correct this in PA47 (to make it pitch neutral).

In DC10, a combination of underwing and high thrust line engines would've most probably caused no pitch changes at all. So I guess the main advantage is reducing inlet distortion.

As MD11 was developed from DC10, it simply inherited this design.

Note: As for the pitch down moment being disconcerting to the pilots, it is better if someone corroborates it. It is simply that most aircraft don't do this.


When sharing an airplane, what liability does the owner bear?

Most of the liabilities (but not all) fall under the insurance of the aircraft. Your insurance policy is your largest liability. This is important not just for protection of your aircraft, but if your insurance ends up void in an incident, you could have a lawsuit on your hands. Don't assume that aviation insurance is similar to car insurance, either.

Insurance

Pilot (on plan)- Aviation insurance has 3 catagories: Pilot, Named Individuals, Other (explained later). The owner pays insurance based on their qualifications and those specifically named. If you are going to be borrowing on a regular basis, weigh the cost of adding you to the plan.
Pilot (off plan) - Insurance specifies whether or not you may borrow the aircraft to others, but also what qualifications that pilot must have. You may have only have 100 hours and are insured, but the insurance company may ask for 500 hours of someone you borrow the aircraft to.
Aircraft - Regardless of the pilot, if the aircraft is out of compliance on maintenance or airworthiness, it is not being flown legally and therefore voids the insurance. As the owner (primary on the insurance), this is your responsibility as an owner and the pilot's responsibility as PIC. Both of you can be hit for this one.
Reimbursement - Just because it is non-commercial use, your insurance may still specify what you can be compensated for. This may be only the actual expenses of the flight (fuel, oil, airport fees) and may include limits on hourly charges for maintenance. Keep in mind that this does not authorize you to break regulation on commercial use. You cannot make a profit.
Legal flight - Above all else, the flight must be legal. The flight needs to comply with all FAA regulations.
Non-commercial use - I keep coming back to this, but this is very important. The pilot may be a commercial pilot, but this doesn't authorize them to use the aircraft for hire. With many insurance plans, you can have a CFI train you since you are the owner, but a CFI cannot train someone else and you cannot train someone else. This makes and aircraft for hire and requires a 100-hour inspection.
Other - Pilots who do not own an aircraft may have their own (renters) policy. While this may cover liabilities of those in the aircraft, don't assume that this also covers your aircraft. A pilot paying $200/year won't likely have coverage for your shiny new Cirrus.

Other

As the owner, you have liability in accurate record keeping. If you fudge documents on your aircraft that make it appear FAA compliant to the PIC, then you can be held liable.

Notes

These are only the items that come to mind. Feel free to add.


Is there a list of directs and preferred routes within USA airspace?

In the US, the National Flight Data Center (NFDC) publishes a database of preferred routes.  You can query it or download the entire database.

Here is the result of entering only BWI to PHX:

A practical resource for planning a real flight is to review the routes of previous flights.  I browse the origin and destinations, or nearby airports to my flight and select a similar aircraft to which I am flying. On FlightAware, the route is shown in the lower right.  Here's an example:


Can we change light aircraft skin from aluminum to foam and fiberglass?

Yes. No. A little bit of yes, but overwhelmingly a NO.

It's possible to design and build an aircraft like the CH-750 with fiberglass instead of aluminum, but it's so far above the skill and qualifications of anyone who would ask the question on the web - as opposed to starting by modeling it in ANSYS - that the only realistic answer is "no".

Not because of any intrinsic properties of fiberglass, but simply because of the level of knowledge involved in redesigning an aircraft of this scale, and the fatal consequences of getting it wrong.


Is it required to memorize checklists for better efficiency?

In the US the closest thing to a standard, and the requirement (per the FAA's practical test standards), is that you make appropriate use of checklists.
As mentioned in that video "appropriate" leaves some room for common sense interpretation (clearly your first course of action if your engine dies in flight should not be to open the operating manual to the Engine Failure In Flight checklist and begin reading: That would NOT be "appropriate").

I expect most other countries have a similar view on the subject.

As far as what gets memorized, the checklists for most simple aircraft (for our purposes let's say that's anything with a single piston engine, unpressurized, with 6 seats or less -- your average Piper/Cessna/Citabria/etc.) can be memorized. They're not that long and there's not that many of them.

Time permitting a good pilot will generally still refer to the printed checklist even if they did the entire thing from memory, if only to read off each item and make sure they didn't miss anything.

More complicated checklists (like what you might find on a 737 or a C-130 for example) will usually have a set of Immediate Action Items (often called "Red Box Items" because many manufacturers put them inside a big red box at the top of Emergency or Abnormal checklists).
It's generally expected that the flight crew have the Red Box Items committed to memory and be able to complete essentially on instinct.

After completing the Red Box Items all the really important stuff is done, and there is hopefully enough time that it's now appropriate to pull out the checklist (or Quick Reference Handbook), verify that the Red Box Items have all been done, and run through the rest of the items.


What happens if full collective pitch is suddenly commanded on most modern helicopters?

I'll assume you're talking about typical turbine helicopters.  The fuel controller on a helicopter's turboshaft is used to regulate rotor RPM via its gas generator's (the compressor/burner/turbine section) speed and torque.  The RPM governor setting is coarsely set with throttle, then fine tuned with a trimming function controlled by a toggle (blip) switch on the collective to set the precise rotor RPM the governor will maintain.

The fuel controller will now govern rotor RPM automatically at that setting as you load the rotor with collective, by increasing fuel flow to increase the torque output of the gas generator.  So torque, fuel flow and Turbine Outlet Temperature (TOT) will all rise as you pull collective.  Both torque and TOT have operating maximum limits, so how much collective you can pull is therefore limited by a torque and/or TOT red line.

Trying to take off in marginal conditions due to load, temperature or altitude, you will find yourself pulling pitch until you are at a TOT or torque limit before you can even hover, and if you really really had to get airborne (like say you were an overloaded medivac Huey in Vietnam), you'd have to get the machine sliding along the ground first to get some translational lift in order to take off (one big advantage of wheeled landing gear).

Anyway, it's a hydromechanical fuel controller/speed governor that just does what it is told, so if you just haul the collective all the way up just sitting there, it'll depend on how much fuel the controller has to dump in to maintain RPM as you shoot off the ground straight into the sky.  You will probably exceed the TOT or torque limit or both, making it a very expensive takeoff.


How is crankcase ventilation handled in R-2800?

In a car the combustion gasses that blow past the piston rings are sucked out by a line connecting the crackcase to the intake manifold by a check valve (the PCV valve).  The suction "pump" is from the low pressure in the intake manifold.  Cars before the PCV valve (developed in the 50s) just vented the crankcase gasses overboard through a hose.  Aircraft engines, including the big radials and the Lycoming engine on my own plane, do the same.

Positive crankcase ventilation was probably the first pollution control device developed for cars.  Piston aircraft engines have never used pollution control devices.  They still use gasoline with lead in it.


Has any aircraft ever been designed such that it could descend safely with no control input?

Broadly speaking most (if not all) light GA aircraft can "glide safely with no control input" - aircraft are generally designed to have positive dynamic stability, such that they will return to a stable equilibrium condition (e.g. "level cruise flight") in the face of most modest upsets. Once configured for cruise flight they can maintain it with little input from the pilot (and if equipped with even a basic autopilot "little input" can often be reduced to "no input" for extended periods of time).
Whether or not the engine is producing power is largely irrelevant here, save for the fact that if the engine isn't producing power you will eventually be descending.

Positive stability alone will not make aviation "accessible to the masses" however, nor will autopilots: As with driving a car or riding a motorcycle there are certain "aeronautical decision-making" skills which a pilot must possess in order to safely fly (and land) an aircraft when everything goes right. If you introduce problems (like engine or instrument failures) the need for a real live pilot becomes even more critical: technology can not yet replace the critical decision making capabilities of a trained human mind.

Particularly in regard to your question about a default flight mode of a controlled descent, even a simple autopilot can already do what you describe: Planes will continue to fly the last autopilot-commanded heading or route until they run out of fuel, at which point they'll start descending (while still attempting to fly the programmed profile).
What they cannot do is select a suitable landing site, update their flight profile, and fly themselves to a safe landing. For that to happen without human intervention requires a huge amount of luck.

In a particularly famous example of this kind of luck a Piper Comanche "landed" itself in a field after running out of fuel, the pilot being unconscious at the time due to carbon monoxide poisoning. The pilot survived and in fact literally walked away from the accident scene, and the aircraft in question is, as best I can determine, still flying.


Does an increase in air temperature actually improve aircraft performance?

Drag (and lift) increases with density. Density decreased and so did drag. So at the same power, you can fly faster.

Now I don't know whether reduction of power of a normally aspirated spark-ignition reciprocating engine at constant throttle setting would be higher or lower than the reduction of drag. But the question says power setting.


Why aren't runway numbers painted in a higher aspect ratio?

Runway numbers need to be readable from multiple angles, they aren't just for those on approach. Joining at uncontrolled airfields is usually done by flying over the airfield or approaching from any point on the compass, aspect ratios opposite to your viewing angle are hard to read and therefore counter productive for those in the pattern.


For a coded departure procedure (SID), Fly-At-Altitude or At-Waypoint instruction has priority in case of conflict?

The textual description says clearly:

  RWY track to 4.5 DME FFM/1.5 DME FRD or 800, whichever is later

The equivalent encoding is:

  [A800+] - DF134 (25C)[L] / DF135 (25L)[L]

The meaning of this is climb to an altitude of 800ft or above, then after passing DF134/DF135 turn left.

From this EUROCONTROL document (Guidance Material for the Design of Terminal Procedures for DME/DME and GNSS Area Navigation(PDF)):

  [Speed, track and altitude constraints are contained within square brackets.]

  If [A Set of Constraints] is not preceded by a waypoint name, the last calculated track must be flown until the constraint is reached

The turn will thus not be initiated before both the 800 ft altitude and the waypoint are reached.


How much power is used by cabin lighting systems during flight?

Almost all lighting systems installed today use Light Emitting Diodes for weight savings, reduced power use and less maintenance. Compared to other aircraft systems, their power use is pretty insignificant. For the reading lights, I found the following quote:

  Passenger reading lights in halogen technology use 11 watts, while the
  latest LED products use only one watt. Source

The actual ceiling ceiling lighting power consumption seems more difficult to find. SAAB in a brochure for converting fluorescent to LED lights for their SAAB 340 & 2000 models states:

  Power consumption is reduced from 8 watts per 12 inch tube to just 5,1
  watts.

Emteq suggests savings of around 15% for LED compared to fluorescent lights, so SAAB's suggestion would be a bit more. This manufacturer quotes 10W for a 16-inch (40cm) LED strip running off the 28V aircraft DC system. Needless to say, power consumption depends on the wattage of light installed.


Where is the radio PTT button on a Robinson R22 helicopter?

You can't realistically mimic the feel of the R22 controls with a joystick because it's an unusual configuration. I've done both simulated and the real thing so trust me when I say it's going to be radically different. This is the Robinson R22 control column:

The R22 has a bent T shaped control arrangement with the control column in between the 2 seats. The T is connected at the pivot point (green arrow), the handling pilot pulls the stick down towards their lap, pulling the other side up. Instructors have to learn to fly with their arm in the air sometimes. The red arrow points to the intercom and PTT buttons. The intercom button is not always there, newer versions generally have a voice activated (VOX) intercom so no button is required.

The blue arrow points to the pin to remove the left hand controls. In most helicopters the pilot sits on the right, if you have a non-flying passenger it may be good to remove the controls so they can't accidentally grab it. The left side pedals are removable too.


Can multiple aircraft share the same logbook?

For pilot logbooks, the requirements of "what" needs to be logged to meet training time and aeronautical experience is specified in FAR 61.51. As long as you record all of the information required by FAR 61.51 (e.g., date, total time, day/night etc.) "where" you place the information is up to you. A single conventional logbook works fine, or you can use a spreadsheet, digital device, or any type of similar recording method you choose.  Separate logbooks for each airplane is not required.

Keep in mind that you must present your logbook (in what ever form that you use to record your flight time) for inspection (upon a reasonable request from persons specified in FAR 61.51 (i)) and, if you are a student pilot on a solo cross country flight, you must carry your logbook with you (proof that you have the required instructor endorsements, etc.).

So, it's a good idea to record your flight time in a method that is easy for you to access.  For this, a conventional logbook works well.


Why do we say certain things three times (e.g., "Mayday, Mayday, Mayday"), rather than two or four?

Yep, the critical commands are repeated 3 times.  This ensures there is ABSOLUTELY zero doubt in anyone's mind (especially on a big crew airplane) of what needs to be done in a critical situation.  It also standardizes these criticalities across different aircraft and aircrew cultures.  "Bail out, bail out, bail out"  "Eject, eject, eject"  "Abort abort abort" "Pan-pan, pan-pan, pan-pan."  I was 27 years a USAF pilot, and this is how the training has worked for over 50 years.  I only saw these terms used 2-3 times, but it certainly gets your attention and amps up the sense of urgency.  A little history:  back in the day of very poor radio communications, it was necessary to repeat to "get someone's attention" or in the event a single "mayday" didn't come across when the transmit button was pressed.


Has the United States Air Force used Contra-rotating Propeller Aircraft?

In short, the US didn't need one.

The main reason for the development of Tu-95 was the rather unique situation existing after WWII, when the Soviet Union needed a heavy bomber to carry the (then very heavy) nuclear weapons. Due to the lack of bases anywhere near contiguous United States, the Soviets were at a significant disadvantage when it came to nuking the US before the ICBMs came into picture (US had bases in Europe and in Pacific). At that time, heavy bombers were the only way to deliver a nuclear payload and it required the aircraft to be fast, have a intercontinental range and be able to carry a reasonable payload.

The first attempt in developing a long range bomber during the last days of WWII by the Soviets didn't work out and as a result, they simply reverse engineered USAAF B-29s which had 'landed' in Russia into the Tu-4 'Bull', which lacked the necessary range. In a way, the B-29 was the forefather of Tu-95. Further development continued on this airframe, culminating in the Tu-80 'Barge', which had the necessary range, but was considered unsuitable as it lacked speed, which would be fatal against jet interceptors.

The Tu-95 was developed at the same time of the B-52 'stratofortress'. Actually the Soviet Air Force preferred the jet powered Myasishchev M-4 and Tupolev had to convince Stalin about the Tu-95's suitability. During the initial design phase, the Tupolev bureau considered two versions- one with four turbojets and another one with turboprops. The turbojet version was discarded as it would've lacked range due to the fuel hungry turbojets (Tupolev turned out to be right about that as the M-4 was sidelined due to lack of range).

The payload and speed requirements required a very powerful engine (the Kuznetsov NK-12 is the most powerful turboshaft engine ever) and the contra-rotating props were selected to overcome the problems associated with the large diameter of the propellers.

Western countries also did a lot work with contra-rotating props, but the advent of jet engines and the complexites associated with the counter-rotating props meant few graduated from the prototype stage. The Huges XF-11, for example had counter rotating props initially; they were changed to conventional ones after Huges crashed in it. The Fairey Gannet and Avro Shackleton were among the few western contra-rotating aircraft to see regular service (both were used in ASw roles, which highlight the increased endurance offered by them). A number of contra-rotating aircraft were tested during the end of WWII, but the advent of jet engines meant that the required speed could be achieved in a far better way.


Can you please identify this aircraft from a BBC show?

Although a little hard to read, the reg is F-BXCP which you can find with a search
https://www.airport-data.com/aircraft/F-BXCP.html
The aircraft is a Max Holste MH.1521 Broussard which is a 1950's era aircraft originally built for the French airforce.
Somewhat interestingly that aircraft is now registered G-HOUR and is owned by the luxury watchmaker "Bremont" (hence the reg). It seems to have first got a reg-change with the same paint scheme and then latterly been repainted.


How much difference in heading/bearing between consecutive legs is "officially" considered a turn?

I will have to answer my own question, since I have noticed that in FAA's PBN Manual it states:

  PBN 8260.58A 1-2-5c . Turn parameters. For OEA construction, a turn is indicated when the course change exceeds the alignment tolerance of 0.03 degrees.

So, at least as far as route design is concerned, the alignment threshold for turn indication is 0.03 degrees.


I'm going with tip tank for a Lockheed P-80 Shooting Star.


Can a nonresident American citizen get a Canadian helicopter license?

In the US it is a license as well, that's why they abbreviate it PPL and CPL.

Canada appears to have no restrictions on flight training of non-Canadians other than proving your own with something like a passport, because your citizenship is shown on your license. See this Transport Canada page as a starting point.

If you need to reside in Canada during your training and you expect to take longer than 6 months, you will need to obtain a Student Visa to remain in the country legally.  You could also use a Tourist Visa, neither of which would all you to work.

If you are planning on returning to the US when you are not training, then the Visa would not be required.

Converting a Canadian pilot license to a US pilot license is governed by AC 61.135a.. It doesn't look very complicated, but it will take time and you must take one or more knowledge tests as well as schedule an appointment at your local FSDO for the final approval.

Note also that while you don't have to surrender your Canadian license when you convert to a US license, if you do not that means that you must stay current based on both the US and Canadian rules.

I suggest you very carefully study the requirements and do the full math. Once you get started on one path it won't be easy to switch to the other if you then realize it was a mistake.

Interesting question, BTW. It was fun researching the answer. :)


How much torque can a Boeing 747 apply when pitching?

The pitching force is coming from the horizontal tail's downforce resisting the airplane's net nose down pitching forces, so the real question is how much downforce is being applied and how far away is the tail's downforce from the lifting forces holding the plane up.

For a given set of parameters, you need to know the All Up Weight, the Center of Gravity location, and the Neutral Point, which is the location of the (gaseous) fulcrum the tail has to work about.  The NP is defined as the longitudinal point at which pitching moments are zero, the "effective" balance point in other words, taking into account the center of lift plus/minus the effects of various pitching moments (airfoil pitching moment, fuselage lift, nacelle lift, thrust effects, flaps and gear hanging down, etc.) which result in the actual net downforce the horizontal tail has to produce to "hold the nose up" in a given steady state flight condition.

If you know the CG location and the all up weight, then the "torque" acting on the fuselage at the Neutral Point is simply all up weight times the distance between the CG and NP.

So if the plane weighed 700,000 lbs, and the CG was 20 feet forward of the NP (just a wild guess; I have no idea the actual number), the "torque" value, the nose-down pitching force acting at the NP, is 14 million foot pounds.  If the aerodynamic center of the tail was 120 ft aft of the NP (another wild guess), that works out to 116666 lbs of downforce required for stable level flight back at the tail.  Of course if you now pull pitch to raise the nose, you are accelerating the mass about the lateral axis now, so those forces go up temporarily.

The values will change with changes in configuration, weight, speed, etc.  Make a change that moves the Neutral Point forward, like adding thrust, and the torque value and downforce required goes down; airplane pitches up from the thrust application because the existing tail downforce is excessive. Drop the gear, which moves the Neutral Point aft, and the torque value and downforce required to counter it goes up; airplane pitches down from the drag of the gear because the existing tail downforce is insufficient.

As far as finding out what is a typical Neutral Point on a 747, good luck with that...


What is the practical usefulness of a small home made wind tunnel?

There are some things about this wind tunnel that are not as good as the best wind tunnel experiments for actual aircraft.
Obvious concerns are that the wing is very close to the bottom of the wind tunnel (relative to the size of the wing), which means there will be a kind of "ground effect."
(Notice how at the high level of attack shown in your photo, the airflow underneath the wing is almost completely pinched off.)
The relative nearness of the top of the tunnel could have an effect too.
The setup shown will not tell much about what happens at the wingtips of an aircraft--an airplane with huge vertical plates attached to the end of each wing (which is what this setup models, with its wing tip practically flush to the side wall of the tunnel) will fly differently than an otherwise identical aircraft without those vertical plates.
Merely testing the wing also doesn't tell us anything about the aerodynamics of the fuselage, which will affect how well the aircraft flies.

There are also scaling issues having to do with things such as
Reynolds numbers and (for jet aircraft) Mach numbers.
Practically all wind tunnels have these kinds of scaling issues.
The "aircraft" that are tested in them are generally scaled-down models.
This is something that wind-tunnel experts have learned to deal with
(see Peter Schilling's answer).

But while those are things of concern to people building the latest passenger jets and fighter aircraft, where flying just a little better than the competition is very valuable, I think a wind tunnel experiment like this is meant to investigate more basic properties of wings.
When the Wright Brothers were building their first aircraft, for example, the aerodynamics of wings was not very well understood at all.
Even a few years ago, incorrect notions about wings were widespread
(there are whole pages of the NASA website debunking them).
If a wind tunnel like this gives you information about the forces on the wings that is 30 percent more or less than the "true" values,
you're still way ahead of someone who is basically just guessing about the forces by combining naïve intuitions about the dynamics of the airstream with calculations based on actual speed, density, and so forth.

My biggest complaint about the design of this apparatus is that the arrow attached to the wing, pointing to the angle scale on the back wall, cannot measure negative angles of attack. This could be fixed by mounting the angle scale with the straight edge of the scale vertical instead of horizontal.


Is the waves and signal dangerous for human at the airports?

No. To people at the airport, the electromagnetic radiation from various sources relating to aviation (or anything else) is not dangerous.

Any electromagnetic radiation is, with enough intensity, possibly dangerous, even instantly lethal, but you can rest assured, that such intensities are not present anywhere a normal person has access to.


Why do larger aircraft need two or more static ports?

Your quote already answers your question:

  larger aircraft with redundant systems will have two.

The key is redundancy. You want to have at least two independent systems to measure altitude and airspeed so if one fails, the other still provides good data. Of course redundancy is also a good thing in a small aircraft, but it always comes at a cost: complexity. With larger aircraft the added complexity and therefore maintenance cost does not make such a large difference any more therefore tipping the balance in favor of redundancy.

For passenger airliners with potentially hundreds of people on board, safety is far more important. They usually have even more than two static ports. E.g. the Boeing 737:

  Air Data

  The pitot static system is comprised of three separate pitot probes and six flush
  static ports. Two pitot probes and four static ports interface with the air data
  modules. The remaining auxiliary pitot probe and alternate static ports provide
  pitot and static pressure to the standby instruments. The auxiliary pitot probe is
  located on the first officer’s side of the airplane.

  The air data modules convert pneumatic pressure to electrical signals and send
  these data to the ADIRUs. Each pitot air data module is connected to its on–side
  pitot probe; there is no cross connection. The air data module connected to the
  Captain’s pitot probe sends information to the left ADIRU, while the air data
  module connected to the First Officer’s pitot probe sends information to the right
  ADIRU. The remaining air data modules are located at the balance centers of the
  Captain’s and First Officer’s static ports. The air data module connected to the
  Captain’s static ports sends information to the left ADIRU, while the air data
  module connected to the First Officer’s static ports sends information to the right ADIRU.

(Boeing 737 NG FCOMv2 10.20.13 Flight Instruments, Displays - EFIS/Map System Description, emphasis mine)

This results in three independent measurements of altitude and airspeed:

Captain's side
First Officer's side
Standby Instruments


Is there a published airspeed and TPA for Class B approach at San Diego International?

Almost every major airport (Class B) would have what's called a STAR, a Standard Terminal Arrival Route. Busy Class B traffic doesn't necessarily follow a TPA (Traffic Pattern Altitude).

For runway 09, the STAR doesn't show a speed limit. Some STARs have speed limits.

But that's not to say the speed is at the pilot's discretion, as the airplane approaches an airport it's standard for the crew to slow down and prepare the plane for landing. The air traffic control (ATC) can also issue speed restrictions to properly space the arriving traffic, they have the bigger picture.

For the downwind leg you can expect something like 200 knots indicated, which can translate to a bit over or under 200 knots of ground speed, depending on the wind. That's 230 mph or 370 km/h.

As the planes join the final approach segment, the altitude would indeed be level in most cases, and further descent would commence as you said, on final approach.

No published speed limit on downwind. The line with an arrow pointing to IFSOX.

For altitude it's 4000 feet, the *3000 is the minimum to clear any obstructions. 2400' for the base leg.

Above is a chart legend.

Final approach descent begins about 10 nautical miles to touch down, as illustrated from 2100 feet for this particular approach to runway 09.

Numbers in this answer are for one particular approach to one runway, figures vary.

Source: skyvector.com

Class B around KSAN is a bit complicated in shape, but the base/floor is mostly 2800' for the southern published downwind area (if you overlay the STAR on a VFR chart). Airline/IFR pilots don't need to worry about that chart as they'll be following the aforementioned STAR or guided/vectored by ATC.

I misread the question, from the north it's 6000 feet and 210 knots, the BAYVU (pronounced bay-view) FOUR ARRIVAL (STAR). That should be downwind for runway 27. The same principles apply, different figures.

See where you live (coordinates), download all the STAR charts, and you'll have a better picture of your night sky. Note: some STAR charts are not-to-scale.


How does the FAA determine which format of location identifier to assign to an airport?

In short, the scheme is as follows:

Busier airports get 3-letter identifiers.
Less busy public-use airports usually get 2 numbers and a letter, sometimes 1 number and 2 letters.
Less busy private airports (which is almost all private airports) get 2 letters and 2 numbers.

More specifically, the FAA assigns airport identifiers (and location identifiers in general) according to the guidance laid out in section 1-2-7 of JO 7350.9F (PDF).
3 Letter Identifiers
For airports, 3-letter identifiers are assigned to airports that meet the following criteria:

Airports:
(a) with a manned air traffic control facility.
(b) with a navigational aid (NAVAID) within airport boundaries.
(c) that receive scheduled route air carriers.
(d) that receive military airlift services.
(e) designated by the U.S. Customs Service as Airports of Entry.

or

Public use airports commissioning Automated Weather Observations Systems, level III (AWOS-III) or higher that have paved runways 5,000 feet or longer.

1 Number, 2 Letter Identifiers

Most one−number, two−letter identifiers have been assigned to aviation weather reporting and observation stations and special−use locations. Some of these identifiers may be assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet the requirements for identifiers in the three−letter series.

The format of these codes is as follows:

In this identifier series, the number is always in the first position
of the three−character combination.

For example, 1AD would be a valid code.
2 Number, 1 Letter Identifiers

Most one−letter, two−number identifiers are assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet
the requirements for identifiers in the three−letter series.

The format of these codes is as follows:

One−letter, two−number identifiers are keyed by the alphabetical letter. The letter may appear in the first, middle or last position in the combination of
three characters.

For example, 25M, 8M1, or M72 are all valid codes.
2 Number, 2 Letter Identifiers

Two−letter, two−number identifiers are assigned to private−use landing facilities in the United States and its jurisdictions which do not meet the requirements for three−character assignments.

The format of these codes is as follows:

They are keyed by the two−letter Post Office or supplemental abbreviation (listed below) of the state with which they are associated. The two−letter code
appears in the first two, middle, or last two positions of the four−character code.

For example, TN01, 1CA3, or 50SD would be valid codes.
The order continues to list a table of supplemental codes that can be used instead of the state's mail code. This allows for states whose mailing codes wouldn't work well as part of the identifier and also for states which need more than the 300 private airport registration codes possible with a given 2-letter sequence in this format.
Changes to Existing Identifiers
Airport identifiers are preferred to keep the same code once it's assigned, except in exceptional circumstances. According to section 1-2-4 of the same document:

Location identifiers are considered permanent and will not be changed without strong and documented justification, primarily concerning air safety or a significant change of landing facility status.

As a result of this, it's possible for an airport which now meets the qualifications for a 3-letter identifier to still have an identifier containing numbers due to it not having met the requirements for three letters when it was assigned. 8A3, Livingston Municipal Airport is an example of this. It has an AWOS-III and a paved runway longer than 5,000 feet, but still retains the code 8A3, which was assigned before the runway was lengthened.


What are the difference between FMC, FMS and MCDU and what do they do? +2 more questions

With specifics depending on aircraft, generally the following applies:

FMC - Flight Management Computer

FMS - Flight Management System (consisting e.g. of two FMCs)

MCDU - Multi-Purpose Control and Display Unit (2 or 3 installed on the aircraft, the screen and keypad unit by which the crew interfaces with the FMS)

Airliners have all of the functions provided by the boxes above, although depending on setup sometimes some of the computers are called differently or are unified. E.g. on Boeings, it’s called a CDU not MCDU, and some retrofit older airliners have an FMCDU which is an MCDU with a built-in FMC.

Of course crew learn how to operate these systems.


How does the pilot check if an engine fire is real?

Engine fire implies that there is a strong heat source (commonly a fire, but could be a hot substance) in a location there should not be, usually around the outside of the engine.

Engine fires do not necessarily need to be connected with a loss of thrust.
Visually, they are pretty diverse- there may be smoke, there may be little smoke (aside from that, what would you do at night?).

The general rule is to treat the cockpit instrument indications as real every time. You do not need a visual confirmation.

You would rather take safe action a thousands times too many than one time too little. The aircraft is designed to fly on one engine and it's probably one of the most common exercises for pilots in simulators.

You are correct that sensors do get it wrong. Here is a very recent incident that involved just that. The reason for the sensor discussion is that a decision is only as good as the information you can base it on, and a human is generally a better decision maker than a computer as it currently stands. Take this very complicated and confusing situation for instance- how would a computer decide and respond?

There is no physical damage in hitting the fire button which will shut the engine down. Discharging the Halon fire agents would normally require a new bottle. It is a bit of a 'hard' engine shutdown: it cuts fuel, bleed air, electricity and hydraulics. If the fire warning (i.e. heat source) persists, you generally escalate it to discharging fire agents, although in most cases shutting the engine off is a sufficient measure.


HOURS/CYCLES

The single most important factor in the value of an aircraft (generally speaking) is hours. This will almost single handedly define what the plane is worth. When a plane is built all the parts on it have a life time. This is traced through a series of logs for the plane. When a part is at or approaching its life time it must either be rebuilt or replaced. If you are looking at a plane that has high hours/cycles chances are parts on it will need replacing soon. This is costly to the new buyer and will often reflect in a lower sale price. Here in the US commercial aircraft require more frequent inspections than general aviation planes. These inspections are not cheap and a plane that needs inspection when compared to a plane that just came out of inspection will be reflected in the price as well.

There are of course other factors like wear and tear, corrosion (which can be very costly to fix) and interior condition but generally speaking when large planes change hands they are at least partially repainted with the new companies livery and the interiors are often redone.

For some airlines it may be advantageous to buy second hand planes if they are already flying that make/model. Lets say smallTimeAir flies almost exclusively 727-200's this means they have a nice store of parts for that plane and a crew well experienced in fixing them. It will be easier for them to add another 727-200 to the fleet than say an A320 for which they will need new mechanics and parts they don't have. This makes some used airframes desirable to some people.


You are confusing some terminology.
RNAV (GPS) approaches can have several different sets of minima.

See the example RNAV (GPS) Y 28L at O'Hare:

It has:
LPV
LNAV/VNAV
LNAV
sets of minima.

LPV is an instrument approach procedure (IAP) with localizer-type precision and with vertical guidance, (hence the name LPV), provides a pilot with a "ILS-style" approach complete with a decision altitude (DA) but using GNSS equipment instead of VHF equipment like that used for an ILS.  Usually the lowest weather minimum of the 3.

LNAV/VNAV is another line of minima with baro-aided (altimeter-based) vertical guidance including a DA but the weather minimum is usually a bit higher than LPV.

LNAV-only is the least precise of the 3 and is a non-precision approach, no vertical guidance, includes a minimum descent altitude (MDA) instead of a DA.  This is a "dive & drive" approach similar to Localizer or VOR approaches.  Normally has the highest weather minimum due to the nature of non-precision approaches.

There are RNAV (GPS) approaches and there are ILS approaches, but there are no RNAV ILS approaches.

Note: There might be a rare exception to this as described in appendix C of FAA Order 8260.58A CHG 2: If the aircraft/aircrew/airline are performance-based-nav (PBN) capable & authorized there could be an IAP constructed with a radius-to-fix intermediate segment leading to an ILS final segment, whereby, the crew would navigate with GNSS equipment on the RF segment and then transition to ILS equipment for the final segment.  I would say in my experience this type of approach construction from the US TERPS is very rare.

I will add that WAAS is to LPV as GBAS is to GLS.  GLS is only available at 2 airports in the US, while RNAV approaches with LPV minimums are available at a great many US airports, adding a "ILS-like" utility to those airports without incurring the infrastructure cost of adding the ground equipment necessary for ILS approaches.

WAAS capable GPS receivers are prevalent; while very few aircraft (the Airbus A350 is one example) have GBAS capable GPS equipment.


Has there been any attempt to use an underground cable system, a la a cable car, to tow aircraft along taxiways?

Way to go on thinking outside of the box. Actually, it might work. Although the logistics of it are above my pay-grade. Maybe, some smart group out there could make it work.
But, your question doesn’t ask for ways to make it works. It specifically asked for reasons it might not works. So, here it goes:

cable car feasibility over all does not have a great track record. If we were to make a Ben Franklin style decision graph of cable car systems that worked versus those that proved ineffective, Wikipedia lists a lot more defunct systems than it does working systems. All of which run on tracks.
If you get more than two runways at the same airport, the taxiway system become increasingly complex. An aircraft would need an alternate means of locomotion when switching from one runway/taxiway to another. The use of one continuous loop cable would be rendered impossible.
As Ron Beyer has pointed out, departing aircraft would still need time to warm up their engines prior to take off. Currently, that time is spent taxiing. Arriving aircraft would still need to power climate control systems. It would be a cheaper and more efficient use of time and resources to design a system that eliminates wait time between start up and takeoff. Keeping the traffic flow moving at all times without having to retrofit airports or entire airline fleets would benefit all.
Most cable car systems operate with cable cars of lighter weight and similar mass to each other compared to commercial aircraft. How would airports be able to account for the sheer mass differences between a single pilot C208 after a long cross country versus an A380 taking off at MTOW.
Power failure.
Power in night time IMC with four or five airliners about to break out at minimums for GPS approaches on parallel runways.
In the case of a constantly moving cable, an aircraft the size of an A320 could cause a lot of damage if it were not able to unhook itself from the cable at the appropriate time,
According to Wikipedia, the efficiency of a large cable car system is questionable. “Approximately 95% of the tractive effort in the San Francisco system is expended in simply moving the four cables at 9.5 miles per hour.“


Does a failure to respond to FAA questions on ME disqualify for sport pilot?

Yes I believe so.

While the Sport Pilot License only requires that you are medically qualified to get a driver's license there is a stipulation that if you had been denied an FAA medical previously then you cannot just use your driver's license as your medical.  If you don't respond to their questions then you will most certainly be denied the medical.

At this point I think it is best to answer their questions and finish out the process.  If your medical condition is under control and manageable the FAA will usually eventually grant you the medical however, a lot of paperwork, time and money may be required.

This is why you want to do your homework before the medical and be sure that you can pass it.  If you don't pass the medical then you cannot just simply fall back to the Sport Pilot License.


Do airliners or business jets have brake temperature sensors?

Brake temperature sensors are quite common on airliners. Turnaround times of large aircraft are often impacted by the required cooling time. This is because during take-off the brakes must be cool enough to absorb the heat of a possible rejected take-off.

Brake temperature and tire pressure indication on the Airbus A330 (note the deflated tire & high temperatures)
Source: Karlene Petitt blogspot


Is the FF (Fuel Flow) the fuel consumption index?

The FF value can show either the fuel flow or the fuel used, depending on the position of a switch on the center forward panel. If it shows the fuel flow rate, then the value shown is in thousands of kilograms or pounds per hour per engine.

1 FUEL FLOW Switch (spring-loaded to RATE)
RATE – displays fuel flow to engine.
USED –

displays fuel used since last reset
after 10 seconds, display automatically reverts to fuel flow.

RESET –

resets fuel used to zero
displays fuel used for 1 second, decreases to zero, then displays fuel flow.

2 Fuel Flow (FF) Readout (digital)
[Option - kgs] Displayed (white) – fuel flow to engine with FUEL FLOW switch in RATE
position (kilograms per hour x 1000).
[Option - lbs] Displayed (white) – fuel flow to engine with FUEL FLOW switch in RATE
position (pounds per hour x 1000).
3 Fuel Used Readout (digital)
Displayed (white) – when FUEL FLOW switch moved to USED or RESET.

(Boeing 737 NG FCOM 7.11.13 - Engines, APU - Over/Under-Displays)


How to read this step climb profile? FL STEPS CYUL/0330/TUDEP/0340/NETKI/0350

FL330 is the initial cruising altitude after departing CYUL. At TUDEP, a climb to FL340 is planned, and at NETKI, there is another climb to FL350.


How can the same runway have two different gradients?

The slope of a runway isn't always constant. In some cases, for example, if you stand at one end of the runway, you can't see the opposite end, because the runway goes up then down.

In this case, the ICAO (in the airport design manual) computes the runway slope as follows: the runway is divided into four equal segments. The average slope of each segment is computed and the total slope follows this formula:

[(slope of 1st quarter) + 1.33*(slope of 2nd quarter) + 2.33*(slope of 3rd quarter) + 3.33*(slope of 4th quarter)] / 8

The runway slope has a greater influence when the aircraft has a greater speed. Therefore, the slope at the end of the runway is given a greater weight.

In the case that you mention, if you walk from the west side of the runway to the east side of the runway, you will go up a little, then down, and end up at a lower altitude than when you started.


Is there an online source for Canadian Instrument Approach Procedures?

Not officially, no. The official approaches are available in a PDF format to download for 20 CAD for each volume.

However, FltPlan.com claims to provide free, up-to-date charts:

  In cooperation with Nav Canada, FltPlan.com is pleased to announce
  free Canadian Approach Plates, also know as CAP (Canada Air Pilot).
  These online charts include all instrument approaches, airport
  diagrams, SIDs, STARs, and special use approach plates for Canadian
  Airports. They work similarly to the already available U.S. approach
  plates.

  CAP is an extension of FltPlan.com's continuously expanding coverage
  of Canada, Mexico, Latin America and the Caribbean. In May of this
  year, we expanded our coverage to include the filing of IFR
  intra-Canada flight plans. The availability of free, online Canadian
  Approach Plates brings a new level of safety and convenience for
  pilots in the planning stages of their trip.

Though I have not seen anything from Nav Canada stating that this is "in cooperation with Nav Canada", they do seem to be an authorised distributor of paper charts.

Note FltPlan.com warns that these charts shall not be printed as a replacement for "proper" paper charts -- I am not sure whether these are deemed to be official or not, but it is rather unlikely.


What is the angle between A330 body and the ground?

TL;DR The angle is about 1 degree.

The best reference I can think of is the aircraft characteristics document provided by Airbus. This provides key dimensions for the A330 family.

I looked at the dimensions for the forward and aft lower deck cargo doors. The document provides both the distance from the ground to the floor of the hold (§2-3-0), and to the door center from the nose (§2-7-0). With this information, an inverse tangent will give the angle of the deck between the doors.

There are two factors that affect these numbers. First, the three models of aircraft have different measurements. The other factor is weight and balance of the aircraft, which affects how much the suspension on each gear is compressed. A heavier aircraft will sit lower to the ground, and the location of the center of gravity will affect how much weight is resting on each landing gear position.

Calculating the angles gives the following angles. Note the larger angle on the shorter -200, and the difference of about a degree between the values on the -200 and the freighter -200F.

Although 1 degree may not seem like much, note the difference of about 33 cm (13 in.) height between the -200 and the -200F at the forward cargo door. This is near the nose gear, which is the reason that modifications were necessary to fit the extra nose gear length in the gear bay.

-300

176,000 kg, CG 26.8%: 1.2 deg
MRW, CG 15%: 1.1 deg
MRW, CG 36.5%: 0.8 deg

-200

119,000 kg, mid CG: 1.4 deg
MRW, CG 21%: 1.3 deg
MRW, CG 37.5%: 0.8 deg

-200F

115,000 kg, CG 20%: 0.4 deg
MRW, CG 20.6%: 0.2 deg
MRW, CG 37.4%: 0 deg


One of the reasons why a private runway owner would "X" it would be to indicate that the runway is not in good condition or closed. This can be for a genuine concern or to avoid liability concerns.


Do lights on aircraft flash in a specific pattern?

Civilian aircraft have flashing lights based on manufacturer design preference.  As others have stated, aircraft like Boeing and Airbus have different patterns.

However, military aircraft can often select the pattern they want to use.  This helps military pilots identify key tactical aircraft during night operations, such as the tanker flying around the carrier.  It is definitely not coincidental that you noticed military aircraft with a unique pattern, although I'm truly shocked at your attention to detail.


Why is landing not usually a continuous descent?

The plane wouldn't be ascending during the descend sequence. It instead follows a stair-step sequence. The times where the plane remained level may have felt like ascending even though it wasn't. It is very hard to judge that in the passenger cabin.

It is much easier for the pilot to have a sequence of descends to a specific altitude alternating with keeping altitude until the next marker. It also provides a timeline during which he can handle his checklist.

Doing a full continuous descend brings the danger of ending up too high and needing to re-intercept the glideslope from above. This needs more vertical speed and if something goes wrong can end up with the plane undershooting the runway in the worst case. Intercepting from below each time is much safer and makes that the airplane will never descend steeper than the glideslope and the horizontal sections allow for a margin to correct any minor mistakes.

It is also safer to change the configuration of the airplane (flaps/gear) while in level flight rather than during descend. Staying level for a bit also allows the plane to bleed off the airspeed gained during the descent.


The wingtips are a unique part of the aircraft in that they really have one job; minimize drag. Their design is easy to see, and they are a fairly recent addition to transport aircraft. Developments continue to be made in the study of aerodynamics, with modern computing power and methods allowing much better modeling of flow patterns to evaluate designs, and improvements in materials allowing more complex designs to be built.

The key is that the winglet must be properly designed. As wing designs change, the flow over the wings changes, and new winglet designs are invented.

Since it is heavily dependent on the specific application, it's more relevant to look at the evolution of the designs on different aircraft. The design chosen is dependent on the technology available at the time, both for evaluating the design and building it, the design of the wing, intended use of the aircraft, and the previous experience of the manufacturer.

The 737 is an old design that has evolved over time: Original/Classic: none, NG: winglet, P-8: raked tip, MAX: split scimitar

The A330 is a fairly new design: Current: small winglet, neo: winglet

The 747 has also evolved over time, and the latest version shares technology with the 787: Original: none, -400: small winglet, -8: raked tip

The A320 has also evolved over time: Original: none, Current: tip fence, neo: winglet

The A380 is a new design: tip fence

The A350 is a new design: winglet

The 787 is a new design: raked tip

The 777 is a fairly new design: Basic: none, -200LR and -300ER: raked tips

You will notice a trend from smaller designs to larger ones. On larger aircraft though, the weight of a large winglet and the loads it produces can get too large. New designs like the 777, A380, 787, and 747-8 all use either raked tips or small winglets.

As for other parts of aircraft, engines are changing more than you think. The jet engines on the early jet transports look very different from modern high-bypass turbofans. The GEnx engines on the 787 and 747-8 have chevrons at the back to reduce noise. All you see on the outside is the nacelle that minimizes drag; most of the changes go on inside. Also, if you look closely at the front, fan blades on newer engines have curves in them instead of having straight edges.

Most other parts of the aircraft have more complex jobs, not primarily external. A fuselage should be efficient at carrying things inside but also keep drag low. If you look closely you will notice that new planes like the 787 and A350 have a lot in common with previous fuselages, but they are shaped differently as well. It's harder to see the other drastic changes like the use of composites in place of traditional aluminum, electric systems instead of hydraulic or bleed air, fly by wire, etc.

Control surfaces must provide sufficient control while minimizing drag. The size and shape has also changed over time, though the general design has remained.


What is the working principle of g-suits?

How do g-suits help in minimizing the effect of high g's on the pilots?

G-suit create extra external pressure on the limbs (legs in particular) to prevent the blood to stagnate far from the heart. In normal conditions specific biological systems automatically return the blood from the extremities to the heart, but when subjected to high G loads these systems fail, as they are not designed for such conditions.

By creating pressure on the body the G-suit alleviates the G load perceived by the body.

  What is the maximum g that a g-suit could handle properly?

The main limitation is not only the amount of Gs, but for how long the human body can sustain them (spoiler alert: not much)

Image source

As you can see the Gs usually experienced in a fighter aircraft (blue line, see diagram on top right) cannot be sustained much beyond 3 seconds if they are of even moderate intensity. The G-suits help the body resist slightly longer.


What is a CRM and what does it stand for?

Crew Resource Management started out in the 70s as an attempt to eliminate human error but over time it's undergone a number of iterations and today the concepts have accepted reality and assume errors can't be eliminated, only mitigated.

Modern CRM tries to mitigate errors by attempting to require multiple errors to stack up in an improbable way before things become dangerous (called the "swiss cheese" approach, as in mutiple layers of swiss cheese where a single hole is unlikely to line up).  It also has added personality factors, human interaction factors, and leadership factors to the mix.

In practical terms, this means that, for example, captains are expected to act as leaders and not bosses. The FO is not just a gear puller and is encouraged to participate in assessment, planning and decision making.  Copilots are expected to speak up when in doubt about something.  Both crew members are expected to make sure that each is aware of the other's actions, and planned future actions, at all times.  Crew members cross check each other's actions continuously. Crew members learn standard phraseology for key actions and are expected to stick to it to reduce confusion. Crew members are expected to follow standard operating procedures and not invent their own ways of doing things.

ATC gives an altitude clearance change?  Pilot monitoring and talking to ATC dials the autopilot to the new altitude, and calls it out something like "Flight Level 350 set".  Pilot flying confirms the correct altitude is set and calls out "350 checks".  You generally announce everything you do as you do it and make sure your partner is aware (usually by responding "check").  It should just flow.  One major bonus is the standardization makes it possible for crews to smoothly interact without flying together for a period of time first.

A cockpit with good CRM will have a well-oiled machine aspect to it with the pilot and copilot well integrated mentally. The capt and FO cooperate on planning and decision making, notwithstanding the fact that it's the captain's final call.  They will look like they've been flying together for weeks when they've actually just met that morning.

I would say that the two biggest factors in the amazing safety record of airline transport in the last 30 years, from a crew performance standpoint, is the success of CRM, and the advent of the 2D moving map presentation when the glass cockpit came along, which massively improved situational awareness by eliminating the need to generate a mental picture of a navigation situation like in the steam gauge era.


Is an F-16 able to fire any of its weapons while on the ground?

Yes, the F-16 can fire on the ground, and it has happened as an accident

A maintenance worker accidentally fired a 20mm Vulcan cannon from an F-16 jet he was working on at Belgium's Florennes Air Force Base earlier this week, destroying another F-16 while damaging another aircraft nearby, according to multiple media reports.
A worker apparently opened fire across the flight line while performing maintenance on Oct. 11, according to Avio News. The F-16 that was racked by cannon fire quickly caught fire and exploded, since it was loaded with fuel and being readied for an afternoon sortie, according to Scramble Magazine.

https://taskandpurpose.com/f16-destroyed-belgium


How can I continue my flying career in the USA?

There are a few things you will need to do to convert it over. You can find a lot of the information on the FAA's website here. This is pertaining to FAA FAR 61.75

Get your foreign license verified by the FAA. This takes 45-90 days and you cant make any moves until this is complete.
Find a local flight school. Once your license has been verified you can start your US training. Assuming you are not a resident you are going to need to get TSA approval to train.
Once you are TSA approved to train you can start to train here. While your hours will count from your previous experience you will still need to pass the FAA written exams and practical exams. As such you will need to learn a bit about general operations here specifically in the US.
Once you have done your training and are prepared to pass the tests and check rides you can schedule them. Your instructor will help you with this.

You will still need to progress through the US certifications PPL->Instrument Rating->CPL and complete all required flight time and tasks to do so. There is no minimum time between check rides so if you have completed all the exams and tasks you can do them all one after another.


How can the lift force be changed without changing velocity?

The problem is:
  Now I want the aircraft to go to balance state to move with constant velocity.
  So all the four forces should equals to zero thus the lift force should equlas the weight force.
  How Can I decrease the lift force?

This can be done by simultaneously reducing AoA (which in-turn reduce CL) by introducing little down elevator and reducing the engine power accordingly to maintain the airspeed.


Why are there vortex generators under the Boeing 737's cockpit windows?

Apparently, they are there to reduce the cockpit noise. From b737.org.uk:

  Notice the 10 small vortex generators above the radome. These reduce the cockpit noise from the windshield by 3dB.

According to this document, the VGs, along with other improvements like damping/insulation changes, window frame improvement and ECS improvements contribute to a total noise reduction of 3 dB (at 35k ft and Mach 0.78). Though their exact impact is unknown, the reason for VGs are there is to reduce cockpit noise.


Aircraft lightning: What are the requirements for airworthiness?

When dealing with lightning protection, there are two significant areas that must be addressed: direct effects of lightning and indirect effects.

The FAA provides guidance on these two areas in the following advisory circulars:

20-155A - Industry Documents To Support Aircraft Lightning Protection Certification

20-136B - Aircraft Electrical and Electronic System Lightning Protection

The lightning zone analysis from the AC 20-155A will define the test requirements for the airframe and help determine the level of testing for installed equipment based on its location in the aircraft.

At the aircraft level it can be a very complex and drawn out process negotiating the specific testing required with the FAA. Once that is done, requirements and verification for the equipment can be developed.  A short summary of that process from AC 20-136B is:

  6. Steps for Showing Compliance.
    a. The following seven steps describe how you may comply with 14 CFR
  23.1306, 25.1316, 27.1316, and 29.1316 requirements for your aircraft’s
  electrical and electronic systems:
  (1) Identify the systems to be assessed.
  (2) Determine the lightning strike zones for the aircraft.
  (3) Establish the aircraft lightning environment for each zone.
  (4) Determine the lightning transient environment associated with the systems.
  (5) Establish equipment transient design levels (ETDLs) and aircraft actual transient
  levels (ATLs).
  (6) Verify compliance to the requirements.
  (7) Take corrective measures, if needed.
   b. The steps above should be performed to
  address lightning transients induced in electrical and electronic
  system wiring and equipment, and lightning damage to aircraft external
  equipment and sensors that are connected to electrical and electronic
  systems, such as radio antennas and air data probes. Additional
  guidance on lightning protection against lightning damage for external
  equipment and sensor installations can be found in SAE ARP 5577.

Testing of individual LRUs is typically under RTCA document DO-160G - Environmental Conditions and Test Procedures for Airborne Equipment.  Section 22 covers Lightning Induced Transient Susceptibility and Section 23 covers Lightning Direct Effects.


What repairs or modifications can be done without approval/certification?

This answer applies to FAA certified aircraft.  For experimentals, there are really no restrictions.  I mean, you can build the airplane from scratch so replace what you want...  but for certified aircraft:

The following is copied and pasted from the AOPA website:

FAR Part 43 specifies who may do what to an aircraft in the way of maintenance, repair or alteration. It requires that only properly certified mechanics work on aircraft and "okay" them for return to service. However, it does allow preventive maintenance to be performed by a certificated pilot, holding at least a Private certificate, on an aircraft owned or operated by that pilot, provided the aircraft is not used in commercial service. The responsibilities for a pilot performing preventive maintenance are very similar to those imposed on the certificated mechanic performing other duties. The FARs require that anyone who works on an aircraft must have the appropriate maintenance and service information available. This means quite simply that before you set about performing preventive maintenance items on your airplane, you must first have the proper maintenance manuals available.

A list of "preventive maintenance" allowed is specifically listed in FAR 43 appendix A (4) c and is copied below:

  Preventive maintenance. Preventive maintenance is limited to the
  following work, provided it does not involve complex assembly
  operations:

  (1) Removal, installation, and repair of landing gear tires.

  (2) Replacing elastic shock absorber cords on landing gear.

  (3) Servicing landing gear shock struts by adding oil, air, or both.

  (4) Servicing landing gear wheel bearings, such as cleaning and
  greasing.

  (5) Replacing defective safety wiring or cotter keys.

  (6) Lubrication not requiring disassembly other than removal of
  nonstructural items such as cover plates, cowlings, and fairings.

  (7) Making simple fabric patches not requiring rib stitching or the
  removal of structural parts or control surfaces. In the case of
  balloons, the making of small fabric repairs to envelopes (as defined
  in, and in accordance with, the balloon manufacturers' instructions)
  not requiring load tape repair or replacement.

  (8) Replenishing hydraulic fluid in the hydraulic reservoir.

  (9) Refinishing decorative coating of fuselage, balloon baskets, wings
  tail group surfaces (excluding balanced control surfaces), fairings,
  cowlings, landing gear, cabin, or cockpit interior when removal or
  disassembly of any primary structure or operating system is not
  required.

  (10) Applying preservative or protective material to components where
  no disassembly of any primary structure or operating system is
  involved and where such coating is not prohibited or is not contrary
  to good practices.

  (11) Repairing upholstery and decorative furnishings of the cabin,
  cockpit, or balloon basket interior when the repairing does not
  require disassembly of any primary structure or operating system or
  interfere with an operating system or affect the primary structure of
  the aircraft.

  (12) Making small simple repairs to fairings, nonstructural cover
  plates, cowlings, and small patches and reinforcements not changing
  the contour so as to interfere with proper air flow.

  (13) Replacing side windows where that work does not interfere with
  the structure or any operating system such as controls, electrical
  equipment, etc.

  (14) Replacing safety belts.

  (15) Replacing seats or seat parts with replacement parts approved for
  the aircraft, not involving disassembly of any primary structure or
  operating system.

  (16) Trouble shooting and repairing broken circuits in landing light
  wiring circuits.

  (17) Replacing bulbs, reflectors, and lenses of position and landing
  lights.

  (18) Replacing wheels and skis where no weight and balance computation
  is involved.

  (19) Replacing any cowling not requiring removal of the propeller or
  disconnection of flight controls.

  (20) Replacing or cleaning spark plugs and setting of spark plug gap
  clearance.

  (21) Replacing any hose connection except hydraulic connections.

  (22) Replacing prefabricated fuel lines.

  (23) Cleaning or replacing fuel and oil strainers or filter elements.

  (24) Replacing and servicing batteries.

  (25) Cleaning of balloon burner pilot and main nozzles in accordance
  with the balloon manufacturer's instructions.

  (26) Replacement or adjustment of nonstructural standard fasteners
  incidental to operations.

  (27) The interchange of balloon baskets and burners on envelopes when
  the basket or burner is designated as interchangeable in the balloon
  type certificate data and the baskets and burners are specifically
  designed for quick removal and installation.

  (28) The installations of anti-misfueling devices to reduce the
  diameter of fuel tank filler openings provided the specific device has
  been made a part of the aircraft type certificate data by the aircraft
  manufacturer, the aircraft manufacturer has provided FAA-approved
  instructions for installation of the specific device, and installation
  does not involve the disassembly of the existing tank filler opening.

  (29) Removing, checking, and replacing magnetic chip detectors.

  (30) The inspection and maintenance tasks prescribed and specifically
  identified as preventive maintenance in a primary category aircraft
  type certificate or supplemental type certificate holder's approved
  special inspection and preventive maintenance program when
  accomplished on a primary category aircraft provided:   (i) They are
  performed by the holder of at least a private pilot certificate issued
  under part 61 who is the registered owner (including co-owners) of the
  affected aircraft and who holds a certificate of competency for the
  affected aircraft (1) issued by a school approved under Sec. 147.21(e)
  of this chapter; (2) issued by the holder of the production
  certificate for that primary category aircraft that has a special
  training program approved under Sec. 21.24 of this subchapter; or (3)
  issued by another entity that has a course approved by the
  Administrator; and   (ii) The inspections and maintenance tasks are
  performed in accordance with instructions contained by the special
  inspection and preventive maintenance program approved as part of the
  aircraft's type design or supplemental type design.

  (31) Removing and replacing self-contained, front instrument
  panel-mounted navigation and communication devices that employ
  tray-mounted connectors that connect the unit when the unit is
  installed into the instrument panel, (excluding automatic flight
  control systems, transponders, and microwave frequency distance
  measuring equipment (DME)). The approved unit must be designed to be
  readily and repeatedly removed and replaced, and pertinent
  instructions must be provided. Prior to the unit's intended use, and
  operational check must be performed in accordance with the applicable
  sections of part 91 of this chapter.

  (32) Updating self-contained, front instrument panel-mounted Air
  Traffic Control (ATC) navigational software data bases (excluding
  those of automatic flight control systems, transponders, and microwave
  frequency distance measuring equipment (DME)) provided no disassembly
  of the unit is required and pertinent instructions are provided. Prior
  to the unit's intended use, an operational check must be performed in
  accordance with applicable sections of part 91 of this chapter.


Help identify an unknown airborne object

My best guess is you saw a high altitude aircraft flashing its landing lights.

Landing lights serve a number of purposes. Besides illuminating the landing surface, they can also be used to signal other planes as they are so bright. To experience how bright they are, stand near the approach or departure path of a busy airport at night.

The reason for the pilots flashing the landing lights in your scenario is unknown. It could be signaling another plane on a potential collision course, or just a way of saying hello to other traffic (hey, cruising a commercial airliner is kinda bored, huh?).

Without any visual reference, judging distances on a nighty sky can be tricky. Flashing a light is a convenient way of saying "hey I'm here!" to other planes. It is likely that your judgment of the flying object's distance was also impaired by the night environment. The only reliable observation I would pick is that you did not hear any sound, which suggests the object was very far away.


May the tower use the runway while an emergency aircraft is inbound?

FAA Order JO 7110.65W - ATC Procedures, Chapter 10 outlines how ATC should handle procedures for emergency situations

Right at he very beginning, we see the most important part:

  10-1-1(d)
  Because of the infinite variety of possible emergency situations, specific procedures cannot be prescribed. However, when you believe an emergency exists or is imminent, select and pursue a course of action which appears to be most appropriate under the circumstances and which most nearly conforms to the instructions in this manual.

In other words, they don't dictate what controllers should do in an emergency; they are to use their best judgment about how to handle it.

So, a controller is free to continue using a runway for both arrivals and departures if they believe doing so won't interfere with the emergency aircraft.

In fact, for non-urgent emergencies like gear extension failures, I've heard them hold the emergency aircraft to get as many others in and out as possible before the runway is closed for a gear-up landing.


Why don't multiengine aircraft have to demonstrate spin recoverability?

Because it would impose severe constraints on their design.

Factors such as mass distribution make many twin-engine and multi-engine aircraft inherently resistant to spin recovery, despite the large rudder or large rudder moment-arm that is often present on these aircraft.  In many cases these aircraft are prone to flat spins.  Also, during the recovery from a nose-down spin, a large aircraft may exceed Vne before pulling out of the resulting dive, or may be overstressed during the pull-out.  In the real world, a pilot should avoid spinning a typical twin-engine or multi-engine aircraft, because recovery might not be possible.

"No multiengine airplane is approved for spins, and their spin recovery characteristics are generally very poor."
-- from https://www.flightliteracy.com/stalls-in-multiengine-aircraft/

Related questions on ASE:

Is spin recovery possible in an airliner?

Why aren't airliners spin-tested?

Other related links:

https://www.flightliteracy.com/stalls-in-multiengine-aircraft/

https://www.pprune.org/flight-testing/226351-spinning-airliner.html

https://www.airlinepilotforums.com/hangar-talk/6370-spinning-airliner.html

google "spin recovery twin" or ("multi") for much more


Yes. There's an old saying: when flying from high to low, look out below! https://sabushpilot.com/high-to-low-look-out-below/ has nice properly descriptive image.

  Airplane is maintaining certain FL with some QNH

Note that if you were at a FL (flight level), you wouldn't be using QNH, you'd be using QNE. You use QNH up to the transition altitude and clearances will be given to maintain a certain number of feet (or meters in some countries). Above the transition altitude, your clearance would be to maintain a certain FL and you would be using QNE, 1013.2 hPa.


Why isn't Vy lower than the speeds for best L/D ratio and best glide ratio in an airplane with a piston engine and a variable-speed prop?

It's because climbing at Vy the engine only has to overcome the airframe drag minus the prop, on top of the thrust lift component reduction in induced drag you mentioned in your answer to another post.

It's as if you took the prop off and towed the plane with a tow line glider style (this was done on a Wittman Tailwind back in the early 60s for some gliding drag studies to learn the plane's true L/D, with the tow line connected to the engine prop hub; the Tailwind turned out to be an extremely efficient airplane, square corners, stubby little wings and all).

Best glide has to take into account the substantial drag of the windmilling prop, so the best L/D is achieved at a lower speed.  I'm pretty sure the POH numbers are based on the worst case of the prop windmilling at flat pitch (where it goes if you are climbing at Max RPM and the engine quits), where the drag is so massive it's like you deployed a speed brake.

You can improve this a lot by pulling the prop to Min RPM when the power is removed to try to get the governor to drive the blades to full coarse pitch. This gets you at least part way to being feathered, and helps quite a lot in the glide.


Can an airplane flying above 35,000 feet be heard on the ground?

Yes
It doesn't even has to be very silent around you.
But because of the speed of sound, you will hear the aircraft later. Here is the approximate time, the sound needs to reach you:

Speed of sound at MSL: ~340m/s
35.000 ft in m: ~10660m
10660 / 340 =
~ 31s

That means you will maybe hear the aircraft but you are not going to spot it where the sound comes from.
Note that this is not an exact value, as speed of sound varies with air density and temperature, which both change the higher you are.


Tiny margin between VFR cruise and over Class C?

I had a similar situation flying over the Class C at Albuquerque New Mexico.  Albuquerque's Class C goes up to 9,400 and I was flying VFR at 9,500.  In this case I was using flight following going from Las Cruces NM to Santa Fe NM and was handed off to Albuquerque Approach.  Albuquerque Approach simply told me to notify them if I needed to make any altitude changes to remain VFR.

I think most pilots would simply call Approach in this situation and let them know they are flying over their airspace.  You would need to know the correct altimeter setting anyway to make sure you are at the right altitude.


What is the business purpose of scheduling two separate flights on the very same route with 5-10 minutes separation?

If you look at just the schedules it says nothing. If you look at the prices you can see that Air Berlin was pricing the flight significantly lower than Air France. As was stated above, it was competition.

Unfortunately, things did not end well for Air Berlin. The airline declared bankruptcy in August 2017, and was unable to obtain further funds from its primary shareholder, Etihad. The company closed its doors in October of the same year.


Why does London need so many? I think two airports is enough. Plus, they are put in bad locations.

As others have mentioned, London is a huge connection point for several parts of the world as well as being one of the big financial cities in the world.

During WW2 a huge number of air bases in the UK were built or expanded by the allies, and post-war several of them were used as civil airports. Several of the ones you mention has roots in this:

Southend was built during WW1, closed after and reopened in the 1930s
Gatwick was built as a civilian airport between the world wars
Stanstead was built during WW2
Luton opened just prior to WW2
Heathrow opened between the world wars as a civilian airport

Several of them saw expansions by the military during WW2, getting improved infrastructure and bigger capacity. Once the war was over, the airfields were available to civilian and commercial use.

  So, is this for a practical, or some kind of other reason?

It is not as if the city of London planned where to put each airport. They were there when the need for additional capacity appeared; in some cases the airports initially served local municipalities and cargo airlines, later to be used by charter and other airlines when the airports closer to London were full. The same thing is done today with budget airlines choosing to operate out of airports further from the population centers where the operational costs are lower for the airline.

The only apparent exception to all this is London City Airport, the only of the airports mentioned built after WW2. It was built in the 1980s as part of a bigger plan to revitalize a part of London; by having a small business airport close to the city it could attract new investors and companies.

  I think two airports is enough.

By numbers alone, London could get by with two Atlanta-sized airports. But to do this you need room to build and the political will to spend money on expanding an airport rather than allowing airlines to use other airports further away.


What is this pattern on the windshield of aircraft?

Short answer
These are the three redundant temperature sensors for the windscreen anti icing and defogging system. The design is similar to what is found on the A330 and A340, and most large aircraft. The sensors are used to control the electric current in the heating film(s) sandwiched in the windscreen ply. Usually three temperatures are monitored:

Outer windscreen layer must be above freezing point, e.g. 1.8°C.
Film mustn't overheat, depends on film used.
Inner layer must be below some threshold, e.g. 50°C.

This video shows how windscreen heating works on an ATR42. Extract related to the sensors:

ATR42 windscreen temperature sensors and film bus bars
The heating film(s) is/are used both to prevent icing and failure of the outer panel (air temperature can be as low as -60°C) and fogging on the inner panel. This can be obtain using a single film, but sometimes there are two distinct films:

Structure of the windscreen on a Boeing 787. Source

On the A350
From A-350 Technical Training Manual:

Windows Anti Icing/Defogging Function, Description and Interfaces
The windows anti icing/defogging system is divided into two
sub-systems (F/O and CAPT). Each sub-system is comprised of one
windshield, one FWD lateral window, one AFT lateral window and a
Window Heat Computer (WHC). [...]
The anti icing and defogging function of the cockpit
windshields is ensured by the heating of one resistive/heating ﬁlm. Each
windshield's resistive heating ﬁlm is powered by 230 VAC, provided by
the WHC.
There are three temperature sensors near the heating ﬁlm that
continually send information to the WHC for the heating regulation and
the overheat protection functions. [...]
The WHC regulates the temperature of the cockpit windows (35 degrees C to
42 degrees C) based on the temperature value it receives from one of the three temperature sensors. The other two temperature sensors are
in standby mode. [...]
If the temperature of the cockpit windows reaches a specific
temperature level (+60 degrees C), the WHC will stop supplying the
specific window. [...] For each window, the WHC uses temperature
values from the three temperature sensors to detect an overheat.
The WHCs interface and exchange data via CRDCs with the
AFDX network.The two WHCs are located in the cockpit: WHC1 is located
next to the fourth occupant console behind the Captain. WHC2 is
located next to the coat stowage behind the First Ofﬁcer.

For this test aircraft:

Sensors are larger than usual.
They may be stuck on the glass instead of being built-in.

This setting might be specific for flight test purposes. Someone may bring additional elements.

Another example, on a Pilatus PC12-NG:

Pilatus PC12-NG temperature sensors and bus bars on the windscreen


Why is 51,000 ft a common service ceiling for business jets?

If for no other reason, its likely because there is a practical maximum descent speed for a given airframe and aircraft must be able to descend from their maximum cruising altitude to 10,000 ft. in 10 minutes or less. Although under part 135 (how many of these planes are likely flown) the regulations have a few variations you can have less oxygen on board if you can descend in 4 minutes.

At 51,000 ft. you would need to lose 41,000 ft in 10 minutes or even 4 minutes. That is a descent rate of either 4100 ft/min or a blistering 10,250 ft/min which likely yields a speed at or near Vne for most of these airframes.

This Gulfstream pilot discusses a bit of it from a practical standpoint here.


Contrails are formed from the condensation of jet exhaust.

When a hydrocarbon, such as jet fuel, is burned, it produces water vapor and carbon dioxide along with some impurities/unburned fuel. High altitude jets are in a much colder environment than ground temperature. Assuming a non-cloudy day, we can expect an approximate decrease of 5.4 degrees Fahrenheit for every 1,000 feet of elevation. Commercial jets fly around 28-35,000ft which translates to a roughly 150-160 degree decrease in the outside temperature. I'm not going to go into all of the physics behind it, but this is the most important point. It is much, much colder up in the air than down on the ground. And it is because of that coldness these contrails exist.

From here the lower temperature and outside pressure of the surrounding air create a ripe environment for condensation, as soon as a particle from one of the impurities in the fuel touch the vapor it condenses forming tiny water droplets and ice crystals. It's the same physical action that occurs when our breath produces a small 'fog' in the cold, and the same one that causes natural clouds to form in the first place.

You can also use contrails to tell the weather, high-humidity causes contrails to be thick and long-lasting which is a sign that a storm may be soon to come whereas a thin contrail or one that doesn't last long is a sign up low humidity.

To answer the rest of your questions:

  What temperatures are needed?

That depends on a lot of factors, but in general they form when the air is colder than -34 degrees Fahrenheit.

  How wet does the air have to be?

The air could be bone dry, the exhaust fumes themselves provide the water; though some of the latent humidity in the air is also heated and re-condensed adding to the effect.

  What exactly is a contrail then? Only condensation, ice, ..?

A contrail is a mixture of condensation, ice, and trapped impurities from the exhaust.

  Is the contrail made from humidity from outside-air or from the vapor of the engine?

The contrail is made from varying degrees of both.

  How does a contrail vanish again? What makes the difference between a 20 second contrail and a 2 hour contrail?

A contrail is basically a cloud and vanishes the same way that clouds dissipate. Namely, temperature increase, mixing with drier air, or air sinking. All three will cause evaporation of the water droplets and dissipation of the cloud.

What makes the difference is primarily the external humidity. The more humid it is, the less a cloud or contrail can evaporate before reaching a state of equilibrium with the surrounding air

  Everything that you know and is important to know.

The disturbance of the wingtips through humid air can kick off the same reaction, even near the ground. Though much less pronounced.

https://commons.wikimedia.org/wiki/File:C27_Spartan_making_condensation_spirals.jpg


What is the battery voltage for a Supermarine Spitfire?

This aircraft museum says that the "Trolley Acc" (Trolley Accumulator) used for Spitfires and other aircraft supplied 12 volts. Lots of sources state that Spitfires had 12 volt electrical systems, including the Pilot's Manual.