What are these elements on the back of a Boeing 737?

① Main outflow valve door

(Source)

A valve used for controlling the pressure in the cabin. Air is pushed into the cabin by the air conditioning packs, and exits by this hole. The flow can be adjusted using a valve which is located behind this door.

(Source)

The valve opening is controlled by the pressure controller when the automatic mode is selected, and by the crew when the manual mode is selected.

The design of the door includes teeth to decrease the aerodynamic noise, by better mixing air from the cabin and air ram air.

For more details about the air system, see this answer.

② Safety pressure relief valve

(Source)

This is one of the two safety valve used in case the main valve mechanism is jammed or ineffective. It's like a safety pressure relief in a pressure-cooker.

It limits the pressure within the cabin below a maximum value, to prevent pressure to damage the cabin vessel and/or create discomfort for the passengers.

③ Drains

(Source: Question)

Unknown function drains. I believe they are used to evacuate flammable fluids leaking from the APU.

④ Tail-strike assembly:

(Source)

This tail-skid is used to limit the contact between the aft section of the fuselage and the runway. It absorbs some of the tail strike force. While I'm not sure for the B737, on other models (B757, B777) the tail-strike assembly contains a sensor to alert the crew of the strike occurrence, by displaying a message on the EICAS (thanks to @RalphJ for questioning).

(Source)

The intensity of tail strike force is registered by the color indicator. A force higher than the maximum permissible hides the green strip and requires a maintenance check before the next take-off.

This strip is checked during the pre-flight inspection (walk-around) to prevent flying with a possibly damaged aircraft.

⑤ APU drain mast.

(Source: Question)

Drains oil from the forward accessory and the compressor bearing of the APU.

⑥ Aft drain mast.

(Source: Question)

Heated drain mast, part of the water system, and used to evacuate water and waste from the aft galley and the lavatory wash basins ("gray water"). Schematics of the B737 NG water system:

(Source: B737 NG General Familiarization)


What open databases with aircraft, airlines and country exist?

Geographic (routes, land-based infrastructure) data:

http://ourairports.com/data/
http://openflights.org/data.html

Coordination (scheduling, flight numbers) data:

http://www.virtualradarserver.co.uk/FlightRoutes.aspx

Aircraft (registration) data:

List of national government registers - http://www.gatwickaviationsociety.org.uk/registers_official.asp
ICAO address country prefixes - http://www.kloth.net/radio/icao24alloc.php
(old) id and routing data - http://www.libhomeradar.org/download/index.php


Did these pilots break any regulations by hand-flying an A320 for most of the cruise?

I think they were humouring you Cloud.  Hand flying a jet at level cruise speed is not fun.  It takes a lot of concentration and the novelty quickly wears off, and there is a high risk of getting busted for an altitude deviation due to a little bit of inattention. Even if you are able to find a sweet spot with the trim where it holds altitude perfectly with no stick pressure, making you think you can relax a bit, all it takes is a temperature change or running into a bit of mountain wave and airplane will climb or descend and if you are distracted.. and drift up or down a couple hundred feet... busted.  RVSM legalities aside, I can't believe even a bushy tailed FO would hand fly more than a few minutes in cruise.

Plus with AP on, just one pilot has to be monitoring the AP, and the other one can do paperwork, sleep, do handstands, play video games or whatever.  When hand flying, the pilot not flying has to be monitoring the pilot flying. For an entire hour plus?  No way.  Just too much work and risk to your livelihood.


Why does the FAA not support UL102 (formerly 100SF) unleaded av-gas as an alternative to 100LL fuel?

The problem is basically bureaucratic delays, helped along by easing of EPA timetables on the banning of leaded fuel, taking some of the pressure off, which has caused the developer of UL102, Swift Fuels, to suspend its 2nd Phase testing until the machine gets moving.


Is it normal to be scared of flying before becoming a pilot?

I think its extremely normal. The fear of the unknown is very powerful. When you are in control, you generally know what is coming and aren't surprised.

Most pilots I know have no desire to sky dive. They love the freedom of flying, but falling uncontrolled is not enjoyable to them.

When I'm not PIC, sudden drops give me that put in the stomach feeling. When I'm in control, that NEVER happens.


Since falling is just the final result of a ballistic arc if you let it go long enough, and ballistic arcs are considered "flight" per the Oxford Dictionary (as in the ballistic arcs of balls, spacecraft, arrows, etc being considered "flights"), then technically, a falling object is in flight.

You could give it just the tiniest lateral push when you drop it so it goes down with a slight ballistic curve;  in the end, no different from driving it laterally so it has horizontal energy/inertia with a high velocity that exactly counteracts gravitational pull, and give it a vacuum so it can do that indefinitely - a satellite - , the only difference being that and the ball being the location in or out of the atmosphere and energy put into it.

In other words, orbital vehicles, baseballs, bullets, are all "falling" and are technically in flight, and so is a ball you drop straight down... if the Oxford Dictionary definition is what you want to use.

In my own airplane, if I push over with just the right elevator input, and go zero G, my plane is now in a ballistic arc.  The wings are superfluous, for a few seconds anyway, and my plane is "falling", just not straight down.  So if you accept that in that condition it is still "flying", the falling is flight.


How is a light plane's nose wheel straightened during retract?

Left: Cessna 172RG nose gear strut (source). Right: nose gear centering cam (FAA).

With the weight off the nose gear after rotation, the strut extends to the unloaded position, and the two internal cams shown on the right mate and center the nose gear.

  Centering cams built into the shock strut structure accomplish this. An upper cam is free to mate into a lower cam recess when the gear is fully extended. This aligns the gear for retraction. When weight returns to the wheels after landing, the shock strut is compressed, and the centering cams separate allowing the lower shock strut (piston) to rotate in the upper strut cylinder (FAA).

On a Cessna 172RG this is achieved by the centering block (circled on the left) during retraction. The rudder is still allowed to move through a bungee link.

  Kinematics of the system automatically straighten the nose wheel as the landing gear is retracted. During retraction, the centering block on the upper torque link aligns and locks the nose wheel in the neutral position. Continued free movement of the rudder pedals is assured by the steering bungee (Cessna 172RG service manual).


How do electric propeller governors (or electrically controlled governors) work and what are their pros and cons?

They are much more prevalent than you think, and have been in use for more than 70 years. Rotax 912 and 914 engines can be installed with electric governors from MT Propeller. Airmaster sells them as well. You may also be surprised to learn that nearly 90% of German operational Luftwaffe aircraft during WW2 used an electrically-actuated propeller system designed by Dr. Hans Ebert of the VDM (Vereinigte Deutsche Metallwerke, or United German Metalworks). One example of these excellent propeller systems is in the Smithsonian's National Air and Space Museum.
This article does a pretty good job of explaining how they work.


What is that CFM56 with a toothed exhaust on an A321?

The “toothed” exhaust are called Chevrons and they reduce noise. They are an option on CFM56 equipped A321 aircraft.

Wikipedia CFM International CFM56

”GE and Snecma also tested the effectiveness of chevrons on reducing jet noise. After examining configurations in the wind tunnel, CFMI chose to flight-test chevrons built into the core exhaust nozzle. The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions, and are now offered as an option with the CFM56 for the Airbus A321”


How does the raked wingtip of the Boeing 787 work?

The raked wingtip of the Boeing 787 is now "le denier cri" in wingtip design, but has been successfully employed by water fowl for many millennia. The use of composite structures has made the three-dimensional shaping of wingtips much easier, and the first airplanes to use increased sweep at the wingtip were indeed composite gliders such as the Schempp-Hirth Discus.

Seagull (left) Schempp-Hirth Discus 2 (right, source)

In the times of metal wings, Dornier introduced their TNT (Tragflügel Neuer Technologie, in English: Wing of new technology) on aircraft like the Do 228, Do 328 and the Dornier ATT flying boat. It used a triangular wingtip with no change in trailing edge sweep, which is easier to manufacture in aluminium.

An Air Alps Dornier 328-110 landing at Fiumicino Airport, Rome, Italy, viewed from Ostia Antica. Picture by Makaristos.

You can think of the raked wingtip as of a winglet which has been folded down. Increasing the wingspan will involve a bigger mass of air into the creation of lift, and the induced drag is reduced. This explains already most of the effect, but the increased sweep adds some more benefits.

Higher sweep lowers the lift curve slope. This helps to reduce the lift contribution (and, consequently, the bending moment!) of the wingtip at high angles of attack. Therefore, raking the wingtip will result in a lower maximum bending moment.
The sweep also shifts the center of pressure of the wingtip backwards, adding a negative torsion moment. This moment lowers the angle of attack over the whole outer wing in gusts and at high load factors, again helping to lower the maximum bending moment at the root.
Especially in gliders, it allows to combine a near-elliptical circulation distribution over a wide range of angles of attack with good stall characteristics. The lower lift curve slope of the wingtip lets it stall at a higher angle of attack and reduces its lift contribution relative to its area at increasing angle of attack.

This aeroelastic tailoring, together with the low fuel consumption of modern high-bypass-ratio engines, allows the Boeing 787 to use a wing of an aspect ratio of 11. Previously, - apart from gliders - only special designs for extreme flying time and range like the B-24 Liberator or the Breguet Atlantique sported such high aspect ratios. Older airliner designs had to use lower aspect ratios (between 6 and 8.5) to have enough wing volume for fuel.


Do turboprop and piston engines perform differently at higher altitudes?

In general, a turbine engine will produce more power than a piston engine at higher altitudes. A turbocharged piston engine, with compressed air intake, will lose less power at altitude than an normally aspirated piston engine. A turbine engine will lose even less.

As a rough example, a normally aspirated Cirrus SR-22 has a service ceiling of 17,500 ft. A turbocharged SR-22 has a ceiling of 25,000.

A turbocharged piston Piper Malibu Mirage has a service ceiling of 25,000 ft., while the turbine powered Malibu Meridian has a ceiling of 30,000 ft.

The turboprop Pilatus PC12 and Socata TBM-850 have service ceilings of 30,000 ft. or above.


Why do aircraft with turboprop engine have black painted anti-icing system?

These are rubber boot deicing systems. When ice forms on the leading edge of a wing, pressurized air is used to inflate the boot so the ice will pop off. Normally, this inflation is not permanent but the air is pulsed. Activation is done by the pilot, so this system is normally switched off. Operation needs some care because if used too late (with too much ice) the boot may become impossible to be inflated.
Historically, it was believed that activation with too little ice would also render the boot ineffective, with ice building up around the inflated boot (ice bridging). This seems to have been a myth.

Deicer boots in operation (source: Wikipedia)
Other deicing systems use heat or constantly seeping deicing fluid. The first method is normally used on jets with bleed air or electricity as the heat source. The second system was for example used on the Beech Starship which had a titanium leading edge with millions of tiny, laser-cut holes for the application of deicing fluid.
Alternatively, surfaces are designed large enough to still be effective under icing conditions.
Fast jets do not need a deicing system - their stagnation point temperature is sufficient to remove ice. However, ice can still be a problem: When the supersonic B-1A was converted into the more stealthy, but subsonic B-1B, ice buildup inside the intake (which now had obstructions added so the engine compressor would be hidden from radar) would result in large chunks of ice building up, then breaking loose and damaging the compressor blades.


Would increasing rotor disc diameter increase efficiency in a helicopter by reducing disc loading?

Yes, increasing rotor diameter increases efficiency by reducing disk loading, exactly as you say.

From J. Gordon Leishman, Principles of Helicopter Aerodynamics, section 2.3:

  ..vertical lift aircraft that have a low effective disk loading will require relatively low power per unit of thrust produced..and will tend to be more efficient; that is, the rotor will require less power (and consume less fuel) to generate any given amount of thrust.


Would using a full span spoiler and a separate flap be a better design than a flaperon for a STOL ultralight?

There is an interesting NACA report on use of spoilers for roll control here.

I think if you want to do that the spoiler should just be around the outer 1/3rd of span (the rolling moment generated inboard is low - barely worth extending the surface inboard. And the spoilers should be at the rear spar.  For reasons I'm not entirely clear on, they work much better close to the trailing edge and the only time you see spoilers at the main spar is on gliders where they are being used only to increase sink rate.

A significant downside to roll spoilers you have to account for is a "dead zone" in the first, say, 10 degrees of extension due to it having to extend beyond the boundary layer to start to work, so you find the stick also has a dead zone a bit to each side of center.  This may be why you don't see more use of roll spoilers on ultralights and airplanes that have airfoils that are fairly turbulent aft of the spar.

On the  other hand, the report says, to my surprise, that roll authority is almost as good while in inverted flight (I guess in that case it acts like a split flap when the pressure distribution is flipped over and is able to move the wing while inverted in the same direction as while right side up - this is the first report I've found that directly addresses this).

I'll also point out that the use of roll spoilers and full span flaps is usually done on airplanes where you want to maximize the speed range like on the MU-2, where you have very large fowler flaps that increase the wing area by about 20% by being full span.  In the end, for an ultralight that flies down to 25mph and cruises at 55 mph, all that trouble to develop full span flaps and roll spoilers might only get you a couple mph reduction at the bottom compared to a large flap and smallish aileron at the tip, with negligible benefit at the top.


Does an AME's advertisement on the back of the medical certificate affect the document's validity under the FAA?

It's an interesting question...
The AME Guide gives the following "advice":

Medical Certificates – AME Completion
(Updated 07-26-2017)

Date the medical certificate to reflect the date the medical examination
was performed, NOT the date of import, issuance, or transmission.
Limitations must be selected from the list in the Aerospace Medical Certification
System (AMCS). Additional limitations may NOT be typed/written in.
Signatures: Each medical certificate must be fully completed prior to being
signed.

Both the AME and applicant must sign the medical certificate in ink.
The applicant must sign before leaving the AME’s office.

Give only ONE certificate to the airman
Use AMCS generated certificates only.
Transmit the exam electronically to the FAA using AMCS within 14 days.
The following are NOT valid:

Copies of medical Certificates;
Typewriter or handwritten certificates;
Obviously corrected certificates;
Paper 8500-8 certificates (any remaining paper forms should be destroyed
by the AME).

Replacement medical certificates must be issued by the FAA.

(Remember, the guide, like the Pilot Handbook, is a guide, not regulatory)
The AMCS also gives:

Certificates will be printed on standard printer paper as a single-sided document. Both the front and back sides will be printed on a single sheet of paper that can be folded.

But as far as I can tell in the FAR, the back side (inside when folded) does not have to be blank. As long as the medical certificate follows the 8500-9 and is in a "form prescribed by the Administrator", then it is a valid certificate.
Technically, even if it was against the rules, the medical certificate wouldn't be invalid, just the paper evidence of it would be. As long as the data was entered into AMCS, which it is required to be, the certificate can be reprinted in the proper format for showing anybody who asked.


Does the radar altimeter's position affect its accuracy?

In the aircraft I fly, the radar altimeter (aka radio altimeter) is calibrated for the installation, and the calibration compensates for the flight attitude of the aircraft at touchdown.  The radar altimeter is considered radio navigation avionics, and in many cases is required equipment.

So in theory, a flight attitude other than a normal approach attitude may cause some error.  However, since the primary use is during approaches, the consequence of this error is negligible, assuming flaps and gear extended.

In practice the avionics tech verifies that the altimeter reads a certain reading on the ground, and that reading is within spec for the installation. Practically, this means that the radar altimeter does not always read "0" when the aircraft is on the ground in a taxi or parking mode, however it is normally close.

My assumption in answering this is civilian aircraft, using normal low level short range radio altimeters, as opposed to delay Doppler or synthetic aperture radar which are used for other types of navigation applications.


What is this 'ball' in front of the cockpit of some fighters, e.g., an Su-57?

That is the infrared search and track (IRST). This particular model of an IRST is known as the OLS-50M in Russia and uses quantum well photodetectors.

Radar has two serious limitations, one is that advanced software can jam it, the other is that you give away your position when transmitting radar signals.

An infra-red sensor can be used to find and destroy targets without giving away the position of the aircraft and cannot be jammed. IRST is especially effective at detecting low-flying vehicles like helicopters that would otherwise be lost against a background. IRST can also be used to find, hunt down and kill ground vehicles.


Why are engines with carburetors hard to start in cold weather?

They are all harder to start in the cold, fuel injected engines included, and need an over-rich mixture for starting.  The rich mixture is required because a lean one is harder for a spark to light off if the fuel/air charge is cold.

Now, it's still cold outside after the engine warms up, so the air charge is still cold, initially, but on a warm engine it gets heated as it extracts heat from the intake passage, valve and cylinder head on its way into the combustion chamber (and on Lycomings, the carburetor, which is bolted directly to the oil sump).

Carbureted aircraft engines use primer systems instead of chokes, as mentioned in AEhere's answer, because it's undesirable to have that sort of obstruction device in the intake passage. The primer injects raw fuel at the intake port using a syringe type hand pump, most of which settles on the intake passage walls and runs down the tubes a bit, and sits there slowly evaporating, and when the engine cranks, the vapours add to the fuel normally drawn at the carburetor.  It does this for a period of time after the engine starts depending on how much prime you used.

Fuel injected aircraft engines are primed the same way, but since there are injectors already there at the intake port they don't require a separate primer system.  You just turn on the fuel pump with the mixture rich for x seconds and it injects raw fuel just like a primer system.

Carbureted aircraft engines also use a slightly richer than necessary setting in the idle circuit to help them run better when cold.  That's why you get a little rpm rise when pulling idle cutoff.

You can have too little primer fuel when starting, or too much, and it varies widely depending on the engine, its temperature, and the air temperature, so you have to learn how much is enough on each engine type.  A typical protocol is:

On a cold engine in warm weather, you might use 4 strokes of prime.
On a cold engine in cold weather, you might use 6 to 8 strokes of prime.
On a warm engine in cold weather, you might use 1 or 2 strokes of prime.
On a warm engine in warm weather, or a hot engine you just shut down, you usually don't need any prime, but may use a little half-shot of prime, or, if the carb has an accelerator pump, a short stroke or two of throttle applied while cranking (to avoid fuel running down into the air box since throttle pumping sprays extra fuel from the accelerator pump right at the carb, and if the engine backfires with fuel in the airbox you can have an intake fire).

Different engine models have different starting quirks, and different primers have varying fuel volumes per stroke.  It's something you learn on that engine type, along with whatever other unique characteristics of a particular aircraft you have to be aware of.


You're asking about this answer by Peter Kämpf, in which he writes (emphasis added):

  Now for turbofans. Here we have thrust which needs to be converted into power first by multiplying it with flight speed. It would be nonsensical to compare the static case – here by definition turbofans do not produce power.

You ask, "What is the referenced definition that results in zero power for turbofans at zero speed, regardless of the throttle setting?" The referenced definition is the sentence in bold above. Peter is defining power as thrust multiplied by flight speed.

Now, let's back up a little bit. Why would Peter define power like that?

For propeller engines (and car engines), defining the "output power" of an engine is easy: it's the power being transmitted through the drive shaft (which is the product of the torque the engine is exerting on the drive shaft, and its rate of rotation). I'm going to call this definition "shaft power."

A jet engine, however, doesn't have a drive shaft, so we are unable to use this definition. We're forced to choose a different definition of power, and so Peter chooses to use the product of thrust and flight speed. I'm going to call this definition "ultimate power". (This generalizes to any vehicle; we can define "ultimate power" as the forward force on the vehicle produced by its engine, times the vehicle's forward speed. Equivalently, "ultimate power" is the rate at which the engine adds kinetic energy to the vehicle.)

However, Peter also points that power as defined this way (ultimate power) can't be directly compared with the other definition (shaft power), at least not when the vehicle is stationary. This is because the "ultimate power" for a stationary vehicle is always zero, whereas the "shaft power" for a stationary vehicle is generally much greater than zero.

It may seem counterintuitive that the "ultimate power" for a stationary vehicle is always zero, but it is. Kinetic energy is proportional to the square of speed, which means that if an object is traveling extremely slowly (as in the first few nanoseconds after it starts moving), it gains kinetic energy at an extremely slow rate (on the order of nanowatts).


Is the "confirmed allocation" string in "A Scandal in Belgravia" a real airline practice?

No

Based on my research for string confirmed allocation, there were no references found related to airlines or their practice.

However, the background scenario about the conversation Sherlock was having, something like the following had happened (references: this and this and this and this and this):

(my paraphrasing, not actually a quote)

  Sherlock knows that 007 is a flight of Bond Air which is leaving for
  Baltimore tomorrow at 6:30pm. He is aware of a terrorist plot of
  having dead bodies on an airplane (14 seats allocations) so that no one actually dies. The
  first 0 in flight number indicates that zero causalities will happen.

P.S.: This question is not about aviation but movies.


If Sweden wants to export JAS39 to a 3rd country, will they have to get permission from the US govt.?

The most correct answer I can give is, It depends. More specifically, it depends on the specific components that are US sourced and it depends on who the ultimate end user is. But the most likely answer is yes.
All technology exports from the US fall under one of two sets of rules. They are the International Traffic in Arms Regulations (ITAR) controlled by the Dept of State and the Export Administration Regulations (EAR) controlled by the Dept of Commerce.
The US engines (F404/F414) that are the source of parts for the Volvo engines are military products controlled by the ITAR. When parts are exported separately from the complete engine, the export controls are set at the part level. So some parts may be controlled differently than others. But, in general any part controlled by the ITAR will require a license from the Dept of State before it can be exported. It is also possible that some components may be EAR controlled and require a license from the Dept of Commerce.
The licenses for export do contain restrictions on use, the end user, and reexport. That is typically spelled out in the individual license. Also, the 'technology' needed to transform the parts into an engine is controlled separately. That includes drawings, software, tooling, etc.
The question of reexport is covered in the ITAR under 22 CFR §123.9 Country of ultimate destination and approval of reexports or retransfers, and 22 CFR §123.10 Non-transfer and use assurances.
Specifically, from §123.9

(a) The country designated as the country of ultimate destination on
an application for an export license, or in an Electronic Export
Information filing where an exemption is claimed under this
subchapter, must be the country of ultimate end-use. The written
approval of the Directorate of Defense Trade Controls must be obtained
before reselling, transferring, reexporting, retransferring,
transshipping, or disposing of a defense article to any end-user,
end-use, or destination other than as stated on the export license, or
in the Electronic Export Information filing in cases where an
exemption is claimed under this subchapter, except in accordance with
the provisions of an exemption under this subchapter that explicitly
authorizes the resell, transfer, reexport, retransfer, transshipment,
or disposition of a defense article without such approval. Exporters
must determine the specific end-user, end-use, and destination prior
to submitting an application to the Directorate of Defense Trade
Controls or claiming an exemption under this subchapter.
(b) The exporter, U.S. or foreign, must inform the end-user and all
consignees that the defense articles being exported are subject to
U.S. export laws and regulations as follows:
(1) The exporter must incorporate the following information as an
integral part of the commercial invoice, whenever defense articles are
to be shipped (exported in tangible form), retransferred (in tangible
form), or reexported (in tangible form) pursuant to a license or other
approval under this subchapter:
(i) The country of ultimate destination;
(ii) The end-user;
(iii) The license or other approval number or exemption citation; and
(iv) The following statement: “These items are controlled by the U.S.
government and authorized for export only to the country of ultimate
destination for use by the ultimate consignee or end-user(s) herein
identified. They may not be resold, transferred, or otherwise disposed
of, to any other country or to any person other than the authorized
ultimate consignee or end-user(s), either in their original form or
after being incorporated into other items, without first obtaining
approval from the U.S. government or as otherwise authorized by U.S.
law and regulations.”


Yes they do, and according to the FAA they're better than paper ones. All sorts of aircraft can have electronic checklists, from large airliners to small Cessnas: modern avionics like the G1000 support checklists and the older but very common GNS430 does too.

In the US at least there's no legal requirement to use checklists in any form - electronic or paper - with some caveats:

They're considered a fundamental best practice in aviation, so if you don't use them then someone could argue that you're acting carelessly or recklessly
Incorrect - especially missing or incomplete - checklist use has been linked to many accidents (see this question too) so clearly it's in your own best interests to use them properly
If you're flying for an airline then your OpSpec probably requires use of checklists, in which case they're mandatory

As for mobile devices, there are already many EFB applications and standalone apps that support checklists. In some cases the app provides a template for a specific aircraft type, in others you have to enter it all yourself. There may be some copyright considerations, but third-party checklists are very widely available so obviously it isn't a huge issue.

Finally, it's worth noting that many pilots - especially those who own their own aircraft - customize checklists for their own needs.


In Spain, can I land and take off from my own property?

It depends on your local and national regulations.  In some jurisdictions, local municipalities can regulate use of land in that way, and in others they can't.  So first check with Spanish national regulations (if separate from EASA) on what constitutes an aerodrome or airport to see if there are any restrictions on use of an unlicensed piece of land as an aerodrome (probably not), then check with local municipal regulations or zoning or use bylaws that may restrict use of your land as an aerodrome (a definite possibility).


What guidance is there for pilots when reporting braking action?

The FAA issued a Safety Alert for Operators (SAFO), "Runway Assessment and Condition Reporting" #16009 on August 15, 2016. In it, it says that:

You'll notice it doesn't say "Fair" anywhere on there, that is because this SAFO replaced the word "Fair" with "Medium" on October 1, 2016.

  Pilot braking action reports will continue to be solicited and will be used in assessing braking performance. Effective October 1, 2016, the terminology ”Fair” will be replaced by “Medium” and pilot braking action reports will now describe conditions as Good, Good to Medium, Medium, Medium to Poor, or NIL. This will harmonize the NAS with ICAO standards.

(Emphasis mine)

Since the accident with Mike Pence happened on October 27, 2016, if a pilot was reporting "Fair", they were in violation of the SAFO and should have been reporting "Medium". You can read the NTSB report of this incident here.


Can Flex thrust be lower than climb thrust?

Yes.  On the CF-34 family, in theory, a maxed-out flex setting can be in the mid 80s N1 whereas climb thrust is normally high 80s/low 90s, and you could see thrust rise when setting climb if an extreme flex setup (max Assumed Temperature) (or in the case of the non-fadec engines like the 3B1, the climb bug appears at a higher value than the flex take-off thrust bug when you select "climb" thrust in the FMS)

The reason is to do with what you might call the mission priority of the two settings, and where the actual benefit in flex lies.

With flex, the priority is distance and gradient for obstacle clearance.  The flex setting is the lowest setting that meets the takeoff and initial departure performance requirement for accelerate/stop and initial climb gradient for that runway and all up weight.  The benefit of using the lowest setting is only partly from lower temperatures; an even bigger factor is erosion from silica particles (outdoor dust) which is most severe below 1000 ft.  The dustier the environment, the larger the flex benefit. (In the Middle East, CRJ operators were wearing out engines after only 5-7000 hours because they were doing max thrust takeoffs all the time and had to be cajoled into using flex.)

Climb thrust has a time priority, from an operational balance-of-factors perspective.  You want to get to altitude in an optimized time-related profile (as soon as possible taking various things into account), and an optimized time-related profile can require more thrust than the minimum required to meet take-off performance, in cases where a very large flex allowance is available allowing minimal take-off thrust.  Setting climb thrust that is a little higher than the flex take-off setting has little negative impact on engine life because you are now high enough that the erosion impact is negligible so there's little engine life benefit to a slower climb to altitude and you might as well optimize climb thrust to get there faster.


Why can't the 737 MAX's horizontal stabilizer autotrim be cut out by control yoke inputs?

Allow me to emphasize the article quote differently:

  That feature was disabled on the Max when M.C.A.S. was activated

For a regular trim runaway without MCAS activation, the yoke can still cut out electronic trim as before. The only change was inhibiting this behavior when MCAS is active. MCAS is designed to improve handling at high angles of attack. One way to get to a high angle of attack is with lot of yoke input, so it would somewhat defeat the purpose to stop MCAS in that situation.

The designers chose to trust MCAS (and its sensor inputs) over the pilot inputs in this situation. It certainly seems now that this trust was misplaced, but this has more to do with the system design than the general philosophy. Fly-by-wire planes have many protections that will change control input depending on sensor inputs. In normal law, Airbus alpha protection will prevent the angle of attack from increasing, even with full aft sidestick input. It compares three sensor inputs to do this, rather than trusting only one, but even that is not infallible.


What is engine power vs propeller thrust relation?

Power P, stationary thrust T, propeller swept area A, and air density rho are linked by this expression, derived from first principles and momentum theory:
T^3 = 2 · P^2 · A · rho
That's the maximum power available assuming a 100% prop efficiency.
Things change if the prop is moving forward, as in a flying plane. With the forward speed component, the blades have their angle of attack reduced in proportion to that forward speed. The blades work as wings, and a wing profile has a coefficient of lift that changes with the AoA. Drag does also change with a growing AoA, Hence, for every section of a fixed-pitch prop's blade, there's an optimum L/D at a given combination of rotating and forward speeds that gives the best efficiency. For a fixed angular speed of the prop, there is a given forward airspeed at which the prop works with maximum efficiency, that efficiency –and hence the thrust– dropping asymptotically as the forward speed grows...
Concerning the power delivered by a propeller in forward motion, it's the product of the thrust and speed...


Is it possible to drive into Gibraltar Airport's runway?

There are no physical restraints to entering the runway when the road is open.

You can see from this video of the crossing that Gibraltar police and the base for the Royal Air Force are present. The runway is owned by the Ministry of Defence. Anyone attempting to drive on the runway will probably be intercepted in seconds, although I am not aware of any reported attempts.

They also have a street sweeper to take care of FOD (foreign object debris).1

There are plans to build a new four-lane diversion road and tunnel section. Construction started in 2008 but it still hasn't been completed as of 2018. The crossing across the runway will be kept for exceptional, specific, or emergency use but pedestrians will still be able to use the crossing.


What are these strange blades behind the N1 fan in a Boeing 747-8 engine?

Those are Outlet Guide Vanes / Fan Exit Guide Vanes. They prevent the flow (bypass flow in this case) from rotating. The these vanes do not rotate, they are fixed to the housing. They also provide structural support.

Because there is no energy lost on the rotation of the flow the efficiency is increased.


Why did the Boeing 787 switch back to separate IRS systems?

There were also other practical end use issues as well. Having worked in the manufacturing and repair of theses fault tolerant units, one of the benefits was supposed to be the ability to plan maintenance. You could have a gyro or acceleromter voted out and still be able to take off and fly, since the F-T ADIRU had six gyros/accels and the SAARU four gyros/accels. Problem was the airlines weren't really taking advantage of this. They'd wait until you'd have two gyros or accelerometers voted out before and then be unable to take off due to restrictions. Some of the sensors sat voted out for years, with no replacement occurring.
Of course the airlines pointed the blame back the design. The F-T ADIRU was the third most expensive part of the 777 behind each engine. Most of them also did not carry spares for their repair inventory due to the costs of spares. Spare F-T ADIRU a couple years ago were running north of 2 million a piece. They found that the aircraft had less down time with a split system then using the fault tolerant system. Largely because they had ample spares for the split systems due the spare parts costing 1/10th the cost of the fault tolerants.


What method does ATC use to calculate distance between two aircraft?

The things you mention would matter, if you wanted to know the distance to 6 or more significant digits. But ATC does not need that precision. They need to be able to tell whether it's 4 nmi (too close), 5 nmi (still sufficient, but getting in trouble) or 10 nmi (no worry, but should not be heading directly towards each other). That is one significant digit.

The controller does not use any formula. They just look at the distance of the targets on the radar scope (which is drawn properly to scale). And possibly use the grid that is drawn over it or compares to the leader lines (indicating velocity) or history trail. The controller doesn't need precision, they need to look and see. And they are not getting any precision; on centre station (controller handling en-route traffic) the radar target blob is about a mile wide.

Until recently, aircraft did not broadcast position at all. Many still don't; not all aircraft are equipped with ADS-B. For those that don't, the interrogator may have precision similar to DME (~ 0.1 nmi) in range and a degree or two in angle. Not great precision either. The radar also has single rotating antena that takes couple of seconds to scan the whole circle, so the position of the aircraft is only updated once every few seconds. Jet airliner in cruise moves some 700 m in 3 s.

On such radar, the scope most likely transforms directly from the angle and distance reported by the radar to the screen coordinates. Altitude was usually not taken into account (so higher targets appear further than they really are!) in the older systems.

New radars with ADS-B support (less busy areas don't need it) need to combine the radar data with coordinates reported by ADS-B, which are in WGS84, so WGS84 is usually used as intermediate format for the collected data. But shortcuts can still be taken in the software.

I don't know what which radar system manufacturer uses, but I work on navigations and we tested the precision. By assuming Earth is flat and the coordinate system is orthogonal and using simple Pythagorean formula, you can still get 3-4 significant digits (unless you are working around north or south pole) for points tens of miles apart, which is more than enough for the radar screen. So the system can simply multiply longitude and latitude with appropriate factors (that depend on latitude of the sector centre) and get sufficient precision.


Do any manufacturers have plans to use turbojets in future aircraft? What is the state-of-the-art in turbojet design?

The first jets were turbojets simply because the turbine could only support its own compressor. They kept an edge for supersonic flight and will be the engine of choice if we ever design another Mach 3+ aircraft. Also, micro jets for cruise missiles and model aircraft turbines are turbojets to keep them simple. However, the analysis of modern jet warfare showed that the overwhelming majority of flight time is spent at high subsonic speeds, and there a turbofan makes more sense.

Now all modern combat jet aircraft use turbofans, even though their bypass ratio is rather low (around 0.5).

Commercial jet transport engines are solidly turbofans since half a century and have slowly increased their bypass ratio to about 9, less for smaller engines. Now three-spool engines or geared turbofans are state of the art, because they allow more freedom in optimizing the rotation speed of the different sections inside the engine.

Turbojets have benefited from better, more heat-resistant materials and airfoils for turbo machinery just as much as turbofans, but modern designs are overwhelmingly turbofans, so turbojets generally represent a much earlier technological level. To give you an example: The first turbojet used in operation, the Jumo 004, had a mass of more than 700 kg and produced 8.8 kN of thrust. The engine of the Eurofighter, the EJ200, is only slightly bigger in mass and has similar dimensions, weighing 990 kg, but produces seven times the thrust of the Jumo 004. With reheat, thrust is more than 10 times that of the Jumo 004, which had no afterburner. The pressure ratio could be increased from 3.2 to 26 (that is the progress in compressor aerodynamics), and the turbine entry temperature from 840°K to 1800°K (that is the progress in materials).


Piloting as a perishable skill - what skills go first and how to self-assess and mitigate skill loss?

I have no hard data answers to your questions. Perhaps others will. I can, though, offer some personal observations.

My last two jobs were at 747 carriers. At the first we had two weeks on, two weeks off. At the second, we had 12 days off a month, which, with a little seniority, you could arrange to have as a block.

For me, the first thing to go was my instrument scan, and I used to joke that it took only 4 days of inactivity to lose that. The joking aside, I did notice a slight degradation the first day or two upon returning to work after time off. I should note that my habit was to hand fly the airplane to the first cruise level, and then to hand fly from the top of descent, so I perhaps would notice a bit of degradation more so than those who used the autopilot as soon as possible and until as late as possible.

I retired 15 years ago, and it had been 30 years since I had flown a light single engine airplane when, a few weeks ago, I decided to check out in a Cessna 172. After three sessions, the instructor said he was satisfied. I wasn't and we went out a four time, and he signed me off for my first-ever BFR.

In general, I did a little better than I had expected. In one area, landings, I did a worse. The problem was the sight picture I had in my head from 10 years of landing 747s. On the first landing, knowing that I'd want to flare high, I delayed rounding out until my gut way saying, "if you don't flare, you will crunch the airplane." When I started the flare, the instructor said, "No, you're way too high." I delayed again, then started again, and the instructor said I was still too high." I delayed again, then absolutely had to start again, at which time the instructor said something like, "Well, you're still high but go ahead." That landing was followed by three sessions of nothing but takeoffs and landings. Each session I improved, but, frankly, I have yet to get a really good landing. My next session will be solo and will be nothing but takeoffs and landings.

So, for me at least, I conclude that we don't forget how to fly, but we definite do lose the touch.

After I get the solo takeoff and landings session in, I'm going to go out with the instructor and shoot a couple of ILSs. I'm expecting my instrument scan to be terrible.


How much fuel does it take to start/land an aircraft, compared to normal flight?

The fuel consumption or fuel burn rate is dependent on the aircraft type, size, engine configuration, cruise altitude, temperature, thrust setting and other factors.

In general: The larger the aircraft, the less economic do short flights become due to weight/size and fuel burn on takeoff/climb.

Here are some values I found for the CRJ2, the source may not be entire citable:

  Approximate total burn pounds / hour

  Taxi: 700 (Both engines and APU)
  Takeoff: 6000-7000 (depending on temperature, elevation, reduced/full thrust, etc)
  Climb: 6000-3500 (reducing as as altitude increases)
  Cruise: 2500-3000 (depending on altitude/weight/etc... subtract 500 for long range, add 500 for high speed)
  Holding: 1800-2400 (depending on altitude/speed)
  Normal descent: 1500
  Idle descent: 600
  Approach: 2000 (fully configured)

(Source: www.airliners.net - Author: Flyf15)

You can also read the following related questions to understand how altitude affects fuel efficiency:
Why do jet engines get better fuel efficiency at high altitudes?
How does flight duration affect the hourly fuel consumption in heavy aircraft?


Why is best angle/rate of climb indicated in airspeed?

Because determining Vx and Vy has to do with the specific aircraft, specific power output of the engine, thrust from the propeller, etc, which is often a function of pressure altitude and airspeed.

Remember that Vx represents a situation where the aircraft has the MAXIMUM EXCESS THRUST meaning a situation where the difference between the maximum thrust available and and the thrust required to neutralize drag force and maintain straight and level flight is the greatest.

Images courtesy of BoldMethod

Vy on the other hand is the point where the aircraft has the MAXIMUM EXCESS POWER available to it, translating into the greatest change in altitude for a given period of time by simple conservation of energy considerations.

Images courtesy of BoldMethod

The airspeed where Vx occurs increases as the pressure altitude increases.  Conversely Vy decreases as pressure altitude increases.  This is due changes in power and thrust outputs with increasing pressure altitudes.  Vx and Vy eventually equal each other at the aircraft’s absolute ceiling, since there is neither any more excess thrust or power available here for climbing.


What are these hooks and tassels on the nose?

The things hanging on the left and right side of the nose are pitot covers. They cover the pitot tubes located here:

(Boeing 737 Airplane Characteristics for Airport Planning)

The covers are there to protect the narrow inlets from contamination or blockage:

  Pitot tubes are normally covered when the aircraft is parked for more than a short period of time to reduce the chance of blockage or contamination.

(Pitot Static System on SYKbrary)

They are usually painted red and have REMOVE BEFORE FLIGHT written on them:

(aircraftcovers.com)

Related:

What is the use of this remove before flight cover on the nose of a Bombardier Global 6000?
What steps have been taken to rule out instrument failure due to blocked static ports or pitot tubes?

The cable connected to the right side of the aircraft (left on your image) is the ground power cable. You can see it larger in this image:

(pinterest.com)

Related:

What is the cable connected to a plane for?
What powers an aircraft prior to the APU being switched on?
What's the plug used on airliners for ground power?


How to calculate pressure distribution over an airfoil from its coordinates?

What helped me was the book "Theoretical and Computational Aerodynamics" by Jack Moran (ISBN 0-471-87491-4). That was 30 years ago, but the physics haven't changed since then. And it is still available.

An online source would not go deep enough to cover all what you need. My advice is to get the book and work through the exercises. It worked for me, and if even I could code a 2D potential code after having read this book, you should have no problems.

There is one trick: At one point you will end up with n equations for n+1 unknowns. Bummer! What you need to do is to prescribe flow direction at the trailing edge, and then you will have n+1 matching conditions for those n+1 unknowns, n being the number of panels you divide the airfoil surface into. Google "Kutta condition" for an explanation.

EDIT

Now you have quite a different question:

  by CFD i meant RANS. how does it compare to RANS methods in term of stall prediction and pressure distribution

@toshiba: The comparison is like between a Volkswagen Beetle and a Mercedes. A potential code is simple, robust and gets you there, like the Beetle. Pressure distribution is good until separation starts. Compressibility can be modelled until locally the speed of sound is reached. Stall prediction is a bit tricky, but with a bit of experience and an added boundary layer calculation you will get good results.

RANS is a simplified Navier-Stokes algorithm which is used for modelling turbulent flows. Like the Mercedes, it needs much more effort to code and run (and computing power - it requires a mesh where the potential code only needs panels on the airfoil surface) but also produces better predictions if the mesh is laid out well. Drag and stall approximation is included while potential flow needs some extra effort for boundary layer modelling. A Navier-Stokes code can also be used for transsonic flow.

If you want to build your own, assume you get the parts only and have to assemble the cars. No plans included. The VW Beetle heap is much smaller and you can figure out quite quickly how it fits together (did that once with a Beetle engine that someone else had disassembled and left behind). When you are finished, the car will run and require little maintenance.

With the Mercedes, there are many more parts, more complicated looking and requiring special tooling. It takes much longer to get assembled and in the end you will have some parts left over and others in the wrong place if nobody experienced guides you along. Maybe the car runs, but it will break down quickly unless you put much effort into maintaining it.

In other words: Start with a potential code. MUCH easier.


Who said "A little of all of us goes with every pilot we lose"?

William Garvey in "Viewpoint"
The authoritative reference is in this article:
Aftermath: Lessons Learned  (Aviation Week)
Excerpt:

The last words of William Garvey's January Viewpoint -- ". . . so a
little of all of us goes with every pilot we lose." -- struck me
("Aftermath," page 7). I had just returned from the small town of
Vesoul, France, where I attended a ceremony marking the 40th
anniversary of the death of a Mirage III pilot. Lt. Patrick de
Barbeyrac Saint-Maurice died while flying an intercept training
mission near Vesoul on Nov. 3, 1966. The cause of the accident was
never fully determined, other than the ...
THIS CONTENT REQUIRES SUBSCRIPTION ACCESS
Paywall stops reading more of it.


How does ATC deal with apparent compass errors when giving vectors?

This question is a partial duplicate of this one and this one.

  When ATC gives a heading, receives the correct readback, but observes a 10- to 15-degree difference between the actual and intended tracks, does the specialist incorporate this difference into future vectors?

Sometimes. The controller issues headings but observes ground track.  If the wind is causing drift, the controller will compensate for it when she provides vectors.  Sometimes, if an aircraft is suitably equipped, a controller will ask for a wind report in order to better judge the winds at altitude.

  Do approach and traffic separation vectors generally have a healthy margins of error?

Yep.  See here.

  How does apparent compass deviation or directional gyro precession factor into vectors that ATC issues?

It's up to the pilot, not the controller, to correct for compass deviation (since only the pilot can see the compass correction card inside the aircraft) and gyro precession (since only the pilot can turn the little knob to reset the gyro).


Under what authority can the AIM overrule the FARs?

The issue you have appears to be that the AIM describes a case where procedures don't follow a rule (91.175) and you don't see where the authorization comes from for that deviation.

What you're missing is that the approach procedures are in fact rules themselves.  They just don't get published in Title 14 CFR.  Standard instrument procedures are covered by Part 97, Subpart C.  It essentially states that the procedures are controlled via the FAA Order 8260 series.

So if the approach procedure specifies minima or other procedures outside the norm of a separate rule, the procedure is the controlling rule.


Why does V165 have two different MEAs over the same route section?

The most likely reason is terrain. Here's what the VFR sectional looks like:

You can see that the terrain rises sharply to over 3000' close to WINLO intersection, which is too high to provide IFR obstacle clearance (1000', or 2000' over mountainous areas) at an MEA of 4000'. An aircraft flying south on V165 would need to be well above the terrain before reaching WINLO, whereas one flying north from WINLO can use a lower altitude.


Why are military drones shaped so strangely?

The whale-shaped forward fuselage covers a parabolic antenna for a high-bandwidth datalink. The operators want to receive the reconnaissance data in real time, and by giving the antenna the best place in the aircraft, it will be able to connect to communications satellites even when they are just above the horizon.

Global Hawk cut-away drawing (picture source)

The V-tail of the Predator is an inheritance from its origins as a Navy drone which could be folded to fit into a torpedo tube. Read all about it in this answer. If you want more info on the benefits of an inverted V-tail, make sure you read KeithS's answer, too.

In the Global Hawk the V-tail was chosen to mount the engine above the fuselage for better IR shielding from below. The two tail surfaces also shield the exhaust from the side without affecting aerodynamics negatively.

The Aerosonde's configuration was chosen after Tad McGeer had experienced in 1990 from the 1/5th scale RC model of the Perseus UAV of Aurora that a tail-mounted propeller would stabilize the aircraft to the point that it became practically uncontrollable. A pusher propeller is more efficient than a tractor propeller, which also explains the propeller location on the Predator.

If it strikes you how many of the UAVs have V-tails: This allows to use fewer components (surfaces, connectors, actuators), and since all are moved by computer control, the issue of a mechanical mixer does not exist. The lower damping of V-tails can also be easily tolerated, since the FCS can react much more quickly and commensurately to disturbances than any human pilot. The lower maneuverability possible with V-tails is also not an issue - reconnaissance UAVs fly mostly straight and level.

The high aspect ratio wings are helping in extending the range and especially the flying time of observation drones. Similar to glider wings, the long and slender wing will offer the lowest drag for a given lift at subsonic speed.

In the end, each detail has been chosen deliberately and can be well explained. There is no conspiracy to make UAVs look different from Cessnas.


What are these wheel-chocks made of and what color do they most probably have?

Those chocks were made out of wood; I am guessing that they were unpainted or painted a bright color, for visibility. Today, they are made out of rubber or a synthetic. Rubber grips better than wood, but the wood chocks were most likely made out of wood, to preserve the rubber for the war effort.


What is the "Brake to Exit" feature on the Boeing 777X?

It is a system that Airbus already uses in the A380
and some A350's. They call it BTV (Brake to Vacate).

It allows the pilot to select a certain runway exit in advance (e.g. while approaching).
After touchdown, the plane automatically brakes so it can vacate the runway at that given exit.

Airbus says:

  When the pilot chooses a runway exit point, the system indicates the estimated runway occupancy time and the minimum turnaround time. During the subsequent landing phase, and according to encountered runway conditions (i.e. 'wet' or 'dry'), the aircraft's deceleration is automatically regulated so it reaches the chosen exit at the correct speed.

(emphasis mine)

The BTE system by Boeing is a similar system with a different name. A related article in Avionics International about the B777X states:

  “We have also added new safety features like optimal runway exiting and brake-to-exit, which will allow a pilot to tie an airplane’s rollout and stopping distance to a specific runway exit,” said Kirk Scarbrough, Boeing’s 777X systems chief engineer.

See also

What is Brake To Vacate (BTV)?
FAST magazine from Airbus, issue #44(PDF, 10MB) from July 2009, section "Brake-to-Vacate system", pages 17-25


Can a Cessna 162 Skycatcher be flown IFR in IMC?

Not in the US. The C162's POH says:

  The Model 162 Skycatcher is not equipped or certified for IFR flight

That means that under 14 CFR 91.9 it may not be operated IFR. But, FAA Order 8900.1 allows an exception for aircraft not certified for IFR to be operated under IFR in VMC only:

  A.    IFR Training in Visual Meteorological Conditions (VMC). Instrument flight training may be conducted during VMC in any aircraft
  that meets the equipment requirements of part 91, §§ 91.109, 91.205,
  and, for an airplane operated in controlled airspace under the IFR
  system, §§ 91.411 and 91.413. An aircraft may be operated on an IFR
  flight plan under IFR in VMC, provided the PIC is properly
  certificated to operate the aircraft under IFR. However, if the
  aircraft is not approved for IFR operations under its type
  certificate, or if the appropriate instruments and equipment are not
  installed or are not operative, operations in Instrument
  Meteorological Conditions (IMC) are prohibited. The PIC of such an
  aircraft must cancel the IFR flight plan in use and avoid flight into
  IMC.

An autopilot isn't required for IFR flight in the US (see 14 CFR 91.205(d)) and the question you linked. I didn't check the full equipment list to see which required instruments are missing from the C162, but even with full IFR equipment if it isn't certified for IFR then it can't be operated in IMC per the regulations above.


How do elevator servo and anti-servo (geared) tabs differ?

There is some confusion on the different types of tabs that can be found on aircraft: servo tabs, geared tabs, trim tabs.

The servo tab is an aerodynamic lever. It is connected directly to the pilot flying controls. When he moves the controls, he deflects the servo tab only, and feels aeroforces acting upon the servo tab only. When the servo tab deflects, it creates a force moment on the control surface ( elevator, aileron, rudder) which then deflects the control surface until aerodynamic moments are in equilibrium. If there is no airspeed, deflecting the servo tab has no effect on the control surface.

The geared tab changes the flight control forces to either increase them (usually in small aircraft) or reduce them (an arrangement used in the pre-hydraulic past of airliners). The control surface is directly connected to the stick/pedals - deflecting them causes the control surfaces to move. In order to alter control forces, a geared tab moves relative to the control surface:

For increasing stick forces, in the same direction as the control surface. Wiki and others mention anti-servo tabs, a less confusing name would be positively geared tabs.
For decreasing stick forces, in opposite direction of the control surface. Whether there is airspeed or not, the geared tab always deflects by a mechanical linkage when the control surface is deflected.

The trim tab has a constant angle relative to the control surface. The angle can be changed by extending/retracting a mechanical link, via a trim wheel or an electric motor with a screw jack.


Why was the experimental MiG 1.44 so similar to the experimental TKF-90?

I once led a group of Antonov engineers through the aircraft exhibition of the Deutsches Museum in Unterschleissheim near Munich. There are two halls connected by a walkway, and from that walkway you can see the restoration workshop which is located between those halls.

When the group had long left the walkway, one engineer still stood in the middle of it and gazed down at the Dornier Do-31 which at that time stood in the shop for cleaning and repairs after many years in the open. I walked back (with one of our interpreters) and asked him what fascinated him. He said to me that this was the first time he saw this aircraft in person. And he continued that he knows every rivet in it. He had studied it in the early Seventies for several years when Antonov was tasked with developing a VTOL transport aircraft. In the end, they abandoned the idea (like NATO did a few years earlier), but this airplane had been the center of a part of his life.

Don't think bad of this - it is just good engineering practice to study what others have done. If you want to develop something, look what others have done before you and try not to repeat their mistakes. You might as well marvel at the similarities between an F-15 and a Su-27, a Concorde and a Tu-144, or a Space Shuttle and a Buran. In the end, they were designs made for the same purpose, and it is no wonder that they turned out alike. It just means the engineers did their job properly.

In nature this is called convergent evolution.


After I brought this to the attention of the local offices, they canceled the TFR and issued a new one expressed in terms of the MCI VOR, which makes a lot more sense. The FAA was incredibly responsive and helpful!

They didn't explicitly say it was a mistake, but I think they decided it was better to use an operational VOR.

(however, a couple weeks later, they referenced the RIS VOR again in a NOTAM.)


A modern replacement for DH.82's Gipsy Major engine

The Avia (now LOM) M132 4 cylinder inverted inline might fit. Some adaptation work is probably required.


How to recognise the Tupolev Tu-154, Tu-204, and Tu-334?

First, the Russian airplane industry is organized differently from its Western counterpart. While both have research organizations and aircraft manufacturers, in Russia and Ukraine design offices are between both. In Russia, TsAGI does most basic research and develops aerodynamic designs which are then put into fully developed aircraft by the design offices (Antonov in Ukraine, Ilyushin, Tupolev, Mikoyan (MiG), Sukhoi, Yakovlev or Beriev in Russia). The finished designs are then transferred to manufacturing plants like Aviakor in Samara which churn out the actual hardware. If the demand for Tupolevs goes down, Aviakor will switch to Antonovs or Ilyushins, so the fluctuation for products of a particular design office can be evened out.

One consequence of this arrangement is that aerodynamicists have the first say on the shape of the aircraft. Russian designs generally have more refined aerodynamics, at the cost of a higher manufacturing effort.

Older airliners from the Fifties and Sixties were designed with dual use in mind, and many of them had a glazed nose, which makes them easy to distinguish from their contemporaries from the West.

Tu-154

This design from the 1960s is similar to the Hawker-Siddeley Trident or the Boeing 727. Its production surpassed 1000 aircraft and ended only in 2013.

Tu-154 of Uzbekistan Airways (Picture source).

Four items make it easy to identify:

The landing gear uses six-wheel bogies, which is unique among three-engined airliners.
For aerodynamic refinement, heavy use of Küchemann bodies is made in the T-tail intersection and for stowing the landing gear.
The aerodynamic refinement also shows in the length of the conical section of the fuselage, which takes much longer to reach its cylindrical shape. This is a consequence of putting aerodynamics before ease of manufacturing.
The central air intake is of elongated shape, while that of the Boeing 727 is round and the one of the Trident was a heavily rounded triangle.

Tu-204

Intended to replace the Tu-154, this two-engined airliner flew first in 1989 and looks similar to a Boeing 757. It is still in production, but less than 100 have been produced.

The main differences from the Boeing 757 are:

Since the cockpit of the Boeing 757 is identical to that of the Boeing 767, it looks oversized for the narrow-body fuselage of the 757. In comparison, the cockpit windows of the Tu-204 are smaller and look more natural.
The top of the 757 fuselage slopes down over the full length of the vertical tail, whereas the downslope of the Tu-204 fuselage starts only at the rudder.
To distinguish the Tu-204 from an Airbus A320, look at the wheels (four-wheel bogey on the Tupolev, two-wheel gear on the Airbus) or the APU exhaust, which in case of the Tupolev is a small tube sticking slightly out from the fuselage, while the Airbus has a metal-colored cover at the end of the fuselage.
Another difference is the Tu-204's much longer fairing for the wing-fuselage intersection.
Also, the winglet shape is quite different between those three types.

Tu-334

The Tu-334 is a shortened Tu-204 with fuselage-mounted engines. Only two have been built, so the chances to spot it are remote. The new location of the engines allows it to use a very short landing gear, and the shortened fuselage gives it a rather stubby, unique appearance.

Similar airplanes are

Short versions of the DC-9 like the DC-9-10 or the DC-9-15; here the low bypass ratio of the DC-9 engines results in much smaller intakes and longer engine nacelles. Also, the fuselage of the DC-9 is more pointed ahead of the cockpit. The cockpit windows of the DC-9 have a separate window above the regular row of windows for better visibility in steep turns, which is missing in the Tu-334.
Comac/Avic ARJ-21, a Chinese development which is based on the DC-9 fuselage, but has a modern, Antonov-developed wing and high-bypass-ratio engines. Here the upper cockpit windows are missing, so the best way to tell the Tu-334 apart from the ARJ-21 is again the more pointed fuselage nose of the ARJ-21, the bigger fairing of the ARJ-21's wing-fuselage intersection, the lower aspect ratio of the Tu-334 vertical tail and the rear end of the fuselage, which ends with a vertical edge in case of the ARJ-21.


Will air traffic control ever ask a plane to not brake hard on a landing?

Yes, we can ask you to plan your landing roll in a certain way. We won't technically instruct you to brake the aircraft in a specific way, but simply to aim for a specific taxiway after landing.
There can be different reasons for this, but generally it is an attempt to expedite traffic flow on the ground at the airport. For example, if you are landing on a long runway and your parking position is near the far end of the runway, I might ask you to keep the plane rolling down the runway and vacate at the end, in order for you to have a shorter taxi time.
It could also be that the taxiway you would normally use to leave the runway is blocked by another aircraft or vehicle, and I want you to leave the runway via a taxiway that is further down the runway.
However, extending the landing roll does extend the runway occupancy time as well, so if there is another aircraft behind you on short final I will not offer you to perform a long landing roll. This is also why you should always ask ATC if you are planning to perform a long landing for one reason or the other – if we have someone else just a couple miles behind you, we might have to instruct them to go around if you do not vacate the runway like we expect you to.
With regards to reverse thrust specifically, there are airports where the use of reverse thrust is only permitted in special situations. This is to reduce the noise level at and around the airport. However, this is purely a regulatory thing, and is not actually related to ATC.
ICAO offers the following guidance on  the subject (DOC 4444):

7.10.3.1    When necessary or desirable in order to expedite traffic, a landing aircraft may be requested to:
a) hold short of an intersecting runway after landing;
b) land beyond the touchdown zone of the runway;
c) vacate the runway at a specified exit taxiway;
d) expedite vacating the runway.
7.10.3.2    In requesting a landing aircraft to perform a specific landing and/or roll-out manoeuvre, the type of aircraft, runway length, location of exit taxiways, reported braking action on runway and taxiway, and prevailing meteorological conditions shall be considered. A HEAVY aircraft shall not be requested to land beyond the touchdown zone of a runway.


Apart from Kenya, what are the current dangerous / unsafe airspaces?

I feel there is more to say than currently answered, feel free to reuse part or all of this content to build an improved answer which could be selected.

There are recaps of flight restrictions, e.g. French DGAC publishes maps and plain text files recapitulating areas, in addition of individual NOTAMS:

Source: DGAC

ICAO announced in 2015 the creation of a specific member-collaborative tool CZRI, conflict zones risk information (currently very poor).

EASA also publishes a list of conflict zones bulletins that can be exported as pdf, and a map:

There are also other initiatives, e.g. SafeAirspace with text summary and maps. "SafeAirspace is managed by Flight Service Bureau, with contributions from The Airline Cooperative (225 international airlines), OpsGroup (1500 members), International Ops Bulletin feedback (40,000 readers), and data from the German BMVI, the UK DFT, the FAA, DGAC France, ICAO, and EASA."


Would a slower speed and lower altitude reduce fatal incidents?

I'd like to answer this question by debunking the premise of the question: that most plane crashes happen when planes fall out of the sky, and that it's like rock climbing where the higher you are, the more likely a fall will kill you.  While it sounds believable, it's almost entirely false, and since it isn't diving out of the sky that kills you, lowering the altitude doesn't really help flights become safer.

Planes don't need speeds of over 300 mph/500 kmh ground speed to be deadly. A car accident for comparison is generally considered to be very likely fatal above 80 mph/130 kmh  (source: DFT London).  Even plane crashes at takeoff and landing speed of around 150 mph/240 kmh can be difficult to survive just due to physics. Every one to three years there's a plane that crashes on takeoff or landing with almost no survivors like TransAsia 235. The most deadly accident ever happened when two planes collided as one was going about 160 mph/260 kmh and the other was almost stationary!

Even if you could easily survive a 150 mph/240 kmh collision, a ground speed of 500 mph at cruise doesn't mean the plane would crash land at 500 mph. Planes don't just dive out of the sky, gaining speed to 500+ mph/800+ kmh (except in total structural failure and breakup, but then you're a goner even at 150 mph). Even in extreme circumstances like loss of all flight controls in UA 232 the aircraft could slow to about 250 mph/400 kmh before crash-landing.  The "Miracle on the Hudson" aircraft slowed a lot after engine loss as it descended towards the river.  Even the dive of Alaska 261 caused by jammed flight controls could be slowed to about 250 knots using air brakes and flaps.  So the actual crash speed for high altitude incidents is usually less than 300 mph even in catastrophic incidents, which you could easily also achieve after an incident at lower altitudes and speeds.

Any serious changes to aircraft have to make enough of an improvement to be worth the disadvantages involved.  When we're talking about things like making flights slower, that's a serious disadvantage.  Probability per flight hour that an engine or flight controls will catastrophically fail is small but very real number in hazard analysis and so longer flights have a higher chance of an incident.  If the cruise portion of a flight takes twice as long, is that portion now twice as safe per minute to compensate?

Edit: As Martin James and Milwrdfan have pointed out, flying lower and flying slower both increase the amount of fuel you need per trip, which lowers the amount of passengers you can take.  This would increase the number of planes in the air which would probably decrease safety per passenger as well.

Finally, the most dangerous parts of a flight are takeoff and landing. Nearly half of accidents occur during final approach and landing, and only 10% occur in cruise (source: Boeing).  If the past few years are any indication, you're about as likely to have your plane damaged by terrorists as to crash during an incident in cruise.  So you're making every flight lower and slower to help less than one accident per year.

Now that this is the accepted answer, I should point out that Dave has some very good points in his answer about the particular dangers of lower altitudes like weather and glide distance.

So in summary, the premise that cruising at 150 mph and 5,000 ft AGL is relatively safe, while cruising at high speed and high altitude is relatively dangerous, is a faulty assumption. So you don't have much to gain by lowering the speed and altitude.


Can a wind tunnel simulate airflow when a vehicle goes around a curve?

Wind tunnel is a tool to interrogate aerodynamics, not to investigate flight dynamics (which relies on aerodynamic results to predict vehicular dynamics). As explained in this answer, the additional aerodynamic effects from induced airflow due to rotation can be lumped into dynamic derivative coefficients. Some examples include:

Pitch damping: $C_{m_q}$
Lift due to pitch rate: $C_{L_q}$
Roll damping: $C_{l_p}$
Cross yaw derivative: $C_{n_p}$

etc. Note that the rates in these derivatives are expressed in dimensionless rates to maintain similitude, which is accomplished by dividing the body rates by $bV_\infty/2$, where $b/2$ is half span and $V_\infty$ is freestream speed.
To estimate dynamic derivatives in wind tunnel, the forced-oscillation method is typically applied. The model is excited in a single axis by a small amplitude sinusoid at representative range of dimensionless rates and reduced frequency. This paper provides a good introduction to the data collection and analysis.
Rotary balance tests can also performed in wind tunnel to measure the effect of sustained rotary motion whose angular velocity is coincident with the air velocity vector. These tests are mainly to explore spin characteristics, which occur at very high angles of attack and sideslip. Forced-oscillation method would not be adequate in these conditions.


Was there ever an accident from in-flight smoking?

24 December 1982; CAAC Ilyushin 18B; Canton (Guangzhou), China: The aircraft was on a scheduled domestic flight when an onboard fire broke out as a result of a carelessly discarded cigarette. The aircraft landed and the passengers and crew evacuated, but 25 of the 50 passengers were killed. All 11 crew members survived. source


Why couldn't the A380 secure any orders for two straight years?

Several reasons:

A380s are really expensive. Unit cost for an A380, depending on interior appointments, is about \$375 million. The 747-8 is about \$357 million. The 777-300ER is about \$320 million, the last variants of the A340 about \$275 million, and the 787 about \$200 million. The 380 might be the biggest airliner ever to fly, but it's also the most expensive. Keep in mind these jets can't fly every day, requiring you to buy a couple more than the schedule requires and rotate them in as maintenance is required on each airframe. That means A380 operators have at least one three hundred and eighty million dollar airframe sitting on the tarmac not making money on any given day (in fact, up to 55 days at a time for the 6-year "D check" maintenance, not counting lower-level maintenance performed more often as well as any unscheduled maintenance).
Airbus could not/cannot build them fast enough to meet initial orders in a timely manner. Airbus received 189 initial A380 orders prior to the airframe's scheduled start of production in 2007, plus 27 A380F variant orders, and has received 128 since production began (though the freighter orders were cancelled). To date, it's only delivered about half due to a combination of issues found during full-scale production that delayed ramp-up, and currently its pace is about 30 planes a year, giving it about a 3 year backlog of remaining orders (some of which have been sitting in the build queue for 10 years). It initially prioritized passenger variants for Emirates, which put in the largest single order (almost half of total orders) to handle that airline's primarily long-haul schedule. As a result, everyone else got pushed off until many (including FedEx and UPS which were waiting for freight versions) cancelled their orders and went to Boeing for 747-8Fs or 777-ERFs.
Jumbos represent a serious cost-revenue risk that most airlines are no longer willing to gamble on. You use a jumbo jet when you need to move a lot of people at one time. That typically means a high-demand, long-distance route that calls for nonstop service, but that you don't want to have to fly any more times than you have to. 747s used to be used for high-volume domestic connectors in the US during and immediately after the regulation era, between major cities like New York, Chicago, LA, Houston, Miami etc. They were also used for major intercontinental flights, primarily because regulations required more than two engines for trips extending a certain distance beyond the nearest divert field. However, the 747 is a 50-year-old design with only incremental improvements made in efficiency. Four engine jets in the modern air transport market require you to fill the plane every time, and with ETOPS-rated two-engine widebodies now making many of the same flights that previously required three or more engines, the A380, even with the most efficient engines ever put on a commercial airliner, is at least three decades late to the jumbo party, and is entering the market at a time when the 747 is being phased out of most fleets in favor of more economical widebodies.
The A380 was designed for an air travel market that hasn't materialized. Airbus was betting big (NPI) on airport congestion and increased passenger counts during the 80s and 90s requiring a shift to fewer flights on larger-capacity planes to reduce pattern and gate congestion. Except for a few major metropolitan areas that simply cannot grow their airports anymore (O'Hare, LaGuardia/JFK, Heathrow etc) that hasn't really been the case. 9/11 and the 2008 financial crisis have seen passenger counts plummet from post-regulation highs, which has reduced total flights and allowed smaller planes which are more efficiently scheduled. In addition, Denver opened up the largest airport by land area in the world (so it has plenty of room to grow), while Atlanta, Dallas, Charles de Galle and others are busy primarily because they're massive complexes with efficient layouts that can support a major airline's hub operations. The use of jumbos in general is therefore very risky, and many airlines, in addition to passing on the A380, are phasing out the venerable 747 that was previously unchallenged in this class, in favor of something a little more economical in the next smaller widebody class, like the 777, 787, A340 or A350. That was Boeing's bet, that smaller, high-efficiency jets would be the wave of the future over pure size, and it seems to be paying off as Boeing, despite higher production capacities, has more 787 orders than it has capacity for the foreseeable future, while Airbus's competing A350 is more or less getting the overflow (and it can't even meet that demand; 700 orders, 5 produced).
The A380 really doesn't solve the problem it was created for, and in fact causes more problems for airports than it solves. A super-heavy like the A380 creates monumental wake turbulence that poses a danger to other planes, which requires ATC to space following traffic further back (up to double the time/distance compared to a midbody), while for smaller jets (even widebodies), approach control can usually get away with a little more than standard 2-minute spacing unless the plane behind it is a much smaller regional jet or GA prop. So, the A380 can carry about 520 passengers in mixed-class configuration (Emirates' 6-star config seating only about 490), but takes up two "slots" in the approach pattern, while a 777 can carry 320 passengers in mixed-class layout and can be spaced much more closely to other airliners. So in terms of maximizing total passenger movement at an airport, two 777s or A340s are better than one A380.

At the gate, the A380 causes even more headaches. It's so honkin' big that adjacent gates typically can't be used while it's parked, and it often requires additional jetways to efficiently board and deplane its passengers. As one example, DFW's Terminal D was fairly recently renovated to be the airport's primary international terminal, including Gate 16 in the southwest corner specifically intended to allow 747s to park with minimal adjacent gate disruption (17 couldn't be used, but 18 was available for smaller jets and 15 around the corner could handle pretty much any size):

When the A380 came to DFW in 2014, with Qantas replacing the 747 on the famous Flight 7 and Flight 8 from Sydney to DFW (the longest scheduled passenger flights by travel time in the world), and Emirates commencing service to and from Dubai with A380s, DFW had to redesign this corner of the airport entirely, basically having the A380 come in diagonally to Gate 15. Gate 15 then services first class, 16's jetway was moved and extended to load and unload the lower deck, and a third jetway, 16X, was built adjacent to 16 solely for the A380's upper deck. The jetways for Gates 14 and 17 then had to be lengthened considerably to allow their use with a 380 at the ramp, otherwise the superjumbo would essentially take up 4 entire gates while parked:

As an aside for scale in the last image, Gate 14 to the right is in Sun Country livery which would make it a 737-700, while the American jet at the very top at Gate 19 is still in older livery, and with its long narrow body the best guess is a 757-200. Gate 17 looks like an Air Canada Rouge so with the body length I'd say A319, and Gate 18 is in new American livery so it's a 737-700. None of them really big aircraft by today's commercial standards, but they're certainly not puddle-jumpers either (all aircraft at this terminal are for international flights), and the Emirates A380 at gates 15/16/16X absolutely eclipses them all. It is a big jet.


No. It's not true in practice.

While the conventional layout puts the whole tail into the downwash of the wing, a canard will add downwash to the center wing and upwash to the outer wing. This means that while the tail of a conventional layout sees less angle of attack variation than the wing (which is good to prevent tailplane stalls), the up- and downwash variations with varying angle of attack will spoil the lateral lift distribution on the main wing of a canard airplane and increase its induced drag.
Since the canard surface needs to fly at a higher lift coefficient than the wing for natural stability, it will have less margin for control. It is no coincidence that successful canard designs are unstable. Also, this means the big wing surface cannot be fully used for lift, which is wasteful and increases take-off and landing speeds.

More on this can be found here.

Since I was a kid I have read endless articles about how canards are more efficient …

The reason for this is simple. It is much more exciting for authors to claim they know better than all the experts than to humbly admit that the state of the art is really the best under the circumstances. The incentive to laud canards above all else is much too enticing, and human psychology tends to prefer the sources which confirm a preconceived opinion. In the end the authors really think they have found a better solution and become evangelists for a better world, especially when their own understanding of the matter is limited.


What is the difference between autopilot and autoflight?

Autoflight is the general term describing all of the following:

Flight Director: A guidance system for the pilot and autopilot with various modes. See What is a "Flight Director"? for details.
Autopilot: A system controlling the flight control surfaces to follow the flight director.
Autothrottle / Autothrust: A system setting engine thrust automatically depending on the selected mode. See also What is Auto-thrust?.

For example, the Boeing 737 NG FCOM describes it as follows (Vol. 2, Chapter 4 - Automatic Flight):

  The automatic flight system (AFS) consists of the autopilot flight director system
  (AFDS) and the autothrottle (A/T). The flight management computer (FMC)
  provides N1 limits and target N1 for the A/T and command airspeeds for the A/T
  and AFDS.

  The AFDS and A/T are controlled using the AFDS mode control panel (MCP) and
  the FMC. Normally, the AFDS and A/T are controlled automatically by the FMC
  to fly an optimized lateral and vertical flight path through climb, cruise and
  descent.

  AFS mode status is displayed on the flight mode annunciation on each pilot’s
  primary display.

Related: What is the relationship between "automatic flight control system AFCS", "autopilot", "flight director" and "flight management system FMS"?


How can I use electric motor data with my prop data to obtain a power available versus velocity curve?

A simple mathematical model for electric motors has very clearly been discussed here
All you need is Kv, no-load current and Voltage to calculate the shaft power, efficiencies, etc.


How should I handle a change of address for a Student Pilot License in the USA?

You can change your address with the FAA online.  You do not need to get a new plastic certificate.

http://www.faa.gov/licenses_certificates/airmen_certification/airmen_services/


What does the suction gauge actually show?

According to the diagram below from a TB200 pilots manual the gauge shows the difference between vacuum line and the ambient pressure:

The pressure difference between the ambient and the vacuum line drives the airflow which spins the gyros in you instruments. In the Socata design, there is an implicit assumption that the air filter is not blocked. If the filter would be blocked, the suction gauge would probably exceed the green area unless the vacuum relief valve opens before the red is reached.

If your vacuum pump stops working, the dial will fall to its lower stop. If the air filter is blocked, and both the vacuum pump and the vacuum relief valve working properly, the dial should exceed 5 inHg.

Other designs are a bit more fault tolerant in the sense that they do not make any assumptions on the working of the filter or the relief valve. In the examples below (thanks to voretaq7) the suction gauge indicates the pressure difference over the instrument itself, which is a more robust presentation of how the system is performing.


You can easily find this out for yourself by searching on the OAM.
This leads to Diamond Aircraft service bulletins relating to the change.

Work instruction

AFM

Software notice

Looks from these that it requires 3 things:
2 placards relating to the different engine operation temperatures, and potentially a software upgrade to the engine management system (depending on the version currently installed).


How would a pilot apply the information found on a 500 Millibar Vorticity chart to a flight?

My understanding is that it shows the Isobars of atmospheric pressure at around the 18000 foot MSL altitude. It will show pressure gradients, low pressure and high pressure zones of the atmosphere at the altitude that demarcates where 50% of the atmosphere resides below. It’s main purpose is to indicate horizontal and vertical spin of air mass movement due to ridges and troughs of atmospheric pressure, wind shear, and the corialis force. This gives a good indication of the upward movement of rising air, energy being infested by a thunderstorm, and how much of spinning force is being applied to a storm to increase its risk of growing to dangerous levels.

Typically, other aviation weather tools would point a pilot to a no-go flight decision way before reaching this one. Some pilots may use it for limited applications (like glider pilots using the skew-t/log-p diagram). This chart can be a useful tool for meteorologists and meteorology enthusiasts to come up with reports of broader scope. You will see it mentioned in Area Forecast Discussions.


How does Boeing park several airplanes on a single runway at Paine Field?

It was tugged to that position via tug.
Angle of photo + possibly trying to offset weight, from centerline.
These planes are just being stored there. They'll be tugged to another location
before they even bother to start them up, and I believe most don't
have engines on at present.
They are quite close together.
(from @ratchetfreak's answer:) Turn the image around as if you are coming to land; it's actually 16L a perfectly normal runway number.
Its just a very compact way of parking aircraft in minimum space. Compare the space taken up by those 4 planes versus any 4 nose-to-tail on the runway.

These aircraft are mostly 787s that are the early teen aircraft that were rejected by the original airlines they were slated for, due to so many out of tolerance issues/rework required. They are just being stored on the runway until Boeing can get them into mod/rework status and get them to spec to be able to sell. Right now the mod line seems to be working on one of these aircraft, at a time, and each one taking many, many months to get fully reworked.


Who applies an airworthiness directive when the airframe is newer than the AD?

I am interpreting your question as asking whether an owner of an aircraft is responsible for complying with ADs that were issued before the aircraft was manufactured.

Short answer: yes.

There are several types of ADs that affect your aircraft. Some of them apply to all aircraft of a specific type, some apply to specific serial numbers or model numbers, and some apply to specific parts that are installed on your aircraft.

Some are one-time and others are recurring. The one-time items would usually have been checked before the airplane left the factory. The exception would be if they were required after a certain number of airframe hours. Recurring items can still apply to all aircraft—even those made after the AD was issued.

The two ADs listed below require the owner to check for excessive wear in the listed parts. I just replaced the Bendix switch in my Cherokee because it failed the required test in the AD.

Here’s one that was issued in 2011 for all Cessna aircraft AD 2011-10-09:

  We are superseding an existing airworthiness directive (AD) for Cessna
  Aircraft Company (Cessna) 150, 152, 170, 172, 175, 177, 180, 182, 185,
  188, 190, 195, 206, 207, 210, T303, 336, and 337 series airplanes.
  That AD currently requires repetitive inspections and replacement of
  parts, if necessary, of the seat rail and seat rail holes;

Here’s one that was issued in 1976 that applies to all aircraft that have Bendix ignition switches AD 76-07-12:

  Applies to all aircraft employing magnetos and using Bendix ignition
  switches listed in the table below except switches identified by four
  digit date code (new) adjacent to the model number or a white dot
  (modified) on the support plate adjacent to the Bendix logo.

Your A&P should have software that allows them to easily check which ADs apply to your aircraft and then create an AD Compliance Report for you. It will list all of the ADs and the date that they were complied with. Most reports also list ADs that apply to your aircraft model, but are excluded by serial number.


Is there a reason to be worried about go-arounds as a passenger?

A go-around is nothing to be worried about as a passenger.  What would be worrying is if the pilots elected not to go around when conditions warranted it.

The dark likely isn't an issue with this go around as approach lighting systems can become exceptionally bright when requested (to the point you'll need sunglasses to look at them if visibility is good).  What was likely a factor was fog.  Airplanes need a minimum amount of visibility to land and if conditions are marginal you won't really know until you fly the approach and either see the lights and land or do not see the lights and go around.  For normal ILS approaches you would initiate this go around at 200 ft above the airport elevation.  For very low visibility approaches this decision height may be 100 feet or less above the airport elevation.

The point at which you go around if you fail to see the runway environment is well defined and procedures ensure obstacle clearance so there is no danger as long as procedures are flown as published.

Another possibility for the go around could be the airplane in front of you failed to clear the runway speedily due to low visibility.  If the preceding aircraft was still occupying the runway then your airplane would have to go around.  There are a few other issues that could warrant missed approaches (e.g. windshear) but in all of these cases the go around is the safer option than proceeding with the landing.

Your pilots made the safe decision to go around and this is what you should take from the experience.  There is zero reason to be worried.

To address your added specific questions:

Flightradar24 flight track data is unreliable.  It is neither true radar positioning or necessarily true GPS positioning.  It is nice for zoomed out flight tracks but is not reliably suitable for the precision during landing/takeoff.  Do not use it as a basis for worrying that your approach was not properly aligned.
Extremely rarely if you mean not being aligned with the runway.  Uncommon if you just mean not seeing the approach lights but otherwise on course to land.  The navigation signals used in ILS approaches are broadcast down the runway centerline for the lateral guidance and from just next to the runway approximately 1000 feet past the beginning of the runway aimed 3 degrees up for the vertical guidance.  These signals are only usable in a cone that radiated outward from the runway.  Furthermore the navigation accuracy of the ILS receivers are regularly tested on the airplane.  Combined with monitoring by air traffic controllers you will not end up on a parallel course that does not intersect the runway.
The vertical data is also not reliable.  Your airplane approached on the glideslope and if it made it down to 50 feet this would have been just over the very beginning of the runway.  After initiating the go around it would climb (likely to between 2000 and 3000 feet) and attempt another ILS approach.  At no time is the airplane lingering at 50 feet above the ground anywhere but over the runway for a very short period of time.

The video below is an example of a very low visibility approach and you can see an example of how low the airplane can get before visual contact is made with the approach lights and runway.  At predetermined points based on the aircraft, airport and crew qualifications the airplane would initiate a go around if these things were not seen.  For standard ILS approaches this would be when the airplane announces "200 feet".  For category II ILS approaches, it would be at "100 feet".  In the video below a category III approach is shown which has an even lower altitude to initiate a missed approach.


Airbus towing: is it necessary to switch on the Y HYD pump?

Please read fully the answer to understand the matter.

Please be careful, with respect to the 320 it depends on the aircraft generation, as I remember if not all, some A320 landing gears are green operated. Nevertheless, by switching on the yellow electrical pump, the green circuit will be pressurized via the PTU, thus preventing the towing force to cause inadvertent retraction of the nose gear.

This is just an explanation, not a procedure to be followed.


Why is this plane flying in such a tight circle?

those look like Holding pattern. Air Traffic controllers manage the flow of air traffic to and from airports. Sometimes it is necessary to hold a few of them before they can start an approach for landing.