How can civil ATC maintain safety with military aircraft around?

Military aircraft do have transponders that can reply to civil ATC radar and TCAS interrogations. Normally military aircraft operating in civil airspace are visible to civilian ATC and also will trigger TCAS advisories and alerts if they are getting close to airliners.

During  wartime operations, and sometimes during combat practice in dedicated airspace, the transponder is operated in a different mode and will not be replying to civil radar interrogations.

Typically when operating in civil airspace, military aircraft will fly under the civil regulations for that airspace. Training flights are usually conducted in dedicated airspace under military traffic control.

In some cases the military ATC assumes responsibility over military aircraft in otherwise civil ATC controlled airspace. In such a case the military ATC will be responsible for the separation between the military aircraft themselves and between military and civilian aircraft.

In other cases military aircraft may be allowed to maintain their separation from each other on their own, without civil ATC interfering in their operations. This allows for operations where military aircraft flying close to each other like formation flying and aerial refuelling outside the dedicated military airspace. In the USA these operations are called MARSA (Military Assumes Responsibility for Separation of Aircraft). Civil ATC is responsible for keeping Instrument Flight Rules (IFR) aircraft separated from MARSA operations. Visual Flight Rules (VFR) pilots have to maintain separation visually from MARSA flights and vice-versa. If VFR pilots are in contact with ATC they will be advised of ongoing military operations.


I overboosted an engine in a Mooney 231 - do I need to do an inspection?

This most likely warrants a call to Don Maxwell the veritable Mooney expert but I would for sure have the engine checked by a Mooney expert or someone that knows their way around the TSIO-360-GB. At the minimum a compression test and possible borescope check is in order.

If you have the early 231 in its original config you have a fixed waste gate that can be over boosted on takeoff.

  The engine also had a fixed wastegate in the exhaust system, meaning
  careful pilot technique was required to keep from over boosting the
  engine on takeoff.  If the pilot inadvertently added full throttle for
  takeoff or a go-around, the engine would over boost, with only a
  mechanical pop-off valve in the induction system to save the engine
  from literally coming apart on the runway.  Fixed wastegates also mean
  high turbocharger speeds (RPM) at altitude, which reduces turbocharger
  life

I don't know much about the gauge itself but it may warrant checking it to make sure it is operating properly.

You can also reach out to continental and ask them what the over boost limit is. There is a chance they have some data on it or can let you know of a good course of action.


Where does the term “throttle quadrant” come from?

The term quadrant refers to the panel containing the levers and is derived the circular arc in which the throttles are placed:

  throttle quadrant

  The recess in which the throttle is located and moves. ... It derives its name from the circular arc in which the throttle is placed.

Looks like the term entered aviation from the rudder controls in a ship:

  quadrant

  A frame fixed to the head of a ship's rudder, to which the steering mechanism is attached.

  3.1 A panel with slots through which a lever is moved to orient or otherwise control a mechanism.

Here's a rudder quadrant

Rudder quadrant; image from titanic-model.com


What is the use of this remove before flight cover on the nose of a Bombardier Global 6000?

These covers are used to keep foreign objects away and out of the air data sensors, pitot tubes, static ports and Angle of Attack sensors (large red covers) while the aircraft is resting on the ground.  Blockage or damage to these sensors by foreign objects prevents the aircraft flight control computers and instruments from collecting accurate data and could be disastrous in flight, especially in instrument conditions.  The wires are essentially a leash to hold the neoprene covers together in a group and both prevent their loss during storage and ensure that all covers are removed from the sensors during pre-flight.


Do Alaskan bush pilots generate a Clmax of 5 with 90° flaps?

The following graph is from Cahill, Summary of Section Data on Trailing-Edge High-Lift Devices. As you can see, for a plain flap, with gaps fully sealed, the $C_{L_{max}}$ maxes out at around 60deg.

When I played around with xfoil, things became unreasonable beyond 40deg. Probably some assumptions in the boundary-layer equations broke down. Since Javafoil utilizes the same computational approach as xfoil, I would expect the same behavior.

On the Alaskan Bush pilots, are we sure they are 90deg deflection, and not just some high deflection that looks almost vertical? With multi-element, slotted flaps, you can do better than plain flaps.


Typically, the way that it works in my local area is that the pilot would request the full procedure when wanting to use a course reversal. This would be interpreted by ATC to mean the pilot was going to fly direct to the IAF requested by the pilot when requesting the IAP. ATC would then vector the pilot in a manner to get the pilot to intercept the course at the most advantageous angle. The pilot may request to self vector, though. The pilot would then fly outbound on the IAP for the PT.

The PT has to be done along the outbound course. Though there is not a specific distance the pilot must fly in order to do the PT, it has to be flown in such a manner that the aircraft does not exceed a specific distance. The pilot can, however do the PT in as little a space as that provided by a hold.

If the pilot chooses to use the hold as a course reversal instead, they would request the hold first. They would follow that request up either with another radio call or within the same radio call with stating the intent of using the IAP to approach for a landing, touch and go, low approach, etc.

If the pilot does not make their intent clear when requesting the approach ATC will ask for the pilot to state their intentions. On a slow day, they may just ask you to report the FAF when inbound for a landing.

Remember though, the procedure for using an IAP would be to have your aircraft established on the lateral guidance, fully configured for a landing, at or prior to the FAF. That would preclude the possibility of flying directly to the FAF from any other angle or direction, then descending down for a landing. Because of that, ATC would be expecting you to do some type of course intercept or course reversal on the intermediate leg.


Why does the A-320 allow 1.3 degrees more left rudder trim than right?

Both engines turn the same way, and the bypass fans exert torque in order to accelerate the air passing through them. The torque needs to be trimmed out using aileron & rudder trim.


What are the meanings of these terms used in ATC ground communications?

If you are driving a vehicle anywhere within the movement controlled area of an airport you need to be in contact with the ground controller.
1 & 3 are virtually synonymous, it is a person, a mechanic, working for the named airline's maintenance department, driving a vehicle.
2 is a person driving a aircraft tug vehicle.


When should I use the global Reynolds number and when the local Reynolds number?

Definitely use the local Reynolds number on each of the flaps! The flap will only work properly if it is allowed to produce its own, fresh boundary layer. If instead it inherits the slow, thick boundary layer of the wing or flap ahead of it, the flow would soon separate and the flap would loose most of its effectiveness.

Note that a Reynolds number is always a local phenomenon. At 2 m from the leading edge, the Reynolds number is twice as large as at 1 m. Only when you compare total coefficients for the whole airfoil would the Reynolds number at the trailing edge be used.

If the distance between your bodies is more than a few centimeters, the boundary layers will not interact, so again the local length should be used for the Reynolds number reference length.


Do FAA knowledge test endorsements have an implicit expiration date? If not, can I add one explicitly?

The last that I looked into it, there were no expiration dates on written test endorsements by CFI and GI.  However, the FAA has made it clear many times that instructors are free to add conditions to endorsements.

For example, when I endorse a student for solo, I will put limitations like:
1.Prior phone call to instructor, 2. surface winds less than 14K, and within 45 deg of runway heading, 3.Five miles vis with VFR conditions.

Of course solo endorsements have implied expiration dates. But you could endorse J Pilot for a instrument written, and add "Endorsement expires Jan 1, 2018."

Since these things are vetted regionally, if you have any concerns, you can always call the FSDO and talk with an Ops Inspector there.

I did that once when I signed a guy off for a Flight Review, and wanted a condition on the sign-off. The pilot agreed with the condition, and I ran it past the Safety Program Manager who was an Ops Inspector, and his words were, "Absolutely! Any restriction you think is appropriate is fine to add to the endorsement."  That was sometime ago, but I have no indication that the policy/latitude has changed.


What is the difference between targeted airspeed and selected airspeed?

These terms obviously stem from an Airbus flight deck.

Anything selected represents pilot's discretion. If you want to keep a certain speed, HDG or altitude, you would pull the corresponding FCU (Flight Control Unit = Autopilot Panel) knob. This means in Airbus philosophy: I have control.

Anything managed represents a flight management calculation. If you want to fly, e.g. in the most economic way, you push the corresponding FCU knob and therewith "handover the controls to the aircraft".

The calculations for managed autopilot options are derived from e.g. gross weight entries on the INIT page or current gross weight, Angle of Attack, Air Data Computers, Cost Index, ... depending on the flight phase.

So, you always prefer to follow the economically calculated way and use managed modes. Whenever ATC requests you to keep a certain speed, sink/climb rate, heading whatever, you pull the knobs and select the target values.


List of airlines and aircraft types at Copenhagen Airport (CPH)

This can be obtained from the Eurocontrol Data, if you are a student they might allow you to acces the data:
https://ext.eurocontrol.int/

You have to request for an account there.


Yes, there is, but it is not by regulation. It is in Advisory Circular 20-97B.

For example, section 7 would apply to most of your pictures:

  (7) In-Service Inspections (Operator).

  (a) Tread Damage Removal Recommendations. Tires that exhibit any of the following characteristics symptomatic of damage should be removed from service:

    (1) Cracking and/or cutting in a tread groove that is undercutting material adjacent to the crack or cutting that has lifted or can be lifted.

      NOTE: Do not probe cuts or embedded FOD when the tire is inflated.

    (2) Undercutting in a tread rib.
    (3) Transverse cracking in the tread that is visible at the surface and shows progression along an angular path down into the rubber.

  (b) General Tire Removal Recommendations. Tires with any of the following conditions should be removed from service:

    (1) Sidewall cuts that penetrate the outermost structural ply.
    (2) Internal separations characterized by bulges or distortions in the tread casing or sidewalls.
    (3) Heat or slippage evidenced by reverted or charred rubber above the wheel flange.
    (4) Tires worn or flat-spotted to the outermost casing ply (bias) or outermost belt (radial).


What are the rules in the UK about overflying built-up areas for fun?

Does anyone know what the rules are for just randomly deciding to fly
  over a built-up area like this for the fun of it?

In UK, the master document for air regulations is The Rules of the Air Regulations (ROTAR). UK being still part of the EU, they refer to a common set of rules at the EU level, the Standardised European Rules of the Air aka SERA (qui sera sera...)

UK ROTAR state a minimum flyover height, one for VFR, one for IFR:

  The minimum heights for VFR flights shall be those specified in
  SERA.5005(f) and minimum levels for IFR flights shall be those
  specified in SERA.5015(b)

and SERA says:

  SERA.5005:

  (f) Except  when  necessary  for  take-off  or  landing,  or  except
  by  permission  from  the  competent  authority,  a  VFR  flight shall
  not  be  flown:

  (1) over  the  congested  areas  of  cities,  towns  or  settlements
  or  over  an  open-air  assembly  of  persons  at  a height  less
  than  300  m  (1  000  ft)  above  the  highest obstacle  within  a
  radius  of  600  m  from  the  aircraft;
  (2) elsewhere  than  as  specified  in  (1),  at  a  height  less
  than 150  m  (500  ft)  above  the  ground  or  water,  or  150  m
  (500  ft)  above  the  highest  obstacle  within  a  radius of 150 m
  (500  ft)  from  the  aircraft.

So for VFR: 150 m, but 300 m in populated areas.

  SERA.5015:

  (2) elsewhere  than  as  specified  in  (1),  at  a  level  which
  is  at  least  300  m  (1  000  ft)  above  the  highest  obstacle
  located within  8  km  of  the  estimated  position  of  the  aircraft.

And for IFR: 300 m above obstacles.

As you see this is not very high. In addition, as you mentioned, aircraft landing or taking off will indeed fly below these minimums.

  Jets landing at LHR with a stupidly shallow glide path angle

Landing cannot be done at high angle, the proper slope is the result of two elements:

Aircraft cannot afford a high descent speed, since the vertical rate determines how hard the landing gears will touch the runway and whether they will be damaged.
Aircraft cannot slow down under a given speed without losing their capability to create lift. This minimum speed and the previous maximum vertical speed determine a maximum slope.

This glide slope has been chosen so that it is compatible with all sorts of aircraft approach speeds and vertical rates.

A standardized value of 3° is common. But when the approach area is limited, or when this is desirable to maintain a higher altitude a longer time to reduce noise on the ground, then this angle can be increased to 3.5 or 4.5°, or even 5.5°, this is the case for some approaches at Heathrow as @TomMcW told us.

Source

Alternatively, some airports have lower angles, down to 2.5°.


Is the landing gear controlled by the pilot or is it automatic?

The landing gear system is operated by the pilots. The extension and retraction, depend on the action from the pilot monitoring, on 2 pilots operation.
The pilot has a lever on their panel, on which they select the extension (down) and/or retraction (up).
Some aircraft has a system to avoid extending them on high speed, to avoid some damage, and on the ground, avoiding retracting, for obvious reasons.
There are lights, green and red, indicating their position.


What is the temperature of the air leaving the combustion chamber of a CFM56-5C?

Quick answer: At the design point considered, which is assumed to be takeoff conditions, a CFM56-5C combustor raises gas temperature to 1360°C (the share of the compressor in this raise is about 600 °C).

This is a common value found in modern turbine engines, a balance between fuel consumption reduction and turbine material capabilities (nickel super-alloy, more on that here and here).

Turbine entry temperature (TET) varies with thrust. Takeoff TET is maximal and top-of-climb TET is about 100°C less. Takeoff TET cannot be allowed for a long time, due to the damages which would be incurred by the high-pressure turbine guide vanes and blades.

Some details about turbine engine principles follow.

Station numbers

In turbine engineering, to facilitate description and comparison, steps in the Brayton cycle are identified by a station number.

(Source)

Additional stations are defined to reflect specific needs (e.g. for the cold flow of a turbofan). The full standard is known as ARP 755, see this old but free description.

The exit of the combustor (which is also the turbine nozzle guide vane leading edge) is station 4. In this nomenclature, Tn is the temperature at station n, Pn the pressure, etc. As an example, the sensor seen in the fan inlet of many turbofan engines is commonly referred as T12 or P12T12 sensor.

Gas temperature and entropy

Thrust which can be produced by the engine depends on the turbine inlet temperature (station 4), which is limited by materials.

There are two means of raising the temperature. The compressor raises the temperature by increasing air pressure, the combustor raises it by fuel combustion at (ideally) constant pressure. The later increases entropy due to the breaking of hydrocarbon chains.

This is visible on a so called temperature-entropy (T-s) diagram, e.g. this one for the CFM56-7B:

CFM56-7B T-s diagram. Source

We can see the compressor work between stations 0 and 3 (with no change in entropy in a perfect cycle) and the (ideally) isobaric raise in temperature and entropy between 3 and 4 as fuel chemical potential energy heats air.

The area under the curve is representative, along with the mass flow, of the net work of the engine (energy produced by the turbine minus energy consumed by the compressor), hence its efficiency. The area depends on two main factors:

How much pressure (and temperature) is raised by the compressor.
How much entropy (and temperature) is added by the combustor.

The goal is to achieve the desired turbine temperature with the highest efficiency. By increasing the pressure ratio of the compressor (the height of the left vertical segment) less entropy has to be added by the combustor (horizontal segment). This means less fuel.

There is a specific PR value, around 30-35, for which the area under the T-s curve is maximal. This value is indeed targeted by the engine designer. Looking at the previous diagram (oblique lines in kPa), we can see the PR used is around 30.

CFM56-5C

Four CFM56-5C were used to power the smallest A340. A340 manufacturing has been stopped, as 4 engines are no more a good option in the era of high fuel prices.

Your question indeed boils down to: What is T4 for the CFM56-5C?

From this document (in French):

Pour une approche analytique de la dynamique du vol

which is a thesis by Elodie Roux, this table on page 198:

tells us the T4 temperature is 1633 K, that is 1360 °C.


Why do airplanes use MAYDAY when in danger but ships send SOS?

The difference here isn't between ships and aircraft: it's between Morse code and voice.

The SOS signal is only for Morse code. It's short, easy to send, and easy to recognise. But it's not as convenient to say. It doesn't actually mean "save our souls". The letters were chosen just to form the simple Morse pattern, and "save our souls" is a backformation: it was made up by sailors later, partly as a joke, partly as a mnemonic.

"Mayday" is an English-looking spelling of French m'aidez, "help me". Spoken out loud, it's short, easy to send, and easy to recognise. It doesn't have any sounds that some nationalities can't say (such as r, th, or v). It's a good signal to use as voice, but would be much worse as Morse code, because it's too long.

Back in the days when aircraft were equipped with Morse code transmitters, they would have sent SOS as a distress call, just like a ship. And a ship with voice radio would send "Mayday" instead of SOS. Now that Morse code has fallen out of use, SOS is also disused. You only hear it in movie plots where the plucky hero doesn't have a working radio but can somehow improvise a way of signalling Morse code (usually by holding two wires together on a broken radio).


What are the particular challenges faced when landing at Bristol airport (UK)?

I have flown into Bristol quite a lot, as I live near there. Most landings are boring, but with good views on a clear day.  Most landings are also from the east, on 27 as the prevailing wind is from the west.

On the fairly rare occasions when you come in from the west on 09 it tends to be in unsettled weather, as that correlates with easterly winds.  You're also coming in over the Bristol Channel (not renowned for good weather, at least at sea level). Final approach from both directions is over some low but lumpy hills, more noticeable to the west of the airport.

"Earlier this year" written in April suggests late winter/early spring, when we had some interesting weather brought in from the NE. With the exact date it might be possible to narrow things down.

Overall it's nothing special but it's perfectly possible for a few things to come together to make it more interesting.


Do I understand the rules of logging cross-country time as a Safety Pilot correctly?

As background, see this question for a general explanation of how safety pilots can log time. Also have a look at the Gebhart (2009) interpretation for the cross-country part (and see this question too).
Note that the two key things to keep in mind in these logging scenarios are:

Acting as PIC and logging PIC time are two different things
You have to be very clear about who is the acting PIC for the flight

With all that in mind (and referring to 14 CFR 61.51):
The primary pilot can log instrument time and cross country time, but not PIC time
The primary pilot can log all three. Whether they're the acting PIC or not, they can still log PIC time as the sole manipulator of the controls (61.51(e)(i)). They can also log instrument time while they're under the hood (61.51(g)) and cross country time.
The Safety Pilot can log PIC time, but not cross country time or instrument time
If the safety pilot is acting as PIC then that's correct. They can log PIC time because they're acting as PIC "of an aircraft for which more than one pilot is required under [...] the regulations under which the flight is conducted" (61.51(e)(iii)). If the safety pilot is not acting as PIC then they can log SIC time.
But either way, the safety pilot may not log cross country time (Gebhart). They also can't log instrument time because they were never operating "the aircraft solely by reference to instruments under actual or simulated instrument flight conditions" (61.51(g)).
If flying a high-performance and complex airplane, both the primary pilot and Safety Pilot must have a complex and high-performance rating
Only the acting PIC requires those endorsements (not ratings), per 61.31(e) and (f). So if only one of the two pilots on board has them, that's the only pilot who can act as PIC.
If only the primary pilot has the endorsements the flight can still go ahead because a safety pilot isn't required to have them. However, the safety pilot couldn't act as PIC and could only log SIC time.
If only the safety pilot has the endorsements the primary pilot can still log PIC time because you don't need the endorsements to log PIC time. But the safety pilot must act as PIC.
The symbiotic benefit of this system is that the primary pilot gets instrument time and the Safety Pilot gets PIC time, both at half price if they split the cost of flying
Essentially, yes. Typical practice is for the pilots to agree that the safety pilot will act as PIC, and they split the costs 50/50 (61.113(c)). That way they can both log PIC time - which is valuable for further ratings - while only paying 50% of the costs. This question has more information on cost-sharing.
And thanks to JScarry for pointing out that if the safety pilot has BasicMed rather than a regular medical, they must act as PIC. See this question for more details.
Whatever you do please be sure that both pilots do know and understand who is acting PIC for the flight. That person has the final responsibility if something goes wrong. Knowing who's acting PIC is important to prevent things like a safety pilot without a complex endorsement agreeing to act as PIC in a complex aircraft, because "I'm just a safety pilot". You might also have insurance or flying club rules on who can act as PIC.


If the cabin temperature controller does not function, does the pilot have to make an emergency landing?

I'll use the B757 as an example, on it you would not divert due to temperature control issues. In fact the Master Minimum Equipment List items 21-61-1 and 21-61-2 give permission to dispatch the aircraft with inoperative zone temperature control.

The Quick Reference Handbook (PDF) for the 757 gives the following instructions for failure of zone temperature control.

I also think most airlines and crew think passengers would rather get to where they are going than being comfortable.

As for the emergency landing, aircraft can and do divert all the time without declaring an emergency (Mayday) or urgency (Pan-Pan). So worse case the crew would choose to divert to a suitable airport.


How Helicopters Change Attitude (Gyroscopic Precession or Thrust Vector Tilt)

This animation shows it better than most.  The swash plate changes the plane of the rotor disc to change the plane of the lift vector.  It's the same thing as an airplane turning by banking.  When an airplane banks it imparts a lateral thrust component to the vertical lift component and it moves sideways, and because it's moving forward as it does so, it moves in a horizontal arc, or a turn.  A helicopter's rotor is just able to "bank" in all directions at any speed.

The swash plate directly flies the blades to the path that will put the overall disc in the desired plane of rotation.  The blades have to fly to their position using the air; if you had the machine running in a vacuum, the cyclic would have no effect.  However, gyro precession is a factor insofar as the input/result of the swashplate's effect on the blade's physical path is offset 90 degrees.

That is, to get the blade tip to its highest point in the circle, the highest blade angle, or highest lift force in the rotational cycle, is imparted 90 degrees before that point.  To tilt the rotor disc forward say, the blade that is on its way to its high spot over the tail boom will have reached its highest blade angle while passing at 90 deg on the left.

On the Bell rotor in the animation you can clearly see this.  The rotor disc angle follows the swash plate angle directly - swash plate tilts forward, rotor tilts forward. However, the linkage being driven by the swash plate acts on blade angle with a 90 degree offset (the control rods coming up on each side of the hub) to account for precession.

The Bell teetering system is interesting because it imparts no bending forces whatsoever to the rotor mast. The machine's body is suspended below the rotor hub as if it was a tennis ball on a string.  When you move the stick you are making the rotor disc fly around on its own account by tilting this way and that and the machine suspended under it follows along. In fact if a bending moment WAS applied to the mast, by having the teetering stops contact the mast while it's spinning, it comes apart and you become a falling object (this is "mast bumping" which cause the deaths of a number of Huey pilots in the 60s and Robinson pilots in the 90s).

Rigid and articulated rotor systems do impart some rolling and pitch moments into the air frame and the rotor head, mast and suspension system for the transmission are designed to transfer these loads.

A good fixed wing analogy between an articulated and teetering rotor is to compare regular airplanes vs hang gliders and trikes.  An articulated/semi rigid rotor is a bit like a regular aircraft where the body is directly acted on by the wings, although with a flexible connection between the wings and fuselage.  The Bell system is more like a hang glider or trike where the wing and body are on a fully flexible connection and you basically fly the wing around and the body underneath follows along without ever reaching the physical limit of the connection.  It's not a perfect analogy but sufficient for visualization.


Why didn't early jetliners use turbofans?

Production turbofans just weren't available. Once they came on the market and were mass-produced, jetliners switched to them.

While turboprops did exist at the time, they were (and are) a turbine engine driving a propeller in place of a piston engine, a straightforward combo of two techs. Turbojet engines were fairly complex machines for the era on their own.

A turbofan involves a large diameter fan, similar in design to an axial compressor, which is more difficult to build than simpler centrifugal compressors used in the first jets and most turboprops. It spins at higher rpm than a prop, and needs to be built and balanced to jet engine tolerances, with the fan tips very close to the casing, but not quite touching it.

The fan also needs to be driven by a core that has enough net power left to produce both thrust and torque, and to do so at low enough rpm to keep the fan (mostly) subsonic. This combination only brings considerable efficiency gains with a two-spool core, using a low-speed shaft to match the fan's optimum rpm, fitted inside a hollow high-speed shaft driving the compressor (unless an aft fan is used). A two-spool with its extra seals is a much more complex engine than a single-spool turbojet or centrifugal flow turboprop.

All of this was done and turbofans quickly became the norm, but it took a few years to develop and ramp up production.


Could a commercial plane seat configuration look like a troop carrier?

Legally, you would need to find a seat that passed the FAA's 16 G "side facing" requirements. The AC that covers the 16G rule has some text that may be of interest on this matter. The FAA admits that its an ongoing area of research and that currently special tests need to be undertaken to certify one. (bolded for emphasis)

  d. Side-facing Seats.

  (1) General. All seats occupiable for takeoff and landing are subject
  to the specified dynamic test conditions. Included are side-facing
  seats and both single occupancy and multiple place seats, such as
  divans. Compliance with the structural requirements should be
  demonstrated for side-facing seats, using the same conditions for the
  test and pass/fail criteria as for fore- and aft-facing seats. The
  seat should be loaded in the most critical case structurally. Means of
  restraining the ATDs may need to be adapted to ensure adequate
  retention during the test. The application of floor distortion will
  need to be assessed on an individual basis, depending on the design of
  the fixation of the seat. The injury criteria of § 25.562 are not
  adequate to demonstrate equivalent safety of side-facing seats when
  compared to fore- and aft-facing seats. To demonstrate equivalent
  safety fully in the absence of such specified criteria, the applicant
  must use other injury criteria which may be derived from the
  automotive industry, which uses side-impact ATDs.

  (2) Assessment
  criteria. Research into side-facing seats is ongoing. As research
  proceeds, the FAA will work toward establishing a more definitive
  policy with respect to the acceptance of side-facing seats. Until
  then, in the absence of specific compliance guidance, the FAA is
  prepared to assess side-facing seats on the following basis:

  (a) The
  seat must demonstrate compliance with the structural requirement.

  (b)
  If an acceptable side impact ATD has not been used with assessment of
  the corresponding injury criteria, it must be shown that the occupants
  are restrained in a manner that prevents substantial energy absorption
  by body to body contact (on a multiple occupancy seat) and which,
  using the best available engineering judgment, minimizes injury to the
  occupant(s).

The way this reads in short (at least to me) is that the FAA does not really test side facing seats all that often but they are willing to if an appropriate means of testing is devised, you can prove that people smashing into each other wont cause any serious problems and that your seats will be ok when a shock wave passes through the floor (same as the forward/aft facing seats).

The FAA also has an extra supplement for potential injury from side seat configurations thats worth taking a read through "Supplemental Injury Risk Considerations for Aircraft Side-Facing Seat Certification"

On the evacuation note the FAA does not really care what the seat orientation is in terms of evacuation. If you are talking about converting a modern airframe you likely could not place a seat in front of the over wing exits but other than that so long as you comply with the evacuation time limits you will be good to go (from a strictly certification stand point). Since this configuration still has rows similar to that of a normal airliner I dont see why you would not be able to properly demonstrate evacuation capacity in this configuration.

The biggest issue I see here is a lot of toes getting run over, and knees bashed by a galley carts...


Is the "glory" optical phenomenon frequently seen by aircraft pilots?

Short Answer:

Yes, pilots frequently see this phenomenon.
No, it does not necessarily present a specific icing hazard.
Yes, in some circumstances it can be in indication of an icing hazard.

Longer Answer:

Speaking for myself, yes, I often see this. I cannot speak for all pilots, but I think many pilots do also see this. The phenomenon depends on several conditions, the primary ones being angle of the aircraft relative to the sun, and the presence of liquid water droplets.

However, I would contest the assertion that it reveals the presence of supercooled water. I see the phenomenon most often in low level fog banks or mist. I do a lot of early morning flying when the conditions are right for the phenomenon. On many of these occasions the air temperature is well above freezing, and all other weather conditions would also indicate that the water droplets are not supercooled. See the following photos from the wikipedia page showing the phenomenon in low level (probably above 0°C) fog banks:

Since the water droplets connected with the phenomenon are not necessarily supercooled, the risk of icing will depend on other factors, primarily outside air temperature. Though the "glory" phenomenon does indicate visible liquid water droplets, it does not necessarily indicate an icing risk. A thorough pre-flight risk assessment for icing conditions should answer that question on a case by case basis.

Now, the conditions in which many airline passengers might see the phenomenon may well be at an altitude high enough that the liquid water droplets may very well be supercooled. In such cases the "glory" phenomenon indicates that the cloud in question is not formed of ice crystals (which pose little icing risk) but of liquid, and possibly supercooled liquid droplets.


Is there anywhere I can find examples of letters seeking interpretation of FARs, sent to the FAA Office of Chief Counsel?

The FAA posts the original submission along with the interpretations, at least for recent interpretations. There's a lot of variation in who they're addressed to; many of them are follow-ups to previous contact with the FAA, presumably with the local FSDO.

This one (Standel-West Coast Aviation Services, 2019) might be useful as a starting point, it simply uses the salutation "To Whom It May Concern" and it has the full mailing address in it. It also uses very specific wording about the scope of the request:

  This letter is a request for interpretation and clarification of 14
  C.F.R. § 135.267(b).


How can I calculate the rolling moment of an aileron for a given plane based on its performance?

If you know the rolling speed at a given flight speed, you can calculate the aileron effectiveness and use that to calculate the forces. The final rolling speed is reached when roll damping and the aileron-induced rolling moment reach an equilibrium: $$c_{l\xi} \cdot \frac{\xi_l - \xi_r}{2} = -c_{lp} \cdot \frac{\omega_x \cdot b}{2\cdot v_\infty} =  -c_{lp} \cdot p$$
Thus, your aileron effectiveness is $$c_{l\xi} = -c_{lp}\cdot\frac{\omega_x \cdot b}{v_\infty\cdot(\xi_l - \xi_r)}$$
The roll damping term is for unswept wings $$c_{lp} = -\frac{1}{4} \cdot \frac{\pi \cdot AR}{\sqrt{\frac{AR^2}{4}+4}+2}$$
and the moment per aileron now is $$M = c_{l\xi} \cdot \xi \cdot S_{ref} \cdot b \cdot q_\infty$$
Calculate the moment for each aileron separately; normally the left and right deflection angles are not exact opposites, which helps to reduce stick forces.

If you only need an approximation, maybe do it like this:
You first need to have all dimensions and the deflection angles. I expect you don't have lift polars of the wing section, so you need to approximate the lift increase due to aileron deflection with general formulas. This is $$c_{l\xi} = c_{l\alpha} \cdot \sqrt{\lambda} \cdot \frac{S_{aileron}}{S_{ref}} \cdot \frac{y_{aileron}}{b}$$
and the moment per aileron now is $$M = c_{l\xi} \cdot \xi \cdot S_{ref} \cdot b \cdot q_\infty = c_{l\alpha} \cdot \sqrt{\lambda} \cdot \xi \cdot S_{aileron} \cdot y_{aileron} \cdot q_\infty$$
Nomenclature:
    $p \:\:\:\:\:\:\:\:$  dimensionless rolling speed (= $\omega_x\cdot\frac{b}{2\cdot v_\infty}$). $\omega_x$ is the roll rate in radians per second.
    $b \:\:\:\:\:\:\:\:\;$  wing span
    $c_{l\xi} \:\:\:\:\:\:\;$  aileron lift increase with deflection angles $\xi$
    $\xi_{l,r} \:\:\:\:\:\:$  left and right aileron deflection angles (in radians)
    $c_{lp} \:\:\:\:\:\:\:$  roll damping
    $c_{l\alpha} \:\:\:\:\:\;$ the wing's lift coefficient gradient over angle of attack. See this answer on how to calculate it.
    $\pi \:\:\:\:\:\:\:\:$  3.14159$\dots$
    $AR \:\:\:\:\:$  aspect ratio of the wing
    $\lambda \:\:\:\:\:\:\:\:$  relative aileron chord
    $S_{aileron} \:$  Surface area of the aileron-equipped part of the wing
    $S_{ref} \:\:\:\:\:$  Reference area (normally the wings's area)
    $y_{aileron} \:$  spanwise center of the aileron-equipped part of the wing
    $v_\infty \:\:\:\:\:\:$ true flight speed
    $q_\infty \:\:\:\:\:\:$ dynamic pressure

Depending on the relative chord length of the aileron, this formula is good for maximum deflections of 20° of a 20% chord aileron or 15° deflection of a 30% chord aileron. Remember: This is a rough estimate for straight wings.


Why do X-wing configurations missile/guide bombs use symmetric airfoils?

Assymetrical wings on missiles/guided bombs do exist. However the goal of all missiles/guided bombs is to hit or come close to its target, which mean different things for various missiles. This drives their design:

Symmetrical airfoils on missiles are used in order to guarantee uniform turning capability. This enables the missile to immediately turn in either direction, therefore not losing time to first roll the entire missile before turning, therefore making the missile more maneuvrable. This is especially needed for air-to-air missiles like the R73-Wympel or the Diel IRIS-T. Cruise Missiles, on the other hand, can be less maneuverable (ground targets seldomly move), which is why they do not necessarily have symmetrical wings. For example, if you look closely at the image of the Tomahawk missile, you will notice the unsymmetrical wingshape.  Such missiles use the bank-to-turn control strategy. *.

I do not know too much about this, but the main design goals for these again are good turn capabilities (aka, pull a lot of gs), and supersonic performance. Therefore basically the same considerations you have as for any other airfoil with the exception that the requirements are a bit more extreme.

* An interesting mix is the MBDA Meteor. It uses bank-to-turn because it has underbelly intakes. I cannot find the source, but apparently in the endgame the control mode is switched to skid-to-turn as it is more important to hit the target, then to keep the motor running


Are CTAF and UNICOM frequencies routinely recorded?

From the AIM:

  4−1−4. Recording and Monitoring

    a. Calls to air traffic control (ATC) facilities (ARTCCs, Towers, FSSs, Central Flow, and Operations Centers) over radio and ATC operational telephone lines (lines used for operational purposes such as controller instructions, briefings, opening and closing flight plans, issuance of IFR clearances and amendments, counter hijacking activities, etc.) may be monitored and recorded for operational uses such as accident investigations, accident prevention, search and rescue purposes, specialist training and evaluation, and technical evaluation and repair of control and communications systems.

    b. Where the public access telephone is recorded, a beeper tone is not required. In place of the “beep” tone the FCC has substituted a mandatory requirement that persons to be recorded be given notice they are to be recorded and give consent. Notice is given by this entry, consent to record is assumed by the individual placing a call to the operational facility.

The use of "may be" for the manned stations would hint at a "no" for the CTAF, UNICOM, etc. (Applies to official recording, liveatc not included.)


How do designers determine the altitude profiles of neighboring procedures for deconfliction purposes?

I have some trouble understanding how the procedure designers take into consideration the traffic flow from neighboring arrival procedures

We don't.
We only concern ourselves with terrain and obstacle clearance. Doc 8168 Vol. II I-2-1-1 refers.
Deconfliction is an ATM responsibility, covered in Doc 4444.


Why are the throttle levers for the Comet's outboard engines shaped funny?

Sean, this will probably surprise you as much as it did me, but the answer is that it is intended to help keep the hand of the pilot operating the throttles on them and not have it slip off. In my opinion, it's a nifty little design detail.


How come there is no attempt at an "inter-meshing rotorprop" high-speed helicopter?

If labelled 1 to 3 top to bottom, numbers 2 and 3 in the illustration are identical.

A pair of rotors that are counter-rotating. One set is co-axial, the other set is slightly separated. Aerodynamically (dissymmetry of lift problem), I don't see a difference.

In plan view it looks like this:

(Source)

My guess as to why it was not tried, is because the transmission for concentric shafts is simpler, less bulky, and lighter, compared to that of intermeshing rotors (shown below).

Also, in intermeshing rotors the lift is not completely vertical, which reduces the efficiency (source). High-speed aircraft need to be efficient.

(Source)


In an airliner, does the Captain or the First Officer fly the airplane?

At the commercial airline level, there is very little difference between a captain and a first officer, other than the amount of time that they have been at the company (seniority).

Typically, each of the two pilots takes turns flying the airplane.  For instance, if today's trip is from Miami to Charlotte to Chicago to Atlanta to Miami, the captain may fly from Miami to Charlotte, the first officer from Charlotte to Chicago, the captain from Chicago to Atlanta, and the first officer from Atlanta back to Miami.

The duties in the cockpit are divided between the Pilot Flying (PF) and the Pilot Not Flying (PNF)/Pilot Monitoring (PM).  These duty positions are independent of the captain/first officer designation.  The PF is responsible for physically flying the airplane (usually only during takeoff and landing) and for controlling the autopilot.  If the autopilot acts up, the PF immediately takes over.


The B-2's pitot plate has actually been the cause of an accident in conditions that may or may not have had the same effect on aircraft with pitot tubes.

Pitot plates work much like pitot tubes; they measure the pressure of incoming air. The main difference is just how they measure it: pitot tubes measure the ram force of air while pitot plates measuring how much air is constricted by an obstruction. Pitot plates direct air through a "plate" with a hole that impedes the flow almost like how a Venturi tube accelerates fluids. Pictured: Pitot/Orifice plate

Pitot tubes are easier to maintain, inspect, and install. Some of their main problems that you might not encounter with a pitot plate, such as icing, are countered with tested and approved safety systems (like heating). In addition, pitot tubes are not the only instrument to measure airspeed; most commercial and GA aircraft use pitot-static systems in which other pressure sensors are used to get a better and more reliable reading. Pitot plates are advantageous in that they reduce air pressure about 5:1 rather than the pitot tube's 10:1 (meaning yes, less drag in some sense) but on such a tiny scale it makes barely any difference. On the flip side, pitot plates have very inaccurate readings at lower speeds (though so low that it probably would not matter for any jet aircraft). Also, it is to my knowledge that pitot plates are used mainly for fluid research, sometimes not even related to aviation.

Since pitot tubes are relatively small compared to the size of an aircraft and are streamlined anyway, there would be little to no noticeable improvement in aerodynamics. You would think that jetliners have completely clean surfaces, but guess again:

Removing a pitot tube won't make a difference. Note: the gray circles outlined in dotted red boxes are pitot-static ports, which, combined with an aircraft's pitot tubes, make up the pitot-static system. They can measure air pressure for both airspeed and altitude among other things.

Final thing I wanted to clear up: flat surfaces are generally less aerodynamic than curved surfaces. Someone got too much of that idea when designing this plane... /s


What is it like to volunteer with Civil Air Patrol (CAP) as a pilot?

There are almost always opportunities to volunteer. However, joining CAP is a larger commitment than simply saying "I'd like to volunteer to fly." You will need to attend regular meetings and perform non-pilot duties such has becoming an administrative officer or participating in recruiting and fund raising activities. For some squadrons, the budgets are tight, and the ratio of pilots to flights can be high. The complaint I heard from CAP members back in Idaho was that they hardly ever got to fly. This may be less true in other areas.

My suggestion to you would be to contact your local squadron. In your case, this will be a squadron within the California Group 2 (San Francisco Bay). They have senior squadrons located in Palo Alto, Oakland, San Jose and elsewhere (senior squadrons are for adults 18+, whereas cadet squadrons are for children under 21. There are also composite squadrons for both seniors and cadets). Talk to them about their mission and what the experience would be like. If you're still interested, attend some meetings (you'll need to do this before they'll let you apply anyway). Then, after you have a good sense of what will be expected, if you believe in their mission, and you're willing to put in the time required, you should join.

If all you're looking for is a way to build cheap (or free) flight hours as a private pilot, then that is probably the wrong reason to join, and you will likely be disappointed.

*Note from editor: The oddity in the ages of membership for the senior and the cadet groups should be explained. A person may join as a cadet in a squadron up to their eighteenth birthday, however, if they became a cadet before that, they may continue as such until their twenty-first birthday. Anyone joining the Civil Air Patrol after eighteen enters into the senior branch.


What is the reason for different engine configurations seen on Solar Impulse?

Solar Impulse 1 had 2 engines right next to the fuselage, and the other 2 further out where the wing bends upwards.

Solar Impulse 2 has a pair of closely spaced engines on each wing, located partway out onto the wing.


How long is a winds and temperatures aloft forecast valid for?

Advisory circular 00-45 "Aviation Weather Services" documents the winds and temperature aloft (FB) product on page 7-39.  Table 7-11 lists the standard forecast periods for these products.

From this table you can see that the 6-hour forecasts are usable from the time they are issued until 3 hours after the valid time.  The 12 hour forecasts are usable from -3 to +6 hours of the valid time and 24 hour forecasts are usable from -6 to +6 hours of the valid time. The products are issued 4 times daily.

While these are standard times, you should consult the specific information available in the product header that has this information.  For example:

DATA BASED ON 010000Z
VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 550252

This says the product is valid at 06Z and for use from 05Z to 09Z and the data is based upon the 00Z forecast model run.


The crash was only one of the (albeit an important) reason for the grounding of Concorde. Actually, the aircraft was retired around three years after the crash. The main reason was that not enough people were flying it to keep it profitable.

The Concorde as a technological marvel, but it had a number of disadvantages:

The aircraft was costly- The program cost over $3B and produced 20 aircraft, of which 14 were used in commercial service.
Maintenance costs- The small number of aircraft and technological sophistication meant that the cost of spares was high and options limited.
Operating costs- The Concorde consumed nearly three times per passenger fuel when compared to the Boeing 747-100. Still, the aircraft made operational profit due to the high cost of tickets.
Recession- After 9/11 attacks exacerbated the global downturn in aviation due to recession, there was an enormous drop in first class air travel, on which Concorde was dependent on.

While announcing the retirement, British Airways cited

  commercial reasons, with passenger revenue falling steadily against a backdrop of rising maintenance costs for the aircraft.


Do pilots ever increase the cabin altitude intentionally?

I've never heard of this "trick" being used or recommended, although the limits of what I've heard are pretty much limited to US commercial aviation.

If you climb the cabin from the usual 8000' to 10,000', the incremental gain in "sleepy" factor is a little bit but not all that much.  If you climb it above 10,000', then you might "encourage" a few of the more tired/drunk/elderly folks to go to sleep, but now you're into the realm of operating outside of normal practices, and you need to start considering things like, the pilots both need to be on oxygen, the flight attendants may get "tired" quicker than the passengers do, anybody who is elderly or in poor health may start suffering consequences, and then there are company policies and national regulations to consider.

If you raise the cabin above about 14,000 - 15,000' depending on your specific aircraft, then you'll end up activating the automatic passenger oxygen masks, and now you've got some serious 'splainin to do!  (#1, it's a bunch of work for maintenance to repack them, and the aircraft is grounded until they do, and #2 you open yourself up to all sorts of issues if you still have a long way to fly at high altitude to get to your destination!)

I'm going to guess that in the history of aviation, this sort of trick probably has been used at some point, but the opportunity for the uncomfortable questions along the lines of, "okay, tell me again, you did what exactly???" to which the best available answer is along the lines of, "um, well, it, ah, seemed like a good idea at the time, sir..." is awfully high.

I certainly wouldn't recommend it.


In Europe, airlines pay so-called route charges for flying through national airspaces. EUROCONTROL, the European aviation organisation, collects route charges from their Central Route Charges Office, CRCO, and then distributes the money to the member states, who in turn will distribute them to the national air navigation service providers (ANSP's) - including private ones. The advantage of collecting route charges centrally, is that airlines only have to pay to a single organisation, in a single currency.

The charge for individual flights is calculated based on distance flown and aircraft weight, which are multiplied by a unit rate. The unit rates are determined by the individual countries - they are not the same across all of Europe. Unit rates are based on the actual costs for providing air traffic services, such as ATC, communication facilities, navigation equipment, meteorological information, aeronautical information service and so on.

Route charges do not apply to aircraft weighing less than 2 tonnes, state and government flights and search and rescue flights. Some states also exempt military flights, training flights, test flights, local flights, VFR flights, humanitarian flights, police flights etc.

You can read more about the CRCO here, and about how route charges are determined here.

Regarding your second question, I fail to see why a private ANSP should be any less safe than a government one.


How can I calculate a flightpath given a set of waypoints?

The Haversine equations will calculate the bearing and distance between any latitude/longitude pair, and can calculate the location and next bearing for points along a Great Circle.

They go back to the days of sail, shortly after the invention of the marine chronometer, which allowed calculation of the current longitude. As such they assume that the points are on the surface of an idea sphere; as Earth is slightly oblate, there is an error of upto 0.6% in calculations of locations. For any realistic altitude, the oblateness (23 km difference between polar and equatorial radius) is likely to be larger than the change in altitude.

A discussion of them is here http://www.movable-type.co.uk/scripts/latlong.html


Will having a history of depression prevent me from flying?

This is one of those questions where you really need to talk to an AME, preferably one who has significant experience working through these sorts of issues.  In order to get the Class II medical that you'll need to fly commercially, you'll end up needing to work through the process anyway, so you're probably better off starting with the expert, rather than with a message board like this one.

The only case where you'd save any money by starting here is if someone here were to accurately tell you that there is no need to go to an AME as there is no way anything could possibly work.  I doubt you're going to get that sort of advice, because (a) we don't have any AME's that post here on av.se, as far as anybody has ever self-identified, at least, and (b) this stuff is sufficiently complicated that you don't want to trust a layman's info or opinions, even one who "knew somebody who had a similar situation."

That said, I'd suspect that the chances are pretty good that you may well be able to get a medical certificate, so I would encourage you to pursue that path.  Let a good AME take a look at the specifics of what your history looks like, and listen to his/her advice about what would need to happen (maybe very little, maybe quite a bit) in order to satisfy the FAA.

This thread deals with an entirely different medical condition, but the answers, and the logic behind them, apply here as well.

Be honest with the flight surgeon, and don't let random posters here talk you out of giving yourself every opportunity to pursue your dream of flying commercially.

Best of luck to you!


Is it allowed to exit the runway by opposites High Speed Taxiway?

It's not really a regulation question, at least not in the way you think. There's 2 possibilities:

A controlled airfield: in an airfield which has air traffic control all movements require a clearance, if the tower clears an airplane to use a taxiway then that is all that airplane is allowed to do unless there's an emergency of some kind. It would be unusual for ATC to direct an airplane to use a taxiway which has such a tight turn, but there's no reason they wouldn't if it the situation called for it
An uncontrolled airfield: in this situation there's nobody in a tower telling pilots what to do, all movements are at pilots' discretion. Pilots can use any taxiway in any way they please as long as it doesn't put them in potential conflict with another airplane


This depends on the airport but at KPNE where I used to fly there was a $5 landing fee (paid to the city of Philadelphia) that was collected at the FBO (where I rented the plane from) when I paid for the rental. I think if you do not pass through an FBO they will hunt the tail number down and send a bill to the party that has the aircraft registered. Its tough to fly into an airport and not pass through the FBO (unless you are just doing touch and goes). I would assume that for commercial traffic the airline/owning body pays and may even be billed by the airport monthly but I don't know the specifics I only know what I have seen for GA traffic.
If you are curious you can check out the Philadelphia Airport (KPHL and KPNE) legislation here which outlines the various fess and collection mechanisms the city imparts. Keep in mind these are city owned airports, see section V for details on collection but in short,

Section V Part d
Non-tenant Air Carriers and Operators not providing adequate surety or security in form and amount satisfactory to the Department of Commerce, to ensure payment of fees and charges, shall be required to pay all incurred fees and charges prior to aircraft departure.

For the point of contrast lets take a small privately owned airport here in the US, Solberg Airport in NJ has "ramp fees" for parking and the such, but like most small airports like this, these fees are waved with the purchase of fuel (usually at least some minimum amount). There would be no way to avoid paying (well Im sure there is) since usually the only way off the tarmac is through the FBO.


What keeps Russian airliners from being as fuel efficient as their Western counterparts?

The engines.

Russian engines were for decades behind the state of the art. One reason was manufacturing tolerances. I remember that we studied the Progress D-27 three-spool turboprop and found that just the cast casing could be made 250 kg lighter with Western tolerances. The Russian designers kept their tolerances wider to make sure that the minimum wall thickness would not be undercut.

Also, since Russian designers had less powerful computers available to them, they could rely less on CFD, so the turbo machinery was less refined. Improved engines explain maybe two thirds of the increase in fuel efficiency over the last 70 years.

Another reason is system redundancy. Russian engineers made sure the aircraft would still be operable after being maintained by a substandard maintenance crew. Especially the military designs were built with the goal of maintenance-free operation for several weeks. This thinking was also applied on the civilian side, since all Russian aircraft were designed with dual-use in mind. In case of war, all Aeroflot planes would become military transporters, and Aeroflot crews received most of their training on military aircraft. Why else would designs like the Tupolev Tu-134 have a glazed nose?

Tu-134 (picture source)


How do you lean mixture using only the instruments on a C172 Skyhawk?

The procedure varies depending on the engine instruments in the panel. Here’s an good explanation using the EGT probe on a Cessna 172.

And here are the manual pages from a Cessna 172SP that explains it.

[


Is there some functionality of an airliner which is not controlled by the cockpit?

You cannot (as far as I know),

Flush the toilets
Control the IFE system (aside from possibly pulling the breaker to shut it off)(there seems to be some debate on this one and it could vary by plane/system)
Open the doors (of a passenger plane, cargo planes this may be possible)
Update the software for glass cockpit planes (if the computers are not located in the cockpit). I'm still looking for the link but FMS units are updated via USB on a unit usually housed with the other flight computers which is often below the cockpit. In some smaller planes these units are in the cockpit as are the USB ports so this may only hold for some aircraft.
General passenger tasks (reading lights etc). Although it should be noted that generally speaking the master breakers are in the cockpit so while they may not have control over individual system components (e.g. single reading lights) they can often shut them down completely if need be.
Ovens (for heating meals) and coffee machines. Only circuit breakers are in cockpit again (and they are needed; faults in these things cause relatively high fraction of diversions).


How do airline pilots relieve the physical stress and discomfort of sitting for long periods of time?

I was on an EMB-145. The longest flight we usually had were 3.5 hours so my experience doesn't compare to Trans Pacific routes. As a crew-member I could get up to use the restroom, but there wasn't enough room to stand on the flight deck. You learn to sit different ways (one leg under you) to makes adjustments. Then the other leg under you later and so one. Some sort of seat Yoga I guess you could call it. My strategy was to walk, walk, walk, and stay off the plane as long as I could between turns. Your body adapts to the environment after awhile regardless of your body being in great shape or not.


How are light weight fillers made for fixing dents on airplane wings?

Lightweight body fillers such as Poly-Fiber's SuperFil are two-part epoxy fillers. The reason they are lightweight is that a significant portion of the filler in the epoxy is composed of microballoons, also known as glass microspheres.


How do services like Flightradar24 and FlightAware track flights?

https://www.flightradar24.com/how-it-works - taken from the FR24 website. They use ADS-B - hence the reason the majority of General Aviation stuff doesn't show (unless it has a mode S transponder).


Is there a way for an aircraft to tell a ground station when the gear is down?

AFAIK, ACARS reports the block time and flight time already. That consists of parking brake release and parking brake set (block time), and weight off wheels to weight on wheels (flight time). These are to help airline maintenance keep track of when they need to do inspections, etc. It would certainly be possible to program it to report wheels up and down, but currently there's no reason to have it report those times.

I'm not sure if you're talking about having this reported in real time or not, but automatic ACARS reports are not exactly in real time. They can transmit things right away (such as text messages from the crew) as long as they have a network connection. But the automated messages are queued for transmission as a block and some types of messages are prioritized over others.

If you're talking about just collecting this data for later analysis, many aircraft are equipped with a quick access recorder (QAR) which records numerous flight parameters. I'm fairly sure wheels up and down times are usually collected. QARs are intended to give information about the flight that can be collected after a flight lands, either by USB, cellular or removable memory cards/disks/tapes. These are collected periodically, such as when the plane returns to the airline hub. This data is used by airlines as part of their flight data monitoring program which looks for incidents that exceed defined thresholds or trends that are occurring to help identify possible safety risks. So the airlines already have a method to collect gear position data.


What is the maximum amount of noise an aircraft is allowed to generate?

If it can be regulated it shall be regulated -- the relevant section of law is FAR 36 - NOISE STANDARDS: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION, with a number of advisory circulars as well.

These requirements are aimed mainly at Transport Category aircraft, and the absolute noise level limits are rather high (certainly nothing you'd want to be standing near without hearing protection).

What's probably of more interest to most people are the FAA's guidelines on Airport Noise, and specifically FAA Order 1050-1E, which deals with the noise you are actually exposed to on the ground (rather than what is generated by the plane's engines).
Order 1050-1E goes into great detail on what is considered "acceptable" noise levels for various types of land use around airports.  Airport construction and/or expansion projects are evaluated against these criteria using computational models to ensure that noise levels will not exceed the FAA's guidelines.


What are the least powerful airplanes that ever flew?

There are a number of human-powered aircraft (list here).  For the Gossamer Albatross, we have

  In still air, the required power was on the order of 300 W (0.40 hp),
  though even mild turbulence made this figure rise rapidly.

As far as top speed:

  Allen completed the 22.2 mi (35.7 km) crossing in 2 hours and 49
  minutes, achieving a top speed of 18 mph (29 km/h) and an average
  altitude of 5 ft (1.5 m)


If all control surfaces were disabled, could a passenger plane be controlled by distribution of the passengers?

There are different degrees of control. The plane could at least be made to crash in a different debris pattern than if the input was not made, and even that's a form of control.

As the whether the plane could be controlled enough to land, and do so, as the question states, with all of its control surfaces disabled, let's see. You get considerably pitch control authority, with poor speed and accuracy, but very little direct roll control. Differential thrust provides a decent amount of yaw control.

So the first question is: Is the plane already on the glideslope of a straight-in approach to an airstrip? If yes, then passenger movement should, with some luck, suffice to get the plane down to the ground.

If not, getting a plane to a suitable landing spot becomes more difficult. Many military transports are designed for rough field landing, so over flat and easy terrain, it should be possible to get some sort of landing that is better than an uncontrolled crash. If the terrain is not so forgiving, it comes down to trying to navigate and fly with greatly reduced control responsiveness and precision, where many inputs will be made wrong, and down to whether they can be corrected in time.

To make an analogy, if a driver transporting a blind passenger falls out of the car, can it be controlled from the back seat by moving controls with the passenger's walking stick, acting on advice shouted from cars passing by? That's how trying to fly a plane that way would probably feel.

That said, much stranger things have happened. People have fallen out of airplanes without parachutes and survived. Planes have landed themselves smoothly after the pilot has ejected. And landings with a loss of most controls have happened as well.


What are the benefits of using thick trailing edge flaps?

The best flaps (aerodynamically, as you ask) will be complicated and elaborate. But complicated flaps add weight and maintenance cost. Airbus wanted to have a variable camber wing for the A340 (Flight), but they didn't pursue it to the end, due to the complexity.

As for the aerodynamic benefits of simple flaps, there aren't any, as the other post shows: slower MMO and smaller MTOW.

Slower MMO is because of the smaller wing sweep because of the simple flaps because of needing a good [slow] approach speed. MTOW is because simple flaps don't carry as much off the ground.

The simple flaps are thicker because:

The flaps are shorter chord-wise: the aerodynamic load (lift and drag) acts on a smaller surface area, compared to the complicated multi-slotted flaps.
Thin flaps would produce even less lift (thanks to @PeterKämpf).
The lack of a thrust gate: they need to be thicker to withstand the jet blast.

Also see comment by Peter Kämpf.

Comparing the A380 and 747-400 flaps. Note the thrust gate and the triple-slotted flaps of the 747.


Why does the low voltage warning light not illuminate when the alt switch is on, but the engine is off?

If the ALT switch is not closed, but the BATT switch is closed, battery power is allowed to flow through the ALT FIELD breaker, through the Over Voltage warning light, and grounds through the Over Voltage Sensor.  If both the BATT and ALT switches are closed, current flows through both the ALT switch and maintains battery voltage at both terminals of the Over voltage warning light which prevents it from illuminating.  This design feature allows the Over voltage warning light to illuminate when either the alternator is not connected to the main electrical bus or the alternator is malfunctioning.


Do aircraft have radar or other forms of traffic sensing?

By far, most civil aircraft lack radar to display conflicting traffic, and certainly to enhance traffic situational awareness.  TCAS and the use of ADS-B are the most effective tools for traffic conflict and situational awareness information.

Lidar is not presently utilized on civil aircraft for traffic avoidance.

Keep in mind that TCAS essentially uses the same mechanisms as secondary ATC radar.


Am I required to report an incident that isn't specifically mentioned in 49 CFR 830?

There are a couple of part 91 regulations that require 'general' incident reporting, but only if the FAA or ATC requests it.
14 CFR 91.3(c) says that if a pilot exercised emergency authority to deviate from part 91 rules then the FAA can ask for a report:

(b) In an in-flight emergency requiring immediate action, the pilot in
command may deviate from any rule of this part to the extent required
to meet that emergency.
(c) Each pilot in command who deviates from a rule under paragraph (b)
of this section shall, upon the request of the Administrator, send a
written report of that deviation to the Administrator.

91.123(d) says that ATC can ask for a report if they gave a pilot emergency priority, even if the pilot didn't deviate from any rules:

(d) Each pilot in command who (though not deviating from a rule of
this subpart) is given priority by ATC in an emergency, shall submit a
detailed report of that emergency within 48 hours to the manager of
that ATC facility, if requested by ATC.

There are also regulations for charters (135.415) and airlines (121.703) that have a long list of "service difficulties" that must be reported, including in-flight fires, brake failures and others. And there are likely non-FAA regulations on things like HAZMAT incidents.


What are the forces acting on the doors of the main landing gear?

Aircraft have a maximum gear extension speed (V$_{LO}$, as in maximum landing gear operating speed), which is normally 1.6 times stall speed, so when the doors move, the dynamic pressure is rather low. Therefore, the forces during gear extension are not the only ones to check.

In cruise, suction on the gear doors might be the limiting factor for both stiffness and strength of the door itself, its latching mechanism or the hydraulic cylinder. I had the misfortune once to live through a flight test where part of one main door broke off in flight: It had no latch and was held shut by the hydraulic cylinder, which was mounted near the rear edge of the door. Suction and elasticity caused the forward edge to be pulled out into the airstream, so it soon became an air scoop, which only increased the pressure difference between the gear bay and the outside. Consequently, the door failed and needed to be redesigned, now with the actuation mechanism near the forward edge and an added latching mechanism.

If the door is aligned with the flight direction, make sure you look at the forces at maximum operating speed and maximum sideslip angle and treat the door like a regular fin. If the door opens into the airstream, use the proper drag coefficients for a flat plate and add some margin to account for oscillating flow separation. Make sure that the eigenfrequencies of the door or its operating mechanism are nowhere near the frequency of such flow patterns.

Here is a short note on the T-38 strut door loads which was written on occasion of the qualification of the T-38 as a chase plane for shuttle re-etries. The maximum gear extended speed had to be raised so the T-38 could follow the shuttle on the way down. Unfortunately, only measurements are given.


Could this helicopter's body be a flying wing?

No, you need sufficient wing span to produce lift without excessive induced drag.

Lifting bodies are only a thing of hypersonic flight where the induced (component of wave) drag is tiny compared to the form (component of wave) drag.

Induced drag is an unavoidable side-effect of producing lift over a finite span. It decreases with wing span, and with dynamic pressure (which in turn grows with density and square of speed; indicated speed is a square root of dynamic pressure). So at slow speed, you need considerable wing span to generate lift efficiently. This applies also to helicopter rotors, which is why they have such large diameters.

Since the other component of drag, form drag, increases with dynamic pressure and cross-section, the optimal wing span decreases with speed. But even jets still have quite high aspect ratio (square of wing span to wing area). Flying bodies without much any wings only become efficient well into supersonic area—and keep in mind that anything resembling a propeller (including tiltrotor) is limited to subsonic.

(At supersonic speeds, the mechanism of drag creation is different, called wave drag, but it still has a form component and induced component and the induced component still depends on wing span and dynamic pressure in the same way.)


The cabin is rigidly attached to the fuselage, with bolts. But in a way the cabins do have suspension: from the wings riding on air.

Elasticity of the wing construction material acts like a spring. Load it with a vertical gust, and it will bend upwards, then spring back.
The wing bending experiences damping forces from the surrounding air, proportional to bending velocity.
The wing sweep angle spreads out the gust: not all of the wing is accelerated upwards immediately.

Modern subsonic airliners with swept wings, flying with near transsonic speeds, experience much less turbulence than the olden days DC-3 type aircraft. So far, so good.

OPs proposal to provide suspension between fuselage and cabin may not be very effective. Notice that car suspensions work best when the unsprung mass is low: independent suspension is able to follow the un-evenness in the road much more effectively than rigid axle suspension, due to the much lower unsprung mass of only the wheel+tyre.

The unsprung mass of the suspended-cabin would be the whole fuselage-plus-wing structure, engines, fuel etc. Considerably more than that of the cabin plus payload. A lot of extra complexity for not much gain.


Is « Shepherd One » really used internationally by air traffic control for Pope's flight?

The FAA declared that as an official call sign for 2015-09-21 to 2015-10-15.

The order it cancels (.pdf here) had the bottom row filled out wrong (SHEPRD1 and "SHEPHERD ONE" were transposed, and "SHEPHERD" was typoed).

A document released on 2016-05-26 lists it in the "deleted special assignment" table (here).

So it's not a permanent reserved identifier in the US; but it might be recurring.

Wikipedia claims here (and here) that in Italy the Papal flights are named "Volo Papale ###", where the ### is a serial number (seemingly the number of times this Pope has flown).  I'll admit that I haven't been able to find anything akin to faa.gov for Italy, France, Australia, or the UK which would corroborate either "Volo Papale" or "Shepherd One".

  Typically, the Pope flies on a chartered Alitalia Jet. The Pope's flight is often nicknamed "Shepherd One" by the press, while the actual callsign is "Volo Papale" (papal flight, in Italian) followed by a serial number.


Would more throttle when using reverse thrust reduce stopping distance?

Broadly speaking, yes.

The standard method of operating reverse thrust on jet aircraft is to use the reverser levers, which are actually thrust levers as well.  As you pull the reverser levers up, you increase engine thrust.  Many aircraft types will have prohibited areas between idle reverse and full reverse thrust which should be avoided (for things such as blade flutter).  Importantly, reverse thrust is not considered when evaluating aircraft landing performance - it largely used to reduce wear and tear on the aircraft for reasons of economy of operation, usually idle reverse thrust is ample for this purpose.   As you suggest, in an emergency full reverse thrust can be used to reduce or prevent a runway overrun.

With propeller aircraft, turbine or piston, you may enter the 'beta' mode (if equipped), creating reverse thrust and selecting appropriate engine power as desired, though as with jets, there may also be prohibited engine speeds which may be passed through on the way to a higher speed, but not left at that level.


Do I need to change cruising altitudes for really short legs?

As you are using the term flight following I'll assume you are in the US. Flight following is an advisory service, you tell them your intentions and they give you any traffic information you may have. If you are changing altitude or course you tell them, you do not ask permission because they cannot give it.
FAR 91.159 clearly states what altitudes you should be at using the semi-circular rule:

Except  while  holding  in  a  holding  pattern  of  2  minutes  or
less,  or  while  turning,  each  person  operating  an  air-craft
under VFR in level cruising flight more  than  3,000  feet  above  the
surface  shall maintain the appropriate altitude or  flight  level
prescribed  below, unless  otherwise authorized by ATC

So if you will be flying 3000ft or more above ground level you will be expected to fly the semi-circular rule, there are no exceptions made except those listed above. From a practical perspective you'll spend more time climbing and descending than at the other altitude so I think it's a fair question, the answer is to make the altitude change.


In cruise, there are no opposite turns that precede every turn.

Human senses and the inner ear are very good at playing tricks, in fact pilots can't judge turns if they have no visibility (e.g., in clouds) without using their flight instruments.

Judging an aircraft's bank from a passenger seat is almost impossible at night, in clouds, over sheets of ice, over hazy oceans, etc.

On a commercial flight, the water in a cup remains level in the lateral during coordinated turns, that's because the load pulling down on the aircraft will still be pulling down perpendicular to the floor.

A shallow roll to the right or left could be just the plane correcting its course in a gust or so.


If a warning emerges, why not land as soon as possible?

As rbp explained, information provided to the pilots is differentiated based on how serious the problem is, from informational up to emergency. Part of designing an aircraft is determining how serious different failures will be.
As technology has advanced, aircraft have become more and more complex. New devices and systems allow aircraft to become faster, safer, more capable, and more comfortable. However, more complexity means more things that can fail. The airplane's systems are analyzed to understand the ways that a system may fail, and how it will affect the rest of the airplane. The results are used to determine how serious different indications may be, and to provide instructions to the crew about what procedures to follow.
With the complexity of modern aircraft, it is much more likely for at least one system to have an issue. It does not make sense to ground an aircraft just because a coffee maker isn't working. Aircraft will have a minimum equipment list (MEL) which allows the aircraft to depart with certain systems inoperative. Circumstances such as ETOPS will further limit which systems may be inoperative. Once in the air, the crew is informed by their checklists about the correct actions to take. Some indications are not critical, others will be. Modern aircraft go even further in determining the severity of indications. Certain less critical information will be suppressed during high-workload phases like takeoff and landing to avoid distracting the crew. Some aircraft will even make it simple for the crew and give them a message like "LAND ASAP".
The basic FAA regulation for crew alerting systems on transport aircraft such as the 767 in your example is 14 CFR §25.1322 (b):

(1) Warning: For conditions that require immediate flightcrew awareness and immediate flightcrew response.
(2) Caution: For conditions that require immediate flightcrew awareness and subsequent flightcrew response.
(3) Advisory: For conditions that require flightcrew awareness and may require subsequent flightcrew response.

It is up to the group certifying the aircraft to convince the FAA whether something requires immediate awareness and/or immediate response.
Some specific alert systems are covered in different sections, such as §25.1305 (d):

(2) A position indicating means to indicate to the flightcrew when the thrust reversing device—
(i) Is not in the selected position, and
(ii) Is in the reverse thrust position, for each engine using a thrust reversing device.

There isn't much more specific than that, but there are other rules that affect the warning system such as §25.729 (e):

(6) Failures of systems used to inhibit the landing gear aural warning, that would prevent the warning system from operating, must be improbable.

So in order to make a failure of the warning improbable, the system may display a false indication rather than fail to indicate a valid problem. Most indications for things such as fires are false. It is much better for the system to assume the worst if in doubt, and for the crew to assume the indication is valid and act accordingly.
So, to answer your questions:

The systems are analyzed to determine which indications are
important enough to alert the crew, and what the crew's response should be. These decisions will be reviewed
at certification to convince the FAA (or local authority) that these
decisions are sound.

As always, the ultimate responsibility of the aircraft lies with the
captain. If the captain feels that diverting is the safest option,
he or she can make that decision. An operator with a good culture of safety will never cause a captain to
fear reprisal for making such an informed decision in the interest
of safety.


What is the final approach fix altitude for this localizer approach?

Coram is not the FAF for a non precision approach.  The FAF for localizer only is Rizer.  You must protect 1400 till Rizer then you may descend to the applicable MDA.


How long does a runway have to be for an Airbus A380 to takeoff?

Airbus's A380 AIRCRAFT CHARACTERISTICS AIRPORT AND MAINTENANCE PLANNING data says that for an A380-800 at maximum certified landing weight landing at sea level a 7000 ft (~2150m) runway is required to land (in dry conditions, presumably).

"A380 Briefing For Pilots (Part 2)" shows a 3750m (~12,300ft) takeoff requirement when operating at 600,000kg at sea level, or almost 5000m if operating at 5000ft at 560,000kg (presumably a lower maximum weight for the higher altitude).  If you can significantly cut back on the weight (no PAX, no cargo, minimum fuel), the bottom end of the chart says ~1600m (~5280ft) for "I don't know how I got here, but I need to get away".

(Trying to find better numbers seems to be difficult because the computer does the calculations, and one document I found claiming to be an FCOM (Flight Crew Operations Manual) only describes feeding the data into the computer, and fun things like how the plane can audibly alert "Runway Too Short!" when landing, but I didn't find any takeoff or landing charts in the 8,100 page manual).


How to take into account man hours in a Service Bulletin?

Elapsed time is the total man hours divided by the number of techs assigned to the task.  So 40 manhours will take one tech 40 hours to complete or 2 techs 20 hours.  If the number of techs to be assigned is up to the supervisor or a scheduler/planner, I would just include the total man hour estimate.  If the job card specifies the number of techs required for the job, then include the elapsed time based on that.

Note that on the first several aircraft modified under an SB, the actual man hours will exceed the SB estimate by a large margin, maybe 50% or more, until the technicians involved get through the learning curve of the task, and even then will probably never get to the SB labour estimate, which assumes perfect conditions and no wasted time.  If the OEM is giving a labour credit that can be charged back to the OEM at some hourly rate, it will be based on the SB estimated labour, which is derived from the proof installation of the SB, not the actual hours used.


How does the noise of a 2-to-4-seat helicopter compare with that of a similarly-sized fixed-wing aircraft?

I found one study comparing helicopter and airplane noise levels and signatures:
Aircraft source noise measurement studies summary of measurements...

Unfortunately this study does not provide conclusions or any  abbreviated comparison in plain language (or I just failed to notice them). It does, however, provide a near endless array of tables to shuffle though and compare.

According to the study there are similarities and differences in noise signatures between helicopters and airplanes, especially depending on the phase of flight and this hardly comes as a surprise.  In real life the biggest problem arises form the differences in how people react to sounds. Some of us might not care much about even the loudest jet noise (I, for example live a couple of miles form an AFB, and I don't mind), and some experience the slightest noise as a terrible nuisance.

What I would recommend, based on my very limited (but still academic) studies on acoustics, is to conduct a series of test flights and measurements to:

verify that legal (if any apply) decibel limits are not exceeded
give you measurement data for comparison and later reference
and, most importantly, to give you and the area residents an idea of the noise related to helicopter operation.

It should be noted that noise charts, such as those presented in the study above, are not easy to interpret. Decibel is a rather tricky unit, and does not necessarily correlate with the way one experiences noise. In comparison, for example, helicopters might be louder in decibels in some stages of flight than same size airplanes, but the noise might not be experienced any more disturbing (or pleasing, depending on how one is inclined)

Human ears are by no means precision instruments, and actually neither are high end decibel meters: their accuracy is typically somewhere in the range of 1 decibel, and considering it equates a difference of 26% in sound energy, and 3 decibels would be doubling or halving the sound energy, it's not very precise... To make things more complicated, an increase of 1 dB is just barely noticeable by human ear (or brain). 3 dB is perceived as about a quarter louder, and 10 dB feels twice as loud.

So: there's not much to distill from decibel charts or measurements unless the differences are huge across the whole frequency range (more than 10 dB), and even then it's still somewhat ambivalent... It's best to get real life experiences when it comes to sounds.


Have bi-wings been used without creating more drag?

Moving the wings vertically apart would mean more and heavier supporting structure, but also a higher pitch moment of inertia. Since this grows with the square of the vertical expansion, a biplane with a lot of distance between both wings will be hard to control and very sluggish.

The real advantage of a biplane is reduced induced drag because less structure needs to be lifted. When cross-bracing enables the top wing to work as the compression member and the bottom wing to work as the tension member of a truss, a very lightweight structure becomes possible, especially when the size of the aircraft grows.

If all you have to power your airplane is a heavy, inefficient piston engine like those at the beginning of the last century, and you can tolerate that your aircraft won't fly fast or far, a biplane is indeed the lowest-drag solution.


What are the differences between radar flight following and traffic advisories?

Depends on the ANSP (Air Navigation Service Provider) to what each term means to them. In most ANSPs they mean exactly the same thing or their individual regulations only have one of these terms/procedures available.

A traffic advisory technically doesn't always require a transponder especially if it is of a snapshot of traffic. The pilot requesting the traffic advisory gives position and a one time traffic picture is provided to the pilot. This is mainly relevant in areas where there is not Secondary Surveillance coverage and/or no surveillance coverage at all.

However Flight Following does require being able to be identified for continual coverage. Some ANSPs also provide additional reporting services with those receiving flight following like SAR services and Hazard Alerting services.

Some ANSPs only provide these services at the discretion of the controller based on their own perceived workload.

Check the local regulations for the ANSP your flying in to get exactly what you will be provided


Why isn't runway 4L/22R at KMDW available as an emergency runway?

Prologue: the quote in the question is from Wikipedia, and the parts there that mention the designation to commercial aircraft emergencies have later been marked as "citation needed". Therefore, for as long as an authoritative source can not be verified, it might well be that in reality there is no such designation.

Actually, should the nature of the emergency require, any runway (or even taxiway) on any airport is available for any aircraft if the crew so wishes. Some more or less famous examples of such situations (Air Safety Network):

Air Canada flight 143 (The Gimli glider, fuel starvation)

United Airlines flight 232 (Sioux City, total loss of hydraulics)

Air Astana flight 1388 (Portugal, reversed aileron cables)

If you are out of fuel or experiencing severe control issues or something of such magnitude, regardless of what you are flying there is no way ATC is going to tell you "sorry you can't land on the 4L, turn to heading..."

This might seem like splitting hairs, but that's how it is. To state that some runway is (or is not) available for emergencies of a certain aircraft type, is somewhat of a moot point.

After you've spoken the three magic words, the ATC has to, and more importantly, they want to do everything they possibly can and more to help you out. You are finally free as a bird, if only you did't have an emergency to deal with...

Speaking of splitting hairs, Gimli glider did not land in an airport at all, but it's the most famous case of the sort...


How can I tune a frequency like 121.62 on a comm radio?

As a complete guess, you're trying to tune 121.620, but you should just be tuning 121.625. From AOPA (emphasis mine):

  All aviation communication, VOR, and ILS frequencies are in the 100
  MHz band, so the first number is always "1." The hundredths digit can
  be only 0, 2, 5, or 7; 1xx.x2 implies 1xx.x25; and 1xx.x7 implies
  1xx.x75--when a frequency is assigned, the ending "5" is often
  omitted. Trailing zeros in the hundreds and thousandths positions are
  always omitted in voice transmissions.

The standard frequency spacing in the US is 25kHz.

Omitting the last digit is also described in the FAA's ATC instructions:

  The separate digits of the frequency, inserting the word “point” where the decimal point occurs.

  (a) Omit digits after the second digit to the right of the decimal
  point.

They include this example:

  135.275 MHz “One three five point two seven.”

And although this probably isn't your issue, it's worth noting that some radios tune in 50kHz increments by default, unless you pull out (usually) the tuning knob to enable 25kHz tuning. I've been momentarily confused by that several times in unfamiliar aircraft. I assume this isn't the issue you have, though, since the manual for the A210 says it uses 25kHz spacing.


Is altitude and heading your discretion when you are cleared visual approach?

Visual approach procedures are discussed in AIM 5-4-23. A visual approach is an IFR procedure and you must be on and stay on an IFR flight plan. It authorizes you to proceed visually clear of clouds to the airport. You may make whatever normal maneuvers necessary to safely conduct the approach and landing including descents and turns. Under most conditions, you are responsible for your own terrain clearance and separation. The exception is if you have the airport in sight but not the aircraft you're following. ATC can still clear you for the visual but will retain radar separation responsibility.

Note that a visual approach is different from a "Charted Visual Approach Procedure," which KSAN happens to have for Runway 27. If cleared for the charted visual, then you must fly it as depicted.


What is the difference between active and passive sidestick?

For references, I've used United States Patent Application 20080156939; BAE Systems Develops Civil Aircraft Active Control Stick; Active and passive side stick controllers in manual aircraft control; & the Side-stick wiki entry. The wiki is a general side-stick discussion listing (some) aircraft that have side-stick fly-by-wire (FBW) technology, but does not go into active vs. passive.

Generally speaking, if you have used a joystick on your PC to fly Microsoft's Flight Simulator, such as Microsoft's Force-Feedback Sidewinder Pro, you've used an active side-stick.

According to the Patent Application cited above, the patent is for an Active Side-Stick technology described as "pilot flight control stick haptic feedback mechanism provides variable force feedback to the pilot flight control stick." One of the 'issues' with the current passive side-stick technology (approved for use) used on aircraft such as Airbus' A380 is that there is no tactile feedback when using the side-sticks, such as a pilot would feel using an old-style column or yoke. In a Cessna 172, for instance, when you pull/push/turn the yoke, there is actual tactile feel, if you pull back strongly in-flight, you'll 'feel' the forces exerted against the airflow. Passive side-sticks have none of this 'feel'.

Active SS technology attempts to replicate the forces on the joystick.

Active SS technology is currently used on most miltary aircraft using side-sticks, but does not appear to have yet made its way into civilian airliners.

(If I've gotten stuff wrong, I'll remove/fix this answer, as I am not an airline pilot and have never had the opportunity to fly military hardware.)


Why are AMRAAMs often mounted on the F-16's wingtip hardpoints?

The AIM-120 weighs in at about 335lb (152kg), and the AIM-9 at about 190lb (85kg). While heavier, the Stores Management System (SMS) and the Fire Control Computer (FCC) know what is installed where, and compensate/adjust flight characteristics as needed.
You put the most capable missile, the AIM-120, out the outboard stations. You'd use that first. Only later might you want to use the shorter range AIM-9.
So, if you were to shoot the AIM-120 from Sta 2 (left inboard), you'd still have the AIM-9 out on the wingtip.
Do it the other way around.
Also, the AIM-9 since the AIM-9G can slave the missile seeker head to the aircraft radar. Target acquisition is not solely dependent on the IR in the missile and line of sight.

The AIM-9G was the first version to include SEAM (Sidewinder Expanded Acquisition Mode), basically an improved AIM-9D seeker head, but was quickly made obsolete by the AIM-9H. The latter was the first model to offer limited all-weather capability, as well as solid-state electronics and double-delta control surfaces resulting in a superior maneuverability compared to older models. SEAM slaves the seeker head of the missile to the radar when in "dogfight" mode, which enables the seeker head to be uncaged, slewed toward a specific target by the aircraft radar, and made to track that particular target before being launched.

(from F-16.net - http://www.f-16.net/f-16_armament_article1.html)


How to achieve shorter taxiing time by elongating the airfield

The cost is that it would required a runway twice as long.

Airports already take up enormous amounts of land. Designers try to build airports near major centers, so taking up twice as much valuable land for longer runways near a major population center is a huge cost.

The longer runways also need to be cleaned, maintained, and snow-plowed.

That is a lot of cost and difficulty just to reduce taxi-time by a couple minutes.   After one has taken a 2 hour cross-country flight, 5 minutes of taxi-time is not a point of concern.


What exactly is the meaning of "detent" in aviation?

A detent is usually a discontinuity in force at a certain position: the control likes to move into that position, and moving it away takes more than average force.

Image source

In the image above, the flap detents are clearly identifiable as the notches in the guide rail: in order to move the lever away from a notch, it needs to be lifted first and can only then be positioned in a different detent.

The flight control sticks often have a detent that indicates force trim position: on either side of stick travel is a preloaded spring, and the stick can only be moved once the breakout force is exceeded. The rest of the stick travel will then simply increase force proportional with the spring gradient - if released to neutral, the force will gradually decrease until the stick falls into the breakout position.