How do piston engines deal with sea spray (saltwater ingestion)?

Seaplanes operate from coastal saltwater all the time, ingesting lots of seawater, and they don't do anything special to the engines to deal with seawater ingestion.  The effort is mostly on keeping salt rinsed from the airframe and engine externally and they normally get a fresh water rinse at the end of the flying day.  Some operators may spray nicely atomized fresh water into the engine intake while running it to rinse salt from intake passages and carburetors etc, when they are doing the external bits.

The other measure is keeping the protective coatings intact, including the paint on the engine.  You really don't want salt on an engine where paint is flaking off aluminum fins or areas of the head, because corrosion pitting results that leads to cylinder head cracks.

So the main protection measure is, keep the salt rinsed off as much as possible with fresh water, and maintain the protective coatings. Even with all that, coastal aircraft operating daily from seawater year-round often require airframe rebuilds to deal with corrosion maybe every 10 years or so.

In any case there aren't any physical modifications you can do to an engine.


Do helicopters ever dump fuel before landing?

Yes

07-NOV-1971
Sikorsky CH-124A Sea King (S-61B)
Suffered single engine failure on take-off. Pilot attempted to return while also dumping fuel.

From what I've read, fuel-dump systems are more common on military helicopters.
Sometimes, a helicopter may not have enough power to hover in ground effect for a normal landing or take-off because of loss of an engine, high density altitude, or being overweight. The alternative procedure is to perform a running take-off or running landing, which is an advanced, but not an emergency, maneuver.
But if the copter is landing in a confined area, such as a small pad on a frigate in a stormy ocean, there's no room for a running landing, so its better to dump fuel to allow the copter to hover into a landing.


Would fuel quantity indications be affected by extended flight at nonzero bank angles?

I don't know what fuel quantity indicating system is installed on the MH-53, but most aircraft use a capacitive indicating system. Basically, there are multiple probes spaced throughout the fuel tank(s). During a turn or bank, the fuel will accumulate to one side of the tank, which increases the capacitance on the respective probes on that side of the tank. Meanwhile, the capacitance decreases on the probes that aren't covered as much. Total capacitance of all the probes is then summed and processed. Basically, no matter how the aircraft is oriented, in a properly operating system, there should be no detectable change in fuel quantity.


Is there a database containing detailed information about airfields and runways?

The FAA publishes the NASR database. This is an official, authoritative data set that covers all airports, airways, routes and navigation aids under FAA jurisdiction. The data files are not human-readable though and require special software to display.
Other civil aviation authorities in other countries have similar products. Some are available for free, some are not. Many countries claim intellectual property rights on their data and it can be quite difficult to get at/use it.
Some companies like Jeppesen do this collection for you: they have agreements with aviation authorities, obtain each authority's data sets (like the FAA's NASR linked above), and compile all of them into a single large database. This database is then reprocessed in forms usable by avionics like GPS receivers or Flight Management Systems (FMS). These countries charge a significant fee for this service, and there are licensing terms that limit your use of the data. The fee is substantial depending on the format you get the data in (up to thousands of dollars or more for FMS systems for large transport aircraft) and puts the dataset out of reach of a casual user.
The U.S. Department of Defense publishes the DAFIF which is a similar compilation of worldwide data. This database used to be available publicly for free, but is now restricted to Department of Defense personnel (it is not classified but it is not available to the public).
There are many websites based on one or more of the datasets above, but as noted in comments, these websites are not official or authoritative. They also generally have their own license terms that limit the way you can use the information and that prevent you from downloading the database in bulk. This all stems from the intellectual property claims made by many civil aviation authorities. It costs countries a lot of money to maintain the data and they want to be able to generate some revenue from it.
So the bottom line is that for some regions like the United States, official data is readily and freely available; for other regions, not so much. (And among developed countries, the U.S. is the exception; most do not offer their data freely.) To get data for these other regions, or to create a global dataset, would involve a lot of effort and money (beyond the reach of a normal individual). Companies that do this work for you charge hefty fees to provide the data to you.


The difference in headings gives you the number of degrees you need to turn. The distance between the two points then becomes a secant to the turning circle which should give you the turn radius by applying some basic geometry. I assume that the turn starts on point 1 and ends on reaching point 2. Like this:

Now you first need to calculate the turn radius, using the equation for secant length: Start with the difference between the two headings and call that angle $\varphi$. Then the difference between two points $s$ is $$s = 2\cdot r \cdot sin\frac{\varphi}{2}$$
Since you know $s$, you can calculate the turn radius $r$ by a simple transformation: $$r = \frac{s}{2\cdot sin \frac{\varphi}{2}}$$
Now you need to check whether the airplane will be able to turn with that radius. This depends on wing loading $\frac{m}{S}$, density of air $\rho$ and maximum lift coefficient $c_{L_{max}}$, and the equation for the minimum turn radius is $$r_{min} = \frac{2\cdot m}{c_{L_{max}}\cdot S \cdot \rho}$$
Compare both values of $r$ and check if $r > r_{min}$. Then the turn is physically possible.
Now I only hope that this is really what you asked. Your question leaves a lot of room for interpretation.

EDIT: @amarender has updated the question. Now the heading is identical at all intermediate points, and below is one of many possible solutions (blue line):

I indicated with pie segments where the turns are; of course, the one single turn condition has to be interpreted as one turn per intermediate point. The sections between the turns are straight, and all bring the aircraft closer to the destination if the heading at the intermediate points is identical to the heading from target to destination.
When do we have a condition where a solution is not possible? Only if the points are too close together to satisfy the condition of the minimum turning radius. By rotating the coordinate system such that the desired heading at the points is parallel to the x axis, this is easier to show:

The distance between two points in the direction of the desired heading $\Delta x$ must not be smaller than the diameter of the minimum possible circle ($2\cdot r_{min}$) using the equation above. The green line above is for $\Delta x > 2\cdot r_{min}$, and the red line for the boundary condition $\Delta x = 2\cdot r_{min}$. To be precise, the equation above does not put a limit on the maximum load factor $n_{z_{max}}$ - if this needs to be considered, the minimum radius is:
$$r_{min} = \frac{2\cdot \frac{n_{z_{max}}}{\sqrt{n^2_{z_{max}}-1}}}{c_{L_{max}}\cdot \frac{S}{m} \cdot \rho}$$
Things get more complicated when the heading at the points is different from the heading from the source to the destination. Then $\Delta y$ becomes important as well, and when it gets large relatively to $\Delta x$, the straight connection between turns will point away from the target very soon.


How does the position of the center of pressure change with the use of different high lift devices?

When I use a high lift device that just increases the chord length, it moves backwards so that it stays at the same percentage of the length of the chord

Only when the Fowler flap does not change the airfoil's camber, which is rarely the case. Normally, the flap will not only move backwards, but also rotate trailing edge down. A bit only for the take-off setting, but a lot for the landing position. This camber change will move the center of pressure back even if there were no surface increase, and the extension of the wing at the trailing edge will move the center of pressure further back again.

  When I use a high lift device that moves downwards, it has the same affect as increasing the AoA, so the center of pressure moves forward

Again, no. The camber change dominates the position of the center of pressure, and it will move back since the wing now sports more rear loading (more lift is created at the rear end of the airfoil due to local camber increase).


The limits of the $V_{r}$ and $V_{2}$ are determined by the regulations in place. The rotation speed is the speed at which the pilot can the aircraft rotation for take off even when one engine is inoperative.

Consequently, this speed should be more than the minimum control speed with one engine inoperative, $V_{MC}$. The current regulations stipulate that the $V_{r}$ should be at least 1.05 times $V_{MC}$.

The safe climb out speed or takeoff climb speed is the speed which the aircraft should have reached at a given altitude. As per FAA regulations, this height is 35 feet above the takeoff surface.

The climb out speed $V_{2}$ should be at least 20% greater than the stall speed $V_{s}$ and 10% greater than $V_{MC}$.

The FAA regulations prohibit lifting the nose landing gear before reaching $V_{r}$ and retracting it till the aircraft is completely airborne.

All aircrafts undergo these tests during their certification process and these data is used by the pilots. Another thing is that both $V_{r}$ and $V_{2}$ are given in terms of calibrated air speed.


Did Clement Ader make the first flight even before the Wright brothers?

Lots of people flew before the Wright Brothers.  Some of them even survived!
The Wright Brothers are credited as inventors of the airplane not because they flew, but because they were the first to take flight in a vehicle which:

Lifted itself using its own power (which gliders and kites did not)
Was aerodynamically controllable by the pilot (which Ader's aircraft was not)
Remained in sustained flight, rather than taking momentary flight before returning to Earth


What caused the loss of "everything" on Swiftair Flight QY-2939?

Without an accident report to go on, we can't know what caused the situation they had.  In fact, from the two links that were posted, we don't REALLY know exactly what they had.  There is the description "we lost everything" from the radio, but that isn't consistent with the statement that they were able to fly headings.

So what follows is a comment on the possible, rather than a statement of what DID occur.

What I can piece together is that they seem to have lost their pitot-static system.  This would remove the airspeed and altitude from all displays, but would leave heading and attitude unaffected.  It would also allow them to fly an ILS approach, with distance from the runway and the on-glideslope indication giving them a way to approximate altitude on final.

There are comments about them climbing to VMC, which strongly implies that they had attitude instruments available.  Likewise, the comment about flying headings would suggest that they had INS information available, since the INS drives the heading indications in the 737-400.  Yes, they could fly headings off the wet compass, but that wouldn't give them attitude information, which they seem to have had.

I don't think the descriptions are consistent with losing the displays in the aircraft, because losing the EFIS displays in an EFIS 737-400 would mean they'd use the analog standby attitude indicator, but the analog airspeed & altitude indications would likewise be available.

Based on all of this, my best guess is that the "we've lost everything" statement is more a reference to having lost all airspeed and altitude displays (along with some other data, including a fair bit of the FMC data that becomes invalid when the FMC doesn't have wind data to work with).  Was the statement a perfectly precise & exact description of the loss of only (only!) the pitot/static instruments?  Not really, but in the stress of the moment it's entirely understandable that what gets said doesn't exactly match what you mean.

In a case like this, the lack of good airspeed information would be the biggest problem, although with reasonably light winds, GPS/INS groundspeed can be a reasonable proxy for your airspeed, and you're flying known pitch/power settings anyway.  Also working in their favor, they seem to have been pretty light, with only "3 souls on board" according to the radio.  So essentially an empty aircraft with something like 25,000 lbs of fuel.  That weight would work out to a fairly slow approach speed, but being light weight they could add 10 or 20 knots above what they think their IAS is (converting GS to IAS without having the winds at altitude is where the uncertainty comes in) and fly the faster speed.  With a heavy aircraft, being 20 knots over your target approach speed could make for issues getting the aircraft stopped on the runway, but with the lighter aircraft those issues are much easier to deal with.

From the one radio transmission caught on the video, they evidently did have radio altitudes from the EGPWS, which is a fair proxy for the altimeter -- albeit with limitations.  If the captain was flying the aircraft using the HUD, or if the EFIS displays on that aircraft include a flight-path vector display, then it's entirely possible to maintain level flight, even if what altitude that is can only be surmised.  (They might also have something in the cockpit that displayed GPS altitude for them -- depends on exactly what they had & if they took the time to get to it.)

Also of note, both links state that the aircraft flew out 2 hours later, which would be consistent with a blockage of the pitot-static system that was cleared out fairly quickly, and at that point the jet is good to go.

Final comment: I'll reiterate, I'm NOT posting this as any sort of statement that "this is what must have happened there."  We don't have enough data to reach certain conclusions.  I'm only drawing inferences from what limited information we do have in those 2 links, and suggesting that the scenario I laid out seems to be consistent with what is in the article and the video, and thus seems to be the most likely explanation.  If new facts come to light, anything or everything above could be subject to revision.

From everything I can see, it was a nice job by the crew to bring the aircraft safely back on what had to be a pretty bad day at the office!


How does landing performance differ on water vs. ice vs. paved/grass runways?

The takeoff and landing performance on different surfaces varies with condition - for example, a wet or snowy paved runway will have different braking and rolling acceleration performance than a dry paved runway. We can make some general/broad statements, but it's important to note that the specific conditions on any given day will play a large part in aircraft performance.

That said, here are some general/broad statements:

Water (and snow on skis)

Water is the odd surface in the group: It is not a runway in the traditional sense. If you "land" an aircraft with traditional hard-surface landing gear (tires) on water it is not a landing, but rather a ditching and is covered under emergency procedures.

Landing a seaplane (either a "flying boat" hull or something with floats) on water is a different beast from a landing on land, and indeed an entire different rating on your pilot certificate. Everything you ever wanted to know about seaplanes can be found in the FAA Seaplane handbook (FAA-H-8083-23), which also covers aircraft equipped with skis for landing on snow (which is in many ways similar to landing a float-equipped airplane on water).

Pavement (Asphalt, Concrete, etc.)

Paved surfaces are the baseline standard by which "land" landings are judged.  The performance charts and tables in your POH are generally given with the assumption of a dry, paved, level runway that is free of contaminants.

Wet or Contaminated Pavement

Wet, snowy, or icy pavement primarily affects braking performance: An aircraft will not be able to stop as quickly on wet pavement as the tires may hydroplane/skid with aggressive braking. This video gives a good overview of the effects of wet pavement, and while it's primarily aimed at Part 25 Transport-category aircraft/operators the same basic considerations apply for light General Aviation aircraft.
Your aircraft performance charts may discuss operations from contaminated runways, but if they do not cover this situation some rules of thumb for landing performance on wet or contaminated pavement are:

Wet Pavement (no puddles): Multiply landing distance by 1.4
Wet Pavement (w/ puddles): Multiply landing distance by 2.3
Snow on Pavement: Multiply landing distance by 1.6
Icy Pavement: Multiply by 4.5 (expecting braking to be largely ineffective)

Similarly allowances must be made for takeoff performance (additional resistance on the tires from contamination on the runway) - The usual takeoff rules of thumb work here ("Have 70% of your takeoff speed by the time you've used 50% of the runway."), with the caveat that you need to consider braking distances in the event of an abort: Aborting halfway down a 3000 foot runway when you expect to need 1800 feet to brake to a stop would be a Bad Thing.

Grass

Grass is the traditional "soft field" surface, though well-maintained grass with good drainage on a dry day may not be all that "soft" when you land on it.
As with a contaminated runway the major difference is rolling resistance: You will stop a little faster on dry, level grass than you would on an equivalent paved field because the grass offers more resistance to the tires, and you will take longer to accelerate to takeoff speed for the same reason.

Again, your aircraft performance charts may include figures for soft field / grass field takeoffs/landings (this is often given as a percentage of the paved surface figures). If your performance charts don't include soft field / grass field data there are again some rules of thumb you can use:

Short grass: Add 10% to the takeoff roll
Long grass: Add 25% to the takeoff roll
Wet grass (Soft Field): Add 35% to the takeoff roll
Muddy field: Add 50% (or more) to the takeoff roll

Paved surface landing distances work well for grass fields, with the exception of wet grass (which can be treated as a soft-field landing on wet pavement to account for your tires skidding on the wet grass).

Gravel

Though not strictly a subset of grass, considerations for gravel runways are similar: Increased rolling resistance during takeoff (as your tires push the gravel around), and diminished braking effectiveness on landing (in particular extreme braking on gravel can lock a wheel and leave a rut, as it would on a soft grass field).
Soft field takeoff and landing distances would be appropriate to use for gravel runways.

Ice

Ice is an interesting surface: It's hard, but it has a very low coefficient of friction. On clean ice your takeoff distance will be similar to pavement, but your landing distance will be significantly increased since your wheel brakes will be largely ineffective.
As for icy pavement you can plan on a landing distance of 4.5 times your paved runway landing distance (or more), and you will likely be nosewheel steering or differential braking will have reduced effectiveness for directional control (tailwheel pilots will be at a distinct advantage here, as the rudder work they do in a normal takeoff or landing is very similar to what's required to keep the aircraft going straight on ice).

Contaminated ice (standing water, snow, etc.) impose penalties similar to contaminated pavement, with the added caveat that water on ice is an incredibly low-friction surface (to illustrate this drag your finger across an ice cube dry, then do the same with a little bit of water on the surface of the ice cube) -- the increase in landing distance required would be substantial if landing on a wet ice runway.

Unique surfaces

While the list above covers the vast majority of runways you're likely to encounter there are some "unique" surfaces out there (for example perforated steel planking which is sometimes used to construct temporary runways can become a special challenge when it rains as friction on the metal is reduced by water and mud squirting up through the perforations with certain types of underlying soil).
If operating from a "unique" surface the best resource you have is other pilots who routinely operate from that surface, or at least have some experience with it -- they can tell you what to expect under different conditions, and you can plan accordingly.


Why is a Lockheed MC-130J Commando II creating such a loud droning sound?

There are two factors reducing the volume of a sound when travelling through the air:

The pressure wave expands as the surface of a sphere, which will reduce pressure as a function of distance $r$:

$$ p(r) \sim \frac{1}{r^2} $$

Since human hearing is logarithmic, we typically use Decibels (dB) as a unit for volume, rather than pressure directly:

$$ L_p = 20 \log_{10} \left( \frac{p_\text{RMS}}{p_\text{ref}} \right) $$

This means that an aircraft that is twice as far away will (at maximum) have a sound pressure of one quarter left, which corresponds to $ 20 \log_{10}(1/4) \approx -12 \, \mathrm{dB} $. An aircraft at 27,000ft will only be $ 20 \log_{10}(1/27^2) \approx -57 \, \mathrm{dB} $ less loud compared to an aircraft on final approach at 1000ft. For a large and loud turboprop, this is easily enough to hear it, considering the engines can reach up to 140 dB and aircraft on approach are typically up 80 dB loud:

The absorption of sound waves in air is frequency dependent. This physics.stackexchange answer explains the details. The following plot shows the absorption coefficient as a function of frequency for different humidities:

(image from Wikimedia)

Since turboprops are producing more lower frequency sounds with their propellers compared to turbofans, they can be heard further (they also typically fly lower).
This also matches the "droning sound" you describe. The higher frequency noise has been absorbed by the atmosphere.


Definition of "Rotation Speed" vs "Lift Off Speed" vs "Fly Off Speed"

Your original understanding is correct.  Rotation speed and liftoff speed are two different things, the former being the speed you are to make an input, and the latter the speed at which you get a result (weight off wheels).

That's almost certainly a typo and is supposed to say 75kts (my guess), which would be the demonstrated maximum distance to weight-off-wheels with rotation initiated late in the 70-75 kt range. Manuals published as integrated handbooks like that tend to never get revised unless a new edition is published, and the Cougar was only in production for a couple of years making a little over 100 aircraft, so I'd be surprised if there is a newer edition than the 1978 one, especially if it involved publishing a new handbook over a minor typo on an out of production airplane.

On a light aircraft the input and result are just about instantaneous and a rotation initiated at 75kt will result in a liftoff pretty much at 75kt or maybe a knot or two higher.  On high performance aircraft rotation speed and actual liftoff may be 1 or 2 seconds apart and it's more obvious that they are different things.


Do most airport use one and only one runway for landing?

In general, any runway can be used for both takeoffs and landings. However, switching back and forth requires substantial safety margins. If you can use one runway for just takeoffs and another for just landings, efficiency goes up. If those runways are parallel, efficiency goes up again. This is why major airline hubs tend to have pairs of parallel runways.

Averaged over a day, the number of takeoffs and landings should be about the same, so the normal mode would be to split the runways as evenly as you can. If the number of runways isn't even, the last runway will often alternate throughout the day to mitigate short surges in one or the other.

As to which runways are used for what, the ones used for landing should be as far from each other as possible to maximize lateral separation of arriving traffic on instrument approaches. (Departing traffic mostly separates itself.) So, if you had four runways organized as two pairs, you'd expect the "inner" one of each pair to be used for takeoffs and the "outer" one of each pair for landings.

In the case of Heathrow specifically, runway usage is largely dictated by noise abatement agreements with nearby towns, rather than what makes the most sense operationally.


100 octane fuel was the best possible aviation fuel at that time,introduced in April 1940 .By December 1942, production of 100 octane gasoline had risen to 5.5 million gallons/day; by June 1943, it was approaching 10 million gallons/day; and, by VE-Day, May 7,1945, production exceeded 20 million gallons/day. Avgas was introduced near 1970s. And, then it is very difficult to find exact price for that . But, the at that time the price of car fuel and aviation fuel were not very different. So, you can estimate it to be at 10-12 cents/gallon range. One other way to estimate the cost is by using the inflation adjusters, the current price for 100LL is about $5.5 . So, by using this calculator, it would have cost nearly 10 cents/gallon. (In 1940, Dollar and Pound were nearly same in value.) So, the final answer should be about 10 cents/gallon.


Was "the right stuff" ever really the right stuff?

Well, kind of,

The technical portrayal of test pilots in that film received negative reviews with real test pilots.  I know Chuck Yeager did not like his portrayal by Sam Shepherd and director Philip Kaufman, particularly with the NF-104 accident at the end of the film.  While the scene is based on a real accident which Yeager did have, it was part of a scheduled test flight with established test points and not Yeager throwing on a pressure suit and jumping into the cockpit for a joyride with a YOLO type attitude.

Flight test and test pilot work is rigorously planned out, methodically didacted and cogitated, with multiple contingency plans and contingency plans for those if they don’t work.  Long gone are the days where you strapped your little pink fanny into a crate, pushed it off a cliff, and hoped for the best on the way down.  Test pilots and flight test engineers are very bright and methodical people who are intimately familiar with the systems of the aircraft they are flight testing and have spent a great deal of time thinking about all the ways something can go wrong and what they intend to do if they encounter this problem.  Hundreds, if not thousands of hours have been spent in systems and and flight simulation scenarios, not only evaluating these hypotheses, but making detailed plans for their test points they want to evaluate during flight.  Finally the flight testing itself is a slow and methodical affair, slowly and carefully increasing the performance envelope with each flight and thoroughly evaluating and addressing anomalies once encountered before continuing.  As one test pilot once put it, “We try to make flight testing as boring as possible.”

As to being cool, calm, unflappable under pressure, quick thinking and courageous being the defining qualities of 'the right stuff' in a pilot.  I would argue that they ARE useful to a pilot anywhere.  Remember US Airways Flight 1549's Capt Chesley 'Sully' Sullenberger?  That guy was faced with one of the most challenging scenarios out there and was a cool as a refrigerated cucumber throughout.  You may not be exploring and mapping out the absolute edges of an F-35's flight envelope, but those skills can come in handy with any kind of emergency situation which you might face.

Remember there is a difference between these qualities and having hazardous attitudes e.g. anti-authority, machismo, etc.  As Yeager once put it "If you want to grow old as a pilot, you gotta know when to push it and when to back off."  In addition flight test is a considerably different animal than it was back in Yeager's day, thanks in part to Yeager and a few unfortunates who now have a street at Edwards named after them.

Test flying isn't about being taking big risks; its a gradual and methodical process of exploring the flight characteristics of an aircraft and having multiple contingency plans to make it as safe as possible.  In short, good Aeronautical Decision Making really IS 'The Right Stuff'.  Risk takers, the macho guys, or the just plain stupid get weeded out, either by their superiors or by Natural Selection.


How to fly IFR to an airport without any instrument approaches?

Yes.  If the airport in question has no operating control tower you need to cancel your ifr flight plan after landing if you choose to not do it in flight.  Once you land you can cancel with air traffic contol, if you are able to establish radio communication, or cancel with a flight service station.  It is usually going to be easiest to cancel with the local approach controller in flight, if there is no operating tower.  Remember all ifr traffic, landing and departing, will not be able to receive their approach clearance or ifr release until you cancel.


Can I use a rental airplane to conduct air tours?

Beyond the aviation angle of this question there are legal liability and insurance concerns common to any business that ought to be addressed.  Any person renting equipment ostensibly for personal use, but in reality is using it to run a business on the side, ought to have a commercial lease agreement in place with the owner of the equipment.  Have you spoken with the FBO about your plans?

Regarding aviation specifics, these sort of questions have come up before and the CFRs don't offer much in the way of ownership requirements for aircraft involved in commercial operations.  Own vs lease just doesn't seem too critical from an operational standpoint as far as the Feds are concerned.  I won't start another "holding out" discussion here, but you should definitely talk to the FBO about your plans before moving forward with this idea.


What is the difference between fuel exhaustion and starvation?

Fuel exhaustion means there is no more fuel on board the aircraft. Fuel starvation means there is fuel somewhere, but it isn't available to the engine(s) for any one of a number of reasons: pilot error, blocked fuel lines or valves, malfunctioning fuel pumps etc. You can read a study of exhaustion and starvation incidents here.

A "fuel shortage" isn't a formal aviation phrase as far as I know, but "minimum fuel" is a formal phrase with a specific meaning. This is from the FAA's AIM 5-5-15:

  Advise ATC of your minimum fuel status when your fuel supply has reached a state where, upon reaching destination, you cannot accept
  any undue delay.
  Be aware this is not an emergency situation, but merely an advisory that indicates an emergency situation is possible should any undue
  delay occur.
  On initial contact the term “minimum fuel” should be used after stating call sign.

  EXAMPLE− Salt Lake Approach, United 621, “minimum
  fuel.”

This question has some more information.


What is the drag of helicopter rotor at jet speed?

There were actually some experiments with stopped rotor. Furthest with the actual implementation was probably the Boeing X50 Dragonfly:

  By Source, Fair use of copyrighted material in the context of Boeing X-50 Dragonfly

The main reasons I can think of why nothing like this reached production yet are:

When the rotor spins, the blade on one side moves aft and needs to have its leading edge face aft, but when the rotor is stopped, both sides need the leading edge facing forward. So either the airfoil must be symmetric, but that has really poor efficiency, or some blades have to turn somehow, which is complicated.
To be light, rotor blades are normally very flexible and rely on the centrifugal force to keep them straight under load. But when they stop, they won't have such force, so they must be much stiffer, which makes them bit too heavy to spin.
Having separate wings and rotor would add a lot of weight, especially since the rotor would still have to be made strong enough to resist the aerodynamic loads when stopped.


What is the difference between a cold-stream thrust reverser and a conventional one?

Turbofan engines don't push all air through the combustion chamber. Instead part of it runs along the sides.

This bypass region is where the (cold) air stream is redirected from to create the reverse thrust.


What is the difference between a positioning flight and a ferry flight?

A positioning flight is a flight for the sole purpose of positioning the aircraft to conduct another flight from another airport. This is often done when the aircraft finishes its day in one city, but is needed in a different city the following day because another plane has broken down.

A positioning flight is technically a type of ferry flight, however the latter is a more broad term. Examples of ferry flights include delivery from the manufacturer, or flying to a different city for heavy maintenance.

Both flights are generally conducted without fare-paying passengers on board, but sometimes extra airline staff are carried.


Shall We Consider Reversers in performance Calculations?

For airplanes certified under Part 23, both takeoff (AMC 23.55b) and landing (AMC 23.75f) performance can take credit for thrust reverser (T/R) if it's shown to be reliable and safe. As detailed in AC 23-8C, much extra work would be required to take credit for T/R for multi-engine airplanes:

For accelerate-stop distance: demonstration of full T/R with one-engine-inoperative and in a 10kt crosswind and on wet runway for adequate lateral controllability is required.
For landing distance: the landing distance used must be that with one-engine-inoperative; differential braking needed to maintain lateral control for this situation may negate most, if not all, of the advantage of a single T/R.

For airplanes certified under Part 25, only takeoff on wet runway may take credit for thrust reverser (25.109f). Similar situation for landing distance as with Part 23, 25.125c)3) allows credit for T/R, but only for that with one-engine-inoperative; therefore, the same problem as discussed before applies.


Why is airspeed different in climbs and descents although the AoA doesn't change?

You should see the same airspeed for the same AOA and non-accelerated flight with a mild climb or descent.

Except with a Buckeye?

The Buckeye has its thrustline low enough so that at different power settings you have different pitch trim settings. Add power to climb and the thrust pitches the nose up. You now have to trim nose down. Nose down trim means less down force on the tail, which means less lift required by the wing, which means a slower speed for the same AOA.

Conversely, pull power off and the nose wants to drop, leading to nose up trim, more down force on the tail, more lift required by the wing, higher IAS for the same AOA.

I frankly never noticed this effect, and never taught it. Wish I could go back and check it out!


A pressurized fuselage needs rounded corners at all cut-outs to avoid the accumulation of stress in corners. If the corners were not rounded, the fuselage skin would need to be locally reinforced, or it would begin to crack there soon.

This was learned the hard way by de Havilland, when their Comet jet airliner began to plunge out of the sky for unknown reasons. In one of the first major crash investigations in aviation history, the wreck of one was lifted from the seafloor off Elba and re-assembled. Then it was learned that the pressurized cabin had burst from cracks emanating from the window corners.

de Havilland Comet I. Note the square windows. The window which caused the destruction of G-ALYP was on top of the fuselage and cannot be seen in this picture. (Picture source)

Finite element simulation of corner stresses in a Comet fuselage skin.  Red denotes the highest stresses. (Picture source)

Other aircraft companies had built pressurized cockpits twenty years earlier and did it right the first time …


When you request flight following generally you contact the facility (either approach or center) responsible for the airspace you're in, so your real question is "How the heck do I know whose airspace I'm in?!"

The answer can usually be found on the charts, or in other FAA publications.
Let's look at your example (I was over the Pottstown VOR (PTW) heading to Lancaster (KLNS) on the 269 radial.) in detail with some convenient visual aids.

Preflight Planning and the A/FD

You don't tell us what airport you took off from, but I'm going to assume KPTW (Heritage Airport) as a convenient starting point.
If we have a look in the Airport/Facility Directory for KPTW we'll get an answer very quickly from the "Communications" section:

PHILADELPHIA APP/DEP CON 126.85 (800-354-9884)

So if we're planning a flight out of KPTW and intend to pick up flight following our call to ATC should be made to Philadelphia Approach, on 126.85 (and if we're going IFR and need to talk to them on the ground there's a convenient phone number).

If you have an application like Foreflight or Garmin Pilot this information is readily available to you in the cockpit as well, so if you're unsure who to contact you can always pull up the A/FD information for the nearest airport and use that as a starting point.

In-Flight - Using the Charts

Let's say you didn't remember to look in the A/FD to see who you needed to talk to while you were on the ground, and the battery in your iPad is dead so Foreflight is out of the picture in the air. You can pull out your paper charts and get most of the same information in flight.

If we plot PTW ... KLNS it puts you on the very bottom of the New York Sectional Chart, and on the Philadelphia Terminal Area Chart for part of the flight, so let's take a closer look at the route on each of those.

First the New York Sectional:

Not much help here - or at least nothing glaringly obvious.

Let's look at the Philadelphia TAC:

AHA! There are helpful white boxes with blue text on this chart that tell you CTC PHILADELPHIA APP ON and list frequencies, altitudes, and active runways.
This looks promising: Since the little box says to contact Philadelphia Approach that's who you should probably call first.

In your case there happen to be two helpful boxes, one above your route of flight and one below it. Both boxes are roughly equidistant from the route of flight, so it's not obvious which one you should pay attention to.   In cases like this you can call on either frequency (at least you're calling the right facility - they may make you call on a different frequency and talk to another controller, but you're in the right neighborhood at least.

You can also go to the Airport/Facility Directory (A/FD) as a tie-breaker (though you're probably less likely to pull the book out mid-air, and if you did you'd probably use the nearest airport like I described above).

The blue boxes are talking about the Philadelphia Class B airspace, so if we look at the entry for the Class B airport (Philadelphia International - KPHL) we'll get more details on which radio frequencies we should use:

If you're flying along the 269 radial from PTW you're somewhere "northwest of the airport", so you would call Philadelphia Approach on 124.35 / 128.4 if you're above 5,000 feet, or 126.85 (the same frequency we got from the A/FD entry for KPTW)if you're below 5,000 feet.

I'd Like To Phone A Friend

There's one final way to figure out who you should talk to, and that's to call someone else and ask. If you're opening your flight plan with Flight Service over the radio they will usually sign off with "For flight following try Philadelphia Approach on 126.85" and the usual plea for PIREPS, and if they don't offer a frequency you can always ask them.


Who pays for Air Traffic Control services?

FAA Funding is currently a mix of General Fund(taxes everyone pays) and Airway Trust Fund(ticket taxes and fuel taxes) money. The breakdowns are shown in: https://www.faa.gov/about/office_org/headquarters_offices/apl/aatf/media/AATF_Fact_Sheet.pdf


How can ADS-B be secure when it is based on self-reporting?

Yes, one can send deliberately wrong position reports. But why would anyone want to do that? We're assuming malicious intent, of course -- but even so?

Could an attacker cause a collision using fake position broadcasts? It is hard to see how. The core meaning of an ADS-B broadcast is basically, "Dear ATC, please don't clear anyone to fly too near such-and-such point in space, because that's where I am." Getting an unsuspecting other aircraft to avoid a particular point in space where in reality nobody is, will not in itself cause any accident. At most some distraction and swearing and "no sir, I reallly don't see that traffic" transmissions.

An attacker might mount a denial of service attack against the airspace by flooding an air traffic controller's monitor with dummy aircraft, so he can't find any safe way to route the real planes he's talking to. But for that effect it's not really necessary to send any fake position reports -- simply jamming the 1090 MHz downlink frequency would do just as well, and not be significantly more illegal or harder to detect.

You could try to convince ATC that someone else is in a different place than they really are. However, unless you jam the entire frequency, ATC would still be able to hear their real position reports, and their computers would be able to tell that they have several inconsistent reports from the same airframe address. It would be simple to handle that by separating traffic from both reported positions (which they need to be able to anyway, just in case someone accidentally misconfigures their transponder with a wrong address), and then we're back in the DoS scenario.

Could a suicidal attacker go up in an airplane of his own and get to ram into somebody else while faking his position as far as ATC sees it? If that's your goal, it would certainly seem helpful to stop broadcasting yoru true position, but that doesn't mean that broadcasting a false position would buy you anything that you don't also get simply by pulling the plug on your transponder so you don't broadcast anything. In both cases your problem would be that you're now a primary radar echo that doesn't correspond to any transponder reply. Depending on where you pull the trick that may or may not set alarm bells ringing -- but to the extent it does, broadcasting a different position wouldn't do anything to silence them.

One thing you can do is rig your ADS-B Out to transmit a wrong altitude and hope to get clearance to pass directly above or below someone which you might then try to ram without being seen -- because primary radar is generally bad at distinguishing altitudes. However, that is not a risk specific to ADS-B -- good old SSR also depends on airborne transponders to self-report their altitude in Mode C, and that can be tampered with just as easily.


Although it is difficult to say from old photos, the tubes doesn't seem to be visible on the prototype or early Vulcans.

Another Vulcan, XH558 started life as a B2 and are fitted with Olympus 202 engines. Looking at a photo of it there are what appear to be intakes on each engine, as seen here. I don't know what engines the Duxford Vulcan has, but according to Wikipedia the 202 was the definitive version for the Vulcan, with the exception of some aircraft which received the 301. As far as I can tell, one of the features with the 202 was that it had a redesigned oil separator breathing system.

Such features require air inlet as well as an outlet for the vented gases, could this be related to that system?


What is an Air-Filed Flight Plan? Are aircraft capable of filing flight plan when in flight?

It is quite easy in the US but it depends on controller workload.  You need to be in a plane equipped for IFR flight and you need to be IFR current....[edit] to legally use a filed IFR flight plan.
If the controller is too busy they will make you file through a flight service station.  This can also be done in flight but requires you to change frequencies, reach the FSS, wait your turn, and then file.  The FSS puts you in the system.  Then you call ATC back and open your plan [edit] -or- open with the FSS.
If the controller has time, they will file you on frequency.


What does the “nose-high” product of inertia represent?

The $I_{xz}$ moment of inertia is a measure for how the weight is distributed in the xz plane.
You can obtain it by multiplying a unit of mass $dm$ by its distance in $x$ and $z$ from the center of gravity and taking the negative of it.
For discrete masses (blocks of mass) it looks like this:
$$ I_{xz} = \{-(x_1 \cdot z_1) \cdot m_1\} + \{-(x_2 \cdot z_2) \cdot m_2 \} + \{-(x_3 \cdot z_3) \cdot m_3 \} ... $$
If you look at the plane in question, you can see that it has a nose - which we can consider as one of the blocks - which is

Far in front of the c.o.g. (large value of $x$)
High up from the c.o.g. (large value of $z$)

If we plug this in the formula, we see it leads to large values of $I_{xz}$.
Similarly, there is also a lot of mass in the lower-right corner

Far behind the c.o.g. (large  negative value of $x$)
Low below the c.o.g. (large negative value of $z$)

In essence, everything that is on the x-z line contributes to this value, and as we see from the marked area in the image of the Valkyrie, there is a lot of mass around this line.
If your aircraft is symmetrical around the x or z axis (in terms of as much mass above/below front/aft the axis) you will get a low value of $I_{xz}$.
I guess that is the case for many aircraft, so they make the assumption of $I_{xz}=0$.
More information about the rotational moment of inertia can be found here.


Is it necessary to strengthen the airframe of an aircraft that is used for sustained low level flight?

Since the question you're ostensibly asking is "Do you need to strengthen the airframes of aircraft used for sustained low-level flight" let's leave aside the military aircraft in your question and just look at "sustained low-level flight" in general.
But first let's bear in mind two concepts:

The first concept is that all aircraft (indeed, all structures) have a finite fatigue life: through normal use, vibration, operating stresses from takeoffs/landings/maneuvers, etc. an aircraft accumulates a certain amount of fatigue, and at some point that fatigue will lead to failures (bending or cracking) in the aircraft's structures.
Aircraft are engineered to withstand a certain amount of fatigue (the "fatigue life" of the airframe) based on a number of factors, and when the fatigue life limit is reached the airframe is either retired (scrapped) or rebuilt/reinforced to extend the fatigue life.

The second concept is something in fluid dynamics called a boundary layer - the region of a fluid in contact with (and most influenced by) some surface.
For purposes of flight we can consider air (the atmosphere) to be a fluid in contact with the Earth's surface. This means down close to the Earth's surface there's a boundary layer with associated meteorological phenomena.
The first article in this NOAA piece talks about some of them, but for purposes of this discussion let's just reduce it to "It's really bumpy and gusty in the boundary layer. Once you climb above the boundary layer the air is smoother."

Bearing these two concepts in mind, an aircraft that spends most of its time operating down load (near the surface of the Earth) is also spending most of its time inside the boundary layer, where it gets bounced around and shaken up more by the turbulence in the boundary layer, and thus accumulates fatigue at an accelerated rate.
Because of this aircraft that spend a lot of time in the boundary layer are usually "overbuilt" to handle a greater degree of fatigue/stress, or have reduced service/fatigue life limits to ensure the aircraft is inspected and repaired/retired before fatigue can lead to a failure.

The accelerated fatigue from spending a lot of time in the boundary layer can also be dealt with by inspections rather than engineering changes. Piper Service Bulletin 886 highlights a particularly dramatic case:

  On March 30, 1987, a PA-28 engaged in pipeline patrol operations suffered an in-flight wing separation resulting in a fatal accident. Investigation revealed the wing failure was due to propagation of a fatigue crack, which originated in the wing lower main spar cap.

Piper then goes on to describe "Normal" and "Severe" usage of the PA-28 family of aircraft, broadly speaking Normal is flying "normally" (Take off, climb to an altitude generally above the boundary layer, fly to your destination, and land), while Severe usage involves spending a lot of time in the boundary layer ("below 1000 feet AGL"). They then recommend inspection intervals based on the type of usage the aircraft is seeing (around 60,000 hours for "normal" usage, and roughly half that for "severe" usage due to the accelerated fatigue accumulation).

TL ; DR

Most aircraft that spend most of their time at low altitudes (close to the ground) are "overbuilt" structurally because there is more turbulence down low, so they accumulate fatigue at an accelerated rate.
Plenty of "normal" aircraft also spend a lot of their life at low altitudes, and this is usually handled by inspecting them for signs of fatigue damage more frequently than their higher-altitude counterparts.


Why wasn't MH-17 flying at 33,000ft before it entered Ukrainian airspace?

This is normal.

A 777 on the AMS-KUL route cannot climb to FL330 right after takeoff - this would only be possible maybe 3-5 hours into the flight.

Airliners fly as high as the available thrust (and ATC) allows, because the thinner air allows to fly at a higher lift coefficient and less drag overall. The limit is given by the combination of available thrust and the actual mass of the aircraft, and it will climb higher during a trip as fuel is burnt off. The maximum range is possible at one particular lift coefficient, and to maintain this during a long trip means to increase altitude, so the lower density compensates the lower aircraft mass. Engine thrust is normally sized during design such that this optimum altitude can just be reached in normal operation.

On eastbound routes in controlled airspace, pilots are encouraged to fly at odd thousands of feet (depending on the local rules), so the climb will not be continuous, but stepwise. See this answer for more on separation rules.

For a rather lengthy answer with more background on the theory how to pick the ideal flight condition for maximum range, see this link.


Why is TO/GA button disabled in 777 with weight on wheels or below 2 ft RA?

Boeing's officially stated reason in the report is:

  ... to prevent pilots from inadvertently activating TO/GA mode at or after touchdown. Inadvertent activation of TO/GA could result, among other things, in the aircraft departing[1] the runway. ...

[1] As in runway overrun/excursion.

Which is in accordance with AC120-29A (also from the report), where:

  ... If an automatic go-around mode can be engaged at or after touchdown, it should be shown to be safe. The ability to initiate an automatic or flight director go-around at or after touchdown is not required or appropriate. ...

It's either Boeing did not want to, or could not, demonstrate it would be safe, hence the inhibition (nor is it a required system). Boeing does not elaborate on the "among other things".

Some remarks on the 777's TO/GA switch:

Applying full power on a go-around on a 777 after consuming most of the trip fuel is tricky because of how powerful the engines are. It would produce a big nose up.

For this reason, pressing TO/GA – unlike most planes – does not command full power, rather enough power for a 2,000 ft/min climb. Pressing TO/GA again, would command the full power (source: FCOM 6.4 Page 51).

So there's logic involved.

The closest Boeing patent I found was the Total energy based flight control system published in 1984, which does exactly that, among other things. A system for commanding elevator and/or thrust based on the plane's current and commanded energies for a target flight path. (Download the PDF for the logic diagram.)

For that to work, the plane needs to know its current flight path. If the wheels touch, and with the drag of the ground friction, which is unaccounted for in the logic, the system can't function as designed, or additional logic will need to be added and certified.

Note: The same inhibition, climb target logic, and a double-push for THR REF is also on the 747-400 (source: FCOM 4.10.17). The patent's date makes it plausible that the 747-400 was of the first to receive this system, and it was carried over to the 777.


What is the "optimal" age of a fighter pilot?

I can't directly tell you what's "optimal" because I don't know what that means, but the US Air Force does provide some basic demographic information so we can indirectly see what they consider to be a good age mix for fighter pilots. I used their report tool to get data on fighter pilots1 and it shows this breakdown:

17-24 :    43
25-34 : 1,341
35-44 :   968
45+   :    83
Total : 2,435

This isn't very fine-grained, but on the other hand we can immediately see that your example of someone over 50 is really at the extreme end of the curve: only 3.4% of fighter pilots are over 45.

Of course, this only applies to the USAF and it doesn't tell us anything about other branches of the military or about what other countries do. But we can say that the USAF appears to consider 25-34 to be the 'optimal' age: 55% of their fighter pilots are in that bracket.

(I should add a small disclaimer that I know nothing about the military, so hopefully I didn't make any stupid mistakes in pulling or interpreting the data.)

1 To be specific, the search criteria I used were: Active Duty Air Force only (excludes Air National Guard, Air Force Reserve and civilians); officers only; AFSC 11FX specialty (fighter pilot) only. The data is from April 2015.


Look up the airport at http://www.airnav.com/airports

It'll show info such as:

Airport Operational Statistics

Aircraft based on the field:        66

Single engine airplanes:        65

Multi engine airplanes:     1

Aircraft oper  ations:  avg 70/day *

52%     transient general aviation

48%     local general aviation

for 12-month period ending 07 April 2015


Could drag in a turn be twice the drag of that encountered in straight and level flight?

Could drag in a turn be twice the drag in straight and level flight?

Yes, but this will be a rater steep turn.

…  in a coordinated turn with the same angle of attack at the same airspeed …

No, this is impossible. Either angle of attack or speed have to be higher so the higher lift required for turning can be generated.

… angle of attack is the same, the lift to drag ratio is the same. In this scenario the load factor is 2

And in order to create twice the lift of straight flight, the speed has to be higher by a factor of √2. In this case, L/D is indeed the same, but speed is higher so twice the dynamic pressure is available for creating the required lift. Since both lift and drag are proportional to dynamic pressure, creating twice the lift at the same L/D means that also drag will double.
In order to turn with a load factor of 2g, the bank angle has to be 60°. That is rather steep.


How do the shockwaves (supersonic and hypersonic) interact with the structure?

Aircraft with Flying wing configuration, such as the B2 bomber, fly at high subsonic speeds. During such a case, the airflow is at a high subsonic speed at the leading edge, and accerelates through to supersonic speeds as it moves over the front - upper portion of the wing surface. As the wing profile (chord wise) changes to converge towards the trailing edge, the airflow attempts to decelerate from supersonic to subsonic speeds. However, this transition is only possible through a chordwise oblique shock wave. Now, this oblique shocks profile will look like the blue line in your diagram above, but will be sitting at some near-mid chord position.
If the flying wing body is increases speed towards sonic velocity of the air, then this chord wise transition shock wave will become stronger and move just in front of the body leading edge. Finally, once the body is moving at supersonic speeds, the transition shock will become a bow shock in front of the leading edge. In addition to this, there will also be two termination shock waves sitting at the leading edge, one for the upper surface airflow and the other for the lower.
The angle of the shock wave profile will be greatest at low supersonic speeds, but beyond the bow stick sitting in front of the leading edge will narrow in angle and so will its spanwise angle. At hypersonic speeds, the distance between the front shock and leading edge will reduce, leading to immense heat energy being impinged onto the body.
Hope this helps


Why is the FDR and CVR put into water again after a water crash?

This is actually a fairly standard thing to do with electronics that have been submerged: They are placed in water (ideally fresh, clean water) to both delay the onset of corrosion and dilute any salts or other chemicals that they came in contact with while submerged.

When you remove electronics from water and let them dry out they begin to form corrosion on all the little exposed bits of metal - chip legs, solder joints, capacitors, etc. - which can badly damage the device when it is powered back on.
Keeping the device submerged in water delays the onset of this corrosion because the dissolved oxygen in the water is lower than the oxygen in the air that would be hitting those parts as they dry out.

The Cockpit Voice Recorder and Flight Data Recorder are water resistant, but they are not necessarily waterproof (particularly after a crash, which may puncture their casings or damage seals), so they get placed in a container of fresh water for their trip to the NTSB's lab.
When the still-immersed equipment arrives at the NTSB laboratory it can be examined and dried in a controlled environment, maximizing the chance to recover data.

  For more gory details check out The NTSB Flight Data Recorder Handbook for Aviation Accident Investigations.

Bonus Factoid: Archaeological recoveries from bodies of water use similar procedures, for similar reasons: If you bring up a clay pot that's been sitting at the bottom of a lake for a thousand years and let it air-dry naturally there's a good chance it will crack and be destroyed.
In archaeological recoveries the usual practice is to keep the item "waterlogged, ideally in waters associated with the original context" (i.e. "in a bucket of water from where you got the thing").


How fixed air, gas and fixed weights in rigid airships is computed in this book?

$D$ is the total displacement (the weight of the air displaced by the airship)
$0.288 \cdot D$ is the weight of helium and air inside the air ship
$0.055 \cdot D$ is the weight of crew, storage, and ballast
$x \cdot D$ is the unknown weight of power plants, power cars, and the fuel system
$0.3 \cdot D$ is anything else (fixed weights)

The total must be one:
$$.288 + .055 + .3 + x = 1$$
or equivalent, the total must be the displacement:
$$D \cdot (.288 + .055 + .3 + x) = 1 \cdot D$$
solve for x and you get:
$$x \cdot D = (1 - .288 - .055 - .3) \cdot D$$
or just
$$x = 1 - .288 - .055 - .3 = .357$$


Are there risks if the side joystick must be handled with a pilot's weaker hand?

I can't speak for all pilots everywhere, but I've flown both sticks and yokes from both the right and left seat (as well as the front and the back seat in tandem aircraft) and found the adjustment process between switching from right to left hand to be very quick. I found getting used to sight picture differences to be a much bigger challenge and, like many others before me, sideloaded my first few landings (along with climbing/descending during turns) until I got the hang of it.

Other pilots I've spoken to about this have expressed the same feelings; there is a learning curve, but it is by no means insurmountable. At any rate, flying is far more of a mental activity, with masterful physical coordination being surprsingly far down the list of innate qualities a pilot needs.

And no, I am not nearly ambidextrous; in fact, my coordination abilities with my non-dominant hand are hilariously poor, as anyone who's ever watched my try to toss a tennis ball during a serve can attest.


How to ignore faulty instrument readings in glass cockpits?

Like in a steam gauge cockpit, you can put adhesive INOP stickers on parts of the glass panel. Stickers for the Garmin G1000 are available commercially, and I had to use them extensively for my instrument rating.

Keep in mind, though, that glass cockpit aviation systems will detect a faulty sensor automatically, and the faulty instrument will just appear X-ed out (like the picture on the INOP sticker) instead of showing wrong values.

But even multiple sensor source cross checks doesn't keep you safe from misinterpretation. See Birgenair 301 accident for example.


Is optimal landing flare related to ground effect?

It depends on the type of landing.  If you are doing a normal landing on a normal runway, the round-out and flare are required steps to put you in a position to be in level-ish flight just above the runway (the roundout), and controlling the touchdown by trading inertial energy for increased lift by pitching as you feel for the surface (the flare).

Ground effect has an effect on the flare phase by giving you more energy margin if the ground effect is strong.  So a low wing airplane with large flaps with a strong ground effect will have a lot more support from ground effect than a high wing airplane with small flaps that has weaker support from ground effect.  If ground effect wasn't there, it wouldn't really change how you land too much, except you may tend to carry power into the landing more, or arrive with a bit more energy by increasing the approach speed a bit.  In some airplanes the ground effect is much more pronounced than others (they like to float).

There are landings where you don't really flare at all.  In an extreme STOL approach, you fly to the surface already in the landing attitude, controlling descent rate with power and maybe little pitch adjustments only as required for speed corrections.  If the engine quits during such an approach close to the ground you are out of energy, already "flared" and will land hard and you live with that risk if you're doing that sort of thing.

And of course, there is no flare in aircraft carrier landings.  You fly a constant descent into the ocean, and the carrier's deck just gets in the way of your descent.


How does early rotation increase the likelihood of a tail strike at take off?

When preparing for a flight, pilots will calculate many things, including their rotation speed. This is the speed in their takeoff roll at which they will start to pitch up, and hopefully the plane lifts off the ground. The rotation speed is dependent on many things such as temperature, altitude, and aircraft weight.

My answer here discusses the lift calculations in relation to rotation. That question covered the importance of speed related to weight. More speed is needed to create the lift to take off with a higher weight.

When the airplane rotates, it increases the angle of attack of the wing, which increases the lift coefficient (if the wing does not stall). The pilots will pitch up at a certain rate, and they do not stop until they reach a climbout attitude higher than what is possible when the main gear is still on the ground (though this may depend on company policy). They count on the plane acheiving enough lift during rotation to leave the ground so that they pass that maximum pitch while in the air.

If pilots underestimate their weight, they will calculate a lower speed than is necessary to provide the lift for takeoff. This means that when they rotate, the plane doesn't have enough airspeed yet to create enough lift to take off. So instead of leaving the ground before fully pitching up, the tail strikes the runway.

It may seem like an easy mistake to make, but thousands of pilots do it every day without a problem.


Are conditional line-up clearances still valid if the referenced traffic initiates a go-around / missed approach?

This may sound obvious, but you should probably ask ATC.

In the sentence given it specifies that you should line up behind the Landing B757, not the Going Around B757. This sounds pedantic, but the situation has changed.

The chances are the ATC is still expecting you to be the next aircraft on the tarmac, but if you're in any doubt whatsoever, do not put your aircraft on a live runway (or anywhere else you can reasonably expect another aircraft to want to be in the next 5 minutes) without explicit, unambiguous permission.


What is the ICAO equivalent of a "point out"?

We have an aircraft that is transitioning through someone else's airspace that we want to talk to we do a "point out".

Basically you want to grab the attention of the other controller wrt a particular plane that they are controlling (or unaware of), in ICAO 4444 lingo that's a General Point message:

  11.4.2.5.19 GENERAL POINT MESSAGES The General Point message shall be transmitted to draw the attention of the controller receiving the message to a flight to support voice coordination. The General Point message shall include details of a flight that may have been previously unknown to the receiving unit, to permit it to be displayed if required. This may include, for example, a flight that had planned to operate in airspace under the control of one ATS unit requesting climb or diversion into airspace controlled by another ATS unit which has no details of the flight.


Does air traffic control identify a distress situation when an aircraft flies triangles in the sky?

To my surprise, this does exist, at least in the UK. According to the Manual of Air Traffic Services:

  7 Emergency Triangle Procedure

  7.1 Pilots lost or uncertain of position and experiencing either transmitter or complete radio failure are advised, as a last resort, to carry out special procedures to indicate to controllers that they
  require assistance.

  7.2 The aircraft fly at least two triangular patterns, before resuming course, as follows:

  Table 1:

  7.3 If a triangular pattern is observed, controllers shall advise the D&D cell of the position and track and continue to plot the aircraft
  whilst it is within ATS surveillance system cover. Controllers should
  also be aware of the effect wind may have on the pilot’s ability to
  fly an accurate triangle.

I say "to my surprise" because there are well-established procedures for comms failure under IFR and under VFR. But having said that, it's possible that the triangle procedure is more useful in the UK (for example) than the US, where there are usually plenty of uncontrolled airports around and many pilots have no need to talk to ATC anyway. In the UK, with a much smaller airspace, fewer airports and more ATC control (at least, that's my understanding), it may be more critical to give even VFR aircraft a "last resort" to contact ATC.


Why can't you have sail-powered airplanes?

High performance sailboats can sail faster than wind speed in certain conditions. Therefore, your question is not as absurd as it might seem at first glance.
However, the technique that enables sailboats to do so is not available to airplanes, at least not in flight. Sailboats use the speed difference between water and wind. Their keel keeps them from being blown with the wind. A glider in the air has no such second medium to resist being blown away by the wind.
Historically, the Andrée ballon used for artic exploration in 1897 tried to "sail" by combining sails and trailing ropes. However, this did not work in practice.
The only way to extract energy from the wind is when this wind changes. Wind gradients allow albatrosses to soar dynamically, and changing updrafts can be exploited by changing the load factor.


Is the US certification process for airliners shorter or longer than in other countries?

Certification is just one part in the design process. Things like design or manufacturing issues can also cause significant delays on a program. Although much of the design is driven by certification requirements, it can be hard to determine whether the delay is due to regulations or just issues with designing for them. Estimating the cost attributed just to certification would be even more difficult.

Also, while the regulator of the country of design certainly is the primary concern, an aircraft must also be certified in any other countries where the type will be operated. An aircraft designed by Airbus, for example, will certainly be primarily certified by EASA. But to operate in the US, the FAA must also certify it. While the authorities do have agreements between them so that the entire process is not duplicated, there are differences in requirements and philosophies between the agencies. So if the FAA has some regulations that tend to cause the process to take a long time, it doesn't mean that Airbus is immune to those issues.

When a manufacturer applies for a type certificate (new or amended), they are also establishing a regulatory baseline. The new type must conform to all current regulations as of that date, unless they are able to negotiate something different with the regulator. This application is only valid for a limited time before the manufacturer must renegotiate.

14 CFR §21.17 (c)

  An application for type certification of a transport category aircraft is effective for 5 years and an application for any other type certificate is effective for 3 years...

While this is not a hard limit, manufacturers would rather avoid having to go back to the table with regulators years into their design process to extend their application and possibly have to step up to more strict regulations, especially for a new type.

Most recent Type Certificates from EASA list the application date and issue date. If the primary regulator is not EASA or JAA (predecessor to EASA), they list dates for that regulator as well.

If we look at recent designs, we can see that most new aircraft took about 5 years to certify, which would seem to indicate that there is no clear time advantage between regulators. This includes the A330, A340, A350, A380, 777, 787, CRJ, E145, and E170. For all aircraft not primarily certified by EASA/JAA, there was either only a minor difference in the time taken for each regulator, or EASA/JAA took a bit less time.

Amended types vary greatly, from much less than 5 years (A330-200, 777-300) to 5 years (747-8) or more (777-200LR). It is difficult to tell whether a longer process means a more complex product or a more involved certification process. EASA/JAA seems to always certify aircraft at the same time or after the primary regulator, but this is probably not due to the EASA/JAA process taking more time.

You mentioned Dassault as well. Although the business jet regulations and market are different from airliners, there seems to be a similar trend of about 5 years for new jets (Falcon 7X, Gulfstream VI, Bombardier Global Express, Embraer Legacy 500), and less for variants.


I had imagined simply mounting your lift and drag sensors on a simple (HO gauge model railroad) track for a DIY homebuilt wind tunnel.

Pitching moments for your wing could be done as a separate experiment.  Your could pivot on your aerodynamic center (as an axle) and measure pitching torque moments with the load cell attached to the end of the fuselage.  Once these moments are established, you can then design the H stab based on area and distance from your wing.  Ideally, the H stab will keep your pitching moments zero through all angles of attack (including stall), leaving pitch control to the pilot (with the elevator).

Similar study can be done with you center of pressure (center of all lifts), once you establish it in your planform design.


When replying to ATC, callsign first or last?

ICAO Annex 10 - Aeronautical Telecommunications Vol 2

When replying, you end the message with the call sign.

  5.2.1.9.2.2 PANS.— An aircraft station should
  acknowledge receipt of important air traffic control messages
  or parts thereof by reading them back and terminating the
  readback by its radio call sign.

  Note 1.— Air traffic control clearances, instructions and
  information requiring readback are specified in PANS-ATM
  (Doc 4444).

Exception to rule:

  5.2.4.4.1 PANS.— When an aeronautical station initiates
  a call by SELCAL, the aircraft replies with its radio call sign,
  followed by the phrase “GO AHEAD”.

However, local procedures should be followed if they are different. See the post, 'Is it bad practice to say my callsign first in a transmission to ATC?' for an answer about UK and Germany. Basically when replying you finish with the c/s, when requesting you begin with the c/s.


Do airliners stall first at the wing tip?

They are designed to not stall at the tips first. Such a stall behavior would be highly problematic because it causes a pitch-up moment which exacerbates the stall. See the answers to this question how nasty stalls with swept wings can become.

FAR 25.203 describes the required stall characteristics:

  (a) It must be possible to produce and to correct roll and yaw by
  unreversed use of the aileron and rudder controls, up to the time the
  airplane is stalled. No abnormal nose-up pitching may occur. The
  longitudinal control force must be positive up to and throughout the
  stall. In addition, it must be possible to promptly prevent stalling
  and to recover from a stall by normal use of the controls.

Such a behavior is easiest to achieve when separation does not start at the wing tip. Earlier swept wing designs sometimes had trouble to achieve docile stall characteristics which led to the introduction of stick shakers. Today, changing the airfoil shape over span (aerodynamic washout) and wing twist (geometric washout) are combined to ensure that stall starts at the wing root.

Regarding washout: With high-lift devices employed, the low deflection angle of the ailerons on the outer wing results in a strong effective washout. Here it is important to extend the slats over the outer wing to enable it to function well above the local angle of attack. The picture of an A300-600 below should illustrate the point.

A300-600 in landing configuration (picture source)

But even in clean configuration some washout remains and allows the outer
wing to fly at a lower lift coefficient which ensures a decent stall margin. A photo of an airliner wing on the ground might be misleading: The lift forces in flight will twist the swept-back wing such that washout is increased.


What is the theoretical maximum RPM of a typical aircraft piston engine?

The size and weight of the pistons is going to be a major hurdle. With a 5.25 in bore and a 4.25 inch stroke, the pistons are massive and don't change directions very easily—there's only so many Gs you can put a shape this large through at the top and bottom of each stroke before the metal starts deforming. Bounce an open umbrella up and down really fast, and you'll start to get the picture.

Cooling would also be a major factor for non-aviation use. Aircraft engines (more or less rightly) assume that there's going to be a large fan out front and/or 100+ mph of airflow. Liquid cooling would allow the heads to maintain a more constant temperature, but would also add weight and complexity.

If you want a faster-revving flat six that will put out more than 100hp and is suitable for automotive use, I might suggest pulling an engine out of a Honda Goldwing or Valkyrie. Given the edited description, though, I'm guessing you're thinking of a drag racer.


Which approach category minimums should I use when conducting an instrument approach?

According to the FAA Safety Alert for Operators issued on 09/20/2012 (SAFO 12005):

A pilot may never use the approach minimums specified for an approach category lower than their certified approach category, even if the actual approach is flown at a speed that would be in the lower approach category.
A pilot must always use the approach minimums specified for an approach category higher than their certified approach category if the actual approach will be flown at a speed that would be in the higher approach category.

Note that this is different in other areas of the world (Canada for example uses the actual approach speed of the aircraft to determine the approach category).


Where do the names "First", "Business" and "Economy" class originate from?

They used to use those ordinal class names (first, second, third), borrowed originally from train and ocean liner class designations. British railway classes were first, second and third classes, while ocean liners typically had first, second and steerage (which itself became a derogatory term that was changed to "third class", especially as steerage evolved from a converted section of cargo space to purpose-built passenger accomodations).

The change to the modern airline classes is an example of the euphemism cycle, and occurred through the 1960s and 1970s as travel in general increased dramatically while the average income of the travelers nose-dived. In the U.S., the primary driver was the stigma of people in those sections being called "second class" or "third class" as "political correctness" started becoming a big thing with the civil rights disputes. This led to a rebranding of lower numbered classes by airlines; second class, being a popular choice for frequent flyers on corporate business seeking a compromise between the low cost of the economy section and the amenities of first class, was renamed "business class", while the main passenger cabin holding the bulk of passengers with the lowest-cost tickets (average Joes going on vacation, visiting family or just needing to get somewhere on a short travel schedule) was called "coach", "economy" or simply "standard". All of these terms have survived at least informally, but "economy" is the one most often used by the airlines to denote this service level.


Is a Compass Swing Platform part of a runway or taxiway?

It could be on a taxiway, but it can also be outside the movement area (e.g. on the apron or ramp in the US). As far as I know, it is never on the runway.

There is a compass rose on a taxiway at Petaluma Municipal Airport (O69). You can see it on the following image (from Google Maps). It is painted in front of the hold short line of runway 11.

Most airports will however have a dedicated position for the compass rose. This image (taken from this question) shows an example at Ramona Airport (KRNM):

It is not part of the taxiway as indicated by the yellow line, which separates the non-movement area from the movement area.


What is the Hot Air Pressure Regulating valve and what's its purpose?

The valve regulates the pressure of hot air from the engine bleed system that bypasses the airconditioning packs. This hot air is then fed to the trim air valves to adjust cabin temperature.


Why can't you ditch your aircraft in the sea?

The writer was dramatizing things a bit maybe, it's possible to ditch a jet fighter and survive, however your chances are much better ejecting.

Ditching is an option for any aircraft, with some airplanes ditching is the only option if there's a loss of power over water, for example commercial jets have no mode of egress other than the doors. I fly light single engine aircraft and the majority of the time I have no parachute, if my engine throws a rod over a big body of water that's where I'm going to go, and even if I had a chute I'd probably elect to ditch anyway. It's survivable, and many cases people do. The "Miracle on the Hudson" is a famous example, they even made a movie about it, but there are many others where a reasonable percentage of people on board survived.

You are proposing a low speed ditching in a fighter airplane, which has a number of drawbacks:

Ditching speed: You can't stop an aircraft by raising the nose higher because at some point you will stall the wings, and they will lose lift. A wing requires smooth airflow to create lift, if the airflow separates from the top surface of the wing it will stop flying, a condition known as a wing stall. In a jet that speed will likely be in excess of 130 knots (150 mph), and there's nothing you can do to slow it further than that. At that speed water cannot get out of the way fast enough and is very, very hard, not some sort of pillow which will cushion an impact
Slow speed controllability: Fighter jets are designed for high speed maneuverability, not low speed flight, fly too slow and you can lose directional stability and control
Loss of hydraulics: most fighters have assisted controls which require engine power for the pilot to operate easily, lose power and they lose effectiveness even with auxiliary power being generated
Unknown sea conditions: Sea conditions can have an enormous impact on ditching survivability, the successful ditchings I can think of were in relatively calm conditions where the pilot was able to make a good, even contact with the water. Dig a wing in and the drag will swing the airplane around, most likely breaking it up. It's very hard to gauge sea conditions from any sort of altitude; what looks calm from 5,000ft up could very well be heavy swells once you're close

So what you are suggesting is that a pilot skims the surface of possibly high seas, bleeding off speed in an airplane with progressively degraded control authority - which is also on fire. It's possible, but highly unlikely to work.

The most critical reason the pilot in the tale you linked to had to escape the aircraft was that a fire in the engine would melt the linkages for the rudder and elevator controls in the tail, or cause a catastrophic structural failure long before he could have ditched, causing a total loss of control. There's no chance that would have been survivable.


Should I do bachelor first or pilot training first?

If you have ready access to university, do the degree first. You won't have time later, and if you get a pilot job in future and lose your medical for whatever reason, you will have an education to fall back on.  In any case, the aviation industry is going to take a number of years to recover from this whole "plague" fiasco, so you shouldn't be in any hurry to get a pilot license.  Thousands of pilots are on furlough and will likely continue to be for quite a while.
Long term, the future is bright, but get a degree first.


Is it possible to estimate the location of aerodynamic center without experimental moment data?

The pressure distribution $c_p$ on an airfoil is necessary to determine the aerodynamic center of an airfoil. From the pressure distribution you can obtain all three coefficients $c_l,c_d,c_m$ (well, for accurate $c_d$ you better have a rake for high $L/D$ airfoils). Having only the first two, as in your case, is not enough. Simply because there are many $c_p$ distributions that will give the same $c_l$, $c_d$ forces and different $c_m$ forces. These airfoils will also have a different aerodynamic center. Thus, the answer is no. If you don't have means of measuring the moment, couldn't you just vary the mounting position of the airfoil to estimate moments and do your job?

However, in case you want only a rough (experimental) $c_m$ estimate you can relate your airfoil basic characteristics ($c_l,c_d$, zero lift angle, camber and thickness distributions etc.) to similar airfoils found in this classic reference and interpolate.


Do lights on wingtips change color at different times of the day?

Every plane has green and white lights on the right (starboard) wing, as in this photo, and red and white on the left (port) wing. These lights are called "navigation lights," and are the same as are used in boating.

The green and red lights are always on, no matter what, and are used to help other aircraft know which direction the aircraft is going, based on whether the other pilot sees red, green or both lights.

The white lights are also on all the time, and flash constantly. These lights are called "anti-collision lights."

(Image Source: Wikipedia)

What you are actually seeing is the green light constantly on, and the white flashing - but because the white is so much brighter and is flashing, it's more apparent than the green (which, especially in the day, is fairly dim)

At night, the green becomes more obvious and the flashing white becomes more visible. The flashing white over-powers the green, which gives an optical illusion that the Green is flashing. The reality is that the Green is always on, and the white is flashing.


Could a controller or airport in the US decide to use English-style landing clearances?

The use of FAA's anticipated separation rule is theoretically optional, and there are indeed times when controllers don't use it. While not common, now and then one hears "continue approach" (or similar) instead of an early landing clearance, as is normal under ICAO rules. Ditto for the occasional canceled clearance.

However, anticipated separation exists for a reason, and a trainee who was unwilling or unable to use it when appropriate would not pass. OTOH, they also have to know when it's not appropriate and not use it at those times.


What are those markings on runway 25L at Frankfurt Airport?

Zooming in further makes it look like vehicle tracks, like someone was going back and forth over the runway at 15-meter intervals. Looking further down the runway, it looks as though it is made up of 15-meter wide concrete plates (in lack of a better name). Perhaps the tracks are a sign of some maintenance of the mortar between these plates?
It's possible to have been WIP (work in progress) for the removal of the unique experimental approach system Frankfurt Airport tested. In which they had two separate touchdown zones, with the one farthest down labelled 26L, thereby allowing two glide-slopes—one higher than the other—to reduce the wake turbulence separation for parallel runway operations. That system is no longer in use (obsolete AIP link).
If not, then the runway closure in the second frame would indeed confirm some sort of intermediate maintenance until the runway could be closed for a proper overhaul.

HALS / DTOP was the experimental special landing procedure at Frankfurt Airport (tested from 1999 to 2004) with the aim of increasing the landing capacity on the existing runways.
HALS is no longer in use and all approach procedures are suspended, as this operational method failed to prove itself in practice. At the end of 2008 or beginning of 2009, all the navigation, corresponding markings, and firing systems to runway 26L were removed.
The acronyms HALS / DTOP stand for High Approach Landing System and Dual Threshold Operation.
— de.wikipedia via Google Translate [edited]

Special thanks to J. Hougaard and mins, they basically answered the question.


What is the difference between a volume-limited-payload and a maximum-zero-fuel-weight-limited-payload?

The Maximum Zero Fuel Weight Payload, is the amount of payload $m_{pl}$ (i.e.: passengers, cargo, but not fuel) required to reach the  Maximum Zero Fuel Weight condition while keeping the fuel weight, $m_{fuel}$ to zeros so:

$$
while \; m_{fuel} =0: \\
MZFW = OEW + m_{pl} \\
$$

The Maximum Zero Fuel Weight ($MZFW$) is an indicator of the maximum loads that the wing structure can bear. For the wing an "unloaded" situation (no fuel in the wing) is critical, since the fuel stored in the wing helps reducing the loads on it in flight. The lift acts "upward" while fuel weight acts "downward", thus the fuel contribution helps relieving loads from the wing structure.

The volume limited payload is an indicator for the sizing of the cargo compartment structures. These are the structures of the cargo area, where the LD containers are stored (under the floor of the passenger cabin). This Volume Limited Payload is set to avoid having too "dense" LD containers, the limit of density for the containers is around 350 $kg/m^3$, you can find some technical specifications for LD container here.


Where can I find Boeing 777 safety records?

The Boeing 777 has an excellent reputation when it comes to safety.

Just under 1500 have been built which have accumulated more than five million flights and 20 million flight hours.
Only 6 aircraft have been lost in a accident, which is a really low number considering the number of aircraft and flights.

Moreover, of those hull losses, at least one (MH17) was due to a criminal act which cannot be attributed to the safety of this specific aircraft type.

Of the other 5 hull losses:

One cause is unknown (MH370).
One (MS667) was caused by fire while the aircraft was at the gate. No fatalities.
Three crashes were during landing.

Of the three crashes during landing:

One (BA038) is caused by ice in the fuel system which clogged a filter. The filter has been redesigned and can no longer cause a problem. The accident did injure 47 people, there were no fatalities.
One (OZ214) was caused by the pilots committing a number of minor and major errors during the approach to the airport. It can hardly be attributed to the aircraft type. The crash resulted in only 3 fatalities, which is remarkable considering the violence of the crash and amount of damage to the aircraft.
The last accident (EK521) caused no fatalities among the passengers but the cause of the accident is still under investigation. So far, the  Investigation  is  working  to determine  and analyze  the  human  performance  factors  that  influenced  flight  crew  actions  during  the  landing and attempted  go-around. The investigation has revealed no  Aircraft systems  or  engine  abnormalities  up  to  the  time  of the  Accident.

Combined you can see that the aircraft has performed an enormous number of flights with very few severe accidents and very few fatalities.

It is considered as one of the safest aircraft around.


What does it cost to get a hot air balloon to 30,000ft?

A Hot Air Balloon should be able to reach 30,000 ft just fine as according to Wikipedia the world record altitude for Hot Air Balloons is 69,852 ft.  Besides the necessary survival gear for the occupants (Pressurized oxygen and environment suits) a special propane tank would be needed as according to wikipedia:

  However, if the liquid propane in the fuel tanks is too cold (0 °C/32 °F or less) it does not generate sufficient vapor pressure to adequately feed the burner(s). This can be overcome by charging the fuel tanks with inert gas such as nitrogen or by warming them, with electric heat tapes for example, and insulating them against the cold.

Another thing to consider is that you would need special permission from the FAA to go into Class A airspace which goes from 18,000 to 60,000 feet MSL. Usually only IFR rated aircraft can fly in this airspace.  The FAA may require you to fly with a radio and/or transponder if you do get the permission to fly in this airspace.

I do not know how much propane would be required as I don't fly Hot Air Ballons but it would probably depend on the outside air temperature (less fuel in colder air).


Why does the use of reverse thrust in flight on the DC-8 cause areas of separated/reversed airflow over the wing?

That's not surprising at all.  What the pictures of the tufts show, and exactly what I would expect to see, is a massive injection of turbulent reverser air into the upwash just ahead of the LE, disrupting everything behind it, and which would include a significant component of flow over the top of the wing.  The tufts show some straight and some pointing forward, which suggests a layer of very turbulent air with random eddies.  Like this:


Are helicopter searchlights fixed or movable?

The question is some what unclear, but helicopters usually have some combination of 3 types of lights.

Landing light(s); fixed, sometimes pulsing, used for illuminating the area directly in front of and below the helicopter for landing.

Anti-collision light; fixed red and green and a strobe on the tail and sometimes the belly.

Search lights; directable, usually only used on military or para-public helicopters that fly at night. [SAR, Police, etc...]


Is the TIS-B traffic filter on board or on the ground?

TIS-B is part of the ADS-B system that will be required in class B and C airspace come 2020. The processing of traffic relevant to your aircraft is done on the ground to keep the airwaves "clean" as it would require transmission of much more data to show all aircraft and then have your local device filter it. In order for you to take advantage of your own "hockey puck", you first need to have installed in your aircraft the appropriate avionics, namely a GPS with WAAS and an ADS-B out or Mode S transponder. Your transponder will broadcast your location and altitude, then the ground station will process which traffic is relevant to you without the 3D boundaries of the "hockey puck" surrounding your aircraft, then it will broadcast that response out to the air. The key is that not only your aircraft can pick up the response - any aircraft with an operable ADS-B In system can read it and thus display traffic/give traffic alerts even if you don't have an ADS-B out. The key though is that without an ADS-B out the traffic information is not customized for you so critical information/traffic may be missing (what is transmitted is might not be in YOUR hockey puck).

Note: It is also possible for you to pick up signals directly from other ADS-B out equipped aircraft in your proximity without an ADS-B ground station to relay that information and they will display directly on your ADS-B in equipped system.


Do stratospheric business and military jets use the North Atlantic Tracks?

The tropopause is in the low to mid 30s in the mid-north latitudes that the NATs reside (and is in the 20s in the arctic in winter) so an airliner crossing on a NAT at 55 DegN at FL370 will be well into in the stratosphere.

Concorde didn't use the NATs simply because the NATs top out at FL410.  And in any case, the NATs are a large band of parallel tracks several hundred miles wide which are mostly just shifted more northerly or more southerly to accommodate weather patterns and the locations of polar jets etc.  The routings aren't really customized much more than that.

Anyway, because they top out at 410, if your jet can cruise above 410, like a Global or Gulfsteam, you can avoid the NATs and can pretty much file for whatever custom routing suits you that doesn't conflict with someone else.


Is "takeoff distance" measured over the ground, or to a point in the air?

Takeoff distance is always measured as horizontal distance.
Under 14 CFR Part 23, which apply to aircraft seating 19 passengers or less and a maximum takeoff weight of 19,000 lb or less, the pre-Amdt 64 specifications are:

For multi-engine jets of 6,000 lb or more, or commuter aircraft, 23.59 applies. Takeoff distance is measured as the horizontal distance between start of ground roll to where the aircraft attains 35 ft off the ground.

For others, 23.53 applies. Takeoff distance is measured as the horizontal distance between start of ground roll to where the aircraft attains 50 ft off the ground.

Note that a lot more nuance is involved since the greater of one-engine-inoperative distance and that with 115 percent of all-engine-operating distance goes into the actual performance number.
For Part 25 aircraft (transport category), there is a further distinction between dry and wet runway (25.113):

On a dry runway, it is measured to 35 ft.

On a wet runway, it is measured to 15 ft.

This information is harmonized with other regulatory agencies, such as EASA and TCCA.


Can I use cellular data to receive in-flight weather on my iPad?

Can you? Yes, but service might be slow or spotty.

May you do so legally? That probably depends. The FAA doesn't specifically prohibit the use of any electronics in GA aircraft; they only state that under 14 CFR §91.21, those aboard an IFR aircraft can't operate electronic devices unless they are

  Portable voice recorders;
  Hearing aids;
  Heart pacemakers;
  Electric shavers; or
  Any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used. [emphasis mine]

It's possibly questionable that you as the pilot are an authority on whether or not your devices will cause interference.

The FCC, however, has banned the use of cellular phones in flight per 47 CFR §22.925:

  Cellular telephones installed in or carried aboard airplanes, balloons or any other type of aircraft must not be operated while such aircraft are airborne (not touching the ground). When any aircraft leaves the ground, all cellular telephones on board that aircraft must be turned off.

Whether or not that can be interpreted to apply to an iPad's 3G connection is pretty iffy.


B-52s that are not in service demolished?

No, some B-52H's in long term storage at the Aerospace Maintenance and Regeneration Group are in Type 1000 storage, which means,

  Aircraft stored in near-flyaway condition. Can be stored without re-preservation for a period of 4 years. Aircraft stored under this category may be downgraded to Type 2000.

Note: This screengrab is from Google Maps and I'm not sure when it was taken.

The USAF is under the process of reclaiming a B-52H from the Boneyard as a replacement.

Source: foxtrotalpha.jalopnik.com

However, all the B-52G models have been destroyed in compliance with the New START treaty.