Why do airports have to close in bad weather? Shouldn't aircraft be able to withstand winds of up to 100 mph? When flying the wind is at a much higher speed than that.
Shouldn't they be able to take-off through fog using instruments alone?
Shouldn't they be able to take-off on a slippery runway, since the wheels are not powered.

Wind

The problem with wind is that it can be from any direction, not necessarily the direction of the runway. When the wind is coming from the side instead of straight ahead, it is called a crosswind. This means that landing aircraft have to point into the wind to remain lined up with the runway. The slower they are flying, the further to the side they must point the nose. Airliners are designed to land in these conditions, but it requires more skill to do it well. The control inputs required to compensate for a crosswind affect aircraft on takeoff as well, as then must work harder to stay lined up with the runway and stay level through lifting off. High winds tend to come along with gusts, which makes it even harder to control an aircraft. Aircraft during flight are flying faster, so changes in wind are less problematic. Once they are flying slower, the wind is much larger compared to the aircraft's speed, and control is much more critical during landing. Aircraft have crosswind limits, and even below those limits, aircraft may need to go around from a landing attempt, which introduces delays.

Another issue is wind shear, which is when the direction and/or speed of the wind quickly changes. A change of 40 knots at higher speeds is turbulence. During landing or takeoff, it can cause the aircraft to stall and crash.

Visibility

Aircraft can certainly use systems like ILS that allow them to take off or land in low visibility. However, there are many limitations with these systems. The crew must be trained to use them, the aircraft must be equipped to use them, and the airport must be equipped with them. However, when the pilots are relying on instruments, they no longer are able to see hazards like usual. Because of this, separation requirements are inreased in these conditions, which means an airport can't handle as much traffic.

Water

It's true that aircraft wheels are not directly powered. However, traction is still very important during braking, since aircraft can hydroplane just like a car can. This means aircraft need more distance to stop, and can slide off the runway if they lose traction. Frozen water in the form of ice or snow makes a plane even more difficult to steer or stop.

Combine all of the above (a typical storm that would cause delays at an airport), and you can see why airports delay flights or close when conditions get worse.


Is it possible to power an ultralight airplane with a single-cylinder weed-whacker engine? Plane:
Weighs 200 pounds.
16 FT wingspan,
36in. by 5 in. airfoil

Engine: 3,000 RPM, 2 HP

Propeller: 4ft with 4 blades and weighs 4 lbs.

Is there perhaps an equation that could determine this?

There are methods of calculating the power required to fly a particular plane.  In your case, assuming that you'll also need to carry ~18 kg of fuel and a pilot (roundly 75 kg), the answer is NO.  A 2 hp (1.5 kw) power plant will be insufficient to give safe takeoff and climb performance -- with the possible exception of a high performance sailplane airframe (some self-launching sailplanes use ridiculously small engines).


What are the guidelines and regulations for building a helipad for multiple aircraft? Are there any guidelines and regulations governing the ownership and construction of a multiple aircraft type helipad in

a) the USA
b) Europe?

The FAA publishes an Advisory Circular on heliport design.  It applies to heliports serving helicopters with a single rotor.  I don't believe that there are any regulations regarding "ownership".  They just have to be operated in compliance with appropriate FAA, state and local regulations (but these can get complicated)


How does a fuel tank fire self-extinguish in an A380? On Qantas Flight 32 there was...

  ...an undetected fire in the left inner wing fuel tank that eventually
  self-extinguished

How does a fire in a nearly full fuel tank self-extinguish?

The Australian Transportation Safety Board's Final Report gives a couple of possible reasons that the reaction was not sustained in Appendix D on page 257:

  The flash fire initially consumed the oxygen inside the tank; reducing the oxygen concentration level to below the threshold required for sustained combustion of Jet A-1.
  The general temperature rise associated with the initial combustion was low and insufficient to increase the temperature of the fuel inside the tank to at least the lower flammability limit of Jet A-1. Quenching of the flame by the cool fuel tank walls (evident from the sooting) and the entry of cooling air through the tank perforations may have promoted this.

Note that Jet-A requires quite a bit of activation energy to vaporize and burn. If the burning of what fuel did burn didn't produce enough energy to provide activation energy for the surrounding fuel, the fire would not be sustained. The fire was likely very brief as the turbine disc fragment passed through the tank.

From what I've heard (I haven't tried this myself,) you can drop a lit match in a bucket of Jet-A and it won't ignite. Using fuel that doesn't easily burst into flames in a vehicle designed to carry tens of thousands of gallons of fuel at several hundred miles per hour is desirable and intentional for obvious reasons.

To illustrate just how hard it is to burn Jet-A, the fuel tanks in Asiana 214 never ignited. The entire fuselage was burned out, but the fuel tanks never burned.

Remnants of Asiana 214's hull Source: Wikipedia


NEXRAD—why is it 2D? If you paid attention to NEXRAD training, you know that the colors of pixels show the maximum activity at any altitude in that air column. (It’s a “composite” view.)

NEXRAD itself samples in three dimensions, so that integration into the composite is being done on the ground before being sent back out on SiriusXM or ADS-B.

Given ADS-B’s bandwidth constraints, it makes sense that you only get maximums—it’s the thing that most pilots will care about. The bandwidth constraints are the same reason pixel granularity falls off with distance—the stations can’t send nationwide data in the bandwidth allotted.

But could SiriusXM give you the raw 3D data in addition to the composite view? They have the bandwidth where you could dial in a given altitude and get a 2D slice rather than just maximums. And you can get other data like wind on an altitude basis, so the capability seems to be there.

I don’t know if it’s a case of cost (considering how SiriusXM charges for subscriptions, I imagine they’d be happy to offer this to pilots as an additional tier), a worry that some pilots could take on even more risk around storms by trying to do 3D rather than just 2D daisy-clipping, or something else (like a technical issue with NEXRAD—as far as I can tell, none of the weather sites offering NEXRAD give the ability to dial in altitudes).

Given how many accident studies (even into incidents where the PIC’s were instrument-rated private pilots) have shown that pilots who flew into unexpected IMC or icing could have survived had they made a different decision about what altitude to seek for safety, it feels like it could be an improvement in situational awareness and safety, and usually we seem to accept those technologies in aviation, even if they may also present greater risk of recklessness.

There is not much gained by the third dimension for your use case. In GA you generally want to avoid any active weather. Why make it more complicated?

can't go over it (performance limited)
can't go under it (microbursts can kill you)

=> only way is to go around it and therefore no need for that 3D information.


How big was the F-14 fleet compared to other US carrier-based aircraft in 1981? Back in the 80's I was away jesting about the F-14 are here to protect the carriers and the carriers to deploy F-14.

I know there are a number of other aircraft here for other purposes but I really don't know the numbers.

So for 1981 what's the proportion of F-14 to other aircrafts and also de percentuals in roles (defence of the fleet, attack, surveillance, etc).

In other words: for US aircraft carriers of that period, what was the aircraft fleet composition?

During the plane’s heyday, the US Navy maintained 26 active duty F-14 squadrons for the 12 carriers certified for F-14 operations, 4 Test and Evaluation squadrons, 2 Fleet Replacement squadrons and 4 Naval Reserve squadrons.  632 F-14s were delivered to the US Navy between 1973 and 1994.  Each Forrestal-, Kitty Hawk-, Enterprise-, Kennedy-, and Nimitz-Class carrier had two squadrons of F-14s aboard, with 12 aircraft per squadron.  Depending on the cruise air wings aboard, there were approx 85 aircraft aboard ship.  This sets the F-14s comprising about 28% of the air wing’s airframes.

The F-14 was used to provide air superiority in the airspace around the battlegroup as well as escorting strike packages and providing a first line of defense against long range enemy interceptors and cruise missiles.  Later upgrades as well as the F-14D variant allow for precision strike capability against surface targets as well.  The genesis of the AWG-9/AIM-54 weapons system was as a defense against TU-22s carrying Kitchen cruise missiles which had a very real chance of sinking a carrier if the missile found its mark.  A secondary role was given to the F-14 in the early 80s as the primary tactical reconnaissance aircraft for the fleet, replacing the aging RA-5C Vigilante and RF-8 Crusader aircraft by means of a removable Tactical Aerial Reconnisance Pod System (TARPS) which mounted on the center body pylons for the AIM-54 missile.  Later systems included ROVER pods for precision close air support.


Is Ducted fan or Propeller better to maximize forward speed of RC aircraft with a given power? I'm designing an RC aircraft of which the final goal is a crazy top speed. I'll be 3D printing and sanding / finishing the air frame surfaces to reduce drag. In order to achieve maximum top speed, should I use open 5 inch diameter 3 blade props (the ones used in racing drones) with a large pitch and beefy motor, or two (60-80mm) ducted fan (EDF) units? Power draw is not a limiting factor here. Also, should I go for a larger EDF than 80mm? (wingspan is about 70 - 80 cm, total mass of about 700-1000g) . I'm aware that EDFs induce a greater delta V on the air they move, but does this actually mean I can expect a larger top speed?
[edit:] I could also go for a single 100mm unit.

A propeller is better. Just look at any pylon race model to see what they use.
DKNguyen put it very nicely:

A duct doesn't beat a larger prop, it only helps make up for a smaller one.

You're right that "EDFs induce a greater delta V on the air they move" but EDF models generally use twice as much power as a similar aircraft with a prop. Moving half as much air twice as fast generates the same thrust but requires twice as much power. This is because momentum is mass x speed, but energy is mass x speed squared.
Ducts (and multi-blade propellers) are used when you don't have space for the right sized prop for the engine power.


What are the most maintenance-intensive parts of a helicopter? Which components of a helicopter are the "driving" ones that require most regular attention and down-time, and how often do they last between inspection or overhaul? I don't have a specific model in mind, but something along the lines of a 4-passenger light transport heli

Along with this, are there developments that might increase these intervals, and how much is defined by the manufacturer vs regulatory bodies (FAA/CAA/EASA etc.)?

The question is a bit broad but in general but I will do my best.

First we must look at how maintenance intervals are determined, normally during the initial certification the manufacture testes there aircraft and determines its limitations both in flight, and for maintenance. the regulator generally looks over testing, and documentation and decide if they will approve the 3 parts: the Aircraft, the Flight Manual, and the Maintenance manual. generally the regulator will not do there own tests, they just decide if the testing carried out is sufficient. (this is my best understanding of this, its complicated and a little different depending where/when the aircraft was developed)

Operators who have larger fleets of 1 type of aircraft, or large maintenance/overhaul facility's  will sometimes develop there own maintenance manuals, during these processes they will sometimes demonstrate to the regulator that with newer testing methods etc. that certain components are actually lasting longer than originally proven. Upon approval of there regulator these new documents become law. Occasionally these changes are driven by the manufacture, often when competing for larger contracts ie. Military that wants different maintenance.

As far as "driving" components most people would think the large items requiring very long overhauls, Ie. rotor blades, transmissions and engines.

To answer your questions on shortest maintenance intervals, older helicopters often have small field serviced items such as vibration damping oil struts, or unsealed bering's that may need to be serviced every day or more. Astars air filters need to be cleaned and oiled something like every 15 hours, and piston engines often need oil filters every 25 hours or less. most of these jobs only take an hour or two.

As far as inspections, all helicopters have a daily inspection that is carried out every day checking for issues.


Are thrust levers synchronized by default when pushed/pulled? When I watched this video about the last flight of Juergen "J.R." Raps from SFO to FRA in an A380 (before his retirement) I noticed he lines up or synchronizes the four thrust levers as shown between 08:05 and 08:20 (while taxiing, if that matters).

I used to think the levers are synchronized by default (same precentage of thrust on each engine) and it isn't crucial to have the levers in a straight line as long as the difference between their positions is below a reasonable amount. I further thought that in case the thrust needs to be distributed asymmetrically for whatever reason (say 70% board and 60% starboard), one would need to press some button on the levers to release some sort of lock and move them separately instead of simultaneously.

I personally would find it hard to move four levers simultaneously at the same angle, let alone people with small hands who may only grab three of them at once.

So how does it work? Or is the pilot's behaviour just a personal habit?

On a non-FADEC engine (older airplanes - not this one) where the thrust levers are connected to the engine fuel control units with a cable circuit or a teleflex cable, you have to manually adjust each lever to wherever it has to go to achieve a given N1 (fan speed), and this can result in small variations in position of each lever when all engines are at the same power setting.  On takeoff on a non-FADEC, you move the thrust levers until power is reasonably close to take off thrust, call "set thrust", and the non-flying pilot tweaks each lever to synchronize all 2 or 4 N1 values to the takeoff bug setting on the N1 indicators.  With mechanical controls, the thrust levers may or may not be perfectly aligned when the engines themselves are in synch (there are limits to the misalignment allowed).

On a FADEC aircraft like the 380 in the video, the engines are managed by computers, and the thrust levers are just electrical input devices.  At the bottom of each lever there are Rotary Variable Displacement Transducers (RVDTs), that tell each engine's FADEC computer where the thrust lever is.  The FADEC will manage the N1 and if all 4 levers are at the same position, each FADEC will achieve the same N1 (within the tolerance of the RVDT's signal).

For takeoff, to make it easy, there is a detent for each lever at the Takeoff Go-Around setting (TOGA) that you can feel as you move them up (a little roller drops into a depression on a cam profile on the lever's arc of rotation).  There is another detent for climb power as well (CL) to avoid having to fuss with lever settings during the departure. When in the TOGA or CLIMB detent, the FADEC computer takes care of setting its engine's computed takeoff or climb power automatically.  So on a FADEC engine, when you take off, you just push the levers until you feel each one click into its TOGA detent, call "set thrust", and the non flying pilot just looks at the N1 indications to confirm they are all at TOGA thrust, without having to tweak the thrust levers (on the RJ I used to touch the levers below the handles as the PF was pushing them up with my finger and thumb to feel for myself that the levers clicked into the detents, although it wasn't really necessary).

At settings other than TOGA or CLIMB thrust however, they tend to work like mechanical thrust levers, where if one lever is at a different position it will have a different N1 value, so at intermediate power settings or on approach you have to individually align the levers, so you end up moving them as together as best you can and fine tuning as required.

What the pilot in the video is doing is synching the levers for taxi because when he pushed the levers up he didn't push them evenly and it looks like the outer ones were a little farther ahead than the inner ones.  Not that big a deal for taxi; he's just being a perfectionist.


Which portion of combustion energy is used to spin the compressor of a pure jet engine? In level flight at constant speed, it is correct to assume that the quantity of energy created by fuel combustion (FE) is exactly extracted by the turbine section (ME) and is used solely to spin the compressor section?

In other words, the propulsive energy (E4) is equal to energy in air the aircraft encounters (E1).

If this assumption is incorrect, what is the correct relationship between energy quantities E1 to E4? Maybe two extremes could be used for illustration: No thrust (idle) and full thrust.

The accelerated air coming out has more energy than the air ahead of the engine, even at idle-power.

Force and mass flow rate:
In constant speed level flight, the forward thrust acting on the jet engine(s) equals all the drag forces acting rearward on the airplane.
The thrust acting forward equals the force the mass flow rate exerts rearward. Neither is the cause (action) nor the effect (reaction), since it's a two-body system (engine and air).

The forces are perfectly simultaneous, and are there for the same reason.

The energy bit:
Energy (work) equals force times displacement.
A non-accelerating plane in mid-air, or a jet engine running on a fixed test stand, still has moving parts and a moving [steady] exhaust: displacement is happening.
Since we can't create energy and it has to be conserved:
Let's say the total energy leaving the combustor (heated accelerated dense air) is 10 pirate-ninjas, then say 5 of which drive the turbine and all what's connected to it (including the air at the compressor). The other 5 leave the engine as an accelerated jet of air.
Say the compressor transfers 3 to the air, and all parts use 2 to rotate. The air comes with its 1 pirate-ninja of stored energy. The 3 gained by the air, now 4, meet the fuel in the combustor and release 10 (perfect lossless combustion, sorry). So, the energy stored in the fuel before combustion is 6.

(Own work)

The turbine-shaft-compressor is one body, the turbine absorbs 5, and transfers 3 of those to the air via the compressor, i.e., the engine parts absorb 2 to rotate, this is what you referred to as mechanical energy.

In other words—
The engine added 4 pirate-ninjas to the air from start to finish, giving the air added kinetic energy (mass flow rate), which translates to forward force as explained early on. In doing so, the engine spent 6 fuel, 2 of which to purely rotate the engine shaft, the other 4 went to the Δ mass flow rate.

The ratios above are not real, only illustrative. If you add more fuel, more energy will be released (excess oxygen is still available, that's how afterburners work), this energy will spin the engine faster, bringing in more air for a better efficient cool combustion.
The more efficiently the fuel energy is extracted, the more thrust we get. The properties of the air will have an impact; how dense is it, is the engine running on the ground, or is the plane transferring some of its kinetic energy into steady air resulting in ram-air energy, and so on.
So the ratios/percentages are not fixed, they depend on the operating conditions as well as the engine design (e.g., bypass ratio, compression ratio, etc.); even for the same type, different variants have different number of stages.


What defines a cycle on a jet engine? Is there a legal definition of a "cycle" on a jet engine?

We must log the cycles, and some maintenance is determined by cycles.  From my understanding, this is partially because of the thermal dynamics of an engine cooling and then reheating, and partially because full takeoff power is used.

The "usual" time that you log a cycle is when an engine is started and the aircraft then takes off (using full rated takeoff power), but what about unusual situations like:

Engine shutdown and restarted in flight
Engine started, aircraft takes off, and then returns for a low pass or a touch and go:  Would this be two cycles (does it depend on the amount of power used during the touch and go?)?
Engine started and then shut down without a flight

A cycle is a start to a shutdown.  Lets say there is a flight that is loaded with pax, bags, and fuel.  They push back and start both engines since the weather is good and their at an outstation.  As they taxi to the departure runway, BAM, ground calls up saying there is a groundstop for the hub and its going to be about 30 minutes.  The flight pulls into some empty ramps space, and shuts down both engines.  Groundstop lifts, both engines started again, and the flight departs.  After landing, pulling into the gate, and shutting down the engines, we can say that for this flight, each engine went through two cycles.  ALL of this info is logged and maintenance can access it.  With some of the newer engines and higher service packages, OEM


How much aerodynamic heating do jetliners endure? At cruise altitude (~ 33,000 ft) and cruise airspeed (~ 500 mph) how much do present-day airliners heat up due to air friction during their journey? Probably not much because there's still ice on the window outside when you're at cruise altitude, but by how many degrees is the plane's hull warmer than in case the plane stood still at that altitude (therefore, compared to the minus 56°C at the tropopause)?
I'm also curious about the Concorde which flew up to 60,000 ft high and at more than 1300 mph. To the air friction there also comes the heating due to supersonic flight, so all in all how much warmer did the Concorde get during its supersonic cruise?

Based on the formula already shown in this answer, we can calculate the TAT (true air temperature), which is the temperature reached at the stagnation point1, from the SAT (static air temperature) and Mach number:
$$ \frac{\text{TAT}}{\text{SAT}} = 1 + \frac{\gamma - 1}{2} M^2 = 1 + \frac{1}{5} M^2 $$
The resulting plot of TAT vs. Mach number at the SAT of -56.5°C (ISA tropopause) is shown below:

As you can see, a subsonic airliner (I assumed Mach 0.85) will still experience temperatures below freezing. Concorde however was reaching temperatures of around 120°C at cruise speed of Mach 2.02. This was already close to the limit:

Maximum Total Temperature (TMO):  127 Degrees Celsius (on nose)

(Concorde Performance)

As requested in the comments, here is a larger speed range including the SR-71:

The temperature could reach almost 400°C at Mach 3.2 (What is the true top speed of the SR-71?), but note that the SR-71 used fuel to cool the skin (the windscreen was the hottest part at 316°C according to Wikipedia.

1The TAT is measured by the aircraft with a probe that brings the air to rest w.r.t. to the aircraft (stagnation). The kinetic energy of the air is therefore converted into thermal energy, raising the temperature. The surface temperature of the aircraft at points where no stagnation occurs will be at a lower temperature. Thanks to Peter Kämpf for pointing this out.


Are the total hours of an aircraft based on flight hours or operational hours? Are the Total Hours and Total Cycles of an aircraft based on the Flight hours or Operational hours of an aircraft?

Cycle
One takeoff and one landing makes up one cycle. Counting cycles is important to keep the number of times the cabin was pressurized (with the assumption that the airplane flies at high altitude). It is also significant for engine maintenance. A cycle and flight/operation time are not related.

Hours
This is the time when an airplane is in operation (more on this below).

Flight Time
Generally speaking, it is the time when an airplane is flying. It is the duration from when landing gears leave the ground to when they touch the ground again. Pilots are not paid by this. In my opinion, it is mostly used by flight trackers to inform people if an airplane has landed or not.

Operation Time
For GA airplanes, when the airplanes is started, Hobbs meter starts and it stops when the engine is turned off. Most commonly, this is how rental GA airplanes' rent is calculated.

For commercial airplanes, pilots pay clock starts when parking brake is released and ends when the parking brake is set.

Hence, total hours is more closely related to operation time.

If you are talking about total time and total cycles in reference of retiring an airplane, that is a different discussion. Each part of an airplane has a certain life. Though most of the time it can be predicted, but sometimes a certain component fails earlier than the expected life and therefore needs to be replaced. Airplane manufactures do specify a design life limit, but that is normally changed because of regular maintenance.


What is the record length of time for single-occupant flight? What is the longest flight time for a single pilot alone in an aircraft?

What is the longest flight time for a single pilot alone in an aircraft?

13 days if a balloon counts as an aircraft.

Balloon

Steve Fossett set a record in 2002

  In 2002, he became the first person to fly around the world alone, nonstop in any kind of aircraft. He launched the 10-story high balloon Spirit of Freedom from Northam, Western Australia on June 19, 2002 and returned to Australia on July 3, 2002, subsequently landing in Queensland. Duration and distance of this solo balloon flight was 13 days, 8 hours, 33 minutes (14 days 19 hours 50 minutes to landing), 20,626.48 statute miles (33,195.10 km).

Other types of aircraft

The following information was volunteered in comments by Scary Spice and Peter Kämpf.

Glider

Charles Atger, stayed aloft for 56.25 hours, solo.

Powered airplane

Charles Lindbergh was all by himself for 33.5 hours.

Spacecraft

Ron Evans, Apollo 17 Command Module Pilot, was alone for 79 hours, 49 minutes.


How come certain airports can have unique rotating beacon colors? The Hershey Medical Center Heliport has a white-red-green beacon as opposed to a normal heliport white-yellow-green beacon.
How is this allowed?

The lighting for private heliports is not regulated by the FAA, but by the individual states. The FAA has an Advisory Circular laying out guidelines for heliports, but it is only a recommendation.

  The  Federal  Aviation  Administration  (FAA)  recommends
  the  specifications
  contained in this AC for all applica
  tions involving development of this natu
  re.  In general, use of this AC
  is not mandatory.

  From FAA AC 150/5345-12F: Specification for Airport and Heliport Beacons

It is only regulatory when the heliport is built using federal funds. In the AC they recommend the white/green/yellow pattern.

Only a couple of states have adopted the FAA guidelines as regulatory.

The state of Pennsylvania incorporates many of the FAA Advisory Circulars in their state law. For example the ground markings and the lighting for the perimeter of the landing and takeoff area for the heliport are required to adhere to the appropriate FAA AC's. But in regards to the beacon it simply states:

  A rotating beacon is recommended to be installed for night operations at public heliports.

  Pa Code § 471, Appendix A, Criteria I, i)

It does not even have that recommendation listed for private heliports.

Although it is not in the FAA Advisory Circular some places list the beacon color code for hospital heliports as white/green/red. I can't find anything authoritative on this but examples are at an aviation wiki, on Quora and on airliners.net.

This company that sells heliport beacons indicates that their beacon is "Available in Hospital Heliport version (not FAA certifiable)." It doesn't indicate, but this is likely a white/green/red version. And since it doesn't adhere to the Advisory Circular it isn't FAA certifiable.


How do airliners with engines mounted on places other than wings suppress wing flutter? Assuming airliners typically have high aspect ratio flexible wings, how are wing flutter suppressed when engines are not available on forward-reaching pylons as weights?

Since flutter is a natural-frequency harmonics phenomenon, it's a matter of "tuning" the wing box structure with the required stiffness and damping to move its natural frequency range outside the range experienced with its C of G and torsional center offset and uncompensated for with engines on pylons.

It's a bit like with flight controls.  With manual ailerons, the aileron/wing system is flexible you could say, and needs mass balancing.  Like wing mounted engines.

With hydraulic controls, the connection between the aileron and wing is rigid outside of movement induced by the hydraulic actuator.  No mass balance required.  Like a wing box with no engines that has to be inherently stiffer than otherwise.

It's one reason wing mounted engines are more common than tail mounted.  Lets you make the wing box structure a little lighter.


Do I need AFSP TSA approval once I get my PPL? I recently got my PPL and wondering if I still require to renew my AFSP TSA approval each year/
I looked into AFSP FAQs but its unclear if I require it again. Any help is appreciated.
Thanks

Merely to exercise the privileges of your PPL, no. Even to take additional training with a CFI for proficiency or endorsements such as complex/tailwheel, no.
To train for an additional rating (e.g. Instrument or Multi-Engine) or certificate (e.g. Airline Transport Pilot, but not Commercial Pilot), yes.


How do wide-bodied commercial aircraft achieve pressure equivalent to 6000 feet altitude? I read an LA Times article which states the following.

To reduce the stress on the traditional metal frame, airlines now pressurize the cabin to be closer to the pressure outside. When a plane is cruising at 36,000 feet above sea level, the atmosphere inside the cabin feels like its 8,000 feet above sea level. For passengers, that can cause shortness of breath and fatigue.
But with new fuselages made of stronger, more flexible carbon-reinforced plastic composites, the plane can withstand more stress, allowing airlines to increase the inside pressure to a more comfortable atmosphere that feels like 6,000 feet above sea level.

Now I'm assuming that these are the twin-aisle wide bodied aircraft we see from Airbus and Boeing. The article mentions something about fuselage but doesn't get into the details of it. Can somebody elaborate?

The killer in fuselage pressurisation is the cycling of the structural loads. Aluminium is very unforgiving of repeated load changes: While steel has a load limit which can be applied infinite times, no such limit exists for aluminium. This means an aluminium aircraft will eventually fail if it flies enough cycles. It also means the plane can be built lighter or operated for more cycles if the pressurisation loads are lower.

Fatigue curves of steel and aluminium (By Andrew Dressel at English Wikipedia, CC BY-SA 3.0, source)

The consequences of this nasty characteristic were illustrated in Aloha Airlines Flight 243 in 1988, when the upper part of the forward fuselage failed at the suction peak aft of the cockpit and more than 5 meters of fuselage skin were ripped away.

Aloha Airlines Flight 243 after landing (picture source)

A fuselage made from carbon fiber reinforced epoxy shows very little fatigue and is much more tolerant of repeated loading changes. Here, thermal and impact loads are the most critical issues. However, the bad historic experience with aluminium structures means that not only the engineers, but even more the certification authorities are very careful to clear any new material for high, repeated loads. As a consequence, the graphite fuselage structure of the Boeing 787 is much stronger than a regular fuselage made from aluminium and can be loaded to a higher pressure without much added risk.

Whether this means less headaches and constrictions for you is less clear. The added pressure does feel better, but the major improvement in creature comforts in the cabin of the most modern airliners results from  higher humidity in the cabin air.

Most single-engined aircraft have no pressurisation; only the high end types like the Piper Malibu or the TBM 700 do. On the other hand, some business jets can keep the cabin at sea level pressure up to 12000 m altitude. In airliners, however, holding the cabin pressure at or above the equivalent pressure at 8000 ft of altitude is mandatory. Citing Wikipedia:

  Keeping the cabin altitude below 8,000 ft (2,400 m) generally prevents
  significant hypoxia, altitude sickness, decompression sickness, and
  barotrauma. Federal Aviation Administration (FAA)
  regulations in the U.S. mandate that under normal operating
  conditions, the cabin altitude may not exceed this limit at the
  maximum operating altitude of the aircraft.


Was there a historical requirement to announce altitude, temperature, etc? It is a common experience of flying on commercial flights that pilots announce certain flying conditions, including altitude and speed.

It has been previously asked on Aviation SE why pilots announce the cruising altitude of flights.  The answer there suggested there was "no real reason".

On Quora, it was asked similarly why pilots frequently announce altitude, outside temperature, and speed.  The first answer there suggested it was previously a historical requirement; however, the answer does not provide a reference to these requirements.

Has there been historically, or is there now, a requirement in any major jurisdiction (FAA, EASA, etc.) for the pilot (or flight crew) of a commercial flight to announce altitude, outside temperature, speed, wind, or weather conditions?  If so, what was/is the specific text of the requirement?

As this may be most common among airlines, this is not a requirement whatsoever administered by the FAA or any other aviation governing body. This is more so considered a tradition usually when the plane reaches cruise or is about to land. No such modern airline or any airline in the past has required this to be announced to its passengers.


What is the En-Route Information Display system (ERIDS) used for? ERIDS is an information display system used at Air Route Traffic Control Centers. It provides electronic access to things like NOTAMs and static documents that previously were only available in paper. It was Implemented around 2006.

I get that it provides a bunch of general information and NOTAMs and PIREPs and such, but who uses ERIDS to access that? I know controllers have their own display, and I was under the impression that NOTAMs and such could be accessed there. I would assume other personnel also have their own displays. Is ERIDS just like a back-up source of information?

Just visited a facility and learned what this is.

ERIDS provides digital access to static documents like standard procedures and things of that nature. ERIDS provides easier access to these documents than would otherwise be possible. ERIDS also provides a way (not the only way) to access NOTAMs or PIREPS or send PIREPS. I know controllers have other ways to access this information; I am not sure about other personnel. Having multiple ways to access or send this information is helpful to controllers as there may be multiple controllers in a sector and they may need to both access these services.

Essentially, ERIDS is just an informational system that is easy to access in an air route traffic control facility.


How can an airline flight crew handle an in-flight oxygen system fire? The first step in the "Smoke, Fire, or Fumes" checklist for any pressurized aircraft is for the crew to put on their oxygen masks and set them to EMERGENCY, so that the crew can breathe, and thus function well enough to execute the rest of the checklist.

However, it's possible on at least some aircraft for a fire to develop that intimately involves the flight crew supplemental oxygen system, as the hull loss of SU-GBP aka EgyptAir flight 667 at its gate in Cairo Int'l demonstrated dramatically.  Fortunately for the EgyptAir crew, their experience happened with the aircraft squarely on terra firma, allowing a swift evacuation with only a few serious injuries.  However, if a similar event happened while cruising over the ocean at 35,000', what could the flight crew do to avoid being incapacitated, considering that such a fire would render at least part of the crew oxygen system inoperable?

Opening the flight deck door may be sufficient in some minor cases at the expense of letting smoke and CO2 invading the cabin volume.

In serious cases: Protective breathing equipment is available in the aircraft:

Smoke hood demonstration video:

Portable oxygen cylinders and masks are also available, e.g. for A320 family:

(source)

The presence of this equipment is regulated, e.g. in US by 14 CFR 25.1439:

  at least one portable protective breathing equipment shall be located at or near the flight deck for use by a flight crewmember.

  In addition, portable
  protective breathing equipment must be installed for the use
  of appropriate crewmembers for fighting fires in compartments
  accessible in flight other than the flight deck. This includes
  isolated compartments and upper and lower lobe galleys, in which
  crewmember occupancy is permitted during flight. Equipment must be
  installed for the maximum number of crewmembers expected to be in the
  area during any operation.

The oxygen supply if for 15 minutes minimum:

  The equipment must supply protective oxygen of 15 minutes duration per
  crewmember at a pressure altitude of 8,000 feet with a respiratory
  minute volume of 30 liters per minute BTPD.

These systems are already necessary to the cabin crew to fight any fire or help passengers in case of cabin depressurization.

If a safe aircraft state cannot be restored within the 15 minutes, then the fire is already uncontrollable. Over the ocean and too remote from usable airports, the crew would have to resign and ditch the aircraft to evacuate it, a last resort and risky escape action.

In the accident you mention:

The oxygen system involvement/malfunction is suspected but not certain.
Considering the damages to the flight deck and panels (seen below), a problem for pilots would have been to be able to fly the aircraft with missing or failed instruments and controls, in a hot flight deck atmosphere. The passengers and crews seem to owe their lives to the accident occurring on the ground.

(avherald.com)


What equipment is used by Boeing to convert the F-16 into an unmanned aircraft (QF-16)? How exactly does this equipment convert the F-16 into an unmanned aircraft?

Is it possible to use this equipment on any other fighter (like the F/A-18 Hornet for example) in order to convert it into an unmanned aircraft?

THE USAF has had a program for converting manned aircraft into unmanned ones for decades. The aircraft used so far include,

QF- 104 (from F-104 Starfighter)
QF- 102 (from F-102 Delta Dagger)
QF- 100 (from F-100 Super Sabre)
QF- 106 (from F-106 Delta Dart)
QF- 4 (from F-4 Phantom II)

Note that both aircraft are piloted. According to fencecheck.com,

  (QF-4s are)..almost always flown with a pilot aboard, unless a weapons launch will occur. Usually he does not touch the controls but stands ready to take over if ground control is lost or the aircraft departs. The pilots fly the aircraft themselves on chase missions and to maintain proficiency.

The QF-16 replaces the QF-4. The conversion of (retired) F-16 to QF-16 involves the following steps:

Removal of non essential items like the Vulcan cannon and the radar (in previous versions like QF-4, the radar was simply deactivated)
Modification of the FCS (Flight Control System) so that both manned and unmanned flights are possible (previous drones were remotely flown)
Installation of Flight termination system to destroy drone in case of flight path deviation, which results in this:

Source: f-16.net

Installation of onboard telemetry systems to control the aircraft from the ground.
Installation of a scoring system to measure the missile success rate. This is required as most of the missiles are launched with dummy warheads or the flight path is programmed to evade the missiles, so that the costly aircraft could be reused. Only in a few cases are lethal missiles used.
The self protection suite (flares, chaffs etc.) are usually left on the aircraft to provide a realistic engagement scenario.
New paint job :), which looks like this:

Source: www.wired.com

It is possible to convert (any) other aircraft into drones. For fly by wire aircraft like F/A-18, only the software portion will change, but it is a minor thing.


How do Rapid Exit Taxiways improve aircraft movements? I have been reading about Mumbai Airport (CSIA) (IATA: BOM ICAO: VABB). On it they mention:

  The airport has two intersecting runways. Both runways have been
  upgraded to Code F, which means they can accommodate larger aircraft
  like the Airbus A380. Following a presentation in March 2011 by UK’s
  air traffic service provider NATS on how the capacity of the airport
  can be increased, MIAL set a target of 48 aircraft movements an hour
  in an effort to reduce congestion at the airport. Both runways were
  operated simultaneously especially during peak hours to try and attain
  this target.MIAL scrapped simultaneous Cross-runway flight operations
  in mid-2013 after it found that single runway operations were more
  effective for increasing Aircraft movements per hour. Runway 14/32 is
  now used only when the main runway is unavailable due to maintenance
  or other reasons. The construction of new rapid exit taxiways helped
  in increasing flight handling capacity from 32 movements per hour to
  44 in 2012.

Can somebody share what are these rapid exit taxiways and how do they help to increase flight handling capacity ?

I did see the OSM page and was able to get this -

Maybe that could help in explaining what is being told to us. Have given/shared a more detailed diagram that I could find from OSM.

Also it would be nice if a sketch/diagram of how these rapid taxiways are laid on CSIA or failing that a diagram of any airport having similar/more/less number of rapid exit taxiways would be good too in order to understand how they work.

See this related question.

Rapid exit taxiways (or high speed exits) enable aircraft to leave the runway at speeds up to 50 or 60 kts depending on the runway and aircraft type (50 kts even in wet conditions).

They have a long, constant radius rather than a 90 degree turn.

You might find this FAA presentation useful.

Source: airlinepilots.com forum.

The purpose is to enable a landing aircraft to vacate the runway more quickly without having to slow down to "normal" taxi speeds.  A large aircraft like a 777 might need to slow to 10 or 15 knots to take a right angle turn.  This would mean spending longer on the runway slowing down to that speed.

Since the aircraft next on the approach cannot land until the runway is clear, this enables closer spacing of landing aircraft.

Aircraft type, airport restrictions, operator standard procedures and weather can all impact what "high speed" means but it is always faster than the 90 degree turn.


How do rotor tangs lock into wheel keyways? How do the rotor tangs lock into wheel keyways? Are there special keys on the outboard wheel half that allow locking the tangs in place?
Also would be great if anyone could provide me with a image of an aircraft wheel from the inboard side looking outboard.

The tangs just slot into mating recesses in the bore of the main wheel so they can float freely laterally as they are squeezed together while transmitting torque from the wheel to the rotors.  Excuse my crude sketch:

Here's a decent cutaway:


Where is the best place to perform a run-up at a busy airport? If you wait to perform a run-up at the end of a taxiway at a busy airport you will probably not make many friends.  Some airports may have designated run-up areas or have runways designated for general aviation but at those that don't would it be acceptable to do a run-up on the ramp before you taxi?

In my humble opinion it is best to ask the FBO for their practices or do it at the ramp with precautions as not to hurt or disturb anyone or anything.

On the Taxi way you might run into difficulties returning to the ramp in case something does not look or perform right during run-up. When in dout I ask Ground for advice.


Why don't piston engines require as heat resistant materials as jet engines? Piston engines often get away with using aluminium as their heat exposed material, while even the early jets required inconel to operate.
Is that because the combustion takes only, for example, half of the time for two stroke engines hence half the temperature?
Still compression ratio of a typical two stroke is twice higher than early jets, while the melting point of aluminium is more than twice lower so it doesn't add up, as if there was another reason for their higher heat durability

Lubrication.
The low wear of piston engines is due to an oil film between piston rings and liner, so both never get into immediate contact. This perfectly thin oil film left on the liner bore by the oil control ring will flash off if temperatures exceed 180° - 200°C, and the piston rings will scuff. This need for lubrication is the weak link which makes improving heat resistance for piston engine materials redundant.
Lubrication in turn requires sufficient cooling which is possible because combustion in reciprocating engines is a discontinuous process with only the end of one and the beginning of the next stroke producing compression and combustion heat while the others allow to cool down the cylinder head and walls.
Contrast this to jet engines. Continous combustion produces much higher thermal loads so any attempt at sealing the compressor and turbine disks against the outer casing is futile. Only the development of heat-resistant alloys has made this possible: Look at how the improving materials allowed increasing compression ratios. Modern turbofan engines reach compression ratios of up to 50:1 while diesels are stuck at around 20:1 and gasoline engines at around 10:1. Aviation pistons with superchargers raise that to levels similar to modern turbofans: The Wright R-3350 turbo-compound engine supercharger increased pressure by 6.5:1 with the pistons compressing air again by 6.85:1 for a total of 45:1. The highest compression ratios were achieved with super- or turbocharged diesels. The Jumo 205D supercharger achieved a compression ratio of 8.85:1 and the engine another 17:1 for a total of 150:1, but in all cases needing intercoolers to keep air temperature low enough and using waste gates or staged chargers to only reach the top compression ratios close to their critical altitude!
Since decades we can read about "adiabatic engines", piston engines using heat-resistant ceramics and doing away with the whole cooling system. Their implementation has so far not happened because the wear between piston and liner has been unacceptable (among a host of other problems, like manufacturing cost and brittleness).


When extreme yoke movement cuts out stab trim on a 737-NG, does it stay off after yoke returns from limits? I've read that the 737-NG has logic built into the stab trim system that will cause stab trim to cut out if the control column (yoke) is pulled/pushed far/hard enough (it's not clear to me if it's travel distance or force thsf causes the cut out).

My question is, given the control column stab trim cutout mentioned above, does it continue to function after the control column is moved back from its hard stops or force is decreased  below a certain value?

From the Boeing 737 NG FCOM v2 (9.20.8 Flight Controls - System Description):

  Control column actuated stabilizer trim cutout switches stop operation of the main
  electric and autopilot trim when the control column movement opposes trim
  direction. When the STAB TRIM override switch is positioned to OVERRIDE,
  electric trim can be used regardless of control column position.

So any opposite movement of the yoke will stop the stab trim. There is nothing mentioned in the FCOM about staying off, so I would assume stab trim would continue immediately after the yoke is released.


Which maneuvering speeds are included in the TCDS? I've been looking at the data found in various type certificate data sheets and found something that is a bit ambiguous. In reading a TCDS (like this one, for example) in the "airspeed limits" section it lists the maneuvering speed. But they don't make it clear whether they are referencing the design maneuvering speed (Va) or the Maximum operating maneuvering speed (Vo).

Can anyone clarify which one they are referencing?

The speeds that they list in your linked TCDS (along with their corresponding V speeds) are:

Never exceed 171 mph (148 knots) CAS - VNE
Maximum structural cruising 140 mph (121 knots) CAS - VNO
Maneuvering 129 mph (112 knots) CAS - VA
Flaps Extended 115 mph (100 knots) CAS VFE

For a list of these V Speeds along with their definitions, see 14 CFR 1.2


Why did my phone's GPS receiver stop working when the plane was descending to land? Recently, I flew on an Airbus A320. I turned my Lenovo A328 Android phone into airplane mode, and then used the default Maps app to watch my position using GPS. For most of the flight it worked normally. However, at the end of the flight, at about the time the plane started to descend so as to land, the GPS position marker suddenly jumped to an obviously wrong spot. After that, it ceased to update — at least until I got out of the plane.

Is it expected behavior of a phone GPS receiver during a flight? If so, what causes it?

It seems the plane does need GPS itself to be able to, e.g., send ADS-B data, so it doesn't seem likely that it jammed the signal. It also doesn't look like the clouds could be an obstacle for GPS signals, since after the landing the operation of my phone GPS receiver resumed (being under the clouds).

For reference, here's flightradar24 data about my flight.

A GPS needs a line of sight to (at least) 4 satellites in order to compute a position. Given that you were able to get a position during the cruise, I assume that you were close to a window and had a clear view of a part of the sky.

During the cruise, the aircraft trajectory was close to a straight line (or changing slowly), so your receiver was able to keep a line of sight to the same set of satellites. But during the approach, the trajectory was much more dynamic (lots of turns), so your receiver didn't had a constant line of sight toward the same set of satellites and "lost" them. It takes time for a receiver to "lock" on the signal of a given satellite, so the receiver it couldn't compute a position from other satellites because they were not in sight long enough.


What was the first airplane fitted with a hydraulic system? What was the first airplane fitted with hydraulic system?

Where was it used?

What are the fundamental differences between the first systems and those that are used now?

What was the first airplane fitted with hydraulic system?/Where was it used?

If we exclude hydraulic disk brake systems.

The Lockheed Constellation most likely had the first hydraulic flight controls (introduced in '43)

Introduced in '27 the Fairchild FC-1/FC-2 had hydraulically operated landing gear and disk brakes.

  What are the fundamental differences between the first systems and
  those that are used now?

Depending on how you look at it, little. Hydraulics are hydraulics. The systems have gotten more powerful but that may be related to the available power to drive the pumps. We arguably have gotten better at building them and they are perhaps more reliable but they are still more or less the same in operation.


Can airliners operate without an operating APU? As the APU (Auxiliary Power Unit) can be turned off when the engines are running, a functional APU may not be needed given you are able to start at least one engine. This question is in two parts:

Is it technically feasible to operate an airliner without APU (with the necessary ground support)?
If so, in what conditions is it legal (number of passengers transported, MEL, test flight,...)?

This question focuses on airliners. If needed, it can be narrowed to best-sellers (B737 and A320).

Yes, you can operate without an APU.  If the APU is inoperative you will need to write it up and coordinate with maintenance and dispatch to operate under the stipulations of the MEL.  This may restrict certain kind of operations but if we assume a route completely over land this has no effect other than needed ground services.

The requirements for no-APU is simply a ground start "huffer" cart at your departure airport.  Ideally you want one at the destination as well but if not available you can possibly coordinate leaving an engine running during the turn.  More generally though, if the destination does not have access to a huffer cart you will get an aircraft swap and the non-APU aircraft will be assigned to a route that does have those ground services available.

The general process of a non-APU flight is keeping ground power and ground air conditioning hooked up to the airplane for pre-flight activity and boarding.  Once the airplane is closed up the ground crew will coordinate with you to provide air via the ground start cart and you'll start one or both of your engines.  After you have an engine running, you'll disconnect all of the ground equipment and push back.  During the taxi, if you only started one engine earlier you'll perform a crossbleed start to start the other engine.  The takeoff engine bleed and pack configuration may be different for a non-APU takeoff but once you are airborne and set the bleeds and packs for post-takeoff you will be operating exactly the same way you would normally operate and the differences cease.

On arrival the only differences are to make sure you keep an engine running at the gate until ground power is hooked up.

The biggest downside to operating without an APU is the lack of decent air conditioning during taxi and ground operations.

Other considerations for operating without an APU are airplane specific.  For example, the EMB-145 has two generators per engine and one on the APU for a total of five generators.  The airplane will revert to "essential" power if less than 3 generators are available which means you will lose certain displays and systems that become unpowered.  This means if you had an engine failure during flight without an APU you will be in essential power and have to land in that condition because you cannot start the APU to get back up to 3 generators operating.


Is AA actually flying the 737 MAX? In flightradar24 I only see 737 MAX flying from Gol Airlines and Aeromexico, but none from AA.
Is American actually flying the 737 MAX or is FlightRadar24 reporting aircraft types wrong ?
I also see a few MAXes with a Boeing ticker flying in the Seattle area, probably delivery tests.

According to their website, they will start commercial flights using the 737 MAX on 29 December, but will be testing their aircraft on non-commercial flights before than:

We’ll begin with non-commercial flights in early December 2020 before the official return of the 737 MAX. On December 29, we’ll resume scheduled service with 2 flights a day (1 round trip) through January 4, 2021, from Miami (MIA) to New York LaGuardia (LGA). We expect to phase more of the aircraft into our schedule through January, with up to 36 departures from Miami.

(aa.com, emphasis mine)


How to select a SID during the planning stage? During the planning stage of an IFR flight how to choose the correct SID for your route in an airport with multiple runways and multiple SIDs? and how to predict the runway you will be going to use?

"File what you want, fly what you get."

There's no way to know for sure what clearance ATC will give you until you actually call them. If you're departing from an airport that you know well then you may be able to make an educated guess but that won't help if the winds change, an incident closes a runway, or any number of other things happen to invalidate your assumptions.

For planning purposes, just use the SID that best fits your needs, based on all the information you have available: direction of departure, aircraft type, weather, local procedures etc. But ultimately, you'll have to fly what you get (or what you can negotiate with ATC).


What type of hoops do I have to jump through to launch high power rockets? If I want to launch high power rockets NOT at a NAR or TRA sanctioned launch, assuming I am properly certified, what do I need to do?  I looked in the FAR|AIM, but I couldn't find anything on rockets, but I think the rocketry section has been omitted from the PPT FAR|AIM.

The FAR section that you are looking for is available on the ecfr website:

PART 101—MOORED BALLOONS, KITES, AMATEUR ROCKETS AND UNMANNED FREE BALLOONS

More specifically, it is Subpart C— Amateur Rockets

The main regulations that apply are (see the above link for the full text of the regulations):

  §101.23   General operating limitations.

  (a) You must operate an amateur rocket in such a manner that it:

  (1) Is launched on a suborbital trajectory;

  (2) When launched, must not cross into the territory of a foreign
  country unless an agreement is in place between the United States and
  the country of concern;

  (3) Is unmanned; and

  (4) Does not create a hazard to persons, property, or other aircraft.

  (b) The FAA may specify additional operating limitations necessary to
  ensure that air traffic is not adversely affected, and public safety
  is not jeopardized.

  §101.25   Operating limitations for Class 2-High Power Rockets and Class 3-Advanced High Power Rockets.

  When operating Class 2-High Power Rockets or Class 3-Advanced High
  Power Rockets, you must comply with the General Operating Limitations
  of §101.23. In addition, you must not operate Class 2-High Power
  Rockets or Class 3-Advanced High Power Rockets—

  (a) At any altitude where clouds or obscuring phenomena of more than
  five-tenths coverage prevails;

  (b) At any altitude where the horizontal visibility is less than five
  miles;

  (c) Into any cloud;

  (d) Between sunset and sunrise without prior authorization from the
  FAA;

  (e) Within 9.26 kilometers (5 nautical miles) of any airport boundary
  without prior authorization from the FAA;

  (f) In controlled airspace without prior authorization from the FAA;

  (g) Unless you observe the greater of the following separation
  distances from any person or property that is not associated with the
  operations:

  (1) Not less than one-quarter the maximum expected altitude;

  (2) 457 meters (1,500 ft.);

  (h) Unless a person at least eighteen years old is present, is charged
  with ensuring the safety of the operation, and has final approval
  authority for initiating high-power rocket flight; and

  (i) Unless reasonable precautions are provided to report and control a
  fire caused by rocket activities.

  §101.27   ATC notification for all launches.

  No person may operate an unmanned rocket other than a Class 1—Model
  Rocket unless that person gives the following information to the FAA
  ATC facility nearest to the place of intended operation no less than
  24 hours before and no more than three days before beginning the
  operation:

  ...

  §101.29   Information requirements..

  ...


What do Fighter pilots' thumbs look like? I have to imagine this question doesn't get asked too often, but I read actress Sienna Miller said her "nipples look like fighter pilots' thumbs" from breastfeeding.

I'm so confused. Do pilots' thumbs have a certain way of looking that is known?

I'm a blogger and want to write about her comment, but I'm looking for some context to explain it to our readers with.

Any ideas?

http://www.eonline.com/news/844242/sienna-miller-prefers-her-postpartum-nipples-they-look-like-fighter-pilots-thumbs

In some fighter aircraft there are several functional switches on the control stick--switching from guns to missles and vice-versa, aircraft trim, firing the weapon(s), etc. A fighter pilot's thumb can get a real workout and over time that could result in a very muscular thumb.


What kind of heaters are used for heated floor panels? In some Airbus planes, they have heated floor panels. So, what kind of heaters are being used there?

Electrical, connected to one of the AC buses. This is an example, absorbing 620 watts/m^2.


What does a dot inside two parenthesis mean on a weather depiction chart? Earlier today, a friend asked me what this symbol (referring to an airport in Canada) on a weather depiction chart represented.  I didn't know. (Full chart available here)

What does a dot inside parenthesis mean on a weather depiction chart?

From here, $(\cdot)$ means that there is precipitation within sight, reaching the ground, not at the station, but < 5 km from the station.

$)\cdot($ means that there is precipitation within sight, reaching the ground, not at the station, but > 5km from the station.

This source and this source give similar definitions, but without a strict distance cutoff, instead just saying "distant" and "near".

I couldn't find any references to this symbol in Nav Canada's weather code and symbol legend.


How did night fighter aircraft manage to shoot down their foes in World War II? I know that those plane had radar to acquire an approximate location of the enemy, but how did they spot them after that? You need to be accurate when you try to shoot down an enemy plane, and deflection can be tricky, even at close range. So how did pilots aim in those conditions?

The night fighting in WWII was mainly between the RAF and Luftwaffe, with the Luftwaffe fielding most of the night fighters due to necessity (the others too had some fine night fighters, though none had their need as much as the Germans).
The first stage in (trying to) shoot down enemy aircraft is to find them. This was mainly done by the ground based radars. The second one is fixing them- this is where the aircraft based radars came into being.
Initially, the fixing of aircraft location was done using ground based search lights, which were sometimes controlled by radar after which the fighters attacked the illuminated target- but this was of little use as was the aircraft based searchlights. It was only in the middle of the war did the development of night fighters gained pace.

A Messerschmidt  Bf 110 G-4 night fighter with FuG 202/220 Lichtenstein radar; By Max Smith - Own workMoved from en:Image:ME-110G-2_at_RAF_Hendon.jpg, Public Domain, Link
The night fighters were usually twin engined aircraft fitted with radars, though there some single engined ones too. The fighters were still vectored into the bomber locations using the ground radar controller. An RAF report on PoW interrogation notes:

...The crews fly by D.R., and the loose formation is simultaneously tracked on a map at Gruppe headquarters. If, in the light of the movements of the bomber force a change of course is necessary, a new bearing will be given to all aircraft simultaneously through the Gruppe commentary.
All crews are given strict orders to navigate by D.R., and to
accept the Gruppe orders if these differ from their own calculations ...

Once the fighters were near the bomber stream (as the RAF usually bombed in strength to overwhelm the defences), they were given a new bearing to intercept the bombers.

... the string of night fighters should be brought up to the bomber stream on a parallel or nearly parallel track. At the correct moment, and in accordance with D.R. tracking at headquarters, the night fighters will be given a new bearing which turns the whole line on to the bomber stream in a broadside.

The enemy aircraft (bombers) were identified by their silhouette (against moon or the burning cities below) or by their exhaust flames.

Recognition of the target aircraft is usually by the silhouette in light conditions or moonlight, and by the four exhaust flames in darkness.

The actual firing of the guns depended on the pilot and different ones opted for different methods- some simply did as in dogfights during day- get into the rear and shoot up, though the rear gunners made this difficult. Others moved towards the aircraft from the sides and a little low, after which they pulled up near the aircraft and aimed for the wing fuel tanks.

The range at which the night fighter opens fire with its forward
armament is determined by the pilot himself; whilst some will close in
as near as 50/60 metres, the more cautious will open up at a range of
200/250 metres. P/W considered, however, that the normal range might be
taken as l00/150 metres.

One of the effective methods used by Germans was the upward firing cannon called the Schräge Musik, which was quite effective with its 20 and 30 mm cannon.

By Source, Fair use, Link
Basically, the pilots flew under the bomber and fired the Schräge Musik. This was quite effective as the bomber crews had little warning of the threat below and the bullets usually tore through the fuel tanks near wing roots.

[These P/W] ... they stated that once this armament (Schräge
Musik) could be brought to bear it was extremely effective; one officer had claimed a kill with two rounds from the 20 mm. cannon.

The night attacks were quite short affairs as it was quite difficult to keep the bomber in crosshairs for any amount of time (and there were enemy night fighters to contend with). Shooting down enemy aircraft took more luck than skill in WWII. According to this site, each enemy aircraft shot down required more than 10,000 rounds fired (the values are more or less equal for both sides), with night attacks probably requiring more ammunition. Also, this infographic has some good details on this subject.


Is there an online source for Canadian Instrument Approach Procedures? The FAA offers instrument approach procedures on their website free of charge, and EASA does too.  Does Canada have them online for us to use?

Not officially, no. The official approaches are available in a PDF format to download for 20 CAD for each volume.

However, FltPlan.com claims to provide free, up-to-date charts:

  In cooperation with Nav Canada, FltPlan.com is pleased to announce
  free Canadian Approach Plates, also know as CAP (Canada Air Pilot).
  These online charts include all instrument approaches, airport
  diagrams, SIDs, STARs, and special use approach plates for Canadian
  Airports. They work similarly to the already available U.S. approach
  plates.

  CAP is an extension of FltPlan.com's continuously expanding coverage
  of Canada, Mexico, Latin America and the Caribbean. In May of this
  year, we expanded our coverage to include the filing of IFR
  intra-Canada flight plans. The availability of free, online Canadian
  Approach Plates brings a new level of safety and convenience for
  pilots in the planning stages of their trip.

Though I have not seen anything from Nav Canada stating that this is "in cooperation with Nav Canada", they do seem to be an authorised distributor of paper charts.

Note FltPlan.com warns that these charts shall not be printed as a replacement for "proper" paper charts -- I am not sure whether these are deemed to be official or not, but it is rather unlikely.


Why is water in the fuel tank bad? I mean, on the one hand it seems kind of obvious, if you had a fuel tank that was mostly water then you would lack combustible materials for the engine, but I get the impression that having any water in the fuel tank at all is considered a really bad idea.

Why is that?  Is it all right to have a very small amount of water in the fuel tanks?  Is there a defined percentage of liquid in the fuel tank that must be fuel in order to operate safely? (say 99.87% or something?)  And does this differ from prop to turboprop to turbofan to jet?

Fuel systems are in general fed by gravity, at least until the fuel leaves the tank, where sometimes (always if the tank is lower than the engine) a pump pushes it toward the engine. This means that fuel is generally extracted from the bottom of the tank (or slightly above the very bottom to avoid having small particles from the bottom of the tank clogging up the fuel filter, incidentally this also introduces the concept of unusable fuel, as the stuff remaining at the bottom of the tank, although there are a lot more factors to this).

Fuel is less dense than water, meaning it'll float on top of the water. Or if you want to think of it the other way around, water is heavier and will sink to the bottom, right where you're trying to get your fuel to feed to the engine. Water doesn't burn very well and the engine will stop. Avgas is generally 0.72 kg/l and Jetfuel around 0.82 kg/l (water being 1 kg/l, see have SI units work well that way?).

A tiny amount of water probably mix with the fuel and simply reduce the power output slightly, whereas anything more will be drained from the tank first, and it'll be very hard to restart the engine. You'd have to pump all the water through the cylinder and out the exhaust, and I don't think this is generally possible in flight, especially right after takeoff which is generally the case when you have water in the fuel (could be right after switching tanks too though).

I don't know much about turbine engines, but I suspect they're less susceptible as the water will not prevent relighting the engine (the pumps will simply push the water out, there's no cylinder that could fill up with water), and you'll generally be using up more fuel on the ground making the problem readily apparent. This is pure speculation though.


what is the mechanism of hydro-mechanical system in power control unit that uses follow up feedback? I read somewhere that the follow up system aids in actuator deflection in specified position by controlling hydraulic fluid to the actuator , but how?

There is a position control loop in there that opens the servo valve until the required position is reached, then closes it. The loop uses position of the actuator as a feedback signal, measured by a position transducer, usually an LVDT. Open loop servo valves just generate an actuator velocity, not very desirable when flying a plane.

A more robust system used on aircraft has the hydraulic actuator moving together with the flight control surface. The pilot control stick is connected to the servo valve, and when he deflects the stick he opens the valve and oil starts to flow. This makes the flight control surface deflect. The actuator moves with it, in doing so closing the valve again.

You mention half powered controls in a comment - I assume you mean boosted flight controls, where the pilot directly deflects the control surface but hydraulics help in overcoming the aerodynamic forces. These work in the same way as described above, with a follow up mechanism that moves the actuator until the valve closes, but the mechanical linkage is different.

Here is a schematic diagram of a hydraulic actuation system with a mechanical servo valve:

You can see that the cylinder is anchored to the airplane structure. The diagram is a bit primitive, but the gist of it is:

The elevator is at rest, not moving.
The pilot gives a control input, which opens the servo valve (the little box on top of the cylinder).
The piston deflects because the servo valve is open.
The pilot input linkage is attached to the piston as well. Because of the movement of the piston, the servo valve closes again.

This mechanical feedback system is robust because there are very few electronics that can fail. In this set-up, elevator deflection velocity is proportional to stick deflection. Other transfer functions are possible bit programmed feedback loops and transducers.

This system is fully irreversible: airforces on the elevator push against the cylinder piston and are not fed back to the mechanical linkage at all.


What is the purpose of Runway Grooving? What is the purpose of runway grooving?
How does the airport drainage system work?
Why do airports remove rubber from the runway?

What is the purpose of runway grooving?

The channels help to remove water from the runway. They also provide an area for the water to build up. With out these channels the water runs the risk of forming a thin surface covering the runway which can be very dangerous. As mentioned by john here in the comments this is usually known as hydroplaning and is the same as what happens to a car.

  How does the airport drainage system work?

This is a bit of a guess but I assume they work like any other road drainage system and it will depend on where the airport is located. Here is a very dated report prepared for the DOT on runway drainage that you may find of some interest. Here is the FAA's full paper on designing surface drainage for airports, it's a bit long but should cover what you are looking for.

  Why do airports remove rubber from the runway?

Tires obtain the best friction when they come in direct contact with the runway surface. Excess tire rubber that wears off and sticks to the runway can affect the tire/runway interactions. This wiki article covers the main points pretty well.


What is an SIC type rating? 14 CFR 61.55 says:

  ...

  (d) A person may receive a second-in-command pilot type rating for an
  aircraft after satisfactorily completing the second-in-command
  familiarization training requirements under paragraph (b) of this
  section in that type of aircraft provided the training was completed
  within the 12 calendar months before the month of application for the
  SIC pilot type rating. The person must comply with the following
  application and pilot certification procedures:

  ...

  (6) The applicant must appear in person at a FAA Flight Standards
  District Office or to an Examiner with his or her logbook/training
  records and with the completed and signed FAA Form 8710-1.

  (7) There is no practical test required for the issuance of the “SIC
  Privileges Only” pilot type rating.

What exactly is an SIC type rating used for and how can someone get a "type rating" without any kind of practical test?

It's an ICAO requirement, basically it's just official documentation showing that you've been trained and are  competent to act as SIC in a given airplane.

ICAO is an organization that standardizes regulations and procedures among the participating countries (close to 200 if I recall).  If you fly as SIC internationally you'll probably need an SIC type rating.

The rating is almost the same as a PIC type rating, except the rejected takeoff and taxi requirements (and maybe some others) don't have to be met.  It's basically a formality for any airline first officer as they will have met all the requirements just by going through the airline's training.


How are helicopter rotor blades balanced? Reading this answer, I realized that the balance of a rotor is critical. When one blade is changed, the whole balance of the rotor may be affected. Moreover, I doubt 2 blades are exactly the same. For a car's wheel, we add small weights, but what about helicopter's rotor? Adding pieces to the rotor may affect its aerodynamics.

Most blades are as close as possible when built at the factory. Yes, it is like a car wheel you use weights to balance. For the Blackhawk helicopter there are inserts on the hub near the blade to add weights. But additionally there are a maximum amount of weight that can be added. If you're unable to balance the main rotor head, sometimes you have to switch blades around to other sides and adjust weights. If it still doesn't balance usually it is due to the installation of the hub to the main transmission then gaps have to be measured.


Why do helicopter flights not appear in online flight trackers? Currently in Indianapolis, IN (19 Mar 2015, ~08:00 EDT -4GMT), there is some sort of big kerfuffle downtown, and I can see 3 helicopters hovering over the near west-side of the downtown area. However, FlightRadar24 for the area doesn't seem to show them at all.

It's dim enough that I couldn't make out the markings on the choppers before I went inside, but at least one or two are local news stations, and the third is either another news station or a police chopper. They are in the (normal) flight path of Indianapolis International (KIND) runways 23L and 23R, though I'm sure they're below the approach altitudes.

Why are they not squawking something that would be picked up on either FlightRadar24, FlightAware or similar flight tracking web sites?

Update: It does appear that they're not using RWY 23 this morning, but are using RWY 5L and 5R.

FlightRadar and similar websites use several sources for aircraft detection, most commonly they use ADS-B. Not all General Aviation aircraft, to which helicopters would count normally, are equipped with transponders that are capable of emitting ADS-B data, so they would not show via regular means on FlightRadar.

The primary technology that Flightradar24 use to receive flight information is called automatic dependent surveillance-broadcast (ADS-B).
ADS-B is a relatively new technology under development which means that today it's rarely used by Air Traffic Control (ATC). Our estimations show that roughly 65% of all commercial passenger aircraft (75% in Europe, 35% in the US) are equipped with an ADS-B transponder. For general aviation this number is probably below 20%. But this percentage is steadily increasing as ADS-B will become mandatory for most aircraft in most airspaces around the world, by year 2020. When mandatory, ADS-B will replace primary radar as the primary surveillance method used by ATC.
Flightradar24 has a network of more than 4,000 ADS-B receivers around the world that receives plane and flight information from aircraft with ADS-B transponders and sends this information to our servers. Due to the high frequency used (1090 MHz) the coverage from each receiver is limited to about 250-400 km (150-250 miles) in all directions depending on location. The farther away from the receiver an aircraft is flying, the higher it must fly to be covered by the receiver. The distance limit makes it very hard to get ADS-B coverage over oceans.
About 99% of Europe is covered with ADS-B receivers. There is also good ADS-B coverage in USA, Canada, Mexico, Caribbean, Brazil, Russia, Middle East, India, Japan, Thailand, Malaysia, Indonesia, Australia and New Zealand. In other parts of the world the ADS-B coverage varies.

The other option is to receive the regular Mode-S transponder signal by a technique called Multilateration (MLAT), however the FlightRadar website states that this is something that only works reliably at high altitude, at least 5 000 to 10 000 ft.

In some regions with coverage from several FR24-receivers we also calculate positions of non-ADS-B equipped aircraft with the help of Multilateration (MLAT), by using a method known as Time Difference of Arrival (TDOA). By measuring the difference in time to receive the signal from aircraft with an older ModeS-transponder, it's possible to calculate the position of these aircraft. Four FR24-receivers or more, receiving signals from the same aircraft, are needed to make MLAT work. That means that MLAT coverage can only be achieved above about 5,000-10,000 feet as the probability that signal can be received by four or more receivers increases with increased altitude.
Most parts of Europe are today covered with MLAT above about 5,000-10,000 feet. There is also some MLAT coverage in North America, Mexico, Australia and Brazil. More areas will get MLAT coverage during 2014 and 2015.

For more information, check FlightRadar's "How it works" page.


Are jet engines affected by small bird (e.g. hummingbird) strikes? If a hummingbird got sucked into a commercial jet engine at takeoff would the pilot notice? This is a serious question.

All turbine engines must pass a series of tests, including water ingestion (flying through clouds) and bird strikes. For bird strikes, the following article does a good job explaining the requirements to pass bird strike testing:
Aircraft Certification for Bird Strike Risk

It cites 14 CFR Part 33-77 'Foreign object ingestion - ice' (although 14 CFR Part 33-76 'Bird ingestion' seems more appropriate) and EASA Airworthiness Code CS-E 800 'Bird Strike and Ingestion' as sources.

14 CFR Part 33-76:

  (4) A small bird ingestion test is not required if the prescribed number of medium birds pass into the engine rotor blades during the medium bird test.

  (5) Small bird ingestion tests shall be conducted so as to simulate a flock encounter using one 85 gram (0.187 lb.) bird for each 0.032 square-meter (49.6 square-inches) of inlet area, or fraction thereof, up to a maximum of 16 birds. The birds will be aimed so as to account for any critical exposed locations on the first stage rotor blades, with any remaining birds evenly distributed over the engine face area.

  (6) Ingestion of small and medium birds tested under the conditions prescribed in this paragraph may not cause any of the following:

  More than a sustained 25-percent power or thrust loss;

  The engine to be shut down during the required run-on demonstration prescribed in paragraphs (c)(7) or (c)(8) of this section;
  The conditions defined in paragraph (b)(3) of this section.
  Unacceptable deterioration of engine handling characteristics

EASA Airworthiness Code CS-E 800

  (d) Medium and small birds ingestion tests. Engine ingestion tests and analysis with medium and small sized birds must be carried out as specified below. Alternative evidence may be acceptable as provided under CS-E 800 (f)(1). The small birds test will not be required if the prescribed number of medium birds pass into the Engine rotor blades during the medium bird test.

  (B) Small birds. One 85 g bird for each 0·032 m2 of the inlet throat area or fraction thereof with a maximum of 16 birds, distributed to take account of any critical exposed

For more information, refer to 14 CFR Part 33-76, and EASA Airworthiness code CS-E 800.

One more thing to add - the documents do not include any tests for single small birds, only flocking small birds, and use birds that weigh 85 grams. Humming birds do not flock, and 85g is more than most humming birds weigh. That being said, the tests do include much larger birds, and all commercial jet engines found on commercial airlines certify large bird strikes, so it's likely that tests with small bird strikes are not conducted. Bouncing off of physics - if a turbine can withstand a large bird strike, it won't even feel a humming bird strike, therefore it is not a required test if the engine already certified with large bird strikes.


How do coefficient of lift/drag variation with speed differs between swept and unswept wings? Trying to understand the coefficient of lift/drag of swept and unswept wings as speed increases.  Some example questions and statements-
A swept wing will have a lower max Cl at subsonic and supersonic speeds.  I understand the lower max cl at subsonic, but the lower max cl at supersonic has confused me?
When the speed increases for a swept wing from subsonic to supersonic Mach numbers, the max CL is more or less?
CL is more at supersonic and less for subsonic.
Comparing swept and unswept wings as angle of attack is increased the swept wing will produce less lift(this i understand) and more drag.  Why more drag?  Is it due to the span wise flow being greater?

It's not so simple.
For swept wings it is essential whether the leading edge is sub- or supersonic.
What does that mean?
If the leading edge is within the Mach cone emanating from the tip of the wing, it is called subsonic. The approaching air will "sense" what is coming and behave much like in subsonic flow. This avoids wave drag and keeps nose suction alive; an effect that can be maximized by the use of conical camber: Here, the leading edge is bent down similar to a cone surface with its apex at the wing root and the cambered part increasing towards the wing tip. This forward-facing part of the wing experiences suction which helps to pull the airplane forward.

Conical camber on the wing of the SR-71 (own work)
Of course, such a swept wing with a subsonic leading edge will also stall quite like it does at subsonic speed. However, the drag caused by a fully supersonic wing is so much higher that the small benefit of a higher lift coefficient does still not make it attractive. The drag at those high lift coefficients is so high that any airplane will quickly decelerate to subsonic speed once it tries to reach those lift coefficients.


Which single pilot aircraft had a range of at least 2160nm in the late 90s? I'm writing a book and looking for an airplane that can handle that distance (2160nm), was available back in the late 90s, and can be operated by a single pilot.
Thanks!

Smaller planes that had this range back in the 90's were not so rare, but they were jets, most of them were not intended to be operated, at least commercially by a single crewmember. It would have been totally possible though.
When considering that you are writing a book, you may take some liberties (in addition to the crew count) when it comes to range: the official figures take into account the fuel reserve regulations, so after the declared range is flown, the plane would most likely be able to continue flight for about an hour before fuel starvation.
So, at least these had the range of 2160nm minimum (some not fully loaded):

Learjet 60
IAI Westwind
Dassault Falcon 20 (some variants)
Hawker 800

(To keep things simple, I'll turn this into community wiki right away)


Can you go around with LAHSO in effect? Some larger airports in the US use land-and-hold-short (LAHSO) operations, meaning you're cleared to land, but only if you're able to do so without going beyond specific point (usually an intersecting runway) on the roll-out.

What if you're forced to go around just before touch-down, perhaps even with the mains hitting the pavement, you will inevitably head straight for, and cross, that intersecting runway. Would there be a risk of colliding with aircraft operating on the intersecting runway?

There's always a risk with LAHSO and pilots can always say "unable"; student pilots are not even permitted to accept a LAHSO clearance. You can always go around if you deem it necessary; you're the pilot in control and empowered to make all decisions affecting the safety of your flight, and the fact that you're landing on a LAHSO clearance is just a factor you need to take into account. Making the decision to go around is, in my estimation, much safer than landing and potentially crossing the hold short line (due to the reaction time others have to deal with the situation).

While there is that risk, the tower is watching and at any sign of trouble they will call other landing aircraft off. The two runways aren't being landed on at the same moment such that normal operations would cause them to collide at the intersection if one didn't hold short.

According to this interesting article on the subject, there were 20 LAHSO incidents between 1994 and 1999.


Is there any application where the crescent wing would be the best wing planform? To my knowledge the only aircraft featuring a crescent wing that was built in numbers was the Handley Page Victor.

It seems that a crescent wing offers the possibility of a high subsonic/transonic aircraft with a thick wing root but not too much drag at the root. It seems that a crescent wing would work well at airliner speeds.

Why there were not more crescent wing aircraft been built?
Why are they not used on airliners?
Is there any application where a crescent wing would be an ideal or even a good solution?

You are right, it helps to de-sweep the outer wing. The main advantages are (read this Flight article from 1965 here for a much more detailed explanation):

An identical critical Mach number over the whole span as sweep is reduced together with relative thickness.
A smooth cross-section distribution in the direction of flow which helps to reduce transsonic drag.
A tendency to pitch up in ground effect such that the wing will essentially land itself, especially when combined with a T-tail.

However, as long as wings are made of aluminum, the manufacturing effort is significantly higher.

The basic problem is the needed two-dimensional bending of the skin panels. Using a straight spar line and a straight leading edge requires bending only in one dimension, but when sweep changes, the skin panels would need to stretch in some corners while being bent. This requires much more expensive tooling, or a break in the structure which increases structural mass.

Even one composite wing I know of has a straight leading edge, even though the aircraft would have benefited from de-sweeping. Both the TKF-90 and the X-31, which were designed by the same people before, had reduced sweep on the outer wing, and for good reason. When the multinational project started and they talked to the BAe engineers, the British side insisted on a straight leading edge for easier manufacture, ignorant of the fact that using composites made their point moot. Yes, that was practically the same company that had built the Victor before.

Another disadvantage is the fact that any sweep change will convert bending moment into torsion. Normally, this reduces the incidence of the outer wing when a swept-back wing is bending under lift loads. De-sweeping the outer wing will introduce an uptwisting torsion which can cancel the torsion from sweep-back, and Handley Page claimed that the Victor wing was close to aero-isoclinic. However, this reduces flutter damping, resulting in a lower wing flutter speed (PDF!). If the wing's aspect ratio is low, this is manageable, but with higher aspect ratios the wing needs to be stiffened.

To answer your question directly: In the majority of cases it is aerodynamically advantageous to vary sweep with relative thickness, but it is not structurally and economically efficient. In the delta wings of combat aircraft which need to operate over a wide range of angles of attack, de-sweeping the outer wing produces indeed the best wing planform, even when economics is included.


How does a hot tip-jet supply fuel to its engines? Some tip-jets move their rotors by running jet engines on each end of the rotor. Obviously there must be some ways to supply fuel to those engines through a rotating body. How is this accomplished?

There are pipes inside the blades which connect the engines to a rotary seal inside the main rotor head assembly. That seal allows fuel to be pumped into the blades from a port outside the main rotor head. Such seals are used in a variety of mechanical engineering applications where a fluid, usually lubricating oil, has to be provided to a rotating piece of machinery.
One example which you can probably find a cross-section of on the web is the method of using oil under pressure to change the blade pitch of a constant-speed propeller.


What is the origin for "squawk" having two different meanings in aviation? In Aviation, a "Squawk code" is a common term for a "Transponder Code".
"Squawk 2345 and Ident"

But it is also commonly a way to report problems with an airplane.
"After I landed, I Squawk'd the broken ADF, and marked it INOP"

Do these two terms share a common history?  Is it purely coincidence that the same term is used for such different meanings?

According to Wikipedia (which has cited sources), the transponder usage comes from...

  The use of the word "squawk" comes from the system's origin in the
  World War II identification, friend or foe (IFF) system, which was
  code-named "Parrot".

As for the maintenance reference, one of the accepted definitions is

  To inform

or

  To report an infraction

It may just be coincidence that they are used as they are.


Why can the A320 VAPP be decreased down to VLS? I read in the Airbus A320 FCTM (p349), normal procedures descent section:

  The flight crew can insert a lower VAPP in the MCDU PERF APPR, down to
  VLS, if landing is performed without A/THR, without wind and no ice
  accretion.

You have no margin against a stall condition. Why is that possible to decrease VAPP till VLS?

... if landing is performed without A/THR...

Then theoretically you don't need the VAPP [setting] and should fly a bit faster, it's only a speed bug in this situation.

... without wind...

Even if the METAR is reporting an average of 0 knots, there is always a breeze here and there.

... no margin against a stall...

You have a 23% margin. VLS is 1.23 VS at 1G (check FCOM 4.03.20). So if the stall is at 120 knots, then VLS is 148 knots.

Note:

  VAPP should be at least VLS +5 kt.

So VAPP even becomes 153 knots, 33 knots above stall. Plus the A320 by design has anti-stall measures if the flight laws are not degraded.


Which commuter flight was forced to land in a cornfield in '96 or '97? Last night a friend's wife was describing her experience as a child being on a flight that encountered a flock of Canadian geese, where at least one engine was lost to a bird strike. I suspect both engines may have been lost, or at least compromised, because she said the plane ultimately landed in a cornfield. She said the oxygen masks deployed, and she used the inflatable slide to deplane.

If her memory is correct the flight departed Indianapolis, IN, bound for Trenton, NJ. Based on her age, we thought the flight was probably in 1996 or 1997. She said it was a "small plane", but it was certainly a commercial flight, and I believe a jet (not a turboprop). She described two seats straddling the aisle.

Her memory of the event emphasized surreal, sensory details, so I suspect some uncertainty among the facts useful for finding this flight.

TL;DR here are the useful details:

Probably 1996 or 1997
Departed Indianapolis, IN
(Update 2.20.2018: She confirms it was Indianapolis International)
Intended arrival in Trenton, NJ
Engine(s) out, presumably due to bird strikes (Canadian geese)
Emergency landing in a field (possibly a cornfield)
(Update 2.20.2018: This was a Pennsylvania cornfield)

To my surprise I've been unable to Google more information, so I'm hoping someone here has a better angle on researching this interesting flight.

From the Los Angeles Times newspaper, Jan. 21, 1989.

  BUENA VISTA, Colo. — A commuter plane carrying 26 passengers lost power Friday and made an emergency landing in a cornfield, but no one was injured, authorities said. Airline officials had not determined what caused the engines of the United Express plane, a Convair 580 twin-engine propjet, to shut down.

Here is the link: LA Times


How can pilots lacking instruments interpret vectors given by ATC? This video is about European Air Transport flight 2939, a Boeing 737, which "lost all the instruments of the aircraft" shortly after takeoff.

  BCS2939: We are flying heading now, and we don't have even altitude and anything, so if you can, give vectors back to the field, please.
  Approach: Roger, Eurotrans 2939, turn right heading 360 and you can climb to 3000 feet.
  BCS2939: Right turn 360, 3000 feet. -pause- We are almost in visual, we don't even have altimeters.

Despite the lack of instruments the pilots manage to fly the headings given by Shannon Approach and land safely.

It seems that the instrument panels of the 737 are entirely digital:

I understand what vectors are:

  A vector is defined by a direction and magnitude. In aviation these represent your heading (the direction) and your speed (the magnitude). However, in normal aviation usage "vector" only refers to the heading and other nomenclature is used to assign/report speeds.

The 737's cockpit seems to lack an analog compass which would survive a power outage like this one:

How might the pilots have flown the headings given by ATC (as the visualisation shows they did) without a compass or altimeter?

14 CFR Part 25 describes the requirements for an airliner like the 737 to be certified by the FAA.

§25.1303   Flight and navigation instruments.
(a) The following flight and navigation instruments must be installed so that the instrument is visible from each pilot station:
...
(3) A direction indicator (nonstabilized magnetic compass).

Indeed the 737 has a magnetic compass, centrally located above the windshield. It's just hard to see in the picture you have, as it's hidden behind the overhead console controls. This is a very typical location for the compass in many large aircraft (but not all), as it's centrally located, allows both pilots to see it, and will have less interference from other instruments.

Even the newest version, the 737 MAX, has a compass.

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