Do runways need some special kind of tar or protective layer? Do runways of the airports have some special kind of tar or protective layer to avoid the wear and tear in comparison to that of the Highways as they need to handle the much high pressure and the weights than normal highways?

Airport designers may use any type of material, based on construction research status and local meteorological conditions. Pavements may be flexible or rigid. There is no single technique to protect against wear and tear, and none specific to airports, this is similar to regular road construction.

Information on pavement types at Texas Dept of Transportation.
E.g. a rigid pavement:

FAA provides advisories to help designers. ICAO requires airports to report their pavement characteristics.

(source: Detroit Free Press)

FAA documentation related to pavement design:

Pavement Design & Construction
Airport Pavement Design and Evaluation

ICAO requires member states to report aerodrome-related aeronautical data, including pavement strength. The standardized method is known as the Pavement Classification Number (ACN-PCN) method.

As a critical characteristic of a pavement is the friction, this matter is refined in Measurement, Construction, and Maintenance of Skid-Resistant Airport Pavement Surfaces. This document includes data on rubber removal frequency, e.g.

Busy runway end:

(source: Bridgepoint Road Markings Ltd)

A technique for rubber removal:

(source: Waterblasting Technologies)

This thesis describes how to optimize runway pavements in order to increase friction and how to remove rubber deposit:

Optimizing Airport Runway Performance by Managing Pavement Infrastructure by Samantha Theresa Pinto. Note that:

  Rubber accumulation on a dry runway is generally not a problem since
  the rubber interaction between the aircraft tire and the rubber on the
  runway creates traction that may actually improve friction. However,
  in wet conditions, rubber accumulation leads to loss of friction on
  the runway by clogging the pavement texture and creating an especially
  slick surface with minimal drainage capability when the runway surface
  is wet. Additionally, rubber accumulation causing decreased friction
  values means pilots have less directional control of the aircraft than
  expected on a bare and dry runway.

Nothing special is needed for light aircraft.  Most don't even require a paved surface.  Western airliners  and military are happiest on thick concrete surfaces.  Most Russian airliners and military aircraft with their bigger wheels/tires can operate from dirt runways.


Why do fighter jets still have guns/cannons? I noticed that the "new" F-35 still has a GAU-22/A cannon installed in it -- albeit with only  182 rounds (more with ammo pods).

Why do fighters still have cannons? The day of dogfighting is long over, now it's just fire some missiles and forget.  Even if they expended all their missiles, 182 cannon rounds is only 6 seconds of firing  (I think the GAU is rated to 1800 rpm).

The only reason (and I'm not sure if I should answer my own question) is that they need something to shoot warning shots over the bow of another airplane. But that seems an awful amount of weight for this rare occasion. And it'd mean loading tracer rounds.

Or is just a vestigial organ, like the sabres on the side of full dress military uniforms?

The idea that missiles will be all a fighter aircraft needs was prevalent in the late Fifties. The McDonnell-Douglas F-4 Phantom II carried initially only missiles, but at the start of the Vietnam war this turned out to be inadequate. The long-range missiles back then were rather unreliable, and in a real conflict things turn out always different than anticipated. As von Clausewitz said, the plan is the first casualty of war.

F-4s frequently found themselves in close-combat situations for which they were inadequately prepared. Even today, a gun gives the pilot a lot more options, and if the situation is unclear, close-up visual inspection before shooting is still vital to avoid politically embarrassing situations.

From the F-4C on, F-4s were equipped with a gun. First in external pods, from the F-4E as an internal gun. What also helped to make the F-4 more effective was better training for pilots and ground crew, so the missiles were in better shape and better applied.

I would also suppose that cannons/guns would be useful against ground targets in certain situations, e.g. tanks or artillery installments.

For example, the A10 Warthog's bread and butter is its main cannon. Though this plane is primarily designed with the elimination of ground targets in mind.
(As someone noted the A10 is an attack aircraft. I'm merely noting this aircraft's reliance on its cannon for ground attacks as a justification for the above supposition. Fighter jets may occasionally be in situations where attacking ground targets is necessary.)


Is this plane landing or departing? I have a picture of Air Force One I took fairly up close several years ago.

Unfortunately, I don't remember if that was on arrival or departure.

Is there anything visible in the airplane's configuration (flaps, angle of gear?) that would indicate if this is arrival or departure?

The plane is probably taking off.  The flaps are hard to see but they don't quite look to be extended enough for landing (Looks like flaps 20).  On a 747 they extend to around 45 degrees (flaps 30, but they curve around more than that) for landing and have a huge, unmistakable profile.  Further, we know it's KBFI and we know the plane is on 31L from the photo.  Looking at the area we can deduce... (click for bigger)

...that the plane is about 3500ft into the runway proper, and 4500ft if we count the displaced threshold (and just off the ground) with the face of the southmost Jorgensen Forge building visible in the background (along with the green GA hangars).

At 3500-4000ft into the runway, hovering over the last markers in the TDZ, this seems quite late to be a landing.  It might be a very deep float, but I would expect more precision from an Air Force pilot flying the CINC around.  Air Force One is heavier empty, but probably overall lighter than a loaded 747-200 (and has powerful engines), so a 4000ft takeoff run for a light 747-200/VC-25 is sensible and probably more likely than an extremely late landing.
The flaps are more than minimum for takeoff, but seemingly less than normal for landing. Maybe 31L was running shortened that day?  Entry at B10 onto the displaced threshold would also give them an extra 1000ft - V1 just past the aim point and rotate near the end of the TDZ markers seems sensible enough.

EDIT
After running a series of simulations, it seems difficult for the VC-25 to be able to takeoff from where we see it, even when starting from B10. The VC-25 is 525,000lbs empty.  With only 100,000lbs load (fuel+people) it can takeoff by B5 at flaps 20, but only by lifting off below V2 (no wind).  This has to be a landing (confirmed by the newly discovered set of photos), but it is a very late landing indeed.
It also seems that military aircraft of the United States are exempt from the requirement to execute a missed approach in the case that they can't make the landing within the TDZ by DA/DH (using "normal" maneuvers), so perhaps the pilot just didn't care and bobbled it in anyway.  The plane did touch down in the TDZ, but just barely.

The absence of any smoke from the tires is reason #1 to suspect takeoff.

The flaps definitely aren't fully extended, but they're extended more than the minimum for takeoff.  This means that more analysis has to happen before taking the position of the flaps as definitive:

If the runway is short, both takeoff and landing would have more flaps than if it were long, and the somewhat intermediate flap setting there would make sense for takeoff, not at all for landing.  If the runway is long, you'd expect a lesser flap setting for takeoff, and the flaps shown might be reasonable for landing. Don't know what their practice is to always land full flaps or not.

Given the GA hangars in the background, I'll go out on a limb and guess that the runway isn't 10,000' long, and thus the flap setting is more appropriate for a short-field takeoff, rather than this being landing on a long runway.

Beyond that, the absence of spoilers isn't definitive, they take some amount of time to extend upon touchdown. Likewise, reverse thrust deployment wouldn't occur until the aircraft is definitely on the ground, so its absence in the photo doesn't drive any conclusion either way.

My best thought is, it's a takeoff.


Can you become FAA/TC commercial pilot with metal implants in hand? I have a friend who wants to be a pilot and he has metal implant in his hand. It doesn’t affect his hand movement at all. I know that he will need to check it out with a Civil Aviation medical examiner first before it can certainly be okay. The problem is he is going to have to travel to Canada or USA to study aviation and do his medical. He just wants to know if in general metal implants are a no go in aviation before he travels to start his process of becoming a pilot.
( yes it’s not a question for me it’s really for a friend... I am already a pilot)

The simplest way to answer this is to have your friend call an AME in the city they intend on training and ask them if they feel they will pass the required medical for a CPL. AME's are pretty forthcoming about this kind of stuff and they will often give you an idea over the phone if they feel there is a real issue. AME's are also the ONLY people that can definitively answer this question for your friend as they are the only people that can issue medical certificates.
Generally if the desired applicant has no practically limiting factors (in this case full use of their hand) the worst I would foresee needing is a Statement of Demonstrated Ability (SODA) which basically means they can show that they can execute the required actions of a pilot.
Under the Musculoskeletal section of the AME guidelines it states:

(b) No other organic, functional, or structural disease, defect, or
limitation that the Federal Air Surgeon, based on the case history and
appropriate, qualified medical judgment relating to the condition
involved finds

(1) Makes the person unable to safely perform the
duties or exercise the  privileges of the airman certificate applied
for or held; or

(2) May reasonably be expected, for the maximum
duration of the airman medical certificate applied for or held, to
make the person unable to perform those duties or exercise those
privileges.

If your friend can perform the duties of a pilot he should be ok.

There are no AME's who post here (as far as we know... maybe one posts incognito, but that's no help either).
The best you're likely to get is, "I know a guy who..." and whatever his result was. Will that match what happens with your friend? Who knows.
The question is different, but the answer is the same as on this thread. (I hate closing "as duplicate" questions that are different than the 'duplicate,' even if the answer is the same.)
For what it's worth, pilots routinely continue to fly after hip replacement, so by itself, having metal inside you isn't remotely a big deal.
Good luck to your friend!  (And, I am serious... and don't call me Shirley.)


Why do airplanes bank sharply to the right after air-to-air refueling? Whenever I see videos on YouTube they bank really sharply to the right after disconnecting from the tanker. Why wouldn't they do a more shallow 30-degree bank?

See this video for reference:

Fighter jets are very maneuverable, so they may make anything from a shallow bank to a breakaway maneuver. The breakaway is a standard way for fighter jets to exit a formation. It provides a way to safely and quickly gain separation from the other aircraft.

In this case the bank is fairly shallow, but when the aircraft disconnects they are already in a shallow right turn, so the total bank angle is a bit larger.

To gain as much seperation as quickly as possible.


Which fonts were used in old (1930s) aircraft cockpit displays and instruments? This is probably more of a graphic design question than aviation but maybe a few hangar rats around here know the answer.

What type fonts were used on the old instruments in aircraft from the 1930s like Lockheed Vegas, Electras, Beech Staggerwings, DC-3s, etc.?  I need it for a web site I’m working on.

I've seen a few times that even hand-written markings were used. This suggests that there hardly was any consistency.

  Photo from Darwin Aviation Museum:

Old Soviet aircraft had pretty standardised fonts, I believe. I shall try and find some to put up here. They were similar to COURIER NARROW but we'll have to see.


When may I change my transponder code to 1200 when being handled by ATC? When am I allowed to change my transponder code to 1200?
Is it after clearing the boundary of regulatory airspace (ie. airspace requiring radio contact and an operating transponder)?

ATC will tell you something like, "N1234R radar service terminated. Squawk VFR. Frequency change approved; good day" which you will repeat back as an instruction.
You do not change from the assigned transponder code until instructed.
If you're in a hurry to get away from ATC, you may request to terminate radar service as soon as you are out of their regulatory airspace.

Normally, as a courtesy, you terminate radar service by notifying ATC in a handshake as in Mortensen's answer. In most cases this never happens, because as soon as you leave their zone ATC will terminate service unilaterally--you don't have to ask for it.

If you are flying under IFR rules in any airspace except G, you must have a clearance and be using the code currently assigned to you under the clearance.

If you are flying VFR, you normally use code 1200. You can change to 1200 whenever you want, but if you previously had a clearance, you will immediately lose your clearance when you switch to 1200.

Therefore, the general principle is that you can switch to 1200 whenever you are flying VFR and do not require a clearance to be where you are. In class B, C, and D you are required to be in "voice contact" with ATC, which could be construed to require a handoff. In class E you are only required to be in voice contact if you are in the vicinity of a towered airport, in which case you have to be in voice contact with the tower (not ATC). So, basically what this means is that if you are in G or E (not near an airport) you can go to 1200 whenever you want. In B, C, D you should always do signoffs ("Cessna 5678 Golf terminating radar service"). If you are in an area that requires a clearance, you must get permission to terminate radar service.

So, your own statement is basically correct: once you leave a radio-contact required area, you are free to go VFR. Note that if you abandon a flight plan and go VFR without notifying ATC, even if you are in a radio-free zone, they can get miffed about that because it messes up their rack, so it is always a good practice to explicitly terminate your service/flight plan before switching to VFR and going numberless.

Example: You are flying VFR through a restricted military operating area and have a clearance to do so. You must stay on code as long as you are in the restricted area, because you require a clearance to be there.


How many serious airline accidents have been caused by design faults alone? That is, in the chain of events that led to death or injuries in an airline accident, how often has a design fault been solely responsible?

By a design fault I mean a problem such that even if the equipment:

were maintained and operated to the highest possible standards
flown in ideal conditions
by pilots who committed no errors
unaffected by manufacturing defects
endured no bad luck

eventually it would still inevitably eventually kill or injure its passengers.

I can think of only two examples: the early Comet's square windows, and the Boeing 737 rudder power control problem.

All the others I can think of include errors of piloting, manufacture, maintenance or just plain bad luck in the chain of causes.

Are there others?

The Douglas DC-10 - The door latching mechanism was not robust and the design of the safety indication was flawed. In the Paris incident Douglas tried to blame the handler who closed the bulk compartment door for using excessive force when latching the door but ultimately the design was at fault.

D-LZ129 Hindenburg, operated by the German Zeppelin Airline Company (Deutsche Zeppelin-Reederei).


Is it possible to fly backward if you have really strong headwind? Is it possible to fly a plane backwards if you have a really really strong headwind? I mean when you are aloft, you have positive airspeed and airflow over the wings but you have negative ground speed.

Yes, certainly! If your airspeed is lower than the speed of the headwind, the aircraft will fly backwards relative to the ground.

Example videos:

from ground (noisy, better turn down your volume)
from cockpit

However, note that headwind cannot cause a plane to fly backwards through the surrounding air. Constant wind does not affect airspeed.

No.  The question asks "Is it possible to fly a plane backwards...", to which the answer is no, for all conventional aircraft (those that depend on airflow over the wing).  Every answer including the word "yes" then goes on to talk about motion over the ground.  Why?  The aircraft is flying through the air and has absolutely no relation to the ground.  The question did not ask about ground motion.

For anything flying in a steady wind, there is no such thing as wind.  It is impossible for the aircraft to be affected by the wind, nor for any person or device in that aircraft to detect that wind, without an external frame of reference (observing ground motion, navigation equipment, stars...).  The ground is moving relative to your flight path, yes, but you're not on the ground.

In a steady wind: You are flying in still air.  The still air in which you are flying, is moving over the ground.


Why are military drones shaped so strangely? Military drones, such as the Predator drone or the Global Hawk, tend to have a weird shape with a whale-like head, and engines concentrated at the back. The wings tend to be of very high aspect ratio, and v-shaped tails seem to be popular:

Why aren't there, say, Cessna-shaped drones? If Cessna 172s work fine for human pilots, why not for computer pilots? The Cessna 172's low speed and stability also seems like a good asset for military recon drones.

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

Global Hawk cut-away drawing (picture source)

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

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

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

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

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

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

high aspect ratios are provided for recon activities like lockheed martin U3 which had aspect ratio of 15 but this types of manned aircraft, pilot should be very high skilled


Would jet fuel for an F-16 or F-35 be producible during WW2? I understand that different types of engines use different types of fuel, and as the description of the [jet] tag says, turboprops and jet engines use different types of fuel.

So if – like in the works of fiction The Final Countdown and 1632 – modern aircraft did find themselves in 1940, which aircraft would you readily be able to find fuel for? And which would you have to (re)develop the fuel for?

Let's take the following aircraft as examples:

AH-64 Apache gunship
Airbus EC 135 P2e
AgustaWestland AW101
Boeing 747 (whatever variant is most prolific today)
Lockheed C-130 Hercules
General Dynamics F-16 Fighting Falcon
Lockheed Martin F-35 Lightning II
Bombardier Dash 8

My assumption is that even the turboprops will not be able to use the aviation fuel available.

Which aircraft could have been fuelled "locally" first? And will any fly with 1940 aviation fuel, maybe with an additive?

Jet fuel is mostly kerosene, with some aromatic hydrocarbons mixed in for stability, temperature range and the like. You could probably run military jets on pure kerosene if they were magically transported back to WWII, but you wouldn't have to as it would have been possible to make reasonable jet fuel. The Jet-A standard was made in the 50s, and there were no major differences in the fractions available from WWII.

Before it was an engine fuel kerosene was primarily used for heating and lighting, and it was widely used across the world for that purpose in WWII. It still is in some places around the world where electricity isn't available. The aromatics in jet fuel aren't anything special, so it would have been entirely possible to make a jet fuel.

You could go farther back than WWII and still run a jet on raw kerosene as the modern process to distill it from petroleum was invented in the 1850s.

I doubt that could be done. Even though jet fuel is mostly kerosene, advancements in fuel production technology have focused on lowering the freezing temperature of the fuel, among other things. You could probably get the engine started on fuel made back then, but it would be difficult to keep the engine going at the altitudes aircraft like the F-16 can fly.


Do the engines still spool up when reverse thrust is selected, but the reversers are not deployed? The recent question When a large commercial jet touches down, is it committed to stopping? referenced the crash of Red Wings Airlines Flight 9268, which overran the end of the runway at nearly full touchdown speed due to failure of the reversers to deploy. According to the Wiki article, due to a crosswind, the aircraft touched down on only one of its main gear. Even once the nose gear was on the ground, the right main gear strut had still not compressed. The pilots selected full reverse thrust when the nose gear touched down. Since the right gear strut had not been compressed, the reversers were not deployed, however, the engines still spooled up, resulting in forward thrust.

I understand the reasoning behind not deploying the reversers when one or both of the main gear struts isn't compressed. However, it seems to me that preventing deployment of the thrust reversers should also prevent spooling up the engines for exactly the reasons that the Red Wings flight crashed. Applying full forward thrust when the pilots have selected full reverse thrust seems like a very bad idea to me.

I'm wondering whether this behavior is typical of modern transport-category jets. That is, would, for example, a Boeing or Airbus aircraft prevent the reversers from deploying, but still spool up the engines (as the Tu-204 did in this accident) or would they also prevent engine spool up when reverse thrust is selected while thrust reverser deployment is locked out?

Am I missing a reason why still spooling up the engines would be desired when reverser deployment is locked out?

Although not exactly the same thing you're asking you might be able to surmise an answer about Airbus from what happened in the crash of TAM flight 3054.

It was an A320 landing in Sao Paulo with a known inop T/R on the right engine. The pilots retarded the left thrust lever to idle to engage spoilers and then into reverse to engage left T/R but left the right lever in CLIMB. The autothrust turned off and due to the lever positions the left engine went into reverse thrust while the right engine went into full forward thrust causing them to veer off and overrun the runway and crash.

According to Airbus this had been a problem before so they changed the procedure for single T/R. It was previously to bring both to idle then only the working one to reverse. This was apparently confusing the pilots causing accidents so they changed it. The correct procedure is now to bring BOTH levers to idle then at touchdown, BOTH to reverse. Obviously if this is the procedure the A320 will not normally spool up the engine that did not have reverse thrust. The only reason it did was because the pilot left the right lever in the climb detent.

I'm not sure if this is true if the T/R's were PREVENTED from deploying due to the wheels not touching down but I would figure it would.

The way the A320 thrust levers work is that you release a catch then pull the levers aftward past the idle detent. (Not a pilot so correct me if I'm wrong here) Other a/c have a separate set of levers, for reverse thrust, sometimes hinged to the main thrust levers.

According to this illustration I found at this site the DC10 did have such a system to prevent the thrust to be increased until the reversers were deployed.

According to a BEA investigation report the B747 has a similar system:

  The thrust reverser mechanism is commanded by one lever located on each thrust lever. In the ground position and when the thrust levers are at idle, it is possible to pull the thrust reverser levers back to the "interlock" position which corresponds to reverse. This unlocks the reversers and initiates their deployment. There is blocking in the interlock position when the reversers are in motion or incompletely extended. The use of full reverse thrust is possible when the "in transit" lights are off and the "unlock" lights are on (see appendix 2) to indicate that the reversers are deployed and locked. (BEA site)

The behavior sounds exactly right, at least in theory. Once you touch down, there are two viable options: Either you perform a go-around (requires thrust) or you come to halt (which can be done with thrust reversers). Continuing at the same slow speed with the same limited thrust never is a good idea.


Why does centre of pressure (drag?) move forward when transitioning from transonic to supersonic? I am studying aerospace engineering at college and I am wondering why the centre of pressure moves forward when the aircraft changes from transonic flight to supersonic flight?

Also, is centre of pressure the same as centre of drag? I can't find anything on centre of drag but I've found loads on centre of pressure.

The center of pressure does not move forward when transitioning into supersonic flight, but back. Let me compare the pressure distribution around a sub- and a supersonic airfoil, and the reason should be obvious:

First subsonic flow, showing an Eppler 502 at a moderate angle of attack (3°):

And here is a rhombic airfoil in supersonic flow, copied from this answer:

While the pressure difference between upper and lower side is highest near the leading edge in subsonic flow and tapers off the more you move backward, the pressure difference between both sides is constant over chord in case of the supersonic airfoil. An uncambered rhombic airfoil is the simplest case: The pressure jumps up when the air passes through a shock and jumps down when it passes trough an expansion fan. In between, pressure is constant because the local inclination of the surface does not change.

As a consequence, the center of pressure is near the quarter point in subsonic flow and at mid-chord in supersonic flow (when tip effects are neglected).

Even in transsonic flight, when the local supersonic flow delays the pressure rise, the center of pressure starts to move back. This is the reason for the pitch-down experienced when accelerating above the critical Mach number which is called Mach tuck.

OK, now I forgot to mention the center of drag so far. It is of minor importance because the drag force is so much smaller than the lift force. The concept is the same: Sum up all drag contributions and find the point where a discrete force applied in the direction of drag has the same effect. While the center of pressure just sums up all pressure (and includes the portions which contribute to drag), the center of drag mixes both shear and pressure effects and looks at the fraction which acts in flow direction.

The Centre of Pressure is the point at which the lift acts on the wings of an aircraft (think about it as putting pressure on the wings to move it up)

The Centre of Gravity is the opposite, it is the point at which gravity acts on the body of an aircraft pulling it down. If you have a nose-heavy aircraft, then your Centre of Pressure is behind your Centre of Gravity (pushing the nose down and the tail up)

I have not heard of the Centre of Drag, but don't just assume that it's the Centre of Pressure as the Centre of Pressure relates to lift, not drag.


What is the best way to give ATC a position report using only a VOR (no DME or GPS)? While cumbersome, is it permissible when asking for a pop-up IFR clearance to state, at the intersection of WWW radial XXX and YYY radial ZZZ?

Obviously, during VMC, you have your pick of visual checkpoints, but in IMC, are there any better suggestions?

Additionally, if you are near a navaid or published intersection, and take a guess at your distance from it, how far off would your guess have to be before ATC wouldn't really even consider it helpful?

I'm going on the assumption you're operating in IMC (or perhaps VMC above a cloud deck) and have no reference to the ground. In a situation if you need a pop-up IFR clearance or ATC is requiring you to provide position reports for some other reason (non-radar, or your transponder is dead and they want to identify you but don't have time to issue you confidence maneuvers).
I'm going to further constrain the scenario with the assumption that all you have are "basic" IFR instruments (6-pack, clock, compass, and VOR -- no VFR/Handheld GPS, DME, or other fancy stuff).

The AIM has some guidance on this subject in 5-3-2, but the general idea is your report should be "as accurate as possible". For routine position reporting like you'd use in non-radar environments (where you're giving an estimate of when you'll reach a reporting point) they're looking for "within 2 minutes flying time" on your estimates in most situations, so you'll want to give your position with the same sort of accuracy.

In the case you describe, with no DME, GPS, or other precision tool for reporting your distance and bearing from a fix your the most accurate option would be to report crossing a published intersection, VOR, or other reporting point noted on your chart - it's the most definite "I am HERE" report you can give, and ATC will certainly know the location.

If that's not an option (ATC needs to know where you are right now, and you're not over a VOR or charted intersection) I would probably start by computing the distance using the intersection of two VOR radials (whether this is a charted intersection doesn't matter, though it would help if your report is relative to one): Break out your chart and mark the location, then take your ruler and measure the distance from one of the stations (or a nearby intersection along the airway you're using) and you've got your position "as accurately as possible".

If you don't have a chart or can't get signal from a second VOR for some reason it's time to work out a time/speed/distance problem in the air:
If you flew over ABC VOR 10 minutes ago and are now flying from the VOR on the 090 radial at 120 knots, and you've got a 20 knot headwind (which you know from the Winds Aloft forecast, updated with data from previous position and time/speed/distance computations) then you know you've traveled about 17 miles, so you're "17 miles from ABC VOR, on the 090 radial".

The time/speed/distance computation has a lot of potential error (winds not as forecast, for one), but sometimes it's your only option.

You don't say whether you talking about center or a tower. I would definitely never give a tower such a position. If I was talking to an ATCSCC, maybe in wierd scenario (broken transponder for example), but in all honesty it is the pilot's job to have charts and report position properly. Trying to get a controller to pull out a chart and compute your position is not a good idea, and I doubt they would cooperate unless it was an emergency.

In real life, what happens when you don't know your position, is that you would have the controller find you with radar, so you just say "Boston Center, Cessna November 54321", and center will answer "Go ahead November 54321", then you say "November 54321, what is my position?" and control will say "Ident", then you push a button on your radar transponder. This causes a "blossom" on the controller's radar screen and he can see exactly where you are. The controller will then give your position to you.

Note that this often happens even when you accurately report your position. So, for example, you might call in "Nashua Tower, Cessna one seven two November five four three two one, six miles west of water tower, maintaining three thousand five hundred, with information Romeo", then tower might say, "November five four three two one, ident", then you push the button. Then, they will know exactly where you are.


Can you be a pilot after being diagnosed with Generalized Anxiety Disorder? Went to my primary care physician who referred me to the psychologist. Went in for two evaluations. The only thing that had been written on my medical record was anxiety, no medications of any sort had been prescribed and the psychologist asked that I enrolled in anxiety classes in college (this was during my freshman year) I am a sophomore now.

Was wondering if this diagnosis of anxiety could prevent me from obtaining a third class medical, although it is not listed as anything that requires an FAA decision especially if no medication has been taken or prescribed.

The first thing is to determine if you were evaluated for anxiety, or diagnosed with an anxiety disorder.  Your primary physician's office can answer that because it will be in their records.

Often (not necessarily applicable in your case) symptoms which do not require ongoing therapy or medication may not have hard diagnosis.

Avoid assuming that you have a disqualifying condition.  Contact your physician and ask if you have that diagnosis.  It might help to explain why you are asking, specifically that you would like to fly and get an FAA Medical, so that they know the context of the question.

You might also want to read this FAA writeup on Item 47:

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item47/et/

As a final note, as an instructor I have had several students over the years who had serious, diagnosed psychiatric issues.  Most of them got effective help. A few became ineligible for a FAA medical. One refused to seek treatment as they were concerned about losing their medical. (I discontinued providing instruction, which aggravated the problem.) However, I know of no pilot or pilot wanna-be who had to take a class on anxiety or anger management, or personal relations, or similar to be denied an FAA medical on that basis alone.

In your case, the anxiety may have been situational, and developmental (as an adolescent) and clarifying whether you have a diagnosis (as opposed to just an evaluation) before you spend the big bucks for an AME exam would be appropriate.

The authoritative answer to your question can only come from an Aviation Medical Examiner - an AME, or "flight doc".  An internet message board is the wrong place to consider all the specifics of your history, and as far as I know we don't have any AME's who participate here.

My expectation is that the answer you'll get will be in the category of, "yes, provided that you accomplish the following..."  What tests, evaluations, observations, or whatever else that entails may range from very minor, to very lengthy & costly. From what you've written, I doubt it would be horribly difficult, but my opinion is from one non-MD guy on the internet, and it's worth slightly less than what you're paying for it.

If flying is something important to you, then you really owe it to yourself to get the authoritative answer from the only source whose opinion counts: make an appointment to talk to an AME.


What does the NCrit parameter indicate in a CFD analysis? When analyzing an airfoil in the XFLR5 software I am asked to input some data regarding the free stream. For this, a dialogue box pops up that has the following options:

One field contains the expected Reynolds and Mach numbers for the flow.

The other field says Ncrit. What is this parameter, and what does it have to do with the trip location (top and bottom) which can be inputted together with it?

The whole setting group is called transition settings, and refers to the boundary layer transition point (from laminar to turbulent).
The forced transition trip locations are exactly that, expressed as a fraction of the chord, for the top and bottom surfaces. They are akin to placing a trip strip at those locations.
The Ncrit value is a measure of free flow turbulence and is used to simulate the transition location when no forced trip location is given. XFLR5 uses the same method as XFOIL, which is an adaptation of the $e^N$ transition theory. Note this linear theory loses its validity at a fluctuation level of 1 to 1.5 percent, which corresponds to an N-factor of 6.9 to 7.3, meaning it is not suitable for highly turbulent flows.

As to what this is important for, the turbulent or laminar nature of the boundary layer affects flow separation and viscous drag. A turbulent layer will generate more drag, but separate at higher airfoil angles of attack.
Where this gets really interesting is at low Reynolds numbers, where a laminar layer will detach, but become reattached if turbulence is introduced into the airflow ahead of the airfoil, such as by a turbulator. It will then remain attached if the turbulator is removed, displaying a hysteresis loop. The same effect will of course occur in the opposite direction, with a barely attached turbulent layer detaching and staying that way if the free flow turbulence decreases enough to cause it to turn laminar.
I must note that this effect is confined to low Reynolds numbers, on the order of $10^4$.

In their first version Smith and Gamberoni concluded from a series of experimental results that an N-factor of 9 very well correlated the experiments. Their value for N=9 is in fact very close to the mean value of 7.8 and 10 as concluded by van Ingen. (...)
If the value N = 9 is assumed to be universally valid, we can “predict” transition for a new case by assuming that
transition occurs as soon as the calculated N-factor has reached the value of 9
(Van Ingen, 2008, p.8) Van Ingen, J. L., 2008, The e N method for transition prediction.
Historical review of work at TU Delft

American Institute of Aeronautics and Astronautics, 38th Fluid Dynamics Conference and Exhibit, 23 - 26 June 2008, Seattle, Washington


Can civilian aircraft fly through or land in restricted airspace in an emergency? This is a super hypothetical question of mine. I was wondering if civilian pilots who happened to be faced with a severe emergency could fly through or possibly request to land in restricted airspace? Mainly I am referring to Area 51?

FAR 91.3 states that any pilot in command may deviate from any regulation or rules to the extent needed to deal with the emergency.  That includes entering restricted or prohibited airspace.

In the example that you suggested, yes you could do so and land at the Groom Lake flight test facility at KXTA, provided you could reach their controllers or contact Nellis Approach Control declaring an emergency.  I will say that if you do enter R-4808 N and land there, don't expect them to roll out the welcome mat.  You will be immediately met by USAF Military Police who will arrest you, most likely at gunpoint, and spend several hours, if not days, there or outside the compound being extensively questioned by Air Force Security personnel, the FBI and Homeland Security.  Your aircraft will be impounded and inspected, possible indefinitely, and search warrants issued for your property.  If they find out that you faked an emergency to enter that compound, you are in very serious trouble and face a variety of federal charges including trespass upon a classified installation and whatever else the DoJ can throw at you.

In addition, you would need a very, very good reason to even be anywhere near Area 51, as it is in the middle of a military reservation geographically the size of the nation of Switzerland in the middle of south central Nevada.  There are no published routes over the airspace and all commercial and civilian traffic is kept far, far away.  Details about the airfield are not published on government aeronautical charts or regional A/FDs.  See the VFR sectionals and enroute charts below.

While Area 51 is a pretty extreme example, people have had emergencies and landed in military or other restricted facilities.  The usual response from the authorities is to detain and question you to determine what happened and inspect the aircraft to verify your story.  If it's a legitimate emergency, no harm is done and they will release you and the aircraft; the NTSB will file and incident report and that's it.

Yes they can if there's no other airport near the airliners reach. Lets say the plane has 2 engines fail on one wing that is counted as an emergency so they will need to land were ever it's safe to land.

The Hudson river landing is one of the best landings done by a pilot with 2 engine failure on both wings.


Can we show through simple geometry rather than formulae or graphs that the best glide ratio occurs at the maximum ratio of Lift to Drag? For an unpowered glider, can we show through simple geometry involving force vector diagrams, rather than mathematical formulae or graphs, that the best still-air glide ratio is achieved at the angle-of-attack that gives the maximum ratio of Lift to Drag?

Let's start with a Lift/Drag/Weight diagram, and draw the velocity vector as well:

Since no thrust is involved, Lift+Weight+Drag must sum to zero. Let's shift the origin of these vectors around a bit:

Now, let's finish the velocity triangle, drawing a (horizontal distance), and b (vertical distance). The ratio between a and b is by definition the glide ratio.

The key idea here is to notice that the triangles L-W-D and V-a-b are similar, that is, they are the same triangle up to a scale.
The similitude goes: W <-> v, D <-> b, L <-> a.
This means that the ratio between a and b is the same as the ratio between L and D. The latter is of course the Lift-To-Drag ratio.
So, in any condition, the glide ratio is the same as the Lift-To-Drag ratio.
It then follows that the best glide ratio is achieved for the best Lift-To-Drag ratio.

First a caveat-- please keep in mind that this answer is focussed on steady-state linear gliding flight.  Throughout this answer, when we talk about what happens when we change the angle-of-attack and L/D ratio, we're assuming that we've waited long enough for the glider to settle back into equilibrium at whatever airspeed is appropriate for the new angle-of-attack and L/D ratio.
All three of the vector diagrams below represent the exact same physical situation-- sustained, steady-state gliding flight along a linear flight path in still air. We've represented the aerodynamic forces in black, and the gravitational force-- the weight vector-- in green. The left-hand and right-hand diagrams are easier to understand than the middle diagram, because the force vectors are arranged into a closed polygon (a triangle in this case), which shows us instantly that the net force is zero. On the right-hand diagram, we've also included the airspeed vector, and its horizontal and vertical components.

Lift is defined as acting at right angles to the relative wind, i.e. the undisturbed apparent airflow created by the aircraft's path of travel through the airmass.  I.e. lift is defined as acting at right angles to the flight path through the airmass.  Drag is defined as acting parallel to the relative wind, i.e. parallel to the aircraft's path of travel through the airmass.
Note that K is the glide angle, and note that on the right-hand diagram, the triangle formed by the force vectors and the triangle formed by the velocity vectors are similar triangles.  This is why the still-air glide ratio -- the ratio of horizontal speed to sink rate in still air -- is identical to the ratio of Lift to Drag.
The still-air best glide ratio -- i.e. the best ratio of horizontal distance travelled to altitude lost in still air -- must coincide with the best ratio of Lift to Drag.
Note that in a steady-state glide, Lift is less than Weight by the same proportion that horizontal speed is less than airspeed.  For many calculations, it is a close enough approximation to assume that Lift and Weight are the same, and that horizontal speed and airspeed are the same.  However, our vector triangle is very sensitive to this distinction -- overlooking it forces our vector triangle to collapse into a straight line, which forces the sink rate to be zero and gives us a glide angle of zero, i.e. a glide ratio of infinity.
Also note that the geometry of the triangle is such that the maximum Lift to Drag ratio also coincides with the minimum Drag value, and the maximum Lift value.
Note that the minimum Drag value does not coincide with the minimum value of the Drag coefficient.  The Drag coefficient is minimized at very low angles-of-attack, i.e. at very high airspeeds.  So we need to be careful about what we mean when we say we want to minimize Drag in order to maximize the glide ratio.  This is only true when we are speaking about Drag as an actual force, not as a coefficient.  The same is true for Lift.  While (for reasonably high L/D ratios) Lift varies much less than Drag as we change the L/D ratio, it is still true that in gliding flight, Lift is slightly higher at the point of max L/D ratio than at any other L/D ratio.  But the Lift coefficient is not maximized at the point of max L/D ratio-- rather, it is maximized near the stall angle-of-attack.  Yet in spite of all this, it is an arithmetic fact that when we maximize the L/D ratio, we also maximize the ratio of Lift coefficient / Drag coefficient -- even though we are not individually maximizing either the Lift coefficient or the Drag coefficient.
Warning: do not mistake the right-hand diagram for an indication that to minimize the sink rate, we simply need to minimize the drag vector.  The force vector triangle and the airspeed vector triangle are geometrically similar, but  they are not identical.  As airspeed changes, the entire airspeed vector triangle scales up or down in size, while the force vector triangle is locked in size by the fact that the Weight vector is constant.  If we miss this relationship, we may tend to assume that the minimum sink rate airspeed must coincide with the airspeed for minimum Drag, which is also the airspeed for the maximum L/D ratio.  This is not the case-- as we'll see below, the airspeed for the minimum sink rate is lower than the airspeed for minimum Drag, which is also the airspeed for the maximum L/D ratio.
Every possible angle-of-attack of the wing is associated with a specific lift coefficient, a specific drag coefficient, and a specific Lift / Drag ratio. If we ignore effects due to changes in Reynolds number associated with changes in airspeed, we can make the approximation that the same angle-of-attack of the wing will always be associated with the same lift coefficient, drag coefficient, and Lift / Drag ratio regardless of whether the aircraft is heavy or light-- a change in weight is expressed as a change in the airspeed associated with any given angle-of-attack, but no change in the lift coefficient, drag coefficient, or Lift / Drag ratio associated with any given angle-of-attack.  If we increase weight, any given L/D ratio-- including the maximum L/D ratio-- will now occur at a higher airspeed.  The increase in airspeed will be proportional to the square root of the increase wing loading.
If the still-air best glide ratio occurs at the same angle-of-attack that gives the best L/D ratio, then it clearly follows that we can minimize the sink rate by increasing the angle-of-attack to slow down slightly, even if this degrades the the L/D ratio and the glide ratio a bit.  In other words, if we fly more slowly down a slightly steeper glide path, we can minimize the sink rate.  Obviously there is a limit to this process-- as we continue to increase the angle-of-attack and degrade the L/D ratio, then at some point well before we reach a full-blown stall, we'll reach a point where the increased steepness of the glide path is too much to be offset by the decreased airspeed, and the sink rate will start to increase again.
In fact, the highest L/D ratio occurs at the angle-of-attack that gives the highest ratio of Cl/Cd, while the minimum sink rate occurs at the angle-of-attack that gives the highest ratio of (Cl^3) / (Cd^2), which is also the highest ratio of ((L^3) / (D^2)) / airspeed.  It's clear that when we want to minimize the sink rate, we gain more by maximizing the lift coefficient than by minimizing the drag coefficient, so we should choose an angle-of-attack that is somewhat higher than the angle-of-attack for the best L/D or Cl/Cd ratio.  This means that the airspeed for the minimum sink rate is always slower than the airspeed for the best glide ratio in still air.
Vector diagrams like the ones included in this answer are surprisingly rare in books about soaring flight.  Materials published by the FAA sometimes attempt to include such a diagram, but they are invariably badly botched, with the length of the various force vectors altered so that they could not possibly form a closed vector triangle, thus eliminating any possibility for the reader to understand the relationship between the force vectors and the glide ratio.  (One might optimistically hope that they are trying to make the point that a glider is not always flying in a straight line with no acceleration?)  (See for example figure 3-1 on page 3-2 of the FAA's "Glider Flying Handbook" (2013) -- here they've even included a Thrust vector!)  Even a theory-rich book like "New Soaring Pilot" by Welch, Welch, and Irving (3rd edtion, 1977) is entirely lacking in any presentation of the Lift-Drag-Weight diagram for steady-state gliding flight.  However, see page 233 of that book for a "polar curve" clearly showing that the max L/D ratio occurs at a higher airspeed than the minimum sink rate.
A couple of additional notes--

Our vector triangles also show that the maximum value of (horizontal speed / sink rate) and the maximum value of (airspeed / sink rate) both occur exactly at the maximum L/D ratio, so we can also find the airspeed for maximum glide angle by looking at the plot of (airspeed / sink rate) versus airspeed and picking the airspeed where (airspeed / sink rate) is maximized or (sink rate / airspeed) is minimized.  Naturally, this will not be the airspeed for minimum sink rate.  The airspeed for minimum sink rate will clearly always be lower than the airspeed for minimum (sink rate / airspeed).

Occasionally one encounters a suggestion that the best L/D speed or the minimum sink rate speed has something to do with the point where Induced Drag is minimized.  The vector diagrams above demonstrate that as long as Weight is fixed, when we maximize L/D, we also minimize Drag.  So at the best glide-ratio airspeed, where the L/D ratio is maximized, Drag is minimized.  Since Induced Drag decreases with airspeed and Parasitic Drag increases with airspeed, it follows that at the point of max L/D -- i.e. at the point of minimum Drag -- half the drag must be Induced Drag and half the drag must be Parasitic Drag.  This is the only point where Drag can be at a minimum.  Clearly, the point of best L/D is cannot be tied to a minimum in Induced Drag or a maximum in Lift / Induced Drag.  The ratio of Lift / Induced Drag is highest at very low angles-of-attack, i.e. at very high airspeeds.

For more on L/D ratios and gliding flight and powered flight, see this related A.S.E. answer, and other linked answers-- 'Gravitational' power vs. engine power


Why might an airliner fly a large U-turn before landing? I was on a flight1 from San Antonio, TX to Toronto and, when arriving in Toronto, the plane went quite a way past the airport, made a big U-turn, and then landed. We were coming from the west.

I thought it might have been a need to adjust for the runway, but as I said, we went quite a way past the airport, meaning after the turn we had to fly "a little bit to get back to the airport". All that even before starting the process of descending for landing (if it was just a matter of adjusting the direction for the runway, what would be the need to keep the high altitude and go so far to make the U-turn?).

Does anyone know the reason? It seems that some flights coming from the west do that move.

Air Canada 7722, October 8, 2017 (history will not persist)

(flightradar24.com) Image shows the flight's route with a final left U-turn prior to landing.

Airplanes prefer to land in a headwind. This reduces their groundspeed compared to landing with the same tailwind.

Braking distance grows quadratically compared to groundspeed. So any significant reduction in groundspeed is worth having.

Successive airplanes should all come from the same direction to land. This removes any danger of collision when a plane fails a landing and goes around into what would otherwise be oncoming air traffic. Planes also prefer to take off into  headwind, so if takeoffs are intermingled with landings (very common in a busy airport) they won't interfere with each other if they all go the same way.

The tower monitors the wind and then decides which way the airplanes should come in to land and directs landing craft to land from that direction.

Although it felt strange to you, it is very common. For efficiency reasons, sometimes it occurs at large airports that aircraft land on a direct approach. But, in general aviation, what you saw is completely standard..


What is this device below the door of a 737 (and other aircraft)? The other day I made a question about the External Power Hatch. Now I would want to know what's that hole below the door.

That is the outflow valve. The outflow valve allows air to leave the pressurized section of the fuselage. The aircraft's pressurization system controls the valve to keep the desired pressure, balancing the air coming in through the bleed system.

Source

Looks like the potable water supply point.

Image from 737 Airport planning document


What happens if a language other than English is used over the radio? In many non-English speaking countries, communication with ATC may be conducted either in English or the native language. Famous examples are China, Russia, France and possibly Germany.

When a pilot who is a non-speaker of the native language hears such communication, which is he to do? Just sit back with no idea of what is going on?

During the 1990s I flew into countries on every continent except Antarctica. As an American English speaker flying U.S. registered airplanes, I never had a complaint that a controller had trouble understanding me, and I was always addressed in English by the controllers. Sometimes, though, I would have trouble understanding the controller's accent and would have to ask them to repeat their instructions.

As you mentioned, in some countries the controllers will address the pilots of that country in their native language. Personally, I always felt that compromised the smooth functioning of the system to a degree, because it denied a good bit of the overall picture of what was happening to the pilots who didn't speak that language. For example, if two airplanes preceding you are being rerouted for some reason, but you can't understand what they've been given (and which you're probably going to be given), you're not as prepared for the reroute when it comes through to you in English.

Even if controllers spoke to you in English, they would typically pronounce place names and fixes as they are pronounced in the native language. My first flights in France were a real problem in this respect. The French controllers were speaking good and understandable English, but the French pronunciation of the place names did not match our English rendition of the names we were seeing (and had never seen or heard before) on the IFR maps (no glass cockpits back then for us). In a couple of instances, we had to request that they spell the names, which didn't make us popular. On one occasion, when we made such a request, another pilot came on frequency and said, "He means ...." and gave us an English transliteration if you will of what the controller was saying.

Interestingly, the worst time I ever had understanding a clearance was one from a nominally English speaking controller. We were talking to Scottish control, and received a reroute into Amsterdam from a controller with a very pronounced accent (Glaswegian?). All I was able to get was that at the end he was turning us over to Dutch control and the frequency. I went over to the Dutch, and asked for them to restate what our new clearance was, and I apologized, explaining that I had been unable to understand Scottish control. His first words were, "That's okay, we can't understand them either."

I don't fly but I would guess it would be the same as computer programming.  The pilots probably learn a set of commands that ATC will give them, these commands will be a standard set around the world, so it won't necessarily be "English" that is spoken on the radio, more an international code language.

When I did amateur radio we had various Q-codes and number codes like 73's, 88's, QTH, QRZ - all these meant the same no matter which country you were from and that way we could speak to each other regardless of language, and it was it's own language known mainly by the amateur radio community.  I would guess that pilots have the same thing - for example in amateur radio the following would mean

1: QTH?
2: QTH Berlin"

1: Where are you?
2: I'm in Berlin

I don't know whether pilots use Q codes but I guess they must have something similar to this

Also there has been other things that have used these radio codes - for example the messenger service ICQ was named because the code for calling for a response on radio is to CQ ("Seek You") someone - "CQ, CQ, this is GW0AAA /MM calling CQ" means that someone with the call sign of G0AAA is in Wales on a boat of some sort and they're calling out to anyone who may be interested in having a chat (also the callsign gives you additional information about the person your speaking to - I assume pilots have similar things a callsign that starts G or M indicates that the persons amateur radio licence is from the UK, the second letter is used to indicate which part of the UK the person is calling from - England doesn't have a secondary letter but Wales has W, Scotland is M, NI is I, IoM (D), Guernsey (U) and Jersey (J) are also included even though technically they're separate from the UK with their own government) and the end bit also tells the person even more information - for example /M = the person is mobile, /T they're in a temporary location, /MM is maritime mobile, etc - but with all that extra information you don't really need to know English to work out roughly where that person is.

And finally with modern translation services and computer systems I would also guess that anything that comes through the radio now on a plane would also probably be sent to a screen on the dashboard, which has the ability to translate - just a guess but can't see why this isn't incorporated into planes (it is on Microsoft Flight Sim and that's supposed to be "As Real As It Gets!" - although I have heard that XPlane is much more real!) - and it wouldn't need to be a very big dictionary of words either for translation because there would only be a select number of phrases you'd need, your not really going to sit there and have a full on conversation with ATC are you - both them and you want to keep communication short and to the point because other people also need to use the radio comms.


Is it possible to detect a pitot static failure (blockage) of air data probe during flight and alert the pilot? Loss of static and pitot tubes affect the display of airspeed, altitude, vertical speed information. Loss of this information can  be catastrophic for flight. How are the pilots communicated about the failure of these ports (ex: when they get blocked). Or is there a system in place already that detects the blockage and unblocks it. Even if such system exists, what is done to ensure that pilot does not trust the airdata information displayed during the time when the ports are blocked?

The crew checks the pitots and static ports before the flight to ensure they are in good condition and not blocked by objects or insects. Pitot tube (pitot-static) can be obstructed in-flight. Static ports are less affected.

Detecting a blocked pitot or static port: This is not done, but is possible (e.g. send some air from the back of the tube in a pitot, and see if it can exit the tube at a normal rate (which is dependent on several parameters).

Unblock a blocked pitot: In some cases yes:

Melt ice or snow by heating the tube in flight, but the tube may be frozen for a minute from time to time. Some pitots are not heated and must be deiced naturally, which will be longer (while cruising in -50°C air, friction prevents aircraft skin to be cold. Concorde skin was about 100°C, meaning air friction just increased its temperature by 150°C).
Drain water using drain holes in the pitot.

Redundancy for pitots: Yes, two or three exist on most airliners.

Alert for blocked pitot: Not a direct alert, since a blocked pitot is not detected, but air data processors compare the different pressure values received from the different pitots, and in case of significant difference alert the crew and disconnect the automated units relying on pitot pressure (like the autopilot).

A message is displayed to emphasize that airspeed is unreliable

Dangerous? Yes because if the unreliability of airspeed is not taken into account by the pilot, then stress and inappropriate actions can occur because the aircraft is apparently not reacting to attitude changes.

AF447 disaster is sadly a perfect demonstration of the stress that can be generated.

If the crew detects correctly the situation, then there is nothing special to do, they just need to continue (manual control) at the same altitude and with the same aircraft attitude until the speed becomes reliable again.

I am working with a leading sensor manufacturer to introduce a system we call 'pitot guardian' using proprietary hardware and software we can detect blockages and alert accordingly in order to ease the burden on the flight crew. The method we use does not interfere with existing systems and can detect problems before start up as well as in flight, preventing aborted take off roll if, at 'air speed active' the cross check shows an anomaly, and giving flight crews more time to make the correct decisions should icing overcome ports at altitude.


What does a helicopter "gas prod" gauge measure? The beginning scenes of the movie "San Andreas" partly take place in a rescue helicopter. One of the panel gauges read "GAS PROD" above it. I googled it but didn't find much. Can someone explain what it does, and how it measures what's it measures? Thanks!

The instrument shows the gas generator rpm in the engine. It think you are referring to this scene (screenshot from youtube):

The Bell 412 in the movie uses a pair of Pratt & Whitney Canada PT6T-3BE Twin-Pac turboshafts, which are free turbine engines. The turboshafts used in helicopters consist of,

Compressor

Combustion chamber

turbine
and other components.

The gas producer (from which 'GAS PROD' came) forms part of the turbine. The gas generator forms the first stage that runs the compressor and makes the engine self sustaining. It also runs the oil and fuel pumps. As it is a free turbine, the gas generator stage is not mechanically connected to the next (power turbine) stage. From faasafety.gov:

The turbine section consists of a series of turbine wheels that are used to drive the compressor section and the rotor system. The first stage, which is usually referred to as the gas producer or N1 may consist of one or more turbine wheels. This stage drives the components necessary to complete the turbine cycle making the engine self-sustaining. Common components driven by the N1 stage are the compressor, oil pump, and fuel pump. The second stage, which may also consist of one or more wheels, is dedicated to driving the main rotor system and accessories from the engine gearbox. This is referred to as the power turbine (N2 or Nr).

In some cases, NG is used in place of N1. The gas generator speed is measured in the PT6 engines using a tachometer-generator mounted  on the engine.
From United turbine training Manual:

The tachometer-generator produces an electric current which is used in conjunction with a tachometer to indicate gas generator RPM. The tachometer-generator drive and mount pad are located at the 5 o’clock position on the accessory gearbox and is driven form the internal scavenge pump.

The short version is that in turbine helicopters they have a gas generator gauge.
Referred to as the "N1" gauge.
It's critical you monitor that gauge when starting, so that you don't attempt to start the turbine when it's internal temperature is too hot.

:)


Why is flying in a slip uncomfortable? It seems that flying a plane in a slip can make passengers uncomfortable.

What is it about that configuration that is unsettling?

A slip is uncoordinated flight and this shifts the effective gravity vector you experience.  Passengers in the back are also at a disadvantage without a visual horizon in front of them.  This can induce a mismatch between what the passengers can see versus what they are physically experiencing.  In some people this can cause discomfort and potentially vertigo.

Other discomfort can be psychological in nature that the airplane isn't behaving how they expect.  Passengers expect if a plane isn't turning that the wings are level.  If you are flying when the plane lands in a crosswind with a slight bank and touching down with one main gear, then the other main gear, many passengers will comment that the landing was incorrect because the main gear didn't all touch down together and the pilot was flying "sideways".  They don't realize the wind requires this technique and that the landing was in fact correct.  The perception of things not being right, however, can cause discomfort in some passengers.

Slipping a plane is a form of uncoordinated flight during such a case the plane is inherently unstable and more susceptible to turbulence as caused by unstable air.

Some of the advantages of coordinated flight are

  Coordinated flight is usually preferred over uncoordinated flight for the following reasons:

  Comfort level of the passengers (the seat of their pants won’t be going this way and that).
  Drag is kept to a minimum, helping to maximize the margin between actual air speed and stall speed.
  Fuel will continue to be drawn equally from tanks in both wings,
  especially important after a long flight when fuel level may be low
  (of course you planned your flight to land with legal reserves,
  right?).
  No cross controlling, no stalls, therefore no spins (bad, very bad).

To answer the question directly its the bumps that are unsettling however this is dependent on the situation. In calm air you, as a passenger would never know (but in calm air you really don't need to slip a plane). In a small GA plane where you can better see whats going on it may appear confusing on final approach the pilot is using heavy control inputs and the plane is moving straight (towards the runway that is)


In order to become a pilot, should an individual have an above average mathematical ability? I would very much like to become an airline pilot however maths has never been my strongest subject. Are most pilots mathematically adept or can I get away with being average?

In short, no.

To quote Patrick Smith, veteran pilot and author of Cockpit Confidential and the blog  "Ask the Pilot,"

  There's a lingering assumption that airline pilots are required to demonstrate some sort of Newtonian genius before every takeoff- a vestige, maybe, from the days when airmen carried slide rules and practiced celestial navigation...
  The basics are what pilots encounter. Routine arrival assignments require some quickie mental arithmetic.

So basically, it doesn't involve super complex math. You need to be able to do some moderate arithmetic and geometry, but nothing so complex that it can't be done, as Smith says, on

  my $6.95 calculator from CVS- the one flight-bag accessory more indispensable than an emergency checklist, aircraft deicing guide, or a bag of ramen noodles.

I actually am a licensed commercial pilot, so I can comment.

you need to be comfortable doing simple calculations, like estimating time
you need to be able to memorize a fair amount, including the navaid frequencies
you need to be healthy and able to reach all the switches and rotate your neck
you need to be able to tolerate sleep disruptions
you need to be able to focus and have confidence in your training and abilities.


Can someone tell me what kind of airplane this is? It says Capt Nungesser on the tail. I’ve researched him but can’t find out what type of plane this is. French?

The aircraft with the inscription on the rudder "Capt Nungesser" is the French aircraft "Potez VIII" 1922 model type, the second version, equipped with a 70 hp. Anzani engine.
http://www.airwar.ru/enc/law1/potez8.html
Here is one picture from that site:

Fairly certain it's a Breguet Br. 14

Do you have any other pictures, or a higher quality one?


Is there a method for calculating change in V-speeds with a change in weight for a Cessna 172? For example, what would the rotation speed (Vr) and stall speed (Vs) be at maximum takeoff weight versus flying with a single occupant? (2297 lb vs 1807 lb)

Instead of doing detailed calculations like you were in a jet, there is a useful rule of thumb advocated by author/instructor William Kurshner for working that out, which while not exact down to a fraction of a knot, is conservative and easy to do and is therefore perfect for regular GA flying.

Reduce Vs/Vr by half of the percentage of the weight reduction.  So if stall speed is 50kt at gross, and the weight reduction from 2297 to 1807lb is about 21%, and half of that we can round up to about 11%, your stall speed is going to be about 45 kt at that weight.

So if I was using say, 55kt as a rotation speed at gross (I seem to remember that's what it was on the 172), I'd use about 49 kt at 1807 lb.  Close enough for 99.9999999999% of normal operation in a Chevy Biscayne Of The Air like the 172.

There is no such thing as "Vr" in a Cessna 172. The concept of Vr belongs ONLY in jets. In a Cessna, you fly the airplane off when it's ready, and you do that by feel, not by numbers.


Why are 4 engine civilian turboprops not produced anymore As per subject why are 4 engine turboprops not produced anymore for civilian flights if turboprops are so efficient?

How comes the military still use them (see Airbus A400 and C130)

It would be amazing to fly on a 150 seater powered by 4 propellers.

What favours jet engines?

Well, military turbo-props are supposed to carry a large load at lower speeds, they wouldn't work well in passenger airplanes now because a jet plane can carry the same amount of passengers for a longer distance and faster than a turbo-prop can. However, they still use double-engined ones because they fly short, low-density routes to save money over using larger jet planes.


What would cause a non-zero indicated airspeed reading on the ground? What kind of failure would cause an indicated airspeed of say 200 knots on the ground (stationary)?

A mechanical blockage inside the airspeed gauge could prevent the needle from dropping all the way back to zero -- assuming the aircraft had exceeded 200 KIAS in the first place.
Whether this or the pitot-related failures in the @CamilleGoudeseune answer, the pitot-static unit, airspeed indicator, and altimeter (also connected to the static port) should be checked and repaired as needed by a qualified person.

If it was something a little more reasonable like 20 or 50 knots, it could be from a headwind.


Why do flight times differ between traveling East versus traveling West? Why does it take longer to fly East to West than West to East?
Which factors affect this?
Does Earth's spinning affect the time difference? Maybe the air circulation?

As Robbie's answer implies, the answer is wind - Trade Winds govern what happens on or near the surface and were historically important for sailing ships, and today in aviation we deal with the the Winds Aloft at whatever altitude your plane is flying.

As an example, consider two hypothetical flights at 30,000 feet with the winds shown below:

With these winds a flight from A to B (East-to-West) will be fighting headwinds the whole way. My handy flight planning program tells me that at 500 knots (airspeed) you'd be in the air for about 5 hours 30 minutes.

Traveling in the opposite direction from B to A you'd have a tailwind, and with the same 500 knot airspeed you would make the trip in roughly 4 hours.

The winds aloft vary seasonally, which can affect flight times for summer versus winter trips. According to one of our folks who is regularly up at those altitudes even the daily variations can be noticeable, and may make the difference between being able to make a nonstop trip or having to stop for fuel on the way.

Pilots and flight dispatchers will often review the wind data prior to flight and try to select an altitude that affords a "good ride" (free of turbulence) and favorable winds (either a tailwind or the lowest headwind they can find).

It is simple. The Earth rotates from East to West. There is hence an eastward shear effect in the atmosphere. If you fly East, this shear adds to the cruising speed. Reverse case if you fly west. So more time if you fly westwards. But how much more depends on the prevailing wind-shear. This cannot be pre-determined except when you actually fly and meter the wind speed.


How does one resume a VNAV climb in a B737 NG after being instructed to level off at an altitude below the Cruise altitude? I am referring to a Boeing 737NG.
Assuming I am on a VNAV climb but I am instructed by ATC to climb only to an altitude lower than my FMC Cruise altitude.
After leveling off, how do I resume my VNAV climb to my FMC Cruise altitude after I am cleared by ATC to do so?
I obviously have to set my FMC Cruise altitude in the MCP Altitude window, but as VNAV is already engaged from before ans is the active mode, will the aircraft start climbing automatically, or do I have to disengage and re-engage VNAV by pushing the VNAV button OFF and ON again?
Or, alternatively, do I have to press the ALT INTV button to resume the VNAV climb to my FMC Cruise altitude?

So your CRZ page shows your cruise altitude as FL 410, but you've leveled off at FL370, which is what's in your MCP Altitude window. Now ATC clears you to climb to 410.
You set 41,000' into the MCP Altitude window. At this point, your FMA vertical mode changes from VNAV to Altitude Hold. The light in the Alt Hold button is on, and the light in the VNAV button is not. To initiate the climb, press the VNAV button, and observe the FMA change from ALT HOLD to VNAV Speed. At this point, the autothrottles advance the power, the autopilot increases the pitch to maintain your FMC-computed airspeed, and you're climbing again.
The key is that when you initially leveled off at FL370, the FMA stayed in VNAV Speed, but as soon as you changed the MCP Altitude, the FMA changed to Altitude Hold. Thus, one tap on the VNAV button re-engages VNAV & you resume the climb.
Side note: why doesn't the FMA change immediately to Alt Hold when you level off at 370? While Boeing may have another answer, my best explanation is that if you change your cruise altitude in the FMC from FL 410 to FL 370 after you leveled at 370, you stay in VNAV, and the FMA just swaps from VNAV Speed (i.e. the climb mode) to VNAV Path (i.e. level-at-cruise-altitude mode). So at the intermediate level-off, it stays in VNAV, waiting to see if you'll reset the MCP altitude (to continue the climb) or if you'll reset the FMC cruise altitude (to make this your cruise altitude). In the former case, the VNAV button starts the climb; in that latter case, no MCP buttons need pressing.
Added:
The case where Altitude Intervention will start your climb is different: in that case, you're AT your FMC cruise altitude, either because you climbed there directly, or else you leveled off at an intermediate altitude and then changed your FMC cruise altitude to match.  The latter is NOT common practice, but there are scenarios where it could happen.
Either way, you're at cruise in VNAV Path.  Now ATC clears you higher.  So you set the new, higher altitude in the MCP altitude window.  At this point, the FMA still displays VNAV Path.  Press Altitude Intervention, and that changes the FMC cruise altitude to what's in the MCP.  With VNAV (still) engaged and your altitude below both the MCP altitude and the FMC cruise altitude, you'll get a climb.
The difference in these two cases is being at, or not being at, the FMC cruise altitude.  In the case discussed first, you're below it.  In the second case, you're at the cruise altitude.  In the first case, Altitude Intervention won't help you (because you're in ALT HOLD and not VNAV); pressing VNAV will.  In the second case, you're in VNAV, so pressing that button won't help you; resetting the FMC Cruise Altitude (either by entering it in the FMC via the CDU, or by pressing ALT INTV) will.
This stuff is complicated, and the manual doesn't generally do a great job walking through every scenario and "what if".  After you've seen it in the jet (or a simulator with good fidelity) a few (dozen) times, it makes much better sense.
I'm not aware of any 737 setup where anything varies varies from what I've discussed above, although if the Smiths FMC is replaced by something else, all bets are off.  There are some things that vary from one aircraft to the next (geometric path descent vs idle descent logic being one -- it's selectable by the airline), but nothing here, as far as I know, is in that category.
As far as simulators go, I can't speak to which ones have fidelity to what goes on in the real aircraft or not.  (The ones I train in are extremely accurate that way, but they're not running on a PC!)

It seems that there are varying software and it all depends on the specific FMC/MCP hardware installed.
See below:

ps://i.stack.imgur.com/iB5Bp.jpg


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.

Skyvector to the rescue!

You will find APP/DEP procedures, maps, frequencies, the whole nine yards!

EDIT:

Because it was stated in the comments, that SkyVector information is incomplete:

the charts show Fayetteville TMA and all instructions
The boundaries will depend on VFR, IFR and altitude, so you need to look at the charts
With the appropriate software to read it, you can download the AIXM files from the FAA, they hold the exact coordinates
the chart tells you, you are in Washington ARTCC
It will also tell you to contact FAY when you are 20NM out
the general information tells you the frequencies for APP/DEP


To what extent have political (race, gender, social class) attitudes been implicated as human factors in the cockpit? This question is related to:

How does cultural difference impinge upon human factors in aviation industry safety?
How have deep-seated cultural human factors (particularly in east Asia) in the cockpit been successfully managed in the past 20 years?

Standard industry practices of cockpit management can invert or disrupt very deep cultural and political expectations of command and authority.

The question

What evidence is there, in research, incident reports or other documented sources, that has identified political attitudes around race, gender or social class as human factors in the cockpit?

For example:

With more women in airline cockpits, have new human factors emerged (for example, a male pilot displeased to be questioned by a woman)?

In regions with troubled racial histories (southern Africa, the USA) have race relations and attitudes in the cockpit been responsible for incidents?

In cultures where social class or even caste is very significant, have these been implicated as human factors in the cockpit?

There are numerous accident reports that state cultural issues as contributing factors, especially respect for elders / superiours / social class in Asian countries leading to poor "Crew Resource Management" - typically the co-pilot failing to challenge the captain.

The first examples that come to mind are:

https://en.wikipedia.org/wiki/Korean_Air_Cargo_Flight_8509 - According to the Mayday episode, the captain was of a higher social class than the co-pilot.
https://en.wikipedia.org/wiki/Korean_Air_Flight_801
https://en.wikipedia.org/wiki/Air_China_Flight_129

As a aeronautics and space student, I can tell you that there are standards(especially US military standards) for the configuration of the cockpit.wethear the hight of the seat and the length of the arm( it is needed to know if the pilot can reach all devices without struggle). You are right, there are many different people with different body shapes and sizes. however, the aircraft manufacturers have standards and pilots who don't fit the standard have it a little bit difficult. Moreover, if you might notice military pilots are picked carefully to match the standard, since a pilot needs to fit in the best way to the plane so he will be focused on flight rather then comfot. To answer your question, there are no modifications special for race or gender, unless you build a  customize plane.


How do airlines train their pilots to deal with the stress of delays? There are some good answers here dealing with boredom during long flights and with the physical stress of piloting, and with what pilots to do during a delay. I'm interested in how pilots cope with the mental stress of delays.

Consider - you're flying home, you've been sitting on the tarmac for three hours with no idea of when you're going to be cleared to take off, and your child has a birthday party you really want to make. Another five minutes and you're going to have head back to the terminal because of the mandatory rest period; the tower starts to give clearance to the planes in front of you but they seem to be taking an interminable time to complete their checklists.

These are the sort of things you face as a passenger; luckily for most of us they're pretty infrequent.

For a pilot, however, they must be quite regular, especially on certain routes. And the added complication is that the temptation to rush or cut corners could lead to disaster.

Do airlines have specific training on how to cope with the stress caused by  situations where they will find themselves under time-sensitive / delay pressures?

Robert Hays under pressure in Airplane!

(My answer is limited to carriers based in the USA, things can be very different in other regions, many countries pay monthly salary and culturally have different view of company expectation verses safety expectation)
Pilots are paid per hour of block time, they are getting paid for all that time waiting on the taxiway after leaving the gate and starting an engine. The flight plan will usually include an extra hour or two for flying to an alternate airport if the weather turns bad at the destination airport, this is not commonly used with modern forecasting but it is part of the plan. So generally a pilot should not have a strong financial motivation causing delay stress. If a poorly timed childrens party is causing distraction then my opinion is that the company should consider strongly encouraging this pilot find a less safety critical career.
Pilots in the USA in recent years do tend to get a lot of general stress-management guidance during training, even a fair bit at the private pilot level.(depending on the school) Often this training is lumped under labels like "Human Factors" or "crew resource management", and FAA materials even include specific advice for avoiding situations just as described in your question they call it "get-there-itis". The free FAA materials tend to be a bit superficial but better than nothing in calling attention to a possible problem, industry training courses on the other hand have some good depth. This type of training has been growing since the late 1960s, but it got a large boost in the early 1980s after the 1977 Tenerife disaster where a KLM captain apperently hot to make up for delays started takeoff without full clearance and slammed his 747 into a Pan-Am 747 taxiing in the fog, just at rotation speed, killing over 500 people.

Most airlines do not give their pilots mental training. However, airlines may provide therapy sessions for pilots if they request for it, or decide that the pilot is not yet mentally prepared to fly. Pilots are also given mental screening. But other than that, airlines don't train their pilots for delays either because training is already too expensive, or they just don't expect that delays will happen.


What is the influence of yaw on P-factor? From William Kershner's “The Advanced Pilot’s Flight Manual”- page 2-17, P-Factor:

If the airplane is yawed, the P-factor effect is encountered. A left
yaw would mean a slight nose down tendency and a right yaw a slight
nose up tendency (you can reason this out).

Unfortunately, I couldn’t reason this out :(
Anyone care to explain?
Thanks!

As a starting point, you need to thoroughly understand why P-factor tends to make a left yaw torque (in the case of a clockwise-rotating prop, as viewed from behind) when an aircraft flies in a nose-high "angle-of-attack".  Note that by the aircraft's "angle-of-attack", we mean the aircraft's pitch "attitude" in relation to the flight path, not in relation to the ground.  Do you see how this increases the lift or thrust generated by the down-going half of the prop disk, and decreases the lift or thrust generated by the up-going half of the prop disk?  Thus creating extra thrust from the right side of the prop disk and making the aircraft tend to yaw to the left, in the case of a clockwise-rotating prop (as viewed from behind)?  If not, you might benefit from reading the section entitled "P-factor" from John Denker's "See How It Flies" on-line tutorial website.
Once you've digested that, you'll observe that for a mental "shortcut", we can model the effect of P-factor as follows:  think of the spinning prop as a solid disk.  Pick the point on the disk that is "tilted backwards" in relation to the actual flight path.  This would be the top of the disk in the case of an aircraft flying at a high angle-of-attack.  Now rotate your chosen point 90 degrees in the direction that the prop is rotating-- which for this explanation we'll assume to be clockwise, as viewed from behind.  So now you are looking at a point on the right edge of the prop disk, as viewed from behind.  P-factor can be modeled as an extra forward "thrust" or "push" applied to the prop disk at this point.  This will tend to make the aircraft yaw to the left.  Note that this has nothing to do with gyroscopic precession-- it's a purely aerodynamic effect.  This mental shortcut isn't meant to explain why P-factor occurs, just to quickly determine in which direction it acts.
Once you are comfortable with this "shortcut" for figuring out which part of the prop disk will be "loaded up" by the P-factor effect, consider that sideslip tilts the prop disk in relation to the direction of the flight path, just as flying at a high angle-of-attack does.  In a sideslip with the nose pointing to the left of the flight path (ball to the right, yaw string to the left), which part of the prop disk is "tilted backwards" in relation to the direction of the flight path?  The left-hand side.  So if the prop is rotating clockwise as viewed from behind, the P-factor effect can be modeled as an extra forward "push" on the top of the prop disk, and a decreased forward "push" on the bottom of the prop disk.  This will create a nose-down pitch torque.
Kershner could have been more clear in his language here, particularly in relation to his use of the word "yaw".  It's critical to note that we are actually talking about the sideslip angle here, not an actual yaw rotation rate.1  An actual non-zero yaw rotation rate creates a pitch torque in the opposite direction, through gyroscopic precession -- yawing to the left will pitch the nose up.  Just as flying at a high angle-of-attack creates a left yaw torque through P-factor, while pitching the nose down (as when a tail-wheel aircraft lifts the tail during the take-off roll2) creates a left yaw torque through gyroscopic precession. One effect is related to the aircraft's attitude in the relation to the direction of the flight path, and the other effect is related to the direction and rate of change of the aircraft's attitude in space.
Footnotes--

Clearly, the word "yaw" is often used in several different ways in aviation.  Most correctly, it refers to an actual rotation about the aircraft's vertical axis, but it's not uncommon to use it to mean essentially the aircraft's "yaw attitude" in relation to the "relative wind" or actual direction of the flight path though the surrounding airmass-- which is exactly the same thing as the "sideslip angle".  (The term "yaw string" is a classic example of this usage-- and the "yaw string" is sometimes also called the "slip string".)  When Kershner says "if the aircraft is yawed", you should read "if the aircraft is yawed into a sideslip or skid and then held there", or "if the aircraft is allowed to fly in slipping or skidding attitude".

Harvey S Plourde's book "The Compleat Taildragger Pilot" contains a great graph showing the individual and combined effects of all the different factors that contribute a left-yawing tendency during the takeoff roll in a tailwheel aircraft, from the start of the takeoff roll all the way to the moment of liftoff.  Different factors are dominating at different points in the takeoff roll.

It is like an helicopter. If it hovering in one place the blades will meet the airflow at the same angle. The forward speed of the helicopter make them to change their AOA(increase) for half of the circle of the rotating blades (the retreated blades)to compensate (bite more air for that) asymmetric vertical pulling . But the aircraft propeller  don't have swash plate to help with this so P- factor bites you. Means that the half of the disc will help you to have a roll rate better for leftside due to the Increased AOA to the one side of the propeller , but when you try to do it to the right side  must use more resources (force on the stick) and rudder That why it is take off trim for rudder @6 degree( angle-of-attack is more than in cruising. Hope you're understand the analogy. It is about the amount angle-of-attack of the propeller  for only half of the rotation when we put the nose up atitude (P factor). it is not identical. About the nose down attitude that came from the  aircraft wings. The yaw change the angle of  incidence for airflow meeting them(specifically if they are straight wings, not sweept)