May an emergency aircraft land on a closed runway?

Preflight Planning

  Let's say that you're on approach to a remote airport to refuel, with
  1-2 hours of fuel remaining in your aircraft. ...

  The nearest airport is 3-4 hours away...

First of all, it looks as if the pilot has already broken several regulations in order to end up in this situation.  He either didn't file an alternate, or if he did then he didn't carry enough fuel to get to it (and additional reserves as required).  If the runway is closed for an extended period of time, there would likely have been a NOTAM stating that the runway would be closed.  All of this sounds like poor preflight planning, and probably the 'ole careless and reckless thrown in for good measure.

The Problem

  Contacting ATC to request permission to land, they tell you that the only runway is
  closed for an unspecified reason and will not reopen for ~2 hours.

Okay, we need to figure out what the "unspecified reason" is because this can change things dramatically.

Is it for endangered migrating turtles?

Is it for construction?

In any case, he needs to use all available resources.  Talk to ATC and explain the situation. Ask them how they can help clear the runway so that we can land.  He should tell them that an emergency is imminent without their assistance.  They will do everything that they can to help you, including coordinating with people on the ground to get out of the way.  Be creative.  Did you know that there is no regulation (in the US) requiring you to land on an actual runway?  Ask them if you can land on the taxiway.  For that matter, land in the grass beside the runway.  It would be better than going for a swim or crashing after running out of gas!

  Let's presume the airport is surrounded by ocean, and the aircraft is not certified for ditching.

Ummm, who cares if it is certified for ditching?  If you are over water, it doesn't matter.  If you are over land, it doesn't matter.  If you have a choice, pick land (even if it's off-airport).

  Supposing ATC refuse to reopen the runway, is the pilot permitted to land anyway?

Well, they wouldn't really do this unless there was a really good reason, mainly meaning that it would be dangerous for the aircraft to land there (like in the second picture above).  In this case, we can't really ignore ATC and land anyway until:

Declaring the Emergency

  ...so you choose to hold, hoping the runway is soon reopened. After
  waiting a while, the runway is still not reopened, so you declare an
  emergency.

At least our poor pilot did this right.  Rather than blindly continuing to hold, he declared an emergency.

Getting on the Ground

Now we have a lot more latitude and options, and ATC is better able to help us because they can pretty much do whatever it takes to save the aircraft.  This can change a "Sorry, there is nothing I can do." into a "Cleared to land any runway or taxiway." all on its own. They may throw in a "Landing at your own risk." if there are still hazards, but that's just to clear them of liability.  Even if they still refuse, you can simply advise them of what you will be doing and go ahead and do it.  Keep in mind however, that it may be better to scope out an off-airport landing site if the danger is so great that ATC won't allow you to land even under such dire circumstances.

Remember, the pilot is the final authority for safe operation of the aircraft.  Get on the ground and sort it out after the fact. (Poor turtles....)

In the end, just do what you can to stay alive, and preferably use the airplane again.  There are going to be tons of questions and probably major legal battles.  Someone will probably go after the pilot's certificate.  On the bright side, he will be around to actually see it happen though.


Do airlines have to get permission from the FAA if they want to change their livery?

Not the FAA, but the manufacturer.

If the parts are composite, only a small range of colors may be approved, depending on the glass transition temperature of the resin matrix. For gliders, only white is allowed for most of the surface area, and similarly composite parts of airliners must be painted in a light color so they don't heat up too much in sunlight. Curiously, the lower surface has the most restrictions, because here the reflected light from a concrete surface and the restricted ventilation create the highest surface temperatures.

Next, the UV absorption capability, moisture protection characteristics and the chemical stability of the paint when in contact with aviation fuel, hydraulic fluids, de-icing fluids and other solvents is important. Composite gliders must use a special topcoat which is more brittle than the composite structure, so cracks will show up. Airliners may use more flexible paints, but must then undergo regular inspections of their composite parts.

Metal surfaces are less demanding and can be painted in any color. Only the area in front of the windshield should be dark enough to reduce glare and irritating reflections.


What are the qualifications for a small airport manager?

There are no formal qualifications required to be an airport manager -- it's not a "regulated professional field" in the same way as Doctors, Lawyers, or Professional Engineers.  If a person had the money they could purchase an airport and name themselves "airport manager" of their own facility.

That said, managing an airport has an interesting set of challenges and could probably be described as like being the mayor of a small city with its own road infrastructure (runways, taxiways, and ramp areas), snow removal services, business districts (FBOs, restaurants, & other tenants), municipal services (ARFF), and utilities (airport lighting, fuel farms, drainage systems). The airport manager will also have to interface with federal agencies: The FAA/DOT at a minimum, and likely also the EPA and Homeland Security (TSA/CBP). Working with the local municipality and dealing with local residents on matters like noise abatement is also usually part of the job.
In many ways "airport manager" is as much a political position as an operational one.

Because of the unique challenges involved in managing an airport there are degree programs specifically focused on airport management, and preference will probably be given to applicants with those degrees. Alternatively relevant operational experience (either from running an airport elsewhere or from working in other municipal departments within the county) might be enough to deem a candidate qualified.
There are also professional organizations for airport executives/managers which offer independent certification for individuals.

As a pilot I would say it's advantageous for an airport manager to be a pilot (and in the case of a small airport like the one you describe it would be helpful if they were an active pilot), but being a pilot doesn't really qualify a person in any of the other key operational areas - snow removal, runway maintenance, emergency response, etc. - so while experience as a pilot or controller might be helpful in that it imparts a greater understanding of the operational impact of certain decisions it would likely be viewed as a secondary qualification.


Why don't contra-rotating propeller configurations with more than two propellers exist?

No, stacking more propellers will reduce efficiency. The case with two is an exception because the second propeller benefits from operating in the slipstream of the first. In total, both propellers accelerate the air backwards without adding swirl losses.

However, propeller efficiency goes down with increasing flow speed ahead of the propeller. This means that every other propeller operating in the accelerated flow of a preceding propeller will have lower efficiency. Generally, it will be better to spread the propellers out sideways than to put them in line.

Note that contra-rotating props are the exclusive realm of very powerful engines with very high disk loading. The most recent designs prefer to use more blades and avoid the heavy gearbox, but the efficiency of such props is poorer than that of propellers with lower disk loading and fewer blades. In a way, the efficiency of the eight-bladed propellers below is similar to that of four two-bladed propellers in sequence, but it is much easier to build with all blades and their pitch mechanism in one hub.

T-56 engines with Hamilton-Sundstrand NP2000 propellers on an LC-130. Photograph by Robyn Waserman, National Science Foundation (Date Taken: November 21, 2008)


How does a CVR / FDR determine when to stop recording?

The CVR and FDR have impact switches to stop recording when they experience high acceleration. In incidents and accidents that don't involve high enough acceleration, the plane remains intact enough for the boxes to be immediately found and switched off manually. In more serious crashes, the boxes stop recording because of the physical destruction of everything but the memory units (only the memory units are built to survive crashes).


How does a horizontal situation indicator (HSI) work?

Your understanding is partly right. Usually HSI indicators are associated with a slaving transmitter that includes the flux gate (the magnetic sensor), but also other elements such the directional gyro unit and a slaving control.

So a typical system will usually include the below components (there are different designs, so check the characteristics of the equipment in your aircraft):

The Horizontal Situation Indicator (HSI) is the panel mounted cockpit indicator that provides a comprehensive display including usually at least heading, course, and glide scope. The heading indicator of the HSI is a remote indicating compass that gets its information from a remote slaving transmitter.
The magnetic slaving transmitter includes the flux gate that is the magnetic sensor itself, and some electronics to send the heading information to the directional gyro and HSI. This transmitter and its associated flux gate is usually located in a wingtip to minimize as much as possible magnetic interference.
a directional gyro unit that is usually remote mounted. It is using its internal gyroscope to keep and provide a stable heading reference during turns. This gyro unit is driven/slaved to the slaving transmitter.
The slaving control is panel mounted and allows to selected either "slaved gyro" or "free gyro" mode. Usually, the system is in "slaved gyro" mode and will be slaved automatically. In "free gyro" mode, a slaving meter indicator displays the difference between indicator display and earth's magnetic field, and it is possible to align manually the switch using clockwise or counterclockwise buttons.

The manual of the Bendix-King KCS 55A provides a good introduction to HSI design and operation.


Why increase the number of cylinders in an engine instead of increasing their volume?

Constraints
Different applications have different constraints:

Aviation: very light weight, highly reliable
Marine: very high endurance
Automotive: moderately light weight, responsive
Motorcycle: very light weight, very compact, very responsive

Different technology ages yield different solutions due to additional constraints, always limited by the then contemporary technology:

Pioneer era: make it work
World War I/II era: as fast as possible
Post-war era: further, faster, better
Fuel crisis era: as efficient as possible

Aircraft Engines
The question is about the optimization of number of cylinders versus displacement volume per cylinder for engines used for aviation. This narrows the scope to “internal combustion reciprocating piston engines” (plus the Wankel engine as a very special case).
Obviously, rockets, pulse jets, turbine-powered,  and electric engines have no cylinders, and steam engines were never  (successfully) used in aircraft.
Number of cylinders and the cylinder displacement are two out of countless parameters that go into the design of any engine. Both may be used to increase the power output.
Power Increase
The power output of an engine may be increased either through the number of cylinder or through increasing the cylinder displacement (or both).
Each change of parameters causes the gain or loss of certain wanted characteristics. These are listed further below under (N), (n), (D), and (d).

Increasing the number of cylinders means gaining (N) and losing (n)
increasing the cylinder displacement means gaining (D) and losing (d)

Adding cylinders is easier than increasing the size of the cylinder. The cylinder geometry does not change. Identical engine parts can be used multiple times in the same engine design (cylinder banks, cylinder heads, or complete engine blocks).
Tradeoff shift
Starting from one engine configuration, the same power output may be achieved by

gaining (N) and (d), and losing (n) and (D)
or
gaining (n) and (D), and losing (N) and (d).

Reasons to increase the number of cylinders (N)

Torque directly scales with the number of cylinders
Increasing the surface-to-volume ratio is advantageous for air-cooled engines
Increase the power: Adding cylinders is easier than increasing the size of the cylinder. The cylinder geometry does not change. Identical engine parts can be used multiple times in the same engine design (cylinder banks, cylinder heads, or complete engine blocks)
Improve balancing of forces and momenta
Reduce the time between power strokes
Decrease the impact of a failing cylinder
Improve the flatness of the torque distribution over revolution speed.
Enable more flexible and more distributed form factor

 Pratt & Whitney R-4360 Wasp Major, 28-cylinder, 28 l, 3500 hp, 2700 rpm, built 1944-1955.
Reasons to decrease the number of cylinders (n)

Simplicity: less moving parts improve robustness,  decrease the need for service, thereby increase the availability.
Enable a more compact form factor

Mercedes 1 cylinder, 1.5 kW, 720 rpm, 84 kg, built 1888.
Reasons to increase the cylinder displacement (D)

Increase power through torque

BMW IIIa, 6-cylinder, 19.1 l, 200 hp, 1400 rpm, built 1917.
Reasons to decrease the cylinder displacement (d)

Smaller displacement means smaller pistons, shorter rods, or both. Either way,  smaller displacement allows for higher revolution speed, and higher acceleration.
Smaller combustion chamber will decrease the time required for the flame expansion (gasoline only, not diesel). This allows for higher revolution speed.
The valves are limiting the gas stream into and out of the cylinder. The valves are subject to the surface-volume ratio. Smaller cylinders are easier to fill and empty through the valves, allowing for higher revolution speed.
At a given compression rate, smaller cylinders have to withstand less total force, allowing for a lighter engine structure (less weight).

JPX PUL 212, 1 cylinder, 212 cm³, 11 kW, 6000 rpm.

Notes

Radial engines belong to the WW I/II era. Most of them were air-cooled. For air-cooled engines, the surface-to-volume ratio matters. Therefore increasing the number of cylinders instead of the displacement per cylinder is obvious.

Aircraft during WW I/II had to be as fast and powerful as possible to attack and defend. There was no good reason to go for less than 6 cylinders.

Four-stroke engines perfectly work with 1, 2 and 3 cylinders. They are used powered paragliders respectively ultralight aircraft.

Certain cylinder numbers are more preferable to due symmetry reasons

6, 8, 4 for in-line engines
odd numbers (per row) for radial engines

Building radial engines with an even number of cylinders is well possible, albeit an even number in one row us not preferable. Multi-row radial engines with even cylinder number have been flown in many aircraft.

Automotive engine developers prefer 0.5 l per cylinder as ideal trade-off.

A high cylinder count would be necessary to build high power piston engines, but this segment is now occupied by jet engines.

Radial engines with less than 5 cylinders exist. Here is a radial 3-cylinder, built 1930 in the USA:


What is a Simultaneous Offset Instrument Approach (SOIA)?

SOIA (Simultaneous Offset Instrument Approaches) allow airports with parallel runways that are 750 to 3000 feet apart to conduct (almost) simultaneous approaches to the two runways. At an airport, one runway uses the ILS PRM approach, while the other runway uses an offset LDA PRM approach (with glideslope). SOIA refers to the LDA PRM approach, where another aircraft is flying the ILS PRM approach ahead. PRM stands for Precision Runway Monitor, which is a high-update radar system allowing for "equivalent" safety with reduced margins.

For a PRM approach is conducted, there must be two frequencies per runway:

a primary frequency for both the transmission and receipt of instructions
a "monitor" frequency, only for ATC to transmit on

The reason for the "monitor" frequency is just in case the primary frequency is blocked and breakout instructions have to be provided. The tower controller will communicate to aircraft on both frequencies, both in normal PRM operations and when providing breakout instructions.

There is also a "monitor" controller that ensures that the two aircraft never get dangerously close together -- if such a situation occurs, the "monitor" controller overrides the tower controller on both frequencies to allow for immediate breakout instructions to be given.

Of the two approaches, the more interesting of the two is the offset LDA PRM approach. In the LDA PRM approach, aircraft fly an approach course that is 2.5 to 3 degrees offset from the runway heading, following the glideslope until the MAP (this course does not meet up with the runway threshold), at which point the pilot should proceed visually to the runway.

The MAP on a LDA PRM approach is 3000 feet away from the ILS approach course, meaning aircraft have to manoeuvre towards the extended runway centreline to be stable by 500 feet -- the less spacing between the two runways, the more aircraft will have to turn. This does mean that it is less suitable to larger aircraft, due to the manoeuvring required at higher speeds (than other aircraft), though most SOIA approaches are designed for larger aircraft as well. Before reaching the MAP, the pilot must have have:

the runway in sight;
the aircraft on the adjacent ILS PRM approach in sight; and
notified ATC that traffic is in sight.

This means that the aircraft on the ILS PRM approach should be ahead of the other aircraft. To allow time for visual contact, aircraft should be clear of cloud before the MAP, which is taken into account when deciding on the minimum cloud ceiling allowed for the approach.

The NTZ (No Transgression Zone) is a 2000 foot wide area between the two approach courses which aircraft must not enter at any time. ATC would immediately issue breakout instructions to both aircraft if an aircraft breaches the NTZ, as there would be very little horizontal separation between the two aircraft. [The FAA AIM][3] states that:

  In the unlikely event that an aircraft "blunders" off its course and makes a worst case turn of 30 degrees toward the adjacent final approach course, closing speeds of 135 feet per second could occur that constitute the need for quick reaction.

Special training requirements vary from country to country. In the US, SOIA special training requirements are:

Parts 121/129/135: operator training as agreed to by FAA and educational video
Part 91 transport category: read about PRM approaches in AIM, video
Part 91 other: read about PRM and SOIA approaches in AIM, video

An example of a SOIA approach is the SFO runway 28R LDA PRM approach:


LPV/LP approach (RNAV with WAAS): What is actually the "channel number"?

This pdf by Jeppesen provides the meaning:

  WAAS Channel Number, unique to each airport, and  Reference Path
  Indicator (RPI), which is made up of the letter “W” plus two or  three
  characters representing the runway number.  These are shown in both
  the Briefing Strip (chart heading) and plan view.

So the Channel Number provides the airport, and the RPI provides the runway number as well as the specific procedure. The combination of the two of them provides a specific approach at a specific airport, in much the same way that the title of the procedure on the approach plate is only meaningful if you combine it with the airport identifier.

As far as what you need to select in a particular avionics package, that depends on the design, but you are correct that it doesn't affect how it processes the GPS / WAAS signals.


Why maneuverability and top speed are still issues in 5th generation air superiority fighter jets

Fighter jets are not bricks with powerful radar and long range missiles. BVR combat is an extremely complex affair conceptually, operationally and technologically.

For BVR combat to be initiated, the enemy aircraft should first be identified and sorted as a threat. However, assuming that both have similar radars, the inverse square law ($S \ \propto \ \frac{1}{R^{2}}$) means that you are exposing yourself to the enemy before identifying him. Combat between two stealth aircraft (F-22 vs T-50) is not unlike two men with a gun and flashlight in a dark room, as someone noted. The first one to switch on the radar is actually at a disadvantage and against a highly trained enemy, possibly suicidal. Also, let's not forget SAM ARM missiles that can home on the aircraft radars.
Though the number of aircraft shot down by radar guided missiles (as opposed to IR missiles, which are usually fired WVR) have risen significantly both in numbers and also as a percentage (of total aircraft shot down), the probability of achieving a kill by a BVR missile is still uncomfortably low. For example, the following table shows the ratio of 'kills' by radar guided missiles post WWII.

Table from Promise and Reality: Beyond Visual Range (BVR) Air-To-Air Combat by Lt Col Patrick Higby, USAF

The high percentage of BVR kills in Gulf war is basically due to two factors- AWACS and IFF(Non-Cooperative Target Recognition (NCTR) system), which gave sufficient confidence to permit BVR shots. It is highly unlikely that such a superiority level and confidence is available in case of war between two peers.
Another thing is that barely any of the BVR shots are fired head on due to the high closing speeds. So in all probability, you have to maneuver yourself in a position where a tail (or an above) shot is possible.
Also, if some missile is fired at you, speed and maneuverability are critical to carry out evasive maneuvers.
Most of the combat aircraft use in present day has nothing to do about air superiority. They are mostly used as precision guided bomb trucks. Optimizing fighters for BVR combat sacrificing other parameters is, at the least, foolhardy.

So far, the most important contributors to BVR victories (in Gulf War, for example) are not due to some inherently superior technology, but due to human factors- pilot skill and opponent's weakness. It is potentially catastrophic to generalize the doctrine against a near-peer opponent.


What is the throttle setting of a piston aircraft during cruise?

Broadly speaking its what ever you chose it to be. You should always refer to your aircrafts POH for the information specific to your airframe and engine. Beyond the POH there may also be supplemental engine information from the maker.

Generally take off and at least initial climb out occur at full throttle. Then at when you reach your cruising altitude you will throttle back to your cruise power setting and level off.

For example lets take a look at the charts for a PA-28

You can chose your desired power setting based on a desired fuel burn

Then refer to this chart to see your airspeed.

You can then use these numbers for your flight planing, or work backwards to achieve a target airspeed.

For a trainer these numbers tend to be not all that large of a range. My Archer will do a full power climb out at 2650RPM then throttle back to about 2450RPM for cruise. Higher performance aircraft may have larger ranges as well as more complex operating limitations. Some engines have time limits on which they can be at full throttle and most have thermal operating limits if you decide to dance on the mixture lever. Turbo or super chargers may also add an additional level of management to prevent over boosting. Modern digital engine analyzers allow for a level of precision previously unachievable.

AOPA has a decent article on power management over all, you can find it here.

Pro Tip: A lot of small trainers print the engine performance data on the inside of the sun shade so you dont need to thumb through the POH in flight.


When and why was runway 07/25 at Kai Tak removed?

The two original short runways (shown above) were actually abandoned c. 1955 in favor of a brand new longer runway built into the bay (completed 1958) to accommodate the new jetliner (the 13/31 you know).

  The year also saw the start of work on a $110,000,000 project to revolutionize Kai Tak Airport by the construction of a 7,200-ft runway on an artificial promontory reclaimed from the sea and projecting out into the waters of Kowloon Bay. In danger of being knocked off the international airline map by reason of its airport being too small and dangerous for the Comet and the larger conventional airliners, Hong Kong has now taken steps to keep itself firmly on the map. The airport project, when completed in 1958, will provide, for the first time since aviation started in the Colony, facilities for day and night operation all the year round.

A note on the design of runways: Two intersecting runways are usually treated as one, as both can't be used simultaneously unless they're sufficiently long and a procedure like LAHSO is used. Kai Tak started with 2 to cover the compass as much as possible, since early on the designers didn't have wind data. It was typical of that era to build 3 runways 60° apart, then later on expand the most useful, and abandon the rest.

Source: https://gwulo.com/kai-tak-airport-history


Can a few random interaction with cockpit controls result in a crash?

There's a real-life example that seems very similar: Aeroflot 593. The pilots let two children sit in the cockpit while the aircraft was on autopilot. One of the children pushed the control column for 30 seconds, which disengaged the autopilot and started a steep turn. The pilots tried to recover but the aircraft stalled and crashed, killing everyone on board.


Travelling at faster than mach 1, how sharp could Concorde turn to avoid injury to passengers?

All aircraft experience the same G force per degree of bank angle, so a 60 degree turn in a Cessna produces 2G just like a 60 degree turn in Concorde would produce 2G.

The difference is that a Cessna doing 100 knots could circle in 0.2 miles by using a 60 degree bank angle.

Concorde doing 1000 knots and 60 degrees would take up 19.5 miles to do the same thing.

In both cases the passengers would experience 2G which even so is pretty severe if you are a passenger and aren't used to it. It would get your attention let me put it that way.

I'm not an airline pilot. However I would think that the risk with higher speeds is in angle of attack or angle of attack combined with bank angles. At higher speeds its much easier to produce a whole load of G by pulling or pushing the controls than it is in your Cessna, and even that can be pretty severe.

So while you might not worry as much about bank angles you would be very careful not to pitch up or down too far especially at higher speeds because you could overstress the aircraft real easy.

Hopefully a pilot who knows Concorde and / or airliner systems can improve on this answer.


GA refers to why you fly your plane, not what kind of plane it is. For example, John Travolta has (had?) his own personal Boeing 707, which is the first generation of jet airliner from Boeing. When he flew it, it was not under scheduled service, so it would be classified as a "general aviation" flight.


Is one-sided thrust reverser deactivation still allowable?

Operating with a deactivated thrust reverser is relatively common on normal line ops.

There are normally type specific operating restrictions e.g. full power take-off, no short or narrow runway ops.

On B757/76 there is a clue that you a have a reverser locked out - you can't select it.


Is any single-axis autopilot for a light piston single certified for unusual-attitude recovery?

You would need a three-axis autopilot. The nature of an unusual attitude is that it needs corrections around all three axes.


The aircraft is almost certainly a Beechcraft B200 or B200C King Air, with a combined Cargo-and-Airstair Door, as can be seen in these photos:

(source)

(source)

The airstair door is essentially a door-within-a-door and opens downwards as usual:

(source)

The larger cargo door opens upwards:

(source)


How fast were propeller planes during landing on aircraft carriers during WW2?

The stall speed of the F4U Corsair may be 89mph, and a safe approach speed might be 95-100mph, but that's airspeed... Measured with reference to the carrier deck, you have to substract 20mph headwind (nothing unusual at sea) and also around 30 mph of the carrier own speed. Hence, that plane touched down at a sedate 45-50 mph, with respect to the carrier deck...


How does the pilot control the Dassault Rafale?

The  Dassault Rafale is one of the new generation of combat aircraft which have a side stick rather than a center stick for controlling the aircraft.

The Rafale follows the HOTAS concept- one where the buttons are placed on the throttle lever and the flight control stick allowing pilots to access vital cockpit functions and fly the aircraft without having to remove their hands from the throttle and flight controls.

There are two sticks in the Rafale cockpit on either side of the pilot. The one on the right of the pilot is the flight control stick and the other one is the throttle.

Image from freerepublic.com © Alex Paringaux/Dassault

The side stick controller on the right is connected to the aircraft computer and interprets the pilots input, which are then executed via various controls. The side-stick controller is force sensing with only a little travel, as can be seen in this video.

Rafale has a single throttle for both its engines- the left stick has more travel (compared to the other one) and controls thrust of both the engines through the computer. You can see both the sticks being operated in this video.

This type of arrangement is quite common in modern combat aircraft- both the F-35 Lightning II and F-22 Raptor use a similar arrangement- only difference is that in Rafale, the throttle and side stick look quite similar.


What software is used for aerodynamic wing shape optimization?

If you follow the AIAA publication number (AIAA-2014-0567) given in the first frame of the linked video, you will find this article which explains in detail that the optimisation shown in the video was done on MACH:

  These tools are components of the framework for multidisciplinary
  design optimization (MDO) of Aircraft Configurations with High
  fidelity (MACH). MACH can perform the simultaneous
  optimization of aerodynamic shape and structural sizing variables
  considering aeroelastic deflections.

If you now google for MACH, you will find this article by Gaetan Kenway which explains in detail how the software works. But this is not what you want, my impression is you need a simple to use software which can be downloaded and run within minutes.

My recommendation would be XFLR5 which incorporates the XFOIL airfoil solver and adds modules for designing and calculating the whole aircraft. YouTube has a variety of tutorials available. Is that what you want?

However, a basic understanding of aerodynamics and the possibilities and limitations of the algorithms used will be very helpful - a good engineer should be able to think both like a scientist and a programmer.


Why does landing gear retract with an offset?

This is called sequencing. The idea is to distribute the high load on the hydraulic system due to retraction over time, so the hydraulic pumps can be smaller.

The linked video shows no such sequencing. The triple redundant hydraulic systems on airliners do not need such optimizations since there is plenty of power if all pumps are running. On top, the video was made in a hangar and the pressure source was most likely external, with enough power reserves. Any asymmetries are most likely due to differences in friction, as Jan remarks in his answer.

Since friction losses in the hydraulic lines increase with flow speed, a difference in retraction speed would quickly be equalized, since the faster moving leg needs higher flow speed in the lines leading to and from its actuator, and less pressure would be available for gear operation. Active syncing is not needed, and a small difference has little influence on flight characteristics. After all, the main gear is close to the center of gravity, so drag differences between both legs do not produce big aerodynamic moments.

When a gear retracts, it first needs to move out of the locks, which requires little hydraulic power. After this, the load gradually increases the more the leg moves up into the horizontal position. Shortly before moving into the final, retracted position the load is highest; the details depend on the gearing of the retraction mechanism. If this load needs to be covered for all three gears at the same time, the hydraulic pump on an aircraft with manual controls and hydraulics only for gear operation would need to be more than twice as large as when you sequence the retraction, so the peak loads come one after the other.

Rockwell 112 while gear retracts (picture source). Some asymmetry is clearly visible.

Technically this is solved with sequencing valves which serve several circuits. They are used both to time the gear door operation, so the doors open before the gear starts moving, as well as the sequence of the main gears.


How did the nose landing gear of JetBlue Flight 292 get stuck sideways?

According to the complete NTSB report, following is a summary of what had caused the nose landing gear (NLG) to rotate 90° on Flight 292.

  During flight, Brake Steering Control Unit (BSCU) performs1
  cyclic tests which slightly rotates NLG from the 0° position. Due to
  this fatigue, two of the four anti-rotation lugs on the NLG upper
  support assembly fractured and separated. This allowed NLG to deviate
  from the 0° position. Another contributing factor was BSCU system
  logic, which prevented NLG from centering. Also contributing was the
  lack of a procedure to attempt to reset the BSCU system under these
  conditions.

This website has some nice pictures of nose landing gear before and after the landing.

A summary of the investigation can be found here.

1: BSCU has other functions too.


Why does the Tu-22M3 nose have this peculiar shape?

Nobody knows why except Andrei Nikolayevich Tupolev, and he is dead.

Andrei Tupolev was known to insist on the fast and adequate at the expense of the theoretically correct, leading to widespread technical debt in his designs. He may have raised the nose cone for no more profound reason than to get the refueling probe in line with the pilot's vision. Once he had energetically dictated where the probe was to go, no one at the design bureau would dare suggest moving it; they would just work the forward avionics into the resulting odd shape as best they could.

Tupolev died in 1972 leaving this and many other of his decisions unexplained.


What is required to fly over Cuba enroute to another country?

The IACC navigation fees are approximately $170 for a small jet, plus there is a service fee to issue. There is a full list at World Air Operations and you can in fact order the permit for Cuba online there too.


What materials are used in a Rolls-Royce RB211-524 Engine?

There is some variation. The RB211 was to be one of the first engines to use a fan stage made in carbon fiber (Hyfil), but that plan was changed in a late stadium and the fan stage was done in titanium instead.  Conways did use Hyfil, IIRC.
Otherwise it's mostly steel and aluminium, with some titanium. Copper for the wiring etc.


Why is the de-icing fluid sprayed on jets coloured orange?

There are actually two types of de-icing fluid, one is orange and one is green. According to a product safety sheet for one brand:

  The dye is intended to indicate which parts of the  aircraft have been
  treated and to differentiate between fluids (Type I fluids are orange,
  Type IV  fluids are green).

As to why orange and green, presumably they aren't easily confused with other liquids used around aircraft. Black would look like oil or another fluid if it pooled on tarmac, hydraulic fluids or oils are often yellow/green in colour and blue is a very common colour in aircraft painted liveries. So I guess that orange and green were sort of the ones 'left over' after all the other obvious colours had been considered.


Why are Category II ILS approaches prohibited in an E-Jet with inoperative pitch trim?

Looking at the report, the airplane does not appear to be certified for CatIII in the first place (it would have to have Head Up Guidance and not that many do - the CRJs are the same) so the QRH doesn't need to mention an approach category that the airplane can't do anyway.

As far as CatII goes, the approach with no pitch trim is going to have to be flown by hand, and probably with the existing trim speed different from Vref, unless the trim failure happened while on final while already trimmed to Vref.  So depending on how far away your current, fixed-due-to-failure trim speed is from Vref, you are going to have the hand fly an ILS while holding 5, 10, 15, 20, 30 pounds of force on the column to maintain glide slope at Vref.

This is quite a challenge because the slightest relaxing of concentration will cause you to relax your push/pull a bit and make you drift high or low.  It's enough of an ordeal to do this and stay on glide slope right down to 200 ft.  To hold it down to 100ft, the normal CatII decision height, is pushing it, so the approach is prohibited.


How is fuel stored in a tanker aircraft?

You might be surprised to learn that most refueling tankers hold a relatively small percentage of their total fuselage volume in fuel. The reason why is simple; a plane stuffed to the gills with fuel would be so grossly overloaded it wouldn't make it off the runway. Tankers, therefore, can double as medium transports with little modification, as they have a sizable upper deck which is more or less empty space when serving as a tanker, but which can ferry troops, light vehicles or other materiel from Stateside bases to various theaters (a dedicated heavy transport like the C-5 or C-17 would be used for transporting large units or for specialized troop transport like airbornes).

Here's the layout of the KC-135 Stratotanker:

To my knowledge, all of this fuel is available both to power the plane and to refuel other aircraft, however the plane would likely draw primarily from the wing tanks for flight, as this is the "standard" configuration for the 707 the KC-135 is built on. Transport of the fuel from these tanks to the refueling systems would be accomplished with an integrated pump and pipe system that could move fuel from anywhere to anywhere.

The bulk of the fuel load, as you can see, is contained in four "body tanks" totaling over 144,000 pounds of fuel. For comparison, the F-15E strike fighter can carry a maximum, with CFTs and 3 droptanks, of just 35,550 pounds.

These tanks are lined with plastic bladders, which contain the fuel (so the entire fuselage doesn't have to be leak-proof which is much more difficult and expensive to ensure) and also allows the bladder to collapse as the fuel inside it is depleted, reducing the volume of air in direct contact with the fuel, thus reducing the vapor hazard. AFAIK the wing tanks do not have these bladders, but they're much smaller spaces overall and more easily accessed.

Separating the fuel into multiple tanks has several advantages:

The tanker is still serviceable with one or more of the tanks unable to carry fuel (leak in the bladder, pump failure, etc).
Sloshing of the fuel in the tanks has less effect on the weight distribution of the aircraft. Imagine trying to take off with a full Olympic swimming pool in your cargo hold; any pitch up or down will cause several tons of weight to move "downslope", unbalancing the aircraft (probably fatally).
Fuel can be pumped between these tanks to fine-tune or "trim" the aircraft's weight distribution and handling characteristics, a process known as "tank trimming" which is more aerodynamically efficient than elevator trimming.


Why are fighter pilots seated and not reclined?

Fighter pilots are far more reclined than you might think.

But seat angles are limited by the need for good visibility.  Pilots frequently need to look to down-and-sideways, down-and-forward, and towards their back-quarters.  These are angles that your F-1 Driver couldn't possibly see.

Also, High-G maneuvers are quite rare.  Most modern military planning is about making sure pilots are never even in a position where they need to evade a missile or dog-fight another plane.


What does the FAA mean by "Make and Model" of aircraft?

TL;DR: The make of an aircraft is the name of the designer (for example, Boeing) and the model of an aircraft (also called the type) is the designation for the general design of the aircraft (for example, 737).  It looks like "basic model" is just an older term for "model".
According to FAA Order 8000.71:

c. Aircraft Make. An aircraft make is the name assigned to the aircraft by the manufacturer when it was produced.  In most cases, the aircraft make is the organization common name of the aircraft manufacturer.  If the organization that holds rights to an aircraft design permits another organization to build that aircraft then the aircraft make would be the aircraft name assigned by the organization that holds rights to the aircraft design in most cases.  If an aircraft manufacturer is an amateur construction, then the aircraft make would be the name of the organization responsible for design in most cases.

and

c. Aircraft Model. An aircraft model is an aircraft manufacturer's designation for an aircraft grouping with similar design or style of structure.
(1) The aircraft model listed in the aircraft TC is the designation used by the aircraft manufacturer to distinguish a particular aircraft or is the designation used by a national military or armed force to distinguish a particular aircraft.
(2) If an aircraft manufacturer is amateur construction, then the aircraft model would be the name designated by the organization responsible for the design in most cases.

Also,

(7) Title 14 of the Code of Federal Regulations (14 CFR) 1.1 defines "type" and provides the basic classification for aircraft as follows:
"(2) As used with respect to the certification of aircraft, means those aircraft which are similar in design.  Examples include: DC-7 and DC-7C; 1049G and 1049H; and F-27 and F-27F."
Examples: 777
DC-9
Note: Historical policy and documentation may refer to type as "basic model."


Why don't aircraft owners put vortex generators on the top of their flaps to extend single flap lift creation past 40 degrees?

Because the separation bubble, that vortex generators attenuate, occurs in front of the flaps.  There's no advantage to putting VGs that far back, on an ultralight or any other fixed wing aircraft.


Did the First Officer of Ethiopian Flight 302 trim in the wrong direction?

On the Boeing 737 the trim wheels are directly connected to the stabilizer jackscrew with cables. The force required to move the trim wheels depends on the load on the stabilizer. The more you are out of trim, the more force is required to move the stabilizer.

From the 737 NG FCOM (9.20.8 Flight Controls - System Description - Stabilizer Trim, emphasis mine):

  Manual stabilizer control is accomplished through cables which allow the pilot to
  position the stabilizer by rotating the stabilizer trim wheels. The stabilizer is held
  in position by two independent brake systems. Manual rotation of the trim wheels
  can be used to override autopilot or main electric trim. The effort required to
  manually rotate the stabilizer trim wheels may be higher under certain flight
  conditions. Grasping the stabilizer trim wheel will stop stabilizer motion.

left: trim wheel with handle stowed (source), right: jackscrew in the tail (source)

The FCTM (8.17 Non-Normal Operations) explains the correct procedure for manual stabilizer trim (emphasis mine):

  Runaway Stabilizer

  Hold the control column firmly to maintain the desired pitch attitude. If
  uncommanded trim motion continues, the stabilizer trim commands are
  interrupted when the control column is displaced in the opposite direction.

  Manual Stabilizer Trim

  If manual stabilizer trim is necessary, ensure both stabilizer trim cutout switches
  are in CUTOUT prior to extending the manual trim wheel handles.

  Excessive airloads on the stabilizer may require effort by both pilots to correct the
  mis-trim. In extreme cases it may be necessary to aerodynamically relieve the
  airloads to allow manual trimming. Accelerate or decelerate towards the in-trim
  speed while attempting to trim manually.

  Anticipate the trim changes required for the approach. Configure the airplane
  early in the approach. When reaching the landing configuration, maintain as
  constant a trim setting as possible. If a go-around is required, anticipate the trim
  changes as airspeed increases.

Note: this FCTM is from a 737 NG, not a MAX. The part about "trim commands are interrupted when the control column is displaced in the opposite direction" is no longer true when MCAS is active on the MAX, the rest is still valid though.

You can also see this procedure applied in this YouTube video by Mentour Pilot.

Regarding the Ethiopian crash: I don't want to speculate on what the crew did, but if

  the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units

then it did indeed move in the wrong (AND - Aircraft Nose Down) direction.


Why would one wing stall before the other?

In general, aircraft aerodynamics can be affected from manufacturing tolerances or consistent asymmetries.

The reason can be due to any asymmetry in the wings or fuselage shapes, or wing-to-fuselage fixtures.


How to get a NOTAM on a Restricted Area?

For SUA NOTAMs, you can find it via sua.faa.gov, in either map or text format.

If an SUA on a chart has defined hours, stick to those.

Example after downloading the text data:

Map example (layer control is useful):

Color indicates if active or scheduled and how far in the future.


Why aren't there simplified fly-by-wire helicopter controls?

Helicopter manufacturers seem to have been slow to adopt fly-by-wire systems. I used to work in the General Dynamics group which designed the fly-by-wire system for the F-16. That was the first production aircraft which had full-authority fly-by-wire (without mechanical backup systems). By the time I started working there, they were in process of updating the system to incorporate a digital flight control computer. The production required extensive coordination between multiple disciplines. As an electrical engineer, I regularly interacted with software engineers, control-law designers, test engineers, and "mechanization" engineers. It took many years for the company to develop such a culture, where each member is concerned with the efficiency and safety of the aircraft. I speculate the helicopter manufacturers didn't catch up for a couple of decades because funding was limited.

Here is an article which describes the Army's experience: Army Slow To Adapt Fly-by-Wire Controls for Helicopters

Funding aside, helicopters are ideal candidates for fly-by-wire systems. The obvious goal is to take a marginally controllable aircraft and make it both stable and maneuverable. That would dramatically reduce pilot workload. Most helicopter fly-by-wire systems accomplish hands-free hover and decoupled control inputs (i.e. sideways flight without needing rudder inputs).

The first helicopter which demonstrated a great fly-by-wire system was the Sikorsky RAH-66. It even achieved sideways flight at 60 knots and backward flight at 25 knots, using only cyclic stick inputs. Unfortunately, that program was cancelled in 2004. The first production military fly-by-wire helicopter is the NHIndustries NH90, which was the first helicopter to fly without mechanical backup controls, in 2002, and entered service in 2007. The first civilian fly-by-wire helicopter, the Bell 525 is currently under development.


Airflow around aircraft and especially over wing is not uniform. The lowest transsonic speed is when the airflow at some point of aircraft (usually over wing) goes supersonic. Depending on aircraft, this happens around M0.8. When the airflow around entire aircraft is supersonic the transsonic region ends.

The excessive drag is due to the shockwave(s) that forms in the airflow at the location where airflow has accelerated to speed of sound. As airflow ahead of it hits the shockwave the energy of flow dissipates and there is sudden drop in air pressure across the shockwave. As there is less pressure behind the shockwave than there is in front of it additional drag is induced in the process. This called wave drag.

This effect can be counteracted by designing an airfoil that forms the shockwave initially as close as trailing edge as possible and then the entire airfoil goes supersonic as quickly as possible as speed increases. See https://en.wikipedia.org/wiki/Supercritical_airfoil

The formation of shockwave is the reason why supersonic aircraft has pointed noses as air is not pushed ahead of an aircraft. The pointed nose creates an oblique shockwave that has creates less drag along the aircraft flight path.

Pointed cones can also be seen in engine intakes of supersonic aircraft (see SR-71 and Mig-21). The additional oblique shockwave formed by the cone ahead of the engine is used to slow air entering the engine to subsonic speeds. The cone is moved back and forth as mach number changes to keep the shockwave away from the actual engine. Concorde used adjustable ramps within engine intake for same effect.


Have we seen the last significant experiments in the configuration of jet airliners?

With current fuel prices: Yes, we have arrived at a mature design which will not change much. Recent trends like the increase in aspect ratio and engine bypass ratio will continue, but the general arrangement will remain unchanged.

Just look what happened in the first 50 years of airline operations, and how much changed after that in regards of aircraft configurations:

If fuel prices rise to 200 USD per barrel and more, expect slower airliners with less sweep, much higher aspect ratio and probably even braced wings. To enable bracing the wings will be mounted on top of the fuselage, like on the Hurel-Dubois HD.31.

Boeing SUGAR Freeze concept. Note the third engine in the back which ingests the fuselage boundary layer, thereby reducing separation and pressure drag.

While you might read about two more new design directions, a supersonic airliner and the blended wing-body (BWB), I am rather skeptical that any of those will be adopted in the future.


Is there a maximum airfield elevation in which a Cessna 172P can operate?

You should look in the POH for your specific aircraft (because it may have had modifications to it which would make it different from a "standard" aircraft) and see what it says.

The 172P POH that I found online contains no maximum airport elevation for takeoff, and the Type Certificate Data Sheet (TCDS) doesn't either.

Therefore, you can only go by the performance charts in the POH.  According to the POH that I found above, assuming that you have enough runway available and can out climb any obstacles (big assumption, you need to make sure of this), you can takeoff at a pressure altitude of up to 8,000 ft. other than in cases where the airplane is very heavy and it is hot, in which case it will be restricted further.

This doesn't mean that the aircraft is not capable of taking off at a higher pressure/density altitude however, and if you have the need to do so then I would recommend contacting the manufacturer directly to see if they have any engineering data available for your situation (often they do but don't publish it; there may or may not be a fee).


What is the main difference between Class C and B Radar Service?

The term is not "approved", it is the complete phrase Approved Separation. This is the standard FAA term for what was previously called either standard separation or radar separation, and means "separation in accordance with the applicable minima in [FAA Order 7110]".

The separation minima are further defined in the JO 7110 family of FAA Air Traffic Control orders, which you can find linked from the page above.


Is it possible to control an aircraft on the runway if the nose gear collapses?

Most aircraft are steered on the ground by pivoting the nose gear. If the nose gear collapses, you therefore lose your primary method of directional control on the ground.

Additionally, parts of the aircraft contacting the ground that are not supposed to contact the ground can cause unwanted yaw, which can contribute greatly to the runway excursions you've noticed in articles regarding gear collapse incidents. This is probably the largest contributing factor to runway excursions in cases of nose gear collapse. However, if it's known that the nose gear did not deploy properly before the landing, the pilots can intentionally hold the nose gear off the ground as long as possible in order to minimize this effect. Holding the nose gear off the ground as long as possible minimizes the time that the contact between the nose and runway surface will be potentially applying yawing forces to the aircraft and also minimizes the speed of the aircraft while those forces are being applied. This gives the pilots more time to respond with differential braking and/or rudder, helping to prevent the nose from moving too far away from the direction of travel and a resulting loss of directional control due to skidding. Of course, this doesn't help if the gear collapse was unexpected, as the pilots wouldn't know to hold the nose gear up.

There are a few additional methods of directional control available to airplanes on the ground, though most are not as effective as pivoting the nose gear and their effectiveness varies with speed:

Rudder - While the aircraft still has high airspeed when rolling down the runway, the rudder will still provide some directional control. This control will diminish very rapidly as the aircraft slows down, though.
Asymmetric braking - Most airplanes allow the pilots to control the brakes on the left and right main gear independently, allowing them to brake harder on one side of the aircraft than on the other. This is more useful for taxi speeds than for high speeds down a runway, though, and can easily cause even more directional control problems if used without proper care at high speeds.
Asymmetric thrust - Multi-engine aircraft almost always allow the pilots to control the thrust (either forward or reverse) of each of the engines independently. However, in the case of a collapsed gear, this is unlikely to be very helpful, due to the large delay between when a thrust change is commanded and when it happens as well as that the engines may now also be striking the ground themselves.


Was the Horten Ho 229 flying wing a three-point-landing aircraft?

The term "3 point landing" is derived from old taildragger (3rd wheel in back) designs.

In reality a 3 pointer is not desirable, as the wheel, front or back, being away from the center of gravity, can produce a nasty pitch if it bounces. At landing speeds this can be uncontrollable.  The term "3 pointer" does imply good landing speed management, as the plane, slightly nose up, has been flared properly, and will "settle" gently to the ground.  Most of the time the pilot will strive to land on the main gear, bleed off more speed, then allow the 3rd wheel down before taxiing off the runway.

The Horton Ho229, if it ever flew, was designed to land under wartime conditions.  Even jets were very vulnerable when slowing to land, and many times paved smooth runways simply were not available (survivable) options.

So the huge front wheel was basically overdesigned for less than perfect landings.  However, landing technique, even for this fantastically futuristic aircraft, would be similar to other planes.


Where can aircraft carriers carry out air operations?

I don't know what permissions are required (guessing a fair bit of paperwork, involving not only the FAA but also port authorities), but taking off in port (in this case, a museum ship) has been done.  The USS Midway was stationary, looks like minimal wind, but on the other hand an acrobatic plane with lots of power. (Youtube)


What does prevent air and fuel to be mixed upstream of the compressor?

tl;dr The flame would progress upstream into the compressor until it and damage it, fatally disrupt the carefully balanced flow and stall the engine, or both.

long answer: In a turbine engine, there is a continuous flame where injected fuel is ignited by the already burning fuel downstream. Now you can't match the flow speed and the flame propagation speed exactly, because a small disruption could then blow out the engine and because both depend on the power setting in non-trivial way.

So in normal operation, the flame can propagate upstream until it gets to the point where the fuel is not yet sufficiently mixed with air to burn and there it stays. If you injected the fuel before the compressor, the flame would progress into it and as it would engulf the last stage, it would damage it and it would also increase the pressure beyond what the preceding stages could maintain, which would stall the compressor and cause the engine to stop, either immediately due to lack of oxygen, or by causing more damage with each stall cycle.

Note that spark-ignition (gasoline and LPG and CNG) engines usually do inject fuel before compression, but it limits their compression ratio to around 12:1 with high-octane gasoline, 14:1 with clever tricks. If the compression ratio was higher, the fuel-air mixture would ignite from the compression heat before the piston reaches the top-dead-centre and act against the rotation. In contrast compression-ignition (Diesel) engines have compression ratio at least 14:1 and inject the fuel only when it should start burning.

While early turbines had rather low compression ratios, the newest generation is getting into the range comparable with Diesel engines where the fuel might ignite due to the compression heat alone—they still use sparks for ignition, because the starter won't build up as high pressures in them, but it clearly shows they can't inject the fuel before it should start burning.


What keeps an aircraft engine from flaming out at high altitude?

The oxygen level at high altitude is the same as at sea level, namely 20.95%. What is lower is the oxygen pressure.

To avoid flameout, pilots must avoid to throttle the engine down too much, so a minimum pressure in the combustors can be maintained.

Designers can increase the altitude performance by building longer combustors. The speed of ignition is pressure dependent, and with lower pressure it takes longer for the fuel-air-mixture to ignite. More length allows more mixing and leaves the mixture more time to react. Also, they can add flame holders which leave pockets of burning fuel close to the injection nozzles, so the mixture is heated more rapidly and ignites more reliably. Normally, flame holders create drag and are reduced to the minimum necessary.


Whenever I hear a plane throttling down quickly, what is happening visually?

Ok I listened and what you are hearing is a turbine powered ag plane.  Most of the rising and decreasing pitch you are hearing that sounds so dramatic is doppler effect from the propeller.  The propeller speed will be constant all this time as the pilot will set the RPM for his activity and leave it, just changing power with throttle.
So in the cockpit, the noise from the prop will more constant without the rising and falling sound, just a steady OOOMMMM of somewhere around 100 hz (three blades at 2000 rpm say), not as intense as the sound heard from the ground, with a roar/hiss from the air passing that rises and falls somewhat with speed as he dives and zooms.
The intensity of the propeller sound will also increase or decrease a lot with the power, but not the overall pitch; because the propeller is constant speed, that remains constant unless the speed is changed, and that won't happen during this maneuvering.
Then the very high pitch zeeeeeeeeee whining sound under the big booming sound is the turbine engine itself. It's sound will change a little bit from within the cockpit as power is added and removed, with some change in the pitch of the whining sound and its intensity.
This video is from the inside of a plane like the one you heard, but the inside sound is being recorded through an active noise cancelling headset, so 80% of the cockpit sound is being suppressed.  But you can hear faintly the airstream, and a bit of the prop's sound and can tell that it's pretty constant to the pilot the entire time.  Way less dramatic for sure.


As best I can tell, ASFC is only used in France and is synonymous with AGL.

First, it isn't in ICAO's list of abbreviations or the FAA's PCG, but it is in the French AIP in section GEN 2.2:

  ASFC / Au dessus de la surface / Above surface

The AIP also lists AGL, but it doesn't explain the difference:

  AGL   / Au dessus du niveau du sol / Above ground level

Second, the AIP uses both terms in a seemingly interchangeable way. For example, in ENR 1.2 (VFR rules). Compare this from 4.7...

  Come over the aerodrome, perpendicular to the runway at 2000 ft AGL,
  lights on, then join the circuit for landing

...with this from 4.10:

  Fly over the runway at 2000 ft ASFC, perpendicular to the runway
  heading with landing lights switched on,

I can't see any reason why there would be any difference in meaning in those two phrases, and the airports in those sections are not particularly near the sea.

Finally, if you consider Wiktionary a valid reference, the definitions for ASFC and AGL are almost the same and they're both stated as the 'opposite' of MSL:

  AFSC (Aviation) Désigne une hauteur au-dessus de la surface du sol ou
  de l'eau par opposition à une hauteur AMSL, dont la référence est le
  niveau moyen de la mer.

  AGL (Militaire) Above ground level : « Au-dessus du niveau du sol »,
  altitude relative au sol, par opposition à l’altitude absolue, mesurée
  par rapport au niveau de la mer.

Although this is a guess, I suspect that ASFC is simply an example of French phraseology that has now been superseded by English but hasn't been updated everywhere. I can't find ASFC used anywhere in a non-French context.


Set aside the barometric stuff.  The simple answer is that what we think of as altitude, on a sphere, is really distance from the gravitational source, the center of the sphere.  Therefore, a "constant altitude" is not maintaining the same plane in 3 dimensional space, but the same distance from the center of the earth.


What is the limit between lower and higher airways in VFR?

Skyvector uses official charts from the US National Aeronautical Chart Office (NACO) where available. For the rest of the world, it synthesizes maps using the NACO style based on data from each country's Aeronautical Information Publication (AIP). This will not match what local charts look like and is not valid for navigation. Within the US, you can select individual charts by name or the "World" layers that do a clever panoramic blend of all available charts into one seamless worldwide chart.

The "Lo" and "Hi" charts refer to the NACO  "IFR En-Route Low" and "IFR En-Route High" charts. These are roughly equivalent to NACO VFR sectional charts. NACO "IFR Area" charts (only available in a few areas) are roughly equivalent to NACO VFR Terminal charts.

You should look at the NACO chart legends for a full explanation of what all the symbols and numbers mean, but for example, the number above the airway label (without a * or G prefix) is the Minimum En-Route Altitude (MEA), which provides both terrain and obstacle clearance and navaid radio reception. The number below is the length between waypoints in nautical miles.

The NACO "Low" charts show airways with an MEA below FL180, which have labels beginning with V or T, and NACO "High" charts show airways with an MEA of FL180 or higher, which have labels beginning with J or Q. Most other countries use the ICAO naming scheme where all "Upper" airways have a "U" prefix plus some other letter, though what "Upper" means varies by country. Skyvector tends to put "U" airways on the "World Hi" chart and all others on the "World Lo" chart, but it's not consistent across countries, so they may be using other data as well.


How can I use a Bluetooth headset in an ATR 72 cockpit?

Flying Magazine reviewed headsets for pilots back in 2013 and four years ago there were already bluetooth-capable headsets in the market from Bose, David Clark, Sennheiser and Lightspeed. You might want to start there...


Is the commonly assumed UFO (flying saucer) design aerodynamically efficient?

They use the concept of VTOL thats vertical Take off and Landing. Click here to know more about VTOL

Regarding the efficiency, well I think no one can give a 100% perfect information on this because, we do not know the fuel used, the engineering behind the structure. There are a lot of factors affecting efficiency like :
Materials, Fuel, Type of Engine, Weight etc. So aerodynamics alone cannot judge the efficiency of the aerovehicle.
Thanks!


What exactly distinguishes a beacon light from a strobe light?

I think there are two points in your question: what is the physical difference between a beacon and a strobe, and what is the operational difference? For the rest of this answer, I'm going to assume that you're asking about an aircraft that has both a beacon and strobes; as you quoted above, it's possible for an aircraft to have neither. I'm also going to assume you're asking for an answer that applies in the US; regulations in other countries may be different.

First, the physical difference is exactly what you've already determined: a beacon is a (relatively) low-intensity rotating red or red/white light; a strobe is a high-intensity flashing white light. (As noted in the comments below, some beacons flash instead of rotating, but they're still lower intensity than a strobe.) This isn't formally defined anywhere (e.g. 14 CFR 1.1 doesn't define them) but the information you found in the AIM is exactly how everyone I know uses the terms. It's also how you find those words used on aircraft part sites, e.g. beacons and strobes. So whatever the 'strict' definition might be, the practical and accepted one is exactly what you've found out.

Second, the operational difference essentially comes down to the question "when do I have to turn them on?" and in addition to what you found in the AIM the FAA gave more details as part of this legal interpretation. The questioner asked two questions about beacons and strobes: when to turn them on, and if they both have to be turned on. The key regulation quoted is 14 CFR 91.209, and note that the FAA considers the beacon and the strobes together to form a single "anticollision system":

  [...] it appears that the strobe light and the rotating beacon are
  part of the same anticollision system.

When to turn them on:

  91.209(b) requires that an aircraft's anticollision lights be turned
  on once that aircraft's engine is started for the purpose of air
  navigation. As a safety precaution, the anticollision lights should be
  on before starting an engine or causing a propeller or rotor to move.

If both have to be turned on:

  [...] because section 91.209(b) does not contain an exception for
  alternative sources of anticollision lighting, turning on the
  anticollision beacon would not relieve a pilot from the requirement to
  turn on the anticollision strobe lights. See § 91.209(b). However, §
  91.209(b), does give the PIC the discretion to turn off the anticollision beacon and/or the anticollision strobe light system if
  the PIC determines that it is in the interests of safety to turn off
  either one or both of these components of the same lighting system.

In other words, the regulations say you should turn them both on, but as PIC it's up to you to determine if using them is safe or not, and if not then you are allowed to turn (or leave) them off.

Practically speaking, I've always been taught to turn the beacon on before starting the engine because it's there to tell people near the aircraft that the engine is running or about to be running. The strobes should go on any time you need to be highly visible (which is most of the time), but not if using them would blind someone else or even yourself, e.g. taxiing or flying in clouds. The AIM 4-3-23 has more details on that, in addition to the parts that you quoted.


What does it mean "the airport has the code A 129" (Nida airport, Europe)?

This is really just an educated guess, but it sounds like it was assigned that identifier by the Lithuanian civil aviation authority. It obviously didn't warrant an IATA code. Since it was closed to most traffic the ICAO code may not have been in use. The wiki page said it was just considered an "airstrip," so it was assigned an ID by the government. (It also mentioned lack of fuel service. That might be a requirement for an ICAO registration. I don't know.)

Here in the US large airports will have an IATA CODE, an ICAO code and an FAA location ID. [example: O'Hare airport - IATA: ORD - ICAO: KORD - FAA: ORD] A small GA airport won't merit an IATA or ICAO code but it will have an FAA location ID. The small airport near where I work has no IATA or ICAO code. It has the FAA location identifier K68.


Is there a parameter that links the areas of the fuselage and control surfaces?

I do not know a method that relates the fuselage area to empennage sizes, but there is rule that can be used to estimate the size of the vertical and horizontal tail. It is using the so called tail volume coefficient. For the horizontal tail given by:

$$ V_h = \frac{S_h \cdot l_h}{S c} $$

With $V_h$, the horizontal tail volume coefficient, $S_h$ the horizontal tail surface, $l_h$ the horizontal distance between the c.o.g. and the tail, $S$ the wing area and $c$ the average wing chord.
Basically, this coefficient says that the moment induced by the wing scales with $S$ and $c$, whereas the counteracting moment given by the tail scales with the area of the horizontal wing multiplied by the distance to the c.o.g., and that there should a certain ratio between the two.

A well behaved aircraft typically has a $V_h$ which falls in the following range $^{[1]}$

$$V_h = 0.30 ... 0.60$$

  If $V_h$ is too small, the aircraft’s pitch behavior will be very
  sensitive to the CG location. It will also show poor tendency to
  resist gusts or other upsets, and generally “wander” in pitch
  attitude, making precise pitch control difficult. $^{[1]}$

We can check the values for some commercial aircraft here (I chose Airbus, but it should hold for others as well) :

$$\begin{array}{|c|c|} \hline
 \text{Model} & \text{$V_h$} \\ \hline
\text{A330-200} & 0.957 \\ \hline
\text{A330-300} & 0.791 \\ \hline
\text{A340-200} & 0.733 \\ \hline
\text{A340-300} & 0.791 \\ \hline
\text{A340-500} & 0.729 \\ \hline
\text{A340-600} & 0.729 \\ \hline
\end{array}$$

You can see that the values are already higher than given by the guideline, showing the issue of the generalization.
Another fact that causes the deviations, is the fact that the Airbus aircraft are designed in families. Thus, they design an aircraft, and then add some extra fuselage length to generate a larger family member. This will possibly drive the tail volume coefficient away from the ideal case.

For the vertical tail there is an equivalent form:

$$V_v = \frac{S_v l_v}{S b}$$

With $V_v$, the horizontal tail volume coefficient, $S_v$ the horizontal tail surface, $l_v$ the vertical distance between the c.o.g. and the tail, $S$ the wing area and $b$ the average wing span.

A well behaved aircraft typically has a $V_v$ which falls in the following range $^{[1]}$
$$V_v = 0.02 ... 0.05$$

  If $V_v$ is too small, the aircraft will tend to oscillate or “wallow” in yaw as the pilot gives rudder
  or aileron inputs. This oscillation, shown in Figure 5, is called Dutch Roll, and makes precise
  directional control difficult. A Vv which is too small will also give poor rudder roll authority in an
  aircraft which uses only the rudder to turn. $^{[1]}$

Again checking the values:

$$\begin{array}{|c|c|} \hline
 \text{Model} & \text{$V_v$} \\ \hline
\text{A330-200} & 0.057 \\ \hline
\text{A330-300} & 0.059 \\ \hline
\text{A340-200} & 0.055 \\ \hline
\text{A340-300} & 0.059 \\ \hline
\text{A340-500} & 0.049 \\ \hline
\text{A340-600} & 0.049 \\ \hline
\end{array}$$

Here the values are quite close to the general guideline.

Another interesting plot is shown by This tail design page by Stanford

Here it shows that the tail volume correlates quite nicely to fuselage height and length.

Image showing correlation of aircraft vertical tail volume as a function of fuselage maximum height and length.

It should be noted that aircraft aren't really designed by these guidelines anymore, all the control surfaces are designed such that they provide the control authority necessary, not to match a general rule.

$^{[1]}$: Lab 8 Notes – Basic Aircraft Design Rules Link


Why is there no lift component when calculating rate of climb?

Power and force are different things. Power is force times velocity.

The calculation is done in the reference frame of the air mass. In the reference frame of the aircraft none of the forces are doing work, and the engine power all goes to accelerating the air, but we don't have formulas for that.

The lift is, by definition, orthogonal to the flight path, so it does not do any work. That's why it does not enter the equations directly (it does indirectly due to reduction of induced drag at high flight path angles).

The “power needed to overcome drag” is needed for overcoming the aerodynamic drag. In climb the “aft” direction is tilted own, so part of gravity is added to drag and the “excess can be used for climbing” means the engine is able to produce the higher thrust needed to balance the sum of them.

Rate of climb is vertical velocity, i.e. velocity in the $z$ direction. But for that derivation to work, you need the velocity in the $x$ (horizontal) direction too.


Could a GE90-115 engine generate enough suction to ingest a typical passenger vehicle?

This question would probably be better answered by an automobile aerodynamicist, so be wary of my assumptions. Hopefully, I can at least outline how to get a rough estimate.

Assuming that a "typical passenger car" is less streamlined laterally than longitudinally, let's consider a car crossing orthogonally to the intake airstream of the engine. Assume also that the intake air only generates a force on the car pointed towards the center of the inlet, parallel to the ground, and low enough to not tip the car over (this may not be a good assumption, as crosswinds can generate other aerodynamic forces on a car, especially if it's moving forward or backward).

The problem then basically reduces to overcoming the friction between the tires and the surface on which they rest; let's assume it's concrete. We can start right at the inlet, because if the engine can't move the car there, it can't move the car anywhere in the intake hazard area.

Here's a helpful paper (if I'm interpreting it correctly) that experimentally determined some dimensional sidewind coefficients $K$ for typical vehicles under a somewhat analogous situation. It's a bit odd to use a dimensional coefficient (and thanks to Koyovis for pointing that out; always check your units!), but with some unit conversion we can make it work. Let's take $K=.003(239.6)=.7188\;\mathrm{kg/m^3}$ as a typical value. The side force on our car is thus
\begin{equation}
F=KAV^2\,\text{,}
\end{equation}
where $A$ is the area facing the flow and $V$ is the air velocity. Let's say a good value for the area of a side of a car is $5\;\mathrm{m^2}$ based on this calculation from these numbers.

The mass flow rate $\dot{m}$ of a GE90 at full thrust is $1350\;\mathrm{kg/s}$ and the intake radius $R$ is $1.562\;\mathrm{m}$. Taking a standard air density of $1.225\;\mathrm{kg/m^3}$,
\begin{equation}
V=\frac{\dot{m}}{\rho\pi R^2}=144\;\mathrm{\frac{m}{s}}
\end{equation}
or about 320 mph.

You've specified a mass $M$ of $907.185\;\mathrm{kg}$, so we'll use that. The static coefficient of friction $\mu$ between dry concrete and rubber is around $.75$. So the force we need to overcome is
\begin{equation}
f=\mu Mg=6675\;\mathrm{N\,.}
\end{equation}
Meanwhile, assuming the whole side area of the car is exposed to the maximum air velocity,
\begin{equation}
F=KAV^2=74525\;\mathrm{N\,.}
\end{equation}

So, under our assumptions, the engine has more than enough suction to ingest our car at the inlet. However, I think a more realistic mass $M$ is about $1270\;\mathrm{kg}$, which yields
\begin{equation}
f=\mu Mg=9344\;\mathrm{N\,,}
\end{equation}
which is still plenty below what the engine produces.

So we've determined that at the inlet the engine should be able to suck up a car. But what about the entire hazard zone? We calculated the inlet velocity right at the lip of the nacelle, but the area over which the engine draws air is much, much larger even inches away from the intake, seeing as the hazard zones extend behind it. Thus, at a distance away equal to a typical car's width, the velocity will be quite a bit lower. Let's model the increased suction area as a half-circle with a radius $R_0$ extending from the point on the ground directly beneath the hub of the fan.

First, let's calculate the actual airflow velocity needed to move the 1270 kg car:
\begin{equation}
V_0=\sqrt{\frac{f}{AK}}=51\;\mathrm{\frac{m}{s}}\,.
\end{equation}

Now, we can calculate $R_0$ based on that velocity:
\begin{equation}
R_0=\sqrt{\frac{2\dot{m}}{\pi\rho V_0}}=3.7\;\mathrm{m}\,
\end{equation}

or about 12 feet. The intake hazard zone for the much smaller CFM56 has a greater radius than this. So if we assume that all the air going into the engine comes from the hazard area and neglect the presumably increased hazard area for the GE90 (quite conservative), our car will still be okay unless it is right in the inlet. So, "would they have to get so close to the intake that they'd notice that they'd better put the pedal to the metal and get out of Dodge before they went for one last, most unfortunate ride?" I say yes.

However, because vehicles in jet blast tend to get tipped over and lifted from the ground, a simple statics problem is probably not the best model, but I don't have enough background in automobile aerodynamics to tackle the full dynamics problem.


Is the bleed air passengers breathe tapped from the engines before or after it comes in contact with fuel? And why? Isn't this unhealthy?

The bleed will be tapped from one or two of the 3rd, 4th, 5th or 6th High Pressure Compressor stages.  Usually there are two bleed ports.  The highest pressure port will supply really hot air for things like anti-icing.  The lower pressure port farther upstream will supply air for air conditioning/pressurization and other pneumatics.  Some systems combine the two ports into one system and draw from the low pressure or high pressure one as required.

The air has to come from the compressor, not after combustion, mainly because it needs to be clean ambient air free of kerosene combustion byproducts, and it's plenty hot enough anyway and taking it from the turbine would be way too hot.  The discharge in the last stages of the HP compressor can be upwards of 700-800F at takeoff thrust.

If the aircraft uses a high temperature "evaporative" anti-icing system, it will tap air from hotter stages of the compressor than if there is a non-evaporative system (Evaporative = anti-iced skin temperatures above the boiling point of water.  The leading edge will be over 100 C, like the surface of a steam iron.)

Even if it is taking "clean" air, the bleed flow will have all sorts of charred bits of things from the atmosphere in it; pollen, bits of bugs, that collect and get everything dirty in the ducting and components (at lower altitudes).  Combusted air would be ten times worse, not to mention the carbon monoxide poisoning the passengers and being way too hot to be usable in the first place.


Why wasn't Avro Arrow program revived ever?

Since I'm not and was never a member of the Canadian Parliament or Canadian military top brass, this is pure speculation as you are likely to get from practically anyone else on this site with the possible exception of Rhino Driver (who is AFAICT a serving U.S. naval aviator).
My guess is that the Canadians looked to their south, saw one of their nation's staunchest allies who also happened to be one of the two remaining superpowers after World War II, and concluded that they couldn't afford to compete in the Cold War arms race but could definitely afford to profit from our R&D. Canada and the U.S. formed NORAD in 1958 as a joint venture to defend North American airspace, so Canada knew the U.S. had its back. Canada, for its part, spent its defense dollars outfitting defensive SAM and ICBM-intercept fortifications along probable Soviet nuclear bomber routes, effectively forming the northern part of the North American nuclear shield.
As far as not reviving Avro Canada now, the biggest answer is that Canada is so far behind the major powers in domestic aerospace technology that it would essentially have to recruit in the U.S. military-industrial complex anyway. In addition, compared to the USAF, the RCAF is tiny, composed mainly of transports to move the Army around, with just 70-odd CF-18 fighters making up the total fixed-wing combat complement, and a handful of ASW helicopters seeing service at naval stations and on the Canadian Navy's dozen Halifax-class frigates. In short, Canada has no real need for a domestic military aerospace program, as demand is very low and it can get all it wants from its southern neighbor at preferential prices. They're in line, IIRC, for a shipment of F-35s once Lockheed gets the bugs worked out.
EDIT FROM COMMENT: The comment says that Canada could build planes primarily for export. Such an effort would be doomed to fail for three reasons:

The RCAF itself, given its small size and its outstanding relations with the U.S., would be unlikely to buy the planes. When looking for export buyers, your best marketing is the success of your design in your home country's military, so not having your military use the design at all is a big black mark (the F-5 is the only fighter I can think of that managed decent export success despite the U.S. never widely adopting it; even then, the USAF did have some test deployments of F-5 squadrons in Vietnam for the primary purpose of giving Northrop their backing to market the plane for export).
This presents a Catch-22 for financing and R&D efforts; you're unlikely to get the funds to start working on a plane without any acknowledged demand for it, and with the Canadian aerospace industry being dormant for over almost 60 years, you're unlikely to generate demand for an as-yet nonexistent fighter from an unproven design team. So you have to get the money to build the fighter, and you have to build the fighter to get the money.

Again, the Canadian aerospace industry is dormant, and therefore way behind the times. A joint venture with U.S. or European firms to provide a knowledge transfer to home-grown aerospace engineers seems like the only option to develop something new, when those same firms would then have to openly compete with the resulting firm and its designs. A new Canadian aerospace company would be reduced, as I said, to sniping U.S. talent to jump-start design work.

Some countries that formerly imported jets are starting to look toward domestic production, making a primary export strategy that much more unappealing. Pakistan is the foremost example; their political relationship with practically all the major exporting countries is pretty shaky, and designs still in production for export are getting really expensive, so they're designing the J-17 jointly with China to have an inexpensive, capable fighter they can build in-house without relying long-term on imports. The resulting fighter (an interesting combination of design features from the F-16, F-18, and European designs like the Gripen and Rafale), on paper, is about 40 years behind the times, comparable to Gen-4 and 4.5 fighters like the F-15, F-16, MiG-29, Su-27, Typhoon and Rafale. But, the J-17 is projected to have a flyaway cost of only about \$15 milion a plane, which is a bargain compared to the aforementioned export choices, which start at about \$40 mil per plane and go up to \$110 mil.


One thing the wing root seal does is keep water out of the join between the fuselage and the main spar. Water in there could corrode the spar or, if it is wooden, cause it to rot.


Simply a matter of fuel burn rate per time in air.  Generally you want to go as fast and as high as practically possible against the wind. (Indicated Airspeed - headwind) x Altitude factor = groundspeed (temperature, atmospheric pressure, humidity may be factored in too)

Trip Time hours = Trip Distance miles/Ground Speed miles/hour

Fuel consumption = Trip Time hours x gallons/hour fuel burn rate at given power setting

The pilot may have thought the headwind would be just as bad at FL 240 as at FL 340.
Weather prediction is not perfect, but apparently they did take enough fuel along to make it.

I would give them credit for that.


Why did the B-29 have so much leftward torque at take-off?

It didn't arise ONLY during takeoff, but it is most noticeable then for several reasons

The engines are at maximum power, therefore producing maximum torque
You've got a very good reason to need to be travelling in an exactly straight line (the runway)
You're travelling at fairly slow speed, so your vertical stabilizer is less effective - at higher speeds, the tail counteracts the torque more effectively (for this B-29 this occurs at 80mph, as mentioned). As soon as you get above 80mph, you can just input a little right rudder to counteract it.... B-29's only travelled below 80mph on takeoff and landing, so it wasn't a problem during flight, and during landing the throttles were at idle or very low power.

It isn't true for all aircraft with more than one engine now (although it is true for some), but it does still happen and was much common back in WWII - they didn't want the extra supply line complexity of two different sets of otherwise identical engines, when it could be solved with a bootfull of right foot. Note also that the B-29 had 4 engines, most modern multi-props only have two, and they're closer to the fuselage, which reduces the effect
I think you're misinterpreting the source: he's not saying this technique was unique to the 509th, just that they were taught the technique. The very fact he says they were taught it, rather than "came up with" it, suggests it was known elsewhere. The 509th are only referenced here because that's the group Tibbets was part of, it's unrelated.


As with everything it varies from airline to airline, but for the most part it is option 2).

Larger carriers will usually give pilots the option of blacklisting another if they wish, but smaller airlines with only a few dozen pilot combinations might just tell the pilot to suck it up.

The airline will also avoid placing a brand new FO with a brand new captain, aka ‘green on green’ pairings. And on top of this are things like fatigue duty limits, workplace agreements, seniority (bidding), currency and other considerations. Rostering is a very complex exercise.


What is the minimum separation for aircraft operating on or intersecting the same runway?

As both aircraft are still on a taxiway, turning into two different intersections it's absolutely normal. Each intersection has a so called "holding point" where all aircraft must hold until a clearance to enter the runway is given.

In this particular situation the tower controller will ensure that only one aircraft enters the runway and waits until departure separation minima are given before clearing the second aircraft for takeoff.

In this way maximum efficiency is reached by using different intersections as the following aircraft can line up (and hold on the runway; only after receiving a clearance to do so of course) immediately behind the first aircraft.


Are the VFR weather minimums in 91.155(d) redundant because of 91.155(a)?

Short answer: pilots need flight visibility, ATC needs ground visibility.

There are two different definitions of visibility in the regulations you mentioned: flight visibility and ground visibility. They're defined in 14 CFR 1.1:

  Flight visibility means the average forward horizontal distance, from the cockpit of an aircraft in flight, at which prominent
  unlighted objects may be seen and identified by day and prominent
  lighted objects may be seen and identified by night.

  Ground visibility means prevailing horizontal visibility near the earth's surface as reported by the United States National Weather
  Service or an accredited observer.

The practical difference is that only pilots can determine flight visibility; ATC and/or ground stations (AWOS/ASOS) determine ground visibility. The regulations aren't redundant because they're talking about different things and also about different needs:

91.155(a) applies to all airspace. At 5000' (or whatever), only flight visibility makes sense to determine if conditions are VFR.
91.155(d) applies to terminal (airport) airspace. That means ATC is also very interested in whether conditions are VFR or not, and they can only work with ground visibility.

Note that the full text of 91.155(d) also covers the case of uncontrolled airports with no weather reporting (emphasis mine):

  (d) Except as provided in §91.157 of this part, no person may take off
  or land an aircraft, or enter the traffic pattern of an airport, under
  VFR, within the lateral boundaries of the surface areas of Class B,
  Class C, Class D, or Class E airspace designated for an airport—

  (1) Unless ground visibility at that airport is at least 3 statute
  miles; or

  (2) If ground visibility is not reported at that airport, unless
  flight visibility during landing or takeoff, or while operating in the
  traffic pattern is at least 3 statute miles.


What are the differences in door types in a commercial airliner?

The only formal classification of door types that I could find is in 14 CFR 25.807, which specifies the emergency exit requirements for transport category aircraft. It defines Type I-IV, Type A-C, ventral and tailcone exits. The doors you usually enter and leave the aircraft through are probably type I or A:

Type I. This type is a floor-level exit with a rectangular opening of
not less than 24 inches wide by 48 inches high, with corner radii not
greater than eight inches.
Type A. This type is a floor-level exit with a rectangular opening of
not less than 42 inches wide by 72 inches high, with corner radii not
greater than seven inches.

These definitions are quite generic, but Transport Canada has a handy list of Aircraft Exit Profiles that gives specific details (often including the type) for many common aircraft. It says this for the 767 main doors:

B-767-200/300ER (Doors 1L/R FWD, 2L/R AFT)
Note: Some models equipped with 2 additional type 1 exits L/R just forward of wing.

H - 1.88 m (6 ft 2 in) W - 1.07 m (3 ft 6 in); Type A
Equivalent force required to move door control handle from closed/locked position to open position (Normal and Emergency): 12 kg
(26 lbs).
Approximate force required to open a door (lift upward) from unlocked to open: 18 kg (40lbs).
"Counterbalance" opening design.
Inward/upward opening doors.
Manually operated except some models equipped with electrical (normal operation) opening/closing option (FWD Entry Door).
Unique arming/disarming mechanism (lever, indicators).

Release button must be depressed and held to move arming lever to "Slide Armed" mode.
Yellow plastic "Emergency Use Only" (bendable) flag moves upward in front of Door Control Handle when slide is in armed mode.
Double channel slides.

Upward rotating Door Control Handle.
"Uplatch" mechanism holds door in open position. Button must be depressed while door is lowered initial few inches, to release.

You can see from that list that the details can vary a lot, even if the basic designs are very similar.
Coming up with pros and cons for every variant would be tough (especially for me, since I know nothing about it!), but obviously some aircraft are larger than others and that will limit how much space is available for the door mechanism. There are also operational considerations: aircraft that frequently operate out of smaller airports without jet bridges may need to have airstairs, which are usually built into the doors.


What is the relation between manifold pressure, RPM, and power, in a constant speed prop?

1. Why if we decrease RPM and maintain throttle lever setting the power output decrease?
Power is energy per unit of time, and since there is fewer revolutions, there is fewer power strokes to release that energy. There is less contention for the air from intake manifold so the manifold pressure will increase a bit and each power stroke will deliver a bit more energy, but not nearly enough to compensate the overall lower number of power strokes.
For this reason, manifold power can only be related to power for constant RPM, and it's still complicated by other things, especially the density altitude. Fuel flow is a better indicator of power as long as you keep the engine properly leaned.
2. Sounds like very basic knowledge but I heard a lot of versions and I want to reassure. Is tachometer on constant speed prop reading engine rpm or prop rpm?
Usually propeller, but may depend on the aircraft. But it does not really matter, because the gear ratio is always fixed and because the pilot does not have any other use for the value than comparing it to some nominal values in the operating handbook, which are aircraft-specific anyway.
In one aircraft the POH might say that maximum RPM (more can't be selected anyway) is 2500 and most efficient for cruise is 2100, but on another aircraft it might say that 2750 is for take off, but for 2 minutes only, 2600 is maximum for continuous operation and 2300 is most efficient. If it instead said 3130 and 2625, it would make no difference.
Because of this, turbine RPM is only reported in percent, which sometimes extends to the propeller on turboprops too. It is still aircraft-dependent, because some engines go up to values like 102.5% and the spread between maximum and most efficient also varies.
3. If we move prop lever we are changing blade pitch and then rpm adjust to it or we are changing engine rpm and blade angle adjust to new rpm
You are setting the desired RPM, which the governor will try to attain by adjusting the propeller pitch. If the propeller is too slow, the governor decreases the pitch, thus reducing the thrust and associated resistance until the engine can keep up, if it is too fast, it increases the pitch until the propeller absorbs all the power the engine is providing. If the throttle is too closed, even the finest possible pitch might have too much drag and the RPM will be lower than selected.
There were some variable pitch propellers where the pilot directly controlled the pitch, but the governor is a fairly simple hydromechanical device (weight on spring measures the centrifugal force and directly controls hydraulic valve that adjusts the pitch) and results in so much more practical handling that it quickly prevailed.
This is further complicated in beta range (reverse thrust) where the power lever switches to controlling pitch directly while throttle is controlled by another governor to maintain RPM. But you'll mostly encounter that on turboprops.


Can a mid wing airplane have no wing spar running through the fuselage?

Yes it can, albeit at the cost of some added weight.

By using reinforced bulkheads, the bending loads can be transferred into the bulkheads which leaves the center section free of structure. That is how large engines and their intake ducts can be placed where normally the spar would go. A classical example is the Lockheed F-104 Starfighter.

Lockheed F-104 Starfighter cut-away drawing (picture source).

Using bracing like on the Mini-MAX reduces stresses in the carry-through, but does not remove the need for something to keep the wings apart. In other words, the compression member of the wing spar is still required to transverse the fuselage where the wings are attached. Also, at high angle of attack the wing produces substantial nose thrust which could fold the wings forward were it not for a second compression strut at the wing nose.

Mini-MAX 1100 (picture source)

In case of the Cri-Cri, which is a low wing design, the pilot sits on top of the spar. Moving the wing up to a mid position would create a much heavier aircraft and would require a wider fuselage, too.

 Colomban Cri-Cri (picture source)


Does two-way communication failure include one-way communication failure?

7600 means a loss of two way communications, it's a way of letting ATC know you have a problem sending or receiving, or both.


The wing has a pressure gradient along the AB direction, is there a pressure gradient along the CD direction?

Yes, but a weaker one than in lengthwise direction.
You can observe the local pressure by comparing the distance between two stream lines. When they move closer together, speed goes up and static pressure goes down. As you move away from the airfoil, the distance between stream lines recovers to its value at infinity.

Stream lines around airfoil (picture source).
This effect depends on the Mach number of the flow. At very low speed, the recovery is rather quick because speeding up contracts the airflow so it is easy to make way for the airfoil. At higher (but still subsonic) speed, speeding up is coupled with a drop in density, so the contraction is less pronounced and it takes more height for the disturbance to die down. At supersonic speed, the pressure change is sudden (in a shock or an expansion fan), and the pressure rise of a shock reaches into infinity.