Why is there a drift value between the IRS position and the FMGC position present even after performing a full IRS alignment on the A320?

TLDR: The FMGC position is a mix of GPS and IRS (called GPIRS), but the IRS position is aligned to the airport reference coordinate, not to the GPS position.

The difference you observe is between the FM position and the MIX IRS position. This difference is called the bias.

Position Computation
Each FMGC computes its own aircraft position (called the "FM position") from a MIX IRS position (see below), and a computed radio position or GPS position.
The FMGS selects the most accurate position, considering the estimated accuracy and integrity of each positioning equipment.
GPS/INERTIAL is the basic navigation mode provided GPS data is valid and successfully tested. Otherwise, navaids plus inertial or inertial only are used.

(Airbus A320 FCOM - Auto Flight - Flight Management)
The FM position will move towards the GPS position in flight, if GPS is available (otherwise to the radio position):

FM Position
At flight initialization, each FMGC displays an FM position that is a mixed IRS/GPS position (GPIRS).

At takeoff, the FM position is updated to the runway threshold position, as stored in the database, possibly corrected by the takeoff shift entered on the PERF TO page.
In flight, the FM position approaches the radio position, or the GPS position, at a rate that depends upon the aircraft altitude.

Note: The FM position update at takeoff is inhibited when GPS PRIMARY is active.

Bias
Each FMGC computes a vector from its MIX IRS position to the radio or GPIRS position. This vector is called the "bias". Each FMGC continuously updates its bias, if a radio position, or a GPIRS position is available.

(Airbus A320 FCOM - Auto Flight - Flight Management)
The MIX IRS position is determined from all three IRSs:

MIX IRS Position
Each FMGC receives a position from each of the three IRSs, and computes a mean-weighted average called the "MIX IRS" position.

(Airbus A320 FCOM - Auto Flight - Flight Management)
I think your confusion comes from the fact that you think the IRS is aligned with the GPS position and therefore MIX IRS and GPIRS should agree directly after alignment. This is however not true:

Initialization
The F-PLN origin airport coordinates are extracted from the FMS database. These
coordinates appear on the MCDU INITA page, and are normally used for initialization.
They are the airport reference coordinates.
If a high navigation performance is desired, (i.e. for long-range flights without GPS
and without radio navigation updates, or if low RNP operation is expected), the crew
should adjust the airport reference coordinates to the gate coordinates, provided that
this data is published or available on board.

(Airbus A320 FCTM - Normal Operations - Pre Start - ADIRS Initialization)
As you can see the IRS is aligned against whatever is in the MCDU INITA page (airport coordinate by default), not GPS. Therefore, the IRS position can deviate from the FMGC position (GPIRS), even right after alignment.
This deviation will remain in flight, only the FM position will move towards GPS and the bias vector will describe the difference.


Per §91.119 of the FARs, yes. That said, you can't just find an open field-there may be local/state regulations regarding helicopter operations.

14 CFR 91.119:

  (1) A helicopter may be operated at less than the minimums
  prescribed in paragraph (b) or (c) of this section, provided each
  person operating the helicopter complies with any routes or altitudes
  specifically prescribed for helicopters by the FAA


Understanding "non-WAAS G1000" in a 2006 Turbo 182

The GTR345R is a transponder that can be purchased with a built-in WAAS GPS (link)—which this one apparently has. So it provides the WAAS GPS positioning required for ADSB. The GPS in the transponder does not provide a GPS source to the G1000.

From what the shop said, it looks like the G1000 is an older version that is not WAAS capable. That’s probably why they chose to install the transponder with built-in WAAS since it was much cheaper than upgrading the G1000.


Does the glide slope flag detect percent of modulation (80%)?

I wanted to post this as a comment, but it's a bit long.
From ICAO Chicago Convention annex 10, vol 1:

2.3 Alarm conditions for ILS airborne equipment
2.3.1 Ideally, a receiver alarm system such as a visual flag should warn a pilot
of any unacceptable malfunctioning conditions which might
arise within either the ground or airborne equipments. The extent to
which such an ideal may be satisfied is specified below.
...
2.3.3 The alarm system should indicate to the pilot and to any other airborne system which may be utilizing the localizer and glide path
data, the existence of any of the following conditions:
...
b) the percentage modulation of either the 90 Hz or 150 Hz signal
reduction to zero with the other maintained at its normal 20 per cent
and 40 per cent modulation respectively for the localizer and glide
path;
Note.— It is expected that the localizer alarm occur when either the
90 Hz or 150 Hz modulation is reduced to 10 per cent with the other
maintained at its normal 20 per cent. It is expected that the glide
path alarm occur when either the 90 Hz or 150 Hz modulation is reduced
to 20 per cent with the other maintained at its normal 40 per cent.

Glide path receiving equipment operational standards are detailed in RTCA DO-192 and EUROCAE ED-47B


Can you continue an ILS approach when weather falls below minimum?

You didn't list a jurisdiction so Ill answer for the FAA: Yes you can continue;

Under part 91 you can both start and fly an approach if the conditions are below minimum.

If you are flying under part 121 then you can't start the approach but § 121.651 Takeoff and landing weather minimums: IFR: All certificate holders. is going to be the regulation to reference and allows you to continue if you are passed the FAF.

  (c) A pilot who has begun the final approach segment of an instrument
  approach procedure in accordance with paragraph (b) of this section,
  and after that receives a later weather report indicating
  below-minimum conditions, may continue the approach to DA/DH or MDA.
  Upon reaching DA/DH or at MDA, and at any time before the missed
  approach point, the pilot may continue the approach below DA/DH or MDA
  if either the requirements of § 91.176 of this chapter, or the
  following requirements are met:


Why is bleed air taken from some stage of the compressor used for de-icing? Why not e.g. exhaust gas?

Using air from the exhaust section either for anti-ice directly, or using a heat exchanger, would create many problems.

The air must first be used to burn fuel before reaching a turbine bleed location. Air taken from the compressor section hasn't required any fuel to be burned (other than to compress that air of course).
The air will be much, much hotter than air from the compressor. Turbines, especially in the high pressure section, are made of specialized alloys and can be additionally actively cooled to prevent them from melting. This means more specialized, and therefore more expensive and/or heavy material must be used for the whole anti-ice system.
Components must also be designed for the case of this bleed air leaking. Hotter turbine air would be a huge problem for this.
The air will have the combustion byproducts in it. This can coat the insides of the anti-ice system, reducing its effectiveness, and possibly requiring it to be disassembled and cleaned periodically.
If there is some type of engine fire, the fire typically goes downstream, which would send it into this anti-ice system as well.
In the case of using a heat exchanger, this would be yet another component to fit into spaces that are already very full, and yet more weight on the airplane.

The air from the compressor is already plenty hot. Take a look at the diagram in this answer. Notice that all the compressor bleed air goes through the precooler before going to cowl or wing anti-ice. This means that the compressor air is already hotter than is required. So taking air from the turbine provides no benefit for creating the problems listed above.

Also, taking air from the compressor does reduce engine efficiency, but you are going to have to get that energy from somewhere.

To address your points about the thermodynamics:

Assuming your numbers are correct, what is wrong with that scenario? Releasing air at -97°C that was initially at -50°C means that you extracted 47°C of energy from it to use for anti-ice, using the systems already available on the aircraft (bleed air, precooler). Kind of like a heat pump, but just using air? Wouldn't it be less efficient to burn fuel to heat this air, which would then leave the aircraft at a higher temperature, and therefore throwing away more energy?

  In principle, one can play with the numbers, increase/decrease altitude/temperatures and discuss how adiabatically this (de)compression processes are.

(Emphasis added) I'm not convinced that your assumption that these processes are adiabatic is a good basis for your model, since that is an idealization (though your initial bleed numbers do seem to match here and here). An important point is the way the air is used. A typical installation uses piccolo tubes. Small holes along the tubes release the air onto the leading edge. This whole leading edge cavity then vents to the environment. (This doesn't seem to match your assumption that the air is cooled at constant pressure) In order for this air to be useful any further, you would have to somehow return this air to for reuse. This adds more complication, when there is already an abundant supply of compressed bleed air available.

Another option would be to somehow maintain the pressure behind the surfaces with ice protection. This may be feasible for the engine inlet, but not for wing leading edges that include moving slats.

Even assuming you can somehow recover this air for use, that would be another system and more complication added to the aircraft. And you can't rely on this system, because anti-ice is not always in use. You have to provide a pretty large gain in efficiency to justify adding weight and complexity to the airplane.

Maybe you would like to see proof that most the work done on the air is used in the anti-ice process, and adding heat from combustion is not necessary. We may need to get someone like Peter Kämpf in here to run some numbers.


Why has Boeing used mini winglets on the 737-200?

When originally Richard Whitcomb of NASA developed the winglets, he developed the split winglets with one above and one below as shows in image below:

The one above starts at 0.4x chord from the leading edge. For a test program on KC-135 tanker, which I suppose was first application of the winglets, they used the type of winglets shown in the question:

Conceptually there is no difference in the "mini-winglets" and the "Blended winglets" While I think almost all the wingtip shapes are more or less of same efficacy, I can think of couple of reasons for variations seen among various aircrafts - One is patents taken for some shapes would force other OEMs to come up with different shapes. Second is weight of the wingtip vis-à-vis the reduction in fuel burn. Typically winglets reduce fuel burn by ~3-8% but in some cases, the increased weight can off-set majority of the fuel burn or even prove to be more than compensating for it, especially on shorter hauls. One may be able to make a lighter blended winglet using co-bonded, co-cured composite structure as compared to the short winglet mentioned in the picture which with say bolted joints might end up heavier. I think it would be difficult to say make any generalised comment on this.


What is this cutout in the Spitfire cockpit glass?

According to flight manuals, this allows the pilot to maintain a view on the outside if the windscreen becomes obscured:

Source: Aircraft manual

This manual locates the panel on the right side. Online forums see this as a typographer mistake, but @TomMcW has found some aircraft had it indeed on the right side:

Source

On the reason for mist apparition:

  Note the punch-out panel on the canopy cover, an early solution to the
  new problem of canopy misting caused by the rapid altitude changes
  possible in the Spitfire.

Source: Flight Journal (pg 28)


Are German, Japanese, and Chinese companies not able to build aircraft jet engines on their own?

Well Rolls Royce designs and builds jet engines in Germany with their RR Deutschland division.  Rolls Royce Deutschland is a subsidiary of Rolls Royce and is a collaboration between RR and BMW.

The Shenyang Aerospace Corporation and Aero Engine Corporation of China are homegrown Chinese jet engine manufacturers, making their names largely for the manufacture of copies of Russian military jet engines for PLAAF need, but are now manufacturing their own designs for military and civilian applications.

Japan’s Aero Engine Corp is a partnership between Rolls Royce and several Japanese industrial powerhouses, most notably Mitsubishi Heavy Industries, who has begun to develop a line of small to medium thrust high bypass turbofan engines for regional airliners use.

While the basics of a jet engine are fairly well understood - it is, after all just a Brayton Cycle gas turbine - the details of designing and manufacturing modern high efficiency jet engines requires quite a bit of technical talent and capital to accomplish.  A new engine program often takes longer, and is more expensive than, the aircraft program it is being designed to power.  Most likely many entrepreneurs and prospective OEMs are deterred by this as any improvement they are likely to offer can be either bought out by an existing engine OEM eg Pratt and Whitney, etc. or simply crushed by the economies of scale.


Some old aircraft (737 Classic comes to mind) don't allow arming LNAV/NAV AFDS mode on the ground, as you normally have to be at least 400ft above ground (ICAO PANS OPS says 396ft) before making turns more than 15 degrees, at which point you would engage LNAV. I guess the regulation takes old aircraft into account.

On the newer aircraft, you can arm LNAV/NAV mode on the ground already and it normally becomes active at 50ft.


Can I fly a "Contact Approach" to this airport?

Here are the requirements for a contact approach from the AIM 5-4-25:

  Pilots operating in accordance with an IFR flight plan, provided they
  are clear of clouds and have at least 1 mile flight visibility and can
  reasonably expect to continue to the destination airport in those
  conditions, may request ATC authorization for a contact approach.

If all those things are true then you can request a contact approach (ATC can't offer it). But ATC has requirements to meet too:

  Controllers may authorize a contact approach provided:

  The contact approach is specifically requested by the pilot. ATC cannot initiate this approach. EXAMPLE− Request contact approach.
  The reported ground visibility at the destination airport is at least 1 statute mile.
  The contact approach will be made to an airport having a standard or special instrument approach procedure.
  Approved separation is applied between aircraft so cleared and between these aircraft and other IFR or special VFR aircraft.

If those things are also true then ATC can authorize it but there's no guarantee that they actually will.

In the example you gave, it looks to me like all the requirements are indeed met (although you didn't say whether the two-mile visibility is flight, ground, or both), so a contact approach would be legal. There's no requirement to comply with the minimums for a published approach during a contact approach.


What counts towards the 250 hours required for CPL?

It's just what the regulation says:  you must log at least 250 hours of flight time and at least 50 of those hours must be PIC time in airplanes and 10 hours of cross country PIC time in airplanes.  As for the other two hundred hours?  They can be in any other kind of aircraft you like.

It's actually a very common way to build raw hours.  A lot of fixed wing pilots get rotorcraft certificates in a fraction of the total time than if they started training from scratch in helicopters.  It also works well with gliders, hot air balloons, you name it.


How to convert an EASA ATPL(H) IR to ATPL(A)?

It looks like the answer is yes, but with some significant caveats, such as only 50% of your helo time will count towards a fixed-wing ATPL. The UK CAA web site has info on this but your best bet is to contact a reputable flight training organization that offers ATPL training. Click on the "Holders of a UK issued Part FCL licence in another category" link (there is no direct URL to this content). If the country in question is not the UK you should check their rules.


Why does Boeing use a trim wheel in the 737 and not their other products?

Trim pitch "wheels" as you describe date back to the time when turning that wheel actually pulled on steel cables that were connected to the hinge mechanism for the control surface itself. This mechanical/manual system was a simple and robust method of manually trimming the aircraft and was very widely used before electronic/fly-by-wire control systems were invented.

Since the 737 is the oldest basic design platform in the Boeing product line, its original design dates back to a time when trim wheels were mechanical and pilots were transitioning out of still older planes into Boeing's new offerings- and those pilots expected manual trim wheels.

It is likely that trim wheels in newer planes are a "legacy" feature, allowing pilots familiar with an older revision of the cockpit layout to transition to another newer plane in the design series.


What is this seaplane shown in this photo?

That's a DHC-2 Beaver on floats. The dead giveaway is the unique trapezoid window.


Why does the Canadair Regional Jet still use CRT screens?

This is just an educated guess, but it was too much info for comments. Maybe someone can come up with a specific answer, but it seems it's probably a certification delay. The CRJ's all use the Rockwell Collins Pro Line 4 avionics suite, which uses CRT's. In 2000 Rockwell Collins introduced the Pro Line 21 suite which uses LCD screens. They have been slowly introducing PL21 retrofits for aircraft with PL4 as they receive STC's. The Falcon 50 and 2000 began getting retrofits in 2008, followed by Beechjet 400A in 2009, King Airs in 2010, Learjet 60 and Gulfstream G100 in 2012, Piaggio Avanti in 2013, then Hawker 800 and Challenger 300 & 605 in 2014.1

My presumption is that the CRJ's have a type cert with the PL4 and they very well may be working on getting a cert with the PL21 or the newer Pro Line Fusion suite. It will certainly become increasingly difficult to find replacement CRT's as there a only a couple of companies still manufacturing them. It seems just swapping display types is not feasible with the PL4 system. The PL21 system was designed to be more flexible so it's easier to integrate improvements in technology.2

1 These dates might be wrong. I'm finding different dates from different sources. For example, Falcons began getting them in the US in 2006 but it didn't receive EASA certification until 2014.

2 http://jetadvisors.com/rockwell-collins-proline-21-avionics/


Why did my IAH-SYD flight avoid Mexican airspace?

Though routing this far north seems to make the flight about 200 miles longer, flight duration doesn't exactly correlate to route length. For a flight this long, wind plays a large role.

Take a look at the image below of the current wind forecast from ADDS, with the two flight paths in blue. You can see if they took the southern route over Mexico they would be flying directly into a pretty strong headwind. But by going further north, they can fly in much lighter wind conditions.


Is a physical lapel pin awarded for FAA Safety Wings?

Yes, the FAA currently offers a lapel pin at the completion of each phase of the WINGS program.

This "reward" is not automatically awarded or delivered, the WINGS participant must request it. Upon completion of each of a phase, for example Basic, Advanced, or Master, the FAA Safety Team will include the following notice:

  If you have not already done so, I encourage you to go to your My WINGS page at FAASafety.gov and claim your Team Member Reward -- a beautiful set of wings for your lapel.

The pins are sponsored and distributed by AVEMCO, in partnership with the FAA.

The pins are available in at least three finishes: bronze, silver, and gold, and a special sea-plane version is apparently available.

Source: own work


Why are airspeed gauges labeled above Vne?

I can think of several reasons, why you would want to have some extra room:

The fact that you should not exceed $ V_\mathrm{ne} $, does not mean you never actually do. It would be good to know by how much you are currently exceeding it, so you can decide how to react to this situation.
Not every aircraft model gets their own specific gauge. Cessna probably has a few gauges available and put the one with the smallest extra room above $ V_\mathrm{ne} $ on the aircraft. This is quite similar to cars, where you get the same speedometer on most models of a car, despite having different engines and thus different maximum speeds. It is simply cheaper to produce (and certify) only a few different airspeed indicators.
The aircraft's $ V_\mathrm{ne} $ might change with modifications installed at a later time (like an aerodynamic upgrade package). It would be nice, if the avionics would not need to be exchanged for this.

As to whether or not it is specific to Cessna: A quick Google search for "PA28 airspeed indicator" shows several Pipers with a lot of extra room (although some only have around 10 knots). I assume this is not much different for other aircraft manufacturers and just depends on which gauges where available.


Can cellular towers be used to correct INS drift?

No, for several reasons:

There is no receiver onboard (granted, this could be remedied easily)
Cells are very small, their antennas are directional privileging ground. Detection from an aircraft is difficult. For an aircraft in cruise, the distance is at least 10 km, only a large cells found in rural areas would be received. In populated area cell radius is much smaller.
Aircraft switch from a cell to the other, most of the time before being able to create a stable link. This may be a problem or not, depending on the distance measurement principle. If the principle is based on measuring radio trip time rather than azimuth, a synchronization with the cell controller is required.
On the other hand, if angles are used to determine distance, triangulation is not really accurate as the angles are small, less than 60° by design. In addition receiving antennas must be phased arrays (or rotating antennas) to determine the transmitter azimuth and elevation.

Last but not least, this would interfere with the cell network working. This reason is among the critical ones cell phones must be powered off while flying on a fast aircraft like an airliner. Cell phones on US aircraft are not prohibited by FAA but by FCC (its scope of interest is frequency protection, not aircraft safety). When a cellular network is available in flight, then there is a tiny cell in the cabin,connected by satellite link to the ground telephone network. Same for WiFi. There is no connection with a ground cellular network.


Is 'make small one turn' a standard phrase?

More standard English, at least in the U.S., would be "make one small turn", but I've never heard such a term used. Also, "small" doesn't explicitly define how much of a turn, and it doesn't indicate the direction of the turn. ATC instructions are usually precise, something like, "turn right 90 degrees for identification." I remember getting that type of instruction from controllers in setting me up for practice PAR approaches (civilian equivalent of GCA) at Kingsley Field, Klamath Falls, Oregon, U.S.A back in 1969. However, in the next 30 years of flying I never heard a like instruction, at least that I remember, for the simple reason that I never had to fly a PAR approach for real.

The abbreviations are:
PAR - Precision Approach Radar
GCA - Ground Controlled Approach


Why is the bypass ratio of a turboprop higher than turbofan?

Bypass ratio is the ratio of the overall flow  to the core flow (which goes eventually through the combustion chamber). Overall flow is either the flow captured by the intake or going through the propeller disc. Even for piston aircraft it is possible to define a bypass ratio if you interpret the air which flows through the cylinders as the core flow.

A turbofan essentially uses a shrouded propeller of high solidity (or activity ratio) which helps to accelerate the flow through it as much as possible. It needs to produce the most thrust from the limited air volume captured by the shroud's intake. The limitation is needed to limit the tip speed of the fan and the overall size and drag of the shroud.

Propellers, on the other hand, accelerate a bigger flow by less and need to cover less of the propeller disc for doing this. To keep thrust constant, a bigger mass flow needs to be involved into the acceleration.

Plot of the thrust specific fuel consumption in lb of fuel per lb of thrust per hour of different engines over the logarithm of their bypass ratio (picture source).

A comparison is only sensible if we look at the same core component: If a turbofan and a turboprop share the same high pressure components. One example would be the Rolls-Royce/Allison 2100 and the Rolls-Royce/Allison 3007. Wikipedia gives the mass flow of the 3007 as 109 - 127 kg/s but gives no information for the 2100. Using the maximum flight speed of the Alenia C-27J of 167 m/s and its propeller diameter of 4.15 m, we can find a lower bound for the mass flow through one of its propellers if we make the heroic assumption that the maximum speed is reached in 25000 ft (7620 m) where air density is 0.55 kg/m³.

Mass flow through the propeller of one 2100 is at least 1242.4 kg/s or about ten times of what it is for the 3007. The mass flow though the core is the same because both engines share the same hot section. The static thrust of the 2100 is higher than that of the 3007 but drops more quickly with speed, so at high speed the 3007 produces more thrust.


Is there a good systematic approach to flying an 800 foot pattern?

The trick of putting the runway half way down your wing strut visually, or a third to a half way down the wing on a low wing works great, because it automatically allows for any altitude agl being flown. As far as the rest of the pattern goes, just fly it with the same power settings and airspeed you would have in a1000 foot pattern. The base leg will get turned maybe a tiny sooner than the usual 45 degrees behind you trick, since you are starting out 200 feet lower (so you don't want to go as far away) I think it's more important that you just fly the pattern no differently...just make sure you're not out wide on downwind. The trick to consistent landings is consistent patterns and approaches. And that only comes from making sure your first circuit around is by the numbers. (i.e. airspeeds and power settings were exactly right and exactly at the proper place when they happened) Adjust accordingly after that first one, but really quiz yourself and make sure you are being consistent in the first place, before you start changing up how you do things.


Cole Kugel, 105

  Born March 14, 1902, Cole Kugel, a resident of Longmont, Colorado, USA is the oldest qualified pilot. He was born one year before the legendary Wright Brothers took to the skies, and has been flying ever since. Kugel earned his pilot's license in 1945 and flew in 2007 for the last time, aged 105, piloting in the company of local veterinarian Lynn Ferguson in his beloved 1976 Cessna 182.

http://www.guinnessworldrecords.com/records-1000/oldest-qualified-pilot/

2005 Photo: Daily Times-Call | Hunter McRae


Is it okay to purposely stall a small single-engine aircraft just before touch down to get a good flare?

"To get a good flare".  Never heard of pilots talking about "wow, I had a great flare on that landing!", although a very famous test pilot really had a beauty landing the XF-92A, reducing landing speed from around 160 to 67 mph.

So why do we flare?  What is a flare?

"Flaring"  is increasing AOA to MAINTAIN lift as the plane slows down.

Why do we slow down as much as possible before landing?

Too fast and the plane will "bounce". Bouncing is not a major problem if it is on the main gear (and not too hard).  Bouncing the nose gear can be disasterous.  Since you have a lower AOA for the same lift when faster, risk of bouncing the nose gear is greater.  For taildragger, the risk is prop strike.

So you flare to increase AOA after rounding out and prior to touchdown, reducing speed and increasing AOA.

Do you need to stall to get a good flare?  NO!

Does the stall warning mean I'm stalled?  Try it at altitude first.  Generally they are set a few knots ABOVE stall, and it is normal to hear it as you touch down.  Know your plane.

Finally, "round out" at approach speed (you don't want to stall here), then reduce throttle and pitch up (flare).  The trick is to hold it a few feet off the runway as speed decreases and AOA increases.  You are now flaring!

Actually landing, well, everyone has their own ideas.  In a 172, I could just start to feel the seat of my pants drop.  At that point, back pressure on the yolk was relaxed just a tiny bit (slightly reducing AOA and lift), and the plane would settle onto the runway.

Flaring as all about speed control.  Keep it safe.


Why haven't quadcopters been scaled up yet?

Wouldn't they be more stable and easier to control than helicopters?

No, they would not.

Quadcopters don't have any special inherent stability. When you increase power of one of the rotors to pitch, the increasing pitch will not do anything to the power difference and therefore the pitching moment.

The advantage of quadcopters is that the rotors can be fixed pitch while single (or double) rotor helicopter needs complex control mechanism. While this is huge advantage for the small scale devices where each rotor can be powered by its own simple electric motor, the complexity of either additional engines or long transmission shafts would outweigh any advantage from the simpler rotors in full-scale vehicle.

And why can't full-scale helicopters use electric motors like the small ones? The reason is that when you scale an airfoil up, the lift it produces increases with its area, which grows with the second power of size, but its weight increases with volume, which grows with the third power of size. Therefore models have much more lift for weight and can afford simple but relatively heavy batteries while full-size aircraft need propulsion systems with higher power density.

And then there is also the factor of safety. In case of power failure, helicopters can still glide to the ground and still land vertically using autorotation. But since the rotor rotating speed can't be changed without power, controlling the helicopter during such manoeuvre requires variable pitch rotor. So there goes the main advantage of quadcopters.


What makes a weight-controlled microlight tumble, and can it recover?

what causes a weight-controlled microlight to tumble

There seem to be several mechanisms. One is an excessively sharp nose-down control input after entering or approaching a stall.

  and is it possible to stop it from tumbling once it starts?

Not without an external safety device (presumably a throwable parachute or something similar)

  The tumble mode is a little known mode of departure from controlled flight experienced by weightshift controlled microlight aeroplanes. It has been a very significant factor in fatal accident records, being non-recoverable without the use of external safety devices. The mode consists of a nose-down autorotation at a rate of up to 400°/s. The tumble entry mechanism is explained, and advice to operators developed which should prevent tumble entry. Evidence is shown of the nature of the developed tumble – both modelled and through wind tunnel results, which explain how the autorotation occurs. It is also shown how this theory may be applied during testing of an aircraft to develop a tumble resistant aircraft.

See A theoretical and experimental appraisal of airworthiness evaluation techniques for small light aeroplanes

This seems to be an excellent paper 255-page dissertation which contains far far far more than the average reader of this website could ever want to know about this phenomenon.

You should note that this contains stills from the Youtube video in the question. It is therefore directly relevant. If you can find a better analysis I will print out my answer and eat it.


Does the wing to fuselage fittings of an airplane ever experience shear load?

In general, the answer is yes. The answer depends on the details of the fittings. Note that most realistic loadings are a combination of tension rsp. compression and shear. If - for example - the wing of your ultralight is held together by shear pins (note the name!) which are inserted in vertical (up-down) or horizontal (forward-backward) direction, they will transmit those centrifugal loads as shear from one wing bushing to the other.

The same goes for the transfer of lift forces inside the spar and - again, depending on the details - into the fuselage. The web of the spar is meant to carry the shear loads and those are transferred by ribs to the attachment points. Other designs use a front and rear spar which attach directly to the fuselage.

The picture shows the front spar attachment of the B-17 (source). Granted, this is not exactly an ultralight, but the same principles apply. At positions C, D and E it uses shear pins to transfer the lift loads into the fuselage bulkhead.


Could the autopilot have rectified the flight path without any crew input on the Aeroflot Flight 593?

The PIC had given his seat and controls to his son (a visitor in the cockpit without any flight qualifications). The autopilot was in perfect control of the A310 until the son of the PIC had disengaged the automatic aileron control by applying sufficient control force. Up to a certain banking angle, fully engaging the AP would have resolved the problem. Without control over the ailerons, the AP could not recover the plane's attitude. The banking angle was out of the operating range, and the plane was not able to maintain its altitude.

Unfortunately, both pilots had trouble to become aware of the situation, and they also had a lack of understanding of the A310 controls. After fully disengaging the AP, the AP could not help with the lateral control any more.

This is very simplified, of course. A lot of elements contributed to this "accident". I recommend to read the Investigation report.


What is the reason for these strange radio altimeter calls?

"Four hundred" was likely annunciated twice due to a bit of a dip in the terrain that would cause it to pass the 400ft level twice. The "hundred above" call-out is for 100 feet above decision height to let the crew know they will need to make their decision soon to either continue or go around. After that, you hear the "two hundred" and "minimum" call-outs right after one another. The "one hundred" call-out afterwards signifies 100 feet above ground level.


What does "1%" mean in ICAO Annex 14 § 3.9.9 (longitudinal slope changes)?

You are referring to ICAO  Annex 14 Volume I, Aerodrome Design and Operations. Section 3.9.9 says:

  Recommendation.— Where slope changes on a taxiway cannot be avoided, the transition from one slope to another
  slope should be accomplished by a curved surface with a rate of change not exceeding:

  1 per cent per 30 m (minimum radius of curvature of 3 000 m) where the code letter is C, D, E or F; and
  1 per cent per 25 m (minimum radius of curvature of 2 500 m) where the code letter is A or B.

To better understand this, lets see what the previous section says:

  3.9.8 Longitudinal slopes

  Recommendation.— The longitudinal slope of a taxiway should not exceed:

  1.5 per cent where the code letter is C, D, E or F; and
  3 per cent where the code letter is A or B.

So: for a taxiway with a code letter D for example, a maximum slope of 1,5% is recommended. That would be 1,5 meters up or down within a distance of 100 meters.

If a part of the taxiway in question is 1,5% uphill, and another part is 1,5% downhill, the transition from the uphill portion to the downhill part should not happen at a rate faster than 1% within a distance of 30 meters.

In addition to this, the radius of the curvature should not be less than 3000 meters. This means transitions must be smooth within that 30 meters distance.


Could a pick up truck save a plane with failed landing gear?

For the Boeing 727 that you see there, that whole procedure is impossible with a pickup truck. Given that the 727 is operating at its Operating Empty Weight, 102,900 lb OEW for the 727-200 advanced, and the force on the nose gear is somewhere around 10% at rest, that would put it way over the limit for that particular truck model (Nissan Frontier at 4,690 to 5,816 lbs GVWR). That would be even less pretty for the truck since the force at touchdown on the nosegear should be higher.

Also, according to this thread, the maximum speed for that truck is about 95 mph. Assuming that this Yahoo Answers is correct, the landing speed of a 727 is 130 to 150 knots (150 to 170 mph). This is way greater than the speed of any pickup truck.

I had to make a response like this some time ago as well to the exact same video someone had a question about.

However, you could land a GA plane on a pickup truck if you had the right equipment.

Nitpick on the video: if the plane's nose gear didn't deploy all the way, then truck or no truck, it should have collapsed on impact.


Why is a blunt trailing edge a better stabilizer at hypersonic speeds?

A converging shape at hypersonic speed in a low-pressure medium will produce close to vacuum pressure on its surfaces (hypersonic shielding). A small sideslip angle will only result in a very small pressure difference between both sides.

Contrast this with a diverging shape which produces higher than ambient pressure on both sides. In hypersonic flow this pressure grows approximately with the square of the inclination angle. The same sideslip angle, therefore, will result in a much higher pressure difference, rendering the diverging shape more effective in sideslip.

A more detailed discussion can be found here, page 11-6 to 11-8.

A wedge shape was chosen since it allowed to predict forces and temperatures with greater confidence than would had been possible with a more complex shape.


Is there a time limit for a line-up and wait?

We can get some idea of what temperature the pavement would be subjected to by looking at some data on different jet aircraft.

Older low-bypass turbofans produced higher exhaust temperatures over a larger area than new high-bypass turbofans. This is due to the high-bypass engines having more of the cooler bypass air mixing with the hotter core exhaust.

Manufacturers provide various data about their aircraft that can be useful for planning operations at airports. Included in the data are figures showing exhaust velocity and temperature for different throttle settings.

It should be noted that aircraft holding for takeoff clearance will be at idle power. The power will be increased only when cleared for takeoff, so the takeoff temperatures will be experienced only briefly.

Although hot air tends to rise, the 737 analysis notes that:

  The buoyancy effects are considered to be small relative to the exhaust velocity and therefore are not included.

The figures for the 707 show the exhaust contours starting at the engines. The highest temperature labeled is 200°F (93°C), though higher temperatures would be expected closer to the engines. At idle power the 150°F (66°C) contour barely reaches the tail and stays above the ground. At takeoff power, the 200°F contour reaches bast the tail, but the highest temperature in contact with the ground would be the 150°F. These figures do note "data not verified by test".

The figures for the 737 note that the contours were produced by computer analysis. These contours only start at the aft end of the aircraft. The engines on the 737 are located closer to the ground than the 707. The original 737-100 and -200 models have the highest temperatures. At idle thrust, the 150°F contour barely reaches the tail of the plane, though it may reach the ground closer to the engines. At takeoff, the 200°F contour extends past the tail, and definitely reaches the ground.

The DC-8 is similar to the 707. At idle power, only small contours are shown for 125°F (52°C). At takeoff power, temperature contours reach 200°F but only the 150°F contour reaches the ground.

Based on these temperatures, it does not seem that an aircraft sitting on the runway with engines at idle would cause issues with the pavement. On a hot sunny day, asphalt could easily reach 150°F or more.


Can private flights between the US and Canada avoid using a port of entry?

CANPASS gives a streamlined entry into Canada, allowing you to land at a port of entry and just report by phone.  To go into the US, you need an eAPIS account.  I think that with eAPIS you still need to meet in person with a customs person.  A friend in Montreal used eAPIS to travel to Vermont regularly.  He said it was a lot of hassle to get set up and go through the process the first time, but after that it was not too bad.  On the way back he just had to land at a convenient POE and call in.
Not quite an avoidance of POE requirements, but otherwise pretty convenient.


Should I wait for Tower to provide runway exit instructions?

Note: I am assuming you are asking about US regulations.
If the tower does not give you an instruction, you should not wait for one. Leave the runway at the next available taxiway and then wait for further instructions:

4−3−20. Exiting the Runway After Landing
The following procedures must be followed after landing and reaching taxi speed.
a. Exit the runway without delay at the first available taxiway or on a taxiway as instructed by ATC. Pilots must not exit the landing runway onto another runway unless authorized by ATC. At airports with an operating control tower, pilots should not stop or reverse course on the runway without first obtaining ATC approval.
b. Taxi clear of the runway unless otherwise directed by ATC. An aircraft is considered clear of the runway when all parts of the aircraft are past the runway edge and there are no restrictions to its continued movement beyond the runway holding position markings. In the absence of ATC instructions, the pilot is expected to taxi clear of the landing runway by taxiing beyond the runway holding position markings associated with the landing runway, even if that requires the aircraft to protrude into or cross another taxiway or ramp area. Once all parts of the aircraft have crossed the runway holding position markings, the pilot must hold unless further instructions have been issued by ATC.

(Aeronautical Information Manual, emphasis mine)


How did the windshield technology evolve?

The two biggest differences both relate to their widely different cruise speeds: the 747 at 500kt and the DC3 at 180kt. The 747 is also pressurized and the DC3 is not.

The 747 is curved for aerodynamics.

It is also much stronger.

PPG Cockpit Windows

The DC3 windshield is weaker and flat. There are two major versions of the DC3, one with a wide flat pane and another that splits it two, though with no attempt at airflow improvements. It seems the smaller pane of the split version could be opened. It also apparently leaked like a sieve.

Birdstrike protection testing was mandated after the DC3 went out of production.

  Section 25.775 requires windshields and their supporting structure withstand, without penetration, impact with a four-pound bird at VC (design cruising speed) at sea level. This regulation has been in place and is unchanged since part 25 was introduced in 1965.

You have undoubtedly heard of the NASA chicken gun, a compressed air device for accomplishing this test. Used by the British it on a train, it caused an extraordinary amount of damage to the cockpit being tested and even went through the rear wall into the passenger compartment. When enquiring of NASA as to the cause, NASA replied "Defrost the chicken".)

Mythbusters chicken gun


Which commercial aircraft can fly Micro-SLOP procedures?

According to the below references, these commercial aircraft are capable of doing the Micro-SLOP procedures with 0.1 NM increments:

INTERNATIONAL FEDERATION OF AIR TRAFFIC CONTROLLERS' ASSOCIATIONS 58TH ANNUAL CONFERENCE – Conchal, Costa Rica, 20-24 May 2019

  2.6.2 Most flight management systems in service today can execute an automatic offset track in whole nautical miles. Unfortunately, as offsetting by tenths of a nautical mile was only introduced in ICAO provisions in 2014, most flight management systems are currently incapable of executing such offsets. Of the major aircraft and flight management system combinations in production, only the Boeing BBJ, 737 and 787 are currently capable of offsetting in tenths of a nautical mile. Depending on the aircraft mix in the airspace, even if a State permits offsetting in tenths of a nautical mile, the majority of aircraft may not be able to participate in this SLOP, and the full benefits may not be realised.

Cir 331 A /192N Implementation of Strategic Lateral Offset Procedures ICAO

  1.3.8 The idea quickly emerged to employ the capability of some modern aircraft to offset in fractions of a mile for this purpose. Both Boeing and Airbus announced that all their future aircraft would have the capability to offset in tenths of a mile and it was therefore clear that using such “micro-offsets” to mitigate the collision risk would be viable in the future.

IFALPA (International Federation of Air Line Pilots’ Associations) Saftey Bulletin (NAT Lateral ASEPS)

  Micro-SLOP is currently authorized throughout the NAT region. The latest information available to ALPA is that the most recent Boeing B737s (NG, Max), B787s, and the B777X (when it enters service) have Micro-SLOP capability. Airbus is planning an enhancement across their product offerings in the 2022+ timeframe. There is no hazard introduced by this mixed implementation of Micro-SLOP.


Do the A380 ailerons act as air brakes on landing?

Answer is yes, good eye. From the A380 flight crew manual:

You can watch it here.


Would ground effect and FOD ingestion be factors at high speeds close to the ground?

The amount of time a plane in a dive spends close enough to the ground to ingest foreign objects and thereby damage its engines is of order ~fractions of a second.

For a plane that is about to strike a building on the ground, the idea of FOD damage to its engines is not even relevant.


What are the design goals for NASA's X-57?

I just found an answer (pointed out by @RoboKaren), on another question. The only reason I am copying this is that the original question was not really about goals. This is from Mark Moore:

source: What are the advantages of the NASA LEAPTech propeller on wing technology?

  The lift augmentation has nothing to do with Magnus lift (or the
  Coanda effect). It is simply an increase in the dynamic pressure
  across the entire streamtube of the wing.

  At the low takeoff and landing speeds (slightly above a 61 knot stall
  speed), the induced velocity of the propeller almost doubles the
  velocity that the wing sees; and the lift is a function of the
  effective velocity squared. But due to swirl and other effects the
  wing doesn't experience a 4x increase in lift, but about 2 to 3 times.

  The objective of the inboard propellers is not to achieve a high
  propulsive efficiency, instead we want those inboard props to achieve
  high induced velocities - think of them as part of the high lift
  system (which happens to also provide thrust redundancy).

  In fact landing is the critical case, and having lower propulsive
  efficiency (and a poorer spanwise lift distribution because of the
  swirl effects) is helpful in creating sufficient drag. The inboard
  props are not active in cruise flight, but simply fold against the
  nacelle (many motorgliders already do this type of folding on the
  nose).

  By only using the wingtip propeller at cruise, we're able to achieve a
  ~95% propulsive efficiency (versus 75 to 85% with a typical fuselage
  nose propeller installation). The reason for this is because we have
  lower blockage and scrubbing drag, as well as being able to take
  advantage of the strong wingtip vortex by rotating against it. Since
  electric motors don't experience a power lapse with altitude (because
  it's non airbreathing) we have far too much power at altitude anyway
  so by only using the wingtip motor it doesn't cause much penalty in
  motor weight (and electric motors achieve ~6x lower weight per
  horsepower than a reciprocating engine).

  In terms of batteries and range, the key is to achieve high efficiency
  cruise flight and it looks like with current batteries a 200 mile
  range is achievable. By adding a small <50 hp range extender motor,
  the aircraft will be able to achieve ~400 mile range. We're currently
  designing an X-plane that will fly in 2017 to substantiate all these
  numbers, with the ground test rig (wing and truck) providing an
  aerodynamic database to validate our analysis.

  Please note that I'm the NASA Principal Investigator of the LEAPTech
  Distributed Electric Propulsion integration approach, and the
  Convergent Electric Propulsion Technology (CEPT) X-Plane demonstrator.
  We have a team across NASA Langley and Armstrong, as well as two great
  small companies, Joby Aviation and ESAero who are retrofitting a
  Tecnam P2006T with a Distributed Electric Propulsion wing system.


What do we mean by taking the lowest of ZFW; TOW and LW to determine the maximum takeoff weight of the day?

If you know how much fuel you'll need for the flight, then the things that can limit your load (which is really what you're interested in -- how much weight can I put on the airplane today, in terms of passengers + cargo) are:

Empty weight + Payload (ZFW) may not exceed Max ZFW
ZFW + fuel for the flight (TOW) may not exceed MTOW
TOW - fuel burned during flight (i.e. ZFW + fuel reserves) may not exceed MLW

Depending on how much fuel you expect to burn and how much fuel you expect to land with (i.e. reserves), any of these may be the most limiting.
Max ZFW will be limiting for a short flight with minimal reserves required... you're taking off with minimal fuel and landing with minimal fuel, but if you loaded up to max TOW or max LW you'd be well over MZFW.
Max TOW will be limiting with lots of fuel burn planned: if you loaded the pax/cargo to MZFW, the fuel load would put you over MTOW.
Max Landing Weight tends to be most limiting when you need lots of fuel at landing for reserves.  (If you envision an extreme case where you need 5 hours of fuel still in the tanks at landing, if you were close to MZFW you'd be way, way over max landing weight, so the latter rather than the former is most limiting.)
Modern airliners tend to have a range of landing fuel that tends to suggest when MTOW or MLW will be the more limiting.  If you're planning to land with min reserves, you can load to MZFW easily enough (max ZFW + min reserve gas will be < max landing weight); you'll probably be limited by either MZFW or MTOW.  If you need to land with significant reserves, MLW will probably be most limiting for how much cargo/pax you can have.
If you can find a typical empty A-320 weight and typical "good weather" and "bad weather" fuel reserve values (maybe 3t and 7t for the latter), as well as some "short haul" and "long haul" burns (guessing, maybe 3t short haul and 20-25t long haul), you can work out various cases of what load you can accept in each scenario of good/bad wx and short/long haul flight using the equations I described above.
EDIT: The discussion above treats MTOW as a constant, although in reality that isn't necessarily the case: the max takeoff weight on a high, hot, and short runway can be significantly less than the structural max takeoff weight.  The basic math doesn't change, but it's fair to note that MTOW is the lesser of structural MTOW or the performance-limited takeoff weight.  (The various performance limits can be any of a number of things: accelerate-stop, accelerate-go, climb performance, etc.)  For some jets, you can also have a performance limitation of Enroute performance, i.e. being able to clear enroute terrain if an engine fails.  Most modern jets, however, have sufficient performance that this isn't often (or ever) an issue.  But it is the stuff of ground-eval orals.


Can helicopters have engines running while rotor blade stays stationary?

Yes, many helicopters (but not all) can do this. There are 2 main methods:

a clutch between engine and rotor system
for turbines only: a rotor brake on the engine output shaft. The engine contains a free turbine (i.e. a turbine stage that isn't attached to the compressor) that drives the rotor system. If you brake this shaft, the engine can run without spinning the rotors.


How close do you have to be to an underwater black box to detect it?

This excellent explanation is taken from Avionics News in 2006:

FDRs are equipped with an Underwater Locator Beacon (ULB). If you look at a picture of an FDR, you will almost always see a small, cylindrical object attached to one end of the device.

If a plane crashes into the water, this beacon sends out an ultrasonic pulse that cannot be heard by human ears but is readily detectable by sonar and acoustical locating equipment.
There is a submergence sensor on the side of the beacon that looks like a bull's-eye. When water touches this sensor, it activates the beacon.
The beacon sends out pulses at 37.5 kilohertz (kHz) and can transmit sound as deep as 14,000 feet (4,267 m). Once the beacon begins "pinging", it pings once per second for 30 days.

Newer FDRs can now transmit as deep as 20,000 ft.
The following table is taken from a fascinatingly detailed article on Hydro International about the retrieval of black boxes. It shows the radius you can pick up the signal of a pinger from:

Notice that if pingers were replaced with more powerful transponders, the range could be drastically improved!
The article also points out, that in very deep water:

under normal conditions, the existing pinger would not be detectable from the surface in depths exceeding 2km


What is an example of a quantitative analysis for the lift using Newtonian mechanics?

The governing equations of fluid mechanics, Navier-Stokes equations, are derived based on Newtonian mechanics (plus thermodynamics). The circulation theory of lift is derived using a simplified form of N-S equations. It's powerful because it's predictive for important things like lift and induced drag. The Newtonian explanation is not that useful because it's not predictive. Good for party talks, but poor for engineering.

That being said, if you couple it with the concept of control volume and mass conservation, you can derive something. Take a look at NASA Memo 1-16-59L. To summarize, as air moves past the wing, it gets deflected, so the lift in the vertical direction (normal to the incoming flow direction) is:

$$L=\dot{m}\Delta V$$

where $\Delta V$ is the portion of air that was induced across the wing interface in the vertical direction, $\dot{m}$ is the total mass flow rate of air through the wing. That's the Newtonian part of the story.

Now from the conservation of mass, what comes in = what goes out. So we can express mass flow rate as, assuming the wing is like a giant circle with diameter equal to its span (note that this assumption is the major pitfall of this analysis, since there is no reason the stream-tube has to be the diameter of the wing):

$$\dot{m}=\rho A_iV_{i}=\rho\pi(\frac{b}{2})^2V_{\infty}$$

where $b$ is the wing span, $V_{\infty}$ is the freestream airspeed, $\rho$ is air density.

As for the change in vertical airspeed, we can parametrize it by assuming the whole stream tube gets deflected by the wing through an angle $\epsilon$. Therefore, $\Delta V=V_{\infty}\sin \epsilon$, and:

$$L=\frac{\pi}{4}b^2\rho V_{\infty}^2 \sin \epsilon$$

That's pretty close to the lift equation that we know. In fact, if you express drag as the loss of horizontal airspeed, apply small angle approximation to the second order, then normalize the lift and drag by $\frac{1}{2}\rho V^2 S_{ref}$, you get (with $S_{ref}$ being the reference wing area, $A$ being the aspect ratio):

$$C_{D}=\frac{C_L^2}{\pi A}$$

That's the induced drag expression for an elliptical lift distribution that we would get from the circulation theory of lift. But that's pretty much as far as you can go. You have no way of estimating $\epsilon$ from first principle, so the theory isn't all that predictive.


How does a flight control computer deal with control surface disengagement?

Well the A320 and A340 have 2 actuators per deflection surface (in case of elevator or aileron, spoilers do not have 2 actuators per 1 surface).

If one of these actuators fail, as in they have no pressure supplied to them by either hydraulic power systems (Blue,Green,Yellow) the other actuator which is supplied by a different pressure supply system (to avoid a single point failure) will take control of the of the surface. The flight control computer would continue working under normal law given that the other 2 Primary flight computers (PFC) are working properly. However, if the secondary flight computers(SFC) take control (after at least 2 failed PFCs), the aircraft would lose the ability of flight with normal law and thus direct law would be activated.

A disconnection between LVDT and a deflection surface would cause a disruption of the feedback towards the PFC. The PFC will notice that it is sending signals but receiving no change in feedback and will consider itself out of order. This would mean the respective PFC will render itself in a passive state and pass control to the other PFC connected to its own actuator. Depending on whether a PFC or an SFC in control, you would have either normal (at least PFCs intact) or direct law (the 2 SFCs are in command)

A Mechanical backup is available in the form THS(Trimmable Horizontal Stabilizer) which is activated by the trim wheel and the rudder which is available through the pedals for the A320 and A340.


What material is used to make the interior sidewalls panels, ceiling as well as luggage bins in a commercial aircraft?

The materials used in aircraft are similar regardless of airline or type of aircraft, since all passenger-carrying craft must meet  flammability requirements.

The side panels, the ceiling and the luggage bins are made out of a Glass Fiber Reinforced Plastic (GFRP) that must meet fire/smoke/toxicity (FST) requirements.The small window shade panels that slide down to cover airline windows, are typically thermoformed polyetherketoneketone (PEKK) plastic sheet. Some other high performance thermoplastics can be found on an airliner's interior, like the polyetheretherketone (PEEK) and the polyvinyl fluoride (PVF) (mostly as decorative surfaces laminate).

Reference: https://www.compositesworld.com/articles/advanced-materials-for-aircraft-interiors


How does the Pratt & Whitney F119 achieve its features?

The afterburner is aft of the gas core of the engine in the jet pipe and bypass air from the fan would have already been mixed with the exhaust gases from the core prior to passing through the afterburner flame holders.
Supercruise is by definition supersonic cruise flight without the use of afterburning, so augmentation would not be in use here
Counter rotation of the spools reduces net torque from the spools upon the structure of the engine requiring less metal and therefore lightens it.  The length of the engine is reduced by making use of a single stage, high efficiency turbine rotor per spool as opposed to multiple turbine stages per spool, which would make the hot section of the engine longer.


Why do flight attendants wear gloves during takeoff and landing?

From Finnair's Facebook page, it looks like Flight Attendancts wear gloves for safety reasons during takeoff/landing and galley preparation. Also it seems they do remove them when greeting passengers.

https://m.facebook.com/Finnair/posts/10151523242117911


What type of fuel is used in helicopters?

It depends on the engine. A piston engine will use avgas (aviation gasoline) or diesel (or Jet-A for availability reasons) depending on whether the engine is a diesel engine (which can burn jet fuel), while a turbine engine will use jet fuel. Essentially whatever the engine is rated to burn.

The fuel tank is somewhere in the fuselage near the center of the rotor. This to avoid the center of gravity shifting with the fuel level.


The topics you describe are certainly part of aerospace engineering, however they are somewhat specialized topics. I am not trying to discourage you, but Aerospace engineering involves a lot of mathematics and physics. If these fields do not appeal to you, you will be having a hard time to get through to the sweeter parts.

Some universities only offer a Master programme for Aerospace engineering, which typically follows on to their Bachelor programme Mechanical engineering. If you are really interested in aviation, I would recommend to select a full (Bachelor and Master) Aerospace programme.

Aerospace engineering programmes generally involve a thorough basis of mathematics (linear algebra, calculus) , physics (mechanics, thermodynamics), material sciences before introducing more specialized subjects like aerodynamics, aircraft performance, and space flight. At bachelor level, you will get an introduction to a diverse set of aerospace related subjects. At master level you will go deeper into an area, although you will have to accept that you won't master all subjects you mention.

I had a good time at Delft University, it certainly has a good Aerospace Engineering programme which I would recommend.
In addition I had the pleasure to work with a graduate from Bristol university, she is very knowledgeable. I'd certainly look into their programme as well.
For Scandinavia I would look into aerospace programmes in Sweden. Sweden has quite an active Aerospace industry. Linköping is their centre of Aerospace Engineering.


Can leaning provide more power when running at full throttle?

Yes. The engine will produce its optimum amount of power for throttle setting when leaned to the correct stoichometric mixture.   The primary risk during operation at peak EGT/TIT is of course the high temperature during operation and greater wear and tear. Engines are usually operated approximately 50° rich of peak for max performance or 50° lean of peak EGT for economy operations, depending on the model of engine, flight regiment, etc.  Rich mixtures are preferred to keep the engine cool and minimize detonation risks, but it can also foul the sparkplugs with lead deposits, reducing engine efficiency, power and causing engine roughness during operation.  Excessively lean mixtures can sip gas during cruise but risk fuel starvation or put the engine at a high risk of detonation resulting in severe damage.  For these reasons, the leaning range I stated above is the most widely used.

Normally aspirated engines are often leaned prior to high-performance operations at high altitude‘s, such a short take offs from a mountain airstrip, etc.


Why don't smaller powered airplanes have better lift-to-drag ratios?

There are plenty of smaller power planes that achieve those numbers; motorgliders.  And motorgliders with L/Ds in the high teens and low 20s are pretty efficient cruisers.

So the real question is; why aren't all light aircraft made to be like motorgliders?

Well, motorgliders have their disadvantages.  The long wing span is a problem fitting in on the ground.  The long wings are heavy, which limits payload.  The long wings result in slow roll rates and general controlability problems.  So if you are going to live with the hassle of long wings, it has to be really worth the trouble.

And probably the biggest one; the long wings stop being an aerodynamic advantage and become an impediment when you want to cruise at significant margins above speed for best L/D.  This is the case for aircraft that cruise at low altitudes if you want to cruise at 2-3 times max L/D speed efficiently.  In this case, < span = better.  WW2 fighters modified to be optimized for low altitude combat had their wing spans reduced.

Airliners are more like the motorglider, and benefit from the L/D benefits of high aspect ratio because of their operating environment.  They cruise at very high altitudes where indicated airspeeds are low because of the thin air.  At FL400, an airliner might be cruising in the thin air at only 280 kts indicated, maybe only 2X its flaps up stall speed (going 500+ true, but it's the indicated airspeed that matters - if you could stick your hand out the window, you'd feel a 280 kt wind blast, not a 500 kt wind blast).

It's cruising a lot closer to its max L/D speed than the low altitude airplane that flies at 3-4 times its stall speed, and so it benefits from the span and area like a motorglider.  To take that to it's most extreme, you have the Lockheed U2, which needs all that span and area to make it up to 75000 ft (where the indicated airspeed is only about 80 kt going, say, 200 kts true or whatever it is).

You do see some aircraft like the Diamond light twins with quite long aspect ratios for what they are.  This is done mostly for rate of climb. because in a light twin, single engine climb performance is critical, and the high aspect ratio really helps (climbing close to max L/D speed) and that's factored into the balancing act of deciding just how long the wings need to be for good single engine performance without giving up too much controlability or taking on too much weight (helped there by composites) or too much space on the ramp.


Do test pilots on commercial aircraft wear a parachute?

To the best of my knowledge, all commercial aircraft being tested have their pilots take on parachutes and hi-vis clothing in addition to creating a possible means of egress on all important flights, such as the first flight and high-speed tests.

Since getting the cabin doors open is practically difficult, the solution I think most producers use is to built a chute down the front cargo entrance which can open.

Bombardier produced a pretty extensive film for their new CSeries.

Here's the solution employed on the Concorde:


Why is the extra allowance for wheel installation on A380 in terms of degrees instead of torque/torque percentage?

The reason is simple, the measurement from the point correct torque is achieved to the location of the hole for the bolt is in degrees, not ft-lbs (the number of degrees is absolute, whereas the force needed to get the alignment can vary). The torque specification has a built-in tolerance for additional torque needed for alignment. If you have to go more than X degrees to align it means you'll be applying excessive torque.


Could an arrow planform be better for a supersonic aircraft than a delta? Why?

The first thing to note is that these papers are from 2003 and 2013 respectively. Since then, they have not set the world on fire.

One concern over their quality arises when I recall that the "Warped NFL wing" is typical of the reflex-cambered supercritical wings first developed around the 1970s. If you check out the inner section of say the Airbus A380 (and I suspect any modern jetliner) you will see a certain amount of that technology incorporated. But laminar flow notoriously vanishes once you fly into a few bugs or some mechanic leaves an oily smear and, despite being touted back then and as far back as the late 1930s, it has only ever produced modest results on any flyable airplane.

Next, what about this braced wing concept. The linked source discusses it on Page 10:

"A possibly viable alternative configuration for the
conventionally sized long-haul CTOL transport mission is the strut-braced wing. Strut-bracing allows
thinner, smaller chord, lower sweep and higher aspect
ratio wings. The smaller chord, leading edge radius
and sweep have a favourable influence upon HLFC,
increasing the amount of wetted area laminarized and
reducing suction mass  ̄ow and roughness sensitivity as
well as increasing attachment line stability. Other
`strut-related’ benefits include large drag due to lift
reductions from the wing tip engines and greater span
enabled by the strut, as well as large wing weight
reductions. Circulation control, powered by the auxiliary power unit, could be utilized on a conventionally
sized tail to work the engine-out problem. All these
benefits produce very large increases in the lift±drag
ratio and range at cruise."

It also notes on Page 5 that:

"More unconventional supersonic applications of [laminar flow control], again by Dr Pfenninger, to a strut-braced high aspect ratio arrow wing configuration indicates phenomenal performance levels, L/D on the order of 15-20 versus the 9-11 typical of advanced conventional configurations (with LFC)."

Now I don't know about you, but when I read of a "phenomenal" 40% drag reduction sought 17 years ago but never realized, I smell a rat. I wonder what software modelling the researchers used - 2D or 3D? At sharp sweep angles it totally matters. Were they naive enough to assume flawless laminar surfaces maintained throughout a transcontinental flight? And engines at the tips of the wings, evidently in a kind of sesquiplane variant of the Busemann biplane? Oh, spare us the FAA's demand for directional stability combined with altitude maintenance and adequate range in the mid-Atlantic one-engine-out condition.

So I think you can see where this is going.


What avionics systems are interfaced with ACARS?

ACARS, otherwise known as Aircraft Communications and Addressing Reporting System, is almost always interfaced with the #3 VHF Communication System. Ordinarily, that #3 VHF system is set for "Data Mode." Some aircraft have the ability to use the #3 VHF as an auxiliary communications system by putting it in voice mode, and other aircraft dedicate it to strictly data mode.

However, I have seen operators tie the ACARS system to the #2 VHF system when there is no #3 VHF system installed. In this case, it's ordinarily up to the pilots to switch between voice and data mode on the #2 VHF system. I can only imagine how annoying that must be!

While VHF is most frequently used on domestic flights, its relatively short range does little good on international flights over water. On aircraft meant for such long hauls, the ACARS system is usually tied to the HF radios and the SATCOM system. If I recall correctly, the ACARS system opts for VHF communications as the primary method. If there is no VHF available, or its rendered inoperative, the secondary method is often SATCOM; failing that, the HF systems.

In order for the aircrew to interface with the ACARS system, there is some sort of display with a keypad they interface with. On the vast majority of aircraft I've worked on, that display is often referred to as either the MCDU or CDU. On aircraft with MCDU's (Multifunction Control Display Unit), the pilot can select the mode they prefer to be in (ACARS, FMS, etc...), and can interface with the appropriate system through that singular central display - kind of like selecting what program you'd like to run on your computer. If the pilot selects ACARS, they can interface with all the relevant data pertinent to the ACARS system. If they select FMS, they can interface with the FMS (Flight Management System); and so on and so forth.

On aircraft equipped with CDU's (Control Display Units), usually there are completely separate displays/interfaces for the FMS and ACARS. In that case, there are a plethora of options from a number of different manufacturers. I've seen touch screens, a secondary but different style CDU dedicated to ACARS communications, and so on and so forth. It's wide and varied.

The MCDU and/or CDU usually interfaces with an ACARS Management Unit. That management unit is ordinarily the "brain" of the ACARS system. All pilot interactions with the MCDU/CDU are sent to the ACARS system, usually via a 429 Databus. The best way to think of this is that the MCDU/CDU setup is like your computer monitor and keyboard. You input data and see those inputs with keyboard and monitor, but the real "action" is taking place with the memory and processor "behind the scenes." That behind the scenes action is the ACARS Management Unit.

The ACARS Management Unit (MU) can then interface with a variety of other systems and subsystems largely based on operator configuration. Some operators choose to log crew hours with the use of OOOI (Out, Off, On, In) times based on subsystem inputs to the ACARS MU. For example, when the beacon turns on, an input to the ACARS MU generates the "Out" time. When the aircraft takes off, the ground sensing mechanism of the aircraft sends a separate signal to the MU letting it know that the aircraft has left the ground. When that ground sensing mechanism changes state again (aircraft lands), it sends another signal to the MU letting it know that the aircraft has landed. Finally, when one of the doors (usually the L1 door) is opened after flight, the ACARS receives a signal from the door switch, and the "In" time is generated.

Sometimes the MU is tied to an ACARS Aircraft Personality Module (APM). This is usually just a separate unit with DIP switches set to a certain configuration so no matter what MU is installed on a particular aircraft, it can pick up the "correct identity" and act accordingly. Other times, there is no APM and the configuration control is handled exclusively by the software load often verified by the mechanic after installation.

Also, with the advent and implementation of ADS-B aircraft, GPS position data has begun to tie in to the ACARS system. If you want to see a mechanic roll his eyes, ask him to do a full functional check of the ADS-B system in the rain or cold. It's hours long, it never fails, and the consequences of what happens if it is failed are negligible. Most of us see it as a giant waste of time... But I digress.

Finally, I'd like to note that all of this information is with the caveat that every operator is different, and so is every aircraft. There are endless combinations of systems that could or could not be tied into the ACARS system. Generally speaking, though, what I've mentioned above is a fairly standard installation.


You are 1498ft above the place where the pressure is 27.83InHg. So how high are you above the place where the pressure is 29.92InHg?

27.83 is 2.09InHg higher than 29.92, ie roughly 2090ft higher. So you are 1498 + 2090 above the place where the pressure is 29.92InHg, ie your Pressure Altitude is ~3588ft.


Why are some aircraft windows painted over?

If you look at the seating chart for that plane, you'll notice that those windows match the location of toilets and galleys.

Note that the exact position of toilets and galleys may change during the lifetime of an aircraft, so it's easier to have all the windows installed by design, and just obstruct some that are not used. Even if it were just obstructed from within, I suppose it's better if in an emergency, if emergency personnel had to look inside the plane (to check for people still trapped inside), they would be able to identify quickly those windows that do not need looking through.


What is the function of the lower vertical fin on a MIG-23?

Directional stability at supersonic speed.

The air above the aircraft is less dense at supersonic speed, and elasticity reduces the effectivity of the fin - it bends and twists from the air loads. Conversely, the lower fin operates in denser air and creates more side force per area.

Also, the lower fin shifts the aerodynamic center of the empennage downwards, which is improving the handling characteristics. Adding area below the centerline helps to reduce the roll contribution of the vertical tail in a sideslip, which improves handling characteristics (more directional stability AND lower yaw-induced roll).

As long as the vertical tail surface sits above the centerline (more precisely the longitudinal axis of inertia - for now we can assume both fall together), any side force will also create a rolling moment.  This is undesirable because now a yaw command will not only create the intended yawing moment, but also a rolling moment.

If you want to yaw in order to turn, the vertical tail above the centerline will even roll the aircraft in the wrong direction, so you need more coordinated aileron command than with a symmetrical vertical tail.

The MiG-23 is not alone: Many supersonic combat aircraft use ventral fins. See the picture below for an example where the effects of additional vertical tail area are compared to the effects of a ventral fin of the same area.

(Source: Ray Whitford: Fundamentals of fighter design)

At supersonic speeds, the stiff, low aspect ratio ventral fin has a nearly constant contribution to directional stability, whereas the wing-like vertical tail loses effectivity in proportion to the Prandtl-Glauert factor $\frac{1}{\sqrt{Ma^2-1}}$ because it bends and twists more due to its higher aspect ratio. The small ventral fin of the F-104 raised directional stability by 30% at Mach 2.

(Source: Ray Whitford: Fundamentals of fighter design)

At high angles of attack, the vertical tail is in the wake of the fuselage which reduces local dynamic pressure and, consequently, effectivity. The ventral fin then is in ideal flow conditions, so it can help to stabilize the aircraft at high angle of attack, just when the fuselage contribution to instability is largest.


What are the differences between single and double annular combustion chambers?

See this answer for the difference between a SAC and DAC combustor. The EASA type certificate for the CFM56-7 also identifies which engines have the DAC and which have the SAC. The answer depends on exactly which -7B26 version you are referring to.


Is a powerback allowed by airlines as a safe maneuver?

Most modern commercial airliners are prohibited to power back.
Ground operations in aircraft fitted with high-bypass engines are usually restricted to idle and low-idle operations (enough to make the craft start moving, after which momentum enables further movement with idle only).
Aircraft capable of power back are predominantly thus turboprops, several operators of these allow their crews to operate accordingly.

It's not in common use anymore, for the following reasons:

Thrust reversing can kick up a lot of debris, posing a safety hazard. This would generally preclude any ground crew or spotters walking under the jet as is often done during pushbacks.
The previous point's especially true for under-wing jet engine designs, so only jets with fuselage-mounted engines are allowed to do it, and most of the bigger designs (DC-9, MD-80, 727) are being phased out of most fleets.
Pilots in most craft can't see behind them, another possible safety hazard requiring multiple spotters to be in contact with the pilot.
Thrust reversing uses a lot of fuel, so it's usually cheaper for the airlines to use a guy on a tractor for an assisted pushback.
Thrust reversing is loud, and during a powerback that noise is in close proximity to the terminal. The tarmac's a noisy place, but usually not that loud.

If you want to see a powerback performed by a commercial airliner, fly out to L'Esperance in St. Martin. The runway there is very short and has no taxiway leading to the end of the runway from either end, so larger passenger turboprops that service that airport have to turn onto the runway about 2/3 down its length, face their desired takeoff direction, then powerback to the end of the runway in order to have enough to take off. The larger and (relatively) busier Princess Juliana International, on the Netherlands side, has taxiways and turnaround areas at both ends of its runway.


Does thrust output in jet airplane remains constant when altitude increases?

It depends, as so often.
With the thrust available at low altitude, the indicated flight speed will be much higher than at high altitude. There, the reduced density and thrust will only allow flight close to maximum thrust and over a small speed range around the minimum drag polar point. In practical terms, at low altitude the airliner will not be able to fly level at the maximum thrust setting because it will exceed its Mach limit. But since the speed of sound is higher in warmer air, it will still fly significantly faster than at high altitude when it flies at the same Mach number at both altitudes.
If, on the other hand, you compare states at the same indicated air speed, the required thrust at low altitude will be a bit smaller due to the higher Reynolds number in warmer air. On the other hand, fuel flow will be a bit higher since the engine is not running at its optimum design point and the higher ambient temperature reduces its thermal efficiency.
While thrust will go down with air density (or dynamic pressure, for the same Mach number at low and high altitude) in the first case, in the second case it will increase slightly.


Why doesn't condensation form on the inside of airliner windows?

The humidity at the altitude airliners fly at is VERY low. However, a tiny bit of moisture does build up - if you look closely you'll see little ice crystals on the window (it's also very cold up there - in the negative degrees F usually). On top of that - airliners have multiple air conditioning "packs" that dehumidify the cabin air so there would be indeed by very little moisture to condense on the inside of the windows. Also, if you look at the windows - they are often two or three layers with quite a bit of space separating the outside of the window from the inside (often multiple inches). Some of this is for pressurization and some of this is for thermal insulation. The VERY cold outdoor air is not in direct contact with the inside cabin pane.


Why would my electric turn coordinator suddenly stop working?

The motor for the gyro in a Turn Coordinator runs off fixed frequency ac power. For this there is a circuit board in the unit that includes a solid state static inverter to convert the airplane's 12 vdc to ac (110 v at 400 hZ IIRC).  When they just die like that it's usually because the inverter or something else on the circuit board has gone south.


Could a turbofan have two adjacent fans?

Generally, it is more efficient to have one large than two small devices.

The twin fan solution not only needs a gearbox and driveshafts that a single fan solution does without, it also has more intake and nozzle surface area per cross section than the single fan. This will cause more viscous losses and lower efficiency. The only advantage would be if size limitations make a single fan impossible, but in that case it would be more straightforward to have each fan driven by its own core engine.

Famous examples of aircraft which used a single engine and two "fans" would start with the Wright Flyer models, all of which had a single engine drive two propellers via bicycle chains. But the list is short.
The list of opposite designs where two engines would drive a single propeller or fan would probably be longer, and my favourite from this list is the LearFan.

@jwenting correctly reminds me that for completeness a single power plant driving two contra-rotating propellers should also be mentioned. This is indeed the only way on airplanes of one engine driving two propellers, albeit not adjacent, that has seen wider adoption, from the RR Griffon on the Avro Shackleton to the NK-12 of the AN-22, Tu-95 and Tu-114.

Of course, all single-engine helicopters also use this one engine to drive their two propellers …


There are many factors that have kept Lighter Than Air Aviation out of the mainstay,

Speed: Airships are not exactly the most efficient means of moving through the air. As such their speed is far more limited than their heaver than air counterparts. For what its worth the main advantage of air travel in the modern world is speed. Its better to fly to Europe in 8 hours from New York than take a 3 week boat trip.

Size: Rigid or even Semi Rigid airships are not small vehicles. They require very large hangars to keep them protected from the elements considering they are fabric covered.

Capacity: The largest airship ever made was the Hindenburg class of airships. Coming in twice as tall and 3 times longer than a modern 747 and in its biggest configuration only able to cary 73 passengers compared to 550 for the largest configuration of the smallest 747 built. Granted the Hindenburg was not laid out like a modern airliner (it was more like a cruise ship) considering the slow speeds it would need to be that way even today.

Even with Helium being easier to come buy, its just not efficient to fly such a large craft for so few people.


Why do some aircraft have wings that tend to bend up?

All wings do flex, but in some modern airliners, the wings are built, fully or in part, with modern composites, that may deform within a larger elastic interval than metals...


Can the landing gear be pulled up while the plane is on the ground?

There is a weight sensor which senses if the plane is on the ground. This sensor prevents gear retraction while the plane is still on the ground. Failure of this sensor would prevent gear retraction after takeoff.

If you note closely, the landing gears (even the non-retractable ones) are not connected using a simple metal pole; rather, there is an oleo strut which is compressed by the weight of the aircraft. Besides airborne / ground detection, the struts absorb the vertical energy during touchdown.

I recall some decades ago engineers experimented obtaining the plane's gross weight by installing weight scales to each landing gear (as opposed to just an air/ground detection). The readings were found to be inaccurate and they soon abandoned the idea.

Landing gear stories cannot be complete without mentioning this incident in 1990:

A training captain of a Saab 340 was betting with his students that the weight-on-gear mechanism would prevent gear retraction while on the ground. On the accident airplane type, the mechanism would lock the gear handle, but the lock can be overridden if the pilot manually pull out and move the handle. The instructor confidently pulled out the handle and to his surprise, the hydraulics started to move and the gears were retracted while the plane was still on the ground.

(image source)

The aircraft was written off. This incompetent instructor pilot was killed 11 years later in another accident.


Do regulations require electronic checklists to be displayed on a cockpit screen or EFB?

No, nothing in the CFRs requires an electronic checklist.  In fact, almost the reverse is true - from experience I know that part 135 operators need to justify the use of EFBs, and have it approved on their operating certificate.  (i.e. FAA doesn't force them, they must demonstrate that the devices meet applicable standards and basically ask for permission...)
And I don't know of any GA aircraft that have electronic checklists built into their displays, although I cannot say that the capability doesn't exist.
Although many airline and GA pilots fly with EFBs, a great many do not.  It would be a tremendous burden to owners and pilots, and a regulatory nightmare to attempt to enforce the use of electronic checklists.
And there is absolutely no compelling reason to do so... The battery will never run out on a laminated paper checklist, so why would you want to force someone to use a less reliable method?


Where must the glider tow line connection be?

It needs to go just under the tip of the nose to have any chance.  This connection is equivalent to the thrust line of an engine, except that because the connection isn't rigid, the longitudinal location matters; the farther forward, the more stable (if the attachment is rigid, like an engine/propeller, it doesn't matter whether the thrusting component is forward or aft, from a stability perspective).
Probably most normal gliders hook up at the nose but a lot of them have hooks near the center of gravity underneath to facilitate winch launching, and when used for aerotow these are less stable and somewhat of a handful to fly for an inexperienced pilot, especially on crosswind takeoffs.
You will have to set the horizontal tail to apply enough trimming force to overpower the nose down component of the pull of the tow line, that is, more nose-up trim than necessary for free flight.
You will find that because the thrust line is more or less concentric with the roll axis, there is not much you can do for roll stability and will be stuck with whatever inherent stability is there from the dihedral effect of the turned up wingtips. Connecting the tow line to each wing tip will not help with roll, since the two lines still run to a single attachment (until you get the angle of the tow line to the longitudinal axis high enough that the "Y" connection is influencing roll, but the thing may still just arc down into the ground anyway), and connecting that far aft will make you completely dependent on the glider's inherent pitch stability and damping.
My prediction is that as is, whether you hook it at the nose or the wing tips, it will go all over the place, than crash, and to get it to just kite along smoothly behind while on tow, you will need a lot of wing dihedral, similar to a 2-control model.


Does anyone know what this approach chart symbol is?

What you want is the Frontmatter to the Terminal Procedures Publication, and in particular the pages under "Approach Lighting System" -- these document all the various permutations of visual approach aids found in the US NAS.

As to the symbols you are specifically asking about -- the "shell" is the standard symbol for an ODALS (OmniDirectional Approach Lighting System) that consists of two steady burning lights at each side of the runway threshold and five sequenced flashers leading down the extended runway centerline for 1500'.  The two circled "P"s are also standard symbols, but for PAPI (Precision Approach Path Indicator) lights -- a set of four bicolor (red/white) lights that sit beside the runway and are aimed so that you can see if you're above, on, or below the glidepath based on the combination of red and white lights you see.

As to the symbols being reverse (not boldened)?  That means that those lights are hooked up to a PCL (Pilot Controlled Lighting) box that listens for sequences of microphone clicks on the airport control frequency (UNICOM/CTAF, or tower for a part-time towered airport) and turns on the lights hooked up to it for a set period of time when a suitable sequence is given by a pilot.


What are the ways to keep the birds away from airfields?

The FAA has an FAQ on bird strikes and other wildlife hazards, which includes a (broken) link to their Wildlife Hazard Management at Airports - A Manual for Airport Personnel document.

Chapter 9 is called "WILDLIFE CONTROL STRATEGIES AND TECHNIQUES AT AIRPORTS" and includes the following techniques:

Change flight schedules
Modify the birds' habitat (food, cover, water)
Physically exclude the animals (not so easy with birds)
Repel the birds with vehicles, chemicals, sound, visual objects (flags, scarecrows, fake dead animals, lasers)
Repel the birds with trained falcons or dogs
Shoot nonlethal projectiles at the birds
Trap, remove and release the birds at a different location
Kill the birds with poison or other means

The document summarizes the various techniques like this:

  Habitat modifications to minimize food, cover, and water and physical
  barriers to exclude wildlife are the foundations of wildlife hazard
  management programs for airports. In addition, an integrated array of
  repellent techniques is necessary to disrupt normal behavior and to
  stress hazardous wildlife that attempt to use the airport. These
  repellent techniques must be used judiciously and backed by real
  threats to minimize habituation. To this end, lethal control of
  selected individuals of common species is sometimes necessary to
  reinforce repellent actions.


Why was the Spitfire's elliptical wing almost uncopied by other aircraft of World War 2?

Interestingly, I couldn't find an answer to this question on the website, but I've found an answer of Peter Kämpf on Quora. He brings forth the same arguments I wanted to mention, so I'll repeat them here.

Elliptical wings are very good - aerodynamically. If you want to minimize induced drag for a given lift requirement, you end up with an elliptical wing.

But a plane is not only aerodynamics.
You also have to consider:

Weight, an elliptical wing is not structurally efficient, and will lead to a higher weight, which leads to higher lift requirements which will lead to more induced drag, even with a very efficient wing.
Controllability, where and how the wing stalls determines if you're able to recover from a stall. Elliptical wings stall tip first, leading to bad stall behavior.
Manufacturability, a fully elliptical wing is very hard to make, with its double curves. This will make the wing more expensive.

If you include these factors, you'll see that you'll end up with a compromise. If you use wing taper (which is somewhat close to the aerodynamic optimal shape) but much easier to make and much lighter you'll see that you'll end up with a better design overall.

An analysis of how the design of a wing changes if you include the structural requirements was done by Jones and can be found here.


Has the wrong engine ever been mounted after maintenance?

January 2016: a "wrong" or non-functioning engine was mounted onto a Qantas 747. QF63 departed from Sydney to Johannesburg with a 5th engine.

The 747 is capable of carrying these kind of loads through anchor points on each of their wings.

Disclaimer: this wasn't by mistake, it was intended to get the "5th" engine to Johannesburg ASAP, to be fitted onto another aircraft.

As for the possibility of mounting an incorrect engine on an airplane by accident, it's very unlikely (impossible really). Jet engines are designed exclusively with the aircraft in mind. Further, jet engines are expensive you would make certain you order the correct engine for the corresponding aircraft. Aviation mechanics also receive sufficient training and the an engine replacement process isn't a one man job. It circulates through a group of individuals prior to actually making a purchase or deciding to fit a new engine.

Besides, even in the case where some unqualified individuals were to attempt mounting an incorrect engine, it wouldn't work. First, they would easily be able to distinguish the existing engines from the replacement. Second, the mounting the engine in the place wouldn't work, the mount points would be of a different shape and would consist of bolts and screws in different locations.


What is the purpose of a departure procedure?

A major advantage is standardization. An aircraft can be given a departure procedure, and assuming everything goes to plan, everyone involved will be on the same page as to what is going to happen. When air traffic control instructs an aircraft to fly a departure procedure, a large volume of information (e.g. climb to this altitude, turn this way, turn that way, etc...) can be communicated just by giving the name of the procedure. This is far more convenient and predictable for both the crew and controllers than giving every instruction individually. This allows controllers to focus on preventing conflicts and dealing with abnormal situations rather than issuing routine instructions, and it reduces the risk those instructions may be miscommunicated or misunderstood.

The procedure itself will have been developed by specialists based on all sorts of criteria, among them:

Obstacle clearance. This can be anything from the huge mountain range near the airport to buildings to towers to anything else. The procedure can be designed with a required minimum rate of climb, and pilots can ensure they are able to meet that requirement to climb over any obstacles. Obstacles might also be virtual, such as restricted areas for military purposes.
Noise abatement. Communities in the vicinity of airports often have noise complaints. Departure procedures can be designed to direct aircraft away from noise sensitive areas.
Traffic flow. Near a busy airport, large numbers of aircraft are maneuvering at low altitudes. Standardizing departure and arrival flows along certain corridors allows air traffic control to deal with aircraft moving in predictable ways and avoids potential conflict between different aircraft. Departure procedures help ensure separation between arriving and departing aircraft.
Regional traffic flows. In congested airspace where several busy airports are located in close proximity, procedures can be developed to ensure that traffic to and from each airport are kept separated. A good example is the busy airspace around New York City, where complicated departure and arrival procedures are used to separate traffic into the region's airports.
Winds. Different runways may be used depending on wind conditions. There may be different departure procedures available for different runway configurations and/or universal departure procedures that have different instructions depending on the runway used.
Navigational aids. While modern RNAV procedures are now available, traditional departure procedures guide aircraft from the runway through routes navigable through NAVAIDS like VORs and NDBs onto established airways.

Of course, an aircraft flying a departure procedure can always be given instructions to deviate from that procedure if it becomes necessary, such as for other traffic. If conditions permit, it's also possible for a controller to give a "shortcut" by circumventing part of the procedure, perhaps by turning early toward the next waypoint on the flight's filed route.