In what situation could the maximum ramp mass limit the allowed take off mass?

@vasin is correct. I'll put some actual numbers in a scenario.

A 747-481F has a max ramp weight of 913000lb, a MTOW of 910000. That 3000lb difference between max ramp and MTOW has been the same for 747s since the -100 airplanes.

The 3000lb is usually sufficient to cover the taxi fuel, but not always. Think having to taxi out at JFK when departures are heavy and the runway in use is the one farthest away from your ramp. Or, same thing at Honolulu and because of your weight you need the reef runway.

The dispatcher/load planner for the flight believes in following the rules, and he believes the taxi out will consume 4000lb. Thus, he has to use 909,000 as the max takeoff weight. Thus the max ramp mass has limited the MTOW

This kind of thing happens most on freighter flights because they're loaded as often as possible right up to their max zero fuel weight, that's where the money is. So let's say it's a freighter flight, JFK to Tokyo Narita. With the airplane near MZFW, you can't load enough fuel to get to Tokyo, but if you stretch a string on a globe between JFK and Narita, it goes almost right over Anchorage, and Anchorage is pretty much at the halfway point. Indeed, Anchorage has been used as the refueling stop for freighters for years and for pax aircraft as well, but especially for freighters.

Anyway, the load planner will put as much cargo aboard as possible to put the actual takeoff weight right up against the MTOW allowed.


Are these questions really on the FAA Glider Commercial written test?

Well, now that I've taken (and passed) the test, I feel somewhat qualified to answer my own question.

The first question, The VOR CDI indication deflection question, was indeed on the test.  There was also a question on VOR receiver checks "from a designated checkpoint on the airport surface".

The second (IFR) question was NOT on the test.

Of course, the test has 100 questions and the question bank is reported to have > 600 questions, so there is no garuntee that it couldn't be on the someone else's test.  IOW, YMMV.


Where is the only Aerostar 800 ever built?

According to this page the airframe was donated to Embry-Riddle Aeronautical University:

  The Superstar airframe was later used as the prototype Aerostar 800. The prototype 800 was the Superstar airframe with two more seats (due to a 32” extension of the cabin) and featured two 400-hp. Lycoming engines. The 800 was under development when Ted unexpectedly passed on in 1976. Piper continued development of the airplane as a replacement for their P Navajo but never certified it and eventually donated the airframe to Emery Riddle [sic] Aeronautical University.

This is the only reference I can find to the ultimate location of the Aerostar 800.


Which single pilot aircraft had a range of at least 2160nm in the late 90s?

Smaller planes that had this range back in the 90's were not so rare, but they were jets, most of them were not intended to be operated, at least commercially by a single crewmember. It would have been totally possible though.
When considering that you are writing a book, you may take some liberties (in addition to the crew count) when it comes to range: the official figures take into account the fuel reserve regulations, so after the declared range is flown, the plane would most likely be able to continue flight for about an hour before fuel starvation.
So, at least these had the range of 2160nm minimum (some not fully loaded):

Learjet 60
IAI Westwind
Dassault Falcon 20 (some variants)
Hawker 800

(To keep things simple, I'll turn this into community wiki right away)


Can the wheel brakes hold an airliner in place if its engines are at full thrust?

Yes they are. In fact this is required for a static takeoff. A static take-off means setting the brakes and running up the engines to takeoff power then when ready they release the brakes and start the takeoff roll.

Besides that one of the test Airliners have to withstand is a worst-case V1 abort.

This means starting a takeoff and at the last second slam the brakes, come to a stop and then taxi around for 5 minutes. This all needs to happen fully-loaded and with worn brakes that are still certified safe to use.

Between hitting the brakes and coming to a stop the engines will not have time to spool down and stop providing takeoff power.

Airliner mechanics also do engine run-up tests essentially powering up the engine and going through the power range and making sure it works as specified. This is usually 1 engine at a time.

In these run-up tests loose debris (including cars) can be thrown around by the engine blast. So it's important to keep the area clear.


Why are emergency water landings the majority of the pre-flight safety briefing if they're so rare?

The entry doors to an aircraft that is required to have life rafts are equipped with "slide rafts," which are dual purpose (land/water) so there is not any material difference in the weight. Some aircraft will also have perhaps one (maybe two) rafts in the cabin overhead (depending on the need for extra life raft capacity not covered in the entry door slide/raft).

I imagine, if controlled water landings were more frequent, design and technology might be modified in some way to make successful evacuations more efficient if that were necessary.  But, as you point out, controlled water landings are relatively rare, so likely the cost/benefit of creating an entirely different fuselage/wings/evac system would not be justified.

Of course, the fairly recent successful controlled water landing and evacuation into the Hudson is ample justification for having personal flotation devices (life vests, etc.) and associated emergency equipment designed primarily for water survival. Also, the design of that aircraft apparently provided for adequate flotation and evacuation as can be seen from the photographs.

The safety briefing before each flight by the Flight Attendants is relatively short and maybe 60 seconds are dedicated to explaining the operation of emergency equipment specific to water landings.


An American armed forces general expression for this is "operational"


When were checkerboard fiducial markers first used in aircraft development?

This was not already established practice in 1942.  Not even in the early 1950's NACA crash tests, which were so methodical that you'd have expected these checkerboards:  seven movie cameras along the runway, a flashing light atop the fuselage for movie synchronization, a pile of onboard cameras and instruments, white paint and red-dyed fuel for better imaging.  The closest this came to checkerboards was dotted lines on the fuselage sides.

This long NASA video includes many images of these aircraft.  No checkerboards anywhere.

A skim through online photos suggests that even automotive crash tests didn't start using checkerboard fiducials until the 1960's.


Using CPDLC makes life easier for pilots so we typically use it whenever it is available and logon shortly after takeoff.

When departing Frankfurt there is no rush as CPDLC is not available until crossing into Maastricht Radar. Continental USA does not have it so you lose CPDLC after Moncton Center.

ATC will often remind you, or ask you to logon if you have forgot as it makes life easier for them too. Where VHF is available we usually use a combination of voice and CPDLC.

Over the ocean, out of VHF range, we have to establish HF radio contact with Shanwick or Gander radio and do a Selcal check to insure we have a backup communication method.


What is the behaviour of ILS when there is an unmodulated interfering carrier signal?

If an invalid signal is received, then it must be modulated since it is only by measuring the modulation, that the receiver knows if the signal is valid and where it is relative to the localiser and glideslope. An unmodulated carrier on the same frequency is additive.

An unmodulated carrier on a different frequency will not affect the receiver (ignoring possible harmonics of course).

I suppose that if you could increase the power enough, an unmodulated signal might cause the signal to noise ratio to drop so low that the failure flag would show.


Does the FAA issue multiple physical certificates for different aircraft categories and privileges?

One certificate would be issued. Your highest rating would be listed on the front and on the back any lower ratings would be outlined.

Before I had passed my rotorcraft ATP my certificate read:

Airline Transport Pilot
 Airplane Single and Multiengine Land

Commerical Privileges
  Rotorcraft-Helicopter


How do I tell a Garmin 430 not to exit a hold?

Press the OBS button to put waypoint sequencing into suspend, as indicated by the green "SUSP" appearing over the OBS button.


Can a completely drained battery be recharged via ground power on an airliner like the B737?

My one experience with this was in a 737-300 that had the battery charger die, and the battery depleted while in flight.  The Battery Bus was still powered by TR3, but the Hot Battery Bus died (interestingly, not a scenario I'd ever seen in the simulator).  We got to the gate & couldn't start the APU and couldn't connect ground power, so when we shut down both engines, we immediately had "one blue light" -- i.e. ground power is plugged in & available, but NOTHING else -- dark airplane.
I don't recall how longer after that it was, but we eventually were able to connect ground power, probably to the ground service bus first.  Then, with the ground service bus powered, the battery would recharge.  I don't recall if we were able to get anything beyond the ground service bus powered after that.  (Presumably, if the battery recharged enough, we could have gone back to normal routines.)
As a practical matter, though, our maintenance does exactly as John K mentioned: if the battery has been depleted, it gets replaced.  How much of that is a matter of what happens during charging, and how much of that is concern about damage to the battery itself, I don't know, but in practice they won't use the aircraft's battery charger in the manner suggested in the OP.  (The battery charger brings it back up to full charge after things like starting the APU or running on battery power for the time between initial power-up and when APU or ground power are connected -- but that's a long way from being fully depleted.)


Where can I find the regulations on the minimum stall speed for a GA aircraft?

On August 30, 2017, a completely new body of regulations for small aircraft has been put in place which does not distinguish between normal or utility airplanes but low speed (below 250 KTAS) and high speed designs (> 250 KTAS). It also distinguishes between four levels depending on the number of seats (0-1, 2-6, 7-9 and 10-19 passengers). The spirit of the new regulation is to no longer prescribe design-specific rules but more abstract goals in order to limit risk, leaving the details to the aircraft builder.

Also, the number of rules has been drastically cut, and their numbering starts where the old numbering ended. Therefore, 23.49 has become 23.2110 and no longer gives a specific stall speed. All it does is to direct the applicant to determine a stall speed and details what conditions must be covered.

I expect that you have not formally started the certification process of your design, because that date determines which regulations apply. You are now free to select the stall speed of your design as long as you can demonstrate that the aircraft can be operated safely without exceptional pilot skill or strength.

But you can always count on Eurocrats when a body of regulations which has grown like cancer is to be preserved and extended. In their version (CS-23), the maximum stall speed of 113 km/h or 61 knots is still alive and well. However, Amendment 5 has now copied the new body of regulations as well and replaces the old certification standard in the name of global harmonization.

The old regulations reflect the experience which has been collected over decades. Many rules can be traced back to a specific accident and it helps to read through them and to consider why this specific rule has been implemented. Your new design might employ a clever way to avoid that particular condition at all, and then the new liberty of the new regulations will be helpful. But it would be foolish to throw all that experience overboard - a lower stall speed makes any airplane easier to fly. When things happen less quickly and less kinetic energy is involved, more accidents can be avoided and the damage in those that still occur will be lower.


Does altimeter setting affect the vertical guidance in a LPV approach?

Short Answer:

No, the vertical component of LPV approach performance is based on WAAS GPS input, not the altimeter or barometric system.

Longer Answer:

Your assumption about LPV performance is correct: Baro-VNAV is not used for LPV approaches.

On any type of approach with a Decision Altitude (DA), the aircraft's arrival at the DA is determined by the pilot's reading of the aircraft's sensitive altimeter.

If the altimeter is set to an altimeter setting report from a distant reporting station, SFO in this case, then the DA may be increased to give additional altitude margin to allow for variance in local atmospheric pressure.

This is true for the DA or Minimum Descent Altitude (MDA) on any approach, whether a GPS approach or not. See the MKT ILS 33 and MKT RNAV 15 for other examples of this. See the following excerpts from the Aeronautical Information Manual on altimeter settings for approaches (emphasis mine):

  5-4-5
  a.
  4. Approach minimums are based on the local
  altimeter setting for that airport, unless annotated
  otherwise; e.g., Oklahoma City/Will Rogers World
  approaches are based on having a Will Rogers World
  altimeter setting. When a different altimeter source is
  required, or more than one source is authorized, it will
  be annotated on the approach chart; e.g., use Sidney
  altimeter setting, if not received, use Scottsbluff
  altimeter setting. Approach minimums may be raised
  when a nonlocal altimeter source is authorized. When
  more than one altimeter source is authorized, and the
  minima are different, they will be shown by separate
  lines in the approach minima box or a note; e.g., use
  Manhattan altimeter setting; when not available use
  Salina altimeter setting and increase all MDAs
  40 feet. When the altimeter must be obtained from a
  source other than air traffic a note will indicate the
  source; e.g., Obtain local altimeter setting on CTAF.
  When the altimeter setting(s) on which the approach
  is based is not available, the approach is not
  authorized. Baro−VNAV must be flown using the
  local altimeter setting only. Where no local altimeter
  is available, the LNAV/VNAV line will still be
  published for use by WAAS receivers with a note that
  Baro−VNAV is not authorized. When a local and at
  least one other altimeter setting source is authorized
  and the local altimeter is not available Baro−VNAV
  is not authorized; however, the LNAV/VNAV
  minima can still be used by WAAS receivers using the
  alternate altimeter setting source.

Note that Baro-VNAV is a type of VNAV system which uses barometric
altimetry as a basis for vertical navigation performance. An LNAV/VNAV approach can be flown using WAAS equipment without a Baro-VNAV system.


Why do we refer to "power" for turboprop engines and "thrust" for turbojet/fan engines?

Ultimately what you want from all three types of engines is quantification of thrust available to push an airplane through the sky. The turbofan/jet engines are self contained and produce thrust directly but a turboprop engine requires the addition of a propeller, which may have differing characteristics based on the installation.

Since thrust is not known for a turboprop until its installation has been determined, manufacturers instead quantify the power available to drive a prop. This allows engines to be compared so that an airframe manufacturer can make the proper selection.

Fuel flow is then related to either thrust or power as a measure of efficiency, depending on type of engine. There is generally no published mathematical relationship between power and thrust for a given engine. It is not needed for turbofans/jets and not possible to determine at time of manufacture for turboprops.


How do pilots hold the runway centerline during takeoff?

Once you've lined up nicely on the runway, you only need the rudder pedals as they do provide enough nose gear steering for the takeoff roll even at low speed.

  Rudder pedal steering is available during takeoff, landing, and taxiing when small directional changes are required. Full deflection of the rudder pedals produces about 7 degrees of nose wheel steering (airliners.net).

The 7 degrees figure quoted above will vary by plane.

Tiller is used when tight turns are needed. Remember most airliners don't have a tiller on the first officer's side, yet they do takeoff without the captain steering for them.

(YouTube)

In the linked video we see the captain let go of the tiller as soon as he is lined up on the runway. Also notice the tiller move on its own afterward, which indicates that the rudder pedal [nose wheel] steering is being used.


Are the flaps of a Cessna 414A fully extended at 15 degrees or at 45 degrees?

A Cessna 414A with the TSIO-520-NB is listed here, from a high-res cockpit photo both questions can be answered.

The flaps extend to 45 degrees
The TSIO-520-NB's red-line is 2700 RPM.


Does the speed of the air molecules matter in aircraft performance?

In some sense, yes it does.  But we usually don't think about it in those terms.  You usually only need to think about individual air molecules when the object you are talking about is very small.  For example, if you are trying determine the aerodynamics of an airplane whose length is 1/100th diameter of a human hair, then you might start caring about individual air molecules. For realistic sized planes, the planes are so big relative to the air molecules that we can just pretend that air is continuous. So instead of thinking about the motion of individual air molecules, we think about continuous variables such as density and temperature.  i.e. when your air molecules "spread out and faster moving" we say that is a higher temperature with a corresponding lower density, and when they are "compacted and slow moving" we say that is lower temperature and a higher density.  By doing that, we've taken the motion of a quadrillion individual air molecules and reduced it down to one single number. And that one single number, density, does have an affect on aircraft performance.

For completeness, you also sometimes need to consider individual air molecules at very low pressures.  e.g. if your air pressure is a millionth of an atmosphere, then there are not many air molecules to go around and so each individual molecule's motion becomes more significant.  But airplanes generally do not fly at such low pressures.  Even at 40,000 ft, there's a lot more air pressure than that.


What are some of the differences between piston engines used in aircraft and automobiles?

The engine in a typical light airplane (say a Cessna 172 or a Piper Cherokee) has a lot in common with the engine in a classic 1960s VW Beetle (Type 1): Both engines are horizontally opposed four-stroke four-cylinder spark ignition gasoline engines. Their parts even have similar metallurgy, and broadly similar failure rates.
In fact if you remove the gearbox and install a magneto ignition system you basically have one of several "Volkswagen aircraft engines" that are popular in the experimental market, and have proven to be very reliable if well-maintained.

Certificated aircraft engines (the Lycoming and Continentals you would find in our hypothetical Piper or Cessna) have a few other features not found on a Volkswagen engine: They have dual ignition systems (two magnetos, two spark plugs per cylinder) for redundancy in case one fails, and an oil sump designed to hold at least twice the capacity of oil needed for safe operation. They typically also have a manual mixture control to allow the pilot to lean the fuel/air mixture as they climb (the VW Beetle generally didn't get too high above sea level, and when they did the local mechanic could adjust the mixture in the garage because those cars would probably stay at a relatively high altitude for most of their life - aircraft have an annoying habit of climbing and descending a lot, so either a manual mixture control or an altitude-compensating carburetor is necessary).

So what accounts for the price difference? Three things: FAA Certification, Volume, and Liability.

FAA Certificated engines cost quite a bit of money: The manufacturer needs to thoroughly document their design and manufacturing practices, and ensure the engine meets the design requirements and can pass the tests described in FAR 33. Doing (and documenting) all of this to the FAA's satisfaction is not a small burden, and it adds to the cost of the final product.

Volume is the next problem: As a reward for complying with Part 33 and getting your engine certified you now have the opportunity to sell your engine. To a very small market. There are far fewer piston aircraft than cars, and although piston aircraft engines are often "worn out" over the life of an airframe most owners overhaul their engines rather than replacing the whole engine outright. As a result the volume of new engine production is relatively low (and with relatively brisk competition in the overhaul market the manufacturer isn't even guaranteed a substantial amount of that business). As with any other product, when volume is small price goes up to allow a profit.

Liability is the last (and probably largest) factor affecting pricing: Jane Q. Pilot is flying along in his brand new just-off-the-production-line Cessna with her two kids and the family dog when the engine fails. She is unable to make a successful landing, and everyone dies, whereupon her bereaved and distraught husband John immediately sues the mechanic who last worked on the plane, Cessna (who made the airframe), and Lycoming (who made the engine).
Being ready to deal with this kind of high-profile and high-cost event requires a substantial legal team (the cost of which is built into each engine sold), and as the manufacturer is accepting a substantial risk the price gets bumped a bit more to provide a balancing reward (profit).

So to answer your bullet-pointed questions which I largely ignored in the explanation above:

Are aircraft engine parts expected to be less likely to fail?
We may have this expectation given the price tag, but in reality they're probably about as reliable as any other well-maintained air-cooled 1960s engine design.  A modern car engine has a number of design and technological advantages over the typical piston aircraft engine, and if we equipped them with dual independent ignition systems and gave them the kind of maintenance aircraft engines get they may well beat aircraft engines in terms of reliability. (Of course a modern car engine also weighs a lot more than a typical aircraft engine, so some money would have to be spent making it lighter without sacrificing that reliability.)
What is done to allow the engine to function at extreme temperatures / altitudes / air densities?
Surprisingly little: The addition of a mixture control for the carburetor, dual independent ignition systems, and a healthy weight consciousness pretty much covers it.
Do changes have to be made to allow a piston engine to function while upside down (in a roll)?
Yes (the fuel and lubrication systems for need to be designed to handle zero / negative G loads for an extended period of time), but your typical piston aircraft engine isn't designed to function while upside down: Aerobatic aircraft engines are a slightly different beast, and they cost a little more than their non-aerobatic counterparts.
What components are different on an aircraft vs automotive piston engine (magnetos vs. spark plugs, oil system)?
The biggest difference between a 1960s VW engine on a classic Beetle and a 2015 Lycoming O-320 is the dual magneto ignition system. The rest of the parts are largely identical, or at least analogous: Spark plugs look like spark plugs, cylinders look like cylinders, carburetors look like carburetors, etc.
Aircraft engines are also designed for component swaps: Cylinders can be easily unbolted and replaced for example, as can the magnetos, the oil pump, the carburetor, the starter, etc.


How can I find the CG of a model aircraft based on its dimensions?

You cannot.

Assuming that by 'dimensions' you mean the values for length, width and height, there is no way to calculate CofG from it. Two planes with exactly the same dimensions, but one with a thicker wings or tail, will have different C of G.

Even if you know the precise shape of the plane, the C of G cannot be calculated. Replacing a wooden tail with a heavier metal one with the same shape would shift the C of G. So would replacing the engine with a heavier one.

You need either the plane itself, or exact plans showing all the components and their weights (and a lot of maths).


How does an airborne DME unit differentiate itself?

As the Wikipedia article states, there are two modes - SEARCH and TRACK. In SEARCH mode, the DME interrogates with up to 150 pulse pairs per second. Similarly, in TRACK mode it interrogates at up to 30 PP/S.

What it doesn't say is that the interrogations are not evenly spaced at a fixed rate. The DME uses a pseudorandom number generator to vary the transmission interval over a set range. Since the DME knows the timing sequence it sent, it can look for replies that match that sequence.

The airborne DME can use the knowledge of when it made an interrogation and the maximum round-trip time for the maximum 200 nm range (just over 2.5 msec) to avoid non-correlated replies (to other a/c). The higher rate in SEARCH gives it more opportunity to detect the replies as it has no knowledge of range in search and thus has to scan for the entire range. Once it has detected the ground station replies by finding a correlated sequence of pulse pairs, it can switch to TRACK mode. The lower rate is acceptable once the range is established and the reply window can be narrowed.

As a note; mode X and Y are in use and differ only in the pulse pair timing, 12 usec  for X and 30 usec for Y.  Modes W and Z were set for DME/P and to my knowledge are not in current use.


Why does the zeppelin NT tail use 3 fins?

The likely reason would be ground clearance.

While it is hard to guess the reason for a relatively minor design decision like this, it seems that using four fins would complicate the tail design. Specifically, the airship would need to have a lower gondola or an X configuration for the tail, which may or may not impose a weight penalty on the tail structure.

As you note V control surfaces tend to be a net weight penalty once you factor in the higher loads placed on fewer surfaces. However, when the choice is between four small surfaces and three larger ones, the latter is likely to be more efficient.

You also note that the loss of one lateral surface would create a rolling moment, which is true, but this is the one situation where an actual "pendulum effect" (sigh) can be observed: the buoyant lift of the airship is directed against gravity, so it has a stable equilibrium point with the gondola pointed down, which simplifies the control problem.

Without knowing the critical load cases for that tail, it is hard to give a definitive answer, but this stands out as a plausible one.


Is there an exact solution for induced velocity during vortex ring state?

By its nature, VRS is not constant over time or location on the rotor disk. Any estimation of induced velocity in VRS is going to be time- and/or location-averaged, this way we can use the same expressions for rotor power and so forth. Well, also in momentum theory, induced velocity is sort of averaged over the rotor disk; there are factors that account for non-uniformities in induced velocity along the rotor radius, but these are relatively simple.
The unsteady nature of VRS changes rotor geometry and this renders any estimation for exact induced velocity invalid. The change/flex in rotor geometry is significant even for one-piece rotors (think multicopters); with hinged rotors, the rotor blade dynamics need to be at the center of any analysis on induced velocity in VRS.
In my experience with a case study with Eurocopter X3, estimations for VRS work OK for high-solidity and rigid rotors; such as fixed-wing propellers in reverse thrust and the X3's propeller generating reverse thrust when the aircraft is in slow forward flight.


Can IATA code for an airport be more or less than 3 letters?

IATA themselves say it's a three-letter code:

  Airlines and CRSs [computer reservations systems] may request the
  assignment of a unique three-letter code to identify an airport

The UN trade locations coding also says the same thing:

  when a three-letter code is used alone to indicate a location, it
  designates the name of an airport or location as adopted by IATA
  (whose code only has three letters)

According to Wikipedia, IATA has several different types of code that can be from one to four characters, but airport codes specifically are always three based on all the sources I mentioned.


Why do these aircraft in long term storage have air and power connections?

The photo is of 737MAX being stored in July 2019. Back then, airlines might still have hoped that this wouldn't be "long-term storage" at all!
Usually, airplanes being mothballed are stripped of corrosive / humidity-sensitive parts (e.g. the interior) as much as possible, stored in the dry desert, and it is considered acceptable if getting them back out of storage requires weeks if not months of refurbishment.
None of these three things seems to apply here. The photo doesn't look like it was taken in the desert, the airplanes are probably fully intact, and the airlines were hoping that with a simple software patch, they might be able to get them off the ground quickly again.
Therefore, they would have opted to, instead of preparing the airplanes for long-term storage, have them partially powered up, or use external air conditioning units. I would be willing to bet that those exact some planes are stored differently in July of 2020!


Engine shaft power: P = 0.58 hp, Propeller diameter: D = 8.5 ft, RPM = 245, Static thrust: T = 18.75 lbf

$\eta_{prop} = \sqrt{\frac{T^3}{(P^2 \cdot \pi \cdot \frac{D^2}{2} \cdot \rho )}} = 49.5\%$

where $\rho=1.2 \frac{kg}{m^3}$

So at an efficiency of 49.5% that propeller is rather poor.

Note: I used the formula that relates static thrust to efficiency, power and propeller diameter from here.


You can use Flightradar24 which will shows air traffic in real time where you can check which airlines are the busiest. Flightradar24 is using the callsign of the flight and compare it with big databases of airline and airport schedules to find the matching flight number, so not all airlines are submitting their schedules.

You can choose Airline fleet database in Data/History where you can check a comprehensive guide about the fleets of the world's airlines. Once you select an individual airline to view, you'll get its entire fleet. However it won't give you exact number, but list of all airplanes flying per airline (e.g. EasyJet).

To display the number, either you should request that information from the author of the site, or there are few workarounds.

Technical analysis of the busiest airline

When you open the page with specific airline (as suggested above, e.g. EasyJet), you can type the following command in JS console (e.g. in Chrome - More tools and choose JavaScript Console):

$("#listAircrafts li").length

and it'll print you the number of flying planes (sometimes less, because of the pager).

Or use Yahoo Developer Console and type the following query:

select * from html where url="http://www.flightradar24.com/data/airplanes/ryanair-ryr/" and xpath = '//*[@id="listAircrafts"]/li'

And in Tree View, you'll see number of flying planes at the moment (e.g. count: 323) based on Flightradar24 database.

To combine all lists together, you need a script as below.

In example the following *nix command (it'll take few minutes to run):

$ time for uri in `curl -s http://www.flightradar24.com/data/airplanes/ | grep -o 'data/airplanes/.*-[^"]*'`; do curl -s http://www.flightradar24.com/$uri | grep -o '/data/airplanes/.*-[^"]*' | wc -l; echo $uri; done | paste -d" " - - | sort -nr | head -n20
521 data/airplanes/airbus-aib/
484 data/airplanes/china-southern-airlines-csn/
411 data/airplanes/china-eastern-airlines-ces/
404 data/airplanes/lufthansa-dlh/
341 data/airplanes/air-china-cca/
324 data/airplanes/ryanair-ryr/
306 data/airplanes/british-airways-baw/
259 data/airplanes/turkish-airlines-thy/
254 data/airplanes/air-france-afr/
246 data/airplanes/emirates-uae/
214 data/airplanes/easyjet-ezy/
193 data/airplanes/saudi-arabian-airlines-sva/
186 data/airplanes/air-canada-aca/
184 data/airplanes/air-berlin-ber/
179 data/airplanes/netjets-nje/
176 data/airplanes/aeroflot-afl/
171 data/airplanes/qantas-qfa/
169 data/airplanes/tam-linhas-aereas-tam/
163 data/airplanes/cathay-pacific-cpa/
157 data/airplanes/sas-sas/

It will scan over 800 different airlines from the web and it'll print sorted list of the 20 busiest airways according to Flightradar24 database at the time of scanning. Tested on Linux and OSX.

Technical analysis of the busiest route

In order to calculate the busiest city to city routes, it's more complex that above example and you'll have to write similar script (or spreadsheet) of fetching all departures/arrivals of each airport (e.g. LGW) from available Airport database over world airports page, extract data from the tables, consolidate the airport/destination and sum it up in similar way.

Example extraction from table for LGW airport:

Extraction formula which I've used to list all departures from London Gatwick in Google Spreadsheet:

=ImportHtml("http://www.flightstats.com/go/weblet?guid=34b64945a69b9cac:4bf2fb3c:1246346ea7d:4597&weblet=status&action=AirportFlightStatus&airportCode=LGW&airportQueryType=0%22", "table", 0)

So theoretically you can extract all departures of the airport per Sheet (it's like over 3000), group Destination (so you know at least the busiest destination per airport) and sum it up, do some consolidation between Sheets plus some magic, and viola. That's why it's better to write some script:) If I'd have too much time on hand, of course I could do it.

So in other words, the busiest air route would be the airport which will have the highest number of the same Destination city (if I'm correct).

You can always simplify the work by choosing top 20 airports to give you some idea how does it work (instead of checking all of them).

Conclusion

Maybe it won't answer your question directly (which route is the busiest), but it's an idea how to extract the data of the busiest airlines and similar statistics. As it seems it takes a bit knowledge and time how to do it.

If you find any easier way of extracting that data or different database, let me know:)

Summary of the busiest airline

So based on above data (and ignoring Airbus), it's:

18:00 UTC/GMT (Friday)

China Southern Airlines (484)
China Eastern Airlines (411)
Lufthansa (404)
Air China (341)
Ryanair (324)
British Airways (306)
Turkish Airlines (259)
Air France (254)
Emirates (246)
EasyJet (214)

The data is indicative and it depends on the time of day and week, so I'm not warrant of any correctness of it as this is only the example.


What this tells me is that I can take off with any legal visibility/ceiling for my type of operation if I can maintain 325’ per nm climb. If I can only accomplish the standard 200’ per nm climb, I need 400’ ceilings and 2.5 miles of visibility, regardless of operation type.

Essentially it’s saying that there’s something out there that you’ll hit if you can’t maintain the 325’ per nm climb gradient. If you can, great, go. If not, you need the increased visibility to see and avoid it.


Is it possible to communicate an everyday computer with the ARINC bus?

Sure. there are appropriate controllers to be plugged in a slot - or even as USB, like the one you found. After all, basic USB is alread way faster than ARINC 429.

  If so, what is the access point where we would connect the wire?

Whatever connector the interface card/box offers. More often than not this may require some special-to-type cable. If you're able to handle a soldering iron and/or crimp pliers, building one is a reasonable job. If not, that's where you may ask the interface supplier to take even more money to sell you a fitting one.

On ARINC 664 (ADFX) it's even less an issue, as there are as well equipment using standard plugs.

  Would there be any other challenges I didn't take into account?

Software. As always it's the software there the main cost and effort is hidden. While basic drivers are usually included (for ARINC 429) or default (ARINC 664), any layer above will be specific to the task you're intended to handle - and usually not exactly low priced.

For ARINC 664 it depends even more on the task intended. While basic communication runs on standard Ethernet layer, 664 adds a quality of service at layer 2. Something you OS default driver may not support. Ofc, one may (buy and) install a driver that does, still this might bring trouble on the 'regular' networkside. Due this (and to avoide collisions) adding a separate interface card with fiting drivers may be advised.

ARINC 664 opens another can of worms depending on the application intended. Basically it is a virtual implementation of a bunch of ARINC 429 busses over Ethernet. To make applications work some translation layer may be needed.

Bottom line, buying and pluging an interface in/to your PC is the least complicated step here. And everything beyond that needs in depth knowledge of what is intended to be archieved.


What is this tube along the right side of a Blue Angel?

The aircraft is the A4 Skyhawk and the probe is for air-to-air refueling.

As you can see, it doesn't really impede the pilot's view which in any case, is concentrated on the refueller.

You can always spot a refuelling probe. For NATO aircraft, and most others, they always have the same tip and are the only appendages which look like this.

The Blue Angels used it since transits to various air shows exceeded the range and air-air refuelling is cheaper and more effective than landing, refuelling and taking off again.


Why is it common to speak of "Concorde" rather than "the Concorde"?

Ultimately it was the chosen name for the project and since it was a bi-lingual project the name was used in by both french and english sides working on it (7:40 into the video), as such the Definitive Article is commonly dropped when talking about it. It also derives from the word agreement and prior to the actually aircraft being built everyone was simply working on an undersigned agreement to build a plane.

  The name Concorde was chosen as, in both French and English (as
  "Concord"), the word means agreement. The plane was to be called
  Concorde in both France and Britain. However British Prime Minister
  Harold Macmillan, decided to remove the "e" from the end, as he was
  annoyed that his French counterpart, Charles de Gaulle, cancelled a
  meeting with him due to having a cold. The British government's
  Minister for Technology, Tony Benn, later replaced it, claiming that
  the "e" stood for Excellence, England, Europe and the Entente Cordial.


Why can't I find a tail number in the FAA registery?

I think wrong to believe N-numbers are not recycled.  The process has changed, but now we (owners) must register every two years (I think two years).  //see comment below, registration update is every 3 years and $5 which is background noise compared to an annual


Why was this cockpit much more complex than any other modern day aircraft

Firstly, as others have noted, you imply Concorde was modern when you compare it with "other modern" aircraft. OK, it was a "jet-age" aircraft, but it wasn't a 21st Century design. it was designed before "glass cockpits" were possible, in the 1960s. There were no real multifunctional displays then, so there had to be a switch or dial for every possible action and every possible parameter the pilots might need to know about.

The main difference is probably the flight engineer's panel on the right. Modern aircraft have two pilots in the cockpit and no flight engineer. I imagine that increased automation in engine controls mean that the engine management by the crew is much simpler and requires fewer controls and dials. These are now typically located in the center of the main instrument panel above the thrust levers etc.

For comparison, here's (a somewhat poorly stitched panorama of) a 747 cockpit

Image by Eric Long, National Air and Space Museum, Smithsonian Institution

and a rather better photo of a 747-300 cockpit (though lower central controls are obscured) ...

Image © aroosh

  or a fighter jet?

A lot of the controls and instruments are duplicated in a two-pilot cockpit. In a fighter jet, you only see one set of instruments and controls. Also a one-engine plane will have a quarter the engine controls of a four engine plane. Fighters probably lack an APU.

Although fighters have additional switches etc for armaments, airliners have additional switches etc for passenger related facilities (seatbelt lights, a/c? etc), security (cockpit door), cabin-crew comms and so on. They also may have more fuel tanks and maybe more means to move fuel around in flight to trim the aircraft.

  It looks to have much more buttons and controls,

Modern glass cockpits just hide all that complexity, just imagine you could rotate 90% of what you see out of view.

  and very small(interesting) screens.

There are no screens at all. There is a colourful moderately-complex artificial horizon instrument which also shows aircraft attitude and a few other things. The visual part is essentially mechanical rather than created by a light-emitting digital display.

  Also, its steering was much different than you would see in any other aircraft.

The shape of the control yoke may be slightly unusual but it operates the same was as any more common yoke design. You push it forward and back to control the pitch using the elevator (or elevons) and you rotate the top part left or right to control roll using ailerons (or equivalent control surfaces). There are buttons on the had grips to control a few functions. I think the shape was partly to make it easier to get in and out of the seat.

Heres a similar yoke design in an Embraer ERJ-145LR

Image © Micheal Catchpole


How do long-haul pilots cope with boredom?

From what I know, airline transport pilots do not get large chunks of free time on a typical long-haul flight which you described. They may get small intervals of free time (e.g. 10-20 minutes), but for sure, not hours. They do need to constantly monitor if the airplane is flying on the correct course, on the assigned altitude, remaining fuel amounts and several other tasks, even when auto-pilot is engaged.

So what do pilots do when they are not flying at all?

Primarily, it depends on company policies. Delta does not allow pilots to do anything not related to flying the airplane:

  "You can't read a novel, but you could read a manual about procedures
  or about the airplane," ... "You can't read a newspaper. You can't use
  a laptop. That's strictly prohibited."

But generally speaking, pilots engage in causal chats between themselves and flight attendants (when they visit the cockpit)1.

When there are more than two pilots, one is generally allowed to get some rest. They can also browse through magazines or read some books or flight-related material, but mostly stay alert and available. Some will study for an upcoming proficiency or rating. One of the two pilots can go to the bathroom too. Getting locked out depends on pure luck.

So in a nutshell, there are several different activities/tasks pilots will engage into, each different for a particular flight.

This is a funny little anecdote I recently read, which fits this discussion very well:

  Murphy's law grants you a heap of emergencies once you start feeling
  bored in the cockpit.

1: As a ordinary passenger, I don't visit the cockpit, but I have noticed a few times what the flight attendants do. When they have free time, they have many things to talk about between themselves. Sometimes, they engage in small talk with passengers. They check their schedule and flights for the remainder of the day. Although the duties of flight attendants and pilots are entirely different, there are a bunch of activities which require their attention, and they can pass the time without getting too bored.


How does the efficiency of a turbofan compare between take off speeds and optimal conditions?

To compare the efficiency we need to use the thrust specific fuel consumption (TSFC). It's the fuel per unit time per unit thrust.

(Georgia Institute of Technology)

The lower the y-axis value (TSFC/TSFC0), the more efficient the engine is. TSFC0 being TSFC at sea-level and standstill. Speed increases TSFC, whereas altitude (more precisely: decreasing ambient temperature) lowers it a bit.

Taking the extremes from the example above:

M0.4 at sea-level is a ratio of 1.45
M0.8 at 11 km (FL360) is a ratio of 1.675

On ground a turbofan engine is more efficient than in cruise when it comes to fuel consumption per thrust given.

But if you're comparing different airplanes, then the distance covered is also taken into account.

  Fuel consumption per [distance] can be a more appropriate comparison for aircraft that travel at very different speeds.

(Source)

For supersonic jet engines it's different as shown above.


Why do commercial flights turn / bank so sharply?

Airplanes are expected by air traffic control to turn at a "standard rate of turn" which is 3 degrees per second.  This will provide a 90 degree turn in 30 seconds.  A standard rate is used so that controllers can anticipate how long it takes for an airplane to turn to a heading and they can line them up easier.  It also makes the turn happen in a smaller amount of airspace so that two airplanes can be flying in the same general vicinity without getting too close.

Unfortunately, at the speeds that jet airplanes travel this would mean a very high angle of bank.  A standard rate turn at 200 KT TAS is about 30 degrees of bank and jets can go much faster than this, which would require even higher bank angles.  They actually limit it to 25 degrees of bank when using a flight director, mainly for passenger comfort.

It can be impressive when looking out the window and seeing the ground, but don't worry, the airplane is more than designed for it!

This is used mainly at lower altitudes where there are lots of airplanes.  Once they are up high and airplanes are further apart (and the turns are also usually smaller) they  can bank even less (by using a "half-bank" mode) which adds to passenger comfort.


What happens when I tell ATC to "mark the tape"?

These days, with digital recording, it's likely that nothing special happens.

"Mark the tape" is a holdover from when ATC recordings were actually on tapes - you could ask a controller to "mark" a tape to hold it and prevent it being recycled for another recording while your request for a copy of the tape is being processed. (Anecdotally I've been told some facilities had tape rotations as short as 15 days, and a FOIA request letter could easily take longer than that to make it to the facility).

Today much (probably most) of what is said on the frequency is recorded digitally, direct to hard drives, and kept around "essentially forever" as one of our local controllers put it when this came up at a recent event.  Basically the virtual "tapes" stick around for as long as the facility's recording machine has disk space to store them, and since audio files aren't that big facilities can store recordings a lot longer than they did in the days of tape.

All that's really needed to pull a record to review it with a controller/supervisor is the date, time, facility, and frequency (and your aircraft callsign would probably be helpful too) - e.g. "April 4, 2014 - JFK Local Control for Runway 04R (119.1) - United 123 Heavy".

"Mark the tape and give me a phone number" survives as non-standard phraseology that lets the controller know that you will likely have a bone to pick with someone when you get on the ground and gives them the opportunity to tell their supervisor that an annoyed pilot will be calling the facility in the near future (and hopefully give the supervisor time to listen to the tape).
The useful part is really getting the facility phone number so you know who to call when you land.


Is there any "copyright" for aircraft's design between different manufacturer?

This is more of a law issue rather than aviation issue. Anyway here it goes: No, there is no copyright to prevent one manufacturer from copying another aircraft because aircraft design is not protected by copyright.

The first rule about copyright is that it "protects an expression of an idea but not the idea itself". It protects technical diagrams, documents, recording etc, but not the idea expressed in them. Therefore if one simply photocopy the schematics, it would be a copyright violation. But if you reproduce what you see, it is legal.

The word you are probably looking for is "patent", which protects an idea. Aircraft manufacturers do have patents when they come up with something revolutionary. A quick search for "Airbus patent" turns up quite a few results. Whether you agree that particular idea was revolutionary enough for a patent though is another story.


Are there any data on the safety rate of gliders vs single-engine GA aircraft?

I had three days to burn so I took a look.)

Comparative data was very difficult to find beyond accident counts, so determining relative safety is problematic. No one that I could find tracks or estimates the number of flights/hours for gliders, even the Soaring Society of America, so this is all interesting but essentially meaningless. Even if such data existed, the difference in use models would cause problems making a fair comparison. So now that I've told you this was a waste of my time to compile, I will make you waste your time to read.

If you could extrapolate single mode pilot certificate counts to a common usage basis, flying a glider is 2.5x safer than flying an airplane, but of course you can't.

NTSB accident count for 2017 shows 56x more airplane accidents and 90x more fatal airplane accidents than glider accidents.

271 fatal and 972 non-fatal GA airplane accidents, total 1243
3 fatal and 19 non-fatal GA glider accidents, total 22

US Civil Airmen Statistics shows 18x more airplane only pilots than glider only pilots, with 40-80% of both numbers muddied by multiple certificate pilots.

14k registered glider only pilots
24k registered glider pilots with multiple certificates
260k registered airplane only pilots, excluding ATPs
190k registered airplane pilots with multiple certificates, excluding ATPs

AOPA had a report for 2009 for all general aviation where the accident rate per 100k hrs is 7.2, and a fatal rate for the same of 1.33.


Yes. For deliberate cross control situations, adverse yaw helps.  This means during side slip or forward slip maneuvers, where adverse yaw means less rudder is required to keep the nose pointed in the opposite direction to the lowered wing.

If you are in a glider or an old classic aircraft with lots of natural adverse yaw, if you lower a wing without any rudder to keep the ball centered, you end up in a mild side slipping turn automatically thanks to adverse yaw.


What do these numbers and symbols on the ICAO SIGMET chart represent?

Green are latitude and longitude.

The purple are major cities, e.g. A for Accra and B for Brazzaville (west coast of Africa traced in red above).
For the top line, here's an example breakdown:

PGCE05 represents the reference to the specific chart.
EGRR represents the WAFC issuing the data (in this case WAFC London. KKCI represents WAFC Washington). In the case of a backup situation, this will remain the same even if the data is issued by the other WAFC.
161200 represents the day of the month (16 in this case) and the hour in UTC (1200 in this case) of the analysis on which the forecast is based. Note, this time will always be 24 hours earlier than the validity time of the forecast as specified in the main legend on the PNG forecasts.

Source: Guidelines for interpreting World Area Forecast Centre Significant Weather forecasts


Interesting question!

In the background, a Lufthansa Boeing 747-400 can be seen. Therefore, I assume the airport is a Lufthansa destination. Since the 727 is not exactly a long range aircraft, but the 747 is, my first thought would be that the airport is in Germany.

I couldn't really see what livery the 737-200 in front of the LH 747 was, but soon in the take-off roll (0:10 seconds) a propeller aircraft (Dash 8?) with a South African Airlines tail appears. Then during the rest of the video many SAA tails are visible and also a number orange tails. I needed to get my first aircraft book (printed 1989) to discover that the old livery of SAA featured an orange tail.

It is thus pretty safe to assume that the airport is in South Africa.

That makes it quite rare for a British Airways 727 to appear there. The range of the aircraft is approximately 2000 nautical miles which is a bit short of the almost 5000 nautical miles that London - Johannesburg measures.

I then remembered a recent accident in South Africa involving a Comair Boeing 737-400 in British Airways livery. This led me to believe that this particular Boeing 727 in the video may be a Comair 727 in BA livery too.

A little search turned up this picture on airliners.net, confirming that Comair indeed operated the 727 in BA livery.

The airport is O.R. Tambo in Johannesburg:

A still from the youtube video showing some buildings in the background

The same buildings in Google Maps


What can I do to prepare for private pilot training? (India)

It's hard to give you specific advice for India because I'm not familiar with the regulations and standards there (your best bet would be to give the DGCA a call and ask if they have any publications you can review).

Broadly speaking all countries are going to expect you to know much of the same material however (because all airplanes essentially fly the same way). Along those lines, the FAA publishes some of the best flight training resources out there, and it's all available online for free.
I would recommend two of the publications to anyone considering flight training:

The Airplane Flying Handbook
This is where I'd generally suggest starting - a basic "How does all this flying stuff work?" textbook on a par with any of the commercially-produced materials.
Details on specific regulations, procedures, how to read charts, etc. may vary, but all of the material on aerodynamics, systems, flight controls, and maneuvers will be applicable.
If you're interested in helicopters there's a Helicopter Flying Handbook as well.
The Aeronautical Information Manual (direct PDF link)
This will be less useful to you as it's written with US regulations in mind (and stuff like aeronautical charting is probably different in India than it is in the US), but again there are large sections that are broadly applicable: Chapters 1, 2, and 8 in particular.

In addition to reading you can gain some experience using simulators if you use them effectively - even relatively inexpensive home simulation software & equipment can be helpful, though it's not a substitute for the real thing. We've got a good Q&A on using simulators to help in training which addresses some of the strengths and weaknesses of learning in a simulator. To help keep you from developing bad habits you would have to un-learn in a real airplane there are also companies providing what's effectively a private pilot flight course via simulators for free, and that will help you get started doing things right - following all the procedures as you would for a real airplane.


What is a typical range of air temperature used for engine inlet cowl anti icing?

Anti icing systems that use bleed are either "run-wet" or "evaporative".
Run-wet systems heat the surfaces to below the water boiling point, say 140-160F.  Supercooled drops hitting the surface are kept from freezing on the leading edge, but can run back and refreeze on the unprotected areas. In that case the "lowest" temperature is whatever keeps the water liquid until it's off the protected surface.
Evaporative systems heat the surfaces to above the boiling point of water, say 220-230F, so the supercooled drops that strike immediately turn to vapour, like spitting on a steam iron, and no ice can form farther back.  In that case the lowest temperature is the boiling point plus a margin.
You use an evaporative system if you can't tolerate runback ice (otherwise you'll use a cheaper and less demanding run-wet system).  On a wing, this will be related to the airfoil's stall behaviour with runback ice, and a non-slatted wing with a supercritical airfoil (which tends to have poor stall behaviour) will typically have an evaporative system.  If you can live with run-back ice because the wing is tolerant ice forming aft, or if the wing has a slat system that makes it tolerant of ice forming aft with slats out, you may use a run-wet system because of the lower heat demands and costs.
On cowls, same sort of thing; you'll use a run-wet system if the engine is not too sensitive to runback ice forming and distorting the flow on the inside surfaces of the cowl or breaking off and hitting the fan blades, or if it is, an evaporative system, that will keep the cowl leading edges in the mid 200sF.
On the General Electric CF-34, the bleed that supplies the cowl is blended with ambient air to cool it down using an air ejector at the entrance to the cowl piccolo system, where the hot air is dumped into a larger duct from an ejector nozzle, which pulls ambient air in with it and mixes them together. By the time the air is entering the piccolo duct, it exits from little holes cooled off quite a lot, and then it has to fill a space and transfer heat through the skin to the leading edge outer surface, so the it might still be 300-400F (after leaving the bleed port at 500F) or more even when being dumped into the leading edge of the cowl, in order to keep the leading edge skins heated to more than 220F.
If a cowl has a run-wet system, these temps will be much lower obviously.
The upper temperature limit is mostly related to the temperature tolerance of the leading edge and adjacent structure (such as heat treat state and the effects of heating/cooling cycles on the structure etc).


The Mig 21 and the Mirage III have been criticized for lack of range, is this a limitation of the wing configuration?

No. Their range limitation stems from their original concept: relatively cheap simple lightweight agile fighter (MiG-21) or interceptor (Mirage III).

There are plenty of long(er)-range aircraft with delta wing (if that's what you mean). Concorde, for one. B-58. Eurofighter.

For a given class of aircraft, range is primarily a function of fuel quantity and therefore (almost directly) of the maximum takeoff weight. JF-17 is 35% heavier and so has significantly greater range. (It also helps that it and its engine are two generations newer). J-7 is practically the same as MiG-21 and has very similar performance.


Which refers to CFI renewal based on pass rate, "activities" or "duties and responsibilities"?

You want to check the Activities box.
The phrasing is a little weird, and it certainly doesn't line up with the regs (see 14 CFR §61.197), but that's what you want:

(2) Submitting a completed and signed application with the FAA and satisfactorily completing one of the following renewal requirements—
(i) A record of training students showing that, during the preceding 24 calendar months, the flight instructor has endorsed at least 5 students for a practical test for a certificate or rating and at least 80 percent of those students passed that test on the first attempt.
(ii) A record showing that, within the preceding 24 calendar months, the flight instructor has served as a company check pilot, chief flight instructor, company check airman, or flight instructor in a part 121 or part 135 operation, or in a position involving the regular evaluation of pilots.
[...]

So, best as I can tell, that means:

§61.197(2)(i) is activity - 80% pass rate on 5+ students in the preceding 24 calendar months.
§61.197(2)(ii) is duties and responsibilities - serving in a position that involves standardization flights or stage checks.

Disclaimer: unfortunately, all of the AOPA material on CFI renewal is designed to get you to buy their FIRC (eyeroll), and the unhelpful FAA IACRA document for instructors says squat as well. I'm having a hard time finding a reference that proves my interpretation, but I know it's correct!


Why are turboprop intakes placed below the propeller?

Inertial separators are augmented by gravity when located under the engine. It is easier to discharge ingested ice and debris downward, rather than some other direction, so that is where they go if possible. Inertia keeps solid matter low at the indicated point while air makes the turn into the engine.

C130 Nacelle


The FAA publication "MEDICAL FACTS FOR PILOTS" Publication #OK-06-002 states the time periods shown below. I don't know of any rule that mandates a response in any specific time period.

We will respond to your request for duplicate medical certificates within 3 working days of receipt.

We will respond to your request for full review of medical records within 30 working days of receipt of all the necessary records and testing.


Can FMC be programmed to do fast maneuvering in fighter jets?

Pre-programmed high speed maneuvering is already being done in the case of target drones derived from fighter aircraft like the QF-16 (which is derived from F-16). According to multiple reports,

  The QF-16 ... is capable of pre-programmed maneuvers such as high-G turns, barrel rolls, split-S, etc.

While some research has been carried out on fully autonomous weapons systems, at present there is always a human being in the loop (at-least) for pressing the 'kill switch'. A few of the problems in a fully autonomous system operating in enemy airspace are:

Operating the UAV in hostile area and responding to threats. Though the QF-16 drones can fire chaff and flares to escape from incoming missiles, drones that can operate in hostile environment are still in their infancy. This requires significant improvements in ability of the UAVs to detect, differentiate and prioritize the threats and respond to them.
The UAVs should have the ability to search/track, acquire and engage the target while not ignoring friendlies or neutrals. Though some tests have been carried involving automated target tracking and some missile do have the ability to discriminate between the target and surrounding buildings (based on prior information),the technology is still some way off.
There are significant political, legal and ethical issues in using automated killing machines.

Some missiles like the Tomahawk has the ability to navigate along a predetermined path and hit targets, though they cannot do high speed maneuvers (or return, obviously).


How to calculate the Lift Coefficient for the A320?

I found a  different number for $C_L$, please check your calculation:

$C_L=\frac{2 m g}{\rho V^2 S}$

substitute:
$
m = 50000 \textrm{ kg}\\
g = 9.81 \textrm{ m}/\textrm{s}^2\\
V = 462 \textrm{ KTAS} = 237.67\textrm{ m/s}\\
S = 122.6 \textrm{ m}^2\\
\rho = 0.475 \textrm{ kg}/\textrm{m}^3
$

This will give:
$C_L = 0.298$

Note that this lift coefficient is for the total aircraft. It includes the lift of the wing, the fuselage lift and also the negative lift of the vertical stabilizer. There is also a small vertical component of thrust that is neglected.

Now that we have an estimate of the lift coefficient, we can estimate the angle of attack. Normally the lift coefficient is assumed to vary linearly with the angle of attack:

$C_L = \frac{\textrm{d}C_L}{\textrm{d}\alpha}\cdot (\alpha-\alpha_0)$

$\alpha_0$ is the zero-lift angle of attack, the angle of attack at which the wing does not generate any lift. For symmetric airfoils, $\alpha_0 = 0$, for chambered airfoils $\alpha_0 < 0$.

I don't know what that angle is for the A320, it will be difficult to obtain. Let's assume for now it is -1.2 degrees.

For infinite long wings in incompressible flow the lift slope $\frac{\textrm{d}C_L}{\textrm{d}\alpha}$ is $2\pi$.

$(\alpha-\alpha_0) = \frac{C_L}{2\pi} =0.0474 \textrm{ rad} \approx 2.72^\circ$

This would result in an angle of attack of $\alpha \approx 1.52^\circ$

Because the wing of the Airbus A320 is not infinitely long but has a span of about 30 meters (excluding the fuselage) we need to correct for that. The reason we need to correct for the finiteness of the wing is that the circulation will cause the local angle of attack of the wing to be lower than the free stream angle of attack. The effective angle of attack $\alpha_{eff} = \alpha - \alpha _i$

The induced angle of attack $\alpha_i$ is given by:

$\alpha_i = \frac{C_L}{\pi AR} = \frac{C_LS}{\pi b^2}$

substitute:
$
S = 122.6 \textrm{ m}^2\\b = 30 \textrm{ m}
$

gives $\alpha_i = 0.0129 \textrm{ rad} \approx 0.74^\circ$

Adding this to our earlier angle of attack results in:

$ 1.52 + 0.74 = 2.26^\circ$

This may not be very accurate as

a) the zero-lift angle of attack may be very different,

b) the lift slope may be flatter due to compressibility effects


What could be the cause of an uncommanded roll at high speed?

I once went on-site to troubleshoot an airliner with an uncommanded roll problem.  The operator had rigged this and rigged that and were in the process of ordering new aileron power control units, pretty much out of desperation.  I asked about the trim actuator, which they had replaced with a known good unit off another aircraft, making them think that couldn't be the problem.  I centered the trim and went to look at the position of the rig pin holes in the aileron control circuit.  They were mis-aligned.

The trim actuator on this airplane was an electric linear type with an internal Linear Variable Displacement Transducer (LVDT), that supplied the position signal to the cockpit trim indicator (or EICAS in this case), that was "dithering", that is, the signal was drifting around.  When you thought the trim was centered, it was actually offset, and this error would randomly change as the actuator was moved.  On the original airplane the actuator was installed on, the dithering wasn't enough to cause a snag to be raised by the flight crew so its internal problem went undetected.

The variations in roll you saw at speed may be some other phenomenon, or it just could have been coincidental variations in the trim indication on that flight.

So, if it was me, the trim system itself would be an item to cross off the list before proceeding to more desperate measures. Do a thorough functional test of the trim system and its indication, and also look for things like backlash within the actuator itself or in the linkage.


What is the physical explanation for the formation and position of stagnation points on an object moving in a fluid?

The forward stagnation point is easy to explain: Imagine the flow path of molecules which approach an airfoil. Some will continue above and some below the airfoil contour. Between them there must be one flow path which will neither go above nor below, but hit the airfoil straight on. The point where it hits the airfoil is the stagnation point.

The rear stagnation point is similarly explained: When the flows from above and below meet, there will be a line dividing both. Continue this line forward until it hits the airfoil: This is where the rear stagnation point is located. A rear stagnation point is only possible in inviscid flow, which exists only in theory. In both points the speed of air relative to the airfoil is zero, and air molecules will never completely arrive at the stagnation point, but slow down on their way into it.

An airfoil of zero circulation and zero camber will have its rear stagnation point right at the trailing edge. Only when you add asymmetry by giving the airfoil positive camber, the flow has to develop an asymmetric pattern which shifts the rear stagnation point away from the trailing edge to satisfy the zero circulation condition. Give the airfoil negative camber, and the rear stagnation point will duly relocate below the trading edge.

The Kutta condition postulates that the rear stagnation point is fixed at the trailing edge. Make the trailing edge blunt and you need to define where precisely your stagnation point will be. Note that your choice of location will influence the circulation at a given angle of attack! The Kutta condition imposes an arbitrarily chosen stagnation point which just helps to explain real flows better. This does not mean that real flows will observe the Kutta condition closely.

If you look for the "real" stagnation point, you should really search for the point where local pressure reaches a maximum, fully knowing that a full deceleration to stagnation will not happen in reality. This can only be outside of the boundary layer, since the energy loss of the boundary layer flow will result in a pressure loss. Now the picture from the second paragraph will help: Find the line separating upper and lower flows and follow it upstream until it hits the airfoil. This procedure will land you straight at the lowest speed section of the boundary layer, and near the airfoil the pressure there is too low. But now move back again and watch how the slow center part of the boundary lower gets accelerated by shear with the neighboring flow. At some point pressure will peak: This is the closest you can come to for a rear stagnation point.

Below I plotted a quick XFOIL calculation of a NACA4418 with a 5% trailing edge gap to get something similar to your airfoil. Note how the $c_p$-value of the viscous flow (solid line) peaks at some point behind the blunt trailing edge. For the outer flow the airfoil looks as if it is slightly longer, the void behind the blunt trailing edge being filled by separated, slow flow. Also note that the upper boundary layer is thicker, shifting the "rear stagnation point" a little up.

XFOIL Plot of a NACA4412 with 5% blunt trailing edge at 4° AoA (own work).


Why does Qatar Airways fly over Syria and Iraq?

They are trying to save themselves money, and their customers time.

First of all, why do the planes follow that route?  From your comments, you are going from Philly to Doha.

You might want to take a look at great circle routes to see why the planes are coming into Doha from that direction.  The Great Circle route depicted goes right through Syria and Iraq: it's the most efficient way to get there. Beyond that, Qatar has a few limitations that other airliners don't have, in that region, due to some diplomatic problems with their neighbors, who won't let them overfly their airspace: Saudi, Egyptian, and UAE airspace for the time being is closed to them.  (thanks @reirab)

Diversions cost money

Some typical diversions in that region are well spelled out in this article in the Economist.

What you may be seeing is that, for some flights that pass over the region, rather than landing within the region, they are accepting the risk that their airliners at 30,000+ feet might, maybe, get targeted on a really bad day (see the Malaysian Airlines flight shot down over the Ukraine a few years ago (MH 17)). But the odds of that are very low.  They most likely will not be disturbed.  (Or so a risk management case can be made).  A more conservative view of risk is offered here, in an Ops Group posting from September of 2018.  (Thanks to @ZachLipton for the link).

Route diversions have very real fuel costs, and costs in time.

Image from the Economist, Oct 20, 2018 edition.

The article mostly addressed flight into Lebanon by Middle Eastern carriers.  Flying into Beirut is of higher risk since the aircraft have to come down through the risky / war zone airspace for final landing, but it's instructive to illustrate how costs go up when more direct routing can't be taken due to safety precautions around conflict zones.

  But for years the airspace over Syria has been crowded with warplanes. The Gulf airlines no longer use it. Instead Emirates, the flag carrier of Dubai, detours across Saudi Arabia and Egypt, adding 700 km to the trip.  The journey takes even longer on Qatar Airways, which was barred from Saudi airspace after a dispute between the Gulf countries erupted last year. Its route from Doha to Beirut resembles a crook: north over Iran, west across Turkey and south down the coast. What should be a 1,825km flight drags on for 2,865km. {snip}
  For travellers this is a nuisance, adding an extra hour or two to journeys. But for airlines it imposes real costs.  Qatar Airways posted a 766 million dollar  profit in the 2017 financial year.  In the 2018 financial year, it lost 69 Million dollars. Operating costs were up by 15%; passenger numbers were down 9%. “We didn’t raise the ticket price,” says Akbar al-Baker, the CEO. “We had to absorb the additional cost.”

  Emirates and Etihad, the flag carrier of Abu Dhabi, run five daily flights to Beirut. With the detour around Syria, they log an extra 2.7m km every year. Depending on the aircraft, that means up to 19 million litres of additional jet fuel, about $11.4 million at current prices. {formatting changes by me to make this fit}

@DavidRicherby points out, fairly, that this local problem is a bit different from the great circle route's need to make an adjustment, in terms of how much extra time and effort a given regional route costs, but it's useful as an illustration of how costs go up when these problems have to be dealt with.

I don't want to have to worry about ...

Then don't.  What you worry about is under your control.

How many airplanes has Qatar airways lost in the last seven years (the length of the Syria civil war) to being shot down? Zero.
What does that say for your odds of this being a low probability
risk?

If you still worry, have you investigated one-flight life insurance?  I used to always buy that whenever I flew, through American Express, back in the 80's and 90's since I was just married and I had young kids.  I'd buy a million dollars worth for about 14 dollars each way.  If you are that worried, buy the life insurance.  It's about the same odds a winning the Lotto for your family.

Full disclosure: I do not now work, nor have I ever worked, for Qatar Airways.


Does Boeing use a similar display to Airbus ECAM to view a particular system?

Boeing 777 fuel-system display; A.Katranzhi, CC BY-SA 2.0, via Wikimedia Commons

The following:

747-400 and 747-8
777
787

... display aircraft systems digitally. Except the -400, they also have electronic checklists. For Boeing, it started with the 747-400. The main drive for it was customer demand. After which it was to be like the 757/767, but the "Airbus style" second-generation synoptics was settled on:

One launch customer, Cathy Pacific, originally wanted the standard electromechanical instruments, to avoid retraining. Boeing's initial approach too was "minimum change", but in 1985 other customers, happy with their Airbus and Boeing glass-panelled Efis twins and two-pilot efficiency, pressed for Efis.
(...)
Boeing first responded with the 757/767 flightdeck, keeping the same autopilot. "Minimum change" was still the watch-word. The users' committee became a formal body with chairman and minutes, and the Airbus A320 was now influential.
(...)
The lower Eicas display presents engine data—compressor speeds, oil pressures and temperatures—[and] a major change in Boeing philosophy, [a] systems "synoptics" Airbus style.
— Boeing's two new 400s. FLIGHT INTERNATIONAL, 16 January 1988

Further reading for how it evolved:

Stoll, Harty. "Boeing flight deck design philosophy." (1990). https://ntrs.nasa.gov/citations/19910001624


What is the name of the maximum altitude at which a helicopter can fly?

Like with fixed wing aircraft, it is called the ceiling. Usually two ceilings are distinguished;

service ceiling, where the aircraft can still achieve a positive rate of climb of either 100 fpm (propeller) or 500 fpm (jet).
absolute ceiling, the theoretical altitude at which no positive rate of climb can be achieved. In other words: the maximum altitude at which the aircraft theoretically can fly under maximum engine power.


Can the design for neutral stability reduce trim drag?

Terminology first: Trim drag is the drag component added by adjusting the incidence of the horizontal tail rsp. the deflection angle of the elevator for trim. The increased parasitic drag of a larger tail surface itself is already part of the aircraft's zero-lift drag.

Sizing criteria for tail surfaces

The horizontal stabilizer surface must be dimensioned with these criteria in mind:

Sufficient static longitudinal stability. To achieve this, the tail volume (tail area times lever arm) must be high enough. Use similar aircraft and copy what has been found to work well.
Sufficient pitch damping. This is driven by tail size times the square of the tail lever arm.
Sufficient control power at the most forward cg location over the whole speed range.
Sufficient control power at the most forward cg location over all load factors (including pitch damping effects).
Sufficient control power when flaring in ground effect (which reduces elevator effectivity)
For T-tail configurations: Sufficient control power over all sideslip angles. Sideslip produces a strong pitch-down moment in T-tail configurations.
For gliders: Sufficient compensation for the force of the tow line, both at the beginning of a winch launch (tow line horizontal) and at the end (tow line vertical).

The other criteria (upper and lower limits on stick force gradients over speed and load factor) can be tailored with elevator chord, so the horizontal tail surface is not directly affected.

In the end your horizontal tail will be as large as you want your cg range to be wide. Operators like wide cg ranges, so the small drag penalty of a bigger tail surface might be worth it.

Wing airfoil

Also, wing airfoils with a high pitching moment (think rear loading, i.e. high camber in the rear part) will need a bigger tail surface due to the larger shift of the center of pressure over speed, but have less drag and a higher maximum lift than comparable, old-fashioned airfoils (think NACA 4-digit range), so the wing can be smaller and has less drag, which easily compensates for the increased tail surface.

Do not optimize each surface separately

If your wing has already an optimized lift distribution, adding more lift in the same Treffz plane will spoil the end result. In the end, it does not make much of a difference at which position in streamwise direction lift is created, only the sum of it counts. Therefore, it might be better to have as little tail loading as possible in the design point.

If you take the mass of the wing structure in consideration, your optimum lift distribution over the wingspan will change to a more triangular shape, and now it might even make sense to create a small downforce on the tail to reduce the downwash angle in the center section. A lighter wing will require less lift and help to reduce drag.

Think of it this way: The triangular lift distribution produces a higher downwash angle at the tail, and any downforce there would actually point slightly forward, creating induced thrust. Effectively, it helps to equalize downwash over span in the Treffz plane of wing and tail.


Where can I find examples of ADS-B surface (ground) position data?

The best source for that data would be EUROCAE Document ED-102A or RTCA Document DO-260B. These are the Minimal Operational Performance Specifications for ADS-B on 1090MHz. They include all the requirements on the ADS-B transmitter, including test data to demonstrate that the requirements are met.

However, if you don't have access to those documents, you can try and receive some ADS-B messages from aircraft on the ground using an ADS-B receiver and decode those. If the surface position messages indicate good position integrity (format type code 5, 6, 7 but not 8) and the decoded positions appear on airport paved surfaces consistently than you are sure that you've got it right.

Note that ADS-B surface decoding is not globally unambiguous; you need to know where approximately the receiver is (as in which N/S,E/W hemisphere) to unambiguously decode the surface position message.

The table below shows some encodings that can be used to verify wether your surface CPR decoder works.

The first four columns show latitude and longitude (in decimal and 32 bit angular weighted binary hexadecimal notation), the next 6 columns show the CPR data.
\begin{array}{|c|c|c|c|c|c|c|c|c|c|}
 \hline
 \text{Latitude}&&\text{Longitude}&&\text{Lat.}&\text{Lon.}&\text{NL}&\text{Lat.}&\text{Lon.}&\text{NL}\\
(Decimal)&(HEX)&(Decimal)&(HEX)&(HEX)&(HEX)&(Dec.)&(HEX)&(HEX)&(Dec.)\\
 \hline
-27.93897726&EC21DD4A&153.00998&6CCE9DE7&0BF7F&03636&53&15E70&0CFC1&53\\
\hline
27.938976&13DE22A7  &45.0000&20000000&14081&10000&53&0A190&00000&53\\
\hline
\end{array}
source: EUROCAE ED-102A , table 2-214 (truncated), page 699


Did the Doolittle raid run their engines over square?

According to this transcript of the actual mission report from one of the pilots, they did indeed run over square

  I flew the last 500 miles into Tokyo at altitudes ranging from 1000
  feet to 4000 feet in order to fly in the thin overcast and clouds to
  avoid detection. I used 28 inches of manifold pressure and about 1370
  RPM and indicated between 150 and 165 MPH.

And for the latter part of the mission

  I made the trip from Tokyo to China at about 500 feet altitude and
  1300 RPM and started at 29 inches of mercury and gradually reduced to
  25 inches as my gas load reduced. I indicated about 160 to 165 MPH.

Question 2: According to this copy of the manual (page 155) the engine is almost always run over square in cruise.

As for question 3 you can find a discussion on operating over square in this question and ill avoid answering it here to keep it form being a dupe.


What was the first airplane fitted with a hydraulic system?

What was the first airplane fitted with hydraulic system?/Where was it used?

If we exclude hydraulic disk brake systems.

The Lockheed Constellation most likely had the first hydraulic flight controls (introduced in '43)

Introduced in '27 the Fairchild FC-1/FC-2 had hydraulically operated landing gear and disk brakes.

  What are the fundamental differences between the first systems and
  those that are used now?

Depending on how you look at it, little. Hydraulics are hydraulics. The systems have gotten more powerful but that may be related to the available power to drive the pumps. We arguably have gotten better at building them and they are perhaps more reliable but they are still more or less the same in operation.


How can filling a tube with foam help prevent buckling?

A simplified analysis of column buckling shows that the axial load required for buckling is directly proportional to the second moment of area of the column's cross section: $F=\pi^2EI/(KL)^2`$`, where F is the buckling load, E is the elastic modulus of the material, I is the second moment of area, and KL is an effective column length based on the geometric length of the column (L) and a variable factor K that is based on the boundary conditions.  The critical term for this question, though, is I.

For example, look at the picture below of a beam that someone is trying to bend.  You can do this yourself with a ruler or a paperback book.

In the upper image, you're trying to bend the book/ruler by pressing down on the spine, and it's really hard to do.  Rotate the book 90 degrees and press down on the cover...and it's relatively easy (unless you picked a phone book).  The material of the book didn't change, only how the area of the cross section that you were bending was distributed in the direction that you were trying to bend the book.  In the same way, adding foam to the tube increases the total area that needs to bend in order for the tube to buckle, which, if you'll allow an approximation, increases the strength of the tube by 5% from the baseline case (a hollow, aluminum tube).  Double the radius, and that becomes 10%.  Double it again, and that goes to around 25%.  Don't take those numbers as gospel, but it should give you an idea that adding area -- even with a relatively low stiffness material -- you can increase the strength of a material significantly.

However, buckling is different from strength.  Buckling is a bending instability caused by compressive loads, and failures in buckling often occur well below the failure load for the structure.  Let's run some numbers for this, using the expression I mentioned back up at the top.

For example, if I run an analysis for a 4.5 ft long, hollow, 1 in diameter tube with a wall thickness of 1/16 of an inch made out of 7075-T6 aluminum (E = 10.3 msi) with both ends effectively pinned, I get a buckling load of 714 lbf (note: the axial compressive load that would make this structure yield would be closer to 8,000 lbf).  Naturally, one could fill that in with metal and increase buckling load dramatically to 1,727 lbf, and, while that's not the query, I am adding some bending stiffness to the tube by filling in the center.  Buckling of a composite column (insofar as I know) is tricky, but, here is an approximation (which will undershoot the actual buckling strength).

If I add foam and say that the foam will not buckle (as it is fully constrained by the tube and cannot deform in any direction save axially, let us say), and then assume also that the purely axial load on the column will be divided between the foam and the aluminum according to the proportion of their elastic moduli (polystyrene has a Young's modulus of about 2.5 GPa), then the aluminum will only absorb about 88% of the load placed on the column.  This increases the buckling load by about 100 lbf (without causing the foam to yield).  However, this does not take into account how the foam will add bending stiffness to the structure, which would further increase the benefits of adding the foam.

In short, you're using a low-weight, cohesive filler material to increase the bending stiffness of a structure, dramatically increasing its tolerance for compressive loads.


Why can't there be more than 4 anti-shock bodies on each wing?

There is no reason to limit the number of anti-shock bodies to 3 or 4. In most modern aircraft, the anti-shock bodies are the flap track fairings which usually house the flap mechanisms.

As such, their number is determined by among other things, the wingspan, the size of control surfaces and the number of actuators required for their actuation etc. This usually limits their number to around 4 due to weight and other considerations.

However, there is no reason there should only be 3 or 4 of them. For example, the Antonov An-225 Mriya has a whole lot of them.

Source:www.avioners.net


Why do the Lycoming HIO-360 A1A and IO-360 engines produce different power?

Helicopter engines have different operating parameters than aircraft engines. They operate in a narrower power band and the difference in horsepower would be due to  camshaft lift and duration optimized for that power band.


Do the blades of the rear disk have different geometry to the blades of the front disk on a contra-rotating assembly?

The conditions at the rear disk are obviously different, so something must be different.

First of all, if the rotation direction of the disks is opposite, you'll have 'right' and 'left' blades. (Blades nearly always have asymmetric airfoil, so you can't swap them). That's 'different geometry' already.

Normally, the efficiency of the rear disk will be somewhat lower (zymhan's answer provides some sources). If so, an optimal design should provide more power/torque to the front disk. The most powerful turboprop NK-12 delivers about 20% more torque to the front disk.

Source

This doesn't mean, however, that the blades must be substantially different (other than mirrored). Indeed, on most coaxial assemblies they are the same (including the aforementioned NK-12). How does it work? All these props are constant speed units (at least, I'm not aware of others). The governors will simply set the appropriate blade pitch such that the RPMs were the same, despite different torque and conditions. This means in practice that the blade pitch on the rear disk will be lower. This may count as 'different geometry'.

Finally, there are rare examples when the disks are substantially different. One of them is the SV-27 propfan on Antonov-70, which has even different number of blades (8 vs 6). (This, I believe, is a prop with the highest disk loading ever).

Wiki source


How long can passengers survive after ditching in the ocean?

Well, your scenario is a bit unlikely because if the aircraft did ditch in the ocean they would have the emergency rafts and slides to take cover in instead of "floating around in their inflatable vests".

However, if someone were floating in the ocean without any protection, how long they could survive depends on various factors.  Temperature is the biggest factor in the amount of time before they would succumb to hypothermia.

Take a look at this chart to figure out the average temperature of the area in question.  If we go by the latest news, that is going to be somewhere in the neighborhood of 14C.

This page says that the Expected Time of Survival is 1 to 6 hours.

The same page also says:

  Maximize your chances of surviving by:

  Wearing a personal flotation device (PFD)
  Adopting a survival position
  Keeping clothing on
  Getting as much of body out of the water as possible
  Remaining still and in place UNLESS a floating object, another person, or the shore is nearby
  Keeping a positive mental outlook (a will to survive really does matter)

  Swimming isn't recommended unless there is little chance of being
  rescued and shore is less than a mile away. Putting on a PFD after
  falling into cold water is almost impossible – SO WEAR IT. If you find
  yourself in cold water without a PFD and nothing to climb onto, tread
  water. Traditional drown-proofing by repeatedly lowering your head
  into the water and floating speeds up heat loss.

Lots more information is available on that page!


What is the meaning of first flight and introduction in aircraft production?

The first flight of a new aircraft type refers to the first time the aircraft is flying during the development and testing phase. If the testing goes smoothly, it might be that no more changes are necessary and the aircraft can be delivered to customers as it is. But if problems show up during these test flights, changes might be necessary before finishing the final design.

The introduction refers to the first flight by a customer (an airline for commercial airliners or a military unit for military aircraft). This is also referred to as entering service. This could happen in the same year as the first flight (e.g. Boeing 737 Classic series in 1984) or many years later (e.g. Concorde in 1976, 7 years after the first flight in 1969).

Another term commonly used is the launch of an aircraft type, which refers to the start of the development program.

The IPTN N-250 you mentioned was never introduced into service. Wikipedia claims the 15 June 1997 as introduction date, but on this day the aircraft was shown at the Paris Air Show:

(image source: airliners.net, taken by Peter Vercruijsse in Paris - Le Bourget on June 15, 1997)

The image description says:

  "Gatotkoco", the prototype N-250 returning from a demonstration flight at the Paris Air Show. The N-250 programme is currently (early 2000) on hold due to a lack of finance.

This does not count as introduction and is therefore a mistake in the Wikipedia article.


How do airplanes maintain separation over large bodies of water?

To expand on DeltaLima's answer:
They use routes called the NATs (North Atlantic Tracks), which can be different each day depending on things like weather and wind speeds. Each track is a set of coordinates. A pilot will do a position report at each coordinate or every 10 degrees of longitude. The aircraft has to get special clearance to fly oceanic about 30 minutes prior to crossing the entry waypoint for the NAT. Each NAT is 60 NM apart.
To clarify a bit more, HF radio is used to communicate, since it has a longer range than VHF, but is much noisier. This is where systems like SELCAL come in, but I won't talk about that here. They can also do position reports over the radio or over text (CPDLC/ACARS), taking advantage of ADS B/C, which I also won't talk about here. These communication systems are pretty complicated, so I recommend you search it on the web or look at the sites I linked below.
Aircraft are required to be 1,000 feet apart vertically. Eastward flying aircraft have odd altitudes such as 37,000, 39,000, 41,000, etc, while westerly flights will be the opposite. They are also required to be about 10 minutes apart from each other.
Gander Radio (notice not "radar"!) controls much of the North Atlantic airspace from Gander, Newfoundland, Canada. Shanwick is another major Radio station. New York controls further south, along with Santa Maria having relatively small airspace.
There is a similar system over the Pacific ocean, with stations in Anchorage, Alaska, and Oakland.
Links:
I highly recommend you read this article about North Atlantic Tracks, and this one too.
You should at least watch this video, it's only 3 minutes, and it's summarized:

More about ADS-B
More about SELCAL
More about position reports
If you want to learn more about ACARS:


After the most recent US instructions, are there any prohibitions against transporting spare lithium ion/metal batteries in the cabin?

Short answer: Yes.
Slightly longer answer: IATA changed the regulations within the 58th Edition of the Dangerous Goods Guidelines, effective January 1st, 2017. For passenger aircraft, lithium batteries are only allowed if they are installed in equipment. Standalone lithium ion cells or batteries are no longer permitted on passenger aircraft.
If you want to air freight lithium batteries: Air transport of Lithium batteries is only allowed if they are charged to 30% or less of their nominal capacity. Also, the cell must comply with the United Nations (UN) Manual of Tests and Criteria, Part III, Sub‐Section 38.3 (see page 394ff in this document) and proper packaging and documentation must be ensured.
The rules in the US and elsewhere differ slightly. From this Energizer document on US air freight:

Batteries must be of a type proven to meet the requirements of each test in the UN Manual of Tests and Criteria.

Batteries must be packed in strong outer packaging and be packaged in a manner to prevent short circuits and separated so that electrically active terminals cannot come into contact with each other.

The gross weight of the shippable container shall not exceed 30 kg. 

For lithium‐ion cell, the equivalent lithium content is not more than 1.5 g; or lithium‐ion battery, the aggregate equivalent lithium content is not more than 8 g.

The shippable container must be capable of passing a 1.2 m. drop test in any orientation without spillage of the contents of the packaging, damage to the batteries inside or shifting of the contents that could lead to short circuit.

The shippable container must be marked to indicate lithium batteries are present and that special procedures should be followed if the package is damaged.


Are there any full-size airplanes flying with a Selig S1223 airfoil?

Based on a quick perusal of the "Incomplete Guide to Airfoil Usage", my initial answer is no.  If you look up any of the big name manufacturers that are present on that list (Schempp-Hirth, Schleicher, Grob, Schweizer were my picks offhand), they use a mixture of Wortmann FX, NACA, and Eppler airfoils.  That said, the truer rationale comes a look at a Cl vs Cd curve, or how the lift and drag of an airfoil change with respect to one another.

I have a representative Cl vs Cd curve below (Cl on the vertical axis and Cd on the horizontal axis), where the purple line is a Selig S1223 airfoil, the yellow is a Wortmann FX 61-163 (used on a number of Schleicher sailplanes), and the green is the Eppler 603 (used on a number of Grob sailplanes).  Obviously, the S1223 produces far more lift than any of the other airfoils, and hits its most efficient point (maximum lift for minimum drag) at a very high lift coefficient -- just a shade over 1!

However, this is not necessarily a good thing.  If we work some numbers, it starts to become apparent.  Using a the definition of lift coefficient, we can estimate the typical lift coefficient () of a Grob 103 in trimmed flight something like this, where  is the density of air,  is the aircraft's wing area, and  is it's flight speed.

For a Grob 103, let's assume that it's flying at maximum gross weight (so maximize the necessary lift), so 5978 N, at sea level the density of air is 1.225 kg/m^3, wing area is 17.9 m^2, and its best L/D speed is 52.5 knots (27 m/s). Plugging all those in, we get a wing lift coefficient of 0.75.  Admittedly, this does not translate exactly into an airfoil lift coefficient, but it suits the need for a comparison.

Looking on the Cl vs Cd chart, this value is below the S1223's minimum drag point, and is actually where the S1223's drag is starting to spike.  However, it does hit right in the lower drag region of the Eppler and the FX quite well.  Furthermore, gliders aren't flying straight and level, which is what this calculation implies, but are, actually, descending (when outside a thermal/ridge lift/etc.), so the actual lift coefficient we need is probably somewhat lower, leading to even higher drag production from the S1223 but falling right into the "sweet spot" of the Eppler and FX airfoils' lift/drag characteristics.

In short, while the S1223 does have amazing lift characteristics (at lower Reynolds numbers -- these trends may not hold to a Reynolds number of 3,000,000, which would be closer to an operating sailplane), it is actually not the right airfoil for a regular sailplane.  For model-scale aircraft, however, it does have application, especially when wingspan is limited.