What are the pilot responsibilities for "maintain visual separation" clearances?

Visual separation is addressed specifically in the AIM (see below).  It is an ATC instruction sometimes given when the pilot reports another aircraft in sight.   ATC is then able to instruct the pilot to "maintain visual separation" from the other aircraft, and it doesn't matter if they are IFR or VFR.

Then it becomes quite simple:

Don't hit the other airplane!

Do whatever you have to do in order to avoid them.  (Usually this is nothing since you just get closer than ATC is allowed to let you otherwise.)
If you are on a specific ATC clearance, then notify ATC immediately if you have to do something contrary to that clearance.

Keep the other aircraft in sight.

Immediately report to ATC if you lose sight of them.

Avoid the wake turbulence of the other aircraft.

Standard radar separation no longer applies since the pilot has accepted separation responsibility from the one specific aircraft that the clearance applies to.  This allows ATC to let aircraft fly more efficient routes (not having to turn to avoid the other aircraft) and also lets more aircraft land in a given amount of time because they can be closer together on final.

Pilots have to use good judgement as to how close they get to the other aircraft, but it is done visually.  They can use any tools at their disposal to help (TCAS, asking ATC how far away they are, etc.) but it all comes down to "that looks good enough for me".

  Section 5. Pilot/Controller Roles and Responsibilities

  5-5-12. Visual Separation

  a. Pilot.

  1. Acceptance of instructions to follow another aircraft or to provide visual separation from it is an acknowledgment that the pilot
  will maneuver the aircraft as necessary to avoid the other aircraft or
  to maintain in‐trail separation. Pilots are responsible to maintain
  visual separation until flight paths (altitudes and/or courses)
  diverge.

  2. If instructed by ATC to follow another aircraft or to provide visual separation from it, promptly notify the controller if you lose
  sight of that aircraft, are unable to maintain continued visual
  contact with it, or cannot accept the responsibility for your own
  separation for any reason.

  3. The pilot also accepts responsibility for wake turbulence separation under these conditions.

  b. Controller. Applies visual separation only:

  1. Within the terminal area when a controller has both aircraft in sight or by instructing a pilot who sees the other aircraft to
  maintain visual separation from it.

  2. Pilots are responsible to maintain visual separation until flight paths (altitudes and/or courses) diverge.

  3. Within en route airspace when aircraft are on opposite courses and one pilot reports having seen the other aircraft and that the
  aircraft have passed each other.

More info is here:

  4-4-14. Visual Separation

  a. Visual separation is a means employed by ATC to separate aircraft in terminal areas and en route airspace in the NAS. There are
  two methods employed to effect this separation:

  1. The tower controller sees the aircraft involved and issues instructions, as necessary, to ensure that the aircraft avoid each
  other.

  2. A pilot sees the other aircraft involved and upon instructions from the controller provides separation by maneuvering the aircraft to
  avoid it. When pilots accept responsibility to maintain visual
  separation, they must maintain constant visual surveillance and not
  pass the other aircraft until it is no longer a factor.

  NOTE-   Traffic is no longer a factor when during approach phase the other aircraft is in the landing phase of flight or executes a
  missed approach; and during departure or en route, when the other
  aircraft turns away or is on a diverging course.

  b. A pilot's acceptance of instructions to follow another aircraft or provide visual separation from it is an acknowledgment that the
  pilot will maneuver the aircraft as necessary to avoid the other
  aircraft or to maintain in-trail separation. In operations conducted
  behind heavy jet aircraft, it is also an acknowledgment that the pilot
  accepts the responsibility for wake turbulence separation.

  NOTE-   When a pilot has been told to follow another aircraft or to provide visual separation from it, the pilot should promptly notify
  the controller if visual contact with the other aircraft is lost or
  cannot be maintained or if the pilot cannot accept the responsibility
  for the separation for any reason.

  c. Scanning the sky for other aircraft is a key factor in collision avoidance. Pilots and copilots (or the right seat passenger)
  should continuously scan to cover all areas of the sky visible from
  the cockpit. Pilots must develop an effective scanning technique which
  maximizes one's visual capabilities. Spotting a potential collision
  threat increases directly as more time is spent looking outside the
  aircraft. One must use timesharing techniques to effectively scan the
  surrounding airspace while monitoring instruments as well.

  d. Since the eye can focus only on a narrow viewing area, effective scanning is accomplished with a series of short, regularly
  spaced eye movements that bring successive areas of the sky into the
  central visual field. Each movement should not exceed ten degrees, and
  each area should be observed for at least one second to enable
  collision detection. Although many pilots seem to prefer the method of
  horizontal back-and-forth scanning every pilot should develop a
  scanning pattern that is not only comfortable but assures optimum
  effectiveness. Pilots should remember, however, that they have a
  regulatory responsibility (14 CFR Section 91.113(a)) to see and avoid
  other aircraft when weather conditions permit.

For even more information, there is an entire section of the Air Traffic Control job aid which the controllers use about visual separation.


What happens to Ryanair aircraft after they leave the airline?

Most of Ryanair's fleets is sold upon delivery and leased back from lessors. The lessors will then lease the aircraft out to another airline for as long as its safe for the aircraft to be flying.

An example for MSN 29921 would be:

EI-CSF    24. May 2000    Ryanair
C-FTCX    28. Mar 2008    CanJet
OK-TSJ    05. May 2015    Travel Service
C-FTCX    05. Nov 2015    CanJet
C-FTCX    04. Dec 2015    Air Transat
SP-ENO    30. May 2016    Enter Air

(planespotters.net)


What aircraft fly faster than 250 knots indicated airspeed under 10,000 feet for safety reasons?

A 747 taking off at or near max gross weight will have a flaps up, minimum safe airspeed and climbout airspeed speed greater than 250 knots. In such cases you didn't notify ATC as they expected it.

I tried to find what the exact numbers would be at 840,000 lbs, but I seem to have thrown out that manual. I did, however, find a reference for a 747-200 with JT9D-7Q engines that gives the flaps up holding speed at 800,000 lbs as 259 kts at 5,000 feet.

Also, I do remember being on an arrival once, with the weight low enough that we could safely maintain well below 250, but that when we saw we were icing badly, we speeded up to somewhere around 300 to get the ram air temp above freezing. In that case we notified ATC that we were doing so.

Also, ATC occasionally requests max speed. For example, on Hajj flights into and out of Jakarta Halim airport in the late 1990s it was common practice for controllers to put you down low to get you under the traffic into Cengkareng airport. They would then often request max speed.


Why evacuate wing at the front side after water landing?

When I worked as a flight attendant back in the 80's we were told that water landings frequently resulted in very damaged trailing edges to the wings.  Flaps and spoilers will most likely have been deployed prior to landing and the velocity of the water impacting these extended surfaces would tear them up badly, along with the hinges and fairings that support them.  To avoid serious injury to passengers from ragged sheet metal, we were to direct them off the leading edge of the wing.

This wouldn't be a problem with an evacuation on land so in that case we would direct them off the trailing edge.  The upper wing surface makes a good slide and a more natural and controlled drop to the ground.

Edit:  I forgot to mention that additionally, water landings mean passengers would be wearing life vests and life rafts would be deployed.  Jagged sheet metal would make short work of these inflated devices as well.


How do a helicopter's cyclic and collective transfer commands to the swash plate?

The mixer is mainly found in larger helicopters where their expense is not such a large part of the purchase price. This answer explains more of the function of the flight control mixer: it de-couples degrees of freedom from the control inputs.

The helicopter in OP picture shows unmixed inputs into the swash plate: tilt swashplate forward for longitudinal control, sideways for lateral control, pedals connected to tail rotor only. Picture below is from Principles of Helicopter Aerodynamics by Leishman, and shows a schematic of the cyclic longitudinal

Three actuators are connected to the Non-Rotating Plate, which can be tilted and lifted. The Rotating Plate follows the fixed plate, and cyclically pitches the rotor blades so that they adjust their circular path up/down. The swash plate arrangement is quite complicated, as shown in the photo below, from the same book.

The mechanical linkage from the cyclic and collective sticks to the main rotor actuators does have some input summation involved, as the picture below shows (from this source, which indeed calls it a mixer).

There are always three swashplate actuators. The collective stick always deflects all three simultaneously so that the swashplate lifts, while cyclic stick movement deflects one or two in such a way that the swashplate tilts.


Is there a minimal approach speed for airliners during rush hour?

ATC can not only ask for a minimum speed, but rather instruct each aircraft to (more or less) exactly fly at a particular speed. This is essential for maintaining separation. As J. Hougaard pointed out in the comments, the speed on the last 4 NM is always up to the pilot to slow down to final approach speed.

It is the duty of the pilot to evaluate if it is safe to comply with this restriction. In case the aircraft cannot fly as slow as asked for, the pilot can simply reply UNABLE and ATC will either try to make it work or instruct the aircraft to go around.

Some airports also publish speed restrictions on the approach charts. This is an example of a minimum speed from the ILS approach into 01L/R at Stockholm-Arlanda (ESSA):

More precise speed restrictions are for example given on the STAR charts of the (now closed) Istanbul-Atatürk airport (LTBA):


In aircraft construction, what is the difference between a firewall and a bulkhead?

A bulkhead is any kind of structural panel separating two spaces in a fuselage.  Like a solid panel in the tail cone that has only small holes for cables to pass, or the panel that forms the end of the baggage area.  Pretty much any solid lateral partition with a structural use. On a large aircraft, any structural partitions separating parts of the cabin, like the flight deck bulkhead, or terminating the pressure hull at each end, the "pressure bulkheads".

A firewall is a firebreak.  It's a bulkhead that is fireproof to separate a "hot" area like an engine compartment from adjacent structure, so that if you have an engine fire, you'll have more time to try to land, or if at high altitude, say your prayers.  To be a firewall, the material of the bulkhead has to be flame resistant, with a much higher melting point than aluminum.

On GA airplanes, the firewall is usually stainless steel, but can be galvanized steel (antiques and homebuilts), or even special flame proof coatings on a normal bulkhead (some composite homebuilts).  On transport airplanes, a firewall will be stainless or titanium.

So in a nutshell, a bulkhead is a structural lateral panel in a fuselage.  A firewall is a "fireproof" bulkhead normally separating the engine compartment (or other flame source) from the rest of the plane.


co-pilot incapacitation: land alone or with a passenger-pilot?

There are risks either case. There are no hard rules for or against calling a pilot from the cabin for help; it is up to the pilot to evaluate the situation and select the best course of action.

The risk of landing solo is greatly increased workload, which increases the chances of human error. There are quite a few things to attend to when flying an airliner (compared to a small aircraft). It gets worse when you're in busy airspace.

The risk of asking someone to help is the uncertainly of whether this person will do more harm than good. There would be differences in flight experience and operation procedures. However, Crew Resource Management and handling ATC radio applies to pretty much all types of flying.

Historically there had been examples of either choice, and they both turned out fine.


Can an airline schedule two same-number flights to leave the same airport on the same day?

Short Answer:
Flight 634 LAS-PHL at 0645 was most likely "US Air 634" on those dates, while flight 634 LAS-PIT at 2257 was most likely "America West 634" on those dates.  Even if both were to have flown with the ATC callsign "Cactus 634," that wouldn't be a problem for ATC since they were separated in time by several hours. (No more an issue than N12345 flying KABC to KABC more than once in a day.) But most likely, they flew with separate callsigns too, as explained below.
Why is this the likely answer?
The LAS-PHL flights in the OP were flown by aircraft whose registrations end in "AU" such as N628AU for example. The airfleets website shows that this aircraft was a US Air (later, US Airways) jet until it was re-registered in December 2006 (the dates on that site are DD-MM-YYYY format). Generalizing from that example, these jets were legacy (pre-merger) US Airways jets.
The LAS-PIT flights in the OP were flown by aircraft with registrations ending in "AW" such as N810AW. Airfleets shows that this was an America West jet until it became a US Airways jet in October 2006.  Again generalizing from this example, the "AW" jets were "American West" aircraft at the time of the OP's data.
So at the time, the one flight was being flown by jets in US Airway livery, and the other by jets in America West livery.  And to the passengers, they almost certainly were sold under the respective brands, so one could buy a ticket for "US Air flight 634" from LAS to PHL in the morning, or a ticket on "America West flight 634" from LAS to PIT in the evening. You'd have to use two separate websites to do so, but there would be no confusion.
Okay, so the remaining question:
Why do they both have the "US" (presumably meaning US Air) uniquecarrier ID in the table?
As described in this paper from Embry Riddle Aeronautical University,

America West Airlines acquired the bankrupt US Airways on September 27, 2005
to form the US Airways Group.

The two airlines became fully one in 2007, when a single operating certificate covered them both.  During the interim,

Both of the merged airlines retained their names and continued operating until September 25, 2007, when America West's FAA certificate was merged into US Airways.
(source)

This interim period is when the flights shown in the OP occurred.  At this point, the airlines were in the process of merging their operations, although their website weren't merged until May 2006.  Thus, in the January/February timeframe posted, the tickets for each would be sold separately.
The wikipedia article notes that the callsigns remained separate until 2008, as "US Air" and "Cactus"; after October 2008, the entire operation used "Cactus".
While it's hard to retrace each step along the way from two separate carriers to one unified carrier, it's clear that various steps are involved, so it seems probable that whatever data source gives the uniquecarrier identifier in the table, either switched over separate identifiers before the dates of these flights, or else it was retroactively changed over to make them all "US" even though at the time some would have been "AW".
In the general case...
So, is it possible, to have two flights with the same number at the same airport at the same day? Yes, although the data shown above probably doesn't indicate that LAS saw a "US Air 634" twice a day during the timeframe shown.  But as long as the first flight and the second don't overlap in time, there is no ATC constraint that prohibits is.  (Military aircraft do this all the time... Cool06 can fly from KDLF to KDLF on a training mission multiple times during the day -- Laughlin AFB in this case.) It's possible, but sufficiently unwise because of the potential to create confusion, that it probably happens for an airline somewhere between very rarely, and never.
As a matter of avoiding confusion, an airline would probably work to avoid scheduling their flight 123 more than once in a day:

"I'm here for my flight 123."
"Sorry, but YOUR flight 123 isn't for another 10 hours; this is the other flight 123 today."

But, if flight 123 is scheduled to depart at 2300 and one day it runs over an hour late, the next calendar day will have two "Flight 123" operations, and nothing will break.
All that to say, what the data in the OP most probably shows, is an artifact of how US Air operated during the transition from two airlines into one, and may not really be particularly indicative of anything more widespread, nor generalizable, than that.


Are there examples (current or historical) of commercial aircraft seating arrangments beyond the standard today?

Some of the old flying boats had a seemingly haphazard arrangement

Source

Source

Source

But maybe all flying boat passengers were effectively first class?


If I have a VOR receiver and a GPS, which should I use to navigate VOR airways?

will the GPS get me closer to the centerline, or the VOR receiver?

GPS is usually more precise than VOR. Even when selective availability was used this was true, and that program hasn't been in effect since 2000.
The GPS will also have approximately the same error along the entire airway. The VOR's error will increase with distance from the VOR station.
That said, IMHO there's a difference between "which is more precise" and "which one should I use". Airspace features such as airways increase the chances of a collision by concentrating air traffic. An airway isn't as bad as an intersection or airport, of course, and flying appropriate altitudes for your direction of flight mitigates this risk even more. But I would tend to want to avoid being right on the centerline.
Many GPS receivers (and other RNAV devices) allow you to offset your course, so you can fly the airway that way, with a randomly selected offset that remains within the airway†. Or just use the VOR, and let its natural lack of precision help you to avoid being smack where all the other air traffic that's flying exactly on the centerline is.
† Strictly speaking, one should request the deviation from ATC, to avoid running afoul of FAR 91.181, which requires flying the centerline…it is unlikely they would object, but if they do, then you will find out the safe way


What are the differences between PNL and PNR messages?

PNR is a passenger's/party's record.

PNL is the full list of all the PNR's.

Example:

7 01SMITH/JOHN...

John Smith is a party of 1, that's the PNR entry. And he is number 7 on the PNL.


Do I have to prove my flight training time abroad when applying for a standalone FAA license?

You can find the detailed requirements for a FAA PPL in Part 61 Subpart E.

The total time of 40 hours can be met by any flight time you have logged, either DUAL or PIC.  (In theory, SIC should qualify too, but I can't think of any legal way for a student pilot to have that.)

DUAL time can only be logged when you are receiving "training" from a CFI, who must endorse each such log entry along with a description of said training (maneuvers, procedures, etc.) in the remarks.  This endorsement is what allows those hours to count toward the 20 hours of "flight training" required for your PPL.

The "solo" time of 10 hours can only be met by flight time where you are the only person in the plane, meaning that it can only be logged as PIC time. PIC time does not need to be endorsed--ever.

Where I think you're getting hung up is that a student pilot cannot legally act as PIC without getting an endorsement before the flight, and those endorsements have limitations.  For instance, my first endorsement only allowed me to fly around the pattern at my home airport, the second allowed me to fly between my home airport and a neighboring airport, and the third was for a specific cross-country trip that I'd previously flown with my CFI.  However, the resulting PIC time was not endorsed by my CFI after those dozen or so flights.

In your specific (and unusual) case, you were able to legally meet the solo time and cross-country time requirements without an endorsement before those flights.  Still, like me, you don't need any endorsements after the flights.  Just logging the PIC time yourself was enough for it to count.

Your records and history will undoubtedly look strange to your CFI (and eventually your DPE), so it's best that you make it easy for them to see which specific log entries you're using to meet each requirement.  I'd suggest marking those entries with sticky flags, noting which FAR(s) they fulfill, and including a translation of the remarks if they're not in English.  Don't note or translate your entire logbook, though; they don't care about anything beyond seeing that you've met the minimum requirements.  And, while it shouldn't matter according to a literal reading of the regs, common sense suggests a preference for time logged in US aircraft (N reg) at US airports (Kxxx).

Finally, FAR 61.103(j) says that any applicant for a US PPL must "Hold a U.S. student pilot certificate, sport pilot certificate, or recreational pilot certificate." There's nothing in the regs that says a validated foreign PPL qualifies, so you'll need to discuss with your local FSDO; if they say it does, it's best to get that in writing so there's no paperwork problems with the DPE on the day of your checkride.


What is the benefit of having baro-VNAV in addition to a WAAS GPS?

LPV and non-baro LNAV/VNAV requires that a Space-Based Augmentation System (SBAS) be available to the GPS receiver.  In the United States, that system is called Wide Area Augmentation System (WAAS).  Similar services operate in other parts of the world (e.g. EGNOS in Europe, MSAS over Japan, GAGAN over India) but coverage is not worldwide, and not all GNSS (Global Navigation Satellite System) approaches are approved for LPV.

Having a baro-VNAV system in the aircraft allows you to shoot LNAV/VNAV approaches if SBAS is not available. While not as useful in the United States, as we have robust and reliable coverage with WAAS, it is nice to have in parts of the world where SBAS is unreliable or non-existent.

FAA fact sheet on RNAV (GPS) approaches: http://goo.gl/cIhIJa

Worldwide SBAS information: http://goo.gl/eooOau


How should a glider pilot signal turns to the towplane?

The glider flying handbook is wrong. The glider signals to the tow pilot by moving to the outside of the turn.

We glider pilots have been trying toget the FAA to fix this and many other errors in the GFH for years. See the newsgroup rec.aviation.soaring

Also, many tow pilots ignore tow steering directions because they think they know better than the glider pilot where the lift is.


I answer directly to the title of the question:

  What is the average time and distance needed to reach cruising height?

The Takeoff takes very little time, but the climb phase depends on the cruise flight level clearance. Assuming you climb with a vario of 2000ft/min with an average IAS of 200kts. The time to reach the cruise level is equal to:

(Cruise level in ft - takeoff terrain elevation if ft)/2000, the result is in minutes.

So if the departure is at sea level and the cruise altitude is at 30000ft, the climb phase will take : 30000/2000=15min

The descent till arrival could be more complicated because in addition to the pure descent you have to level before intercepting the approach phase which occurs relatively at lower speed. If you are lucky, not having to hold above the airport, the total descent might take 20 to 30 minutes

Routes are not necessarily straight lines, nevertheless you may assume an average cruise True speed of 500 knots.


Why would Air France fly to Algeria when it had a civil war?

A civil war yes, but it still had a government and this was supported by France.
A flag carrier like Air France does not really have all that much leeway in terms of what they can do and it was probably in the nation's interest to show support to the legal government. Since they had asked, the answer was probably yes they had to fly(but no politician worth his salt would be on record as stating that! Without an airlink to the outside world a lot of things would come to a halt. I would imagine a lot of people who were trying to assist in finding a conclusion (mediators) would be users of the flight. There would also be a steady stream of people leaving the country and AF may be one of the few options available.
Most airlines treat flights into danger-area differently and where unions are strong having volunteers to operate the flight may be an acceptable solution to both the airline and the union.


How to calculate on ground aircraft yaw rate knowing the longitudinal speed and inferred yaw angle

Do I have enough information to calculate it?

No.

Yaw rate is $rad/s$. You have an angle, $rad$ (or degrees), and you have a linear speed, in $m/s$.

You cannot obtain a $rad/s$ value from these two data points.

You need the time interval over which the change in yaw has been observed.


What is the meaning of GPS IAP RNP that appears in Notes?

The AC covering RNP APCH can be found here. Under RNP APCH Operations it lists:

6.3 RNP En Route, RNP Terminal, and RNP APCH Operations:

The pilot is not required to monitor ground-based NAVAIDs used in position updating unless specified by the Airplane Flight Manual
(AFM).

The pilot must comply with published and assigned altitudes, and airspeeds.

Note: Pilots operating aircraft with a barometric vertical navigation
(baro-VNAV) system must ensure compliance with all altitude
constraints as published in the procedure by reference to the
barometric altimeter.

The full qualifications can be found in APPENDIX A. QUALIFICATION CRITERIA FOR REQUIRED NAVIGATION
PERFORMANCE APPROACH (RNP APCH) OPERATIONS (not copied for brevity)
The landing minimums in the parentheses are non civilian minimums and generally for use by the military although the chart reference strictly says " All weather minimums in parentheses not applicable to Cilil Pilots. Military pilots refer to appropriate regulations" so there may be other qualifiers (Im not a military pilot and cant comment beyond this)

(source)


What is this "No Hand Hold" thing in the P-51 Mustang cockpit?

It is part of the gyroscopic gun sight:

Source: WarRelics Forum

It is not a "hand hold" because you don't want to damage the sight by grabbing the scope to situate yourself in the cockpit (getting in/out) or otherwise pulling on it. Since it is aligned to your guns, you would want to avoid misaligning it.


What are the differences between hand and hold luggage screening?

As ratchet freak pointed out you do have some more flexibility in ensuring that a small cellphone-sized explosive device is positioned to cause maximum damage if it's in your carry-on baggage as opposed to if it's in checked baggage/cargo. As such there is an inherently higher risk here.

Counterbalancing that risk is the fact that we already have good screening tools to detect explosives or other anomalous things (like say knives or tear gas) concealed in what purports to be an electronic device:

Electronic devices are subject to X-Ray inspection.
Trained operators can spot quite a few anomalies using these "classic" tools (though rechargeable batteries can often look like explosives).
Explosive Trace Detection machines are already a part of security screening.
There are also swab machines which operate on a similar principle. They are not foolproof (they have false positive results occasionally, and may miss well-packed explosives), but they're a good tool.
Airport security has already asks to see suspect devices power on.
I had an old Compaq laptop with a completely useless battery, and security would let me plug it in if the battery was dead.

These same techniques (and others) are available for use on checked baggage.
Checked baggage may also be opened for inspection, which could conceivably include powering on any electronic devices in checked baggage (but note that the TSA recommends you not pack your electronics in checked baggage).

It's worth pointing out that, at least from a technical standpoint, faking a "power-on" is trivial with today's technology. Unless they're making folks do a full functional demonstration of the device in question a motivated individual with malicious intent would have no problem making a device that's mostly filled with explosives but can still "power on" and display a home screen, which makes the additional security benefit here dubious, at least in my estimation.


Definition of aircraft longitudinal axis?

Aircraft designers use many different axis frames, depending on what is the most convenient under the circumstances.
In the context of the question, I need to mention only two of them, or rather even - two classes of them: body axes and wind axes.
The body frame is tied, well, to the body. It is rigidly fixed to the body and moves with it. By convention, the X axis points "forward", to the nose.
The wind frame is aligned with the streamflow "at the infinity", and its X axis points against the free stream. If you rotate the wind frame by the wind angles - angle of sideslip and angle of attack - you get to the body frame.
The term "longitudinal axis" refers specifically to the body X axis.
But where is the origin? It depends!
For most calculations, especially in flight mechanics, it is best to put the origin at the centre of mass. Furthermore, the direction of the longitudinal axis, over which the designer has some liberty (that arbitrary "forward"), should be such that it formed (one of) the principal axis of rotation.
This is not always easy, nor necessarily convenient. Centre of mass moves, the aircraft may not be symmetric, and the airframe designer will not like the reference axes moving about.
To avoid ambiguity, it is often necessary to state in which system the calculation is done, and how exactly it is defined. Oftentimes, engineers in a certain sub-field (e.g. flight mechanics) assume a certain frame and understand each other well, but this assumed knowledge is not carried to other fields, leading to errors and misunderstandings.
The situation is exacerbated by the fact that in many practical cases, the difference between the frames seems to be small, and the result may be "approximately correct" in most of them.1
So, as a designer, you decide how you define the longitudinal axis. If the aircraft is relatively symmetric, draw it as the axis of symmetry.
Your choice will affect how you read angle of attack (AoA). There is nothing strange about that: AoA of the aircraft is also "conventional": it is with respect to an essentially arbitrary axis. It will likely be different to the AoA of the wing, which is of the most concern for the aerodynamicist. (One of the conventions in pure aerodynamics is to choose the X direction such that it resulted in zero lift at zero AoA).
Whether the airflow will align with the axis at cruise depends on your choice. You will need to choose the angle of incidence of the wing to minimise drag, but the AoA may not be zero if you chose the axis direction with other considerations in mind.
Note that the choice of origin will not affect the wind angles. Essentially, you can leave the choice of origin until you need to decide on the other two axes.

1 A common example: Lift is defined in the wind axes. It is normally linearly dependent (~proportional) on AoA, but this only holds perpendicular to wind, and not with respect to "up" of the aircraft. But the difference is small for small angles.


Has the cause of the engine failure of Cessna's 182JT-A been determined?

Apparently, yes, it has -- see Cessna 182 JT-A Certification 'Imminent'.  As the article reports, the issues appeared to be related to the turbocharger, but I'm not sure how far (if at all) accident reports or details go beyond that.


How can this aircraft be stable/maneuverable?

What strikes me is a lack of a surface that creates a force to
  counteract the moment generated by the distance between the wing's
  lift and the gravity force.

You are not alone. Believe it or not, Lilium contacted me for advice, and I asked them basically the same thing. They never responded.

I agree with you, this thing will never fly and investors will get burned.

My advice to them would be to sweep the wings forward. This allows to keep the fuselage basically unchanged - you don't want the main spar to go where the pilot sits. But given the small wings this needs substantial sweep.

Update to this answer, February 2020:

Now they have beefed up their canard and skipped retractability, but all they can show is hovering flight for a few minutes at most. Sill no aerodynamic flight. The 300 km range and hour long flight time still are impossible with near-term technology. My verdict stands: Investors will get burned.


What is the biggest airplane that does not need a paved runway?

Military transports are designed to be operated from unpaved runways- by extension, any of these converted to civilian use can operate from unpaved runways.

For example, the Antonov Airlines operates a number of Antonov An-124 'Ruslan', which can and do operate from unpaved runways regularly. The Volga-Dnepr group specifically states:

  Multi-leg landing gears equipped with 24 wheels allow to operate the aircraft on unpaved runways ...


Why do commercial helo pilots wear helmets?

The same reason as anyone would wear a helmet - to protect their cranium in circumstances when there is the possibility of damage to that area of the body.

Helicopter operations are often low level, sometimes over dangerous terrain and, unlike fixed wing aircraft, they do not have the option to glide away from an engine failure. Low-level operations may not afford the pilot the altitude required for a successful autorotation landing so there is the possibility that they will be going down hard and fast.

Taking an example of low-level flight over forestry resulting in a forced landing, this may be survivable, but the pilot will be thrown around quite a bit as the aircraft is buffeted by the trees as it goes down. Some head protection would be important to the survivability of this crash.

There are a few other reasons I could think of apart from the main one above

Some helicopters operate with doors open, up where the birds fly around. A seagul to the head would not make for a happy flight
Noise - helo's can be louder than Fixed wing and the helmets could provide better noise cancelling
Specialist helo operations such as S&R use equipment such as night vision, which could be mounted on a helmet
Habit - ex-military helicopter pilots could just be in the habit of wearing a helmet, and carry this over to civilian operations.


How long is the EASA ATPL theory exam valid?

FCL.025 is very clear on that and it says:

  (2) The completion of the airline transport pilot licence (ATPL) theoretical knowledge examinations will remain valid for the issue of an ATPL for a period of 7 years from the last validity date of:
  (i) an IR entered in the licence; or
  (ii) in the case of helicopters, a helicopter’s type rating entered in that licence.

ATPL theory exams are valid for 7 years of the date of expiry of IR, entered in EASA licence. So it depends when your EASA IR expired. ICAO IR unfortunately does not count in this case.

If your ATPL theory exams are not valid anymore, you will have to do them again. It is possible to transfer A320 rating from CAAC (ICAO) licence to an EASA one - depending on your experience. You would need, however, to do LST (licence skill test) on A320 in the simulator and pass all 14 EASA ATPL exams again.


What has happened to make me experience negative G with the control stick FULL AFT near the top of a loop?

You were too slow.

Start the loop with more speed and pull more (if the g limit of your aircraft allows) at the beginning, so you have more speed at the top.

  Aerodynamically, what happened?

Without aerodynamics, you feel -1 g at the top of the loop, simply by having inverted the plane. Since the plane feels the same acceleration, both of you move together - until vertical speed picks up and drag will keep the airplane back. This is when you have the sensation of negative gs. In order to stay with positive gs, you need a centrifugal force to compensate for earth's gravity. This is the product of pitch rotation speed squared and the radius of the loop. If your flight speed drops, the radius will drop as well and leave little centrifugal force, even at a high rate of pitch. Dan Pichelman correctly describes how this kind of loop looks to an outside observer.

So there is little aerodynamics involved here besides drag - low speed will reduce all aerodynamic forces. The angle of attack on the wing is insignificant - what counts is the inertial force of the moving aircraft (besides gravity, of course).

If your airplane places you behind the center of gravity, pulling hard will give you the sensation of negative gs even when the aircraft as a whole is still at positive gs. Any maneuvering will add inertial effects which grow with the pilot's distance from the center of gravity.

  How can I change my technique to prevent this?

Fly faster, and be fast enough at the top to push in order to round out the loop, so it will look more like a circle. But make sure to stay within the limits of your plane. Again, Dan is right: It really sucks when the wings fold up.

Negative gs are completely normal at the top of the loop. When I did my first loop in an open-cockpit aircraft (a Boeing Stearman, no less), I did exactly that: Push near the top. However, this did not last long because my instructor immediately whined "pull, pull!". He had not closed the pockets of his flight jacket and started to lose their contents. So make sure that all equipment is secured before doing aerobatics.


Flying Considerations during an Eclipse?

Do Pilots flying during this time need to be Night Current?

No, that time does not fall within what the FAA considers "night"

The FAA defines night currency in FAA FAR 61.57

  FAA FAR 61.57

  (b) Night takeoff and landing experience. (1) Except as provided in
  paragraph (e) of this section, no person may act as pilot in command
  of an aircraft carrying passengers during the period beginning 1
  hour after sunset and ending 1 hour before sunrise, unless within
  the preceding 90 days that person has made at least three takeoffs and
  three landings to a full stop during the period beginning 1 hour after
  sunset and ending 1 hour before sunrise, and—

  Can time logged during the eclipse be logged as Night Conditions?

Nope, same reason as above it does not fall in what the FAA considers "night".


What are the requirements to convert an FAA certificate to EASA/JAA?

As @Pondlife states, this will depend on each member state's implementation of the EASA rules but I would expect that the implementations would be similar -- otherwise what is the point of EASA?  (That would be a good question except it would no doubt be closed as being too "opinion based".)

I've added a link to the relevant UK documentation and marked this as a Community Wiki answer so that hopefully others can expand on this for other states and perhaps add personal experiences.

UK

CAP 804 Section 4, Part Q deals with "Validation and Conversion of Non-EASA licences issued by States other than the UK".


What is the strongest jetstream ever encountered in commercial flight?

Jetstreams generally don't stay perfectly straight. They tend to follow a meandering, curved path so it would be rare for a flight to stay in the max tailwind for very long.

Dispatchers will often take advantage of jetstreams and plan the routing to follow part of the jetstream core.

There is a website called Ground Speed Records where pilots can post photos of high groundspeeds for an "Unofficial" record.

Here is an example from that website giving a groundspeed of 736 knots from a 240 knot jetstream tailwind. That is probably about the highest jetstream speed you will see:  B747-400 Ground Speed Records


Why does the US President fly in an obsolete 747-200?

The 747-200 derivatives used for transporting the President of the United States are VC-25's operated and maintained by the United States Air Force. The US Air Force tends to keep planes for a long time, as they still operate 707 and B-52 aircraft twice as old as these 747's. The E-4 aircraft, also based on the 747-200, have been in service for 40 years. The reasons for keeping the VC-25 aircraft flying are similar to these other examples.

A lot of work went into the VC-25 aircraft. They have been modified to add aerial refueling capability, defensive mechanisms, and include extensive additional electronic equipment for communications. Installing the special interiors was also a major task. As with a bomber or AWACS, there is a large initial investment in development to design the systems and build the aircraft. Upgrading components and providing proper maintenance allows these aircraft to perform their missions long after their entry into service.

Another difference is the engines. The 747-200B model has GE CF6-50E2 engines producing 52,500 lbf thrust each. The VC-25 aircraft have newer CF6-80C2B1 engines producing 56,700 lbf thrust each, which is the same engine as the 747-300. Newer engines go a long way towards improved performance.

As DeltaLima notes, these aircraft do not spend nearly as much time in the air as commercial aircraft. Yet there are many commercial aircraft in service with similar or greater age, including some 747-200 aircraft.


Declaring an emergency - protocols for commercial aircraft

The procedure would likely be the same as any other medical emergency: get the plane on the ground (which is a thing that pilots are good at doing, and have the training and skills to do) so that the medical crews can handle the medical emergency (which is a thing that pilots are not good at doing, and have neither training nor skills to do)

The initial radio call might be something along the lines of "Mayday mayday mayday, Oceanic 201 requesting immediate vector to LAX for a medical emergency, multiple passengers"

"Mayday" indicates several things all at once.

"Everyone else currently on this radio frequency, shut up."
"I am in the middle of an emergency, therefore I am now the most important person in the sky."
"I will do whatever I need to in order to keep this plane safe. Air traffic controllers, you will get everyone else out of my way."
Saying it three times has no relevance other than to make sure that it's heard and the number three indicates distress in general.

"Oceanic 201" is the callsign of the aircraft.
"Requesting" is used to tell ATC that the crew requires action from them, in this case a vector to a suitable airport.
"for a medical emergency, multiple passengers" prepares the emergency crews for whatever situation they're about to have dropped in their laps.

For further examples of cockpit-to-ATC communication under critical circumstances, you might find it helpful to read the cockpit voice recorder transcript of United flight 232, or other in-flight emergency transcripts.


How does a higher temperature when programmed in the FMGC affect REC MAX FL?

FMS calculates REC MAX in cruise by calculating temperature from actual OAT and TROPO inserted in INIT A page. It assumes standard -2C/1000ft until inserted tropopause altitude which after it uses constant temperature.

During climb it calculates temperature profile from inserted tropo/temp. If your REC MAX seems to be off during climb check the inserted values. Also, when A/C reaches CRZ ALT entered to PROG page it starts to use measured OAT at once, so REC MAX can change suddenly if it was off in INIT A page.

Note that REC MAX is only function of A/C weight, TROPO and OAT. Cost Index does not affect REC MAX.


What does a pilot mean when he tells ATC that he "has the numbers"?

This is from the FAA's Pilot/Controller Glossary:

  HAVE NUMBERS − Used by pilots to inform ATC that they have received runway, wind, and altimeter information only.

The AIM has some more information in 4-1-13 and 4-1-18, which comes down to "having 'the numbers' is not the same as having the ATIS". The equivalent controller information is in the ATC Orders 3-9-1, 3-10-1 and 7-1-3. For example:

  3−10−1. LANDING INFORMATION

  Provide current landing information, as appropriate, to arriving
  aircraft. Landing information contained in the ATIS broadcast may be
  omitted if the pilot states the appropriate ATIS code. Runway, wind,
  and altimeter may be omitted if a pilot uses the phrase “have
  numbers.” Issue landing information by including the following:

  NOTE−
  Pilot use of “have numbers” does not indicate receipt of the ATIS broadcast
  [...]

In most cases, pilots will just tell ATC that they have the ATIS anyway, as Ron described in his answer. But, there are some towered airports that have no ATIS, only AWOS, e.g. Columbus, Indiana (KBAK). In that case, telling the tower controller that you have the numbers is the only thing you can actually do (other than not tell them anything and let them give you the information, of course).


Do you know the exact model and use of this rotorcraft?

It's a Bell TH-57, most likely a TH-57C, which is the Navy's variant of the Bell 206 JetRanger.  It's used for VFR and IFR helicopter primary flight training for the Navy and Marine Corps.  Most likely that picture you took was of a TH-57 out of Pensacola NAS on a training flight.  They like to come out to KBFM and Jack Edwards in Gulf Shores to practice flying, pattern work, etc.


What is the difference between regulatory and nonregulatory airspace?

Non-regulatory airspace is MOAs, Warning Areas, Alert Areas, and Controlled Firing Areas (source 1), (source 2).

Other information should be located in the AIM Ch 3-4, Special Use Airspace. Specifically 3-4-1(c)

Basically non-regulatory areas mean that the FAA does not make regulatory enforcement in those areas due to special (military) operations. Usually the non-enforcement is only for participating aircraft, and generally recreational/commercial aircraft would not fall under any non-regulatory rules.

For example, in an active MOA with aircraft practicing low-altitude speed runs, the FAA would not enforce the 250 knot speed limit on participating aircraft.

This is in the AIM, Ch 3 Section 4, Part 5(b)

  Military pilots flying in an active MOA are exampted from the provisions of 14 CFR Section 91.303(c) and (d) which prohibits aerobatic flight within Class D and E surface areas and within Federal Airways. Additionally the Department of Defense has been issued an authorization to operate aircraft at indicated airspeeds in excess of 250 knots below 10,000 feet MSL within active MOAs..

For another example, consider warning areas, which are areas extending 3 miles from the coast. Since this area may include international waters (think of the area between Alaska and Russia), the FAA can't really regulate operations in all these areas. The US Navy also controls some of these areas and "shares" jurisdiction with the FAA.


What happens if an aircraft tries to land at MTOW (if greater than MLW)?

Most (all?) modern airliners are, in fact, certified to land at any weight up to MTOW if necessary, but if they do land at more than MLW then a special "Overweight/Heavy Landing Inspection" must be performed before the aircraft can be used again.

As this Boeing document states:

  Overweight landings are safe because of the conservatism required in the design of transport category airplanes by FAR Part 25.

  FAR criteria require that landing gear design be based on:

  A sink rate of 10 feet per second at the maximum design landing weight; and
     A sink rate of 6 feet per second at the maximum design takeoff weight.

  Typical sink rates at touchdown are on the order of 2 to 3 feet per second, and even a “hard” landing rarely exceeds 6 feet per second. Additionally, the landing loads are based on the worst possible landing attitudes resulting in high loading on individual gear. The 747-400 provides an excellent example. The 747-400 body gear, which are the most aft main gear, are designed to a 12-degree nose-up body attitude condition. In essence, the body gear can absorb the entire landing load. The wing gear criteria are similarly stringent: 8 degrees roll at 0 degrees pitch. Other models are also capable of landing at maximum design takeoff weight, even in unfavorable attitudes at sink rates up to 6 feet per second. This is amply demonstrated during certification testing, when many landings are performed within 1 percent of maximum design takeoff weight.


"Inertial GPS"

Inertial navigation is separate from GPS navigation. Inertial navigation senses accelleration and uses that to estimate changes in velocity and hence estimate changes in position. GPS is a GNSS system that determines position from timing of satellite signals. There's no such thing as Inertial GPS although there are systems marketed as sat-nav which can use inertial navigation when GPS is unavailable (e.g. when driving through a tunnel).

10th Character

Digits are about precision not accuracy. Any sat-nav or GNSS receiver can produce location digits to much greater precision than their accuracy.

The number of digits, and their implications regarding accuracy and precision, depends on the units being presented. For example, I have a handheld GNSS receiver that I set to display UK Grid-references for convenience in conjunction with Ordnance Survey maps. The meaning of the 10th and 11th characters in terms of positional precision is therefore different.

TQ
395012
775012

In this case, the 10th digit is something like kilometers north of the OS origin. Accuracy of ±1 Km can certainly be achieved by unaugmented GNSS.

It is probably better to state a desired accuracy in terms of distance on the ground - for example many handheld GNSS receivers will display something like "Accuracy: 23 feet".

Base stations

All GNSS receivers (including GPS, GLONASS, Galileo etc) use multiple satellites to determine their position. Typically three or four are required for a fix. Pure GNSS receivers don't use base stations.

SBAS capable receivers (such as those that can use WAAS, EGNOS, etc) use additional satellites to achieve higher accuracy. They do not directly use base stations on the ground. The additional satellites transmit positional corrections that have been gathered from ground stations but the GNSS receivers do not receive data directly from the ground stations.

Higher accuracy GNSS units are used by, for example, site surveyors. These are larger and more expensive and in some cases do use ground base stations for greater accuracy.

Aviation

Generally, I don't think aviators have any use for knowing their aircraft location to centimeter accuracy in flight.

A GNSS with SBAS (e.g. GPS + WAAS) can provide the accuracy needed for  precision flight approaches but Garmin state "Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity and availability"

Glossary

GNSS = Global Navigation Satellite System.

GPS = Global Positioning System, US operated GNSS.
Galileo = EU operated GNSS.
GLONASS = Global Navigation Satellite System, Russian operated GNSS.
BDS = BeiDou Navigation Satellite System, China operated GNSS.

SBAS = Satellite Based Augmentation Systems.

WAAS = Wide Area Augmentation System = US operated SBAS.
EGNOS = European Geostationary Navigation Overlay Service, EU SBAS.

GBAS = Ground Based Augmentation Systems.


Flying in a helicopter with open doors: why don't people fall out?

Aircraft, fixed-wing or rotorcraft, have limited capability to produce a sideways force, so they simply can't throw you out.

It is a matter of physics. Inertial forces (gravity and centrifugal force) act on you and the aircraft the same, so they won't make you move relative to the aircraft. The only force between you and the seat is caused by the aerodynamic forces. And the wing or rotor can only produce significant force vertically, and some torque with help of control surfaces. But for lateral force there is only drag of the fuselage and the vertical stabilizer and, in most helicopters, anti-torque rotor, which don't produce that much force unless there is really bad turbulence or in some cases if the handling is really bad.

When aircraft turns, it banks to be able to produce the necessary side force, so the resulting force is still mostly straight to the floor.

Of course the other reason is that all aircraft and helicopters have seat-belts and the people sitting by open door usually have them on—except for skydivers, who have the parachute on already, and rescue divers who are tied to the winch instead.


Which European (EASA, EU) regulation corresponds to US FAR 91.13 on "careless or reckless" operation of aircraft?

This is covered by SERA.3101 (Page 19) for the UK:

  SERA.3101 Negligent or Reckless Operation of Aircraft
  An aircraft shall not be operated in a negligent or reckless manner so as to endanger life or property of others.


Under EASA regs who is responsible for part m continued airworthiness? Lessor or Lessee?

It really comes down to the lease contract.  I don't think any of the regulatory authorities much care who pays to maintain it or what's in the lease contract, as long as the airplane is airworthy when it leaves the ground, which is basically up to the operator.  What we are really talking about here is who pays.

Pretty much anywhere, the lessor is expected to deliver the unit in an airworthy condition, then the lessee is expected to maintain it and return it to the lessor in an airworthy condition at the end of the lease. Like a car.  But it depends on the details in the lease.

The lessor is frequently a non-operator (Like GE Capital) who has no means to maintain the airplane in the first place so in any case it's the airline that will actually do the work, or contract the work, for something like an AD.

Who is on the hook to pay for Service Bulletins and AD compliance will be up to the lease contract (on an aircraft that is out of warranty).  If someone leases an out-of-warranty airliner from GE Capital, and the contract says that GEC will pay for ADs, then the airline will do the work but charge back the expenses to GEC.

Plus, GEC may have a clause in its purchase agreement with the OEM to cover AD costs beyond the warranty period and extend that protection to the lessee.  There are large variations in terms and conditions between OEMs, leasing companies, and airlines on a given type, as it's all part of a negotiated package.


Does the TIS-B "hockey-puck" contain VFR mode-C targets with unconfirmed altitude?

The AIM covers most of the operations and limitations of TIS-B on page 4-5-18

  TIS−B is the broadcast of ATC derived traffic information to ADS−B
  equipped (1090ES or UAT) aircraft from ground radio stations. The
  source of this traffic information is derived from ground−based air
  traffic surveillance sensors. TIS−B service will be available
  throughout the NAS where there are both adequate surveillance coverage
  from ground sensors and adequate broadcast coverage from ADS−B ground
  radio stations. The quality level of traffic information provided by
  TIS−B is dependent upon the number and type of ground sensors
  available as TIS−B sources and the timeliness of the reported data.
  (See FIG 4−5−8 and FIG 4−5−9.)

According to the AIM all transponder equipped (A/C/S) aircraft are included

  Only transponder−equipped targets (i.e., Mode A/C or Mode S transponders) are transmitted through the ATC ground system
  architecture. Current radar siting may result in limited radar
  surveillance coverage at lower 10/12/17 AIM Surveillance Systems
  4−5−19 altitudes near some airports, with subsequently limited TIS−B
  service volume coverage. If there is no radar coverage in a given
  area, then there will be no TIS−B coverage in that area.

section d. TIS-B Limitations offers some more info

The system is not perfect and unconfirmed altitudes may display as shadows

  (b) The ADS−B−to−radar association process within the ground system
  may at times have difficulty correlating an ADS−B report with
  corresponding radar returns from the same aircraft. When this happens
  the pilot may see duplicate traffic symbols (i.e., “TIS−B shadows”) on
  the cockpit display.

More on transponder requirements

  (d) The TIS−B system only uplinks data pertaining to
  transponder−equipped aircraft. Aircraft without a transponder will not
  be displayed as TIS−B traffic.

So pilot A in his Cherokee with a mode S transponder will show up but pilot B in his cub with no electronics and only a hand held who may be on radar will not show up.

This technical order covers the topic important phrase

  TIS-B is the ADS-B In function that provides for the in-cockpit
  display of other aircraft (without ADS-B) in the vicinity that are
  being seen via FAA secondary radar. General observations can be made
  during the flight to verify that known radar targets are appearing in
  the correct relative position on the ADS-B display(s) in the flight
  inspection aircraft. Of course, if there are no such
  targets-of-opportunity in the area during the flight, the opportunity
  to check TIS-B in this way will not be possible.

So if you are coming up on secondary radar you will be included in the ADS-B/TIS-B broadcast. ATC receives 1200 codes with altitude (encoder provided) so they will show up, and in my recent experience flying in the northeast most VFR traffic does show up. Aircraft with no transponder will not show up (radar target only). Im not sure what happens in the case of no altitude reporting.


Is there a way to register for updates on certain NTSB investigations?

No, the NTSB does not have such a service on their web site. In theory you could track the progress by downloading their database and parsing it to determine if status has changed, or by figuring out how their query system can be invoked, but those options require programming skills.


How would a new "clean sheet" General Aviation piston engine with all the latest technology differ from existing Continental/Lycoming types?

It would have a gearbox between the crankshaft and the propeller. That is certain.

Other very likely details would be:

overhead camshafts
four valves per cylinder
water cooling at least for the cylinder heads
electronic ignition
single lever control

This would enable it to run constantly at about 4000 RPM and create the same power from a smaller displacement. The consequence would be a more compact and lighter core engine. Compared to a car engine, the cooling system would be more capable, so the weight would still be higher than that of a car engine of the same nominal shaft horsepower. But it should be lighter and allow for a more aerodynamic cowling than the current piston aero engines.

The Porsche flight motor (PFM 3200) was like that, and for a reason. Yes, it did not outperform the older engines in terms of mass, but it was noticeably less noisy. Starting from a dated six-cylinder boxer design, the engineers could not fully optimize the engine for its intended purpose.

Once a gearbox is fitted, it makes sense to reduce propeller speed, so the diameter  of the propeller fitted to that engine would be a bit larger than that of a comparable propeller on a conventional engine.

Once Jet-A is widely available at GA airfields, a diesel version would also be very likely. Note, however, that the system weight of a piston engine (engine + accessories + fuel system + fuel) will be higher for a diesel on short ranges.


Are VFR pilots required to avoid an isolated cumulus cloud like any other cloud?

I suppose the FAA could violate you if you approach a cotton ball, but other than that, is there any reason to deviate and go slaloming around the sky just to keep distance from FEW clouds?

Aside from the legal reasons, keeping a healthy distance away from clouds is a Good Thing because other aircraft, birds, or alien spacecraft may pop out of them. Mid-Air collisions are no fun for anyone.

As far as going "slaloming around the sky", there's generally no reason to do that to avoid clouds:
If you're respecting the cloud clearance requirements (or at least the intent behind them) you shouldn't be getting close enough to clouds that you have to aggressively maneuver to avoid them - you've got plenty of distance to decide what you want to do.

Remember too that you've got 3 dimensions to work with: If we're only talking about a "puffy cotton-ball" or two you can always climb above or descend below them and stay on-course, or if they're all lined up inconveniently right along your flight path just offset your track a little bit (no reason to keep zig-zagging if a mile left or right of course keeps you clear).


How do you request a 3D block of airspace to to freely maneuver your privately owned military jet?

As @jamessqf points out, once the aircraft is no longer owned by the government1 there wouldn't be any regulatory difference between you requesting air work and, say, a Gulfstream acceptance or post-maintenance flight that needs to fly around at odd altitudes and attitudes to check out various systems. That said...
Below FL180 you can fly VFR as you like. Of course you still have see-and-avoid responsibility, which might be helped by any onboard targeting radar on your military jet but then again might not be.
If you want to go higher (and have a smaller chance of turning someone's Cessna into a hood ornament) you need an IFR flight plan. Ideally you'd ask someone for permission to enter a Military Operations Area (example) and/or Air Traffic Control Assigned Airspace (which is the same concept as a MOA but exists in Class A airspace). FAA Order 7400.10 will tell you who the controlling agency and using agency are for each MOA; if you wanted you could try cold-calling Albuquerque ARTCC and asking if they'd take the Mt. Dora MOA hot for you, but the Air Force's 27th Special Operations Wing is the using agency and the line controller probably won't help you unless you run it by the military beforehand.
Assuming you can't get clearance into special-use airspace your only other option is to request a quadrant clearance in conjunction with a block altitude assignment.
A quadrant clearance (7110.65 4–1–1i) allows you to fly between two specified radials of a navaid and within two defined radii (DME arcs). Depending on the performance characteristics of your jet you might need a significant amount of distance, e.g. between the 10-mile radius and 40-mile radius, in order to get a large enough slice of airspace to work in.
A block altitude assignment (7110.65 4–5–7g) is more commonplace and allows you to operate anywhere between the two indicated altitudes. Again you'd probably want a good eight-to-ten thousand feet or more.
For both the vertical and lateral considerations you'd probably have the most luck over the Western states (ZLC, western ZMP, ZAB, etc). You could also try going offshore as long as you checked to make sure the warning areas weren't hot.

1Or operated on behalf of the government; I've seen a couple N-numbered British/European fighters operate using tactical callsigns as aggressor aircraft for military training exercises.


When does a 'flaps/slats misconfiguration' warning sound during takeoff roll?

For the Boeing 727-100 and 747-100/200 the answers are:

  when does the system know when to sound the alarm?

When the thrust levers are advanced to begin the takeoff, if flaps and slats and a few other things are not in takeoff position, a loud horn sounds.

  figure out at what speed they can take off without flaps and slats.

Takeoff is not permitted without flaps and slats. You have to have them. Depending on how many were not in the takeoff position, the takeoff speed would be inordinately high, require runway lengths not available, and might be above the maximum tire speed. In short, as I said, you have to have them.

On the aircraft I mentioned, if you're starting the takeoff roll from a stationary position and advance the thrust levers at the usual rate, you'll get the horn before your ground speed is little more than walking speed, if that. The thrust lever position, while above anything you would use for taxi, is not anywhere near what you could take off with. It's not far along the travel of the thrust levers from idle to full throw.

The procedure taught for a takeoff warning horn at the carriers I flew for was to bring the thrust levers all the way back to idle, brake to a stop, and request clearance from the tower to vacate the runway. Once off the runway, brake to a stop and troubleshoot the problem. In no case were you to troubleshoot the problem while moving on the runway.

In practice, if there was no traffic, once stopped some would stay on the runway to troubleshoot after getting tower clearance to do so. The assumption was that the problem would be quickly corrected and takeoff resumed.

Troubleshooting was a simple matter of checking that everything that was supposed to be done had been done. For the 747, the items that would trigger the takeoff warning horn were:

leading edge flaps not extended, there were lights on the f.e. panel that showed their individual positions,
stabilizer not in the green band, there was an indicator by the trim wheel on the center console.
flaps not in 10 or 20 degrees position
body gear not centered, lights on the f.e. panel showed its position.
speed brake lever not in the down detent.

Recalling these items from memory was a standard question on oral exams.

If everything had been done that was supposed to be and you still got the horn, it was usual to recycle everything. If that didn't fix the problem, which if the problem was the warning system itself would be the case, it was back to the gate for maintenance.


How does the G1000 differ from an airliner’s avionics?

The CRJ's Rockwell Collins FMS-4200 as used in the CRJs is a 1980s design and is far "cruder" than the G1000.  You have a little control head with a small display screen and keyboard where you interface with it.  The G1000 is more like using any modern computer application where much is presented on the main screen with trackball or mouse selectable commands and data with a fairly intuitive presentation.  On the FMS-4200, you have keys on the side of the display to select options that appear next to each key, keys to select various modes on the control head, and you have a one-line "scratchpad" where you can type in text commands or other data.
You could say it's a bit like the difference between using the icon based Windows operating system and the older direct key entry MS DOS.  With a system like the 4200 you have to learn the selections and menus and keystrokes directly, instead of just knowing how to find your way around a pictorial presentation on a large screen that you use like any modern computer application.
If you've mastered the G1000 and you later find yourself on a CRJ type course having to figure out its 1980s FMS system, your G1000 skills probably won't help you that much and you'll just have to figure out the "old school" interface as something new.  To get though the type course in one piece, mastery of the FMS is critical, so if the opportunity to go on that course comes along, get hold of the training material as early as you can to get as much of a head start as possible.


Is it allowed to start engines during push-back?

It is common. In fact, for aircraft parked at a gate (i.e. not a hardstand), it is quite uncommon NOT to start the first engine during pushback. The wing-walkers stay well away from the intakes, and with the engines at idle power, the danger zone isn't all that large - not nearly as large as if the motor were running at a high power setting.


What is this airplane I saw with propellers behind the engine and canards on the top of the plane?

The "propellers behind the engine" is called a "push configuration". One you look through aircraft that are private business planes, the Piaggio P.180 Avanti comes up as a likely contender.


Why is the intake of the 757 (RR) engine slanted?

This is the case frequently, as the aircraft doesn’t have the same pitch angle on ground while accelerating, or at rotation, or at climb or at cruise. So the intake slant is calculated to the best appropriate as an average. As a summary this is not specific to this engine on this aircraft


Need communication example departing and arriving uncontrolled airport within class D

I fly out of Addison, McKinney, Mesquite, Denton, Rockwall, Sulphur Springs and Aero Country a lot. I am also friends with the A&P located at Airpark. If you would like a safety pilot who knows the local area, maybe we can hook up.
A few things to remember when operating out of airpark:

The runway is barely maintained. But, it is not perfectly smooth. Treat it like a soft field.
When taxiing anywhere besides the runway, you will be taxiing on turf. Protect your nose wheel.
In the daytime watch out for chickens.
At night, beware of coyotes.
Do not park, walk, or stand under the concrete bikini hangars. They are off-limits due to instability and collapse.
The windsock is in disrepair. Do not trust it. Look for other nearby flags and smoke from local bbq restaurants.
The runway has non-standard markings
The runway is a lot shorter than you think due to displaced thresholds at both ends due to buildings, fences, and trees.
Make all of your radio calls on the CTAF while taxiing. Make a few CTAF radio calls while in the pattern and right before taking the runway for takeoff. All of your other radio calls will be on Addison or Fort Worth frequencies. There is very little traffic at Airpark (1-2 aircraft a day). All of the other traffic in the area will be on Addison or Fort Worth frequencies.
The runway is aligned with the runway at Addison. You will be on a very similar final and departure leg.
Addison is only 3 miles away. You can almost see the Airpark area from the Addison Tower.
Because of Addison Tower’s Proximity to Airpark, contacting them as soon as practicable means
as soon as you start the engine.
Addison Tower does not like hearing from pilots directly as an initial radio call. They prefer pilots to contact Ground first and get transferred to them via a frequency change. At Airpark, it would be best to get Clearance Delivery and/or flight following first through Fort Worth Approach. Then, contact Addison Tower.
Inbound to the Addison Class D, you are required to listen to the ATIS first. There will be a frequency given over ATIS to contact Fort Worth Approach. You must contact Fort Worth Approach before contacting Addison Tower. Period! Trust me when I say Addison Tower will not like it if they are your first point of contact.
Addison is an extremely busy Class D. It caters to jet and turboprop business aviation. If it did not have DFW and Love Field about 10 miles away, it would probably be a Class C or at least a TRSA.
There can be as much as a 15 minute and sometimes up to an hour wait in the run-up area for clearance to takeoff. And, they will sometimes utilize a line up and wait clearance. This can affect your takeoff clearance at Airpark.
Good visual reference points for Airpark are the Dallas North Tollway and the President George Bush Tollway. Airpark is located in their Northwest corner.
The Airpark area is extremely congested. Climb out to a safe altitude as soon as possible. If you have an engine out upon takeoff you have very few options. None of them good. To the North, you have a green space on the East side of the Dallas North Tollway. To the South, you have Addison Airport.
Do not contact the Airpark airport owner, operator, or manager listed as points of contact. They are anti-aviation real estate developers who bought the land as an investment. They will try to steer you clear of Airpark as much as possible. Their acquisition of Airpark is very similar to Meigs Field in Chicago. They bulldozed the operating FBO and fueling area. But, it took a court order to keep them from bulldozing the runway.
Most pilots choose to go North and East to practice maneuvers, to practice instrument approaches, and to beat up the traffic pattern at other airports.
If you have at least a private pilot certificate, do not worry or be intimidated by the Class B. If you are flying to, from, through, or above the Addison airspace, you will need to be in two-way communication with ATC anyway. Just ask for clearance through the Bravo.


It exists as a mathematical abstraction for conventionally shaped aerofoils at moderate speeds. In the end it is derived from the centre of pressure. The centre of pressure is the point where the moments of the individual aerodynamic forces over the aerofoil give 0 momentum. This always exist on any aerofoil. Now, the centre of pressure is not at a constant location, it is continually shifting as a function of angle of attack, and it moves quite a lot. However the rate of movement and change in lift force is in proportion to each other, and based on that, the stable point can be found, which for conventional aerofoils at normal speeds is about 25% chord.

Note, that to get this, the proportionality between lift and CP location is a must. You can create any shaped wing cross sections (might not want to call it an aerofoil) which will not have this property and won't necessarily have an aerodynamic centre. Whether it is fit to fly is questionable though. However, they will always have a CP, as it is a simple mathematical property, and it will very likely move with angle of attack. Also note, that the AC does change location with increasing speed, for supersonic speeds it moves significantly backwards.


Where can I find reliable data on maximum turn rates for jet fighters?

Imformation on the F-22, particularly performance and mission systems data remains classified, as with the F-35 airplane.  To the best of my knowledge there isn't much technical data available to the public on those subjects.

Now flight manuals for older fighter aircraft are readily available to the general public.  PublicIntelligence.net is a great source for these documents, as they have them for the F-14, F-16, F/A-18E/F, AV-8B, A-10, just to name a few.

Janes/IHS is not a great source for this stuff; their entries are more on the level of intelligence briefs and encyclopedia entries and are not likely to contain the information you ar looking for.


Does an aircraft with higher aspect ratio wings produce more wingtip vortices in a turn than one with lower aspect ratio wings?

Easy to follow diagramFor two wings with the same area, the higher AR wing will produce LESS wingtip vortices simply because there is not as much area close to the wing tip that can be affected by the vortices.

The Ta-152H has a wing area of 253 ft^2 while the P-51 has a wing area of 235 ft^2

With those area's being so close together (7% apart) while the AR's are very different (35% apart) it would be a safe assumption to say the Ta-152H produces LESS wingtip vortices than the P-51.


Single vs Twin motor for an electric RC airplane

You should keep in mind that adding an engine adds wiring, extra propeller (a larger single prop might to be lighter in RC than an equal setup of two), overall complexity etc.
As I understand it, electric motors have a "sweet spot", or rather an area of (iirc) certain load and rpm. You should desing your configuration so, that the motor(s) would operate in this rpm/load range in cruise. This sweet spot is (again, iirc) much higher than half load. So it is likely you are better of with a single engine than two that are only utilizing about half their rated pwr.
This sweet spot is very motor specific, so you need to dig deep into spec sheets.


What are the fonts used in MCDU screens?

My guess is that these are raster (non-scalable) fonts without any special name.

At least initially, the screen resolution wasn't (and needed not be) particularly high, and the characters were the typical 8x8 pixels or only slightly better. Such fonts are drawn by hand (by pixel) and don't have too many variations to speak about. (Although the sales people might disagree).

Later models with higher-resolution screens probably modeled the same terminal-type font to keep commonality. I still doubt MCDUs have an operating system (if any) with scalable font support.


Is the cargo door on this airplane really malfunctioning?

It appears as though the locking handle for the door has some sort of switch in it to allow for full extension of the door only if the locking handle is pulled full forward and, for whatever reason, the door handle won't move into this fully extended detent on its own.  While the workaround is jury rigged at best, it doesn't seem to pose a flight safety issue unless the door can't be locked when fully closed.  It's just another video from an ignoramus in the terminal with a cellphone camera.


Does lift-to-drag ratio asymptote to 4 (or 6) at high Mach numbers?

My source is STUDIES OF HIGH LIFT/DRAG RATIO HYPERSONIC CONFIGURATIONS by John V. Becker, to be found online here. It is from 1964, so more than 50 years old, but since a lot of research had been performed already before that date, it might still be relevant.
In short: It depends. On thickness ratio and Reynolds number, for example, as can be seen in this plot for flat plates from the above linked report:

Note the grey areas noting the maximum for glide rsp. reentry vehicles. Their performance is roughly half as good as that of a flat plate.
Most of the report uses the volumetric efficiency parameter $\frac{V^⅔}{S}$ for comparisons. This is the volume $V$ to the power of ⅔ divided by the reference area $S$. Below is a carpet plot for a variety of wedge shapes, valid for Mach 6.8 (same source as above).

An infinitely thin wing will achieve an L/D of 6.5, irrespective of its leading edge sweep, and a more realistic t/c of 0.09 will not get above an L/D of 5.5 at 85° sweep, dropping below 5 for 70° sweep.
It seems the Küchemann approximation holds up well for single-digit Mach numbers but becomes too optimistic above this speed. And impact theory alone is not sufficient to predict L/D with any confidence.
The plot below explains why the Shuttle is a low wing configuration: Above Mach 10 it is cleary advantageous to put the flat side on the bottom:

The index FB represents the flat bottom version of the vehicle.


What do you call the portion of a tail-dragger takeoff when the tail is in the air?

There is no term (that I am aware of) referring to only the portion of the takeoff while the tail is off the ground.

In general, the attitude where just the two main wheels are touching the ground is called "two-point." Likewise, with the tail wheel also on the ground, it is called "three-point."

Specifically, a two-point landing is sometimes called a "wheel landing".

Source


Do GA pilots routinely request "flight following" from ATC, and why?

I typically like to get VFR flight following if I haven’t filed a flight plan for longer distance flights. The biggest advantage here is that somebody knows where I am if something should happen.

I don’t typically find the chatter too bad, but you do have to be on the ball, especially when handed off from a local airport to an Air Route Traffic Control Center (commonly referred to as just “Center”) frequency. Often on flights out of my airport (KGRB) I will get handed off to Minneapolis Center, which is relatively busy frequency.

Another nice thing is that it gives you some practice talking in busy airspace. You really have to follow the rules and jump in when able. Sometimes they won’t hear you because you are transmitting over other aircraft that you can’t hear, so the frequency will appear open. It’ll sound like they are talking to themselves.

So here is how I see it:

Pros

You are talking to somebody and working with other traffic in the airspace
You are on a frequency you can broadcast an emergency to. Yes we all know about 121.5, but you are not guaranteed to get somebody on the other end.
ATC knows where you are, and if you fall off the radar and don’t respond, they will initiate a search. If you just file a VFR flight plan they won’t even start until 30 minutes after your planned arrival, and then they start calling airports and contact numbers, then start a search. They may not know where you fell off your flight plan so the search area is much bigger.
They can help route you around active MOAs, TFRs, and other airspace/weather issues that don’t show up well on paper maps.
Traffic advisories (as others pointed out)
Can provide a vector to where you want if you get lost.
Don’t need to open a flight plan if you can get following all the way.
Good radio practice

Cons

Flight following is “workload permitting.” They may call up and say Radar services terminated; squawk VFR at any time, turning your flight back into normal VFR. If you didn’t file a flight plan, now you should call up FSS and open one en route, which is more difficult.
Requires you to be on-the-ball with your radio transmissions on busier frequencies. If you frequently fly from uncontrolled airspace, this can be intimidating.
You may get vectored around a bit, but I usually don’t have that problem. I’ve typically contacted the destination airport by 20 miles out and either got clearance or vectors anyway.


Are engines fed differently in reduced gravity aircraft?

Zero 'g' aircraft are basically commercial aircraft.

In general, it is mainly the fluid systems like the fuel and hydraulic systems in the aircraft which are affected by the zero gravity conditions.

In the case of jet engines, the fuel is transferred by pumps operating under pressure and the fuel injection is also under pressure in the combustion chamber. Consequently, the engine fuel system does not need any modification. In a few aircraft, the fuel tanks themselves are pressurized (like C-5) but this is for safety and wouldn't affect operations.

The engine oil and lubrication system is also usually pressurized and can operate briefly under reduced gravity conditions.
Work done by NASA indicates that aircraft can be used in zero gravity conditions without any major modifications to systems.

The zero 'g' aircraft don't operate in weightless environment for more than 20-30 seconds and the engine systems should be able to cope during that time. The main concern appears to be the training levels of the pilot.


Is it possible to detect a pitot static failure (blockage) of air data probe during flight and alert the pilot?

The crew checks the pitots and static ports before the flight to ensure they are in good condition and not blocked by objects or insects. Pitot tube (pitot-static) can be obstructed in-flight. Static ports are less affected.

Detecting a blocked pitot or static port: This is not done, but is possible (e.g. send some air from the back of the tube in a pitot, and see if it can exit the tube at a normal rate (which is dependent on several parameters).

Unblock a blocked pitot: In some cases yes:

Melt ice or snow by heating the tube in flight, but the tube may be frozen for a minute from time to time. Some pitots are not heated and must be deiced naturally, which will be longer (while cruising in -50°C air, friction prevents aircraft skin to be cold. Concorde skin was about 100°C, meaning air friction just increased its temperature by 150°C).
Drain water using drain holes in the pitot.

Redundancy for pitots: Yes, two or three exist on most airliners.

Alert for blocked pitot: Not a direct alert, since a blocked pitot is not detected, but air data processors compare the different pressure values received from the different pitots, and in case of significant difference alert the crew and disconnect the automated units relying on pitot pressure (like the autopilot).

A message is displayed to emphasize that airspeed is unreliable

Dangerous? Yes because if the unreliability of airspeed is not taken into account by the pilot, then stress and inappropriate actions can occur because the aircraft is apparently not reacting to attitude changes.

AF447 disaster is sadly a perfect demonstration of the stress that can be generated.

If the crew detects correctly the situation, then there is nothing special to do, they just need to continue (manual control) at the same altitude and with the same aircraft attitude until the speed becomes reliable again.


How much power is generated by a Ram Air Turbine (RAT)?

According to the Flight Crew Operations Manual of the Boeing 777:
Hydraulics

The RAT, when deployed, provides hydraulic power only to the primary
flight control components connected to the center hydraulic system.

Which leaves out:

Nose gear
Main gear
Steering
Brakes
Flaps
Thrust reversers

Electric
The RAT powers both C1 TRU and C2 TRU, which powers the captain's and first officer's flight instruments, respectively.
The RAT can supply electrical and hydraulic power simultaneously. However, if the RAT is unable to maintain its RPM, the electrical load is shed and provided by the main battery, until RPM is satisfactory.


Do other countries create the equivalent of a TFR when US VIP's visit?

Absolutely!  The same airspace restrictions that are in the US are regulated by the FAA and ICAO.  The FAA (or the US) is a signatory to the ICAO standards, and as part of that governing body instituted the same rules worldwide. Those restrictions are also issued through the NOTAM system.

Incidentally, flying in the UK, we had restrictions on where we could fly depending on where the Queen was flying (if our missions coincided with her flights).  They even had a rather unflattering name for those flights in the pilot community.

Here is an article that talks a little bit about th e roles and responsibilities of the Queen's pilots.

You can also check UK NOTAMS (although i don't see any current ones fo rthe Queen at the moment).


If a passenger steps in for the crew, are they eligible for a reward as in maritime law?

The short answer is no but it really depends on what kind of "pilot" is on board.

  "Is there a pilot on board"

If the pilot in question is a Private Pilot as per FAA licensing (although its often similar elsewhere in the world). They would be legally prevented from receiving compensation for flight time as per the FAR's.

  § 61.113 Private pilot privileges and limitations:

  (a) Except as provided in paragraphs (b) through (h) of this section,
  no person who holds a private pilot certificate may act as pilot in
  command of an aircraft that is carrying passengers or property for
  compensation or hire; nor may that person, for compensation or hire,
  act as pilot in command of an aircraft...

If the pilot in question was a commercial rated pilot they could in theory receive compensation for the flight time but as far as I know there is no aviation law like the maritime law.

Furthermore maritime law generally allows you a portion or all of the recovered cargo value (think treasure salvage) in the case of a hull loss. Here in the US if an aircraft were to go down be it over land or water it becomes an accident scene which the NTSB would have jurisdiction over and is generally in charge of finding and salvaging for their investigation. If you were to recover a piece of an aircraft that was part of an ongoing investigation you may be required to turn it over to the authorities.

The closest scenario that I know of like this, was when a bomber pilot helped land a plane after one of the crew members had an issue. However he was not pilot in command and was only providing support.

All things considered you will probably get a book deal out of the whole thing if it were to happen...


Can an airline rewrite a flight's origin airport for the day, following an earlier diversion?

No.  They've sold tickets for people to get from A to B. They've not sold tickets to anybody looking to get from C to B.
The aircraft would be ferried into position empty, then they'd operate the schedule that has been advertised & sold.
The scenario as presented doesn't really work, though... you don't get to just strand your passengers in C who bought tickets to A & tell them "sorry, good luck." Either you bus them the rest of the way, or you use AN aircraft and A crew to get them where they need to be. Whether it's the same aircraft and/or the same crew as originally planned depends on various things, but as a matter of flight numbers, you fly what you've been selling tickets for (as much of that schedule as you can) and you ferry planes & crews into position when you have to.
But rewriting things so that "flight #X now starts in C instead of A, today" doesn't happen.


Are there special safety considerations when flying to/in Atlantic Canada?

Plan for unexpected weather amid limited options for dealing with it.  I've flown a number of times between Newark (EWR) and Halifax NS (YHZ), Moncton NB (YQM), and St Johns, NL (YYT).  It can be quite foggy and windy and in the cold months braking action can become a factor.  A lack of options can be problematic.  When we flew EWR-YHZ we often chose EWR as an alternate and I've turned around as late as talking to Halifax approach as braking action become NIL and we didn't have gas to wait it out.  Going out to YYT we'd only have enough gas to get to Gander (YQX) if we couldn't get a good approach in at St Johns.  I flew a capable jet under IFR with Cat II approach capabilities so your concerns will be slightly different down low and VFR.

Although you are VFR, I'd play by IFR rules as alternates and fuel is concerned.  Plan enroute alternates and carry enough gas to get to your destination and get to your second choice with some gas to spare.  The weather can turn quickly and the fog in any of the maritime airports can be thick enough to turn even IFR GA planes away.  Have a plan to be able to get on the ground somewhere else.  Also consider how fatigue will play into your decision making once you are out there.


What FAA license does the EASA LAPL convert to?

Unfortunately, an LAPL license isn't ICAO compliant. This is from the UK CAA:

  Licences which do comply are known as ICAO licences and those which
  do not are known as non-ICAO licences. Non-ICAO licences are not fully
  recognised internationally, and therefore are only valid for use
  within certain states or Europe; for example, the LAPL is only valid
  in Europe.

That means that the FAA won't recognize it and you can't use it to get an FAA PPL under 14 CFR 61.75, because that requires you to hold an ICAO compliant private pilot's license. As far as I know, there's no other way to convert a foreign license to a US one (a sport or recreational pilot license would be the closest US equivalent).


Naively, it seems that this would pump more audio power into the ear. Granted, it will be in opposition to the original noise, but it seems it would be very tricky to get the cancellation exactly in phase.

If the headphones succeed in reducing the noise you hear, then they will also have succeeded in reducing the power delivered to your eardrum (at the relevant frequencies) -- because those are one and the same.

It is conceptually and mathematically convenient to imagine that the original noise and the canceling noise both reach your eardrums and interfere there -- but if you actually work out how energy moves in the combined situation, what actually happens is that the cancellation speaker sets things up such that much of the sound energy will get reflected away from your ear canal instead of entering it.

The core mathematical point is that the air displacements and minute pressure differences that make up the sound do indeed (to a good approximation) behave linearly -- so you can take a description of the noise and a description of the cancelling noise separately and simply add the displacements at the location of your eardrum.  But power goes as the square as the displacement, so it does not add linearly. You can't take the power transport of one sound along and add it to the power of another sound to get the power of the combination (except averaged over time if the sounds are not coherent in frequency, which is specifically not the case for noise-cancelling headphones).


There are two big advantages to windowless aircraft:

Cost
Design complexity/structure

Cost is a fairly obvious one; the plexiglass used for aeroplane windows is not expensive, but designing around it increases costs all the way from conception to manufacture of an airliner. Plus the airline needs to think about blinds/curtains, seat placement, and the extra processes involved in cleaning all the windows on the aircraft regularly - inside and out.

To the second point: design. Not only do windows complicate the design of an aircraft (thus increasing the cost) but they're also structural weak points. An aerospace engineer would like nothing more than a simple tubular fuselage without these vulnerable stress points (aircraft windows are round rather than rectangular to reduce these).

Here's an interesting example of a windowless concept aircraft: the Reaction Engines A2. This hypersonic aircraft flies so high and so fast that the stresses and heat on the fuselage are simply too much for big windows to handle. Any windows would have to be tiny (like on Concorde) - so they're simply left out.

So to sum up: windowless aircraft certainly an option for future superfast and high-altitude air travel, but for today's commercial airliners the only point would be a slight saving in cost. Whether the idea of a windowless airliner would affect passenger number is unknown, but I imagine a lot of people would be uncomfortable with the idea.


During the holding procedure is it required that the pax must have the seat belt on?

There are no regulations which require passengers to be seated when the plane is flying a holding pattern, but there are a few practical advantages to keep the seat belt sign on during this phase:

The plane is flying at a lower altitude, where it is more likely to encounter turbulence and other unstable weather conditions. Up in FL330 it is usually clear skies all along.
The plane may need to get down quickly after an approach clearance is issued (after all, it is busy airspace). From that point onward the pilots may deploy the spoilers to lose altitude (which shakes up the plane a little), turn towards the approach course and without you noticing, landing gear is down and locked already. At the same time, we know it takes quite a few minutes after the seat belt sign has been turned on until everyone is seated (passengers won't just rush back to their seat after hearing the Ding Dong tune). If the seat belt sign is not illuminated in this period, there may not be enough time for the cabin crew to prepare the cabin for landing.
It reminds the passengers that if they wish to get out of their seat for whatever reason, they should make it quick.

If the flight deck tells the passengers it is going to be a delay, the cabin crew is usually a bit relaxed at enforcing the seat belt sign. E.g. if someone is going to the bathroom, they won't block unless that person is hanging around standing. When the approach clearance is given, another announcement will be made, and the cabin crew will now make sure everyone is seated because landing will commence shortly.


How are "Local Flights" defined in European regulations?

In the UK at least a local flight is one that begins and ends at the same aerodrome. This flight could be remaining in the circuit (pattern) or flying a 3 hour navigation exercise a long distance but as long as you come back to the same place without landing away it's a local flight. It is the same in all the other European countries I've flown to, I haven't been to Greece though so there's a chance their definition may be different.


Why didn’t the 757 have manual-reversion capability?

When you have controls designed to be operated manually, in an airplane that heavy and that fast, you have to include things to provide aerodynamic force compensation like servo tabs and offset hinge lines (look at the IL-82's rudder hinges; like a B-29's...the most obvious tell-tail of manual controls on a large aircraft) to make the control forces reasonably manageable, and even there, I can say with pretty much total certainty the IL-82 required muscles the size of fence posts to operate comfortably.  A jet like that with B-29 flight controls is hardly a leap forward.  You also have to mass balance the surfaces because there are is no flutter damping capability afforded by the mechanical control linkages.  All rather heavy.

When you have hydraulic controls, you can get away without mass balancing the surfaces, without servo tabs, and without offset hinges, because the hydraulic actuators (plus flutter dampers in some cases) provide all the required force, AND the required flutter resistance.

So, if you are going to design a hydraulically boosted system with manual reversion, you have to incorporate some of those aerodynamic force aids to be able to operate the controls manually.  But once you have a design that is sufficiently robust from a design/risk/failure tolerance perspective to operate with hydraulics only, there is no point in including manual reversion.  It's a step backwards, adding all kinds of complexity and weight for no benefit.