Can a turbofan have a fan driven electrically so as to run at optimal speed?

There are plans to run a turbofan-like engine with an electric motor rather than the gas generator used today. But the weight of electric engines does not promise an immediate advantage - only when the electricity is generated in a much more efficient way that what today's gas generators offer will the overall propulsion mass be lower. An example is a hydrogen-powered fuel cell somewhere in the fuselage.

We had a similar discussion here and here.


Why doesn't the Tu-154's center engine have a thrust reverser?

Several I guess:

There is no way to store them on the middle one in a way not increasing drag during flight.
In any possible configuration they would blow hot exhaust always against some body part, thus making it rather inefficient.

But maybe most important:

Two reversed engines already produce more than enough breaking power, no need to spend money on another. In fact, even one would be good for all purpose, but asymmetric force isn't a good idea either :))


Are there surveillance cameras in aircraft cargo bays?

Any burglary of cargo would happen outside the aircraft, after unloading the cargo. External cameras on the ramp are much more effective for this purpose. I don't know of any aircraft that has internal cameras just for the cargo area.


What is the weight limit for a pilot to eject from an F-100?

Firstly, welcome to Aviation Stack Exchange! As for your question, I actually could not find the exact model used for the F-100 series (sorry), but as far as I can tell most American first and second generation jet fighters were installed with Martin-Baker Mk.1-3 ejection seats. These were some of the first examples of explosive charges being used as the main propellant, and for the sake of a shorter answer I will assume you understand their basic operation. The Martin-Baker website states that the for the given size range of crew (between the 5th and 95th percentile), the seat could manage to lift a 224lb pilot/aircrew at a maximum of over 400 knots indicated airspeed.

[Edit] I want to address @GypsyRanger's answer: I think we can all assume that the pilot being ejected from the fighter has undergone and passed Air Force criteria for qualification to be a fighter pilot. I personally think his question is simple but a good one because he is just asking the weight limit, and in terms of mass this shouldn't be too hard to answer. I myself couldn't find the exact model, but all main-stream American jet fighters of the F-100's era were fitted with Martin-Baker seats ranging from the Mk.1 to the Mk.3. If you take the time to look at the specifications for each and compare, or knew beforehand you'd know that the improvements between each model were mostly pertaining to reliability and safety for crew, something that they were lacking in at the time (the firing mechanism was practically the only thing changed throughout). Really though, don't be too quick to criticize if you won't put in the time to read it or because it's a short question.


Sensitivity of aircraft stability with respect to the CG location

It sounds like it has a horizontal tail, so you basically need to increase the tail volume which will allow you to move forward CG limit forward, allowing you to move the median CG forward and expanding the overall range. So just make the horizontal tail a bit bigger.


What happens if a private pilot's license isn't used for some time?

In the US (under the FAA) there are 2 things that must be maintained (lets assume this is a VFR license).

First there are some basic flight requirements. You don't need an instructor to complete these. It basically boils down to 3 take offs and landings every 90 days to be current to cary passengers. Here is the full legislation.

  Sec. 61.57

  Recent flight experience: Pilot in command.

  (a) General experience.

  (1) Except as provided in paragraph (e) of this section, no person may
  act as a pilot in command of an aircraft carrying passengers or of an
  aircraft certificated for more than one pilot flight crewmember unless
  that person has made at least three takeoffs and three landings within
  the preceding 90 days, and--

  (i) The person acted as the sole manipulator of the flight controls;
  and (ii) The required takeoffs and landings were performed in an
  aircraft of the same category, class, and type (if a type rating is
  required), and, if the aircraft to be flown is an airplane with a
  tailwheel, the takeoffs and landings must have been made to a full
  stop in an airplane with a tailwheel.

  (2) For the purpose of meeting the requirements of paragraph (a)(1) of
  this section, a person may act as a pilot in command of an aircraft
  under day VFR or day IFR, provided no persons or property are carried
  on board the aircraft, other than those necessary for the conduct of
  the flight. (3) The takeoffs and landings required by paragraph (a)(1)
  of this section may be accomplished in a flight simulator or flight
  training device that is--

  (i) Approved by the Administrator for landings; and (ii) Used in
  accordance with an approved course conducted by a training center
  certificated under part 142 of this chapter.

  (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-

  (i) That person acted as sole manipulator of the flight controls; and
  (ii) The required takeoffs and landings were performed in an aircraft
  of the same category, class, and type (if a type rating is required).

  (2) The takeoffs and landings required by paragraph (b)(1) of this
  section may be accomplished in a flight simulator that is--

  (i) Approved by the Administrator for takeoffs and landings, if the
  visual system is adjusted to represent the period described in
  paragraph (b)(1) of this section; and (ii) Used in accordance with an
  approved course conducted by a training center certificated under part
  142 of this chapter.

Every 2 years you will also need a flight review which is administered by an instructor.

  Sec. 61.56

  Flight review.

  (a) Except as provided in paragraphs (b) and (f) of this section, a
  flight review consists of a minimum of 1 hour of flight training and 1
  hour of ground training. The review must include:

  (1) A review of the
  current general operating and flight rules of part 91 of this chapter;
  and

  (2) A review of those maneuvers and procedures that, at the
  discretion of the person giving the review, are necessary for the
  pilot to demonstrate the safe exercise of the privileges of the pilot
  certificate. (b) Glider pilots may substitute a minimum of three
  instructional flights in a glider, each of which includes a flight to
  traffic pattern altitude, in lieu of the 1 hour of flight training
  required in paragraph (a) of this section. (c) Except as provided in
  paragraphs (d), (e), and (g) of this section, no person may act as
  pilot in command of an aircraft unless, since the beginning of the
  24th calendar month before the month in which that pilot acts as pilot
  in command, that person has--

  (1) Accomplished a flight review given
  in an aircraft for which that pilot is rated by an authorized
  instructor; and
  (2) A logbook endorsed from an authorized instructor
  who gave the review certifying that the person has satisfactorily
  completed the review. (d) A person who has, within the period
  specified in paragraph (c) of this section, passed a pilot proficiency
  check conducted by an examiner, an approved pilot check airman, or a
  U.S. Armed Force, for a pilot certificate, rating, or operating
  privilege need not accomplish the flight review required by this
  section. (e) A person who has, within the period specified in
  paragraph (c) of this section, satisfactorily accomplished one or more
  phases of an FAA-sponsored pilot proficiency award program need not
  accomplish the flight review required by this section. (f) A person
  who holds a current flight instructor certificate who has, within the
  period specified in paragraph (c) of this section, satisfactorily
  completed a renewal of a flight instructor certificate under the
  provisions in Sec. 61.197 need not accomplish the 1 hour of ground
  training specified in paragraph (a) of this section. (g) A student
  pilot need not accomplish the flight review required by this section
  provided the student pilot is undergoing training for a certificate
  and has a current solo flight endorsement as required under Sec. 61.87
  of this part. (h) The requirements of this section may be accomplished
  in combination with the requirements of Sec. 61.57 and other
  applicable recent experience requirements at the discretion of the
  authorized instructor conducting the flight review. (i) A flight
  simulator or flight training device may be used to meet the flight
  review requirements of this section subject to the following
  conditions:

  (1) The flight simulator or flight training device must be
  used in accordance with an approved course conducted by a training
  center certificated under part 142 of this chapter.

  (2) Unless the
  flight review is undertaken in a flight simulator that is approved for
  landings, the applicant must meet the takeoff and landing requirements
  of Sec. 61.57(a) or Sec. 61.57(b) of this part.

  (3) The flight
  simulator or flight training device used must represent an aircraft or
  set of aircraft for which the pilot is rated.

The license its self (as the laws currently stand) is good for life, barring you having it revoked for some reason you will not need to fly your check ride again (unless you go for something like an instrument rating or a higher license).

Until recently here in the US you also needed a valid medical certificate. However recent regulation change has altered that a bit. You can read up on some of the changes here as they are still in progress.

On a bit of the more practical side there are some things to consider. For example many people here in the US rent aircraft. Your local flight school or rental facility may impose other rules on flight currency for you to be allowed to rent a plane. Likewise if you own a plane your insurance company may require certain experience or other things in order for you to be allowed to fly your plane. Generally this is based on your experience as well as time in type.


What causes the horn-like noise during the start-up of some jet engines?

Almost all jet engines will have one or more "resonance" conditions where the combination of turbine RPM, mechanical elasticity and aeroelasticity constructively reinforces to cause mechanical or aerodynamic vibration.
Think of it this way:  If you have a slinky spring (mechanically elastic) toy you can hold it by one end and let the rest drop freely below that.  Now if you move your hand up and down at different frequencies (up and down and back up again in 5 seconds, 4 seconds, 3 seconds, 2 seconds, 1 second, 1/2 second) you will find that there is one rate that will cause the most deflection/movement of the spring toy even though you are moving your hand through exactly the same distance. This is the one closest to its resonance.
Now the ductwork and spools of a gas turbine engine are just a little more complicated than our Slinky toy, but still a mechanical (in this case, aero-mechanical) system susceptible to resonance conditions.  The trick is to design the system so that these resonance conditions, which can be mechanically destructive, don't happen often or for very long.  As the turbine RPM increases through the resonance range things start to vibrate (in this case at ~250-275 Hz) wildly enough to create that extra sound.
In fact, the designers of that GE F414 engine could tell you exactly the RPM range where that happens.  The aviators and groundcrew are attune to the sounds of this machine and would likely shut things down and have a closer look if this particular phenomenon didn't happen as expected.
So, the horn-like noise is vibration of the mechanical parts of the engine ductwork and the air flowing through it for the short period of time that the engine RPM and airflow align to make this condition happen.


How is the pressure difference in passenger plane toilets generated?

The pressure in flight is generated by using the vacuum outside. This dosen't work on the ground or at low altitude, so there's a pump as well to draw out the air to create an artificial vacuum.

  Considering that the toilets should also work on the ground, I presume
  pumps are used - on the other hand, maybe the low pressure is stored
  inside the tanks from the last flight?
  Also, pumps would mean the toilets don't work when the aircraft is not
  powered up - is this true?

Not sure about this one, but since the aircraft is seldom not powered when a person is onboard (maintenance can't do much without power either), I can't think of this being a significant problem. There might be a little bit of leftover pressure.

Airbus states that the vacuum pump is powered off the AC power bus, so it may be powered from the ground or the APU when the engines aren't on.

  Also, how was the engineering problem
  solved of keeping the pumps or the tubes connecting to the outside
  free from waste?

As is seen in the picture below, the tank is rinsed out through with the help of a second port on the access cover to clean it out. The rest of the system I believe is designed to last until the next maintenance, when (I think) it's connected up to a high pressure hose to thoroughly clean it out.

A320 Toliet System:

A320 System Details.


How did this incident report detailing a flight taking off and landing at Glasgow result in safety changes at a distant airport?

The precise truth cannot be known without consulting the authors of the report.  However, assuming it was not a typo, there are several contributing factors that may lead to this result.

Primarily, aviation is a very conservative business, and every opportunity to mitigate risk will be taken.

In this instance, not only did the aircraft lose a tire, the tire also damaged the hydraulic "A" line, and the flaps.

The main issue to address was the tires themselves, but it was noted that the tire blowout appeared to occur at "rotation", which puts the greatest stress on the main gear tires.

While the airplane may be about to take wing and unload the landing gear, the moment the aircraft's nose rotates up is the moment of peak main gear loading.  The weight of the aircraft is no longer supported by the nose gear, and not yet supported by the wings.  The elevator pushes the tail and empennage downward in order to raise the nose, which further burdens the main gear.  And during takeoff, the aircraft flaps will be lowered to aid in generating more lift while still at low air speeds, BUT, lowering the flaps aerodynamically causes a nose-down "moment", which makes the elevator's job that much harder, and that additional force is also transferred to the main gear at the moment of "rotation".

A couple ways to help alleviate the burden on the main gear are to not drop flaps as much, and to "rotate" more gradually.  Also, since flaps were damaged in the tire incident, having your flaps tucked up higher puts them less in harm's way of a possible exploding tire.

But why that directive in Malta?

According to the link below, the main runway at Malta Luqa Airport is 11627 feet long (3544m), which is fairly long as runways go, so an aircraft can take its time getting airborne if necessary.

Malta Luqa Airport charts, at SkyVector

It's not the longest runway around, but it's longer than necessary for most commercial aircraft, especially at sea level.  Malta is also a very flat place, with its highest point only 253m above the Mediterranean. (830 feet)  This makes it a reasonable place to use a procedure that would result in a longer take-off roll and more gradual climb (from the less-deployed flaps.)

So there are reasons it would possibly be more doable there than at some other airports.  However, I think the dominant factor is this:

  Boeing 737-33A, registration 9H-ADH, is a Maltese registration (as indicated by the 9H, and the aircraft belonged to Air Malta at the time of the incident.

I used the past-tense, since the current ledger of aircraft registered in Malta does not include that aircraft.  In fact it was transferred (sold?) to Air New Zealand in 2008, and is now in Bahrain, to the best of my knowledge.

737 s/n 27459 registration history

While I do suspect there is more to the story details than we are privy to in that one publication, it's my opinion, as a certified aircraft mechanic and persistent internet sleuth, that the change in practice was made as a matter internal to Air Malta operations at their home airfield.

Bonus: A photo of the actual aircraft, after the incident in question, sitting cordoned off, on the ramp at Glasgow International Airport (GLA).  Click the link above the pic for a little more info, and additional resources.

Boeing 737, registration 9H-ADH

Cheers!


What is the point of making one control surface play the part of multiple control surfaces?

Flaps which only extend over part of the wing will cause lift changes mainly over that part of the wing, which will result in a lift distribution over span which is far from the elliptic ideal once the flap is deflected. Therefore, it makes sense to move the ailerons in the same direction, especially when the inboard flaps are simple camber-changing flaps.

In order to give an aircraft wing docile stall characteristics, the planform should not be elliptic, but be "fuller" (= having more local chord than the ideal ellipse) at the wingtips. With an elliptic planform and an elliptic lift distribution, the local lift coefficient will be identical over the whole wing, and gusts might easily cause a local stall at one outer wing in slow flight. The consequence will be an uncontrollable roll, which can ruin the pilot's day when occurring close to the ground. Therefore, it is better to leave some margin by increasing local chord and adding some washout towards the tips.

Now this wing will have an elliptic distribution only at one angle of attack. If the angle of attack is higher, the lift distribution will be fuller, and if it is lower than the "elliptic" angle of attack, some lift will be missing towards the tips. Both conditions will cause higher induced drag than necessary. Flaps help by adjusting local camber such that if they are set correctly, the spanwise lift distribution will be much closer to the elliptic ideal than without flaps. This requires the flap schedule to make bigger deflection changes towards the root - watch any modern high performance glider change flap settings, and you will see what I mean: The flaperons will change deflection less that the inboard flaps. This has the additional benefit of leaving more margin for aileron deflections.

This is the disadvantage of combined control surfaces: What is needed for one function is no longer available for the other function, because the maximum useable deflection range is limited.

For the nitpickers: Please understand the term "elliptic lift distribution" as "elliptic circulation distribution". Then all is well.


How much does it cost to add a glider rating to a PPL?

If you're in Romania, are a Romanian citizen and are under 23 you can do it for free in the Romanian Airclub.

Otherwise it's 15 eur/winch launch and  25 eur/tow at around 300m.
I'm not sure if there's any deduction from the glider training if you have ppl but I know that if you have the glider licence you get a shorter training plan for motorized aircraft.


How do "tip jet" helicopters cancel the torque effect of the main rotor?

This is a basic physics question, involving Newton's third law of motion  (For every action, there is an equal and opposite reaction.) When a centrally mounted engine applies force to turn the rotor, the equal and opposite reaction creates torque on the fuselage.  With a tip jet, the force is applied by the jet shooting its exhaust perpendicular to the blade, so the reaction is that the blade moves in the opposite direction.

So the answer is that tip jets don't CANCEL the torque, they simply don't create the torque in the first place.


Does the cyclic in a helicopter re-center automatically?

Helicopters (I have flown so far) does not have such detent positions for their controls just because, as you have said, the instability and the effects of controls on other controls. To reduce the workload some helicopters have systems which probably changes from type to type. While AB-206 helicopters does not have a system for cyclic centering or holding its position, UH-1 helicopters have force-trim system to hold the cyclic where you have centered or left.
AS-532 Cougar ( Eurocopter or Airbus Helicopters now. ) helicopter's cyclic has a cyclic-trim system which returns the cyclic to the position where the pilot set by pushing trim-release button on cyclic.
This is all I can tell for now. Not a complete answer for your question but I hope this helps.


How did this plane get into this position and orientation?

Option A is out of the question. This would have been a VERY late and unlikely touchdown. Option B is possible, but option C is the correct answer, especially when zooming in: https://www.google.com/maps/@-33.9413253,151.1742231,145m/data=!3m1!1e3

Judging by the tire marks on the runway (which appear to go left) this is clearly not the first aircraft (an Air China A330 if you wondered) to perform this maneuver.

The reason is clear: taxiway A2 (the high-speed exit just before the runway intersection) appears to be closed for maintenance: https://www.google.com/maps/@-33.9433411,151.17333,205m/data=!3m1!1e3

This is also evident by the following NOTAM:

  Q) YMMM/QMXLC/IV/M /A /000/999/3357S15111E A) YSSY B) 18/09/21 13:00
  C) 18/09/23 19:00 D) DAILY 1300-1900 EXC SAT E) TWY A BTN TWY G AND
  TWY L NOT AVBL DUE WIP TWY A2, TWY A3, TWY A4, TWY B5, TWY B6, TWY B7
  AND TWY B9 NOT AVBL TWY B3, TWY B4, TWY K AND TWY B8 BTN RWY 16R/34L
  AND TWY B NOT AVBL TWY H BTN TWY Y AND TWY A NOT AVBL TWY J MAX 52M
  WINGSPAN TWY B BTN TWY G AND TWY B10 MAX 36M WINGSPAN REFER METHOD OF
  WORKING PLAN 17/003


Exactly what kind of radios are prohibited for passengers inside an aircraft?

There is actually a simple answer, but it probably isn't exactly what you are looking for:  Refer all questions about what is allowed to your specific airline.

Each airline has to come up with their own list of allowable electronic devices, and submit that list to the FAA with appropriate documentation in order to gain approval to allow passengers to use them during flight.

Some airlines allow almost everything as long as it can be put into a non transmitting mode (airplane mode), while some still require ALL electronic devices to be completely powered down at all points during the flight.

Because of this, every airline is a little different and you are required to follow their rules while on their flights.

The GPS receiver would not cause problems, but this doesn't mean that you are necessarily allowed to use it, and there are other things in your phone that could cause a problem though.

In general, no electronic device that has a transmit function may be used because of possible interference though, unless specifically approved.


Will the Boeing 737 MAX 8's software update require recertification of the aircraft?

Nope

Updates like this are generally deployed under an Airworthiness Directive ("AD") and in this case will likely be required although not all AD's technically are. AD's are issued against Type Certificates or serial number ranges, or possibly even individual parts. They are publicly published and when it becomes available the FAA will post it here.


Are there any privately owned large commercial airports?

Building an airport is a very expensive endeavor and usually involves government subsidies or is completely done by the local government. In recent decades, most government owned airports in Europe have however been transformed into companies that both own and operate the airport, usually with the government as initial owner of this company. Since this privatization, some governments have sold their shares of the company resulting in completely privately owned airports.

Going through the 20 busiest airports in Europe from Wikipedia's list, the following airports are completely or by majority privately owned:

London Heathrow Airport owned by Heathrow Airport Holdings
London Gatwick Airport with a majority ownership by GIP
Rome Leonardo da Vinci-Fiumicino owned by Aeroporti di Roma (3.8% government owned)
Zürich Airport owned by Flughafen Zürich AG (38.38% government owned)
Copenhagen Airport owned by Københavns Lufthavne (39.2% government owned)
Lisbon Airport owned by Vinci SA, although operated by the government

The following airports are run by a private company, but they are majority government owned:

Paris Charles de Gaulle Airport and Orly Airport owned by Groupe ADP (50.6% state owned)
Amsterdam Airport Schiphol owned by Royal Schiphol Group (92% government owned)
Frankfurt Airport owned by Fraport (51.47% government owned)
Madrid-Barajas, Barcelona-El Prat and Palma de Majorca owned by Aena S.A. (51% owned by ENAIRE, which is a public corporate entity)
Munich Airport owned by Flughafen München GmbH (100% government owned)
Oslo Gardermoen owned by Avinor (100% state owned)
Manchester Airport owned by Manchester Airport Holdings (64.5% government owned)

The following airports are directly owned by the local governments:

Istanbul Atatürk Airport
Dublin Airport

I am not sure who exactly owns Sheremetyevo and Domodedovo in Moscow.


Is it possible to prevent plane accidents due to fuel explosion?

"We know that most of the plane accidents and deaths result from the explosion of fuel tanks in the planes"
This is a fallacy. Most deaths don't happen because of explosions, but because of impact damage, fire, and inhalation of toxic fumes (in no particular order).
Next to that, many people tend to get killed because they are crushed by fellow passengers during evacuations. And some die on the ground being run over by emergency vehicles or from environmental conditions (heat, cold, wildlife).
Ratchet Freak correctly points out why your "solutions" won't work (in fact one of them will make the problems worse). And yes, research is being done and has been done. Modern jet fuel has a much higher flame point and vapour pressure than does regular gasoline as a result. Fuel tanks are fitted with baffles and sometimes coolers to keep the fuel liquid so it doesn't explode easily. This is in part a result of what happened to TWA800, one of the very few accidents to be caused by a fuel tank explosion (and there the explosion was itself only possible due to a combination of rare circumstances and chance events, made worse by maintenance problems with the aircraft).
The image of aircraft (and cars, trains, ships, buildings, anything really) blowing up in a wall of flame at the least trouble is one created and perpetuated by Hollywood and has no reflection in reality whatsoever.


How does washout increase static pitch stability in subsonic swept wings?

Since its earliest days during the pioneer era, washout on a swept wing has been accurately described as "putting the tail at the end of the wing." It works in exactly the same way as a tail stabilizer.

As long as the change in moment of the rear surface is greater than the change in moment of the forward surface the plane will be statically stable. It matters not whether the tail is inboard, outboard, moved ahead of the wing (as a canard), tacked on the end of a swept wing, or even tacked on the back of a straight wing in the form of a reflex trailing edge.

On a straight, unswept wing washout can delay the stall a little, but stalling is a complex subject and best treated separately.


How can the Perlan II glider climb to 90,000 feet?

Perlan II will climb to extreme altitudes on wave lift, not thermal lift. Wave lift is created when strong winds blow approximately perpendicular to a mountain range, and the wind speed increases steadily with altitude. This creates a standing wave in the atmosphere, kind of like the ripple behind a rock in a fast moving stream of water. On the leading edge of the wave, air is moving up, and that's where gliders fly. Standing waves can reach very high into the atomosphere, which is why Perlan II is expected to reach 90,000 feet.

Perlan II is different from normal gliders in that its wing is optimized for minimum sink, instead of best glide ratio. It's meant to float along while losing a minimum of altitude, which makes sense if it's going to fly in nothing but wave. Normal gliders are usually optimized more for gliding long distances, for which glide ratio is more important than minimum sink. Interestingly, Perlan II's wing looks a lot like RC model glider wings, which are also optimized for minimum sink, since RC gliders don't typically fly cross country.


Twin engine helicopters: is the throttle controlled separately for each engine or together?

Most employ separate throttles, either twist-type, on the collective or levers in an overhead quadrant.

Bell products use duel collective mounted, twist type throttles, in series. Sikorsky uses overhead levers. French SA > AS > Eurocopter > Airbus > Leonardo use levers overhead. Agusta uses overhead levers.


Source: FCOM A320 familly

From the flight crew operating manual (FCOM) about the pack flow selector (4):

  Permits the selection of pack valve flow, according to the number of
  passengers and ambient conditions (smoke removal, hot or wet
  conditions).
   LO (80 %)  - NORM (100 %) - Hl (120 %).

  Manual selection is irrelevant in single pack operation, or with APU
  bleed supply. ln
  these cases, Hl is automatically selected.

  lf LO is selected, the
  pack flow can be automatically selected up to 100 % when the cooling
  demand cannot be satisfied.

So to answer your question directly:

The normal flow (100%) is when the selector is on position NORM.
Position HI adds 20% to the air flow, and LO removes 20%.

In addition:

In LO position, the flow can be increased by the controller up to 100% in case the temperature cannot be obtained with only 80%.
In case of single pack operation, the flow is automatically set by the controller to 120%.


In the US, they are assigned by a division in the FAA called Aeronautical Information Management (AIM), per FAA Order JO 7400.2J (Procedures for Handling Airspace Matter), section 3-3-2:

  a. Service area office are responsible for assigning and changing names of NAVAID and aeronautical facilities, and must follow the instructions contained
  herein and in FAAO JO 7350.8, Location Identifiers, Chapter 1.

  b. AIM is responsible for issuing five−letter names for radio fixes, waypoints, marker beacons, and compass locators. Five−letter names must be issued by AIM to the Terminal Procedures and Charting Group, Major Military Commands (MAJCOM) and Air Route Traffic Control Centers (ARTCC) for future assignments.

It's conceivable they accept suggestions from ARTCCs or other entities. I don't know. I doubt paid sponsorship is approved but have no first hand knowledge there. Suggestions are probably casual and intormal.

They are often quite amusing, like ITAWT ITAWA PUDYE TTATT. Very often enroute fixes are named for small towns or other points of interest near the fix.


What is the relationship between STARs, IAPs, and feeder routes?

Definitions
From the FAA's Pilot/Controller Glossary, an instrument approach procedure (IAP) is:

A series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.

A feeder route is:

A route depicted on instrument approach procedure charts to designate routes for aircraft to proceed from the en route structure to the initial approach fix (IAF).

A standard terminal arrival (STAR) is:

A preplanned instrument flight rule (IFR) air traffic control arrival procedure published for pilot use in graphic and/or textual form. STARs provide transition from the en route structure to an outer fix or an instrument approach fix/arrival waypoint in the terminal area.

So you can see that a STAR and a feeder route serve the same general function: to allow IFR aircraft to transition from the en route structure (meaning Federal airways, the Victor, Tango, J- and Q-routes) to the beginning of an instrument approach procedure. The major difference is that STARs are published for busier airports to make things easier and more predictable from ATC's point of view; a STAR can contain any number of waypoints/fixes and, more importantly, can have altitude and speed restrictions pre-published at those fixes so ATC doesn't have to issue them to each individual arrival.
Example
Let's look at the ILS Runway 11 approach into Portland International Jetport (PWM). We can see that there are three Initial Approach Fixes: Kennebunk VOR/DME, BUXTO intersection, and PARSO intersection. If you can somehow navigate to any one of those three fixes, you can follow the approach procedure to safely get down to the ground (or at least pretty close to the ground).

Now say, for example, you're navigating via V93 from the southwest. When you reach CON you could continue to follow V93 to ENE and start the published approach by flying on the ENE030 radial to BUXTO and performing the hold-in-lieu-of-procedure-turn. But that takes you rather out of your way, so if you could you'd rather start the approach at PARSO and avoid having to perform a procedure turn.
Well, PARSO is on V3, so you could fly CON.V93.SATAN.V3.PARSO. But that still isn't the most direct route.
Happily for you there's a published feeder route starting from CON! When you arrive at the VOR/DME you leave the airways and navigate on the CON067 radial directly to PARSO. Hooray!

Enroute L-32 IFR chart

This plan might work if you were flying a Skyhawk at 5000 feet. But say you're flying Southwest 1982 from Baltimore, descending out of the flight levels at 250+ knots. ATC would rather have you flying a certain procedure that's the same as all the other jets coming in to Portland, and your dispatcher knows this—so they've filed for, and ATC has cleared you via, the SCOGS THREE arrival.

Some time before you reach SAACO, and probably long before then, ATC will tell you to expect Runway 11. Therefore, when you reach SAACO, you will make a left turn towards BIDDE and continue following the published route until you reach BUXTO. By this point ATC has cleared you for the ILS Runway 11 Approach, so you transition from the STAR directly onto the instrument approach. Note that you arrive at BUXTO on a track of 081, meaning you only need to make a 29º turn to intercept the localizer (track 110).
A different example
The SCOGS arrival is designed to get you from the enroute structure down to the ground with little-to-no ATC intervention. But at many even busier airports, the arrival will not smoothly transition onto an instrument approach. Instead, you will depart the final fix on a published heading (likely the radar downwind heading) and expect vectors to final from ATC. This allows ATC to give you extended vectors, or shortcuts, as necessary to account for the mixing of different arrival streams. The arrivals into Charlotte/Douglas International are like this, for example the CHSLY FOUR:

If you're landing Runway 23 the arrival has you navigate to JEPHS, the initial fix for the ILS approach for that runway. But if you're landing Runways 18 you come off the arrival on a heading for a left base, while if you're landing Runways 36 you're on a heading for a right downwind.


What is the relationship between EGT, Fuel Flow, N1, N2 and Air Temperature?

I am not really sure what sort of engine failures you want to predict, but ECTM is usually used to detect things such as;

Worn air seals
Blade tip wear (compressors and turbines)
Compressor fouling
Eroded blades and turbine nozzle guides

These hardware issues cause changes in the “state variables”;

N1 (LPC) compressor efficiency
N2 (HPC) compressor efficiency
N2 (HPT) turbine efficiency
N1 (LPT) turbine efficiency

These changes in component efficiency then result in changes of the engine parameters;

N1 rpm
N2 rpm
Fuel flow
Exhaust gas temp
etc.

By detecting changes in the measurements, ECTM aims to tell you which module (LPC, HPC, HPT, or LPT) has degraded. Usually, it’s not possible to say why the efficiency has decreased (i.e. you can’t tell if it’s erosion of the blade leading edge, or worn blade tips), you can only tell which module is affected.

But the relationship you want between changes of efficiency and the measured parameters, is very complex. For that step, you need a performance simulation program, to give sufficient accuracy if you are actually going to apply the approach to data from a real engine. Otherwise, all one can say is, when an engine degrades, fuel flow, temperature, and rpms will go up. And they go up for most (or all) of the faults above. So, unless you know how much they change for each fault, you can’t tell which module has degraded. Then, your method is just saying “the engine has degraded” (not so useful), rather than why (and, only the LPC needs a repair, for example, which is cheaper and quicker than an HPC repair, because it requires a lot more disassembly).

But, if all you want to do is test an approach in theory, you could just make up the increase in each parameter, it doesn’t have to be accurate, because it’s just a mathematical example, you are not going to apply it to an actual engine, so the predicted effects of degradation don’t need to match reality closely. Just make up 4 different patterns of degradation;

degraded LPC: 50 rpm N1 increase, 200 rpm N2 increase, 5% inc in fuel flow, 200 deg inc in EGT
degraded HPC: 100 rpm N1 inc., 200 rpm N2 inc, 7% in in fuel flow, 150 deg inc in EGT

etc...

Then, create multiple examples of each fault by add a random amount of noise to each parameter, say < or up to 1% of full scale value (and you can make full scale up as well, let’s say, N1 = 8,500 rpm, N2 = 12,250 rpm, fuel flow = 3.2 lb/s, EGT = 650 deg C.)

Now, you have examples with noise, of known faults. See how well your method can correctly find the faults....

Sure, it’s a little crude, but if you can’t get hold of a performance simulation program that lets you change the efficiency of the modules to generate the degraded fault behaviour, at least it lets you do something. You can play around with the numbers, and see what size enables you to detect a fault, and what size does it start to get confused/ wrong.


Where can I find FAA procedure amendments?

As far as I know, you're looking at them: that number is telling you that the current procedure is AMDT 1 14317. Have a look at the other procedures throughout the same document and you'll see they're all numbered in a similar way.

In your example, AMDT 1 14317 is Amendment 1, made on November 13, 2014. The date format is a Julian date or, if you prefer, YYDDD: it's the 317th day of 2014, i.e. November 13, 2014. The format is explained in the FAA's FAQ on obstacle data (and it's mentioned in other documents).

If the procedure has never been amended it's marked ORIG, e.g. at Beaver Muni (U52):

  BEAVER, UT
  BEAVER MUNI (U52)
  TAKEOFF MINIMUMS AND (OBSTACLE) DEPARTURE PROCEDURES
  ORIG 07242 (FAA)
  TAKEOFF MINIMUMS: [...]


I believe PPL also requires some night flying time (at least the 141 school I am at does). I believe Sport Pilot License is not valid at night so you may have to gain some night landings and hours to go for the check ride as well. However I do see that you have all the hours signed off so I will assume this includes night hours.

But AFAIK you will need to pass the written, oral and check ride to get the PPL.

As per your updates this is what you will be checked on for your check ride. Its a bit dated but this video has some nice coverage on what you may get on your oral exam. If you have the Jeppesen study materials you should have some good lists of what you will find. I did find this in the FAR

  §61.103   Eligibility requirements: General.
  To be eligible for a private pilot certificate, a person must:

  (a) Be at least 17 years of age for a rating in other than a glider or balloon.

  (b) Be at least 16 years of age for a rating in a glider or balloon.

  (c) Be able to read, speak, write, and understand the English language. If the applicant is unable to meet one of these requirements due to medical reasons, then the Administrator may place such operating limitations on that applicant's pilot certificate as are necessary for the safe operation of the aircraft.

  (d) Receive a logbook endorsement from an authorized instructor who:

  (1) Conducted the training or reviewed the person's home study on the aeronautical knowledge areas listed in §61.105(b) of this part that apply to the aircraft rating sought; and

  (2) Certified that the person is prepared for the required knowledge test.

  (e) Pass the required knowledge test on the aeronautical knowledge areas listed in §61.105(b) of this part.

  (f) Receive flight training and a logbook endorsement from an authorized instructor who:

  (1) Conducted the training in the areas of operation listed in §61.107(b) of this part that apply to the aircraft rating sought; and

  (2) Certified that the person is prepared for the required practical test.

  (g) Meet the aeronautical experience requirements of this part that apply to the aircraft rating sought before applying for the practical test.

  (h) Pass a practical test on the areas of operation listed in §61.107(b) of this part that apply to the aircraft rating sought.

  (i) Comply with the appropriate sections of this part that apply to the aircraft category and class rating sought.

  (j) Hold a U.S. student pilot certificate, sport pilot certificate, or recreational pilot certificate.

In regards to section H you have to pass the practical for the PPL specifically so it would seem you will be retested. Although part J would allude to the fact that your SPC comes in here it seems that it just counts in place of a student pilot certificate.


On modern fighter aircraft, why do most carry a rotary cannon when they tend to have little use against aircraft?

I think this question is highly opinion-based and should be closed.

But here are my $0.02

Historically there were attempts to remove cannons but turns out too early: Missiles are not that good. The benefit of fallback weapon indeed outweight the weight.

  MIG21 VS RF-4C

  One instance of combat during Project Dark Gene was an engagement on
  November 28, 1973 between an RF-4C aircraft piloted by IIAF Major
  Shokouhnia and backseater USAF Colonel John Saunders and a Soviet
  MiG-21 flown by Captain Gennadii N. Eliseev. The Soviet pilot fired
  two Vympel K-13 missiles at the Iranian aircraft, failing to destroy
  it. He was ordered from ground control to press his attack at any
  cost, and with his cannon jammed after the first shot,[8] he continued
  by ramming into the Iranian aircraft and losing his life in the
  process. He struck the RF-4C's tail assembly with his wing and then
  flew into high ground. It was the first deliberate jet-to-jet ramming
  by a Soviet aircraft during an interception, a practice common in the
  propeller age of World War II. Eliseev was posthumously awarded as a
  Hero of the Soviet Union.[3][9] The crew of the RF-4C aircraft were
  captured by Soviet ground forces and released after 16 days.2[10]

US military reached the same conclusion around the same time as well, to add cannons to F-4 Phantom II.

Maybe now is the time to rethink this question again after 40+ years advancement of AA missiles. But if you ask the pilot, for the same weight, do they want fuel, gun+ammo, or nothing? A significant portion, if not the majority, would pick the gun I guess.

A lot of fighter pilots, or even astronauts, carry pistols. How useful is that?


Which aircraft is depicted on 1941 U.S. Post Office airmail stamps?

It appears to be only an artist's conception and is an amalgam of several different designs, but apparently largely based on the Douglas DC-3 aircraft, the Lockheed Electra, and the Beech 18.

The livery bears a striking resemblance to American Airline's DC-3 sleeper service, which operated during that era.

http://usstampgallery.com/view.php?id=1021c6191539bc1ca404bccf78595b7fdc0f06fd


Is there a 3-dimensional airspace viewer?

You can download Google Earth airspace files for most countries, and move through them in 3D to explore what they would look like for various areas.  For example, you could see where you would be "under" a Class B shelf, or where you might navigate to avoid B/C/D airspace and "surface airport E airspace" (if you're flying an ultralight, for example).

These files can be downloaded from 3dairspace.org.uk

Here is a screenshot I just captured of the Seattle Class B, looking northwest from the southeast corner.


Check for additional NOTAMS concerning the PIE VORTAC.  It appears that, for whatever reason that VORTAC radial is no longer functioning well at lower altitudes and, for whatever reason, the FAA is opting to not repair it.  As it's a needed navigational aid for that STAR, the additional NOTAM applies.  I'd guess the Orlando FSDO is in the process of decommissioning that STAR and issued NOTAMS until then.

UPDATE: It appears that this VORTAC out in Clearwater, FL has been malfunctioning, causing aircraft to stray off course and overfly noise sensitive areas at low altitudes, causing the Tampa airport management to receive a great deal of complaints.  The FAA has up to now been faced with the repair tasks on that navaid.  But it appears that, with the gradual decommissioning of VOR stations throughout the country combined with the preeminence of GNSS navigation, they have elected not to make the repairs and just leave the VORTAC as is for the foreseeable future.


What year did the seat belt sign come in to use?

The earliest reference to seat belt signs I can find is Scheduled Air Carrier Rules, 14 C.F.R. (1941)

§ 61.342 Seat belt sign. An aircraft shall not be operated in
scheduled air transportation unless a suitable means for warning
passengers to fasten seat belts is provided. [As added by Amdt. 129,
CAR, Sept. 5, 1941, effective Oct. 1, 1941, and Amdt. 130, CAR, Sept.
12, 1941; 6 P.R. 4691, 4753]

https://www.loc.gov/item/cfr1943001-T14CIP61/
The amendment appears in 6 FR 4753
https://www.loc.gov/item/fr006181/
It's unclear where the motivation for this regulation came from, but it is likely mentioned in the Civil Aeronautics Board's meeting minutes for September 5, 1941. Unfortunately it does not appear that these minutes have been digitized. The relevant records should be available in the National Archives RG 197.2.


How is vertical speed managed in Airliners?

Vertical speed is managed, primarily, with controls.

Lift is proportional to square of speed and to angle of attack¹ and angle of attack can be adjusted using the elevators. Pilot, or automation, use those to control the flight path of the aircraft.

As the aircraft accelerates along the runway, at some point the pilot pulls on the control column, which turns the elevators up and the resulting downforce on the tail lifts the nose off the ground². That increases the angle of attack—because the aircraft is still moving horizontally—, lift exceeds weight and the aircraft accelerates upwards.

As it starts to accelerate upwards, the pilot eases the pull on the control column to prevent the aircraft pitching up further. And as the aircraft accelerates upward, the angle between direction it is flying and pitch—that is the angle of attack³—decreases again, until the forces get in balance. Then the aircraft is in steady climb.

When the aircraft reaches the top of climb, the pilot⁴ pushes on the control column. This causes the aircraft to pitch down, which reduces the angle of attack, and thus lift, and the aircraft starts to accelerate downward, that is slow down the climb. At the point the aircraft is moving horizontally, the control column is pushed back to get the forces back in balance.

Now for the details of operating the controls, the longitudinal stability comes into play. Aircraft are normally⁷ designed to be longitudinally stable. That means the aircraft will pitch up as its angle of attack decreases—which increases it again—and pitch down as its angle of attack increases—which decreases it again. Net result is that when the elevators are left alone, the aircraft will maintain specific angle of attack.

As the aircraft climbs, it will tend to slow down unless engine power is increased, because its potential energy increases and it will be taken from kinetic energy if the engines are not providing enough⁸. And as it will slow down, its lift will decrease, so its angle of attack will increase, but that will cause it to pitch down due to stability. The net result is that it will refuse to climb unless enough power is provided.

Similarly when it descends, it will tend to accelerate, because the potential energy will be converted to kinetic⁹ and that will increase lift, which will decrease the angle of attack and the stability will make the plane pitch up. So it will refuse to descent unless power is reduced.

So in the end, vertical speed is actually managed by thrust levers. Which is also much more easily proven from law of conservation of energy.

¹ Up to critical angle of attack, where stall occurs.

² This is called rotation.

³ Angle of attack is properly defined as angle between the relative wind and the chord line of the wing, but aircraft axis is often used in practice. This makes things simpler as you don't have to consider the angle of incidence—angle between the aircraft axis and wing chord—especially since many aircraft have twisted wings where the angle of incidence changes along the span.

⁴ Or more often the autopilot. While take-off is always flown manually, up above FL290⁵ use of autopilot is required as it gets too tiring and unreliable to maintain the altitude by hand with enough precision to ensure separation⁶.

⁵ Flight levels are defined by pressure corresponding to given altitude, in hundreds of feet, on a standard day. So FL290 is 29,000 ft, but more when it is warm and less when it is cold. The reason is that pressure can be measured easily and quite accurately and flying at sufficiently different pressures ensures the altitudes are also different.

⁶ Originally the minimum separation was 2,000 ft above 29,000 ft due to the lower accuracy of altimeters and lower accuracy of flying as the aircraft move faster in the thinner air up there. But because all the aircraft wouldn't fit up there with those separations, 1,000 ft was allowed provided the aircraft is flying on autopilot and has sufficiently accurate altimeter. This is called reduced vertical separation minima

⁷ Some fighters are intentionally designed as unstable, because it allows faster control response. All such aircraft have computerized controls that compensate this, otherwise it would be very tiring to fly.

⁸ Alternatively, consider that the lift vector is tilted aft, and thus has bigger aft component, which is drag. Physics always has multiple ways to analyse a situation.

⁹ The lift vector is tilted forward in descent, so there is some forward component that accelerates the aircraft.


Technically speaking, conformal tanks don't take up hardpoints, so I'm not sure what we have today has an equivalent in older designs.

Otherwise, I'd say somewhat common; streamlined fuel tanks and other conformal packages have been used for quite a while in several different designs.

Some World War II Supermarine Spitfires used what was called a "slipper tank" - a streamlined package of up to 90 gallons (additional source).

The early 1960s-era English Electric Lightning used a 'conformal ventral store' that could hold either a fuel tank or rocket engine (?!). The Gloster Javelin used a similar set of "bosom tanks".


Why do some aircraft have multiple ailerons per wing?

General Reasons

There are three main reasons for having multiple ailerons per wing on large aircraft:

Aileron Reversal

On a large aircraft, at high speeds a deflected aileron can twist the wing enough to cause a net roll torque opposite to the one intended.  The further out on the wing an aileron is, the more likely this problem is to arise.  For high-speed aircraft, this necessitates an outboard/inboard aileron, with the outboard being locked out at a certain speed limit. On the Airbus A380, the downwards motion of the outward aileron is locked out at 240 KIAS, and upward motion at 300 KIAS.

Systems Redundancy

Another issue is that on most large aircraft, it is simply infeasible to have cables running through the aircraft, so hydraulic systems are used instead. Having ailerons split would allow for more redundancy of system failures, allowing more controllability in these failure conditions.

Load Alleviation Function

Building on what Bret Copeland has already discussed in his answer, multiple ailerons can be used by fly-by-wire computers to flex the aircraft's wings in a specific manner to allow for less loading on the wing during cruise (counteracts the wing's natural tendency to flex upwards), as well as allowing for dynamic turbulence alleviation.

One of the examples of using this is in Airbus's Safety First magazine (July 2012), where they use the flexibility of having three ailerons to tune out lateral accelerations in the rear of the aircraft changing the gains of each of the controls. By being able to move the centre aileron a fraction after the inner aileron, they managed to avoid these initial shifts during flight testing of the A380.

Other Aircraft

The majority of airliners have multiple ailerons, however in some instances (such as the Airbus A310), there is no outboard aileron -- this function is replaced by spoilers.

Another example of using computers on multiple ailerons is the Boeing 747-8, with the use of the outboard aileron to fix issues relating to the development of flutter in certain extremes of the flight envelope, called the Outboard Aileron Modal Suppression (OAMS) system.


What is the rationale behind placing arrestor gear on a long runway?

I can think of 4 reasons:

Pilot Training to use the cable arresting system
Rejected takeoff, fighters don't usually have reversers and may take long space to arrest
Under certain bad runway conditions, like ice, the required landing distance may be very high, and a military airport should work (ideally) under any weather condition
Runway partial unavailability, if part of the runway is unavailable, with an arresting cable system you can still use the other part. This is especially important during a war, when the enemy may damage half of the runway and you don't have time to fix it. Military airports are designed considering also these possibilities.

Source for 3 and 4: https://www.wbdg.org/FFC/AF/AFTTP/afttp_3_32.12.pdf


Are parked airliners always connected to a ground power unit?

Being connected to ground power is the usual case, but there are exceptions.  Typically, the most common reason to not be connected is if the ground power unit at the gate isn't working.  (Because aircraft use 400HZ AC current at some fairly high amperage, you can't just plug in directly to the standard electrical mains -- a dedicated Ground Power Unit is required, which incorporates some safety features so that equipment isn't damaged even if the unit is unexpectedly disconnected.)

Other reasons could be in the case of a quick turn, the pilots signal to the ground crew not to bother.  Also, if high winds prevent the ground crew from connecting the large yellow air conditioning hoses to the aircraft, then the jet's APU will be running anyway to provide air conditioning, so there's no great need to connect & later disconnect the ground power... the pilots just let the APU power the electrical system as well at this point, saving the ground crew a couple of steps & a couple of minutes.

All of this is less common than the alternative case, though, where the ground power and ground air are connected and the APU is shut off.  The air & electricity from the gate are cheaper than running the APU to provide those, so most often we prefer to turn off the APU until we get close to time to push back.


How to get data from Aeronautical Fixed Telecommunication Network?

So the AFTN is essentially one of the first e-mail systems, before email was even a thing. If you want to pass a flight plan, you'd select the AFTN addresses for the owners/ managers of every FIR along the route, as well as all the different offices at your destination airfield that would need to know you're coming. Unfortunately (or fortunately, depending on your perspective) unless you have access to an AFTN terminal and your AFTN address was included in the To: column, you'd have to hack the system to gain access.

And when I say "Hack", it's not necessarily in the traditional sense. The AFTN dates back to the 1950's, and maybe earlier. It is unencrypted and built on good ole' fashioned copper wire! Whilst I'm not a hacker, I believe one needs to gain physical access to the system in order to exploit it.

Nations which are considered "developed" have mostly transitioned to a digital version of the system called Aeronautical Message Handling System (AMHS). Because the AFTN copper wires are still in use in many developing nations, "bridges" are in place to digitize the analog signals allowing for interoperability between the two systems.

So the long of the short, no, you cannot legitimately access any and all AFTN messages whilly nilly.


How do planes maintain constant speeds at cruise altitudes?

The autopilot pitches to hold the flight level when it captures the level at the top of the climb, so later on as the aircraft gets lighter and wants to climb further, the A/P will lower the nose as required to hold the flight level (the A/P is able to move the elevator through its servo's link to the elevator controls; it can also work the trim if the servo has to hold too much out-of-trim force for too long, to avoid wearing out the servo - in effect it does what the human pilot does, more or less).  It happens very slowly and significant amount of pitch over is not apparent until some time has passed.

Effectively, AOA is being reduced by the A/P to compensate for the reduction in wing loading.  Because induced drag is being reduced, if thrust is not reduced to compensate for the drag reduction, the A/C will accelerate.  If your clearance requires you to maintain a certain Mach #, this is a problem.

If the jet has an autothrottle system that can be configured to hold a Mach # while the A/P holds the altitude, the thrust is adjusted automatically.  If not, the pilot monitoring at some point will notice the Mach # creeping up, and will reduce thrust in very small increments compensate and maintain the flight planned/cleared Mach #.


Are there any documented example usages of film (ie, film film, not video or digital) for in-flight entertainment?

I know film projectors were definitely used on early 747s - converting part of the passenger area into a theater is part of the design. I was able to dig up the photo below showing the projector mechanism, which is pretty impressive to look at.

I'm not sure whose system that is, but it looks like a 35mm projector so it probably predates the TRANSCOM cassettes.

Can't help you with #2 or #3 though.


Ratchet freak gives already most of the reasons. I might add that on a grass field the taildragger is easier to handle. The relatively high drag and long lever arm of the tailwheel or skid will help to pull the aircraft straight at low speeds when rudder control power is low. On a hard surface, however, the tricycle gear is easier to handle. Also, not only the weight, but also the drag of two wheels is less than that of three.

If you look at modern airplane designs, those where weight must be kept low (like aerobatic planes) still have a taildragger gear. It is also used in gliders and motor gliders, because they will operate mostly from grass strips and do not want to include internal space to accommodate three retractable wheels.

Big taildragger designs from the early days vanished with the emergence of concrete runways from the 1930s on and the need to brake more during rollout when wing loadings and landing speeds went up. On concrete runways, the tricycle gear handles better and gives much better visibility. Without the ability to brake hard, the rollout lengths of  taildraggers would prohibit todays wing loadings. With retractable gears the drag disadvantage is no more, and the increased weight can be tolerated.


Is it possible to do a Live-stream web cam on an airplane over the oceans?

No, there is no mid-ocean real-time streaming video useful for positioning purposes.


What are the pros and cons of practising figure-eight landings on perpendicular runways?

There's nothing stopping you from doing this at an untowered airfield, at least in the US, UK and most of the places I've flown to. There just isn't any benefit. What you should be looking to do is keep up the practice you need to fly safely, which is the spirit of the law rather than the letter of the law which is to maintain currency within regulation.

Could you fly some weird-ass pattern and save about 5 bucks? Sure! Does cutting corners make you a pilot I'd fly with? Absolutely not, because you are looking for ways to economize rather than fly diligently. Flying the pattern is good because it puts you where other pilots expect you and keeps you out of conflict, it also means you know what to do when you arrive at an airfield for an approach. If you're constantly flying some strange bent figure-eight you're bound to mess it up and that could get you into trouble. Take-offs and landings are the busiest and most dangerous times when flying, the whole point is to standardize and reduce risk, if you are flying to a different runway every time the approach constantly changes which isn't good. A good landing comes from a good approach, which starts from a consistent circuit.

Flying the same pattern is also good for your practice and improving your technique. Flying repeated patterns with the same wind conditions means you practice in those conditions until you nail them. It allows you to hone your technique. If you have a different wind, runway and visual cues every few minutes you don't get the consistency to learn what you're doing wrong and improve it.


Why do the A320's centre tank pumps stop working 5 minutes after the low level has been reached?

To elaborate on Ron's commment, the pumps are timed because the when the level of the center tank is depleted to the minimum level that can be sensed by a low level sensor, there is usually still residual fuel sloshing around that the pump is able to draw.  For both electric pumps and ejectors, you don't want them sucking air for extended periods, so you want to be able to fully deplete the tank without having the pumps run too long un-ported.

Airbus would have done testing to establish the average time to suck the tank completely dry, added a margin of some sort, then added the timer to the low level shutoff signal with the appropriate delay to achieve that end.


Why are flight simulators bad at predicting drag and lift values at high angles of attack? (the nonlinear flow regime)

Laminar flow is easy. While there is a complete set of differential equations that describes any fluid flow, there is a wealth of simplifications and assumptions that you can use on laminar flow. This means that X-Plane doesn't need to model all the air around the wing, but can do the calculations based on wing profile and local velocities. Everything is relatively linear, so you can just change some variables and use predetermined parameters. Furthermore, it's completely time-invariant in steady state. You can now easily solve the equations, integrate the calculated pressure profile along the wing, and done!

For turbulent flow, none of that holds. The current way of simulating turbulent flow is to do a Finite Element analysis or similar (e.g., FDM). Basically, you will need to consider all the air in a large volume around the wing, divide it up in a small grid and simulate it. For a good calculation, this takes in the order of seconds to minutes for a single 2D cross-section on my pretty decent laptop. And then we're neglecting the 3D influences. Furthermore, turbulent flow changes w.r.t. time. For example, open your car window on the highway - you will hear the wind roar and pulsate. This means that you will need to get your previous pressure- and velocity field, and use that as a starting point for your next FEM/FDM analysis. Finally, turbulent flow is extremely hard to predict correctly, even with above methods: a slightly rougher surface, a small bolt or a small wind gust can delay flow separation for a few inches, completely invalidating your results. Perhaps this YouTube video (note: this is not simulated in real time!) might shed some light on the vast complexity and time-dependency of turbulent flow - and remember that your horizontal stabilizer will see disturbed air in stall conditions, making it necessary to simulate the entire flow field around the airplane for a correct simulation, not just the wing sections.

Of course, X-plane has a framerate measured in frames per second, not frames per hour. This means that they use a bunch of assumptions to calculate the wing lift. I'm guessing they just have some values for location of flow separation and turbulent pressure for some fixed velocities and angles, and interpolate to the actual values. My guess is that they also have some parameters that aren't actually calculated, but are chosen such that some very basic maneuvers are possible like spin recovery, regardless whether these values correspond to any actual physical phenomena - it's a game, after all.


Is it possible to install a bike rack on a Cessna 172?

Is it practically possible to do that? Is it okay in terms of
  weight, CG?

Bikes (depending on make and model) are not all that heavy and in this picture they are more or less center mass and would most likely fall in the CG range.

  aerodynamics

Again this depends on the bikes and the placement but with proper care you could be ok. Admittedly a bit different these bikes would create no more drag than say a wing walker would and people have been doing that for some time,

(source)

keep in mind bi-planes fly a bit slower than a 172. But on the small vehicle transit front the PBY-Catalina carried a full sized rowboat under its right wing for use when you arrived at your destination. Interestingly it seems to be mounted backwards which I would think is the non aerodynamic way to mount it...

(source)

It looks like at least one guy has actually managed to pull this off in New Zealand

(source)

  In case you were wondering if it’s legal, the Civil Aviation Authority
  of New Zealand has approved the design.

And he used a Cessna 185. Important to note that these are mounted under the wing which keeps them out of the way of the rudder as Dan mentions but more importantly should anything go wrong the bike would shear away and fall down away from the aircraft instead of back into the rudder.

It looks like this kit plane also offers a similar rack.

  ....If it was possible, would there be any chance it gets certified for use?

In New Zealand yes, in the US under the FAA, depends how good you are at paperwork.


Is it ok to use an iPad (or similar consumer hardware) and electronic charts for GA in Europe?

No, these kind of apps (AirNav, VFRNAV etc.) are not meant to replace paper charts. You'll find phrases like this on most of the websites which offer those apps you will find paragraphs like this:

  Please note that this software is not intended to replace a certified navigation device. You should always use official aeronautical documentation when preparing and performing a flight. You should always use certified navigation devices when performing a flight. [Source: https://itunes.apple.com/us/app/air-navigation-pro/id301046057?mt=8 ]

There is certified software like for example Jeppesen Mobile TC available.


What is the typcial descent rate of a helicopter?

That is of course dependent on airspeed at approach, and the approach angle. I have a flight manual of an older type helicopter, I cannot reproduce the contents, but it shows True Airspeed on the horizontal axis, Rate of Descent on the vertical, and a set of inclined lines for the angle of Descent.

In the Emergency Procedures - Normal Approach, an Angle of Descent of 8 - 10º is specified, and a typical TAS of 65 knots. This amounts to a Rate of Descent between 800 and 1100 ft/min. Maximum allowable ROD at that speed is 1600 ft/min which is marked as Approximate Autorotation.


Is there a time limit after the ATPL theory exam to get the license?

Generally you have 7 years for your ATPL theoretical knowledge, but actually it depends whether you already have Instrument Rating and Commercial Pilot License. If you do not have CPL and/or IR, you have only 36 months. If you have IR, you have 7 years.

Moreover, according to FCL.025(c), you have to pass your IR in 36 months after the theoretical exam (nevertheless, IR or ATPL), and then, if those exams were ATPL (I believe that you are going to pass ATPL without separate IR and/or CPL theoretical exams), your theory will remain valid 7 years from the date of your IR.

For more information you can refer this document, part FCL.025(c)(1) and FCL.025(c)(2).


Since when are ground-based starting devices no longer in common use? Are there any jetliners flying that would still require them?

What was uncommon about the experience in Harare, Zimbabwe that you reference in your question was the arrival of a 747 with an inoperative APU. If I had to bet money, I would bet that they had never had that happen, or if it had, the captain had enough sense to leave an engine running. Harare's ground crew experience was having to start much smaller engines requiring far less pneumatic power from the ground carts. Thus pneumatic carts (huffers) that had had their output degrade over time still had sufficient output to start smaller engines.

  Since when are ground based starting devices no longer in common use? Are there still any jetliners in service that would require them?

As of my retirement in 1999, ground based starting devices were in common but infrequent use. I would suspect that's still true, although hopefully less frequent. Any jetliner engine of size will require a ground pneumatic source to start if the airplane itself cannot supply that with its APU or an already running engine.

Back to my experience in Harare, the first mistake made was that of our dispatch department sending an aircraft there with an inop APU.


Can confirmed passengers preview or request flight plans before the flight?

Yes, and you don't even have to be a confirmed passenger (that would be kind of weird). There are probably several sources for this, but FlightAware includes filed route information for upcoming flights. Note that this link won't work very well in a week, since it's datestamped to the future. However, they show the route on the map, and also print out the current planned route:

UAL1
KIAH STYCK1 DOLEY ADM J21 IRW HYS LBF RAP GGW YEA YEG 5600N 12000W BINGA NCA11 COHIL WUXAN 6000N 16000W 5900N 17000W 5700N 18000E ONEIL R580 OPAKE R580 OLCOT R580 OATIS Y802 ARMOR Y810 KETAR Y811 VEPOX Y811 MELON RJAA


What is the reason for the detour flight route from AUH to BEY?

It's for political reasons.The flight is clearly avoiding Syria and Israel. To fly a direct route between the two you must overfly either Syria or Israel.

Looking at the flight paths from the last week or so of the two airlines that service that route and it becomes very clear. The flight in question is (as it would appear from flight paths) Etihad Airways, the flag carrier for Abu Dhabi. All flights between the two from Etihad take this same circuitous route. The reason is that they can't fly over Syria or Israel. The UAE (of which Abu Dhabi is a part of) does not recognize Israel as a state. Israeli citizens are not even allowed in the UAE. Etihad does not serve Israel nor are Israelis allowed to fly on it. Many Arab states do not allow El Al to overly them so it's a safe bet Etihad is not allowed to overly Israel's territory.

In the past that would just mean flying over Syria instead. But Abu Dhabi is a member of the Arab League which has invoked sanctions against Syria. This would make it risky to fly over Syria and is most likely prohibited by the sanctions. So their only option is to go the long way around.

On the other hand, the Lebanese carrier Middle East Airlines/Air Liban also serves this route. Although Lebanon is a member of the Arab League, Lebanon refused to be party to the sanctions on Syria. Due to this they are still able to fly over Syrian airspace, so they have a much more direct route.

And it would appear that Etihad is still avoiding flying over northern Sinai since the Metrojet 9268 crash.


What should be done in case of the avionics failure?

In the U.S. (other jurisdictions may be similar)...

Avionics are a convenience in VFR day flight. You should be able to fly your airplane by sight picture alone. There are aircraft flying today without any electrical system at all. In a fixed-gear aircraft, none of the equipment required by Part 91.205(b) require electric power. There are standard protocols in place if you have to fly to a destination without electric power.

If you are not on a flight plan or flight following when you lose electric power, stay clear of Classes A, B, and C airspace as well as the 30 nautical mile mode C veil around Class B airports, and the airspace above Class A, B, and C. Stay or descend below 10,000 feet MSL if possible or 2500 feet AGL when not possible to descend below 10,000 feet MSL.

If you lost all electric power before communicating your situation and intentions to ATC, you can assume that squawking 7600 on your electric transponder will do no good, either. Find a VFR Class D, E, or G airfield where you can land. Land as soon as practicable. Remember, you can not enter Class D airspace (normally a 4 mile radius from the field) until you have established two-way communications with them. You can, however, circle above the traffic pattern or tower at an altitude outside of the usually 2500 foot AGL ceiling of Class D until you get light gun signals from the tower. Wagging your wings or following their instructions will be your acknowledgement of light gun signals. Two-way communication will then be established.

Remember, an active IFR plan will give you clearance to your declared destination or declared alternate(s) at your ETA. Neither a VFR flight plan nor flight following prior to an expressed clearance will give you clearance into A, B, C or D airspace.

You should follow this plan of action at any Class D, E, or G airport with an operating control tower. Typically (but not always), a Class E or G airfield will not have an operating control tower. At those airfields, follow the AIM recommendations for entering the traffic pattern for a landing. An overhead flyover well above traffic pattern altitude would be advisable beforehand. Be very cautious of existing traffic. And, make your flight path as predictable to other pilots as possible. Although communication is strongly recommended, it is not required.

If you are flying on an IFR flight plan in IMC, follow the directions of Part 91.185.

If you are flying VFR at night, make it a habit to have the phone numbers of nearby towers, TRACON, and ARTCC in your cell phone. Call them to tell them of your predicament. Declare an emergency via cell phone. Then, use your Part 91.3 PIC authority to request clearance to land at any airport where the runway lights will be lit regardless of airspace or class. ATC can coordinate your clearances, then call an airport official or radio a passing airborne aircraft to turn the light on for you. You won’t be able to do it yourself without an operating radio. And, landing at a dark airport without a landing light will be challenging at best.


Are there any airplanes with the Centre of Gravity behind the Centre of Pressure?

In steady flight both points are exactly at the same lengthwise location. The pilot is able to shift the center of pressure somewhat by moving the elevator. Therefore, every aircraft that pitches up will become one where the center of gravity is behind the center of pressure.

But I guess you did not request this answer but a different one. That, however, would require a different question: Are there any airplanes with the Centre of Gravity behind the Aerodynamic Centre? Please read here about what those different centres are.

Most aircraft are indeed built such that the center of gravity is ahead of the aerodynamic center. This allows the pilot to let go of the stick momentarily and gives him valuable force feedback on the stick when the aircraft's speed or load factor changes. And it is required for civilian aircraft so they can be certified.

However, placing the center of gravity further aft has become a de facto standard for military combat aircraft with supersonic capabilities. Please read here why this helps. To summarize:

Agility is enhanced
Supersonic trim drag is greatly reduced
Smaller wing and tail surfaces are needed for the same take-off and landing performance.

The first aircraft which was designed with the center of gravity behind the aerodynamic center was the Wright Flyer I. When designers found out that aircraft could be made naturally stable, they placed the center of gravity more forward, and only with fly-by-wire controls did they return to the rear center of gravity location. The first design to do so on purpose was the F-16, and today every fly-by-wire combat aircraft with supersonic capabilities follows the same path.


Is there a way to calculate the difference in pitch required to reach a certain vertical speed?

I'm surprised no-one has attempted to answer this question, as it is mostly a pilot's daily job to guess a pitch change that would give a certain rate of climb. :-)

This will not be a technical answer, but I suspect some of my attempts at controlling the rate can be ported to a PID algorithm.

Keeping math aside, if you draw the lift-drag-thrust-weight diagram, there is probably a tan(x) dependency there between pitch and rate. For the small angles of pitch we are talking here, a linear dependency is good enough on the assumption of tan(x) ~ x . So basically, if I want to half my climb rate, I start by reducing my pitch to half and then I take it from there.

Secondly, the larger planes will still fly by the numbers, so I have a pretty good idea of how 2.5 deg will give me level flight at 250kts, 5 deg will give me around 1000fpm at climb thrust ,etc. I initially pitch to the memorized pitch angle and then adjust as necessary.

Short answer:

Build a table of pitch vs speed vs climb rates with climb thrust, and a table of pitch vs speed vs descent rates at idle thrust.  Assume linear dependency between pitch and rate. Adjust PID from there. Voila'!


In an emergency, how much runway does an A320 need to stop safely?

Airbus's charts for the A320 suggest that it requires approximately 4,500ft for a sea-level landing at typical landing weight. I've extracted this from this Airbus document (the A320 landing chart is on page 49), which is admittedly more of a promotional brochure than an operating manual.

Wellington's runway is 5,955 ft between thresholds, and 6,827ft overall, so there is some room for error. However, depending on the nature of the 'flat-out emergency' a pilot may approach faster implying a longer landing roll, or choose a firm landing and significant abuse of the brakes to shorten it.

Christchurch and Auckland airports both offer much longer runways at 10,787ft and 11,925ft respectively, so I'd speculate that a pilot faced with a known problem with brakes or thrust reversers might elect to divert there if range permitted.


What is needed to certify an aerodrome as an airport in Canada?

Original Answer
Aerodrome
It is an area where:

aircraft land
aircraft take off

Runway may not be present (in case of a water aerodrome).
Airport1
By definition2, an airport is an aerodrome with facilities for commercial aviation flights to take off and land
It is an aerodrome which has:

facilities to store and maintain aircraft
at least one designated operational landing/takeoff area (runway or helipad)
hangars
terminals
fixed base operators
airport aprons
air traffic control centers
passenger facilities (restaurants and lounges etc.)
emergency services
customs3
immigration3

Edit
I noticed that the question is updated to be only for Canada. In that case, airport requires the following:

have a safety management system in place
comply with airport safety standards and security requirements

Further reading
Aerodrome
Airport
Airport Design and Engineering Standards (by FAA)
Aerodrome Standards (PDF by ICAO)

1: Not all airports must have all of these to qualify as an airport.
2: I could not find specific regulations which define an airport.
3: In case of an international airport


What is the meaning of the crosshatch marking on altimeters?

It looks like the crosshatch (or barber pole) indicator doesn't have a consistent meaning (a similar marking is used on some airspeed indicators, by the way). I found several different examples of when it can appear:

Below 10,000' (FAA PHAK; Army RC-12H manual)
Below 15,000' (instrument service catalogue)
Below 16,000' (another instrument catalogue)
Above 0', i.e. above sea level (instrument repair information)

The only source that gave any explanation is the last one:

  When the altitude is below sea level the barber pole is no longer
  visible. This is provided to avoid the error of reading –1,000 Ft. as
  being +10,000 Ft.

After following a bunch of links and skimming some discussion forums, my conclusion is that @RalphJ is probably right: manufacturers added the flag to highlight that the aircraft is at a relatively low altitude, in a way that's much easier and quicker for the pilot than 'parsing' multiple hands on the altimeter face. And the fact that different sources give different altitudes highlights an important point: it's always a good idea to read the handbook or manual for all your instruments because you can't assume that everything works the same way in every aircraft, even something as 'simple' as an altimeter.


Why is the aircraft boneyard in Tucson, Arizona still active?

If the number of planes waiting on getting gutted isn't decreasing even though scrapping activities are happening that means there is a steady influx of end-of-life planes arriving to get scrapped.

As long as there are planes and new planes being built (most have a lifespan of a few decades) there will be planes that need to get scrapped.

You can't just dump the plane on a landfill or you will get nature activists on your case about the hazardous materials (hydraulic fluid, remnant fuel, ...) and recycle potential. Plus most components (instruments, engines, the espresso machine in the galley, etc) will still be usable and airliners will want to buy them as spares.


What is this stem on the underside of a Cessna 172R (1997)?

Ok - got word from the local a&p that this stem is a part of the aux fuel pump. It drains the motor side of the pump of any fuel in case the seal that separates the motor from the pump fails. You wouldn't want fuel getting inside of where the motor has current and sparks, hence this "stem" is the safety backup. The entire pump had to be replaced because overhauling made less sense due to the age of the pump. Turns out it wasn't in the diagrams at all!


Is it recommended to get a life raft for short overwater operations?

I used to be a bush pilot flying Cessna 180s on floats. If you ditch in a 172 on wheels with a life raft in the back seat, it's going to flip inverted when it contacts the water and start to sink immediately, and getting your own carcass and your passenger out of the thing without drowning will be enough of a challenge.  Forget about trying to pull a life raft out of the back seat of a sinking inverted 172 after you just escaped.  It's gone.

If you are that wary of overwater flight, the normal practice, for things like trans Atlantic ferries, is to wear an immersion suit. With the water at 64F, you could get by on a warm weather immersion suit or a sailing dry suit plus life jacket, but even without, it takes quite a few hours for 64F water to kill you, and the Coast Guard is going to be there within 30 min.

In any case, a 172 has an L/D of about 9, which means from 10000 ft you can glide somewhere around 17 miles.  At mid point between between Long Beach and the island you are less than 15 miles from shore, so there's really no need to worry about ditching in the open ocean, unless you want to do the flight at a couple thousand feet.

Even if you only climb to 5000, you could glide to a few miles of either shore.  And the actual "risk exposure" time of the engine spontaneously blowing up in your face without warning, while out of gliding distance of land, is only a few minutes. The probability of this happening, that is the engine doing something like throwing a rod suddenly, in that little time window, is a fraction of the probability of driving your car off a bridge into the water on your way to the airport.


What would happen to the rudder on an A320 if both FAC systems failed?

The A320 has a mechanical link from the rudder pedals to the hydraulic rudder actuators. Computer-generated rudder commands for yaw damping and turn coordination are added to the mechanical signal from the rudder pedals, but in the event of a two-sided computer failure the rudder can still be controlled.

The elevator trim wheels are also mechanically connected, so rudimentary control of the aircraft remains even in the event of a total electronic failure, as long as there's hydraulic power.


Why has aluminium, rather than steel, prevailed in airliner construction?

You are right, on first sight it is actually surprising that aluminium prevailed. It comes with some disadvantages:

Crack growth must come first in this list. With only a small cyclic load, cracks in aluminium will relentlessly grow. This requires frequent checks and has caused many accidents. Fortunately for aluminium, this fact was only discovered after WW II when the lifetime of aluminium airframes shot up from dozens to thousands of hours, so aluminium was already firmly established as the premier structural material.
To connect two aluminium parts, only riveting or bolting are available. Recently, bonding has become viable, too. Steel offers a third choice in welding, which gives it the advantage in vehicle construction. Again, history gave aluminium a head start, because when the first metal airframes were designed, welding was still relatively little developed, so the restriction to riveting was not felt as the disadvantage it is.
Corrosion: Here it is generally better than steel, but far worse than stainless steel which would be the prime candidate (next to maraging steels) for airframes were aluminium not available. During the Berlin Airlift, salt or baking powder could only be transported by seaplanes because it would had permanently damaged the landplanes. Seaplanes used special, corrosion resistant alloys which were needed in the marine environment.

In the end, however, this is still outweighed by the principal advantage of aluminium: Its low density. This allows to use thicker gages for the same weight, so the buckling strength of aluminium skins is far better than that of equally heavy steel skins. In aviation, the demands of aerodynamics make the use of crimps or reinforcing seams impossible, and only the labor-intensive addition of closely spaced stiffeners could remedy this. Such a stiffened steel skin would still be inferior when it comes to hail damage or handling loads, though, so aluminium was the obvious first choice.

In order to keep material cost down, Junkers built his first metal aircraft from steel but had to switch to corrugated aluminium in order to make them light enough. Note that the structural integrity of his designs was ensured by a steel truss, and only the covering was from corrugated aluminium. Later stressed-skin designs did away with the steel truss.

To compare the strength and stiffness of different materials independent of their density, you can use their breaking length and specific modulus, which can be expressed as their strain length. Surprisingly, most structural metals have a comparable value and only composites can set themselves apart.

Despite its nasty failure characteristics, aluminium has defended its position as the dominant structural material: By the time composites were developed, the engineers and certification authorities had learned how to handle aluminium and had created a barrier to entry in the form of a host of tests and approved construction techniques which severely harmed composites. If all the materials we know today had been available a century ago, aluminium aircraft would had become an oddity, not the norm.


Why do airline pilots have shoulder harnesses?

pilots need to be able to do work during turbulence.
passengers don't really like to be fully restrained.


Why does it feel like a plane accelerates just before touching down?

The aircraft flares just before touching down. It descends with a constant velocity, and just before touching down pulls the nose up to reduce the descent. This results in a higher angle of attack, more lift, and a vertical deceleration of the airplane. A passenger perceives this vertical deceleration as a force. Direction of the force is straight down and the aircraft is nose up, you're leaning back, so there is a component of (gravity + vertical deceleration) that pushes you into the back of your seat.

This same effect is used in flight simulators with a motion base. Upon accelerating, the simulator pushes forward like the aircraft does, but also slowly rotates backwards so that the pilot feels sustained seat back pressure. He cannot see the leaning back angle inside the simulator because the horizon of the projected outside visual image does not move. As happens in the aircraft: look forward in the aircraft and your view of the inside of the aircraft is always the same, irrespective of aircraft angle.

So for your eyes there is no apparent tilt, the inner ear senses rearwards force, and there is increased pressure from the seat backrest. The brain translates this into perceived forward acceleration.


Can the center of gravity ever fall outside the mean aerodynamic chord?

Yes it can be. Whether the aircraft can fly with the centre of gravity outside this range is a different matter altogether.

When flying, the aircraft is balanced around the centre of gravity of the aircraft. Aerodynamic forces from the wing and the tail provide the balance, but up to a maximum. At some point the aerodynamic lift capacity of the tail is saturated.

In order to make sure that the balance can be achieved, the centre of aerodynamic force must be within certain limits of the centre of gravity. Or the other way around: CoG must be within certain limits of centre of lift, which is the better way to define it, making the CoG the variable.


What is the freezing point of 100LL Avgas?

ExxonMobil China says their Avgas 100LL will not freeze above -58°C.

The 'typical' freezing temperature is not given, but I would expect we'd be more interested in the maximum freezing temperature.


Is there any limit to how many times an aircraft evacuation slide may be deployed?

The slide has to be removed from the aircraft completely (generally) and sent back to it's manufacturer to be inspected and repacked, but yes, it can be reused.

This article talks about it in more detail.

As a far as "how many times", I would assume until it breaks ;).  Though honestly, I doubt a slide would ever be deployed more than once, maybe twice in it's life span.


Why are lavatories located near the exits of an airplane?

There could be numerous reasons,

Putting them near the galley centralizes non seat related things. It also allows you to run less piping as you can pump the same water to the sink in the lav as you would to the galley.

They may be located in a place where a tank can easily be fitted beneath them so as to minimize the amount of piping needed from unit to holding tank.

They are generally a convenient way to segment cabins as they provide an inherent wall (think between first and coach).

As for an emergency situation, Lav doors can generally be locked from the outside (I have seen the little metal flap above the slide often opens and allows you operate the slide). Its common place to do this prior to takeoff and landing. I would think its part of the emergency decent checklist as well so as to keep them shut. There is a discussion on it here.


What is the difference between a functional check and an operational check?

From the ATA spec 100 which is the standard for aircraft maintenance documentation, they provide the following definitions:

  (c) Following are definitions of three categories of test that shall
  apply:

  1 Operational Test

  a.  That procedure required to ascertain only that a system or unit is
  operable. These tests should require no special equipment or
  facilities other than that installed on the aircraft and should be
  comparable to the tests performed by the flight crews. It is not
  intended that the operational test of the unit shall meet the
  specifications and tolerances ordinarily established for overhaul, or
  major maintenance periods.

  2 Functional Test

  a.  That procedure required to ascertain that a system or unit is
  functioning in all aspects in accordance with minimum acceptable
  system or unit design specifications. These tests may require
  supplemental ground support equipment and should be more specific and
  detailed than an operational test. It should contain all necessary
  information to perform proficiency tests to maintain system or unit
  reliability at an acceptable level, without reference to additional
  documents.

  3 System Test

  a.  That procedure containing all adjustment specifications and
  tolerances required to maintain system and/or unit performance at
  maximum efficiency and design specifications. It shall be
  self-contained and may duplicate other tests. It is normally used at
  major maintenance periods.

I would expect that these definitions are pretty universal in aviation.


How does the PTT button on the radio work?

The standard microphone plug on GA planes is the PJ-068 plug, which has three electrical contacts (tip, ring, and sleeve). The tip of this connector is a push-to-talk signal (the ring carries the actual audio signal, the sleeve is ground).


It looks like a Kellet K-3, I believe...
Photo from 'Cierva Autogiros', by Peter Brooks.


When is a transponder required below class B airspace?

Short answer: mode C is required unless the aircraft was originally certificated without an electrical system; but ATC can always authorize you to operate within the veil anyway.

Your question isn't exactly about class B airspace itself, it's about the mode C veil; those are separate things although they do go together. (Note that from 1 Jan 2020, you'll require ADS-B out to operate within the veil so the name will be a bit outdated).

The AIM section 3-2-3 has a good explanation of the transponder requirements but the regulations are more precise and complete. They're in 14 CFR 91.215(b)(2) (and see 91.225(d)(2) for the ADS-B ones) and they apply within the veil, not within class B:

  All aircraft. In all airspace within 30 nautical miles of an airport
  listed in appendix D, section 1 of this part from the surface upward
  to 10,000 feet MSL;

That means that the shape of the class B airspace has nothing to do with the shape of the veil, which is always a cylinder 30nm across and 10,000ft high.

As for operating without an electrical system, that's covered in the same section. If the aircraft has no electrical system by design then you can operate within the veil but clear of class B:

  any aircraft which was not originally certificated with an
  engine-driven electrical system or which has not subsequently been
  certified with such a system installed, balloon or glider may conduct
  operations in the airspace within 30 nautical miles of an airport
  listed in appendix D, section 1 of this part provided such operations
  are conducted—

  (i) Outside any Class A, Class B, or Class C airspace area; and

  (ii) Below the altitude of the ceiling of a Class B or Class C
  airspace area designated for an airport or 10,000 feet MSL, whichever
  is lower; and

If the aircraft has an electrical system but it isn't working (i.e. you're taking the aircraft for maintenance) then you can request authorization from ATC to operate within the veil:

  (d) ATC authorized deviations. Requests for ATC authorized deviations
  must be made to the ATC facility having jurisdiction over the
  concerned airspace within the time periods specified as follows:

  [...]

  (2) For operation of an aircraft with an inoperative transponder to
  the airport of ultimate destination, including any intermediate stops,
  or to proceed to a place where suitable repairs can be made or both,
  the request may be made at any time.

You can also request ATC authorization if you don't have a transponder, or if it doesn't have mode C. But if you don't have a transponder, you need to request authorization at least one hour in advance, you can't request it "at any time" as you can in other cases (see 91.215(d)(3)).


No, they are not. Most (not sure if all) Airbus door are not plug-type. And neither are cargo door on most Boeing types.


In turbojet engines, does the fan play a key role in the air intake to the inlet?

In turbojet there is no fan. Very simply, turbofan means turbojet + fan in front connected to the LP shaft.