Was the Hughes H-4 Hercules capable of flying out of ground effect?

The answer can only be given by comparing it to other, broadly similar aircraft. My three references would be the British Saunders-Roe Princess, the Martin Mars and the Boeing 314 Clipper, all three at their time huge flying boats.

Obviously, the H-4 has the highest wing area relative to its installed power and its intended maximum take-off mass (MTOW), but does not look totally out of the range of the two smaller specimen. The Princess was conceived as a pressurized airliner and is of a more advanced design than the other three. With the lower wing loading come lower speeds, so the lower power loading looks adequate. Another huge military transport plane of that time which was derived from a cargo glider (the initial requirements asked for a cargo volume equivalent to a Reichsbahn standard cargo wagon) had a wing loading of just 150 kg/m², a very similar power loading of 23.56 HP/m² and flew just fine. Stick forces were massive, however, and stability was marginal.

The exact performance would depend on details like airfoils, aspect ratio, flap settings, hull design and stability, but in general it looks as if the H-4 would have been capable of flying out of ground effect. But its performance would not have been spectacular - a little more installed power would had made it better.


The rotation direction of the propellers produces a rotating slipstream.  This slipstream pushes the exaust from the (engine's) right side downward, but the exhaust on the other side would be pushed up, producing potential heat problems where it impinges on the wing (as well as depositing lots of soot).  By bending the exhaust pipe upward as you see, the exhaust on that side passes over the wing, in an airstream that will both protect the wing surface from the exhaust heat and reduce soot deposition.


What is this pod at the wing-tip of a U2?

The pod contains the Radar Warning Reciever (RWR). The variant in the picture is the TR-1B, which had wingtip mounted RWR units. According to globalsecurity.org:

  The Air Force has fielded new electronic countermeasures on the aircraft, giving it a jamming capability and upgraded radar warning equipment with wing-tip mounted digital receivers.

As an another exmaple, SAAB seems to have put RWR on the wingtips of Gripen, though the equipment are certainly different (U-2 uses AN/ALQ variants).

Note that the bottom of the 'pod' has (wingtip) landing skid at the bottom and navigation light on the side. The RWRs face outside at an angle of ~45$^{\circ}$. This (containing RWR, skid and nav lights in a single package) is a later design and was added to the exiting U-2Rs as retrofit. It was not avialble in the earlier models.


How to match ATC requirements to work in EU?

I would suggest to contact the IT ANSP and ask if they accept applications for ready entry ATCOS: https://www.enav.it/sites/public/en/LavoraConNoi/Traduzione-di-Contatti-n.html

In Germany we have plenty of so called „ready entries“ who applied for a job as ATC in Germany while holding a valid non-EU ATCO license.

After an assesment by our company and - hopefully - signing the contract they participate in some weeks of sim training to learn the procedures of the new sectors. After succesfully completing the sim phase the OJT (on the job training) begins. During something between 6 and 12 months they will train working in real world with a coach and finally take one examination per working position.
That‘s it!


What to do when fuel is exhausted and we are denied landing by ATC?

You should have declared an emergency long before your fuel was exhausted. If you haven't yet, do it now.
Land Anyway
You are authorized to do whatever it takes to get the aircraft down, worry about regulations when you are alive enough to do it. Until then, ATC will clear out anything around you, just say "declaring an emergency" and then fly the plane regardless of what ATC "authorizes" you to do or not.
The literal call to ATC will be:

KXYZ, Unable, emergency, landing now.

But only if you have time to make the call.


What was Korean Air 672 doing at the time of Malaysia Air 370's disappearance?

With the way in which it suddenly switched back and forth it appears to be either a software glitch or bad data from one of the feeders.

All aircraft displayed in yellow on FlightRadar24 are detected by volunteers with their own ADS-B receivers, of varying quality in hardware, software and range. When aircraft reach the very edge of someone's receiver range you can occasionally get corrupted data, perhaps showing the aircraft somewhere back along its path or far off it.

Another scenario is when a receiver is having trouble uploading its data to the FR24 servers because of a bad internet connection or similar, so position updates arrive later than they should.

Sometimes the FR24 servers get conflicting info, for the same reason, where one ADS-B feeder is providing good data and the other bad. When that happens you can see the plane seem to jump backwards and forwards until one of the receivers is out of range.

It's something I've seen fairly often, even with my own receivers. FR24 does try to filter the anomalies out but it's a difficult task.


Can a delta wing fighter engage an arrestor net without its main landing gear?

In August 2009, a Saab Gripen pilot forgot to extend the landing gear, and walked away from the landing unharmed. And this was without any preparation of any kind.

There is no reason to eject from a perfectly good airplane just because you can't extend the landing gear. Belly landings are a pretty "routine emergency" (if that term makes sense).

The metal scraping across the runway will probably generate as much if not more friction than the tires would, so the risk of a runway overshoot is rather negligible, and there is no need to use any arresting gear at the end of the runway.

What could make sense, though, is to use arresting gear at the beginning of the runway, if the aircraft is equipped with an arresting hook and the runway is equipped with arresting wires.

It might make sense to drop the drop tanks if they are full.

The delta wing does not play a role here, this applies more or less to all kinds of wing planforms.


Why don't tanker aircraft have ejection seats?

When I was flying the KC-135 tankers - A model and Q models - all crew members had parachutes, and all parachute packs had supplemental oxygen bottles that were good for at least 10 minutes - which was enough time to descend to the point where you did not need supplemental oxygen. If you had to bail out, it would be through the crew entry hatch, on the port side just behind the pilot's seat and in front of the boom operator's seat. If you had to pull the handle for bailout, the crew entry hatch would be jettisoned and a metal air dam would be pneumatically deployed about 4 feet down at the leading edge of the hatchway, to provide a wind block to allow crew members to fall free of the aircraft before getting into the slipstream. This prevented crew members from being blown back onto the body of the aircraft.

I have never heard of any tanker crew ever having to bail out of a KC-135, so perhaps this is why they got rid of the parachutes? Of course, I retired more than 20 years ago, and much has changed since then. But the KC-135s are still flying, even though they are older than anyone flying them today.

To answer the original question - both the KC-135 and the KC-46 are modifications of civilian aircraft, which do not have ejection seats; whereas fighters and bombers are designed for their specific mission.

Finally, I'm not aware of any cargo aircraft that have ejection seats, either.


Do aircraft owners need to purchase insurance?

Aircraft insurance for personal aircraft is not legally required by any part of the US FARs, nor to my knowledge is it required by any state government, though I'm only familiar with New York in that regard. (As you'll note from the Wikipedia page you linked to, not all states require automobile insurance either, though most do now...)

Aircraft insurance is most directly comparable to marine insurance.
It's generally required by:

Your lender (if you didn't pay cash)
They want to be sure you have hull coverage so if the plane is damaged they still get paid.
Your FBO or Airport Management.
As a condition of having a tiedown/hangar most FBOs require some form of liability insurance in case you taxi into a building or another plane.
Good old-fashioned common sense.
A light piston single is unlikely to take out a building, but if you have an incident costs can rack up fast. Having someone else to step up and pay those big bills is beneficial.


Is trimming aircraft to relieve pilot of applying force on control stick/Pedal still applicable?

Almost all airplanes have trim (I'm fairly certain that the Wright Flyer didn't, so I can't say all airplanes do), but a lot of newer designs don't use trim tabs because they are less aerodynamically efficient than alternative designs.

For instance, the Falcon 50 & 900 that I fly doesn't have a single trim tab on it.  Normally the flight controls are moved by hydraulics and a small electrical actuator is used to adjust the position of the aileron and rudder for trim purposes.  Pitch trim is accomplished by moving the front of the entire horizontal stabilizer in order to adjust the angle and amount of lift produced by the tail.  This is done so that the elevator can be neutralized and not create the additional drag caused by being in the airflow.

On FBW airplanes, they may or may not have manual trim that is used (under normal circumstances) by the pilot.   Trimming is still taking place on FBW airplanes without manual trim, but it is simply automated.

Boeing typically designs their FBW airplanes so that they behave like a "normal" airplane, and require the pilot to trim in order to relieve the control forces.  This is all completely artificial though, programmed simply to give feedback to the pilot.

Airbus on the other hand doesn't give any feedback to the pilot through the side stick so there are no control forces to relieve.   When you release the side stick, it centers and the aircraft maintains its current pitch and bank angle.  In this case, the autopilot automatically trims the airplane for the current conditions, and the pilot doesn't need to worry about it.


How much would it cost for a large airline to switch engine manufacturer for their planes?

Many (especially larger) airlines have a history and infrastructure for engines from a specific manufacturer and are unlikely to change that, the cost would extend far beyond just the cost of changing the contract. E.g. KLM has a massive investment in maintenance facilities for GE engines, workshops, spare parts warehouses, highly trained specialised technicians. Retooling to RR would be prohibitive for them.

Of course a smaller operation without maintenance facilities of their own might be more flexible in that and just buy whatever is cheapest at the time, contracting out maintenance to various companies as needed. But even then, it's often more economical to have a single maintenance provider doing all your work for you, which might well mean a provider who's specialised in a single series of engines, for example if you're based at Schiphol there's a good chance you'll be contracting out your maintenance to KLM and their GE specialised shops.

So there are many good reasons for airlines to stick with a single engine supplier (and to a degree with a single aircraft manufacturer), even if the cost of buying those engines is higher than selecting competing engines from another manufacturer.
Say you're going to save 0.1% in your fuel bills for the 2 new aircraft you're buying to increase the fleet of 20 with other engines you have already (and that's a big if, those engines are pretty close between manufacturers for a specific aircraft). You'd need to fly a LOT for it to be worth building an entire duplicate maintenance network just for those few new aircraft.
Of course if it's part of a long term plan to replace the entire fleet with aircraft using that other manufacturer's engines, that's a different story. But mixed engine fleets tend not to be the most economical way to go, even if on one type manufacturer A is marginally more fuel efficient and on type B manufacturer B is marginally more fuel efficient (and that's what you're going to see, marginal differences only).
If you're talking an operation like Delta or United, with hundreds of aircraft of each type, it might be a different story. But then too you're talking about more aircraft with each manufacturer's engines than most other airlines have in total, and they'll have multiple maintenance shops themselves, making it easier to have a facility for each manufacturer (and of course in case of the big US airlines, they tend to have ended up with that in the course of gobbling up other airlines anyway).


Why are FDR's called "black boxes" when they are actually orange?

The Wikipedia article on Flight recorder offers a possible explanation for the origin of the term:

  ... they were essentially photograph-based flight recorders since the record was made on a scrolling photographic film. The latent image was made by a thin ray of light deviated by a mirror tilted according to the magnitude of the data to record (altitude, speed, etc.). Since the inside of the recorder was pitch black, this may be the origin of the "black box" name, often used as a synonym for a flight recorder.

Interestingly, the Wikipedia article on Black box claims that the term entered the English language around 1945, which is a few years after the first flight data recorder was built.


The reason is that EASA cannot provide legally binding interpretations of EU Regulations, and the Certification Specifications are an interpretation of the EU Regulations.

Within the European Union (EU), legally binding interpretations of the EU regulations are exclusively provided by the national and EU courts and the European Commission.  The EU Member States are responsible for interpreting and implementing EU law in their national legal system.

The European Commission (EC) has created the European Aviation Safety Agency by decision EC 218/2008, recently repealed and succeeded by EU 2018/1139. The EC tasked EASA with creating certification specification and other material:

  EU 2018/1139, Article 76

  ...

  The Agency shall, in accordance with Article 115 and with the applicable delegated and implementing acts adopted on the basis of
  this Regulation, issue certification specifications and other detailed
  specifications, acceptable means of compliance and guidance material
  for the application of this Regulation and of the delegated and
  implementing acts adopted on the basis thereof.

And thus EASA is tasked with creating certification specifications that allow application of the high level EU aviation safety regulations, which requires of course the interpretation of those regulations.

At the same time, they don't have the power to give a legally binding interpretation, because that is reserved for the national and EU courts and the EC.

Consequently the Certification Specifications published by EASA that give the required detail to comply with the regulations, are not binding. They are referred to by EASA as "soft law", whereas the Regulations and Implementing Regulations on which they are based and which are published by the EC are referred to as "hard law"

As an aircraft manufacturer, you may argue that there are alternative ways of complying with the EU aviation safety regulations (hard law), whilst deviating from the Certification Specifications (soft law). If you make your case well, you will still get a type certificate.

This is not any different in the US, where aircraft can be certified with deviations from FAR 25. You don't necessary need to show compliance with all of FAR 25, if you can convince the FAA that the deviation from FAR 25 is reasonable and safe, a type certificate will be granted.

For example, see this table of granted exemptions from FAR 25 for the Boeing 737-8 and 737-9:

source: 737 type certificate(PDF)

Relevant EASA FAQ's:

What are the areas of responsibility for the Agency?
What is the definition of an IR, AMC and CS and GM and what differences can be proposed?


What are possible explanations for fuel being expelled in this video?

I can think of 4 possible causes, 3 of which can probably be discounted.

Tank venting. The fuel system is designed to deliberately "leak" if
the tanks are overfilled or, the fuel expands due to temperature
changes. Whilst I haven't seen this happen on a B767, I have seen it
on numerous other types and when it happens, it does not gush out
like it does in this video.  It's more of a seep of fuel which drips
off the underside.  Whilst it can be a lot of fuel, this video does
not fit a venting scenario.  Additionally, the flight crew would be
very familiar with venting which would be a normal event and would
not have abandoned the flight.
A fuel leak such as a ruptured pipe, a failed seal and so on.  I
would expect to see fuel ejected like this but only from a
pressurised part of the system, downstream of the fuel pumps.  The
location of this leak is not from a pressurised part of the fuel
system and in my opinion, there is simply too much fuel for it to be
a result of gravity.  It also appears to be coming from a nozzle
rather than seepage
As can be seen in this video, the source of the fuel is
coincident with the location of the fuel dump nozzle.  It is
possible that the crew accidentally activated the fuel dump but
unlikely (inconceivable?).  The switches are very clearly surrounded
with "don't touch this" markings and require two separate switches
to be activated.  Additionally, the jettison valve switches are
"guarded" such that you have to lift a spring loaded flap up in
order to be able to press the button.
The APU draws it's fuel from the left main tank. This flight was
close to the  maximum range of a 767 so  would have been at or close
to maximum fuel load. If the APU had been running for a long time,
longer than expected, it's possible that the crew started a fuel
transfer to balance the tanks by pumping fuel from the right tank to
the left tank and forgot to switch the transfer off.  This could
have pressurised the left tank causing fuel to overflow into the
surge tank and vent out (the surge tank vent is also very close
to the jettison nozzle).  I believe that this is the most likely scenario.

This is the only authoritative source I could find showing the fuel jettison switches.

All supposition of course but a strange incident.  I'm sure there may be other possible causes and I'm sure that comments and other answers might expand on this.


What was the value proposition of the 767-400ER over the 777?

The -400ER was a strategic response to the Airbus A330-200
... but it didn't have the range and ultimately didn't sell well.
If you can get the customers who want to replace their DC-10s and L-1011s with the more comparable A330-200 (which entered service in 1998) in talks about the 767-400ER, you have a shot at selling the bigger 777 as well. But if you only have the bigger 777, the negotiations will be harder.
Flight noted the following in 1999:

Anyone seeing the 61.4m (201ft)-long aircraft emerge for the first time could be forgiven for experiencing a certain deja vu. Not only is the -400ER a mere 3.6m shorter than the 777-200, but almost exactly 10 years ago, a similar "767-X" design was being proposed to airlines. This soon evolved into the all-new 777, and for a while the stretched 767 plans were shelved.
(...)
Delta's TriStar replacement competition therefore provided the expected battleground for yet another Airbus versus Boeing fight. Airbus pushed hard to get Delta aboard the A330-200 as part of a wider fleet deal involving widebodies and narrowbodies. Boeing was equally desperate for victory, as much to keep Airbus from gaining a foothold in Delta territory as to launch the strategically vital 767-400X.

I've also put together this derivative work showing the similar length noted by Flight above.


What are these aircraft at AMARG? Why are they dismantled this way?

Some B-52s and other aircraft were put out of commission as part of the START treaties.  They were dismantled in such a way that the Russians could verify this with satellite reconnaissance, just as in the photo above.


Why should a Piper Seneca not take off after an engine failure below 100MPH?

I finally found out an answer which makes more sense to me . By test pilot , vmca masured with a lot of citation and one of them Is 5 degrees angle of bank towards the live engine . So it means that we can't have that 5 degrees because we are still on the ground.
for each 1 degree , our speed decreases 3 knots .So 5 degrees = 15 knots which is equalls to 20mph !
 80+20 = 100 mph !
This was the best answer I have got until now.


Why is Airbus proceeding with both the A330neo and A350 XWB?

Actually the A330neo is already eating up into the A350-800 orders so much that they have abandoned it.

“Their A350 strategy has failed -- they’re really down to one successful model,” Boeing Marketing Vice President Randy Tinseth told reporters at the Farnborough expo near London. “If they didn’t make this choice, they’d be headed for a 30 to 35 percent share in the 200- to 400-seat market.”
Customer feedback about the A350-800 spurred Airbus’s decision to abandon the plane, said Fabrice Bregier, who leads the airliner unit at the Toulouse, France-based company. Stopping work on that jet will let Airbus focus on the more successful and larger -900 model and respond to some airlines’ concerns for fixes to the biggest version, the -1000.


How do Rapid Exit Taxiways improve aircraft movements?

See this related question.

Rapid exit taxiways (or high speed exits) enable aircraft to leave the runway at speeds up to 50 or 60 kts depending on the runway and aircraft type (50 kts even in wet conditions).

They have a long, constant radius rather than a 90 degree turn.

You might find this FAA presentation useful.

Source: airlinepilots.com forum.

The purpose is to enable a landing aircraft to vacate the runway more quickly without having to slow down to "normal" taxi speeds.  A large aircraft like a 777 might need to slow to 10 or 15 knots to take a right angle turn.  This would mean spending longer on the runway slowing down to that speed.

Since the aircraft next on the approach cannot land until the runway is clear, this enables closer spacing of landing aircraft.

Aircraft type, airport restrictions, operator standard procedures and weather can all impact what "high speed" means but it is always faster than the 90 degree turn.


How is close formation flying possible with things like thermals and turbulence?

Disclaimer: I'm not a Blue Angels pilot so don't know their exact procedures/limitations, but have done a fair share of military formation flying.

Answer:

It is possible, it's just a more "bumpy" ride. Not a huge issue if the turbulence is not severe enough (or of a "rotor" type) to cause uncontrollable rolls in three dimensions.

When flying formation you are separated from other aircraft in three dimensions. In turbulent weather conditions the aircraft position usually results in vertical displacement, not so much in horizontal displacement.

This means the aircraft will not roll into the adjacent aircraft (the roll effect happens when you fly into wake turbulence or through rotors for example), but do more of an "up and down" jump.

The same air disturbance will effect several (if not all) aircraft in the formation, sometimes with just a tiny delay.

Also, the heavier and faster the aircraft is, the less effect the same amount of turbulence will have. If weather doesn't permit a small single-engine piston to fly formation, it may still be workable for jets.

Ultimately, it is up to the flight lead to:
- determine if conditions permit close formation
- fly the formation to avoid known hazards (for example if the wind is from the N, don't fly on the S side of hills/mountains)


Why does the temperature rise in the boundary layer after a shock wave?

Due to no-slip condition, the flow immediately adjacent to the wall has no velocity relative to the wall. If the flow is adiabatic everywhere and there is no significant viscous stresses (more on that later), then the total enthalpy ($h_0$) is constant; if we assume that the gas is calorically perfect (good assumption for air at low supersonic speeds) and that the heat capacity is constant (good assumption for small temperature variation), then:

$$h_0=c_pT_0=c_pT+\frac{1}{2}V^2$$

where $T$ is the static temperature, $T_0$ is the total temperature, $V$ is flow speed.

Immediately adjacent to the wall, the flow static temperature will increase toward the total temperature (around 315K in your example). This occurs in boundary layer both before the shock and after. The boundary layer before the shock is thin, so you can't really see it when zoomed out. After the shock, the boundary layer is greatly thickened along with an amplification in turbulence, so the effect is much more prominent.

Now let's revisit the part about viscous stresses, which are prevalent in the boundary layer. Viscous deceleration is not exactly adiabatic (Ref. Hill, Mechanics and Thermodynamics of Propulsion), so there is decreased total temperature immediately adjacent to the wall (characterized by the recovery factor), and an increase in total temperature farther away, before tending to the free-stream value.


Why does the landing gear control have 3 positions (up/down/off) on Boeing 737-800?

With the gear handle in the UP position, the retraction side of the landing gear actuators remain pressurized. The gear will stay in the full up position, however they will not be hanging on the mechanical locks designed to hold them in the up position. They've simply hit the full up mechanical stop.

When the handle is placed in the OFF position, hydraulic pressure is removed from the retract side of the gear actuators, allowing the gear to settle down and onto the mechanical uplocks, which are essentially hooks that just hold the gear up.

There are a couple reasons why it's beneficial to select OFF. One is that if they remained pressurized, then the gear are essentially hanging in space, at a mechanical stop provided by the actuator. Hydraulic actuators are delicate components, and these weren't designed to hold landing gear for an extended time in the retracted position. Imagine the loads imposed on the actuator in turbulence for example, as the gear are loaded vertically with each bump. Removing hydraulic pressure allows the gear to hang on the mechanical uplocks that were specifically designed to hold them, without putting additional wear on the actuators.

The other reason is that gear actuators are major users of hydraulic fluid volume, and the actuators and the lines that supply them are a potential for leakage. If they were to remain pressurized for a several hours long flight, that increases the amount of pressurized lines and components that can leak and cause a complete loss of the hydraulic system.

Note that if you look at more recent Boeing airplanes such as the 777, 787, and 747-8, you will not see an OFF position on the gear handle, only DN and UP. The OFF function is done automatically on these models. After you select UP and the gear are all fully retracted, there's a short time delay and the system automatically depressurizes the retract side of the actuators. It removes one After Takeoff checklist item for the pilots to do.

To answer some of the questions posed in the comments:
If you selected OFF while the gear were still in transit in some intermediate position between up and down, they would simply freefall into the down position since you've removed the retraction power.
If there's a leak in the landing gear actuator or its associated hydraulic lines, it would cause a loss of that hydraulic system, and all other users of that system would be failed. The 737 has two (and a half) hydraulic systems. The half is a standby hydraulic system that's very limited in its function, but I digress.


Do flight schools typically have dress codes or expectations?

If you are learning to fly as a hobby and are paying the school your painfully earned money, you can dress however the hell you want, within reason.  Formal attire in that circumstance is ridiculous.  If you are in a professional school in some airline related program, or a government subsidized school with a formal dress code, that's another story, and you follow the rules as they are.

Anyway, the problem with hoodies and track pants is really loose clothing and hoods can be a problem in a cramped cockpit and especially if trying to get out in a hurry on the ground.

A cotton or wool shirt without a hood and good pockets, and cotton or wool cargo pants (cargo pant pockets are really handy) is my favourite dress for flying.  Avoid "plastic" synthetic fabrics.  Having fibres made from plastic, your clothes will melt into your skin if things get "hot".

Same with shoes.  Wear shoes that will let you walk at least some distance on a rough surface.  You may find yourself walking a mile over rough terrain after a forced landing.

Dress for comfort and contingencies, without getting carried away (like buying a nomex flight suit) in other words.


How far away should the vertical stabilizer be from the leading edge of the main wings?

The reference point is not the leading edge but the center of gravity (CG), which is a little further back.
The ability of a fin to generate a yawing moment is proportional to both its area $A$ and its distance $l$ behind the CG. It is therefore also proportional to their product. This has units of $L^3$ so it is known as the tail volume $V$:
$V = A.l$
So the nearer the fin is to the CG, the larger it needs to be. On the other hand, the smaller a fin is, the farther back you have to build it out.
In practice everything in front of the fin, usually the fuselage and/or wing, can affect the airflow over it and reduce its effectiveness. This is especially significant at high angles of attack, such as when taking off or landing, and extra height is often added for this reason.
However a very tall fin also exerts a strong rolling moment, which can cause awkward stability problems such as Dutch roll.
At supersonic speeds, the pressure above the rear of the wing and fuselage falls, reducing the effectiveness of the fin. However the pressure under them increases, so underside strakes become very effective for their size.
Placing a very large fin above and close to the main wing is about the worst thing you can possibly do.
The optimal distance back depends on many design factors but is usually around a half- to three-quarter span, though it can be further for supersonic aircraft.


Could "Mimiron's Head" or "flying machine" fly in the real world?

Could they fly... ...Maybe

The second device looks quite a bit like an Auto Gyro which is very much capable of flight.

The first device looks like (as has been mentioned) the center of gravity would be an issue. If those side pods generated enough thrust along with the main rotor you could get it off the ground however I would think it would be very hard to control.


What does the autopilot do if activated in a stall condition?

In the AF447 accident, the autopilot disconnected because of inconsistent airspeed:

Temporary inconsistency between the airspeed measurements, likely following
the obstruction of the Pitot probes by ice crystals that, in particular, caused the
autopilot disconnection and the reconfiguration to alternate law;

(BEA - Final Report)
As long as the airspeed remains inconsistent, it is not possible to re-engage the autopilot:

Two ADR outputs are erroneous but different and the remaining ADR
is correct, or if all three ADR outputs are erroneous but different. The
AP and A/THR will disconnect. If the disagreement lasts for more than 10
seconds, the PRIM triggers the NAV ADR DISAGREE ECAM caution.
Flight controls revert to ALTN 2 law. The SPD LIM flag is displayed on
both PFDs, however VLS and VSW are not displayed. This condition is
latched until a PRIM reset is performed on ground without any hydraulic
pressure. However, if the disagreement was transient, the AP and A/THR
can be re-engaged when the NAV ADR DISAGREE message has
disappeared.

(Airbus A330 FCTM - Non-normal operations - Unreliable Airspeed Indications, emphasis mine)
It is not known if the crew attempted to re-engage the AP with the pushbuttons on the FCU because this is not recorded by the FDR:

It is also impossible to see whether there have been any attempts to re-engage the autopilot.

(BEA - Final Report)
The BEA did a study of similar incidents and found that the AP was re-engaged in some of these:

The BEA has studied thirteen unreliable indicated airspeed events involving the
temporary loss of this reading, or other anomalies, for which it had access to crew
reports, recorded parameters and PFR. [...]

The aircraft’s autopilot disconnected in all cases, with no intervention from
the crew;
[...]
In seven cases, an autopilot was re-engaged during the event. In two of these,
the re-engagement occurred even though two speeds were consistent with each
other, but erroneous;

(BEA - Final Report)
So it is possible to re-engage the AP after it automatically disconnects due to unreliable airspeed, but these events were not fully developed stalls. Your question seems to ask about the situation later on where the incorrect manual inputs had already resulted in a stall. In these cases, re-engagement of the AP would likely not be possible due to the engagement conditions:

AP Engagement
AP can be engaged when:

Aircraft speed is within VLS and VMAX.
Aircraft pitch angle does not exceed 10° nose down or 22° nose up.
Bank angle is less than 40°
[...]

(Airbus A330 FCOM - Auto Flight - Flight Guidance - Autopilot)
In a stall the speed or pitch limits are likely exceeded preventing autopilot re-engagement. This is a part of the FDR recording from AF447 (you can see that pitch never exceeded the 22°, but the airspeed went down to 38 kt towards then end of the flight while the F/O pitch command was at the nose-up limit):

(BEA - Final Report)
If the autopilot would re-engage successfully, it will do what it is programmed to do: follow the flight director inputs, which depend on the selected mode on the FCU (therefore just turning on the AP is not enough, one also needs to select appropriate modes on the FCU).


Is it normal ops to dispatch an airplane after a stick shaker was on throughout the previous flight (Lion Air 610)?

Well, if the shaker was running abnormally like that, the crew would have done a QRH procedure, if any, for that condition, and reported the snag at the next stop, and something would have been done by maintenance to release the plane.  Like a part was changed, or the problem went away and couldn't be duplicated after a test was done on the ground, whatever was required to get a maintenance release.  It would have to have been released as serviceable, one way or another.


What categories/classes is a Ground Instructor able to instruct on?

The basic ground instructor covers everything you quote.  The only additional privileges you can get are those granted by the advanced ground instructor rating.  My ground instructor certificate just says "Ground instructor" on the front and "advanced instrument" on the back.  No other ratings or limitations.

Things like reading charts, familiarity with regulations, weather information, fundamentals of flight and other required knowledge topics do not depend on category or class of aircraft.  You just need the BGI (and IGI for instrument) to teach ground and endorse written tests regardless of the aircraft the student is or will eventually train in.

The only other benefit to having a ground instructor certificate is that it is required to get a gold seal on your CFI certificate.


What are the pros and cons of using shielding as opposed to liquid cooling the skin of supersonic aircraft?

I’m not aware of any supersonic aircraft which use ‘shielding’ to protect them from atmospheric friction heating, save for rockets, and a few experimental platforms like the X-15B which used an ablative coating, mostly of cork or rubber, which slowly burnt off during the flight, protecting the aircraft structure underneath.

As for cooling systems, I suspect that the weight of a network of tubes throughout the skin of the aircraft coupled with a heat exchanger and pump to circulate cooling fluid through them was too expensive and complex.  A more efficient method is simply to use the aircraft’s fuel as a heat sink and absorb atmospheric friction heat be slowly warming the fuel in the tanks.  It’s a lighter and simpler solution.

Ceramic protective layers, such as the tiles on the exterior of the space shuttle orbiter can be made fairly light when they are a matrix of nitrogen gas pockets inside of them.  They are quite effective a heat protection on a unit mass basis but can be difficult and expensive to maintain.

Since the 1970s there have been few aircraft programs venturing past Mach 2 so practical applications of heat protection for airframes has been limited.  We will have to see what new developments in military hypersonic vehicles, such as Lockheed’s SR-72 reconnaissance aircraft, are using to address atmospheric heating.


Can I get an EASA Class 1 medical if I have monocular vision?

The Irish Aviation Authority's aeromedical site directs you to the underlying EU regulations (Part-Med), which say:

  Applicants for a Class 1 medical certificate shall be required to have
  normal fields of vision and normal binocular  function.

That seems to rule out monocular vision completely, which is very strange (to me) considering that the FAA is very clear that binocular vision isn't needed to fly safely. But medical issues are complicated, so I would definitely consult an aviation medical specialist in Ireland before making any decisions.

As for using an FAA medical certificate instead of an EASA one, that should really be a separate question. However, it's highly unlikely to be possible: generally speaking, your pilot's license/certificate and medical have to come from the same country.


How many landings per year are performed using the integrated standby instrument system?

None, as far as I have ever heard of. There may be an instance out there of failure of both/all of the INS’s or displays, but in the airline world at least, it would have to be absurdly uncommon.

It is nice to have the standby ADI as a tie-breaker between the two primary displays in case they should happen to disagree (which was more likely with mechanical instruments than with electronic displays), but actually losing everything else & using just the standby to landing - between really rare and unheard of.


What is the lifespan of commercial airframes (in general)?

Metal fatigue is normally the limiting factor of an aircraft's lifespan. Fatigue cracks build up every flight (at start & landing), called a cycle. Therefore the design life of an aircraft is typically given in cycles.

Metal fatigue cracks, source: Boeing

For long haul aircraft, that make relatively few cycles, the design lifespan is in the order of 40 000 cycles. For short haul the number is higher, sometimes up to 111 000 cycles.

For example, the Boeing 747 has a design number of cycles of 35 000, the MD-80 has 110 000.

An aircraft should be operable for about 30 years before reaching the cycle limit. The lifetime can be stretched by special inspection and maintenance programs.


How are there some Victor airways that exceed the service area of the VORs they are identified by?

It says it right there on the page where the service volumes are described in the AIM:

  1-1-8. Navigational Aid (NAVAID) Service Volumes

  c. Standard Service Volume limitations do not apply to published IFR
  routes or procedures.

So V267 has been flown at the MEA by an FAA plane, and it obviously met the signal accuracy requirements to be usable at the distances charted.


Which FAA regulations cover the certification of aircraft engines?

The relevant section of the FARs for engine certification standards is 14CFR33 - AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES, with 33.31 through 33.57 dealing with reciprocating (piston) powerplants & their testing requirements, and 33.61 through 33.99 being the equivalent for turbine powerplants.

There are also the 33 series Advisory Circulars dealing with such fun topics as how to comply with the Bird Ingestion Certification Standards (33.76-1A).


Is it possible to become a commercial pilot if one suffered from depression in the past?

I really can't speak for the Canadian standards for Airmen Medical Certification, though I did find this on Transport Canada's website.

https://www.tc.gc.ca/eng/civilaviation/regserv/cars/part4-standards-t42402-1412.htm

Transport Canada also lists the following concerning anti-depressant medications (SSRIs).

https://www.tc.gc.ca/eng/civilaviation/opssvs/cam-ssri-347.htm

This sounds very similar to the FAA's position in that people who are diagnosed with depression requiring medication are prohibited from obtaining a medical certificate.

OK, don't throw yourself off a bridge just yet; there's some good news.

The good news is that this is applicable if you are currently on mood altering medications perscribed by a physician.  If you have a prior history of depression but are not currently on any medication, there is a good chance that Transport Canada could issue you a Special Issue medical certificate, if you are willing to go through all the extra paperwork and documentation with your physician.  You are going to have to document, probably with the written concurrence of your physician, that you are no longer depressed, your case history was acute, not chronic with recurring episodes, and that you no longer require medication to maintain a normal mood.  Transport Canada will probably issue you a Special Issuance Airman Medical Certificate, valid for about a year, which will allow you to obtain your license.  As long as you are not diagnosed with further episodes of depression during this period and your doctor can confirm this, TC will probably issue you a regular airman medical certificate thereafter.

What I would suggest is that you make an appointment with a physician near where you live who is a Designated Medical Examiner for Transport Canada and talk with them about what TC's disopositon is on disqualifying conditions for medical certification.  NOTE WELL: Do not - NOT - make the appointment so as to indicate that you want an official airman medical certificate examination; we do not want any kind of official diagnosis entered onto your permanent record with Transport Canada just yet; this will only complicate things and we need to know exactly what TC's position is on these issues BEFORE we proceed down that road.  Select a DME who is also a pilot and will tend to be more sympathetic to your plight.

I hope that helps and good luck to you on your future aviation endeavors.  There is hope for you.


Covid-19 - Why are there still a lot of international flights?

The simple answer is that no one has shut down any airspaces yet and that is what stops planes from moving.

While many governments have put travel bans in place for people airplanes often carry other things like mail and cargo and it may still be viable and profitable to fly them. There is also the compounded fact that many people are trying to get home to quarantine them selves and in the short term there is still high demand for flights to move people back to their home countries.

Airlines are starting to cut flights due to reduced demand and over the next few months you will see a drop in flight traffic but if the airspace is open planes will keep moving.


What is the difference between "closed traffic" vs "stay in the pattern" request?

Actually, "stay in the pattern" is non-standard phraseology and shouldn't be used, even though it means the same thing as "closed traffic".

Specifying the direction isn't required but it is a good idea to ensure that everybody is thinking the same thing.


How to deduce the dynamic general equations for a non-symmetric level turn manoeuvre?

Your equations seem to be in wind-axis, and look a little weird from my literature (referencing Stevens and Lewis, Aircraft Control and Simulation). I'm more used to specifying mechanics from the body-axis.

Legend: $\theta$ is Euler pitch angle, $\phi$ is bank angle, $\psi$ is yaw angle, $p$ is body roll rate, $q$ is body pitch rate, $r$ is body yaw rate, $\alpha$ is angle of attack, $Y$ is aerodynamic side force (in stability-axis), $u$ is body forward speed, $v$ is body lateral speed, $w$ is body vertical speed.

A. Thrust aligned with body-axis

I will assume:

Thrust is aligned with the body-axis.
All aerodynamic forces are aligned with the stability-axis (see this question for the rationale).
No wind, so that the velocity in body-axis is the relative air velocity ($\alpha=\tan^{-1}(w/u)$,$\beta=\sin^{-1}(v/\sqrt{u^2+v^2+w^2})=\sin^{-1}(v/V)$).

For the general 6-dof, we have:

$$T-D\cos\alpha+L\sin\alpha-mg\sin\theta=m(\dot{u}+qw-rv)$$
$$Y+mg\cos\theta\sin\phi=m(\dot{v}+ru-pw)$$
$$D\sin\alpha-L\cos\alpha+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$

In a coordinated turn, the ball is centered, which means that the gravity component cancels out the centripetal force, and the aerodynamic forces in the y-axis must be zero.

Furthermore, in the inertial frame, we should only see a non-zero yaw rate ($\dot{\psi}$) for a steady turn. So translating this back into body-axis, we have:

$$p=-\dot{\psi}\sin\theta$$
$$q=\dot{\psi}\cos\theta\sin\phi$$
$$r=\dot{\psi}\cos\theta\cos\phi$$

To make the matter somewhat clearer, we can choose to make small angle assumptions on $\alpha$ and $\theta$, and $u\approx V$, and eliminate all second order terms. This brings us to:

$$T-D+L\alpha-mg\theta=m(\alpha V\dot{\psi}\sin\phi- \beta V\dot{\psi}\cos\phi)$$
$$mg\sin\phi=mV\dot{\psi}\cos\phi$$
$$-L+mg\cos\phi=-mV\dot{\psi}\sin\phi$$

From geometry, a particle tracing out a constant circular path with a rate of $\dot{\psi}$ will have a radius (i.e. turn radius) of: $R=V/\dot{\psi}$. So the second equation is now:

$$tan\phi=\frac{V\dot{\psi}}{g}=\frac{V^2}{gR}$$

We can define a stability-axis load factor ($n_{z_s}=\frac{L}{mg}$), which would closely approximate the body load factor for small AOA. The third equation can be expressed as:

$$n_{z_s}=\cos\phi+\frac{V\dot{\psi}}{g}\sin\phi=\sec\phi$$

At this point, we've completely reproduced the performance equations relating load factor, bank angle and turn radius from the 6-dof equations.

B. Thrust asymmetric with body axis

Let's say that the thrust vector is angled with the body axis by a pitching angle of $\epsilon$ and a yaw angle of $\nu$.

So in the body-axis, the thrust vector is:

$$\boldsymbol{T_b}=\begin{bmatrix} \cos\epsilon\cos\nu & -\cos\epsilon\sin\nu & \sin\epsilon \\
\sin\nu & \cos\nu & 0 \\
-\sin\epsilon\cos\nu & \sin\epsilon\sin\nu & \cos\epsilon \end{bmatrix}
\begin{bmatrix}T \\ 0 \\ 0 \end{bmatrix}$$

We now have modified 6-dof:

$$T\cos\epsilon\cos\nu-D\cos\alpha+L\sin\alpha-mg\sin\theta=m(\dot{u}+qw-rv)$$
$$T\sin\nu + Y+mg\cos\theta\sin\phi=m(\dot{v}+ru-pw)$$
$$-T\sin\epsilon\cos\nu + D\sin\alpha-L\cos\alpha+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$

Again assume that the ball is centered, thus $T\sin\nu = -Y$. The conclusion from the second equation (relating bank angle to yaw rate and turn radius) would be the same as before.

The third equation can be reduced to:

$$\frac{1}{mg}(T\sin\epsilon\cos\nu+L)=\sec\phi$$


How much of an airplane's forward energy is lost to lift?

In the most simple model for subsonic aerodynamics, drag is split into two components:

Zero-lift drag, that is all the drag created when the airplane produces no net lift. This kind of drag has again two components: Friction and pressure drag, that is the aerodynamic drag parallel and perpendicular to the local surface. This drag would dominate in a vertical dive or a zero-g parabola.
Drag created due to lift. Since that was explained mathematically first by using the Biot-Savart law for electromagnetic induction, this is called induced drag. The simplest explanation is: Lift is created by bending the oncoming air slightly downwards, and the reaction force is perpendicular to the mean angle of that airstream. Induced drag is the force component parallel to the initial direction of motion of the air relative to the airplane, and lift is the perpendicular component of that force. Thus, induced drag is lift times half the tangent of the bending angle.

While zero-lift drag increases with dynamic pressure, i.e. with the square of airspeed times density, induced drag decreases with dynamic pressure. Like this:

Drag components over speed for a typical glider (own work). The nonlinearity at the lowest speed is due to flow separation when the lift-creating limits of the aircraft are approached. The physics for large aircraft are the same, only the numbers will be larger.

Due to the dependency on the square of airspeed, the sum of both components has a minimum when they are of equal magnitude. However, given enough thrust, a motorized aircraft can sustain level flight at the far right end of that diagram when lift-dependent drag almost vanishes.


Need help identifying civilian small aircraft from old turkish movie

It is a Cessna 188 crop duster. The giveaway is the shape of the cooling air inlets on either side of the prop, which are "Cessna-shaped", as opposed to those on the similar Piper Pawnee which are rounded.


May a Cessna 182 land on a major, high-traffic airport, say EDDF (Frankfurt)?

There is the General Aviation Terminal (GAT) in Frankfurt that is handling "executive and private aviation flights" as they say. General aviation airplanes and helicopters are handled at this GAT that is open 24 hours per day. I think the best is to contact them.

Some additional rules related to GA in Frankfurt can be found here. Bus service is mandatory for passengers between aircraft and GAT. The list of services includes a sentence Lashing of small aircraft. So probably some not very big are expected to arrive.

Landing fees in this airport are used solely to refinance airport infrastructures and the resulting operating expenses. They are regulated, and, while not exactly very cheap, they are not astronomic either.


Which air transport aircraft have a lavatory included inside the cockpit?

As far as I know, some Boeing 747-400s (BA, Air France) had lavatories inside the cockpit. Apparently, Boeing 747-8 Intercontinental has a lavatory behind the cockpit door:

  ... Lufthansa Boeing 747-8 Intercontinental is unique in that the flight deck crew have their own lavatory, ... behind the locked cockpit door, allowing for extra security and a non-disruptive cabin service involving trolleys blocking the door.


What is the backup for a glass cockpit, if a plane loses power to the displays/controls?

I'll answer this question as "If the glass cockpit instrument fail, what are the backup? " This answer will also be General Aviation oriented (as I'm a PPL student)

The short answer is redundancy.

At first, let's look at a G1000 (standard GA glass cockpit) architecture :

The most important components are :

One (or multiple for redundancy) AHRS : gives information about Attitude and Heading of the aircraft, thanks to electronic gyrometres / accelerometres / magnetometres.
One (or multiple) Air Data Computer: gives information regarding airspeed / vertical speed / altitude, thanks to static / dynamic pressure informations.
And two Integrated Avionics Unit, that collect data from AHRS / ADC, and generate the content displayed on screen.

Now, Although the two screens usually don't display the same informations (PFD and MFD), These two systems are standalone : in case of a screen / Avionic unit failure, the second can take other.

Here the goal is to remove all single points of failure.

  But what if the whole EFIS fails ?

It is required by law to have backup of essential instruments. The definition of "essential" depends of the type of flight (day VFR, night VFR or IFR?). For some aircraft, there backups are traditional (steam gauge) instruments / others have independent electronic systems, like the new Cirrus SR22 G6 :

all electric !

  And in the case of a complete electrical failure?

Depends of the aircraft. In my case, I fly the Robin DR401 (certified for night VFR):

The EFIS is a Garmin G500 (smaller version of G1000) along with a GTN650 GPS.

With such a cockpit, even if I have a complete loss of electrical power, backup instuments would still work :

Altitude, Airspeed and Vertical Speed indicator don't require any power to operate ;
So does the slip/skid indicator (a simple ball)
And the Attitude indicator gyro is powered by a vacuum pump, linked to the engine ; it would thus still operate.

In that case I'd be more concerned about the loss of radio / transponder / flaps control / trim than the loss of instruments!

To summarise, Glass Cockpits are designed to avoid the creation of single point of failure, to reduce the risk of complete loss of instruments, thanks to redundant system / backup instruments / displays... And for all-electric planes, I guess backup power supplies!


Can construction of an airport lead to more foggy weather?

The statement is apparently from the Introduction to Airports Design and Operations of
Center for Air Transportation Systems Research at George Mason University.

One form of fog that is formed in airports usually is radiation (or ground) fog. As the flat open surfaces in airport are prone to cooling overnight due to thermal radiation, the air close to the surface is also cooled to the dew point. This reduces the ability of the air to hold moisture, allowing condensation and fog to occur.

One reason for the statement may be that open areas in the airport give up their heat much quicker than urban heat islands, which does not have flat surfaces prone to thermal radiation.


What are the consequences of flying GA without a license (certificate)?

First, if you fly privately without a license can you avoid trouble with the FAA? Yes, if you don't attract attention to yourself.

It's essentially the same as driving a car without a license or insurance: it happens because some people just don't see why they should have to get a license, and it's possible because no one regularly checks every car and every driver. Anecdotally, there are plenty of pilot stories about unlicensed pilots in rural, remote areas who fly out of private strips or small, uncontrolled airports. Alaska in particular is notorious: I've heard the 'joke' several times that the FAA used to have the goal of getting at least 50% of Alaskan pilots certificated.

Second, if you do get caught by the FAA or by law enforcement, what happens? As you said, the FAA can revoke your certificate but state or federal officials can go after you with criminal charges. This is from the criminal indictment of someone who was accused of lying about his pilot's and mechanic's certificates:

  At sentencing he faces a maximum of five years in prison and a
  \$250,000 fine for each of the two criminal counts of making false
  statements to the FAA, and a maximum of three years in prison and a
  \$250,000 fine for each of the three counts of flying without proper
  authorization.

I couldn't find out what happened with that case, though, so I don't know if he was found guilty or not and penalties - if any - he really faced. @mins found another example that did result in a prison sentence.

Finally, there is one legal way to fly in the US without a license: fly an ultralight under part 103.


What are these parts on STOL/bush planes?

Those are not specifically STOL hardware, they are bungee covers that happen to have an airfoil shape.

Aircraft like the one in your picture use bungees (also called "shock cords") to absorb the force of landing: As weight is transferred to the gear the bungees are stretched. The installed bungees look like this:

The bungees are literally just "aviation-grade" bungee cords, and would be quickly deteriorated by weather if left exposed, so they are usually covered. The most basic covering is a leather or plastic boot:

The boots are not much more aerodynamic than the exposed bungees however, so some aircraft (including many with STOL kits) have a cover with an aerodynamically favorable shape to reduce the drag caused by the bungee bulge. That style of cover is what's shown in your picture.
Here's a closer look:


Can a flight instructor without instrument rating legally provide instrument training?

Long story short, a CFI without an instrument rating can provide training on the instrument flying required for a private certificate only. To provide instruction on the use of instruments for an instrument rating, a commercial certificate or an ATP certificate, the CFI must have an instrument rating.

You can read all the details in the Grayson (2010) legal interpretation and the FAA apparently revised 61.195 in 2009 to make this whole topic 'clearer':

  §61.195   Flight instructor limitations and qualifications.

  A person who holds a flight instructor certificate is subject to the
  following limitations:

  [...]

  (c) Instrument rating. A flight instructor may conduct instrument
  training for the issuance of an instrument rating, a type rating not
  limited to VFR, or the instrument training required for commercial
  pilot and airline transport pilot certificates if the following
  requirements are met:

  (1) Except as provided in paragraph (c)(2) of this section, the flight
  instructor must hold an instrument rating appropriate to the aircraft
  used for the instrument training on his or her flight instructor
  certificate [...]

As the interpretation explains, the instrument training requirements for a private certificate are very general (61.107 and 61.109): "basic instrument maneuvers", " control and maneuvering of an airplane solely by reference to instruments". But the commercial and ATP requirements are much more specific (this is from 61.129): "attitude instrument flying, partial panel skills, recovery from unusual flight attitudes, and intercepting and tracking navigational systems". For that reason, CFIs who provide instruction for the private requirements only do not need an instrument rating.

Practically speaking, I've never met a CFI who didn't have an instrument rating. I'm guessing that a CFI without one would have limited value for employers and might even have issues with insurance.


How much aerodynamic heating do jetliners endure?

Based on the formula already shown in this answer, we can calculate the TAT (true air temperature), which is the temperature reached at the stagnation point1, from the SAT (static air temperature) and Mach number:
$$ \frac{\text{TAT}}{\text{SAT}} = 1 + \frac{\gamma - 1}{2} M^2 = 1 + \frac{1}{5} M^2 $$
The resulting plot of TAT vs. Mach number at the SAT of -56.5°C (ISA tropopause) is shown below:

As you can see, a subsonic airliner (I assumed Mach 0.85) will still experience temperatures below freezing. Concorde however was reaching temperatures of around 120°C at cruise speed of Mach 2.02. This was already close to the limit:

Maximum Total Temperature (TMO):  127 Degrees Celsius (on nose)

(Concorde Performance)

As requested in the comments, here is a larger speed range including the SR-71:

The temperature could reach almost 400°C at Mach 3.2 (What is the true top speed of the SR-71?), but note that the SR-71 used fuel to cool the skin (the windscreen was the hottest part at 316°C according to Wikipedia.

1The TAT is measured by the aircraft with a probe that brings the air to rest w.r.t. to the aircraft (stagnation). The kinetic energy of the air is therefore converted into thermal energy, raising the temperature. The surface temperature of the aircraft at points where no stagnation occurs will be at a lower temperature. Thanks to Peter Kämpf for pointing this out.


Has the Boeing 737 MAX MCAS system successfully prevented a stall or approach to stall condition outside testing?

We don't know - until we hear about such a case!

A positive answer would require

a trace of MCAS action
sufficient evidence that the pilot could not have handled the (near) stall without MCAS.

This information could come from

a pilot who

notices the trim interference, and
perceives the situation as dangerous, and
reports the event

or

a flight data recorder that is analyzed, and

corrective MCAS action is found, and
it is evident from the data the pilot(s) did not / could not control the situation.

[ Am I missing any other way how MCAS could leave a trace? ]

A well-trained vigilant pilot can handle (near) stall situations in most cases.

MCAS is designed not only to get out of a stall, but to prevent the airplane from stalling in the first place. That means that
 the plane should never get into a critical stall situation, if MCAS does its preventive work.

All that just to say, it would be possible to answer "yes" as soon as there is knowledge of one averted incident, but it is impossible to conclude "no" from the absence of information.

I am very well aware that I wrote this theoretical answer while sitting in an arm chair, and I will happily remove it as soon as anybody with hands-on knowledge can provide more satisfying information.


Is there any engine that doesn't use a propellant to produce thrust?

Yes there are. Although they are not for commercial aviation. One example are solar powered engines:

Source Wikipedia

Alternatively, there are other means of storing energy - rubber bands, but this one is just for model aitplanes.

Source: Pinterest

But in either case, you need store energy somewhere, and best way is to use oil-based fuels.


Why does a sharp leading edge result in a larger pressure peak?

Envisioning the air flow at 15 degrees AoA is very helpful in understanding the negative pressure distribution on the upper wing.  Smoke in wind tunnels is used so the airflow pattern can be seen.  Yes, it is illogical for a thinner wing to have a higher pressure peak,
but notice the TOTAL negative pressure area of both 4408 and 4415 is very close.

What is going on here is the larger frontal area of the 4415 creates a larger, but not as low pressure bubble at 15 degrees AOA (look at graph) than the 4408.  Try superimposing the two airfoils at 15 degrees angle of attack and also throw in a flat plate too.

Remember, a higher pressure peak does not mean higher total negative pressure.  It means, like @Jan Hudec says, air molecules, which have mass and velocity (inertia), can not turn a sharp corner as easily as a small turn.

Imagine 20 race cars going down the track together.  They will make a small turn together, but if too fast into a very sharp curve, there will be a vacuum peak (lack) of cars on the near side of the turn!


What does it mean to move a single flight control to its full deflection?

Yes, that is correct. Moving any control surface until you hit the stops is considered "full deflection". For the purpose of maneuvering speed, this is the speed at which any single control surface can be fully deflected without risking damage to the control surface or structure.

Pitch is full back/forward on the yoke or stick, which is where the elevator stops movement. This isn't always 90 degrees for ailerons, especially in aircraft that have stick controls versus yokes.


What are the differences between wings made for 2 engines and wings for 4 engines?

The differences are surprisingly small, and the implications of two versus four engines are not very great as far as design of the wing is concerned.

Weight implications

The wing is an immensely strong structure - after all, it's able to bear the weight of the entire aircraft, including of course the engines.

Engines are heavy, but only a small fraction of the weight of the whole aircraft.

A similar aircraft with four engines rather than two will have smaller engines, so the total weight difference will not be large.

Space implications

You need more space to fit two engines on each side, but not a vast amount. For example, the British Aerospace 146 has four remarkably small Lycoming ALF 502 engines. What's more, four small engines can be easier to mount, because they need less ground clearance.

Same wings, more engines

In practice, it's not very difficult to add engines to a wing (for aircraft companies, that is; I don't think I'd be able to do it without seeing someone do it first at least once).

For example, the 747 can optionally carry a fifth engine - obviously, this engine is just being carried, not used, but it shows that simply placing the engine there doesn't present insurmountable aerodynamic or other engineering difficulties.

And then we have the Airbus A330/A340, designed and built in parallel, which are essentially the same aircraft - same fuselage and same wing - one with two engines and one with four. (Actually the -500 and -600 A340 variants do have slightly longer wings, but that's because they are heavier, and nothing to do with the additional engines.)

That's not to say that there are no implications in having additional engines. In this case, wing flutter caused by the outboard engines of the A340 required some stiffening.

And of course, additional engines will require additional fuel and control lines. However, these aren't part of the structure of the wing itself, and are not in themselves likely to have implications for it.


What is the fatigue life of a fuselage based on?

Most (large) aircraft life times are measured in cycles.

  "Aircraft lifespan is established by the manufacturer," explains the
  Federal Aviation Administration's John Petrakis, "and is usually based
  on takeoff and landing cycles. The fuselage is most susceptible to
  fatigue, but the wings are too, especially on short hauls where an
  aircraft goes through pressurization cycles every day." Aircraft used
  on longer flights experience fewer pressurization cycles, and can last
  more than 20 years. "There are 747s out there that are 25 or 30 years
  old," says Petrakis.

But that only applies to pressurized aircraft, there are large planes that are un-pressurized and their life is generally measured in flight hours. However most large aircraft like say the DC-3 don't have any imposed hourly limit on the fuselage but other parts may be hour/life limited.


How does a typical passenger jet come to a stop when it lands

The main components that stops the aircraft are the brakes and spoilers and secondary would be the reverse thrust and flaps.
When a airplane lands it still has some velocity and that velocity still creates lift.
When the spoiler goes up it stops the wing from create lift and sits the plane on the ground, so the brakes have more efficiency.
Some aircrafts would need twice or three times longer runways to stop with the spoiler inop.
As a secondary resource there are the reverse thrust and the flaps, witch when is full down creates more drag than lift and helps the aircraft to stop.


Thanks to the research of the other two answers, I finally found the context for these two photos. They are indeed of Clarence Chamberlin (a contemporary of Lindbergh) and were taken on June 15, 1927 at the Stuttgart-Boeblingen Airfield in Germany. The following page describes the events leading up to the photos, although the original is in German:

https://www.boeblingen.de/,Lde/start/WirtschaftEntwicklung/Chamberlin.html

Long story short, he was attempting to beat Charles Lindbergh on the transatlantic record, but Lindbergh won due to numerous delays. Chamberlin decided to go a little further, to Berlin, and beat the distance record instead. There were numerous technical problems with his plane, however (the Miss Columbia), and he ended up having to land in Eisleben, about 90 miles west of his goal on June 6, 1927. After a day spent repairing the plane, he then proceeded to Berlin. The event seen in the photos is a parade/celebration thrown in his honor as he leaves on the 15th.

By comparison, here's a photo from the same event showing Chamberlin in the same clothes:

I was unable to identify the specific plane behind him in the photos, but it was NOT the Miss Columbia. Due to the many technical problems experienced during the race, Chamberlin elected to return by sea. What we see in the photos is him about to board a passenger plane that will take him to the ship. As far as I can tell, the Miss Columbia was shipped back separately, although his co-pilot (and the plane's owner) Charles Levine wanted to fly it back despite the problems.

What About the Plane Type?

The plane that Chamberlin is boarding in the photos looks to be a Dornier Mercury, which was a common passenger plane in Germany at the time. The door size/shape and top of the plane (what we can see, at least) match up quite nicely. Here's a shot of one from a similar angle:

Thanks to @TomMcW for finding that.


How does CDI work when flying to VOR without DME?

The VOR and ILS CDI indicates difference, in degrees, between the radial selected and the radial sensed.

If the plane was far from the VOR and we turn the course pointer 5 degrees, the CDI will move to one side. If the plane was close to the VOR and we turned the course pointer 5 degrees, the CDI would move exactly as much, because it indicates the angular difference in degrees.

This is in contrast to a CDI slaved to GPS, which indeed indicates lateral distance from the selected track in miles (en-route; GPS approach has to simulate ILS).

VOR does nothing with DME. DME is completely independent piece of equipment that was introduced later than VOR. The only relation is that there is a standard correspondence between VOR and DME channels and the DME receiver automatically tunes to the DME frequency corresponding to the VOR or ILS frequency tuned on your VOR/ILS receiver.


Can an aircraft operate IFR without ground-based navigation?

The AIM contains the information required to operate under IFR using GPS1.

To summarize the requirements,  WAAS (but not "traditional" GPS) may be used stand-alone without an alternate means of navigation provided:

Installation requirements:

The WAAS navigation equipment is approved in accordance with TSOC145 or TSOC146
The installation is done in accordance with AC 20-138

Operational Requirements:

The WAAS AFM procedures are followed
It is not be used by a commercial operator

Preflight Requirements:

The GPS database is current
The GPS database provider does not have any notices prohibiting the use of any fix or procedure that you are going to use
GPS NOTAMs/Aeronautical Information is reviewed prior to each flight
A RAIM prediction for the time and route is done that shows no loss of RAIM
The flight plan navigation equipment is listed as RNAV

Note that commercial operators are required to have redundant systems or ground based backups in order to use it, and while not required for you, it's a pretty good idea.

1 More specifically, see:

AIM Chapter 1, Section 1 - Navigation Aids

1-1-18. Global Positioning System (GPS)

d. General Requirements
e. Use of GPS for IFR Oceanic, Domestic En Route, Terminal Area, and Approach
Operations
f. General Database Requirements

1-1-19. Wide Area Augmentation System (WAAS)

c. General Requirements


Listening to KSEA, what does orange, green, or blue line mean?

If Seattle works anything like a number of major German airports, these instructions refer to literal coloured lines on the ground.

Taxiway markings are usually yellow, but some large airports have started to use different colours for marking taxilanes on the apron ("ramp"). This is a way of maximizing use of available space in areas used by many differently sized aircraft.

One example is Munich, Germany (EDDM) where yellow, orange and blue taxi lines are used.

(snippet from APDC EDDM, from DFS)

Two medium sized aircraft can pass eachother when following the blue and orange lines, whereas a larger aircraft will have to follow the central yellow line, thus taking up the entire width of the taxiway.

As @ymb1 pointed out in a comment, the system in KSEA appears to be similar. The colour of the taxilines are varied, and signs (or markings on the ground) describe the colour code for certain taxi lines:


What is the best way to keep logbook entries backed up?

The FAA requirements are for the information to be logged, without specifying the details of how it is logged.

It's OK to use electronic log books, and multiple log books. Scanned images are as good as photocopies. Just print them if you ever need them on paper. Some items are required to be signed, so scanned signatures and endorsements may be necessary in an electronic logbook.

The older the information, the less its importance. Log books are normally examined to see if what you're doing is legal, checking ratings, currency, training and reviews, etc. If you are flying without required night or IFR currency, for example, it is conceivable that they'd want to check previous flights to see how often that has happened in the past.

An insurance company might want to make sure you've got the hours you claim, but the FAA's interest is to see if you are legal.


Why would a propeller have blades of different lengths?

You are right.  They are unequal length blades.  Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub.  And obviously, the blades will be mass balanced to place the center of gravity at the hub axis.

I'll go out on a limb here and say that some genius figured out a way to reduce the horrific noise level caused by such a small propeller by having the blade tips each run in a slightly different path of rotation.  Brilliant.

And here it is in action where the eccentric blade disc can be clearly seen.


Could modern unmodified Airbus aircraft be used for zero-G flight?

According to this source and this source, the relevant A320 control laws (CLAWS) limitations are:

Normal load factor limitation in clean configuration down to -1g
Nose down pitch attitude down to -15deg
High Speed Protection (HSP) to prevent exceeding VD/MD

The problematic one would be the pitch attitude limiting. Since the pitch attitude will keep decreasing at zero G, the limiting function will pull the aircraft up and increase the load factor after some point. This could limit the time in zero G below the requirement.

Given the constraints and objective, more analysis would be needed to ascertain whether aircraft in Normal Mode is acceptable.


Does an aircraft equipment suffix denote how many VOR radios are installed?

If you look at the AIM TBL 5−1−3 Aircraft Equipment Suffixes it is split into two parts. The first part has the codes for RVSM which don’t apply to you since I presume you aren’t flying above FL 290. The second part doesn’t mention VORs at all, presumably because historically VOR and DME were almost always used together for IFR navigation. So ATC doesn’t know if you have any VORs based on your equipment suffix. However, if you use /A then they would assume you have VOR capability.

If you have a GPS installed in your plane, then you would be a /G and ATC would know that they can give you an RNAV approach. If you have a GPS installed, then you can use it in lieu of DME. The footnote to Table 1-1-6 gives the conditions when it is applicable.

  3 Requires current database or verification that the procedure has not
  been amended since the expiration of the database.

ATC wouldn’t know if your database is current, so it is up to you to accept or reject the clearance.

AOPA has a good article describing when you can use GPS in lieu of ADF and DME.

There is also a StackExchange question that discusses it as well.


The equation refers to instantaneous thrust in unaccelerated flight. The weight in this equation is instantaneous weight.
Indeed, this weight changes over time. This is for example the reason we have to use the  Breguet range equation instead of just divide thrust by thrust specific fuel consumption to calculate the range of an aircraft.


Are there regulations for unmanned aerial systems avionics?

The flight control software on military grade UAV/UAS has DO-178/DO-254 requirements, per briefings I attended, and also that software provided for embedding in those had to meet those and other requirements.

I am not an expert on the UAS platform we used (Global Hawk RQ-4) but it is safe to say that it is a complex bird with multiple capabilities. A typical mission flight crew consisted of a launch and recovery pilot, and mission pilots and sensor operators, in sufficient numbers to handle extended missions.

I am unaware of any consumer grade UAS utilizing those standards, and doubt there are many, if any at all, due to the increased development cost. I am unaware of any type certificated sUAS.

To give you an example, I had a certain nav sensor related function integrated for VFR use on a sensor platform (Twin Otter).  The development cost was about 4.5 million. If we were to apply the standards so that we could operate that platform in an IFR environment, the estimated cost was about 9.5 to 11 million.  Sure there were just a few additional capabilities, but a big part of it was systems engineering and test.


Do ANR headsets affect pilots' perception of engine problems?

Although its possible to detect engine problems audibly, I don't think that's the primary mechanism (except for engine out) by which pilots are expected to detect engine anomalies. Part 91.205 requires that every aircraft be equipped with the following instrumentation, and these should be the primary mechanism by which engine malfunctions are detected.

  (4) Tachometer for each engine.

  (5) Oil pressure gauge for each engine using pressure system.

  (6) Temperature gauge for each liquid-cooled engine.

  (7) Oil temperature gauge for each air-cooled engine.

  (8) Manifold pressure gauge for each altitude engine.

  (9) Fuel gauge indicating the quantity of fuel in each tank.

That being said, ANR headsets attenuate sound, but don't eliminate it entirely. Having flown with an ANR headset for most of my flying career, I can certainly hear variations in engine noise in the mag check and prop exercise during the runup, as well as during throttle and prop changes. I can also hear a fouled plug during runup, as well as verifying it visually on the gauges.


Could the Mars helicopter Ingenuity have been test-flown outdoors at JPL just for the heck of it? (not that they would)

No, Ingenuity was too heavy and underpowered to fly while on Earth.
From 27:30 to 29:00 in the video of a 2021 May 13 press event, one of its designers, Matt Keennon, manually pilots what he called a "terrestrial version of Ingenuity,"  officially named Earth Copter, nicknamed Teri or Terry.  (Reporters have had to guess at the spelling.  The transcript of a 60 minutes segment has Terry, but that neglects I for Ingenuity.)
At 24:45 Matt explains that its only significant hardware differences compared to Ingenuity are that it is lighter (he doesn't say how much), and that its motors are taller, with twice the torque.  Aerovironment hasn't published any hard numbers about Terry, or possibly even any text at all since even its name remains disputed.
But it's clear that they designed Terry to closely mimic how Ingenuity would fly on Mars (see the section "Iterations" in Inside Ingenuity With AeroVironment), so they wouldn't have lightened it and used much more powerful motors for capricious reasons.  It had to actually fly.  A direct quote from Matt at 24:45:

We also reduced the weight of Terry compared to Ingenuity because it's flying in Earth's gravity.

Co-designer Ben Pipenberg also says:

Terry is designed to fly here on Earth, so the motors were redesigned and are more powerful and have a higher torque to handle the denser atmosphere and the higher gravity.


Proportionally, what is more affected by a hot and high takeoff - a electrically driven propeller or a turbofan?

Is this assumption correct?

Generally, yes. However, specific combinations of powerplant and propeller might make that difference moot.


Did every X-15 pilot become weightless when flying into the upper strato- and mesosphere?

Yes they did. Take away both rocket thrust and wing lift, and the plane goes into free fall. In this condition everything on board becomes weightless.
The pilot would feel only the light bursts of thrust from the small manoeuvring rockets, and the slow return of aerodynamic lift during re-entry.
You don't even need to go into outer space; check out the vomit comets used to train astronauts.


Is roll control achieved exclusively with spoilers on an A320 on final approach?

Downward aileron travel must be restricted when flaps are deflected. Since flaps change the local incidence on the flapped part of the wing, the outer wing will experience an increase in its local angle of attack. The increased suction over the inner wing will accelerate not only the air flowing over the inner wing, but also that air which will flow over the outer wing as well. Left to itself, the outer wing would stall if powerful Fowler flaps are deployed on the inner wing.

Adding slats will push the stall angle of attack up, and now the outer wing is back in business. However, if the aileron is deflected downwards, the stall angle of attack is reduced again. The outer wing could stall simply due to the aileron deflection!

I do not need to point out that an asymmetric stall on approach is extremely undesirable.

Now roll control could still be achieved by only moving one aileron upwards. But this would decrease the induced drag at the wingtip at low speed. Remember, at low speed the induced drag is dominant (it is proportional to the inverse of the flight speed squared), so the drag change due to an aileron deflection will cause an inverse yawing moment at a time when the pilot wants to keep the aircraft lined up with the runway.

Using the spoilers instead will incur a higher lift loss for the same rolling moment, but will also increase local drag, which creates a helpful yawing moment into the opposite direction of the one created by upward aileron deflection. Also, the change in local lift from spoiler deflection is much greater once the flaps are fully deployed. This means that spoilers are much more effective for roll control in the landing configuration than in the take-off or cruise configurations.

THAT's why spoilers are preferred for roll control on approach. I am surprised, however, that you observed no aileron motion at all. Normally, the ailerons are still used, but with a much restricted travel range, as @DeltaLima mentions in his answer.


What is missing from a non-afterburning engine to prohibit the use of afterburning?

The afterburner, of course.

In simplest sense, the afterburner is just an extension attached to the engine where the fuel is dumped into the exhaust, resulting in an inefficient but huge increase in thrust.

Turbojet with and without afterburner; image from aerospaceweb.org

In the above image, you can see the basic schematic of the afterburner- it basically consists of a long tube placed in between the turbine and the nozzle in which additional fuel is added and burned. The (afterburner) tube is quite simple, consisting of mechanisms to spray fuel into the exhaust and ignite it.

This image shows an actual afterburner, from the F/A -18 (F404 engine). As you can see, its quite simple.

... sailor Ryan Draper ... inspects an F/A-18 afterburner in the jet shop aboard the Nimitz-class aircraft carrier USS George Washington (CVN 73). Image from gizmodo.com


What's the pilot's typical reaction time to co-pilot's callouts?

The best research on this is done with real crews & expensive simulators, and I think their results are exactly the proposition you're looking at, namely that the callout "V1" needs to be said something like a second or two before the actual latest-point-of-first-action to reject the takeoff.

The reason that we can't just say, how long does it take me to respond to the other pilot's callout routinely is, it's a different world between the routine stuff and the abort decision close to V1.  As an example, if I'm flying an approach, I know when the callout 100 feet above minimums is coming.  If I'm not badly tunnel-vision on some isolated part of my scan (very, very rare when you're at that point in an approach... not impossible but quite rare), I can see the altimeter unwinding toward the minimums bug, and so when the other pilot makes the callout, I'm ready to reply "going outside."  And I know that a few moments after that, he's going to call out "minimums" and I have my next callout to make.  No surprises, and if you measured how promptly I respond to his callouts, you'll probably get results showing that I'm pretty prompt.

Compare that with the one takeoff in thousands where things are getting weird close to V1, and I'm actually processing the "is this actually worth stopping for now that we're high speed" decision. I've never had to do that in the actual aircraft, but talking to guys who have, there is some very real time compression -- events happen fast. On a normal takeoff, I'm almost always aware of exactly when the "V1" callout is coming.  But if it is "that dark & stormy night" and I'm trying to sort out the difference between fluxing indication, minor burp, or beginning of an engine failure, that will be the time when the "V1" call WILL catch me by surprise, and how quickly I react to it & remove my hand from the throttles may not correlate to how quickly I've taken it off during the last 999 takeoffs.

On a normal takeoff, my habit is a fairly spring-loaded motion where my hand comes up and away from the throttles immediately at the "V1" call, so that if we get the proverbial big bang, lotsa yaw, and the fire bell right after the callout, I'd be able to catch myself & not go reaching back toward the throttles to initiate an abort-after-V1.  So on those days, you might could get away with pushing the callout closer in time to the latest-first-action-to-stop point.  But not every day is going to be like that, so the Boeing procedures build in the greater level of reaction time.

Because taking the aircraft flying even when you had another second or two that you could have stopped it, is generally (looking at the historical track record of takeoffs rejected & takeoffs continued) less dangerous than stopping the aircraft a couple of seconds after you shouldn't have.

References:

Boeing Article
Boeing Slides - 2002 Presentation This has some good time numbers for you


Can you file an open-ended IFR flight plan?

If operating within a single area (TRACON) then file from KABC -> KABC and in remarks put "Practice APCHS KXYZ KDEF".  The controller will be asking you what your next approach will be at some point.
Another tactic is to file to ABC VOR (or some other fix) and request a hold. I like this method, as the student gets a hold with an EFC and that gives me time to decide how many orbits they will need as well as the next approach request. I normally have the student ask for the next approach, as it keeps their workload up.
The first suggestion is generally preferred because in the event of lost com, in a true IMC environment, it is clear that you will be returning to KABC, unless you encounter VFR first.
Remember that an IFR clearance can end at a fix (even a pilot defined fix) and when you are in VMC that can be useful. Similarly, an IFR clearance can begin at a fix, and that can be accomplished in a non-radar environment.
Addendum #1
Frequently this type of plan is often referred to as a tower clearance, or if it spans TRACONs it may be called a tower-to-tower.  However, where there are no local approach facilities, center handles this type of clearance as well. Other than just normal approach practice, an area clearance is used to permit photographic missions with cloud cover and instrument student experience with lake effect icing.  For example, a photographer wanted photos of a water fall, through an opening in the clouds.  We got on top, stayed IFR, and maneuvered for his shots.


How much thrust is lost due to the bleed air system?

For the Boeing 737-800:
Bleeds off:

If bleed air is turned off, it gives ~1% N1 increase. This higher N1 also means a 1 or 2 knot faster $V_1$ and/or $V_{mcg}$. Bleeds on adds about a 2.5-tonne correction to the gross weight.

For the various anti-ice:

The penalty can be as high as 5% N1. Note the single- and dual-sources figures. Dual means APU is running and is providing bleed air.
Exact loss in thrust (force)
That will be very hard to calculate without test bed data from the engine maker. Not to mention it varies with the different elements: pressure altitude, temperature, forward speed, etc. That's why I included the V1 and weight impacts.
Based on the graph below, 1% N1 at high takeoff power equates to about 2.4% of total thrust. That should be treated as a ballpark figure.
(Source)
In cruise however, having all anti-ice on might warrant flying lower due to the decreased thrust.
Other uses and alternatives
Bleed air used for cooling the turbine blades for example, helps increase thrust, not decrease, as the burners can run hotter without damaging the turbines.
The "all-electric" Boeing 787 uses bleed air for engine anti-ice. Using the generator to run the other anti-ice elements also reduces the thrust due to the shaft off-take. But, there is the benefit of weight reduction.


What is the stall speed for the Dassault Rafale?

80 knots for an aggressive pilot, as said here.

It is 148 km/h, a speed of fast but rather typical long range passenger train. No new technology is required for the train, this plane could easily follow a Pacific steam locomotive (top speed 203 km/h).


What is the weight at which an aircraft no longer requires a licensed pilot on board in Europe?

The aircraft weight needs to be 70 kg or less. FlyNano mentioned this on their FAQs page (my paraphrasing):

  Do I need a pilot's license to operate FlyNano?

  According to the European Aviation Safety Association regulation
  ... FlyNano is below the necessary weight of 70kg ... In Finland for
  example no classification, no aviation license or medical
  certification are needed. But skill is needed. Nevertheless a good
  understanding of water plane operation, rules and aviation safety is
  requested. ...

I found that any aircraft less than 70kg is not affected by EASA regulations. But regardless, and emphasized by FlyNano also, pilot skills are required.


Does runway center lighting increase runway lifetime?

No, runway centreline lights do not increase runway lifetime, and it is not their purpose to do so.


What does two 'high-low' chimes in the cabin of a 737-800 mean?

As far as I know, the chimes work the same on all 737 NG (and Classic) versions, although as was mentioned in comments, how they are employed will vary from airline to airline.

The two tone "high-low" chime described in the OP is the "crew call" system. The pilots have a button, the forward F/A station has one, and the aft F/A station has one.  Regardless of which button is pushed, the "hi-low" chime is the same.  In many, though not all, cases, this chime is a signal to the F/A's to answer the interphone.  If the pilots press their button, they're asking to speak to the F/A's; if one F/A station presses the button, they're asking to speak to the other F/A station.  (They can also press a different button that calls the cockpit, but passengers won't hear that chime. In the cockpit, we hear that "call" as the two-tone chime; we don't hear the chimes in the cabin unless we're listening to PA audio.)

At one carrier, a single high-low chime may mean "answer the interphone," while at another carrier, one chime might be used to mean "secure the cabin" while two chimes is "answer the interphone," three chimes is "answer the interphone - urgent," and so on.

You'll also hear chimes when the F/A Call Button above a passenger row is pressed; this is a distinct chime (a single, relatively high note).  There is also a chime when the Fasten Seatbelt sign is turned on or off, this is again distinctive, a single lower note.

Note that you won't necessarily hear the chimes when the interphone is in use; it's simply a "Hey!" call to the Flight Attendants in the cabin.  While it's often followed by a conversation on the interphone, they two are separate systems and one can be used without the other.


Why do turbofan jets fly faster in cold weather?

They don't. They fly slower.

Most aerodynamic effects depend on dynamic pressure. More precisely, lift is proportional to dynamic pressure and drag has parasitic component, which is proportional to dynamic pressure, and induced component, which is inversely proportional.
Therefore there is an optimal dynamic pressure at which the aircraft flies most efficiently, and minimal dynamic pressure needed to maintain flight.

Now dynamic pressure is (half of) air density times velocity squared ($q = ½\varrho v^2$) and due to its significance the “indicated airspeed” shown in cockpit actually corresponds to dynamic pressure expressed as equivalent airspeed. All the desired speeds for various phases of flight are referenced to that.

Since cold air is denser, the same dynamic pressure will occur at lower velocity, and because the pilot will maintain the same indicated airspeed, they will actually fly slower.

One more thing: the maximum speed is one of the few exceptions that is not dependent on the dynamic pressure. There are three effects that may limit maximum speed:

Aeroelastic flutter depends on true airspeed (velocity), so the temperature does not, actually, have an effect on it. However because true airspeed is not usually indicated in cockpit, the pilots will use tabulated indicated airspeed values and since these are only tabulated for altitude, they will actually fly slower.
Mach tuck i.e. loss of lift, accompanied with undesirable change in trim, due to exceeding critical Mach number. Since speed of sound increases with temperature, critical Mach number corresponds to lower true airspeed (velocity) in colder weather, so they'll fly slower again.
Engine power. Engines are able to produce more power in colder weather due to being able to achieve higher mass flow with the higher density air. However, engine power is limiting factor mainly for smaller general aviation aircraft, which have low power engines, or fighters at the other end of the performance spectrum, which are designed to fly supersonic and resist flutter. But transport category aircraft generally hit the other two limits first.

Original answer for the version before the reason they fly at higher altitude was explicitly excluded from the question:

There are two, distinct, effects:

Aircraft fly faster at high altitude due to the lower air density. This is because both lift and drag are proportional to air density. So at higher altitude, the plane both have to fly faster to generate enough lift, and can do it because the drag is lower.

More precisely, lift is proportional to dynamic pressure and drag has parasitic component, which is proportional to dynamic pressure, and induced component, which is inversely proportional.

Therefore there is optimal value of dynamic pressure where the drag is lowest. The optimal cruise speed is slightly above this point. Since dynamic pressure is proportional to density and square of speed, the same dynamic pressure corresponds to higher true airspeed at higher altitude.

Dynamic pressure is usually expressed as equivalent airspeed, which is the speed to which current dynamic pressure would correspond at sea level. The indicated airspeed shown on the instruments is approximation of this value.
Heat engines are more efficient at lower temperatures. This is because efficiency of a heat engine (applies equally to both piston and turbine engines and both internal combustion and external combustion (steam) ones) depends on the ratio of temperature, but the combustion increases the temperature by the same (approximately) difference. So if the starting temperature is lower, the ratio is higher and the engines produce slightly more power for the same fuel flow.

Additionally, the maximum temperature is often limited by what the materials can withstand, so at higher altitude the engine can be operated at higher power (well, not really; the power is also proportional to the density, but the engine will again run more efficiently).


Is there any regulation that force(or recommend) to change flight number in case of flight delay?

An airline's flight number for commercial purposes is not necessarily the same as the identifier the aircraft uses for air traffic control purposes. For example, British Airways flight may show up on a flight tracking web service as BA### but air traffic control identifies them as "Speedbird ####" where the number may or may not be the same as the airline's commercial flight number.

So, to answer your question, there is no FAA regulation that forces the airline to change commercial identifiers. The ATC identifiers are set when the dispatcher files the flight plan, and they must be unique to ATC. The system will reject it if the identifier is in use, or will be during any period of flight.


What is typical thrust to braking force ratio for a passenger airliner?

If we assume that the braking system is designed to leave no unused braking capacity, the maximum braking deceleration is determined by the friction coefficient of the tyres. This NASA report gives a friction coefficient of around 0.5, for dry concrete with a functioning anti-skid system. This results in maximum braking deceleration of 0.5 g, around 5 $m/s^2$

A typical maximum thrust acceleration would occur for a typical airliner, at TO thrust, and medium range TO weight. Let's take typical numbers for an A320:

A320: TO thrust = 2 * 120 = 240 kN, TO weight = 70,000 kg, a = F/m = 240/70 = 3.5 $m/s^2$
B777: TO thrust = 2 * 500 = 1000 kN, weight = 300,000 kg, a = 1000/300 = 3.3 $m/s^2$
Fokker 100: TO thrust = 2 * 67 = 134 kN, weight = 40,000 kg, a = 134/40 = 3.35 $m/s^2$

So across the board, the braking-to-thrust force ratio is around 5/3.3 = 1.5.