What aircraft "don't respond well to tarmac runways"?

No airplanes absolutely need a grass strip, but for some taildraggers (airplanes which have a tailskid instead of a wheel) it's a real benefit because the grass is softer on the skid, and the friction of the grass improves control on the ground and helps slow the plane down. Pavement isn't that big a problem for skids make from more modern materials, but you can imagine it's not going to do a slab of wood much good. Many vintage designs have no brakes or poor brakes, so having grass makes a big difference when landing, on pavement you'd end up rolling a lot longer and have less directional control at low speed.


Can I get a pilot's license following a vehicular homicide charge?

I'm assuming you're asking about training in the US because "vehicular homicide" is an American term, at least as far as I know. If that assumption is wrong, please update your question to include the country. You also didn't mention if you were only charged, or actually convicted.

Anyway, if we assume the US then you need TSA approval before flying solo (for citizens) or before starting flight training (for non-citizens). I have no idea how the TSA would view a vehicular homicide charge (or conviction), but obviously it's a potential issue.

But assuming you get TSA approval, you'll also need a medical certificate. Criminal charges or convictions shouldn't really matter for that, unless they involve drugs and alcohol (as you mentioned) or if the incident led to you needing long-term drug treatment, a major operation or psychological/psychiatric treatment. The FAA views psychiatric treatment in particular (including most counselling) very negatively, so if you had any that would almost certainly result in a lot of extra paperwork and potentially denial of your application.

Alternatively, you could go for a sport pilot license and fly an LSA without any medical if you have a valid driver's license. But if the FAA has ever denied a medical application from you, you can't use that option, so research and plan accordingly.

But if there are no medical issues the only other thing I can think of right now would be insurance. There's no legal requirement in the US to have any insurance in order to fly but most people who rent aircraft (including students) will have renters' insurance in case they damage the aircraft or injure someone or whatever. If your homicide charge resulted in a conviction, that could be a problem for an insurance company. Even if you don't get your own insurance, you might have to sign something for the flight school's insurers stating that you've never been convicted of a felony or motor vehicle charge (I have no idea, by the way, if vehicular homicide is a felony or not). I'm not saying that it would be impossible to get insurance, just that it might come up when/if you apply for it.

Finally, if you eventually want to get an ATP license then a felony conviction is a potential concern: see this question for more information.

Disclaimer: I'm not a lawyer or a flight instructor so don't take my word on anything important (or unimportant, for that matter). Legal issues are always tricky and for a real answer you should consult an aviation attorney or join AOPA and ask them.


When flying a circling approach, is it permitted to begin the visual circling segment prior to the final approach fix?

While researching this subject, I found a few things that shed light on the subject:

Procedures

FAA ATC Order 4-8-1 Note 1 says:

  1. Clearances authorizing instrument approaches are issued on the basis that, if visual contact with the ground is made before the
  approach is completed, the entire approach procedure will be followed
  unless the pilot receives approval for a contact approach, is cleared
  for a visual approach, or cancels their IFR flight plan.

So we have to follow the entire approach, which includes all mandatory altitudes.

Aspen Approach

AIM 5-4-20. Approach and Landing Minimums says:

  c. Straight-in Minimums are shown on the IAP when the final approach
  course is within 30 degrees of the runway alignment (15 degrees for
  GPS IAPs) and a normal descent can be made from the IFR altitude shown
  on the IAP to the runway surface. When either the normal rate of
  descent or the runway alignment factor of 30 degrees (15 degrees for
  GPS IAPs) is exceeded, a straight-in minimum is not published and a
  circling minimum applies. The fact that a straight-in minimum is not
  published does not preclude pilots from landing straight-in if they
  have the active runway in sight and have sufficient time to make a
  normal approach for landing. Under such conditions and when ATC has
  cleared them for landing on that runway, pilots are not expected to
  circle even though only circling minimums are published. If they
  desire to circle, they should advise ATC.

The key part for this discussion is that, for approaches that would be straight-in if it weren't for the high descent rate on final (like the KASE approach), pilots are not expected to circle even though only circling minimums are published. If they desire to circle, they should advise ATC.

Well, in this case we can't land straight-in after making the last crossing restriction, so what can we do?

Combining the two quoted passages, our options are:

Get approval for a contact approach
Get approval for a visual approach
Cancel our IFR flight plan
Get approval to circle since we can't land straight-in.

The first three are pretty straight-forward and can be used if you pick up the airport visually in time.

If you need to circle, I found a great article called Circle-To-Land Tactics which was written by a former chairman of the ALPA TERPs committee.  He suggests overflying the runway and then flying a modified pattern:

Teterboro Approach

We can't start our circle until we are within the protected circling area.  This means that for my category C airplane, I have to wait until 1.7 NM from the runway threshold before I can begin my turn.

We could make a right 90 degree turn followed by a left 90 degree turn to line up on final, but that would eat up about one mile just by turning.  Since runway 1 is actually closer to us than 6 at this point, I have even less distance to work with and can't even see the runway during the first turn because we are banking the wrong direction.  This would be pretty tight.

In this case, the previous article recommends a circle like this (which would be modified for our actual runway layout):

In good visual conditions, I would just ask for a visual approach so that we can start the turn a little sooner and land "more" straight-in without flying all over the airport.

One last point:  Since there is a control tower at both of these airport, make sure that they know what we are going to do!


Downwash distribution on basis of Lift distribution

You are confusing downwash ($w$) with circulation ($\Gamma$). As per Kutta-Joukowski theorem, lift per unit span (in the case of a single lifting line) depends on the distribution of circulation along the wing span:

$$L'(y)=\rho_\infty V_\infty\Gamma(y)$$

If you have an elliptical lift/circulation distribution, the circulation decreases towards zero at the wingtip, therefore lift at the tip is zero. Induced downwash, on the other hand, is constant across the span.

Source: Anderson, Fundamentals of Aerodynamics

You may believe that downwash is the largest at the tip due to the presence of wingtip vortices. However, the vortices are better understood as downwash rollover at the wingtips. The vortices themselves do not contribute to lift generation (but unavoidable for finite span).


Why does TAS increase as altitude increases and why does my C-152 POH seem to contradict this?

Imagine that IAS measures the number of air particles hitting your aircraft per second. As you get higher the air is thinner — there are progressively fewer air particles around the higher you go so to get the same number of particles hitting you per second (ergo the same IAS) you need to move faster through the air - your TAS increases.


What is the best route for my 18 year old son to become a pilot with a major airline?

Look for a community college with an aviation program, they're quick and VERY affordable. I attended Iowa Lakes Community College, I was able to get my Private, Commercial, Instrument, Multi-Engine, and Instructor ratings in 2 years for $38k. DO NOT send him to a large university like UND, the programs are insanely overpriced and they take 4 years solid. At Iowa Lakes, you can get done as fast as you can, people have gone from student to instructor in a year, it all depends on you, at universities you HAVE to stay all 4 years which is a killer in an industry so heavily reliant on seniority. I have the exact same ratings as a kid coming out of UND only I have 1/4 his debt and I'm probably already a captain at a regional when he first gets to the airlines. Airlines are REALLY hurting for pilots, this is absolutely the best time to be a pilot.


Can a GPS signal sent to a plane be spoofed?

Spoofing GPS means broadcasting a false GPS signal - This is harder than jamming GPS which can be done relatively easily by broadcasting a strong random signal at the relevent carrier frequencies.

GPS receivers use GPS ephemeris tables which tell them where exactly they should expect each satellite to be. So the false GPS signal has to look enough like a real GPS signal that the receiver will accept it and use it's transmitted data in it's calculations.

Of course, if, for example, the expansionist president of a country with advanced avionics capability decided to supply sophisticated equipment and the associated personnel to a separatist group in a neighbouring country, it might be possible for them to bring about this kind of result.

There have been reports of this kind of spoofing actually happening, so it appears to be possible.

  The U of Texas students built a GPS spoofing device for about $3,000. A pair of students, the “attackers,” then sat aboard the upper deck of the White Rose, where their GPS spoofer emitted a counterfeit signal slightly stronger than the real GPS signal.

This was a yacht at sea, presumably out of sight of land on a featureless ocean.

It may be more difficult to achieve this with an airliner, which have a variety of navigational instruments, including radio navigation beacon receivers. Inconsistent indications may alert the pilot to a problem.

Non-GPS navigational instruments/systems that may be found in an aircraft include:

VOR
DME
NDB/ADF
TACAN-DME
ADIRU


What does the 'hp' rating actually signify, with respect to an aircraft engine?

What is horsepower? It is a measure of the work a horse can do in an hour, invented in the time of the steam engines in order to make sense of what they could do, in a time when all work was done by humans and horses. As usual before the SI, there were many definitions of horsepower. Here is the one from wiki, on what a metric horse could do:

Notice that there is a time element in the picture: if the horse takes all day to raise the weight one metre in height, he is not very powerful.

Nowadays, the unit of power is the Watt, after James Watt who coined the horsepower unit to sell his steam engines. It is defined as the force in Newton, required to move 1 kilogram over one meter in one second:

$$1 W = 1 \frac{N \cdot m}{s} $$

In these units, you can see a force times a velocity, and that is one way of looking at what power is: you need more power to drive faster up a hill. But these are linear entities, and most power is made by rotary engines. Rotary units are torque (N*m) and how fast the engine is spinning (rad/s).

With engines, it makes a difference where power is measured. There are always losses caused by friction and by energy conversion, and the closer you measure at the output shaft of the engine, the higher the reading. This is what vehicle manufacturers rather do: car engine power is measured at the crankshaft, not at the wheels that actually propel you over the roads, because between engine and wheels there are transmission losses.

The question why power is used for engine rating, and not force or torque, is an interesting one. It is force that accelerates us: $ F = m \cdot a$. We can gear the motor force or torque output as required - if the gearing had no losses, power before and after gearing would be the same. So horsepower is useful to compare capabilities of engines, regardless of gearings. However they wil always be maximum capabilities.

With an aircraft, the engine power needs to propel the aircraft via the propeller. The propeller delivers thrust T, and can drive the plane at speed V, maximum speed being where drag equals thrust. Engine power is thrust times airspeed, plus the power required to overcome losses: mechanical losses due to friction, and aerodynamic losses due to propeller efficiency.

Your question on having an aircraft a quarter of the weight and similar size. The thrust is required to overcome aerodynamic drag, both friction drag and induced drag from lift. Friction drag will remain equal, lift induced drag will be 1/4th of the full weight version. You will need more than 45 hp to get the quarter weight aircraft to travel at the same cruise speed.

The picture is from this most informative source: parasitic power stays the same, induced power reduces by a factor 4. Notice that at low speeds induced power is dominant, at high speeds parasitic power is dominant. So with a 45 hp engine you will get off the ground if the weight is reduced by factor 4, but the maximum speed will be way less.


Boeing designs its own airfoils for its aricraft. According to this site, the following airfoils are used in 737:

Boeing 737-100: Wing root- BAC 449/450/451; Wing tip- BAC 442

Boeing 737-200: Wing root- BAC 449/450/451; Wing tip- BAC 442

Boeing 737-300: Wing root- BAC 449/450/451; Wing tip- BAC 442 mod

Boeing 737-400: Wing root- BAC 449/450/451; Wing tip- BAC 442 mod

Boeing 737-500: Wing root- BAC 449/450/451; Wing tip- BAC 442 mod

The 737 wings are manufactured at the Boeing plant in Renton, Washington.


What practical alternatives are there to 100LL in 2021?

Right now, Mogas is the only alternative fuel because the unleaded avgas program still seems to be going nowhere, although the industry testing program is supposed to restart this year.
You could put an aircraft diesel engine in your plane if you're rich, and run it on Jet A, but if you can afford that, you can probably afford other alternatives as well.
The most practical thing for a prospective owner to do is to buy an airplane and incorporate the Petersen Mogas STC (it's just a paperwork/placard mod for a lot of high wing airplanes, but physical parts may be required in other cases), and run the plane on mogas when possible, and avgas when not.
Overall, Mogas is better, because the tetraethyl lead in avgas used to get its octane rating is just bad news all around (the lead combustion byproducts contaminate the oil, leave crud in the cylinders, etc.) Mogas's main caveats are higher Reid Vapor Pressure (it boils more readily) and long term storage.  Mogas is more volatile and needs fuel stabilizers if a fuel supply is left for more than few months.  The volatility also means more susceptibility to vapour lock.
On airplanes with gravity feed fuel systems, vapour lock is less of a problem because there is positive fuel head pressure all the way from the tank to carb.  On low-wing pumped-fuel airplanes, there is pump inlet suction, which to the gas is like going up a several thousand feet depending on how hard the pump sucks, so on a very hot day with a hot engine, there is a chance of vapour lock and it can be prudent to install cooling shrouds on fuel system components like engine driven pumps (you'll know it's happening as the fuel pressure fluctuates).  I was having incipient vapour lock indications on my plane during heat waves (only on the ground) and installing a cooling shroud for my engine-driven fuel pump seems to have solved it.
Those issues aside, any 80 octane engine will be MUCH happier running on Mogas than 100LL, so if you can do it, it's a no-brainer.


What is the feasibility of converting an F-22 to carrier use?

In general, land based aircraft do not lend themselves well to carrier conversion. On the other hand, conversion in opposite direction is (relatively) easy, as shown by F-4 and F-18.

Conversion of aircraft to carrier use require a number of modifications:

Tail hook has to added and rear fuselage reinforced for arrested landings.
Landing gear has to be strengthened for high sink rate (~24 ft/s).
Atleast in USN, the front landing gear and fuselage has to be strengthened for catapult launches.
Also, it requires additional equipment, like th Carrier Landing system, redesigned refueling system (pretty much everyone use a system different from USAF).
Carrier based aircraft usually are expected to have better low speed capabilities as they have to fly slower approaches and wave-off (go-around) at lower speed compared to the land based aircraft. This dictates the wing loading, resulting in increased wing area and/or high lift devices.
There are also issues in corrosion prevention etc.

The weight penalty due to these reasons can be non negligible. For example, the naval Rafale M version weighs nearly 500 kg more than the Air Force Rafale C variant (which has ~10 ton empty weight). USN calculated that the NATF (Naval Advanced Tactical Fighter) will be around 1800 kg heavier than the Air force version (ATF was supposed to weigh ~15 ton).

Another thing is that the USAF and USN had different requirements, for example, the USAF wanting a single seater and USN wanting a double seater, requirement of different sensors (for fleet defence) etc. in the end, the aircraft proposed for the NATF looked nothing similar to the one that finally became the F-22 and the project was quietly buried.

F-22 NATF proposal, image from aerospaceweb.org

Note that the design has swing wings, as the aircraft was being proposed for replacing F-14 Tomcat. Another important result of the navalization of the aircraft is the reduction in the number of planform alignments, and their negative impact on the stealth characteristics.

Carrier conversion of F-22 could have been done if it was considered early in design. Doing it now (note that NATF was considered due to the insistence of Congress; it is doubtful if USN ever wanted it). Doing so later in the design process will result in another F-111B fiasco. As for doing it now, it is better to design a new aircraft (which was what the F-35 is).


What's wrong in this engine test cell picture from the book 'Ignition'?

I think there's a mix-up in the labeling of the photo.

Here's the photo and caption from a copy of "Ignition" that I just downloaded:

Here's the photo and caption from the next page:

Seen together, those two photos and captions make sense.

Somebody mixed up the images and the captions in the copy you are reading.


Is there a benefit to having the motors for a multi-rotor copter on the top vs the bottom of the frame?

It could be just for looks, but rotor placement has a noticeable effect on the behaviour of the quadcopter.

The higher the rotors are on the frame the higher the center of lift will be (the center of lift for quadcopters is the center of the plane created by the rotors.) A high center of lift means that the frame will be more stable. A low center of lift means the opposite. The reason for that is that the quadcopter can better naturally deal with lateral rotational forces on its frame. The center of lift being above the center of mass means that the frame is "hanging" like a pendulum from it. If you apply a lateral force to it, it will naturally swing back to place and the more you push the "harder" it becomes to move the frame.

A center of lift that is in the same spot as the center of mass of the frame means that there is no pendulum effect. This is like balancing a ball on top of another ball. All lateral forces, either internal like variations on each rotors' force or external like wind perturbations have maximum effect in moving the frame.

Contrary to what you might think, stability is not something you want in a quadcopter. The more unstable the frame, the more agile it becomes. Small variations in rotor force will create large rotational movements. The penalty you pay for that (small, unpredictable external forces also create large rotational movements) you make up with processing power. Processors are now so fast and sensors so sensitive that they easily can compute the external forces and create a response fast enough to keep the frame flying.


Are turbine and compressor blades and vanes cast or forged?

As a summary,

The fan blade is made by shaping molten titanium in a hot press. When removed, each blade skin is welded to a mate, and the hollow cavity in the center is filled with a titanium honeycomb.

The compressor blades are made by casting

Turbine blades are made by forming wax copies of the blades and then immersing the copies in a ceramic slurry bath. After each copy is heated to harden the ceramic and melt the wax, molten metal is poured into the hollow left by the melted wax

Please refer to the following website, it is very interesting for the manufacturing process of the main engine parts:

http://www.madehow.com/Volume-1/Jet-Engine.html

Concerning the fan blades:

  Each fan blade consists of two blade skins produced by shaping molten titanium in a hot press. When removed, each blade skin is welded to a mate, with a hollow cavity in the center. To increase the strength of the final product, this cavity is filled with a titanium honeycomb.

Concerning the compressor blades:

  Casting is used to form the compressor blades. In this process, the alloy from which the blades will be formed is poured into a ceramic mold, heated in a furnace, and cooled. When the mold is broken off, the blades are machined to their final shape

Concerning the turbine blades, it is multi-process:

  Turbine blades, however, are made by a somewhat different method than that used to form compressor blades, because they are subjected to even greater stress due to the intense heat of the combustor that lies just in front of them. First, copies of the blades are formed by pouring wax into metal molds. Once each wax shape has set, it is removed from the mold and immersed in a ceramic slurry bath, forming a ceramic coating about .25-inch (.63-centimeter) thick. Each cluster is then heated to harden the ceramic and melt the wax. Molten metal is now poured into the hollow left by the melted wax. The internal air cooling passages within each blade are also formed during this stage of production.

  The metal grains in the blade are now aligned parallel to the blade by a process called directional solidifying. The grain direction is important because the turbine blades are subjected to so much stress; if the grains are aligned correctly, the blade is much less likely to fracture. The solidifying process takes place in computer-controlled ovens in which the blades are carefully heated according to precise specifications. The metal grains assume the correct configuration as they cool following their removal from the oven.

  The next and final stages in preparing turbine blades are machine-shaping and either laser drilling or spark erosion. First, the blade is honed to the final, desired shape through a machining process. Next, parallel lines of tiny holes are formed in each blade as a supplement to the interior cooling passageways. The holes are formed by either a small laser beam or by spark erosion, in which carefully controlled sparks are permitted to eat holes in the blade.

The cost of old models parts could be very expensive because they are manufactured upon request, that was the case for Concorde engines.

The financial aspect of the question is beyond my scope


What airport proposal(s) has London seen after WWII?

There was one more proposal before Thames Estuary Airport. That was the Cublington airport, which was rejected by planner Colin Buchanan,as "an environmental disaster." Later the government rejected the proposal of this airport, and rather went for Thames Estuary.

Other than that, there are no more proposals for new airports, but there are certain plans for expanding existing Heathrow and Gatwick.

The Airports Commission says there is a need for one additional runway in the South East of England by 2030.
It has shortlisted three options:

A third runway at Heathrow
Lengthening an existing runway at Heathrow
A second runway at Gatwick

Read in detail about all of them HERE


Why do aircraft fly over land rather than over the Adriatic Sea?

Most air routes in Europe are unchanged since the days before GPS, when they were defined by radials from VOR and NDB radio beacons. As these have a limited range, they could easily be used to define routes across the Adriatic, but less so down its several-hundred-mile length. Routes would therefore normally be defined over land where the plane can route from beacon to beacon, rather than over the sea where (unless you are flying towards or away from a coastline) you cannot fly with as much navigational precision as when following a radial to/from a beacon.


Why Lift-induced Thrust Required(Tr) decreases and Zero-Lift Tr increases with the increase of velocity?

This happens because Angle of Attack required to maintain flight at a given weight decreases with the increase of speed.
As for the zero-lift Tr, also known as "parasitic drag", while its coefficient is a constant, its formula is not: it actually has a cube of velocity.


Do commercial aeroplanes use ABS to brake?

Yes, they do. They are called Anti-Skid and they go from Mark I of 1948, with simply an on-off switch triggered by wheel lock, till Mark V (or at least that's the last I've seen), with quite complex control systems and sensors behind.

The full details are a bit long to include them all here (there are entire book sections about them). For a brief overview, see this presentation from slide 12 till 18.


Why aren't tilting propellers used as an alternative for ailerons or elevators?

It isn't done because a moving control surfaces is easier to design and build than an engine mount that rotates.

Plus the associated structure needed to accommodate the thrust, p-factor, and gyroscopic loads is going to be a lot heavier than ailerons, spoilers, moving tail plane, etc.

Another issue is if one loses one or both engines, your roll and pitch control disappear as well.


Depends on how bad is the sea state, but the general technique for seaplanes is to land parallel to the swell, preferably on top of a wave:

  When landing on a swell system with large, widely
  spaced crests more than four times the length of the
  floats, the best landing heading parallels the crests and
  has the most favorable headwind component. In this
  situation, it makes little difference whether touchdown
  is on top of the crest or in the trough.

If forced to land against the swell, it is recommended to land on the backside of the wave:

  If crosswind limits would be exceeded by landing parallel to the swell, landing perpendicular to the swell
  might be the only option. Landing in closely spaced
  swells less than four times the length of the floats
  should be considered an emergency procedure only,
  since damage or loss of the seaplane can be expected.
  If the distance between crests is less than half the length
  of the floats, the touchdown may be smooth, since the
  floats will always be supported by at least two waves,
  but expect severe motion and forces as the seaplane
  slows.
  A downswell landing on the back of the swell is preferred.


Has anyone attempted to board a flying aircraft mid-air?

Sure. It was regularly done by the aerialists or barnstormers of flying circuses during their heyday in 1920s.

  Barnstormers performed a wide range of stunts. Although many of them handled all their own tricks, others became specialists, either stunt pilots or aerialists. Stunt pilots performed daring spins and dives with their planes, including the well-known loop-the-loop and barrel roll maneuvers. Aerialists, on the other hand, performed such feats as wing walking, soaring through the air with winged costumes, stunt parachuting, and midair plane transfers.

These were mostly done using army surplus biplanes after WWI. The performers boarded aircraft from a variety of vehicles, from cars to speedboats. This ticket for one of the performances clearly mention the midair plane transfers.

Ticket for a flying circus; Image from all-things-aviation.com

As time went by, lack of cheap aircraft and tightening federal regulations put an end to barnstorming. I'm not aware of anything like that in modern times. Anyway, mid-air transfers are not easy and are quite dangerous, as Simon Crane found out while shooting for Cliffhnager.


Why are vertical stabilizers always at the rear of an airplane?

With sea creatures the dorsal fin acts as a keel providing the actual sideways force during the turn. They remain level while turning.

Planes on the other hand bank to turn where the sideways force is provided by the lift of the wings.

To provide yaw stability the vertical stabilizer should be as far from the center of mass as possible. They are not in front because that would be unstable as the minor deviation from straight ahead would increase the force into the deviation rather than provide a force to counteract it.


Is there an ideal air temperature for best performance in a light aircraft?

Good Evening Alex,
just for the record I'm a Private Pilot with about 150 hours of flight time, I would recommend speaking to a Flight instructor if you have any more questions about Aircraft POF. (principles of flight and performance)

Best Performance can be narrow down to a simple formula
Best Performance = High Pressure + Low Temperatures

1 hectopascal is equal to 30ft change
1º celsius is equal to a 120ft change  br>

If you are looking for the landing and T/O I would suggest looking a Performance charts-which


How far could the Airbus A321XLR actually fly commercially?

Airbus is quoting the ranges in nautical miles (nm) which is typical for aircraft. The Great Circle Mapper you linked is using statute miles, which are shorter. If you switch it to be in nautical miles, you get 4115 nm, which is well within the quoted range.


What is the possibility of a depressurization emergency during a commercial flight where all or some of the oxygen masks fail?

The oxygen system for passengers in an airliner is generally powered by a chemical oxygen generator.
The generator contains chemicals, which when they come into contact with each other, commence a reaction that produces oxygen for a few minutes.
The act of pulling down the mask triggers the contact between the chemicals.
A generator typically serves two or three seats, and each generator is independent of the others on the aircraft. They are not part of a single system with common points of failure.
The panel behind which the masks is opened by a pressure switch, and can also be opened manually.
However the crew will use bottles of oxygen, and the flight crew will use a more complex system that also includes smoke hoods.
Conceivably (anything is possible) a manufacturing fault or sabotage could render every single one of the generator/mask sets inoperative, but it would be an extraordinarily unlikely thing to happen.
People often imagine a system of pipes carrying oxygen to all the masks, but in fact such a system is rarely used. One notable example is the earlier (-100 to -400) variants of the Boeing 747, in which the oxygen is indeed piped. And, apparently, may have not always worked as expected:

The flight crew donned their oxygen masks and manually deployed the passenger oxygen masks.
[...] The PIC was also advised that there appeared to be no oxygen flowing through any of the passenger cabin oxygen masks, however this did not seem to have had any ill effect on the passengers. After the PIC cycled the passenger oxygen switch, a momentary surge of oxygen through the passenger masks was observed.

(from an Australian Transport Safety Bureau report into a November 2001 incident)


An 'aerodynamic force' (just one force...) appears when a body is immersed in a fluid stream. By convention, two components are chosen, one of them parallel to the stream direction, called 'drag', and the other one, perpendicular to that 'drag' is termed 'lift'.


What does this symbol on this Aerodrome Chart mean?

It is the Aerodrome Reference Point, ARP.

As per ICAO annex 14 vol 1, chapter 2.2:

  2.2 Aerodrome reference point

  2.2.1 An aerodrome reference point shall be established for an aerodrome.

  2.2.2 The aerodrome reference point shall be located near the initial or planned geometric centre of the aerodrome and
  shall normally remain where first established.

  2.2.3 The position of the aerodrome reference point shall be measured and reported to the aeronautical information
  services authority in degrees, minutes and seconds.

The FAA likes to use the term "Airport Reference Point"

Please see the Jeppesen AWM introduction - airport chart legend (pdf). Chart on page two has the symbol with refrence number 17, and on page three this is explained as:

  17 — The geographical location of the Airport Reference Point (ARP) is depicted when known.


Why isn't the application of "carb heat" in initial piston multi-engine failure emergency procedures?

Partly because carb heat is ineffective once the engine is no longer making power, but mostly because the initial engine out procedure isn't intended as remedial action to get the engine running again; the drill is to make sure the airplane is configured to be able to climb (somewhat) in the moments after the failure, so the priority is everything balls to the wall, gear and flaps, identify, confirm, feather with the aim of establishing a climb foremost.

In any case, if you applied carb heat to both engines as part of the drill, the dead engine would be getting probably insufficient heat anyway, and the live engine will enjoy a few percent power reduction from the application of heat.  On a piston twin like a Seminole or Duchess at gross on a hot day, that alone may be the difference between barely climbing or descending, so that the remaining engine takes you directly to the scene of the crash as the old joke goes.


Is it possible to upgrade a Boeing 747-8 and Airbus A380's engines for greater speed?

I just wanted to comment on this question since some of my code is on the A380's GE engine.

Those engines are optimized for fuel efficiency at their cruising altitude and speed.  The tradeoff that you fight against when designing the engine for cruising altitude is that it makes the engine hard to start, and the stall margin (the pressure and fuel combo you need to keep the engine from stalling) is razor thin when they are on the ground.

Just to echo what Kevin said, any improvements to allowing the engine to start without stalling would surely go to the fuel efficiency, not to speed.


As noted here

  A thin edge is called a feather edge and can lead to preignition; the
  valve edge would burn away in a short period of time, and the cylinder
  would have to be overhauled again.

Basically during a rebuild over-grinding the valves can lead to a feathered edge which in turn can lead to higher/faster engine wear. Essentially by grinding the edge to thin you cause the limited remaining metal to wear out much faster. This can also lead to valve seating issues and out right leaks.


What do air traffic controllers do on a slow day?

The airspace around the world is divided into sectors within a Flight Information Region (FIR) /Air Route Traffic Control Center (ARTCC) / Area Control Center (ACC), which range from very small and tight airspace pieces to larger combinations or enroute sectors. Enroute sectors will usually be larger than Terminal Maneouvering Areas (TMA).

During peak-hours, these sectors will be handled by one controller responsible for each sector. If capacity and traffic flow permit, these sectors can be combined and two sectors will be handled by the same controller.

Below is a picture of the Paderborn Lower Sector, ranging from GND to FL135. This is usually a stand-alone sector which only covers approaches to Paderborn (EDLP) and Dortmund Airports (EDLW).

(Image Source: Own Work - Author: SentryRaven)

If traffic permits, the adjacent sector Hamm Lower from GND to FL115, handling arrivals and departures to Münster (EDDG), will be handed over to the controller responsible for Paderborn Lower. This can also be done vice-versa, where the Hamm Lower controller becomes responsible for the Paderborn Lower sector.

(Image Source: Own Work - Author: SentryRaven)

TMA controllers not only handle IFR aircraft approaching or departing from airfields within their sector, but also any enroute traffic crossing the sector, VFR traffic requesting to cross airspaces which require prior permission and other tasks.

As Chatty already pointed out in his answer, controllers take breaks between working their sectors and sometimes often switch sectors during a shift. A controller working Paderborn Lower during the beginning of his shift can end up working Hamm Lower towards the end of his shift with adequate breaks in between their sessions.

See this related question:
What is the maximum number of planes a controller can control?


What would happen if multi engines operated symmetrically?

A single engine plane yaws to the opposite direction of the engine spinning. This is called the p-factor It's the same with a twin, with both engines rotating into the same direction. Rudder input is needed to fly straight.
When the engines operate symmetrically, this effect cancelles out. The plane is easier to fly.
It's also explained in this video about twins.
An example of a counter-rotating multi-engine plane is the Lockheed P-38 Lightning.

[The P-38] featured two 1,000 hp (746 kW) turbosupercharged 12-cylinder Allison V-1710 engines fitted with counter-rotating propellers to eliminate the effect of engine torque.
Counter-rotation was achieved by the use of "handed" engines, which meant the crankshaft of each engine turned in the opposite direction of its counterpart.

If the engines are turning in the same direction, then if either fails, the net p-factor will not be the same. See: Critical engine.


Can current fighter jets perform a deadstick landing?

Here's an F-16 doing it.

Apparently there is an emergency APU that runs on hydrazine to power the hydraulics instead of a RAT.  They mention it at the end because they have to call out fire trucks because of the hydrazine hazard.

I used to have an F-104 flight manual, which I must have loaned out to someone and never saw again.  It could actually glide fairly well, with an L/D of about 4 or 5 to one at about 190 kt if I recall.  It had a section on gliding engine out.


The suction peak is the point of lowest pressure on an airfoil, in other words the highest point on a typical pressure or Cp graph of an airfoil. On an airfoil it's typically located just after the leading edge on the upper surface, take a look at this image for instance. In that image you can also see that as you increase the angle of attack of the symmetrical airfoil (i.e. as you increase your lift), the suction peak becomes higher. At your stall angle of attack, the "adverse pressure gradient" becomes too high and the flow separates. An adverse pressure gradient means that the pressure increases.

Note that if you would put a symmetrical airfoil at a negative angle of attack, the pressure peak would appear on the lower side, just behind the leading edge.

Also, the suction peak doesn't have to be just behind the leading edge. It is for many airfoils because the point of highest thickness is quite close to the leading edge, but take a look at a natural laminar flow airfoil for instance. The suction peak is around 65%. Here the goal is to keep the flow laminar as far as possible. An adverse pressure gradient will also favour transition of the flow.


Could sprinkling cool water on the runway in hot summer decrease air density?

There are a few problems with this idea:

The water evaporating would increase the humidity, likely canceling any cooling benefit.
The effect would be localized in a very small region just above the pavement.
The effect would be temporary as any breeze would quickly blow the cooled air away.


How do aircraft stall warning systems work?

Audible Warning
On light aircraft there is a reed (much like used on a musical wind instrument) mounted on one wing root, which is angled such that at the Angle of Attack which would cause a stall, the reed "plays" which can be heard in the cockpit.
Here is a view of where this system is mounted on a Cessna:

(source: weekendcfii.com)
On some aircraft, it is a similar principle; however instead of a reed, it uses a fin which at critical AoA pushes a micro-switch which activates a buzzer/horn inside the cockpit.
Here is the assembly on a Beech 18:

(source: eaa1000.av.org)

So, if you ever see anyone doing this:

They are not kissing their aircraft for good luck, merely testing the stall warn as part of pre-flight checks!
Tactile Warning
In addition to an audible reed/buzz/horn, most aircraft also provide tactile feedback to the pilot of an impending stall. In purely mechanical aircraft the aerodynamic forces on the control surfaces are transmitted through the mechanisms and are felt directly by the pilot when approaching a stall. In hydraulic or fly-by-wire aircraft, this is provided by a mechanical "stick shaker" linked to the same system as sounding the audible alarm.


How should night time be calculated when it is not night during the entire flight?

By the time that you're operating a 777, the amount of "night" time in the logbook is probably of little to no concern, so getting things exactly right to the minute may not be a great worry.
I'd simply grab a location every 15 minutes, either by GPS if your app has that, or else as (time elapsed / total time) * total great circle distance, and then for that location determine if you're between EECT & BMCT at that time. If so, log those minutes as night.
You could get fancier by interpolating the BMCT (for instance) between the last point you were in "night" and the first point you weren't. Then you have "the" time that you passed from night into day.
To implement that, you'll need to calculate the EECT & BMCT for an given point, plus find points along the great circle route. I'd expect that algorithms are available for both of those functions, but it's not something I've ever implemented.


Why might an airliner fly a large U-turn before landing?

Airplanes prefer to land in a headwind. This reduces their groundspeed compared to landing with the same tailwind.

Braking distance grows quadratically compared to groundspeed. So any significant reduction in groundspeed is worth having.

Successive airplanes should all come from the same direction to land. This removes any danger of collision when a plane fails a landing and goes around into what would otherwise be oncoming air traffic. Planes also prefer to take off into  headwind, so if takeoffs are intermingled with landings (very common in a busy airport) they won't interfere with each other if they all go the same way.

The tower monitors the wind and then decides which way the airplanes should come in to land and directs landing craft to land from that direction.


What is the difference between a trim tab and a servo tab?

A trim tab is operated by an independent control to a variable position that is normally fixed once set, unless readjusted, and is done to cause the control surface to aerodynamically want to hold a position that is different from its normal "trail" position, without any input from the cockpit end.  Think the typical elevator, aileron, or rudder trim used to correct a roll or yaw tendency, or to set the "hands off" trim speed in the case of elevator trim.

A servo tab is integrated into the flight control's operating components in such a way as to drive, or help to drive, the control surface during normal control inputs.  Sort of "poor man's power steering".

You can use a servo tab to operate the control surface, that is otherwise free to trail in the airstream, completely on its own.  The stick in the cockpit is connected only to the servo tab itself.  Such control surfaces will often hang down at the bottom of their travel until airspeed "blows" the surface into its normal trail position, from where the servo tab then drives the surface up or down based on cockpit control inputs.  DC-9s and Bristol Britannias use pure servo tab operated flight controls.

Or you can use the servo tab in conjunction with a normal control circuit to boost a normally mechanically operated surface, by mechanically gearing it to move in a way that applies a local aerodynamic load that helps with the pilot control input, like having someone push on the trailing edge to help you while you move the controls.

There is a kind of hybrid arrangement you will see sometimes, called a "Spring Tab".  This is a servo tab who's input linkage is also connected to the control surface by a torsion spring torque tube, typically on an elevator system.  When you move the control in the cockpit, the control circuit input drives the surface directly, but though the springy torque tube so the surface lags the input to the extent that the torque tube twists under load.  When the torque tube twists, at the same time the input side is connected to a servo tab that displaces to help the surface move.  The surface works like a pure servo tab driven one with small inputs, but as the inputs get larger there is more of a direct force acting on the surface from the torque tube like a regular control.

This is used to get the light control forces you get with a pure servo-only driven control surface, but with the ability to still drive the surface directly to full travel when called for.  Spring tabs are popular on DeHavilland Canada transports like the Dash 7 and Dash 8.

Then there is the "anti-servo" tab. The anti-servo tab, by gearing to move in the opposite direction to a servo tab, is used to deliberately increase the normal restoring forces working on the surface when displaced from its trail position. You might add an anti-servo tab because the control forces are too light, or you want light forces near neutral but want the forces to build faster than they would without the anti-servo tab.

Mechanically operated "all flying", or Stabilator tails, such as used on the Cessna Cardinal and Piper Cherokee line, depend on an anti-servo tab to provide all of the restorative forces for the control surface, for basic stick-free static pitch stability.  They actually do double duty, and at the same time have an adjustable fixed "neutral" position, varied by the trim wheel in the cockpit, that provides for normal elevator trim (speed seeking).


How can I take 360° panoramic pictures in an aircraft or helicopter?

This is as much a photography question as an aviation one. The type of aircraft you might want depends on the type of picture you want.

If you want a picture from low altitude, showing the area nearby, a helicopter or a quadcopter (depending on local regulations) would be ideal. This would let you hover in one spot, and rotate to cover the full panorama. The movement of the aircraft could easily be compensated for in processing the photos. A quadcopter holding a position by GPS should be very stable for long enough to take the photos.

If your picture is at a higher altitude, focusing more on things further away, a small plane could work. Many general aviation aircraft can fly fairly slow. With only more distant objects as the subject, a plane in a turn at under 100 knots should be slow enough that the perspective change would be negligible.

If you could get something like a simplified version of Google's street view setup, and send it up on a quadcopter, that would probably give the absolute best result.

See also this more general question:

What is a good plane for aerial photography?


How are these Airbus A350s flying in formation without being affected by wake turbulence?

You are right that wake turbulence would be a danger when flying behind another aircraft like that.

The perspective of the photo makes it hard to see the actual position of the trailing aircraft relative to the ones in front of it. Pilots do this sort of thing in airshows when they fly in formation. The trailing aircraft are generally slightly below the ones in front of it. This allows good visibility of the plane they are following. At the higher speeds that these jets are flying at, the wake vortex will not drop enough to impact an aircraft fairly close behind and below.

See this old photo of the Thunderbirds. From this perspective, it is easier to see that the trailing aircraft is also below the flight path of the leading aircraft.


When is an aircraft required to be pressurized?

The main reason is that it's simpler than having everyone wear supplemental oxygen masks. There is no specific requirement for pressurizing an airplane but there are requirements for supplemental oxygen as per FAR 91.211

  (a) General. No person may operate a civil aircraft of U.S. registry--

  (1) At cabin pressure altitudes above 12,500 feet (MSL) up to and
  including 14,000 feet (MSL) unless the required minimum flight crew is
  provided with and uses supplemental oxygen for that part of the flight
  at those altitudes that is of more than 30 minutes duration;

  (2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required
  minimum flight crew is provided with and uses supplemental oxygen
  during the entire flight time at those altitudes; and

  (3) At cabin pressure altitude above 15,000 feet (MSL) unless each occupant of > the aircraft is provided with supplemental oxygen.

So by pressurizing the plane to under 15,000 ft you can fly over that altitude and not need to supply the passengers with supplemental oxygen for the duration of the flight. There are unpressurized piston planes that fly well into the flight levels but are required to carry supplemental oxygen and everyone aboard needs to use it, it's a look some people in general aviation don't mind,

(source)

On a slight side note the engine does have an effect on this choice when it comes to light singles. Pressurization systems on turbo props/light jets pull their air from the compression stage of the turbine which is already compressing air so no extra compression hardware is needed. If you have chosen a piston engine for your design you need to drive some form of pressurization system which can add weight and complexity. There are a few pressurized piston planes out there like the Mooney Mustang, Cessna 210 (came in both pressurized and un pressurized) and the Piper M350 (the only one currently in production).


How to design a near vertical take off airplane?

Yes that is conceptually correct. You might have to mount a huge area, since lift is proportional to $V^2$.

Issues to resolve that I can see:

The craft would be relying upon aerodynamic forces to maintain attitude, which will be very ineffective at 20 mph. A secondary pressure relief valve system for attitude control would be advisable.
Landing at 30 degree nose up will be not easy from ground view perspective, and for landing gear design.
Ground effect will change the attitude of the craft if not carefully designed.
A wing that does not stall until 30° will be a tall order, and landing at the brink of stall is not advisable, you'll need some margin.


Is it standard procedure to unlatch the cockpit door before an emergency landing in a small aircraft?

As always check your POH for procedures, however most light aircraft call for unlatching the door in the event of an emergency landing or ditching.  Two principle reasons: 1. It aids egress, which can be difficult with a jammed door. 2. It allows better energy absorption of the front part of the fuselage, by permitting it to crumple better.


What is the average deviation from the PAPI glide slope at the threshold?

If one approaches with three red and one white light what will be the
  average deviation from the standard threshold height of 50 feet?

Short answer

It depends on the location of the PAPI (and its slope). For a 3° PAPI at 1,000 ft (305 m) from the threshold, three red lights means you cross the threshold between 43 and 49 ft.

PAPI heights at runway threshold

Explanation

There are different ways to calculate this. One is to start from the distance of the change from  red to white for the third light, which is given in this table (line B):

Source

The right side is for APAPI, let's ignore it. d2 is the distance from the PAPI (not from the threshold) an aircraft flying at a height of 1,000 ft sees the system switching from 3 red lights to 2 red lights.

If at this point the aircraft starts following the B glideslope, it will maintain this 2/3 red lights limit until landed. It will have lost 1,000 ft over a distance of d2.

A simple application of Thales theorem, about proportionality, says:

height at threshold = 1,000 * d / d2

where d = distance PAPI to threshold.

Example:

PAPI slope 3°
d2 = 3.33 NM = 6,167 m
Distance PAPI to threshold = 305 m

so height at threshold = 1,000 * 305 / 6,167 = 49 ft

If we do the same calculation for the other light transitions, we get: 60, 55, 49, 43 ft respectively.

Actual height

To elaborate on CVn's comment: A PAPI isn't corrected for parallax error. The sensor being the eyes, and having a difference between eyes height and wheels height, the PAPI glide path is always higher than the landing wheels.

In particular when the glide path crosses the threshold at 50 ft, the wheels are a bit lower, the actual height depending on the particular aircraft configuration and attitude. This error comes in addition of the glide path inaccuracy itself (+/- 3 ft at the threshold between lights + angular setup error). A PAPI is not a precision instrument, and the landing has to be done visually.

Larger aircraft performing precision landings are fitted with radar-altimeters located on the belly, well below the pilot eyes and close to the main wheel. Their raw value is usually corrected, by adjusting the aircraft installation delay beyond what is required for line length cancellation, to indicate the main wheels height.

This improved precision allows for lower decision heights (the point where the pilot is not allowed to pursue the landing if the runway isn't in sight).


Why do military turbofan engines use a low bypass ratio?

It's not military vs civilian, but subsonic vs supersonic-capable

Note that subsonic military aircraft use the same engines as civilian aircraft, even if their names might be different.

The KC-135 used initially the J-57 which was called JT-3C when used in the Boeing 707-120. Now they fly the CFM-56, which is used on the Boeing 737 and the A320.
The C-5 Galaxy uses the GE TF39 which became the CF6 when mounted to a Boeing 747-100 or a DC-10.
The Fairchild A-10 uses the GE TF34 which is called CF34 when mounted to civilian aircraft like the Bombardier Challenger.

No, the differences arise only when the aircraft is designed to fly supersonic. This requires a very different approach to the integration of the engine:

Supersonic aircraft engines are mounted close to the centerline. If possible, they are straight behind the intakes, so the intake flow does not need to change direction. Exceptions like the SR-71 are rare.
Supersonic intakes are longer and have sharp edges as opposed to the short, blunt intakes of subsonic aircraft. Also, most have a variable geometry to adapt to the very different flow conditions at supersonic speed.
Since it is the job of an intake to slow down the air going into the engine, supersonic intakes cannot have a big capture area, or their spill drag in supersonic flight would be excessive. Supersonic engines need to create their thrust with much less airmass than purely subsonic engines. Forget stealth, this is the real reason for the smaller diameters of supersonic-capable engines.
The nozzle of a supersonic aircraft is also variable, in contrast to the fixed nozzle of subsonic aircraft. This again helps to adjust it to the flow conditions, but in this case the major difference is between reheat on and off. Afterburning engines are capable of much higher exit speeds to compensate for their smaller diameter. They accelerate less air to a higher speed to create comparable thrust.
The last point mentioned it, but it deserves a bullet of its own: Supersonic engines use afterburners in order to have enough thrust for going supersonic at all. The hot exhaust gasses have a much bigger volume than the cold intake flow which needs to be accommodated by widening the nozzle.

Note that the civilian Concorde used also a variable intake and nozzle and afterburners. It had an engine which was used on the BAC TSR-2 before, a supersonic military aircraft.

The real distinction is not between civilian and military, but between purely subsonic and supersonic-capable. Initially, both was achieved with the same engines. The J-57 mentioned above was also used on the supersonic F-100 military jet. Only in the 1960s did those lines diverge, and the subsonic aircraft grew ever bigger low-pressure compressor stages. These were again driven by the high-pressure cores which were used on supersonic aircraft.

Background

Thrust is air mass flow multiplied by the speed difference between flight and nozzle speed of the engine. To increase thrust, subsonic engines try to maximize mass flow (by increasing the bypass ratio) while supersonic engines rely more on increasing the nozzle speed (by using afterburners). Since net thrust is only possible when exit speeds are higher than the flight speed, the engine's exit speed needs to increase with the design flight speed.

The core engines do not differ much - after all, the intake will make sure that air reaches the engine at a speed of Mach 0.4 to 0.5, regardless of flight speed. The core of the General Electric F110 (installed in the F-15 and F-16 fighters, among others) became the core of the CFM-56 turbofan which is used in the Boeing 737 or the Airbus A320. The main difference is in their bypass ratio. The slower the design speed, the bigger the bypass ratio may become. At very low speed, the ungeared, shrouded fan is exchanged for a geared, free spinning propeller, in other words, the jet changes to a turboprop. The intake and nozzle, however, are very different indeed.

The optimum bypass ratio changes continuously, but since the drag coefficient drops after crossing Mach 1, airplanes are either designed for a maximum Mach number of 0.9 or less, or 1.6 and above. The corresponding bypass ratios today are up to 12 for subsonic engines, and less than 1 for supersonic engines. This produces a sharp boundary at the speed of sound, and many military engines designed for supersonic flight lost their afterburners and were fitted with a big fan to become the engines for subsonic transport aircraft.

The differences between sub- and supersonic engines grow bigger the more you move away from their core. High-pressure compressor, combustion chamber and high pressure turbine look and work the same, but the low pressure compressor of subsonic engines swallows a lot more air and has a much bigger diameter. Supersonic engines in turn mostly have an afterburner. The biggest difference, however, are the intakes (large pitot intake with blunt lips for subsonic aircraft versus adjustable spike or ramp intakes for supersonic flight) and the nozzle (fixed for subsonic flight versus a complex, adjustable convergent-divergent nozzle for supersonic flight). This is due to the very different air speeds and the much higher exit velocities required for supersonic flight.

Look at the intake section of the XB-70 pictured above (source). The capture area is rather small, and then the intake tube widens to enable the slowing of the airflow. The inclined sidewalls of the intake section cause a lot of drag at Mach 3. Now think the six GE YJ-93s are replaced by engines with an even bigger diameter. The increase in wave drag due to the even blunter intake would cancel out all advantages of a higher bypass ratio.

What is less obvious is the fact that this intake section also creates maybe half of the overall thrust of the propulsion system. But this answer is already too long, so I save this for another answer.


Why does the FMC in B737 limit the climb speed to 230 knots on the VNAV mode until the leading edge devices are fully retracted?

The non normal checklist QRH will answer your question.  If the LE flap transit light remains illuminated I.e the leading edge flaps and slats haven’t retracted or disagree with the flap handle position, then the QRH directs you to limit the speed to  230 kits until you have rectified the issue.  VNAV is honouring that restriction.

Hope that answers your question.


How does turbojet thrust change with altitude?

The thrust variation with altitude would be highly engine specific, but the general trend is nicely depicted in the image below:

Read this for further details.


Can time logged in foreign aircraft be applied towards an FAA certificate or rating?

Yes, it counts: the FAA doesn't care where flying hours are accumulated provided that the US written and/or practical test requirements are met. I learned to fly in South Africa then applied for an unrestricted FAA license (i.e. not a foreign based license). The FSDO told me that I could count all my time in SA (cross-countries, night flights etc.) towards the FAA license requirements, but I would still have to pass the FAA written and practical tests like any other student pilot.

One practical issue in this situation is that hours may be logged slightly differently in different countries, by regulation or simply by local practice. The two examples I encountered were that PIC time is (was?) defined differently in SA and the US, and the number of landings is not relevant in SA for currency so no one logs them.


How different is flying through Free Route Airspace (FRA)?

Short answer: We do nothing differently in the cockpit when flying in a FRA. The route segments are filed as a long direct and simply flown like that.
As ususal conflict prevention/solving lies with the controller. Only short term conflict solving lies with the cockpit crew (think TCAS RA). In a FRA this is nothing different. In a "regular" airspace with airways and waypoints the problem is the same. Only are your conflict hotspots concentrated on waypoints where you have crossing or converging airways.  This presents similar problems to the controller.
The FRA I mostly fly through is in south-east Europe (Vienna, Ljubljana, Bratislava and Budapest FIRs). Often the Austrian controller clears us from our western entry point on a direct all the way to the eastern exit point of the adjacent Budapest FIR. So there is some trans-national coordination going on in the background.
From the Eurocontrol Free Route Airspace FAQs:

Have ANSPs developed strategies to mitigate the potentially more
difficult detection of conflicts that comes with FRA implementation?
[...] ATC systems across Europe [...] include conflict detection tools
[...] using aircraft trajectories calculated by the ground system which
are updated in real time as a flight progresses.  [...]  The tools help
controllers identify conflicts well in advance of them occurring [...].
At the same time, the implementation of Free Route Airspace generates a
much better spread of conflicts compared to the concentration of
conflicts generated by the fixed route network.

source: http://www.eurocontrol.int/articles/free-route-airspace, omissions by me
Route deviations from cockpit side (to avoid weather for example) are handled like everywhere else. Ask the controller for an avoidance heading and you're good to go. Possible arising conflicts are then solved by the controller. Same works for conflict mitigation from controller side. You might get a heading until clear of conflicting traffic and then a direct clearance again.
In my experience this works just fine in the daily operation.


While the combat military role of a wingman is established, the term is entirely appropriate and is used for non-combat formation flying as well.  And unless there is a better term, it would be logical to extend the use to civilian formations also.


What really causes a low-pressure gradient over the top of an aerofoil?

This is my understanding: A combination of the shape, angle of attack and movement of the wing creates high pressure on the front side of the wing and low pressure on the back side. By front and back I mean the part that is facing the oncoming air and the part that cannot "see" the oncoming air.

The low pressure is there because of this. This is the pressure difference which causes lift. Some lift also comes from the downdraft caused by air moving downwards at the trailing edge of the wing due to the angle of attack.

This article has a video that shows airflow over a wing.
http://www.cam.ac.uk/research/news/how-wings-really-work


What is this abandoned airplane parked in Tegel airport?

In the far corner of Tegel Airport, to the southwest (here a satellite image), lonely a plane with a special story rots: The Boeing 707 was a gift from the manufacturer to the Lufthansa and landed in 1986 by tricky preparations as the first Lufthansa aircraft in West -Berlin. Otherwise only Allied aircraft could fly through the east corridor. Lufthansa donated the plane to the Berlin Technikmuseum, which, however, can not do anything with it. Every now and then, the airport fire brigade on the Boeing exercises in case of emergency.

https://www.tagesspiegel.de/mediacenter/fotostrecken/berlin/flughafen-tegel-das-vergessene-flugzeug/13531996.html


What is the most effective way for a VFR pilot to scan the instruments during manoeuvres?

A VFR pilot shouldn't really be "scanning" the instruments in the sense that an IFR pilot does; he should be scanning the sky for traffic (see my first answer) while using his peripheral vision to maintain attitude.  Yes, he should periodically (and briefly) check the instruments to make sure nothing is amiss, but then go back to scanning for traffic.  I wasn't taught any particular "scan" for that, just to look at whichever instruments seem most useful for what I'm doing at the moment.

If you're having trouble holding proper altitude and airspeed as a VFR student pilot (from a comment to other answer), you may be spending too much time looking at the instruments rather than not enough.  That may seem counter-intuitive, but the key to both is attitude.  Get the right attitude, using the artificial horizon or other instruments at first if necessary, then look outside at the real horizon (in particular, the relation of your nose to it) and then just maintain that picture while you do your traffic scan.

The only time a VFR pilot is supposed to be "scanning" the instruments is during hood training.  For that, I was taught the "T" scan: assuming you have a six-pack in the standard arrangement, you focus on the AI (top center) and then briefly look left at airspeed, then back, then down at heading, then back, then right to altitude, then back.  Repeat until the hood comes off.


How do FAR 23 takeoff requirements compare to FAR 25 requirements?

The single biggest difference is that FAR 25 has rules that pertain to wet runways. Aside from that, FAR 25.113(a) uses the greater of two tests to determine accelerate-stop distance:

(1) Accelerate to $V_{EF}$, then reject the takeoff
(2) Accelerate to the highest speed required for takeoff (somewhat unclear?), then reject the takeoff

...while 23.55(a) is more or less equivalent to 25.113(a)(1).

Comparing the three methods, the rules are mostly comparable. The only major difference is that under Part 25 "a distance equivalent to 2 seconds at the $V_1$ for takeoff from a dry runway" (25.113a.1.iv and 25.113a.2.iii) must be added to the other factors.

Because aircraft certified under Part 25 must use the greater of two different tests and add a distance equivalent to 2 seconds at $V_1$, accelerate-stop distances will likely be greater than for Part 23-certified designs that are otherwise similar.

For reference:

FAR 23.55(a)
FAR 25.113(a)


Could liquid alkali metal fuels be used for ramjet/scramjet propulsion?

How long does the lithium take to evaporate and then to react with oxygen? Air in a scramjet is moving extremely fast (supersonic by definition!), so there is very little time left for mixing and combustion if you desire to create thrust from the the combustion heat energy.

Your lithium engine will most likely trail a bright contrail of burning lithium but develop rather little thrust. The high flame speed of a mixture of hydrogen and oxygen makes hydrogen the preferred scramjet fuel.


What is this board given to world war II pilot?

The photo in the question is a screenshot from the movie "Midway"(2019).

The board is a Mark 3A Plotting Board used for navigation by pilots flying from U.S. Navy aircraft carriers during World War II.  It can be seen carried by various SBD Dauntless pilots in this scene from the movie "Midway" (2019) from 0:24 to 1:07.

Photo credit: National Air and Space Museum, Smithsonian Institution

Plotting Board Instructions

Photo credit: National Air and Space Museum, Smithsonian Institution


What is the shape of the power required curve?

What is the shape of this power required curve for a small GA airplane, and for a large commercial airplane?

The answer depends on the span loading and flight altitude of the aircraft. For most practical cases, the left hand side power curve is more realistic, but it still can be entered if the pilot is unaware of what he/she is doing. Just witness AF447 …

The power curve is the sum of two drag curves, times flight speed:

The induced drag is dominant at low speed and decreases with increasing dynamic pressure, and
the friction (and parasitic and interference) drag grows with increasing dynamic pressure.

Below I have plotted the theoretical power curves for a small GA airplane at sea level. The dashed lines show the power curve if no flow separation would happen.

Aircraft with low span loading will exhibit low induced drag, so the friction drag (zero lift component) will become dominant soon. The higher the airplane flies, the more the available power is reduced and the induced drag is increased, so the power curve will shift to something resembling your right plot. The point splitting the left side of the curve from the right side is the point of minimum power. Where is this point for actual configurations?

We can calculate the lift coefficient at minimum power in order to know where the speed range of the backside of the curve starts. In this answer, I derived this already, so here is only the result:
$$c_{L_{min.\:power}} = \sqrt{\frac{2-n_v}{n_v+2}\cdot c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$$
The symbols are:
$\kern{5mm} c_L \:\:\:$  lift coefficient
$\kern{5mm} n_v \:\:\:$  thrust exponent, as in $T = T_0\cdot v^{n_v} $
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's Oswald factor, normally between 0.8 and 1.0

Now let's input the values for a glider ($n_v$ = -1):
$$c_{L_{min.\:power}} = \sqrt{3\cdot 0.00935\cdot\pi\cdot 21.43\cdot 0.98} = 1.36$$
So the minimum power speed for the ASW-20A is very close to its stall speed. Falling into the backside is practically equivalent with stalling.

Now the values for a jet fighter ($n_v$ = 0):
$$c_{L_{min.\:power}} = \sqrt{0.0172\cdot\pi\cdot 2.45\cdot 0.76} = 0.317$$
So the Starfighter pilot is on the backside of the curve until he accelerates beyond 191 m/s or 371 knots (at maximum take-off mass). That is already Mach 0.54 at sea level (and more the higher you go), and explains why the Starfighter prefers to be flown fast. Its best climb speed is at Mach 0.9!

Since you asked about a commercial airplane, here we go:
$$c_{L_{min.\:power}} = \sqrt{1.67\cdot 0.01277\cdot\pi\cdot 9.58\cdot 0.74} = 0.687$$
This is for the clean configuration of course and falls between the glider and fighter values. The numbers for a GA aircraft are a little higher (around $c_L$ = 1) due to the piston engine, with a higher Oswald factor due to an unswept wing and a somewhat lower aspect ratio. Commercial aircraft prefer to cruise close to the minimum drag point, which for this example is at $c_{L_{min.\:L/D}}$ = 0.532, so at altitude their operating point is already quite close to the backside range. In contrast to that, a GA aircraft in cruise will fly low (no pressurisation) and much faster that at its minimum power, so its cruise point will be far to the right of the backside range, making the power curve look more like your left hand side example.


What course of action to take when having to go missed during IMC and lost comms?

91.185 doesn't say anything about missed approaches but there is some information in the AIM 5-4-21:

  In the event a balked (rejected) landing occurs at a position other
  than the published missed approach point, the pilot should contact ATC
  as soon as possible to obtain an amended clearance.
  If unable to contact ATC for any reason, the pilot should attempt to re−intercept a published segment of the missed approach and comply with route and altitude instructions.
  If unable to contact ATC, and in the pilot’s  judgment it is no longer appropriate to fly the published missed approach procedure, then consider either maintaining visual conditions if practicable and reattempt a landing, or a circle−climb over the airport.

That indicates that ATC expects you to fly the published (or instructed) missed approach procedure if possible, or climb over the airport if not.

As for what happens after going missed and climbing to a safe altitude, that's up to you. Even if you were in contact with ATC, they would ask for your intentions because they don't know why you went missed and whether you want to try the same approach again or divert. ATC also doesn't know your filed alternate airport (see the AIM p. 5-1-24) and there's no requirement to go there anyway. It's up to you as PIC to determine the best course of action; ATC will help by keeping other aircraft away from you as far as they can.


Do small helicopters like the R44 require an FAA type rating?

SFAR 73 is Robinson R-22/R-44 Special Training and Experience Requirements and lists the specific training requirements for that model. Here's one relevant piece:

  (1) No person may act as pilot in command of a Robinson model R-22
  unless that person:

  (i) Has had at least 200 flight hours in helicopters, at least 50
  flight hours of which were in the Robinson R-22; or

  (ii) Has had at least 10 hours dual instruction in the Robinson R-22
  and has received an endorsement from a certified flight instructor
  authorized under paragraph (b)(5) of this section that the individual
  has been given the training required by this paragraph and is
  proficient to act as pilot in command of an R-22. Beginning 12
  calendar months after the date of the endorsement, the individual may
  not act as pilot in command unless the individual has completed a
  flight review in an R-22 within the preceding 12 calendar months and
  obtained an endorsement for that flight review. The dual instruction
  must include at least the following abnormal and emergency procedures
  flight training: [...]

SFAR 108 has similar requirements for operating the Mitsubishi MU-2B.

Finally, note that the type certificate is for the aircraft, and has nothing to do with whether an individual pilot is qualified to fly it or not.


Why didn’t the Concorde have flap-canards like the Tu-144?

It did not need them. Concorde could operate from most commercial airports and did not need especially long runways. Retractable canards add drag and the mechanism is a point of failure.

I fail to see how Tu-144 canards is a “superior” feature as they were added to support a less effective wing.

Very much related: Why is the Tu-144 the only commercial airplane with canard configuration?


Why is Transition Altitude fixed but Transition Level is not?

The point of flying on QNH is to keep you from flying into terrain, which is at a constant altitude above sea level, so TA is fixed.
Once you are high enough that terrain can’t be a problem and you only have to worry about hitting other planes, everyone can transition to QNE. However, because TL must be physically above TA, the difference between QNH and QNE will dictate what the lowest usable flight level is.


How much electrical power is available in a Gulfstream G550 and from which power sources?

There are some answers to common electrical questions about the G550 here according to them the engine integrated drive generator (IDG) unit delivers 40KVA, 400HZ, 115V; they don't list a power factor but lets be conservative and assume .8 (it must be between 0 and 1). This would result in 32 Kilowatts per IDG. So you have 64 Kilowatts at your disposal. The minimum load will depends on the avionics installed and can vary from plane to plane. At night load will be increased as a result of the use of interior lights as well as landing lights during takeoff and approach. Your load will be highly variant on the interior of the aircraft. As this is a luxury plane there could be a whole host of things inside like TV's, lights, kitchen equipment etc. You can find specific equipment installations in the POH/loading info for a given airframe. You can find a nice breakdown of the G450's electrical system here.

As for how you can add it, you can simply add it as you would add any accessory, to the main bus (by an A&P of course). You will need to make sure the item can be added to the craft and in some cases there may be a stipulation along the lines of not using it during takeoff or landing. The amount of load will vary by aircraft and dependent on what else is installed.

  I'd like to understand what electrical power sources are available
  (engines? APU? GPU? Other?)

The engines (while running) are generally the main source of power. The APU is often used on the ground when the engines are off but the plane needs electronics on and can also serve to help start the engines. It does appear the G550 has an APU. According to this data sheet the G550 runs a Honeywell RE220 APU that can output 45 Kilowatts. According to the site it will operate up to 37,000+ Ft. so it in theory could be run for the duration of a flight.

A GPU is only available on the ground and only at airports that have them. Their output varies widely and a large variety of types may be available at any given airport.


Low visibility spins and spirals: difficult-to-understand explanation of false perception

Your vestibular system can only recognize acceleration. Your brain combines that with visual inputs to produce spatial orientation. (If the two disagree, you may get motion sickness.)
When you are in a sustained left bank, your vestibular system stabilizes and feels no acceleration. Without a usable visual input, your brain will convince itself that you are instead straight and level. This is spatial disorientation.
If you then look at the instruments and try to correct yourself to actual straight and level flight, the vestibular system feels that change in acceleration as starting a climbing right bank, which now feels wrong. It orders you to bank back to the left even harder to make itself feel “normal” again.
It’s not a 50/50 chance; once disorientation sets in, your body will consistently tell you to do exactly the opposite of what you should do. That’s why it’s so deadly.


In high-altitude piston aircraft, what type of forced induction (boost) is used?

You can have either (turbo- or super-) or both (superturbo-), there is also the turbo-compound engine.

Most WWII aircraft engines had mechanically driven superchargers, and the turbosuperchargers (with intercoolers) were added to achieve desired altitude performance.
Modern aviation piston engines designed to run at high altitudes typically include a turbocharger rather than a supercharger. The change in thinking is largely due to economics. Aviation gasoline was once plentiful and cheap, favoring the simple, but fuel-hungry supercharger. As the cost of fuel has increased, the supercharger has fallen out of favor.
— Wikipedia [edited for context; citations missing from main article]

During WWII, two-speed two-stage intercooled superturbocharged engines were common.
(Frames from YouTube)
Compressed air via the exhaust-driven-turbine is channeled to a geared mechanically-driven supercharger. (The jet-engine must have had a laugh.)

You get the super part, which is a mechanically-driven compressor boost.

The turbo part, which is a turbine-driven compressor boost.

Intercooler for cooling the air.

The two speeds and stages are for low- and high-altitude operations. Otherwise the engine could blow at low-altitude.

A good example is the Wright R-3350 Duplex-Cyclone used on the Boeing B-29 Superfortress and other aircraft. Delivering up to 3,800 shp (2,830 kW).

Above is an example of having both, however as noted in the comments, superturbocharger as a term is nowadays used to describe a turbocharger.

Here's a declassified training film—from which the above frames were taken: Turbosupercharger: Master of the Skies (1943)


How does the Mil Mi-35M compare to the Boeing AH-64D Apache?

TL;DR It's really mission related.

1) not the same role

2) Cargo compartment is important (see below)

3) Soviet doctrine had helicopters fighting with troops so I'm guessing a soldier on the ground is more worried about the dude with the AK-47 and bayonet charging them so they don't have time to take pot shots at choppers

4) Mast mounted radar came later. The original Apache didn't have it and even the new Super Cobra doesn't have it

I'll expand on my comment about the Mi-28 Havoc below but to stab at the Mi-35 you have to look at the Soviet air doctrine when these aircraft were designed.

This student research paper aptly named The Soviet Attack Helicopter describes the role helicopters were seen taking in the Soviet Union

  In April of 1976, Belov reflected an evolutionary change in Soviet attitude toward attack helicopters stating that fire-support helicopters may be regarded as a highly effective weapon for land forces. He felt that these helicopters could be used not only to support subunits on the battlefield but also to destroy various targets independently, to accompany airmobile troops and landing forces both inflight and after landing, to fight tanks and other armored targets and also to destroy enemy aircraft and air-mobile troops both in the air and on the ground.

Contrast this to US forces where there are very defined roles for helicopters. Attack helicopters at the time (Apaches and Cobras) and transport units (Huey and Chinook) had very defined roles. Transport choppers provided some cover fire and limited rocket capability. Attack helicopters provided close air support and sneak attacks on various mechanized and fixed targets.

the soviets though saw helicopters as one in the same. As one author put it in the soviet tactical air doctrine paper from 1976

  The one constant in all Soviet use of tactical air power is that air power is only one component that must be used in concert with other military forces in order to be effective.

So their helicopters were not tools that happen to occasionally transport or support ground troops they saw them as integral components in a land/air strategy.

this brings me to the Mi-28 Havoc. Note that on the wikipedia page it looks similar to an Apache. Swiveling gun turret, guided/unguided rockets, etc... But also note it has a small compartment that can fit 3 people.

Imagine an aircraft goes down: pilot, co-pilot, navigator (or some combo like that). In the US an attack helicopter would provide cover fire if needed. a transport helicopter would come in to retrieve the crewman.

BUT in the Soviet strategy even the smaller Havoc could land quickly and evacuate the wounded! It's a stark contrast in CONOPS.

The Mi-35 is really a big version of this strategy. Bring in lots of troops and stick around with rockets and guns to provide heavy gun fire. Unlike the precise shots that the Apache/Havoc can take; the Mi-35 and even the armed versions of Huey's/Black Hawks provide a 'pray and spray' mentality. A lot of fire on a lot of entrenched troops/light armor in a treeline or foxholes.


What is the role of a flight control computer during a steep approach?

On the Airbus 318, it appears that the flight control computer does more than just monitor and handle annunciators.

  In March 2006, the European Aviation Safety Agency (EASA) certified a modified control software enhancement to the Airbus A318 designed to allow the aircraft to perform steep approaches. The aircraft is the largest commercial aircraft certified by EASA for steep approach operations. The software modifies the control laws of the aircraft when the steep approach function is selected by the crew, by automatically deploying some of the spoiler panels to provide additional drag when the aircraft is in the landing configuration. It also provides alternative aural alerts to the crew and modifies spoiler deployment automatically below 120 feet (37 m) on landing. The A318 steep approach procedure allows the aircraft to perform approaches at descent angles of up to 5.5°, as opposed to the standard 3° for a normal approach.

A318 Wikipedia

The answer to your question #2 can be found in the aircraft operations manual.

The answer to your question #3 is that an aircraft can stall at any attitude and configuration. A stall is when the critical angle of attack for the wing is exceeded.


How are airliners secured on the ground during hurricanes?

Looking at the hurricane manuals for a few airports, evacuating flyable aircraft to a safer location tends to be the most common choice.
From the Boca Raton Airport:

Effective with the issuance of a Storm WARNING and/or Hurricane WARNING:
Relocate flyable aircraft to other geographical areas, place under suitable shelter, or secure as appropriate.

Also, from the Miami International Airport:

Upon receipt of a Hurricane Warning, Airside Operations will:

Initiate evacuation of all flyable aircraft and post Airfield Operations Senior Agents and Agents in detail to insure compliance and report results.


When does an UAV need an internal structure?

I very much doubt that you will hit your mass target (kg is a unit of mass, btw) if you build those wings without a proper spar. The shell is for carrying shear loads to provide torsional stiffness, but it cannot give much bending stiffness, especially if there is no internal structure that keeps the upper shell apart from the lower one under bending loads.

So build a light shell and add spar caps, a web and a couple of ribs where loads are locally introduced or where cutouts (say, for ailerons) start.

Regarding the fuselage: If there are many point loads inside from the payload and systems (camera gimbal, engine mounts) it makes sense to have local reinforcements. Otherwise, a shell should be fine given the higher curvature of a typical fuselage. On the other hand, everywhere you have large radii or flat panels, a local stiffener will be advisable.

As for calculating the shell thickness: At that size I expect that handling loads and inertial loads from point masses will determine the minimum size. There is no simple formula and you need to balance ease of operation with performance. Depending on your priorities, the shell will become thicker for a more rugged device or thinner for a lighter but more delicate one.


What are the common mnemonic devices used to remember equipment required by 14 CFR 91.205?

For VFR Day Flights, you can use "A TOMATO FLAMES":

A - Altimeter

T - Tachometer for each engine.

O - Oil temp indicator for each engine

M - Manifold pressure gauge for each altitude engine

A - Airspeed indicator

T - Temperature gauge for each liquid cooled engine

O - Oil Pressure gauge for each engine

F - Fuel quantity gauge for each tank

L - Landing gear position lights (if retractable gear)

A - Anti-collision lights (aircraft certificated after March 11, 1996)

M - Magnetic direction indicator

E - ELT, if required by §91.207

S - Safety belts / Shoulder harnesses

For VFR Night Flights, you can use "FLAPS". This will be in addition to all the equipment required for a VFR Flight in Daylight.

F - Fuses (spare set)

L - Landing light (if for hire)

A - Anti-collision light

P - Position lights (navigation lights)

S - Source of power (such as battery)

Additionally, as @wbeard52 pointed out below, you can use "GRABCARD" as a mnemonic device to memorise the equipment required for IFR Flight. Again, these would be in addition to all the equipment required for VFR Day and Night Flight.

G - Generator/alternator

R - Radios (two way and navigational equipment
appropriate for the ground facilities to be used)

A - Altimeter (sensitive) adjustable for barometric pressure

B - Ball (slip-skid indicator, which is part of your turn coordinator)

C - Clock (shows hours minutes and seconds and installed as part of aircraft equipment)

A - Attitude indicator

R - Rate of turn indicator

D - Directional gyro (Heading indicator)


Who must approve a globally distributed satellite to ground laser communication system?

(I've taken a wild stab at an answer, despite my not being a lawyer or legal expert of any kind, since nobody has written an answer in nearly four years.  If you don't like my answer, please feel free to write a better one.  I apologize in advance if I've abuse any legal terms.  It's quite possible that I have come to an erroneous conclusion.)
Your question seems to presume that there is some multinational body, or multinational rules, governing laser beams in the atmosphere.  However, there is no multinational agreement to regulate laser beams in the atmosphere.
Countries are sovereign, with no higher legal authority, and are not required to make any rules, laws, or enforcement bodies without voluntarily agreeing to do so.  Often countries realize that uniform standards or regulations are in their best interests, and make treaties or agreements with other countries to create laws and rules and enforce them.  Sometimes countries voluntarily abide by existing treaties or agreements without actually signing onto the agreement.  In the absence of such formal treaties or agreements between countries, individual countries are free to write, or to not write, whatever rules and laws they like.
One of the functions of the United Nations is to create a list of international treaties and agreements.  The list, known as the United Nations Treaty Series Cumulative Index, can be found here.  The most recent list as of this writing, current to 20 March 2013, sorted alphabetically, is here.  A quick search of the index for the term "laser" reveals only an "Exchange of notes constituting an agreement between the United States and Japan concerning a program for the cooperative research of Eyesafe Laser Radar."
In other words, there is no multinational agreement to create rules or laws regarding laser beams in the atmosphere, other than those that pertain to aviation safety.  Existing aviation safety legislation seems to agree that pointing powerful lasers at aircraft is something that should be regulated.  However, it seems likely to me that aviation safety treaties are silent regarding laser beams through the atmosphere that are not pointed at aircraft.
To sum up, it has been left to individual countries to write whatever laws they like regarding laser beams in the atmosphere not aimed at aircraft.  Currently it seems likely that few countries have written any such laws.  So companies can currently feel free to plan communications networks using laser beams between ground stations and satellites, since there are few or no laws to stop them, as long as they take care to not accidentally aim laser beams at aircraft.


What might a pilot mean by "uncontrollable"?

"Uncontrollable" is a technical term (actually, in literature it's more often called "loss of control"). It means the aircraft is not responding to at least one normal command. Be it elevator or ailerons or rudder etc.

Really, really good AND lucky pilots can sometimes still control aircraft that's uncontrollable. Either by using another control surface to influence the control desired (eg. by using rudder to get out of a bank) or by using non-primary surfaces like trim tabs or flaps.

When no control input will influence what the aircraft is doing then it's called total loss of control (or totally uncontrollable).


This is most likely the minimum visibility (in metres), with the compass direction given as "//" (not possible to determine). A single slash is more common, i.e. 0650/. WMO Publication No. 306 - Manual On Codes - Volume I.1 - Part A, Section A, FM 15 METAR, FM 16 SPECI (emphasis added):

  15.6 Groups VVVV VNVNVNVNDv

  15.6.1 The group VVVV shall be used to report prevailing visibility.
  ...

  15.6.2 Directional variation in visibility
  VNVNVNVNDv

  When the horizontal visibility is not the same in different directions and when the minimum visibility is different from the prevailing visibility, and less than 1,500 metres or less than 50% of the prevailing visibility, and less than 5,000 metres, the group VNVNVNVNDv shall also be used to report the minimum visibility and, when possible, its general direction in relation to the aerodrome reference point indicated by reference to one of the eight points of the compass. If the minimum visibility is observed in more than one direction, the Dv shall represent the most operationally significant direction.


Can a paying passenger ride in one of the cabin jumpseats?

If you're talking about one of the jumpseats in the flight deck (as opposed to the ones FAs use in the passenger cabin,) then, no, it's definitely not allowed during flight, at least not in the U.S. or E.U. It may be allowed elsewhere, though.
The United States
Relevant regulations for the U.S.: 14 CFR 121.547 for domestic air carriers and 14 CFR 129.28 for foreign ones.
The regs are a bit too long to quote here, but, to summarize: You're not getting into the flight deck during flight unless you have a valid, FAA-approved reason to be there. The mentioned exceptions were mostly FAA, NTSB, airline, or manufacturer employees and, even then, only ones with legitimate safety or operational reasons to be there. It is also mentioned that the PIC retains the emergency authority to deny access to even the FAA/NTSB/etc. personnel in the interest of safety.
Apart from all of the aforementioned categories of people allowed "a crewmember" is listed separately as being allowed, of course.
Also, there's 14 CFR 121.557(a) which says:

In an emergency situation that requires immediate decision and action the pilot in command may take any action that he considers necessary under the circumstances. In such a case he may deviate from prescribed operations procedures and methods, weather minimums, and this chapter, to the extent required in the interests of safety.

This exception allows the pilot of a Part 121 operation to deviate from any Federal Aviation Regulation when it is required in the interest of safety. So, the Pilot-in-Command may allow you to sit in the flight deck if he deems it's necessary for safe operation of the aircraft. As such, this exception allows other pilots to access the flight deck in the very rare instances where one of the pilots falls ill and the pilot-in-command decides to get another (non-airline) pilot who happens to be on board to sit in the right seat to help out for the remainder of the flight.
See Pondlife's excellent answer here for more information regarding emergency authority of the pilot-in-command.
The European Union (EASA)
This answer over at travel.SE also mentions that CAT.GEN.MPA.135 is the relevant EASA (E.U.) regulation preventing passenger access to the flight deck during flight.
Exceptions
As a notable exception, this answer here at aviation.SE does mention that South Africa allows licensed pilots to visit the flight deck during flight and that you might even get to ride in the jump seat.
Conclusion: I need to visit South Africa. :)
Other Related SE Questions

Can a passenger request to visit the cockpit during a flight? (Aviation)
Can I get a photo with the pilots? (Aviation)
Can a child still visit the cockpit during flight? (Travel)
Can passengers visit the flight attendants' sleeping quarters? (Travel)


How does the particular piece of flap behind an engine on a B777 work?

It is called "inboard aileron" or "high-speed aileron" and is actually a flaperon. It will deflect with the flaps but not extend backwards. At high speed, the outboard ailerons are locked and all roll control is achieved by deflecting the inboard ailerons (and spoilers, if needed). This helps to reduce wing torsion and twist.

Background: Since the trailing edge's sweep angle has a break at the wing station of the engine, and since in Boeing aircraft the flaps extend perpendicularly to the hinge line, there must be a gap between inboard and outboard flaps, otherwise they would collide during extension. This gap is best placed in the station of the engine blast, and is filled with a simple hinged flap. Note that Airbus aircraft have rear-sliding flaps, which stay at a constant span location and can be adjacent to each other even at the wing station of the sweep change.

Boeing 767 from below. Picture by Adrian Pingstone (source)

The picture is of a Boeing 767, but shows the flap arrangement nicely. Note the offset of the forward and rear part of the Küchemann bodies which house the flap tracks.