What kind of horizontal stabilizer does a Boeing 737 have? Does this plane have fixed horizontal stabilizers and elevators or has it been fixed with stabilators instead?

A Boeing 737 has a movable horizontal stabilizer for pitch trim with elevators for pitch control (also known as a THS – Trimmable Horizontal Stabilizer). This is true for all 737 variants, including the MAX. Note: The term stabilator is typically used when the entire tail is rotated for pitch control, like e.g. on a Piper Cherokee.

The following image (taken from this question) shows the horizontal stabilizer (the black arc indicates the range of movement of the whole stabilizer):

From the 737 NG FCOMv2 9.20.7 (Flight Controls - System Description):

  Pitch Control

  The pitch control surfaces consist of hydraulically powered elevators and an
  electrically powered stabilizer. The elevators are controlled by forward or aft
  movement of the control column. The stabilizer is controlled by autopilot trim or
  manual trim.

  Elevators

  The elevators provide pitch control around the airplane’s lateral axis. The
  elevators are positioned by the pilots’ control columns. The A and B FLT
  CONTROL switches control hydraulic shutoff valves for the elevators.
  Cables connect the pilots’ control columns to elevator power control units (PCUs)
  which are powered by hydraulic system A and B. The elevators are interconnected
  by a torque tube. With loss of hydraulic system A and B the elevators can be
  mechanically positioned by forward or aft movement of the pilots’ control
  columns. Control forces are higher due to friction and aerodynamic loads.

  [...]

  Stabilizer

  The horizontal stabilizer is positioned by a single electric trim motor controlled
  through either the stab trim switches on the control wheel or autopilot trim. The
  stabilizer may also be positioned by manually rotating the stabilizer trim wheel.

  Stabilizer Trim

  Stabilizer trim switches on each control wheel actuate the electric trim motor
  through the main electric stabilizer trim circuit when the airplane is flown
  manually. With the autopilot engaged, stabilizer trim is accomplished through the
  autopilot stabilizer trim circuit. The main electric and autopilot stabilizer trim
  have two speed modes: high speed with flaps extended and low speed with flaps
  retracted. If the autopilot is engaged, actuating either pair of stabilizer trim
  switches automatically disengages the autopilot. The stabilizer trim wheels rotate
  whenever electric stabilizer trim is actuated.


Why does the F-16 canopy have a K-shaped 'latch'? Why is the F-16 canopy latch (the yellow painted part) shaped like a K? It's a very funky shape, and I'm wondering if that functions as more than just a latch.

The function of the form is to act as a throttle stop when the part is in the position shown in the picture. It prevents full movement of the throttle when canopy is not securely closed and sealed.

When the canopy is closed, the latch is moved by pushing the bottom part of the latch towards the outside of the plane. This moves the throttle stop out of way and actuates the canopy seal.

See this Youtube video for an example, latch operated at 0:25.


Conducting a Precision Approach on a Non-Precision Runway - What are my limitations? Let's take ILS, for example.

As stated in the FARs, the minimum RVR for a CAT I ILS approach would be 2400ft (1/2 SM) for a runway that does not have TDZ and Centerline Lighting. So, that is one limitation for such a scenario.

A couple more would be the limitation to the visual references available under 91.175 of the FARs.

Can you think of any other disadvantages if one were to conduct a precision approach on a non-precision runway?

Your limitations are exactly the same regardless of runway -- you cannot descend below the published DH without the published flight visibility minimum and the visual references required by 91.175.

What the limited runway markings and lights change is the number of visual cues you have to be able to descend below MDA and land, which affects the likelihood of a successful approach in minimum weather.  Whether this is a disadvantage or not depends on the actual weather and your preparation.  If you know what lighting and markings are available (and you should), then you know what to look for.  If you are looking for lights that don't exist, you won't find them and worst case you may mis-identify other lights.

The only other disadvantages I can think of relate to ground movement and ILS critical area protection.  If there are no centerline lights on the runway there probably aren't lighted runway turnoff lead lines either and extra care needs to be taken when taxiing.  If the runway is located at an non-towered field and the ILS critical area has a hold short line on the taxi way, it may not be protected properly.  This is mitigated, however, by taxiway placement which probably avoids the critical area at non-towered fields (not universally true though).


What is the expected range of handheld radio? For a handheld VHF radio carried as an emergency backup, how should I expect the effective radius of a handheld radio to compare with on-board radios in two-way communications? I figure reception should be the same. But transmission would probably be different, dependent on the power. Would the difference be significant? What factors would change the useful radius of a handheld radio?

This ICOM hand held has a max output of 5W compared with their panel mount radio which outputs at 8W. Unfortunately they don't quote effective ranges on their website (and its highly dependent on many factors anyway). In any case you are limited by line of sight which depending on the plane you are flying (and how high up you are) may be more of an issue. There is some discussion here on the matter and generally people say the work pretty well. Keep in mind also that the aircrafts installed radios have their antenna that are mounted on the exterior of the plane which has an effect on the reception and transmission ability. Using a hand held inside a plane may in practice yield different results even if it has the same transmission specs as an installed radio.


What flying machine is this model? Help with this flying machine. I think it is a concept / prototype designed in Europe in the nineteenth century.

A friend sent me this. Thanks for the answers.

Gull-wing by Werner Siemens, Germany 1847.


Is it possible to start the engines while on push back? I was recently on a flight and the the engines started after push back has been initiated. I was always under the impression that the process required a GAU to feed pressurised air or use of the APU.
But the APU wouldn't be used at a major London airport when ground services are available?

How did they start then?

Aircraft engines are started using the APU or a Airstart Cart. The GPU is for electrical power only and the engines are started off air power. It may be a Airstart was not available or they were running late on the block time and they blocked  using the APU to start the engines to make the block time. After engine start and before takeoff the crew will shut down the APU. Most US airlines start their engine off APU air unless the APU is not working then they will start off a Airstart Cart.


Does a Tower controller need to see an aircraft on final to give landing clearance? If there is an IFR aircraft on approach that has already received an approach clearance, and he reports being at the final approach fix but the controller does not have him in sight yet, can the controller give the aircraft clearance to land at this point, or does he have to wait until he has the aircraft in sight (which may be on short final)?

And what are the rules for (let's say) a VFR flight on final (maybe the controller can't see him due to rain over the field, etc.)?  Also, are there any reference documents (ICAO/FAA/Eurocontrol) that have information on this?

Here's a more specific IFR scenario: let's say the aircraft is making a CAT I ILS or maybe a VOR DME approach, in a non-radar environment. Does the tower need to see the aircraft before giving a landing clearance? The runway itself is clear from other vehicles or aircraft. Does the controller issue a "continue approach" instruction until he can see the aircraft and then clear it to land? O does he just issue the landing clearance at the final fix ( if the runway itself is clear)?

The FAA's ATC orders cover this for the US. Note that controllers can use radar instead of visual contact:

  3−10−7. LANDING CLEARANCE WITHOUT VISUAL OBSERVATION

  When an arriving aircraft reports at a position where he/she should be seen
  but has not been visually observed, advise the aircraft as a part of
  the landing clearance that it is not in sight and restate the landing
  runway.

  PHRASEOLOGY−
  NOT IN SIGHT, RUNWAY (number) CLEARED TO LAND.
  NOTE−
  Aircraft observance on the CTRD satisfies the visually observed requirement.

(A CTRD is a Certified Tower Radar Display.)

As others have said, operations in poor weather would be very difficult if controllers needed to see all aircraft before clearing them to land.


Why does an aircraft pitch up when the speed increases? Can anyone please explain why aircraft pitches up when the speed increased? (please consider an aircraft, Wing AC, CG and Tail AC lies on a line.)

The ideal explanation I'm looking for should have something to do with the static margin.

Here I am talking about a powered or unpowered aircraft, trimmed for steady flight, reacting to an EXTERNAL velocity perturbation which increases the airspeed. (Like a sudden, substantial, sustained increase or decrease in the speed of the wind, e.g. due to wind shear.)

I have seen that when faced by this kind of a perturbation, the aircraft tries to slow down/keep the airspeed unchanged by increasing the pitch angle.  My question is how it happens

Peter Kampf wrote:

  However, I can imagine what might have happened to let you observe a pitch-up. This needs several conditions:
      A propeller-diven airplane with the propeller in the front
      A sufficiently large static margin so the empennage produces a down-force.
      Speeding up by opening the throttle.

Let me clarify these are not necessarily the cases for what I'm asking,
    1. If we throw a glider hard enough, which is trimmed for a certain airspeed it will pitch up and climb.
    2. At least for now I think it doesn't matter whether the tail produces down-force or upward force. Say the velocity is increased by factor of 2 and the forces on both wing and tail increased by a factor of 4. Equilibrium is still maintained as moment around CG has not changed by this. (and this is what stands against my observation)

Mike Sowsun wrote:

  The horizontal stabilizer always provides a downward force to balance the forces of lift and weight with the center of gravity. This also provides stability because if the aircraft pitches down and starts to speed up, the increased airflow over the tail will result in more downward force and cause the nose to rise and the aircraft to slow.

I think there is no need for the tail to make downward lift always. The tail can be uplifting as well. Anyway, if we agree that to be the case for now, when the aircraft gains airspeed, the flow speed over the wings increases as well as tails. Isn't it? What I can't understand is, what makes the aircraft pitch up when both the wing force and tail force increased by the same factor, due to increase of airspeed.

Any further input is much appreciated.

What you ask is: If a model glider is thrown at a higher speed than its trim speed, why does it pitch up?

Short answer: Because the rear horizontal surface produces less lift per area than the forward surface. When flying at a speed different from its trim speed, the combined center of lift of all surfaces is shifted such that it creates a pitching moment around the center of gravity. This pitching moment causes the flight path change.

Note that I try to explain things in terms that work equally well for canards or even flying wings. That may sound odd in places, but needs only one explanation for all cases. For unswept flying wings read forward wing = forward part of the airfoil and vice versa.

Long answer: Let's assume an airplane that is rigged for flight at an angle of attack of 9°. For simplicity, let's assume that both airfoils are symmetric and both surfaces have the same lift curve slope, for simplicity 0.1 per degree. The local incidence is 0° on the forward and -5° on the rear wing. Neglecting downwash effects, this results in a lift coefficient on the forward wing of 0.9 and on the rear wing of 0.4. The zero-lift angle of attack is +1° when the forward wing lift coefficient is at 0.1 and the rear wing lift coefficient is at -0.4.

Let's further assume that the tail surface has 25% of the area of the forward surface. Lift on the forward wing is 90% of weight and on the rear wing it is 10% of weight. The center of lift, therefore, sits at 10% of the line connecting both neutral points and that is where the center of gravity is as well for trimmed flight. Like this:

Now the model is thrown at twice its trimmed speed. Let's assume that the angle of attack is also 9°, but that does not matter much. Lift on the forward surface is now 360% and on the rear surface 40% of weight. Again both forces combine for a common center of lift at 10%, so no pitching moment is created. But lift far exceeds weight, so the aircraft immediately climbs. Climb without pitching motion means that the angle of attack decreases immediately. Therefore, the aircraft will slightly accelerate upwards and settle at a new, lower angle of attack where the combined lift is equal to weight. But how is lift now distributed?

To have lift decrease to a quarter needs an angle of attack change to 25% of its initial value, relative to the zero-lift angle of attack. For this, the new angle of attack on both surfaces has to decrease by 6°. The local incidences result in an angle of attack of 3° on the forward and -2° on the rear wing and lift coefficients of 0.3 and -0.2, respectively. Again neglecting downwash effects, the new lift contributions are 120% on the forward wing and -20% on the rear wing. Like this:

Now the center of lift is 20% of the distance between the two wing's neutral points ahead of the forward wing's neutral point and 30% ahead of the center of gravity. That causes a strong nose-up pitching moment which will let the aircraft pitch up. Together with the initial flight path change of 6° for lift correction this will make the airplane climb until its flight speed drops below the trimmed condition and the condition reverses. Since pitch damping is high, very few cycles are needed to arrive at the trimmed condition but at a height over the launch point which corresponds to the extra energy provided by the high launch speed.

This can be run with different numbers and will work regardless of lift or downforce on the rear surface, provided that lift per area is lower there than on the forward wing.


What was used instead of the failed engine when ferrying the Air France Flight 66 aircraft back? After engine 4 failed in Air France Flight 66, the airliner (an Airbus 380) landed at Goose Bay in Canada. I am aware that following that, the failed engine was removed and then something "nonfunctional" was installed in its place "to balance the weight". This looks like a strange story to me:

What was this "non-working replacement" and where did they get it? It still needs to have the required weight, shape and mountings. Was it quickly manufactured? The source referenced by Wikipedia even calls it a "spare engine". Did they install the engine intended for a different airliner?
In general if the goal was just to have a non-operational engine on the wing, why not leave the failed no. 4 engine where it was? Or was there a risk of it falling to pieces during the ferry flight?

Here's another article from Oct 15th. They flew out a spare A380 engine. As of the 15th, it wasn't clear yet if this engine will be connected and running during the flight, or if it'll just be there to complete the airframe and act as a counterweight.

Leaving the broken engine in place would do more damage to the engine, complicating the investigation.

Pieces breaking off from the engine may have damaged the wing, the pylon or the connectors on the pylon (power, fuel, electronics etc.), they need to inspect for damage before deciding if the spare engine can be connected and running.

The plane will be empty for the recovery flight, so there's some margin to fly on 3 engines. They have to account for the possibility of an engine failure, leaving 2 operational engines, so the flight is planned to ETOPS rules.
There's a procedure to reduce the effects of asymmetric thrust.

If the engine is left off and windmilling, it needs lubrication, this may limit the length of the flight.


Is a pilot allowed to sleep during a flight? While in a flight, a pilot wants to sleep.  Given that the aircraft has an autopilot facility, are they allowed to sleep for a while (e.g., half an hour)?

What would happen if it's not allowed, but they still did it?  Would air traffic controllers know?

Airline flight crews generally consist of at least 2 pilots. One pilot is designated as pilot flying, the other is the pilot not flying, observing instruments and flight parameters. If required, pilots can use Flight Crew in-Seat Rest:

  Flight Crew in-Seat Rest
  This is the process whereby pilots may take short periods of sleep (naps), while temporarily relieved of operational duties in accordance with carefully prescribed ‘controlled rest’ procedures, when part of a two-man operating crew of an in-flight aeroplane.

This is not communicated to ATC and only allowed with two pilots present on the flight-deck. It is prohibited to have both pilots participate in in-Seat Rest at the same time.

See also these related questions:How do pilots rest on long-haul flights?
What if pilot feels too tired before his flight?


Is the airspeed for the minimum the same for the theoretical power required curve as for the shaft power required curve? I am aware that the efficiency of the propeller implies a difference in the values of the theoretical power required curve and the corresponding shaft power required, but does that efficiency correction change the abscissae of the respective minima...?

In this diagram (taken from von Mises' 'Fluglehre') the power is specified as 'Zugleistung', i.e. as the theoretical power drag (thrust) x velocity. All usual power required diagrams use that 'theoretical power'. My question is: If we took instead the shaft power, would the airspeed for the minimum of shaft power be the same...?

The OP is asking about power required, not power available, which, in my mind, would change the answer.

From an aircraft performance perspective, power required is the product of total aircraft drag and inertial speed ($P_R=TV$), applicable only for steady unaccelerated flight. Thus, the minimum of that curve is dependent on profile and vortex drag. In potential flow, it would be where $3C_{D_0}=C_{D_i}$ (see this answer for derivation).

Shaft power required is the power needed to be transferred to the propeller in order to achieve the aforementioned $P_R$. From the actuator disk theory, we know that it must be larger than $P_R$. The shape of this curve would depend also on the propeller itself (e.g. pitch, diameter, airfoil) and its control system (e.g. constant vs variable pitch). Therefore, the minima of the two curves do not have to coincide.

To illustrate this, I've gathered some RC propeller data from APC, which according to its website are generated based on vortex (potential) theory. The drag polar is based on a joke planform designed to accentuate the curvature of the polars:

$C_{D_0}=0.02$ (this is way too low for an RC planform)
$e=0.85$
$W=25lb$
$A=8$
$S_{ref}=15ft^2$

The figure below shows the power required (P_R) for level flight and the shaft power (torque * rotation speed) needed to sustain the level flight for a few prop configurations.


Why are twin engine airliners more fuel efficient than three or four engine airliners? It is said that given roughly similar aerodynamic and engine technology that twin engine airliners are more fuel efficient than 3 or 4 engine airliners.  Why is this?  The twin engine airliners tend to have more excess power so I'm thinking that they can climb faster and fly higher, lowering the amount of time spent climbing (uses more fuel than cruise) and lowering fuel consumption during cruise.  I suppose that fuel consumption is less while the engines are idling as well.  Are there other factors that go into the 2 vs 3 vs 4 engine fuel consumption issue?

Not a fully definitive answer, but a large part of the "efficiency" of an aircraft is drag and weight. Two (larger) round engines will have less surface causing drag than four smaller ones. In addition, each engine will add complexity to the aircraft (fire monitors, fuel piping, extra hydraulics) as well as necessitating duplication of things like thrust reverses, all of which add extra weight and sometimes drag.

So, all things being equal, one huge engine would be most "efficient". This would obviously be difficult, and impractical for most passenger jets, so when they will fit, without scraping the ground, two are used. If more thrust is needed, then they break it down into three or four.

(Note, the main reason 4 engines were used in the first place was for redundancy. At least one country's [US?] regulations stated that the aircraft must be capable of sustained flight, including climbing, with the loss of an engine. 2-1 = 50% thrust lost where as 4-1= only 25% loss, therefore requiring less reserve power)

*Edit note #2

"Twin engine airliners tend to have more excess power" they climb faster may be relevant in terms of efficiency, but part of the reason a twin will usually have more reserve thrust is due to the redundancy "keep flying" rules described above.


What would happen if the sole pilot dies while flying an aircraft? An aircraft is flying in cruise flight on a long distance flight. The autopilot is turned off. The only occupant of the aircraft is the pilot.

Suddenly that pilot dies, what will happen?

It has happened before that the single pilot lost consciousness while flying. What then happened is that the plane just went on until out of fuel after which it will glide down and skid to a stop (pilot survived). This is assuming there is no obstacle in the way.

Another example is the cornfield bomber, a fighter pilot eject and the plane still under power just kept going in a straight line and "landed" in a field.

A more deadly example is the helios flight 522. A mistake in the pressure regulation setting let the plane become unpressurized while climbing to cruise altitude. Both pilots lost consciousness and the plane's autopilot followed its programmed path following the waypoints and ending up in a holding patter until it ran out of fuel and crashed into the ground.

Survival depends on luck with obstacles, whether the plane is properly trimmed and which order the engines flame out in, asymmetric flame-out may result in a spin.


What was the first aircraft designed with a plug-system fuselage, and why? Nearly all modern transport aircraft are designed with a plug-system fuselage, allowing longer and shorter variants to be built by adding or removing plugs.

In addition, the plug system simplifies construction, as large sections of the aircraft can be assembled from modular parts.

What was the first aircraft to employ this system?

And what was the reason for adopting it in the first place:

to make possible the construction of variants
to enjoy efficiencies and economies of design and manufacture
both of the above?

This should be a Zeppelin. You said "aircraft", not "airplane", so lighter-than-air systems qualify also.

Already the model submitted with the patent application in 1895 (yes, back then the inventor had to demonstrate that the invention is actually implementable!) showed several cylindrical sections, akin to a train of cylindrical balloons. The final patent (Reichspatent No. 98580) was for a "Lenkbarer Luftzug" (dirigible aerial train). Adding more sections would increase length and payload.

Later, when the maximum diameter of Zeppelin airships was limited by the size of available hangars, their mid section was of constant size and allowed to add plugs to increase payload and range. This was, among others, the case with LZ 104 which turned out 30 m longer than initially planned.

The last big airliner not designed for stretching was the Lockheed Constellation. It had a continuously varying cross section from tip to tail.


Why don't helicopters always takeoff from a hover out of ground-effect? I've read enough crash reports to see that helicopters discovering too late in takeoff that they lack the power to fly out of ground-effect is a serious problem.

I am wondering why the following isn't standard takeoff practice: Establish positive climb rate out of ground effect before beginning any translational flight.  Failure to climb out of ground effect would be cause for immediate ATO, and there would be this nice landing zone to abort into!

(Only in exceptional emergencies, like when a mountain takeoff gives the rotor-craft a clear glide-path into denser air, would it be reasonable to ignore this procedure.)

(I note that I am assuming that translational flight out of ground effect is always more demanding than hovering.  I vaguely remember that this is not the case, but I don't remember why, and it seems counterintuitive since translational motion always establishes a retreating blade with lower lift that then needs a higher angle-of-attack and more power to maintain lift.  So if the helicopter can't climb under full power with no translation, it would not be able to once it tries moving forward.)

Forward flight is much more efficient than hovering.  As airspeed builds, lift increases from "translational" lift as the air moves more horizontally over the disc.  Since the relative airflow is more horizontal, the angle of attack for a given pitch angle is increased.

The vortices and turbulence move behind and down from the helicopter so undisturbed air is drawn over the disc to be accelerated downwards to produce lift.  Lift is more efficiently produced by accelerating a large mass by a small amount rather than a small mass by a large amount.

It is more efficient to remain in ground effect and slowly increase speed to gain translational lift than to increase power to HOGE (Hover Out of Ground Effect) and attempt to translate.

The problems you refer to are where an unwary pilot attempts to transition from HOGE whilst allowing the aircraft to climb or attempting to maintain height.  Without enough power, the loss of ground effect before the benefits of translational lift are gained will result in a rapid descent back to earth (as vortex ring state or settling with power is pretty much impossible to avoid) or you overpitch and drag the RRPM (rotor RPM) down so low that you cannot produce lift or even worse, stall the blades.

Bottom line, it takes more power to establish positive climb out of ground effect than to gain translational lift in ground effect.


What was the first monoplane airliner with a full cantilever wing (no struts)? By Towpilot - Own work, CC BY-SA 3.0, Image source

By the mid 1930s, the gold standard of airliner construction was achieved: the DC-3 was a full aluminium aircraft with monocoque construction and a cantilever wing. But which aircraft was the first airliner with a full cantilever monoplane wing, no struts?

I nominate the Junkers F.13. All metal, transport, and monoplane.

  It was the world's first all-metal passenger aircraft and Junkers' first commercial aircraft.

First flight was June 25, 1919. 322 were built for various military and civilian operators.

(Source)


Why are the best glide and best range airspeeds different for a C172? According to Cessna 172 POH the speed for max range with power off, or glide speed, is 65, and achieved at the best L/D ratio.
However with power on the speed for max range will be around 75.
Why is there a difference between speeds for max range with and without power?
Edit-
Is this because with power off we are just looking for the lowest point on the drag curve, and with power on we are willing to accept the increase in drag from speed of 65 to 75 since I guess lift increases more then drag between those speeds?

Maximum range depends not only on the variation of lift to drag versus airspeed, but also on the efficiency of the engine and propeller versus airspeed. The C172's fixed pitch prop, fixed ignition spark advance timing, fixed valve lift and closure timing and other characteristics all have effects on the miles per gallon attained at different indicated airspeeds along with the lift to drag of the airframe.


How to lose an aircraft? I've just read this article about the disappearance of QZ8501 and was surprised by the following statement:

  Even with automated beacons (we can assume these weren’t used, weren’t
  on board or were intentionally disabled) and EPIRBs, losing an
  aircraft is actually not that difficult.

Now, is it?

I was under the impression that if Breitling can make a watch with a 406 MHz distress beacon, a €70 million aircraft must surely be equipped with an automated ELT that can start to transmit automatically and whose signal can be picked up by [LE/GE]OSAR.

As it seems, US-registered civil aircraft are not required to carry 406 MHz ELTs while aircraft registered in Australia must be equipped with ELTs that operate on both 406 and 121.5 MHz (see the same reference).

Can you shed some light upon what is the current state of ELT regulations, how ELTs fitted to commercial aircraft operate in case of distress (automatic/manual?), what are the relevant regulations for EU-registered aircraft, and how can one lose an aircraft when all these systems operate?

I don't buy that “losing an aircraft is actually not that difficult” if all available technology is used (even assuming little redundancy and an adequate price range).

It is certainly possible to build an aircraft using modern technology that is hard to lose. After all, aircraft have GPS receivers and passengers can watch YouTube in the cabin. All you have to do is integrate those two and send the exact GPS position to a ground station as frequently as you want.

However, the global aircraft fleet is not so capable. Some aircraft have satellite internet capability; some do not. For those that do, the internet connectivity is completely isolated from the aircraft navigation systems. (After all, you don't want any possibility that an aircraft in flight could be "hacked" by someone on the ground.)

Retrofitting an existing aircraft (which could be up to 40 years old or more) to add such capability would be a very expensive job. Retrofitting an entire fleet (with perhaps many different aircraft models) is astoundingly expensive. Existing aircraft navigation and communications systems are so good that losing an aircraft "almost never" happens (yes, it's happened at least twice this year), compared to the number of successful flights. The airlines probably consider upgrading their fleet to support this kind of continuous surveillance not worth the expense, when compared to the probability that one of their aircraft actually goes missing.


Does FedEx use other airlines? I have an International Priority parcel being shipped by FedEx from Zurich, Switzerland to Perth, Australia.
Currently the parcel is located in Singapore, I presume with FedEx at Changi Airport.  It is scheduled to be delivered by 1700 on 09 October (GMT+8).  The parcel (tracking #771679606750) is showing in tracking at Singapore since 0636 05 October (GMT+8).
From what I can see on FlightAware and Flightradar24 there are no scheduled FedEx Express flights from Changi to Australia, at least up to Wednesday 07 October as I can't see past that date.
This raises the question given the parcel is scheduled to be delivered by 09 October (GMT+8), if FedEx uses other airlines for parcels, or for International Priority parcels?
Note that Sydney is the usual point of entry for FedEx, and Perth is a day's flight from Sydney, and another day for distribution at Perth.

There are regular flights between Singapore Changi and Sydney operated by FedEx Express. Here is a list of past flights from Singapore to Sydney (FDX9075):

(flightaware.com)
There are regular flights on Monday, Tuesday, Wednesday and Saturday. You can see that there was no flight on Monday, 05 October. This is likely because the aircraft coming from Sydney (FDX9077) diverted back to Sydney on Monday:

(flightaware.com)
I don't know the reason for the diversion, but as you can see, there is an MD11 enroute to Singapore right now. It is therefore likely that the same aircraft will depart Singapore back to Sydney later today as FDX9075, possibly carrying your parcel.
Update: Return flight is in the air right now:

(flightaware.com)

To answer your question about using other airlines:
Normally, FedEx does not use other airlines for international flights. They operate their own network of flights with their own airline FedEx Express. In these special times, it is quite possible that things have changed1, but I could not find anything official.
FedEx is however using a lot of other airlines for local transportation. They are called FedEx Feeder airlines. Wikipedia has list of them. They only operate regional aircraft (most of them ATRs).
1 Normally, a lot of air cargo goes on passenger aircraft (below the passenger deck). Due to the COVID pandemic, passenger travel is significantly reduced right now, which means more cargo needs to be transported on dedicated cargo aircraft than before.


How does wing bending relief of an a340 compared to an a330 allow it to carry 30t more fuel in a center section of nearly identical wings? From this question this reference in ymb1's answer states that the a340 and a330 have nearly identical wings.

Because of bending relief from the weight of its outboard engines, the bending moment of a four-engined aircraft is substantially lower than it is for a twin at the same maximum take-off weight. For the same fuselage weight, therefore, a twin needs a stronger, heavier wing than a quad.
It follows that, for the same wing, the payload carried in the fuselage must be less for a twin than a four, which is exactly what has happened with the A330/A340: the latter carries about 20% more payload. This translates to about 30t of extra fuel, giving the A340 its long-range capability and requiring the addition of a centre-fuselage undercarriage leg. Design strength required was "only 1% higher than the A330", says Jeff Jupp, BAe chief engineer, Airbus.

(Original: A330, A340)
The reference states that bending relief by having four engines instead of two is the reason 30t more fuel can be carried in a wing center tank.
How can moving 4t (per engine) outboard 10m create enough bending relief to add 30t in the center of the wing?

Short answer: they lied, it's 12, not 30 tonnes extra carrying capacity on the A340 due to being a quad.

How does an wing-mounted engine provide extra payload?

The weight (force) of the engine times the distance to the wing root is a torque (force * distance) that bends the wing down. The farther out the engine, the bigger this torque.

This downward torque reduces the upward torque (from the lift) experienced by the wing. You can think of it as the lift force from the spanwise aerodynamic center $y_{MAC}$ to the wing root -- more on that in a bit. So, if the plane is wing-limited (structurally), any extra bending relief will allow more weight to be lifted.

It was also why the 707 had better payload compared to the Vickers VC10 (its 4 engines are tail-mounted). The wings had to be built stronger (heavier), which ate into the payload (vc10.net).

  That is one of the reasons that especially the Standard VC10 is more expensive to operate than a 707, its structure is slightly heavier for the same number of passengers (25,7% of MTOW as opposed to 24,6% for the 707).

Does it really account for 30 tonnes?

No. It turns out Airbus was lying. But it does account for some.

The lying part first. According to John Leahy -- an Airbus exec of 33 years -- from a Jan 2018 interview on leehamnews.com (good thing you asked in 2018):

  The 330 was intentionally being held down in takeoff weight and performance because they didn’t want it to overlap the 340.

So, how much was engines and how much was being held back?

The A330 (and A340) like many jet-liners gain MTOW as they fly more. Small steps at first after design validations, then big steps after modifications. So in order to have a fair comparison, we need to go back in time.

The quoted reference is from 1991, but the A330 entry-into-service (EIS) MTOW was not 30 tonnes below the A340. That figure was based on the 1986 MTOWs of 204 and 232 tonnes for the A330 and A340 respectively (flightglobal.com).

(Graph: Airbus) A330-300 MTOW increase over the years. Note that the neo starts at where the ceo left -- at 242 with further development to reach 251 tonnes as announced in March 2018 (leehamnews.com).

As you see, the A330's EIS MTOW was 212 tonnes (a 20-tonne gap, not 30). Without major modifications it reached 217 (a 15-tonne gap, not 30).

Are the 15 tonnes due to the outboard engines?

Yes. First, back to the $y_{MAC}$. See: Where is the lateral position of the aerodynamic center?

Calculating it for the A330 based on its available plan view and ignoring the Yehudi gave me an 8.9 m figure (from wing root). Taking into account the complex shape would, I believe, move it farther inboard, giving the engines an even bigger edge -- so we are okay there.

The engine stations are at 6.4 and 16.5 m from the wing root. And the engines weigh 6.16 (Trent 700 on the A330) and 3.99 (CFM56-5C on the A340) tonnes.

With those figures, the A330 engines provide a downward torque (bending relief) of 39.4g kNm (per side). The more spread out A340 engines (but also each ~2 tonnes lighter) provide 91.4g kNm (per side).

By taking into account the 8.9 m $y_{MAC}$ and the higher 217-tonne MTOW, my results are:

11.67 tonnes of the 15-tonne gap are indeed due to being a twin and not a quad. The remaining 3.33 tonnes are likely due to my lenient $y_{MAC}$ -- moving it more inboard gives the engines more credit.

If you are wondering about the original 204-tonne figure, then they held back 16.3 tonnes (72.6g kNm per side). So the original statement should have been an approximately 12 tonne extra carrying capacity, not 28 (or 30) -- but they didn't want to hurt the A340 sales.

This was a lot of fun, and it's nice to see how the A330 EIS final gain (13 tonnes from 204) is close to my estimate.

Original 3-view drawings:
- https://commons.wikimedia.org/wiki/File:A330FAMILYv1.1.png
- https://commons.wikimedia.org/wiki/File:A340FAMILYv1.1.png


Why do Air Forces still use bombers? Something I have wondered about recently, since the advent of ICBM's what is the point of long range bombers like the B2? I understand they have longer range and can carry more payload but wouldn't they be easy prey for fighter jets or SAM's? Surely missiles are a much more attractive option. I don't get why the effort and expense goes into bombers?

Once you launch an ICBM, you're pretty much committed.  Even if there is a self-destruct on the missile (I don't know, nor am I making that claim.  Additionally, I think debris from such an act would be a big concern.).  A bomber also allows you to send something part of the way, and rattle your sabers in the face of the other party without again having committed to the act of the warhead being launched.  You can always recall a bomber without having to worry about a debris field or other unintended consequences.

As to the claim that bombers are particularly vulnerable, there are numerous ways they get around this.  For instance the B-2 employs stealth to get around this.  The B-52 can use standoff weapons to reach out to a target (such as cruise missiles or JASM).  Also, the B-52 can use low altitude routes to avoid radar and detection (if you’ve never seen a B-52 do a low level, I recommend you find a route and observe, it’s something else).  And on top of all that, the aircraft have defensive systems to help them on their missions (chaff, flares, RW gear, etc.).

Also, with a bomber, you can employ different types of weapons that give you a broader range of response options.  You can use bombs of anywhere from a 250lb laser/GPS guided bomb to something much larger.  These delivery mechanisms are generally much more accurate than a TBM (Theatre Ballistic Missile) or even an ICBM (InterContinental Ballistic Missile).  Those systems are generally inertially guided (some have GPS capability), which can lead to a larger CEP (circular error of probability), meaning that it may not hit exactly where you aim.  Those systems rely on a much larger warhead to get the job done than bombs from a bomber.  You don't use a Nuke to swat a mosquito, as a bit of military wisdom goes.  And, even ballistic missiles can be intercepted by systems such as the Patriot, so they are not a panacea against being stopped.


Why do IFR charts show TACAN paired frequencies when there is no collocated VOR? The image below shows a low IFR chart with a VORTAC on the right and a TACAN on the left. I understand the VORTAC is labelled with both VOR frequency and TACAN channel so that a civilian user could tune the VOR and a military user could tune the TACAN.
Why does the TACAN on the left show the frequency 112.3? I understand it's a paired VOR frequency, but if there's no VOR then why show the freq? My best guess is that perhaps a civilian user could tune 112.3 to receive DME information from the TACAN...

Your supposition is correct. Tuning the paired frequency will allow you to receive DME information from the TACAN.
If your DME tuning is through your VOR/ILS receiver, the VOR output will be flagged no computed data (NCD) as there's no VOR signal to receive.
The DME will tune the appropriate paired frequency and the DME should display normal data.
Having DME data alone is not all that helpful. However, if you have an FMS and a multi-channel DME, the FMS will tune the DMEs independent of (or in conjunction with) the VORs. This will allow the FMS to perform DME/DME navigation. That was the primary FMS navigation method until GPS came along. These days, DME/DME is a backup to GPS or GPS/IRS navigation.


Is it possible for more than one flight to have the same departure and arrival time slots? I'm working with real ATFM data such as the planned departure and arrival times of several flights within a given period of time, and I came across a surprising feature.

I found out that some flights have the same departure and arrival time slots. Taking into account that each time slot covers 15 minutes, I was wondering: is it possible for more than one flight to have the same departure and arrival time slots?

When I was working at the FedEx hub in Memphis the pushback times were scheduled every six minutes from 1:48 to 4:00. That's 22 slots for well over 100 flights, so there were several scheduled in each slot. They were set up so only one aircraft in any particular section of ramp would be trying to push back at the same time. There would always be a queue at the runway.


How are jet engines certified against birdstrikes? I recall that during US1549's birdstrike incident that resulted in it landing on the Hudson, a large amount of migrating geese weighing upto 20lbs each were sucked into the A320's engines — far bigger and heavier than previously certified.

I believe that at the time the engines were tested & certified by throwing small chickens or similar, one at a time, into the engines. Has this certification process been improved at all since this incident?

There are hundreds of tests that need to be performed for certification of a turbine engine.

The FAA requirements and tests are listed in CFR part 33 E and F.

Amongst them are:

Maximum static thrust tests
Vibration tests
Endurance tests
Water ingestion test
Hail ingestion test
Ice cloud test
Bird strike test

A number of them can be seen in this video of the GE90-115 Engine

The specific requirement for bird ingestion are described in §33.76. The number of birds to be used and their weight depends on the area of the engine inlet.

There have been several changes to the bird ingestion requirements for certification since the A320 engine was certified in 1996. However, once an engine is certified there is no need to demonstrate compliance to the updated requirements; the engine remains certified as it was.

The latest update to these requirements was in 2007, prior to the Hudson accident. To answer your question: no, there have not been any changes to the bird strike testing requirements of engines in the aftermath of the Hudson accident.


Where does the Departure End of Runway (DER) exactly begin? I am having trouble understanding the concept of Departure End of Runway. Most sources state that DER is at the end of the portion of the runway that can be used for takeoff (which, as far as I can tell, excludes the threshold at the end of the runway). But from the official FAA's Aeronautical Information Manual one can clearly see that DER starts at the "utmost" end of the runway (including threshold). Many other sources seem to support this, like this picture. Could someone point me to the right direction?

The picture you linked is from an FAA publication. As pictured the threshold is the end of the runway pavement, it is a thin line that separates usable runway from either taxiway, blast pad, grass, or an emergency overrun area. It is marked at night with a single row of green or red lights (depending on your direction). It can be displaced or reloacated from the original pavment but in this case it will have noticeable markings that include a well defined line marking the exact end. Some ends are usable for takeoff but not landing or vice versa but that is down to individual runways.

The paint bars near the threshold of an instrument runway are simply for visual reference to help indicate the width and length of landing zone during approach, they have nothing to do with takeoff or departure. VFR runways only have a number and dashed center line, no white bars at all.

To summarize: the threshold is a line not an area, it separates usable runway from non-runway, it may be marked with paint or lights but it can also simply be a change in surface such as tall grass to short grass. Standard departure obstacle clearance climb gradients are calculated with the plane at 35feet above the ground, directly over the threshold at the departure end of the runway.


Which is better a push fan, a pull fan or both intricate examination of modern by pass jet engines is despite where it is mounted, they use a pull fan configuration to generate thrust, which set up the most efficient, a pull fan or a combination of both on a single engine?

I would say pull fan, as that is what most engines use.

https://en.wikipedia.org/wiki/Turbofan

  Modern turbofans have either a large single-stage fan or a smaller fan with several stages. An early configuration combined a low-pressure turbine and fan in a single rear-mounted unit.

  Aft-fan turbofan.
  One of the earliest turbofans was a derivative of the General Electric J79 turbojet, known as the CJ805-23, which featured an integrated aft fan/low-pressure (LP) turbine unit located in the turbojet exhaust jetpipe. Hot gas from the turbojet turbine exhaust expanded through the LP turbine, the fan blades being a radial extension of the turbine blades. This aft-fan configuration was later exploited in the General Electric GE36 UDF (propfan) demonstrator of the early 80s. One of the problems with the aft fan configuration is hot gas leakage from the LP turbine to the fan.

So perhaps fans in front can use less expensive material since they don't have to contend with hot exhause temperatures.


In a Vmc demo, why is it important to lose 1 knot per second? I got asked two questions on my checkride:

Why is it important to lose 1 knot per second (approximately) in a Vmc Demo?
How do we know we're losing 1 knot per second?

My answer to question 1 would be be: because you are flying with one engine simulated inoperative and creating asymmetrical yaw, if you lose airspeed too fast you might blow past the stall indicator and actually stall the aircraft with a large yawing effect throwing you into a spin. Does that make sense?

For question 2, other than counting 5-10 seconds while losing 5-10 knots of airspeed is there any other way?

Why do we want to lose 1 knot per second in a VMC demo?

To more accurately determine where VMC is:
As Carlo Felicione's answer says, VMC changes day by day, and you want to determine it precisely.  You can't do that if you're slowing too rapidly.

To permit smooth control of the aircraft:
During a VMC demo, rudder required is determined by aircraft speed. The slower you go, the more rudder you need.  The more abruptly your speed changes, the more abruptly your rudder needs to adjust to compensate.  Since the point of a VMC demo is to determine when your rudder fails to control your heading, abrupt speed changes should be avoided.

To allow consistent control techniques:
Have you noticed that it's really hard to hold a particular vertical speed using the vertical speed indicator?  Usually, you select a pitch, hold it, and then reference the VSI to determine whether a pitch adjustment is necessary. The same is true of airspeed loss.  During a VMC demo, usually, the pilot will configure the airplane for engine-out flight and then pitch to an attitude that will create a 1 knot per second loss of airspeed. As pitch settings are fairly unchanging from flight to flight, this allows you to do the maneuver with more consistency.  You can put the rate of airspeed loss more or less in the back of your mind and concentrate on your rudder control, which is the point.

How do we know we're losing 1 knot per second?

Counting: As you say, looking at the airspeed indicator and counting seconds is a simple and reliable way to do it.

Known pitch settings: As mentioned above, pitch to a known setting and you'll get pretty close to 1 knot per second without the fuss of counting.  As you gain more experience this will become the way you'll do it.


Would it be feasible to use graphene in the gearbox of a large turbofan engine? What is the possibility or are the drawbacks of substituting graphene for metal in a gearbox of a geared turbofan the size of a Trent 900, given its strength properties(graphene), harder than a diamond, cheaper than a diamond and 10 times the strength of steel?  Previous answers here, on the reasons why large bypass turbofan engines cannot be fitted with gears for efficiency have alluded to torque vs metal gear strength with metal not being strong enough and net energy losses to heat

Well, just because it is stronger than steel does not mean that it is a useful structural material.  For example, the tensile strength of spider silk is higher than steel, but no one is building gearboxes out of spider silk.  For a graphene gearbox, the big challenge as I see it: graphene by definition is one atom thick. You aren't going to build a gearbox which is one atom thick. You can stack multiple sheets together to get something thicker, but the sheets will just slip against each other, so not useful as a structural material.  i.e. you can build a gearbox out of a big chunk of solid aluminum, but nobody tries to build a gearbox by taking 10,000 sheets of aluminum foil and laying them on top of each other.  What you would need is a graphene composite.  E.g. like we make carbon fiber composites today, which consists of carbon fibers held together by a polymer matrix.  Graphene composites are an active area of research, but I don't think they have reached the point where aerospace companies are considering them.


Is the "glass nose" Tu-134 design for easier conversion to military use? Early versions of the Tu-134 had a glass ('glazed') nose that is unusual for a passenger airliner. It was removed from the later versions.

Source: wikimedia.org

How probable is the hypothesis that this early design was for the easy conversion of Tu-134s into bomber? Glass noses are common in bombers.

Converting a Tu-104, a Tu-124 or a Tu-134 to a bomber only would had worked if there had also been provisions for a bomb bay. Including this in a pressurized fuselage would had incurred a severe weight penalty, so there was no easy way for a bomber conversion. This should make the speculation about dual use as a bomber moot.

However, there are several good reasons to use the glazed nose:

Easier conversion of trained bomber crews (trained on the Il-28 and Tu-16) for civilian duties. Remember that the Tu-104 was the second jet airliner in service and the only operational jet airliner worldwide between 1956 and 1958.
Operation as a military transport on improvised flights (where the better view of the navigator in the nose would help in visual navigation).
Civilian operation on flights on routes without navigation aids.

The last point is added by @JanHudec as a comment to this answer, but would exclude the operation on a scheduled service, because the aircraft would not be able to navigate in fog or at night.

Since the glazed nose was removed quite early in the production run of the Tu-134 (from the A-2 version on), it seems that the first reason (dual use of Tu-16-trained crews) is the most likely. While more than 1,500 Tu-16s were built, the Tu-104 (201 built from 1956 to 1960) and Tu-124 (164 built from 1960 to 1965) were relatively rare. From the Wikipedia page on the Tu-104:

  Pilots with previous Tu-16 experience transitioned into the Tu-104
  with relative ease


How do altimeters cope with varying lapse rate? How do barometric altimeters measure altitude above atmosphere datum if the laps rate of the pressure is not uniform, not constant? Imagine these lines representing pressure lapse rate:

560hpa
570hpa
580hpa
600hpa
700hpa
800hpa
1000hpa sea level

And so on. Now imagine your plane flying through these numbers vertically, and in your kollsman windows you set the datum line 1000 so, when you get lower (in numbers) the altimeter will read higher. Now when you’re passing trough the 500hpa pressure lines you can see the lapse rate is decreasing even if your climb rate is constant. My question is, does the altimeter misread your true altitude? Does the altimeter “think” it’s lower than what it is in reality, due to lapse rate?

Yes, but it doesn't really matter.

The error that seems to be an underlying assumption in your question is that you're treating the pressure altimeter as measuring altitude. It doesn't.

Rather, it measures the difference between the static pressure and a reference pressure (the latter being the "altimeter setting").

That difference is expressed as an altitude, but it really is a difference in pressure. It could just as well be expressed as just ρref−ρstatic, the value of which would also increase as the aircraft climbs, but that would be less intuitive (and likely less precise, if not necessarily less accurate) especially when close to the ground.

(This isn't much different from how an airspeed indicator doesn't really tell you speed, it tells you the difference between static and dynamic pressure, but the scale is such that this difference in pressure is expressed as a speed. That's why the ASI acts up when the pitot tube is blocked.)

To be airworthy, an altimeter is required to display the correct value to within some margin of error which I don't know the exact value of. Vertical separation is then chosen such that the minimum difference in actual altitude, given the same altimeter setting, between two aircraft is sufficient to ensure vertical clearance between them even if both have instrument errors that are maximally unfortunate.

IMC minimum safe altitudes are also selected in a similar manner, to ensure obstacle clearance even if the altimeter is maximally out of calibration.

Since every aircraft within an area is supposed to be on the same altimeter setting, or (above the transition altitude) on the standard setting of 1013.25 hPa, as long as everyone sets their altimeter properly, the errors will all be very similar and everyone at, say, "5000 ft" or "FL310" is flying at very close to the same static pressure level, even if that level doesn't correspond exactly to 5000 ft AMSL or 31000 ft AMSL. Thus, while you're correct in theory, it is not a problem in practice.


How can you calculate the gliding distance for a remote controlled jet? Is there a way to calculate the gliding distance for a remote controlled (RD) jet aircraft, in case of engine failure? We have some telemetry data on the model, giving us speed and altitude so as to plug them on an equation or other model in estimating the glide distance, but we would not want to actually risk destroying the jet by testing a real life scenario.

So, for example, our maximum allowed altitude is 500ft Above Ground Level and its speed is about 150 knots; we are interested in calculating the gliding distance if engine power is lost or cut off (the engine is automatically cut off if the jet flies outside radio control range).

I think the only way is to test it.

Choose a day with very calm wind.

Set the plane up for fixed speed anywhere between obviously-lower-than-best-glide-speed and obviously-higher-than-best-glide-speed, and make multiple tests with incrementing the speed in small steps (like 5kt). You can probably think out the details of the experiment yourself, but this should work well.

It's very difficult to compute these things. Companies like Airbus or Boeing have (probably proprietary) software for this, large clusters, etc., perform test in an aerodynamic tunnel and do many test flights. Since you likely don't have all the equipment, the only thing you can rely on is the test flight.


Why do flying wires hum louder in a sideslip? Page 50 of the Feb. 2021 issue of the EAA's magazine Sport Aviation reports that

Like any good vintage airplane, the Sea Bird likes to fly coordinated,
and the flying wires will sing out loud if the
ball
gets off-center.

Why would the wires hum or sing more when the airstream impinges from one side?
All else being equal, a sideslip converts some of the flow's transverse component to an axial component, from the wire's point of view.  (Like many airplanes, the Sea Bird's rigging is mostly parallel to the wing.)  That should reduce vibration, because axial motion in a wire under tension is hard to provoke: try bowing a violin with the bow nearly parallel to the string.

Here is one reason.
It once was common for suspension wires to be flattened rather than circular in cross-section, to reduce drag. those wires were then aligned with the airflow past the wing and fuselage in cruise. However, any time that airflow was not aligned with the wires, they would present an angle of attack to the slipstream and generate lift, which would pull them out of position, stretch the wires, and twist them to increase the local AoA. Then the wires would shed a vortex, stall (killing the lift), untwist, snap back, and then get pulled out of position again, etc., etc. and the result was the wires would "sing".
You can think of this as a special case of aerodynamic flutter.


Is it legal to land when an airfield is reporting low IFR due to fog with a visual approach? Suppose you are on an IFR flight plan and are coming in to land at your destination.

The weather at the destination is reporting 600RVR due to dense fog.  The fog isn't very high as you can see through the fog while on approach and can see the approach lights and part of the runway lights.  The weather above the fog layer is VMC. The lowest visibility for an ILS approach that can be executed by the pilots is 1800RVR.

Can the pilots accept a visual approach even though the airport is reporting IMC?
Are there other factors that should be considered on an approach like this?

A visual approach can not be authorized by ATC during true IMC.

  5–4–23 Visual Approach
  a. A visual approach is conducted on an IFR flight plan and authorizes a pilot to proceed visually and clear of clouds to the airport. The pilot must have either the airport or the preceding identified aircraft in sight. This approach must be authorized and controlled by the appropriate air traffic control facility. Reported weather at the airport must have a ceiling at or above 1,000 feet and visibility 3 miles or greater. ATC may authorize this type approach when it will be operationally beneficial. Visual approaches are an IFR procedure conducted under IFR in visual meteorological conditions. Cloud clearance requirements of 14 CFR Section 91.155 are not applicable, unless required by operation specifications.


What is the highest number of airliners shown flying together in a single photo? I was re-visiting this question about a timelapse photo of multiple airliners and started wondering about the maximum number of jetliners that could be photographed together while flying.  I have found cases of Airbus aircraft flying in formation for promotional purposes, (see 5 here  and 6 here) and I'm sure Boeing have done the same.  However I was thinking that a busy airport with a lot of aircraft in holding patterns waiting to land might provide an opportunity for more, even though they would be maintaining vertical separation.  Does anyone know of photos like that?
To be a little more precise in what I am asking for, I am looking for a non-edited photo showing the most airliners where the aircraft must be originally built to carry passengers commercially and must be flying (not one of the many reasons photos of planes in "storage" on the ground or stacked up for demolition)

The image found here shows 13 DC-3's in formation which were used as airliners at one point but these are in military livery in the photo.
Here is the kind of photo you describe but only 3 aircraft are in view. Keep in mind aircraft are generally turned onto the final approach path and only a few may be lined up straight off the runway at any given time.
The airbus operation you link, may be the biggest instance of passenger jets flying in tight formation.


Is it normal procedure to lower flaps at high altitudes? I was flying on a Boeing 747-800 today and the pilot opened up flaps at high altitude. This caused sharp descend for about 5 seconds ( Causing slight panic onboard ) , the pilot leveled the flaps again after about a minute and the aircraft became much smoother. Is it normal to use flaps like these or this might be an error?

What you saw and felt was the normal operation of the Speed Brakes.

Speed Brakes can also be called Spoilers. They are panels on the top of the wing which open up to create  drag and reduce lift. Some of the panels are also used for roll control.

They are often used in flight when ATC requires a steep descent or an immeadiate reduction in airspeed. They are also used in an Emergency Descent in case of cabin pressure loss. During landings they automatically deploy to increase wheel brake effectiveness.


Why don't turbofan engines have shrouds affixed to the fan blades? For a turbofan to be efficient the gap between the blades and the shroud has to be extremely small. Why don't we just attach the shroud directly to the blades and let it spin as one? Would that decrease the efficiency of the fan or is it just not structurally sound?

This has actually been done, at least on the CFM-56 series at some point.

The image is taken from here, the article is about the F108 engine which is the US military version of the CFM-56.
In newer versions of the engine the blade-tip shrouds have been replaced by mid-span shrouds as below (from Wikipedia), or have been removed.

As pointed out by Camille Goudeseune, turbofans have to accomodate a lot of situations, and a blade-tip shroud adds a lot of mass and therefore increases loads in the blade, further reducing fatigue life.
Among the advantages of this configuration that were not mentioned in the question or in the other answer is that shrouds help reduce vibration amplitudes through frictional damping. This explains why mid-span shrouds are still in play in several engines, while these do not participate in reducing blade-tip losses.
Finally, while this configuration is seemingly not used anymore on fan blades, it is still used in other parts of modern engines, specifically the turbine module.
As an example, the picture below is from the GE9X website, see the Low Pressure Turbine blades.


What are SIDS and STARs? I’ve been exploring the FMC(flight management computer) on the PMDG 777 and noticed that under the route section you can insert VIA and TO points. From what I’ve learnt this is where you would insert SIDs and STARs. What are SIDs and STARs? And how are they different?

Both are predefined routes through the air which connect the airport areas (terminal areas) to the enroute airway system in a way remotely similar to local roads that everyone follows from and to highways. This ensures (in theory) an orderly fashion of after departure reaching (SID) and leaving towards the airport (STAR) the enroute airspaces for all aircraft.

SID stands for Standard Instrument Departure.

STAR stands for Standard Terminal Arrival Route.

The links touch upon everything else.


What is the future for auto-pilots? What is going to change with auto-pilots on commercial aircraft in the next decade or so? Will airlines allow an auto-pilot to control an aircraft when it lands and takes off? Will we start using

A decade is not a long time at all.

What the future holds for the next decade is the new aircraft-ATC communication system, CPDLC. All of the focus is on that. Enabling data links between pilots and ATC is a hard prerequisite for any significant autopilot development.

It's very possible and likely that nothing revolutionary will happen in autopilots.
It's possible and likely that something more minor is going to change.

Some believe autopilots will get more sensor and control fusion. Still nowhere near full control. Others believe more manual flying will become standard procedure, to reduce the damage when the electronics fail and reversion to direct law is required.

No one knows that for sure, so it would be pure speculation. What is known is that autopilot development will not be the next decade's primary focus. For any major new system to fly passengers in 10 years, it would have to be in advanced testing stages already.


What is the table top runway maximum slope? What is the maximum permissible slope for a table top Runway (elevation 1600 m) to be made on hill top ?

Most Part-25 certified aircraft have an operating limit of roughly +/-2% for runway slope, as most of the runways fall into this category.

It would be probably possible to certify aircraft for steeper slopes, however at a significant cost, as the flight test program would have to be extended to collect sufficient data.

It is also worth mentioning that anything over 1% upslope requires a bit of a different flare technique as opposed to a flat runway. Usually a bit earlier flare with a bit late thrust reduction does the trick. Extending the limit beyond 2% would probably require additional training, as the flare characteristics would be significantly different than that at a normal runway.


What is an "all-weather" aircraft? I've read a few times that such-and-such a plane is an "all-weather" aircraft, for example:

  The McDonnell Douglas F/A-18 Hornet is a twin-engine, supersonic, all-weather, carrier-capable, multirole combat jet.

This is quite intriguing and a rather odd thing to specify.

A fighter that couldn't be operated in for example rain (perhaps because it might dissolve, rust or leak) wouldn't seem to be much of an asset to one's air force.

Similarly, I would not expect a supersonic fighter to be unable to deal with gusty winds, or a heatwave, or really, anything else the weather might be expected to throw at it.

What sort of jet would not be an "all-weather" aircraft?

“All-weather” is a little bit of a hold-over from the WWII days where severe weather was much more of a threat to the aircraft. Between less reliable engines, delicate and finicky instruments like artificial horizons, and limited anti-ice technology, flying in adverse conditions was much harder then. Becoming completely disoriented in low visibility was almost a death sentence.

Special planes were made with the sole purpose of fighting at night, and certain designs were better than others for all-weather operation.

Nowadays, world class military aircraft are all pretty much all-weather because of the 70 years of avionics, propulsion and airframe improvement.


How to decode this METAR published during huricane Harvey? I have the following METAR from the FAA Aviation Weather Center (AWC) website for KCRP (Corpus Christi Airport):

 KCRP 260551Z AUTO A2935 RMK AO2 SLPNO 6//// 402610239 53014 PWINO

A few questions:

How do we know what the altimeter setting is if the sea level pressure indicator is inoperative?
What does 6//// mean?
What does 402610239 53014 mean?

I suggest changing the title, else this question is of relatively limited interest: the METAR message for KNGP has been already updated with new values.

How to set the altimeter when the "sea level pressure" information is not available?

ATC will be able to provide the information. When aerodrome QNH is not available, the Regional Pressure Setting is used ("safe" setting for the highest location of the region).

6////: Group 6RRRR, 3- and 6-hour precipitation amounts

3- and 6-hour precipitation amounts are missing, sensor not operative or not reachable.

402610239: Group 4snTTTsnTTT, 24-hour max/min temperature in tenths degrees

Maximum temperature in the past 24 hours + 26.1 °C.
Minimum temperature in the past 24 hours + 23.9 °C.

53014: Group 5appp, hourly pressure tendency and and actual change in tenths hPa

Atmospheric pressure now higher than 3 hours ago. Decreasing or steady, then increasing; or increasing then increasing more rapidly.
Variation is 1.4 hPa

PWINO: Sensor status indicators (RVRNO, PWINO, PNO, FZRANO, TSNO, VISNO_LOC, CHINO_LOC)

Precipitation identifier information (rain or snow) not available.

See this decoder and this list of METAR abbreviations.


How does change in airspeed affect pitching moment? In aircraft with conventional elevator control, if I increase the speed, the horizontal tail sees higher velocity and hence higher lift. Does it mean that increasing airspeed creates nose down pitching moment (i.e. decrease in AoA) and vice versa ?

If So, it means if i want to increase the speed keeping altitude constant, the aircraft automatically gets trimmed at new trim AoA or i manually have to change the AoA using elevator?

How exactly do you plan to increase speed? You can add thrust. The aircraft is trimmed for a specific airspeed (normal flight assumed) so the added thrust will introduce a climb.

If you want to increase speed in level flight, you trim down (the engine power force vector rotating down, shrinking the vertical component and increasing the horizontal, so converting more engine power to forward movement and losing a little lift) AND add power to compensate for the lift loss.

It follows that there is an optimum: when there is no more vertical component, you cannot increase forward component of the engine force vector. But by that time the aircraft is already converted into a rock (no vertical force = only gravity = fall).


Is the “competent observer” a required crewmember? This question came up as a followon to another answer.
14 CFR 91.109 reads in part, with added emphasis:

§91.109 Flight instruction; Simulated instrument flight and certain flight tests.
(c) No person may operate a civil aircraft in simulated instrument flight unless—
    (1) The other control seat is occupied by a safety pilot who possesses at least a private pilot certificate with category and class ratings appropriate to the aircraft being flown.
    (2) The safety pilot has adequate vision forward and to each side of the aircraft, or a competent observer in the aircraft adequately supplements the vision of the safety pilot …

Is the “competent observer” a passenger or a required crewmember?

Yes, the "competent observer" is a required crewmember in that situation, by definition.

According to 14 CFR 1.1:

  Crewmember means a person assigned to perform duty in an aircraft during flight time.

Clearly, a "competent observer" operating as such under §91.109 (c)(2) is a person assigned to perform a duty in an aircraft during flight time; such an observer is therefore a crewmember. The operator is required to operate the aircraft with that observer performing their observation duties, and that person is therefore a required crewmember.

There are no other requirements as to who this person may or may not be other than the qualifying term "competent". The aircraft operator bears the burden of determining the observer's competency. One might argue that a certified pilot would be a competent observer.

An implied question here might be, is this competent observer a required crewmember that is able to log time for the performance of their duties? To this I would say, no, there is no provision in 14 CFR 61 for the logging of flight time for a person designated as an "observer", competent or otherwise.

EDIT to further explain the above paragraph in consideration of discussion in the comments: 14 CFR 61.51 allows pilots to log PIC and SIC time for flight in, among other conditions, "aircraft for which more than one pilot is required under the [...] regulations under which the flight is conducted". The "qualified observer" is indeed required in the situation in question, but need not be a pilot, and—unless otherwise qualified—is not acting as one of the required pilots in an "aircraft for which more than one pilot is required under the [...] regulations under which the flight is conducted". Obviously, if the person fulfilling the duties of a "competent observer" is otherwise also a required pilot, then the pilot may log the flight time as the required pilot.


Is the airspace at KUGN class G from the surface to 1200' AGL where class E starts when the tower is closed? The chart supplement for KUGN here says "AIRSPACE: CLASS D SVC 1200-0200Z other times CLASS E."

Does that mean that when the tower is closed, the class D airspace switches to class E surface area entirely, or is there class G from the surface up to 1200', and class E from 1200 up to 18000'?

SVC means Service, not Surface, that would be SFC. 1200-0200Z is a time range, that means the zone is class D between 12:00 UTC (that's what the Z or Zulu time means) and 0200Z, which would translate to 07:00-21:00 local daylight savings time in Waukegan. Basically, the tower is open during those times and then it closes so it becomes a class E zone, traffic would presumably use unicom if the airport is still open.

The zone is not defined in the sheet, you'd have to look at a chart to get the details on size, shape and how high it goes.


How to convert a pressure height (ADS-B) to a geometric height? As far as I know, ADS-B broadcast a pressure altitude, so I want convert it to geometric one. How is it possible?

e.g in MSG format: http://adsb-decode-guide.readthedocs.io/en/latest/position.html
which kind of altitude is there?

ADS-B gives both pressure altitude and geometric altitude.

In the position messages you will find the pressure  altitude which is essentially a pressure converted to an altitude. For this conversion the ICAO Standard Atmosphere is used.

In the velocity message you will find the difference between the geometric altitude and the pressure altitude. Since the difference between them is fairly limited a few bits could be saved by encoding the difference instead of the geometric altitude.

If you don't have the geometric altitude and you want to obtain it from pressure altitude (regardless where it cones from) you will have to know the relation between pressure and geometric altitude in the atmosphere.

You can model it according to the hydrostatic equations of the ICAO Standard Atmosphere and correct for actual temperature, lapse rate and local pressure. This gives fairly good results.

For higher altitudes data from meteorological models can be of help to improve accuracy.


Are there non-economic barriers to a 1000 passenger aircraft? I know the number 1000 is just an arbitrary number that happens to have some zeros in it, but is there any non-economic obstacle to making a 1000 passenger aircraft?

Also, assume normal-ish space-per-passenger constraints, so 1087 people on a 747 isn't really a 1000-passenger aircraft.

If money is no object, and we ignore terminal constraints, then no, there isn't. The A380 already supports 850 passengers in a single-class layout, and Airbus has plans to make a stretched version (the wings are designed to give room to stretch the fuselage without needing too much redesign). 1000 passengers isn't really that much of a stretch; we can basically get there now. The issue is that economic obstacles are very real obstacles to building planes; no one has a need for a 1000-person plane on any route (the A380 isn't even used today with max capacity, it's used to give lots of space to first-class passengers with a bit over 500 passengers).

There are certainly at least two airfields out there that would be able to handle a 1000-passenger A380; unfortunately, neither is a commercial airport (the two are Edwards AFB and the Shuttle Landing Facility; the SLF has a 15,000 foot runway that's 300 feet wide, while Edwards has a similarly-sized paved runway). However, if operation is uneconomical, you won't see anyone building a plane to do it.


What are the must-checks for purchasing an airplane? I've always dreamed of buying my own plane. Turns out, they can be had for $20,000 on eBay.  This sounds too good to be true.

What checklist of items are essential to prevent my new purchase from falling out of the sky?

There are plenty of great $20,000 aircraft out there - the hard part is finding them.

"What to look for" is an incredibly broad question, and varies substantially between different types of aircraft: You would not look for the same things on a Piper Comanche as you would on a Cessna 182.
Accordingly the first thing you want to do is find a mechanic who is an expert in the particular type of aircraft to help you check it out and do a "pre-purchase inspection".

Finding those mechanics is actually pretty easy: Look for a "type club" that supports the aircraft you're considering and ask them for recommendations (e.g. for a Cessna I'd talk to the Cessna Pilot's Association, for a Cirrus COPA, for most Piper aircraft the Piper forum, for Beechcraft Beech Talk, etc.

Talk to folks on those forums (and to your mechanic) about what you, as a buyer, should be looking at before you get the mechanic involved for the more detailed inspection. There are lots of things you as a pilot (even a student pilot) can determine just by looking at a plane (and/or the logbooks).

Some key items to look at before you go see the plane:

NTSB Records
Like Larian mentioned go to the NTSB site (or the equivalent if you're not in the USA) and search for accident records. Not every accident will show up in the database, but sometimes you'll find out that the cream puff aircraft being advertised has actually been "substantially damaged" in an accident. The NTSB database search is free and there's no reason not to do it.
Logbooks
All aircraft have logs, so if possible get a copy of them before you even go to look at the plane.
Read through the logs (yes, all of them): You'll find all sorts of interesting things in there, but what you're mainly looking for is good, consistent maintenance and regular use of the aircraft. As a secondary concern you're looking for major repairs (or significant minor ones) that you might want to ask your mechanic about.
FAA Records
You can request a copy of the FAA's records for an aircraft online for a small fee.  This includes registration information and any records of major repairs/alterations ("Form 337") filed for the aircraft.  It is generally an "interesting subset" of the logs.
This is something you'll want to have handy when your mechanic looks at the plane, though it's not something you need to have before you go look at it yourself. Theoretically the owner should have all the documents that this record contains as part of their records/logbooks, but in practice paperwork sometimes gets "lost".

If all that looks good it's time to look at the plane:

How is the overall condition of the aircraft?
Cosmetics can lie, so don't be dazzled by a shiny coat of paint and a nice interior:

Is the on-board paperwork (ARROW) all in order?
Are the tires, hoses, and other rubber components in good condition?
Is the engine bay (relatively) clean? Are there any leaks, drips, or other items of concern?
Are there obvious signs of damage (skin patches, dents, fabric tears, etc.)?
Are there obvious signs of corrosion (bubbles under the paint, etc.)?
Is the paint in overall good condition (no major chips, no cracks, no flaking)?
Is the aircraft itself clean?
(As much as cosmetics lie, a plane that looks like it's been neglected probably has been...)

Does the aircraft pass a very thorough preflight?
Go through the preflight checklist with an eye for anything abnormal -- ask yourself "Would I fly this aircraft today?".
If the answer is no, think carefully about why.
If the answer is yes it may be time to test-fly with the current owner.
Does the aircraft operate correctly on the test flight?

Do the engine and propeller operate properly?
Do all the instruments and avionics function correctly?
Does the aircraft fly well? Can you trim for hands-off straight and level flight?

If the aircraft passes all your checks it's time to turn your mechanic loose on it - they will inspect the aircraft for problems (major and minor) that you as a pilot might not notice which can wind up costing you a lot of money. This pre-purchase inspection (and the ensuing negotiation based on what the mechanic finds) is usually the last stop before handing over your money and taking the keys.


How do airplanes act as corner reflectors despite lacking significant flat surfaces in one of the three necessary mutually-perpendicular planes? One feature common to virtually all stealth aircraft is that they have vertical tails that are tilted away from actually being vertical (or lack them entirely).  This is said to be because the 90° angles formed by, on the one hand, the vertical tail of a typical aircraft, and, on the other, its wing or horizontal stabiliser, act as corner reflectors, reflecting incoming radar signals back towards their source and giving other people a nice bright return from the aircraft; having a non-vertical vertical tail, or no vertical tail at all, eliminates this effect, scattering radio waves away from their source and drastically reducing the aircraft’s radar cross-section.
However, a corner reflector, in order to function as such, needs three mutually-perpendicular flat surfaces (shaped like the inside of a corner of a hollow cube, hence the name) in order to reverse an incoming photon’s motion in the x, y, and z axes and send it back towards its source.  A reflector consisting of two perpendicular flat surfaces would reverse our photon’s motion in only two of the three spatial axes, sending it out on a track deflected 90° from its incoming trajectory, rather than the 180° necessary to return it to sender.
If we take an aircraft’s longitudinal axis (its roll axis, running from nose to tail) as its x axis, its vertical axis (its yaw axis, where you would stick a mounting pin through its fuselage1) as its y axis, and its lateral axis (its pitch axis, running from wingtip to wingtip2) as its z axis, aircraft, even non-stealth ones, generally only have flat surfaces in (or near) the xy (vertical tail[s], opened landing-gear and bomb-bay doors) and xz (wings, horizontal tails, canards) planes, or in other planes at least reasonably close to parallel with the aircraft’s x axis; aircraft tend to avoid having large flat surfaces in the yz plane, as these would create impressive amounts of drag.
So where does the corner-reflector effect of a typical airplane come from?

1: Think of the airplane as a giant butterfly being mounted in a display box.
2: For aircraft with highly-swept wings (displacing the wingtips forward or aft), or where the amount of lift produced by the secondary horizontal surface (horizontal tail or canard) is a large fraction of that produced by the main wing (requiring the wings to be displaced away from the aircraft’s center of mass in order to keep its overall center of lift close to the center of mass), the lateral axis may not actually pass through the wingtips, but this serves as a pretty good approximation.

A corner reflector is the most efficient way to generate a strong radar return from an incoming pulse. However, even if the plane has no corner reflectors in its overall structure, it will still generate a return because it is made of metal, and the characteristic impedance of the metal is sufficiently different from that of air to generate a reflection of the incoming electromagnetic wave. That reflection will not be collectively "aimed" straight back to the source is in the case of a corner reflector but if the incoming wave is strong enough and the radar receiver sensitive enough, the plane will still show up on the radar screen.


Is there an official FAA source for time zone of an airport? Looking at this answer, from TypeIA, to the question How to get timezone from airport code (IATA/FAA) .

This person is recommending the NASR database, which is good because it's official FAA stuff, but like other users I'm not able to find any information about time zone for an airport in NASR.

Is this information available via NASR or from any other official FAA source?

I do know that I can derive the information from lat/long etc., but what I'm looking for is the official FAA time zone designation for each airport, if such a thing exists.

EDIT: Sorry, to be clear, I'm looking for a digital version of this data suitable for use in a database or app.

Each airports timezone is listed in the Airport/Facility Directory. I think the FAA is starting to call these "Chart Supplements" now though. You can search for specific airports here but it looks like the results are in .pdf format. The value you want is circled in red here:

EDIT: As far as digital sources, explicit time zone information seems missing from the NASR airport (APT) data here. The next best thing is Latitude/Longitude it seems.


Are there regulations or adverse effects regarding Bluetooth in the cockpit? Are there any FAA regulations concerning wireless Bluetooth headsets in the cockpit of any aircraft? Moreover, I'm interested in finding out if the Bluetooth protocol (IEEE 802.15.1) will adversely affect any aircraft avionics in terms of radio interference or other Electromagnetic Interference (EMI). If anyone has any experience with this, thoughts and comments would be greatly appreciated.

There are multiple aviation headsets approved by the FAA that have built-in Bluetooth.

Based on that, I'm going to say that this has been tested and will not interfere with the aircraft avionics.  Radio/EMI testing is part of the testing that any device approved by the FAA for use in an airplane must go through.


Where is the aerodynamic center for an A320? Aerodynamic center, aka the Center of Lift or Center of Pressure. I would like to know where this is for an A320 airplane.

Sadly I don't know how to estimate aerodynamic things. I can do it for the center of mass, but when it comes to aerodynamics, I cannot simply find the geometric center of multiple arranged bodies, each one assumed to be uniform density. If anyone knows a trick or method of estimating the aerodynamic center, please let me know.

The location of the aerodynamic centre can be tricky to find in an existing aeroplane, it will shift as a function of speed, Angle of Attack, flap deflection etc. In the pre-design phase the aerodynamic centre is often taken at 25% of Mean Aerodynamic Chord, and since you draw a plan view of the aircraft, we can use this to get an approximation.

If the wing has straight taper over the planform, the MAC can be constructed like in the picture below. Then take the point at 25%: this approximates the location of the aerodynamic centre for one wing, the other side is identical of course, and aerodynamic centre of both wings is halfway the connection line of the two.

 However, like many transport jets, the A320 has a trailing edge sweep of zero next to the fuselage to accommodate the main gear. So the aerodynamic centre shifts a bit aft. You can construct it or estimate it, aerodynamicists may frown upon this. There are many sites that show the graphical method of the picture above (here's mine), because it is nice and simple. To illustrate the complexity of finding the MAC in other cases, here is a graph from the same source.

Update

The above method gets us the MAC, which is the first step in determining the AC of the aircraft. A further method for finding AC in the pre-design phase is presented in Appendix E of Torenbeek:

Find wing AC as above.
Wing/Fuselage pitching moment, Appendix E.7 This is sensitive to the pressure distribution and is therefore hard to predict, except for:

Forward shift due to fuselage sections fwd & aft of the wing, particularly the nose. Based on the ratio of fuselage lengths.
Correction for lift loss in the wing/fuselage lift carry-over according to DATCOM.

Fuselage pitching moment. Equation obtained from Munk's theory for near circular cross sections.
Nacelle contributions. Appendix E.8, cannot be predicted reliably other than by wind tunnel tests, only a statistical correction is given.

The above is used for determining the AC of the aircraft. The contribution of the tailplane is included in the lift equations since it is dependent upon the Angle of Attack of the aircraft.

The complete method including graphs and equations is too lengthy to present in this forum, and can be consulted directly in the referenced Appendix.


Where can the airspace boundary coordinates for Fayetteville TRACON be found? I would like a map depicting the airspace owned by Fayetteville TRACON that includes lat/long coordinates (i.e. not just a cartoon-y outline with no information). Ideally, I'd like to find a site whereby I can look up the airspace map for any ATC facility, but, for the moment, I'd like Fayetteville.

Any thoughts?

I will second @StephenS's image as the best you're likely to find with minimal effort. In fact there are a few of these images available if you do an image search for "FAA STARS TAMR" and I've included all of them at the bottom of this answer.
Real answer
If you need the specific boundaries you can submit a FOIA request. If you're a private citizen who wants the information for non-commercial use this should be free, but it may not be. Here is the FOIA form for the Air Traffic Organization FOIA Coordinator for the Eastern Service Area, which should be who you want. I would probably say you're requesting "A document showing the boundaries of Fayetteville ATCT center-delegated airspace" and that you think it would be found in the SOP and/or in the LOA with Washington ARTCC.
Alternatively, if you have a controller friend who's willing to do you a favor you could ask them to pull up the SOP/LOA for FAY from the FAA intranet next time they're at work. All facilities should have their SOPs and LOAs stored on a system that can be accessed at loa.faa.gov from behind the general firewall. This is probably against policy though, so they might not be willing to do it for you.
Unofficial but likely workable answer
The VATSIM community strives for realism, and from time-to-time submits FOIA requests to the FAA to form the basis for their SOPs and maps. The Virtual Washington ARTCC website includes a page of downloadable "facility files" that you can open in a virtual radar client in order to see the airspace boundary (by enabling the "VIDMAP" map). I have no reason to doubt this map's accuracy, as it looks quite detailed and appears to match the boundaries shown in the maps below, but there is no guarantee it is accurate or current.
To find the geographical coordinate of any given point on the map, you can type <F7>D* and click on the point. This shows the coordinate in what appears to be a hybrid Degrees Minutes.TenthsHundredths format. These coordinates must be defined somewhere in the downloaded "facility file" but I do not see a way to extract them on their own; you could get in touch with the VATSIM community to ask for the originals.
This method would probably work for any facility in the country, and although there is no guarantee of accuracy, airspace boundaries do not change often at all. It may be more time-effective to ask the various VATSIM communities for access to their FOIAed documents than to duplicate their effort by asking the FAA for each individual facility.
Interesting graphical history
An older map, still shows ARTS facilities. No date. FMH and ACK still separate. NMM is an FAA facility. JST not shown. Original

Map from September 2013. FMH and ACK still separate. NMM is an FAA facility. JST not shown. Original, 1620x1080. This is the highest-quality map of the bunch.

Map from September 2014. Very poor quality, hard to tell the differences from 2013. FMH and ACK still separate. NMM is an FAA facility. JST not shown. Original

StephenS's undated map. FMH and ACK have merged to create K90. NMM is an FAA facility. JST not shown.

Map from July 2018. This version shows ARTCC boundaries as well! K90 has been absorbed by A90. NMM is now run by the DOD. JST is a wholly new approach facility running airspace delegated by ZOB, located between PIT and MDT. The facility covering Edwards AFB and the R-2508 complex is now designated E10, "High Desert TRACON," instead of EDW. Also shown are the then-in-progress airspace consolidations (Section 804 or otherwise): MFR to EUG, YKM to PSC, MSO to GEG, RNO to SCT, BZM to BOI, GJT and PUB to D01, SJT to MAF, FYV to FSM, COU to SGF, LYH to ROA. Original

Map from June 2019. STARS is almost ubiquitous, with only two ARTS 2E and four ARTS 1E facilities left that I can see. Transfers of YKM to PSC, COU to SGF, and LYH to ROA are complete (as are the others from 2018, I think, but the arrows are still drawn because the airspace is not contiguous). MKG, MBS, LAN, and FNT have been combined into a super-TRACON at AZO now known as "Great Lakes Approach." Original

As of 2021, I believe there are no remaining ARTS facilities; all facilities are using some flavor of STARS. E10 is now JCF, "Joshua CCF." MFD and CAK have both been consolidated to CLE. PSC is being consolidated to GEG, taking YKM airspace with it. PIA and SPI are being consolidated to T75. HUF is being consolidated to IND. There are probably some more I'm not remembering.


Is there a tool or site where I can see wind vectors overlaid on a prognostic chart? I'm hoping to find a source where I can see wind vectors overlaid on a prognostic chart, to visualize how the wind moves around the pressure systems and fronts.

Curious if anyone knows of illuminating and fun weather data visualizations e.g.
https://earth.nullschool.net

Most pilots here in the states get their weather data from NOAA (The national weather service) you can find all of their charts on their site here.

Localized aviation weather is usually reported out of airports and can be found via their METAR's.

For visualization apps like Foreflight and Garmin Pilot allow certain overlaying of data onto a map (these are however paid services).