Why do the engineers need to be on board during testing?

More and more data is collected in flight testing of aircraft. While 50 years ago they might have only designed for a small number of scenarios, the advances in computing allow them to design modern aircraft for thousands of scenarios. Modern certification standards include more and more requirements, which include flight testing for many of these requirements.

While some information is sent to the ground (like in this video), other information may not be. Airplanes in flight test have sensors for temperature, pressure, stress, and many other parameters located throughout the plane. These generate a lot of data, more than may be practical to send on a live data link. There may be several reasons that the engineers would want to analyze a lot of information onboard.

Some of the tests need to have multiple parameters coordinated with the pilots. If they are flight testing stall, for instance, they need to be sure they have flight parameters are correct for that test. The engineers give the pilots guidance on getting the airplane into the right configuration. The engineers also verify that the the information they collect is sufficient for the needs of the test. It's much more expensive to come back and realize they didn't get what they needed and must go back up to re-run the test.

Some of the data is also critical for safety. One subject of the tests is flutter. Flutter conditions can be very dangerous to the aircraft. The engineers help monitor the data and make sure that things don't get out of hand. If a data link were to be interrupted in a case like this, safety could be compromised.


Where can I find a list of rules of thumb formulas for navigation?

There is no short list but almost all the navigation information you could ever want can be found in this handbook published by the FAA. If you are worried about your nav computer failing you can always get an E6B which is about as close to failure proof as you can get. An E6B will expedite most most nav related calculations in the air (like headwind component). My E6B has some common nav calculations written on the back of it actually.


What are these four little things between the horizontal and vertical stabilizer on the B737?

The objects are vortex generators. In general, vortex generators serve to introduce turbulence which helps to prevent flow separation. More information here:

  This was to reduce elevator and elevator tab vibration during flight to increase their hinge bearing service life.

As mentioned on the site, you can see these on any 737 version from the original -100/-200 up through the NG. Better image from same site:


Why does an aircraft's nose tend to pitch downward at higher bank angles?

The answer is that the aircraft doesn't actually pitch down. When banking (or rolling) into a turn, the angle of attack (or the angle between the center of the wing and the flight path of the aircraft) stays the same. Assuming no correction to maintain altitude is made, the aircraft will continue on the same angle of attack, just banked over by some amount. Due to the bank, the lift produced by the wing is no longer vertical, instead, it is directly perpendicular (at least for our purposes) to the wings. Therefore, if the airplane is in a 30 degree bank, then the lift vector will also be 30 degrees from vertical. Doing some vector analysis, then you can determine that if the angle of attack hasn't changed the new vertical component of lift will be about 86% of what it was in level flight. Therefore, the plane would begin losing altitude. This altitude loss is what you see as the airplane pitching down.


How to leverage Lynx NGT-9000's integrated GPS/WAAS?

Sorry, but windmills approach certified GPS systems do not work that way: A GPS approved for IFR navigation and approaches, like a Garmin 430W or GTN650 or an Avidyne IFD440, are more than just an approved position source such as what's included in the NGT-9000 transponder. They have an approved navigation database and interface with (or provide the equivalent of) a Course Deviation Indicator (CDI).

You can't just suck position data out of the NGT-9000 and fly around using it because while that device has an approved high-quality position source it doesn't have an IFR-approved navigation database, so there's no way to take that GPS data (your position as a point in space) and relate it to known waypoints (VORs, NDBs, airports, intersections, etc.) in a way the FAA considers satisfactory as a primary means of navigation.

You can take the GPS data from it and interface it with an iPad - Foreflight speaks the Lynx L3 language - to use for enhanced situational awareness, which is a huge win, but that's not enough to get you to file GPS flight plans: You would be limited to filing flight plans based on your other installed primary navigation instruments (VOR, ADF, DME).


How to tell the difference between METAR and SPECI reports?

I don't think you can use METARs to produce precise hourly rainfall data. METARs do not express the exact amount of precipitation; rain is only expressed in three categories (light, moderate, heavy).

The way I understand your problem, you want to skip SPECI reports because you only want a single report per hour. A better way of doing this would be to use the time/date stamp in the report and simply dismiss a report if you already have one from the same hour. Say you have a report from 011203Z and you then receive another report from 011220Z. You want to dismiss the last report, because it is only 17 minutes older than the first one.

Alternatively, you can find METARs from a number of other sources, which include the message designator as well. Here is one I find useful: http://www.ogimet.com/metars.phtml.en


Has a life raft ever been successfully deployed on a modern commercial flight?

Passengers used rafts to get off the plane; news.com.au
Miami Air Flight 293 (3 May 2019)

More than 140 passengers have managed to escape from a plane crash as a Boeing 737 jet slipped off a runway and into a river. (news.com.au)

There is a list on Wikipedia for water landings, not counting non-jet and not counting overruns, and by checking photos, it seems none used cabin-storable-rafts. The accident shown and linked above is a runway overrun (although it was not excluded from the criteria listed).
This article also confirms the rafts came from inside:

Eric and the pilot wrestled one of the six life rafts out the forward cabin door, down the evacuation chute [i.e., slide] and into the water.


How do pilots determine the takeoff distance of an aircraft?

Most airplanes have a POH (Pilot Operating Handbook) with a table on aircraft distances.  Here I have included one for the C172.


Why are the minimums between these two ILS instrument approaches to the same runway so different?

The equipment requirement (in the aircraft) are different for each of these approaches.  In the upper-left box of the Z approach, you can see that DME is required to make this approach.  This requirement is not listed in the Y approach.

If your aircraft has the right equipment, you can reduce your minimums by selecting the appropriate approach plate.

In this particular case, the missed approach procedure from the lower minimums is more precise. The procedure includes DME distances that must be used while executing the missed approach procedure.  Without DME onboard the aircraft, you would have to use the less-precise missed approach procedure requirements of intersecting VOR radials. This lack of DME, and thus a less-precise procedure, results in higher minimums.

In Section 4, para. 140 of the TERPS, the reason for multiple approaches to the same runway, using the same navigation system (ILS in this case) allows better-equipped aircraft to gain an "operational advantage".


What is the effect of thrust vectoring effect on the rate of turn?

The standard equation applies to any coordinated level turn (so that the G felt is "straight down" to an occupant of the aircraft, in an aircraft frame of reference). Matters not how it's all achieved - flaps, high-lift devices, helo rotor, thrust vectoring, whatever... a coordinated level turn at "this" bank will take "this" much radius. And it will have a calculable G load.
Actually achieving (and sustaining) that G load may take all sorts of interesting effects, such as thrust vectoring. But once you're there, the standard equations apply.
And, if you choose to fly an un-coordinated turn, with some amount of side-loaded G force (example, a car turning at high speed... no appreciable "bank angle" so the G force pushes you toward the outside of the turn), then all the standard assumptions are out the window. At that point, your radius would be a function of G & not bank... and it'd get uncomfortable really fast!


What is the proper phraseology for a clearance with a named obstacle departure procedure?

Items in parentheses on these charts are not said when referring to them by name. It's the same for other departures/arrivals that are RNAV, and for approaches that may be GPS or RNP.


What is prop RPM control logic on PC-12?

You effectively have a two speed prop (kinda like the 2 speed Power Glide automatic transmission on my first car, a 1964 Pontiac - well, not really).  It's controlled by software, and there is a 1700 rpm high rpm and 1550 rpm low rpm mode, and that's it.
The PC-12's PT-6's FADEC system controls the prop governor, which runs the prop at 1700 rpm for all settings by default. When you want to quiet things down, you push a button that engages a low rpm mode, where it runs the prop at 1550 rpm for all settings below Take Off power (if you are in low rpm mode and push the lever balls-to-the-wall, it automatically brings the prop up to 1700).
So, you take off, and the prop is at 1700.  Come back to Max Continuous, it stays at 1700, come back more for cruise, and it still stays at 1700.  Then when you want to slow it down, you push the PROP LOW SPEED switch/light just ahead of the power lever, and it drops to 1550 for all power settings, except if you go back to full power, where it runs back up to 1700.

Another innovation is a low, 1,550-rpm propeller setting. Down on the center pedestal is a push-button for shuttling between the electronic propeller governor’s normal, 1,700 propeller rpm and a lower, 1,550-rpm mode for a quieter cabin. Except for take-off—when the FADEC will automatically command 1,700 rpm—you can use low-speed mode at any time. In cruise, Pilatus says that the penalty is a paltry one to two knots.

(AOPA PILOT Article - PC-12 NGX)


What are the differences between each ILS category?

The category specs are easily found on Wikipedia. Here is a concise view of the ILS approach minimums, as far as the crew is concerned.

  Cat I

  DH: 200 ft (61 m) or more
  RVR: 1,800 ft (550 m); at some airports 1,210 ft (370 m) is approved. For single crew operations, increased to 2,600 ft (790 m)
  orVISIBILITY 800 m (2,600 ft)

  Cat II

  DH: less than 200 ft and more than 100 ft (30 m)
  RVR: 1,000 feet (300 m)

  Cat IIIa

  DH: less than 100 ft and more than 50 ft (15 m)
  RVR: 600 feet (180 m)

  Cat IIIb

  DH: less than 50 ft (15 m) or none
  RVR: 150 feet (46 m)

  Cat IIIc

  DH: No limitations
  RVR: None

They are based on decision height and RVR (or visibility for cat I).
Note that there are no public transport aircraft certified for Cat IIIc as there is no use for landing without visibility and then staying on the runway because you cannot visually taxi to the gate.

The requirement for equipment certification accuracy itself can be found here.


Why does this shockwave not touch the body that creates it?

After passing through the shock wave, the air still has to evade the body. If the shock-wave touched the body, the air would have to escape through infinitely thin space at infinitely high pressure and it obviously can't do that.

So behind the shockwave there is a boundary layer (called shock layer) in which the air is moving with the body and flows, under high pressure, to the sides where it can escape.

The blunter the body, the thicker the boundary layer, because the air must cover longer distance to the sides and takes longer to do that.

Of course the high pressure between the shock and the body causes a lot of drag, which is why sharp nose and leading edges are preferred for supersonic flight.


Can a commercial airplane overtake another airplane going in the same direction?

Faster aircraft often overtake slower on the same routing. This is usually accomplished by flying at higher or lower altitudes. This is called vertical separation. They can also be separated laterally by radar vectors so that they are 3-5 nautical miles apart. The exact distance will depend on the ATC standards for the particular airspace.

Often as they approach the destination ATC will ask one aircraft to speed up and one to slow down slightly. This can sometimes allow the faster aircraft to pass the slower aircraft, but it also insures they have the required separation when they are on approach to land.


Why do large aircraft have their engines mostly on the wings, while smaller ones tend to have them in the tail or the tip?

Small aircraft need very low mounted wings to allow for a decent cabin height. The last commercial airliner which required the passengers to climb over the wing spar on their way to their seat was the Boeing P-247. Low wings do not allow the necessary space for engines, so the next best location is on the rear fuselage. Also, small aircraft have a relatively short fuselage, and the gear can be made short (and light) without risking a tail strike on rotation.

Fighters need to have small moments of inertia, especially in roll, so they cannot afford to put engines on the wings. Even the Me-262 was initially planned with fuselage-mounted engines, that's why it had this peculiar triangular fuselage cross section. Only when the engines grew in diameter during development they had to be placed on the wing.

Pros of rear-mounted / fuselage-mounted engines:

The wing is clean, having low drag and optimum conditions for lift creation.
The engines are easy to access (if mounted at the rear fuselage. Different story with buried engines!).
Smaller vertical tail needed for asymmetric thrust conditions.
Shorter, lighter landing gear possible (if rotation capability is not compromised).
Low roll inertia.

Cons of rear-mounted / fuselage-mounted engines:

No bending relief for the wing; heavier wing spar needed.
No help in flutter supression (a mass ahead of the elastic line helps).
Possible interference with wing wake at high angle of attack.
Forces the tail to be a T-tail configuration.
More structure needed to carry the thrust forces forward.
Intake noise is more audible, especially for passengers in the rear seats.

This picture of a Cessna Citation X should illustrate the point nicely.


What are the process involved in tire rotation during long term storage?

Manufacturers give the manual for storing/parking periodic ground check.

For Airbus A320 family:

  You can ignore this step if you moved the aircraft for the APU start.

  Turn the wheels by 1/4 turn to prevent damage to the tires:

  a) Move the aircraft Ref. AMM xxxx or b) Refer to the jacking for
  wheel change procedures to turn each wheel separately

This is done if storing is more than 15d, and repeated once every 15d.


(Ref AC 61-65H solo endorsements 61.87(n) and 61.87(p)). When should I give 61.87(n) vs 61.87(p)?

Remember the ACs are guides, not laws, as opposed to the FARs.
14 CFR §61.87(n) reads:

Limitations on student pilots operating an aircraft in solo flight. A student pilot may not operate an aircraft in solo flight unless that student pilot has received an endorsement in the student’s logbook for the specific make and model aircraft to be flown by an authorized instructor who gave the training within the 90 days preceding the date of the flight.

14 CFR §61.87(p) reads:

Limitations on flight instructors authorizing solo flight. No instructor may authorize a student pilot to perform a solo flight unless that instructor has—
(1) Given that student pilot training in the make and model of aircraft or a similar make and model of aircraft in which the solo flight is to be flown;
(2) Determined the student pilot is proficient in the maneuvers and procedures prescribed in this section;
(3) Determined the student pilot is proficient in the make and model of aircraft to be flown; and
(4) Endorsed the student pilot’s logbook for the specific make and model aircraft to be flown, and that endorsement remains current for solo flight privileges, provided an authorized instructor updates the student’s logbook every 90 days thereafter.

The upshot of which is that (n) is, technically the only requirement for the student to possess for initial authorization for solo flight by a student pilot. (p) is also applicable to the endorsement that must be met by the instructor for initial endorsement, but must be met for additional 90 day solo endorsements by the student.
Here’s the thing, as there is no legal requirement for exactly HOW TO PHRASE an endorsement; they can technically be written by a CFI, provided said endorsement conforms with §61.87, you’re perfectly welcome, as a flight instructor, to give an initial endorsement referencing both (n) and (p) if you desire.


I think the GIST here is:

Look far ahead. Don't look at whatever is directly in front of you.

It's the same as driving. If one looks at the piece of concrete just meters ahead, then the barricade will "pop out in front suddenly" or the bumper of the car is "in your face out of nowhere".

Our peripheral vision will guide us to wherever we want. It is natural and in-born, biologically. You just need to know where to look.


Why do some fighter jets have double wheels in the front gear whereas some other aircraft have a single wheel?

Ther are a lot of reasons for doing one over the other, from design trade offs to steering mechanisms to weight savings vs Service life, runway loading requirements, etc.  In the case of the Rafale-N, the nose landing gear is designed to interface with the catapult shuttle on the ship, so a single nosewheel would not be an option here.


Why did this aircraft take off in the opposite direction compared to the one used by other flights right before/after it?

It looks like the reason for the Rwy 6 departure was noise abatement. The climb gradient from 6 is not as steep as for 24. The Jeppesen charts state the requirements:

And it states that if you are unable to comply with the steeper noise abatement climb gradient for rwy 24 (583 ft climb per nautical mile), you should request 6 (300 ft climb per nautical mile). Maybe the plane was fully loaded and the captain wanted to avoid a fine.


How are lavatory smoke detectors connected to the flight deck?

Data Bus

A quick Google search suggests the general approach is to minimise wiring by using a data-bus approach to carry information from multiple sources along a minimum number of wires

See ARINC 629 Data Bus Standard on Aircrafts

  In earlier analogue avionic systems the number of cables used to transfer information between the various
  system components was considerable. With these systems, at least one pair of wires has been required for each signal
  and so a typical installation requires several pairs of wires. With the equivalent digital systems, all the analogue signals
  are converted into their equivalent and are assigned unique address labels to ensure there are no conflicts. These
  signals are then transmitted down a single pair of wires, which makes up a data bus. Aircraft data bus systems allow a
  wide variety of avionics equipment to communicate with one another and exchange data. The type of language used on
  an aircraft data bus is known as the protocol. There are currently different data bus standards (protocols) that currently
  account for most of the avionics data interchange on today’s aircraft, and these are: ARINC 429, ARINC 629, MILSTD
  1553, MIL-STD 1773, CSDB and ASCB.

I imagine that smoke detectors are just one example of the types of sensor that are integrated into such data-bus systems.

I expect there are several data-bus systems for redundancy and perhaps to isolate different categories of data.

Further reading

ARINC 429 as used on  A310/A320, A330/A340; 727, 737, 747, 757 767; MD-11 etc.
ARINC 629 as used on 777
AFDX as used on A380
Smoke Detectors interfaced by a safety critical aircraft
based CAN-Bus Network


As an active area radar controller, I completely agree with @rbp answer.
To better explain relationship between power and responsibility, I will try to describe what a controller would usually do: If I need an aircraft, for example, to reduce speed...
I know approx. what would be the minimum convenient speed for a particular type to ask, so I'd take this into account prior asking. But if a pilot tells me that he's unable to comply with the request, I'll find another solution i.e. radar vectoring to loose few miles or in extreme situation, level change. In short, a controller will never force a pilot to action if pilot answers that he can't do that. A controller must plan in advance that pilot may not be able to fulfil his request and have alternative solution. If you, as a controller, put yourself in a situation where you have no alternative, that is usually too late.
There are usually only few things where I can't make exception:

Minimum separation between aircraft
Danger/Prohibited zone
Terrain

Even then, in extreme case, I've never met: Imagine a situation where you have an aircraft which can't change level due to traffic above and below and has a crossing traffic. Then only remaining action I have available is radar vectoring, but what if the pilot advises me that his unable to turn due to weather, (the described situation is usually the controller fault because he should have predicted that earlier). Then controller probably would give the pilot traffic information (tell the pilot what to expect) and advise the minimum distance but it will not force the aircraft to CB.


What requirements aren't met, that would designate an airspace to be Class E instead of A, B, C, or D?

The simplest answer is that Class E doesn't have a control tower, and the others (Except A) do.

Think of Class E like it's "Class A", but just at the lower altitudes. Both A and E are basically "wide swaths of airspace, not really near a major airport" with control provided by the Area Control Center (similar to ARTCC in the USA). Whereas B, C, and D are designated at airports with Control Towers. The only real difference between A and E is that no VFR traffic is allowed to enter Class A.

Although you're right that VFR traffic does not need to communicate with ATC in Class E, be careful about using the phrase "to them, it's uncontrolled airspace".  It IS still controlled airspace. VFR traffic does not need (nor sometimes want) to be controlled, but that does not make the airspace "uncontrolled".  "Controlled Airspace" is a term one will likely encounter on exams, and one doesn't want to get into the habit of calling it "uncontrolled" just because one is a VFR pilot.


What is the "compression ratio" of air hitting the nose?

I think what you seek is called the stagnation pressure, which is the pressure rise experienced in a given parcel of air if all the kinetic energy associated with that parcel's velocity were to be converted without losses into potential energy (stored work) of compression according to the ideal gas law. The equation for stagnation pressure is

$$ \frac{P_\text{stagnation}}{P_\text{static}} = \left( 1 + \frac{\gamma - 1}{2} \times M^2 \right) ^ \left( \frac{\gamma}{\gamma - 1} \right) $$

where $\gamma$ is the ratio of specific heats for air and $M$ is the Mach number.


Where can I get airport diagrams of non-towered airports?

Many non-towered airports have diagrams in the Chart Supplement, and there is an airport diagram for X26 but not for X59. The difference appears to be that X26 has instrument approaches but X59 doesn't. It looks to me like the airport diagrams are considered part of the terminal procedures.

But I have to say that the FAA is as clear as mud on this. The airport diagrams legend says:

  selected towered airport diagrams have been published in the Airport
  Diagram section of the A/FD

But obviously that's completely wrong, because a) many non-towered airport diagrams are in there, and b) the A/FD doesn't exist any more.

By inspection, it looks to me like airports without an instrument approach have no airport diagram (X59, X25, 2RR) and ones with an approach do have one (X26, X07, AVO). But I only spent a few minutes looking, so I may well be completely wrong on this.

As for your question about the order of diagrams, the legend says:

  Diagrams will be listed alphabetically by associated city and airport
  name


Is a chambered fan more efficient than a ducted fan?

The design is not very efficient:

It does not use forward airspeed to pre-compress the airflow entering the engine.
It blows exhaust air into the air inlet.
It bends the exhaust flow 180 deg, creating friction and loss of thrust.

Short, straight, unimpeded airflow works best.


Are there specific names for airport vehicles used for de-icing?

As far as I can tell they don't have their own name specifically they are part of the airports Ground Support Equipment. They have non-powered and powered support equipment, De/anti-icing vehicles fall under the powered category. Trying to find a better link than the one I found on Wikipedia In case you want to see that link
In case you want to buy one Heres a manufacturers website of GSE


Does the tailplane have a positive/negative camber?

The tailplane should produce less lift than the main wing, for pitch stability. That is to say, its lift is negative relative to the wing lift. Its lift need not be wholly negative (pointing down), although it usually is during takeoff and landing.

But yes, as a first approximation, the direction of camber matches the direction of lift.

Also yes, negative lift (at the tail or anywhere else) can be called downforce (at the tail or anywhere else).

Here is Peter's explanation.


Could a big plane glide significant distances, same a ordinary glider (1000 km or about)?

No, there's no way an airliner can glide 1000km, this is because its wing is designed for fast cruising speeds, and it's much heavier compared to the lift generated than a glider. Gliders are light and have huge wings for their weight, which means they can get lifted by powerful air currents. An airliner is not going to be able to do that.

The longest glide of an airliner I know of was Air Transat 236, which glided about 98 miles (almost 160km) from cruising altitude to the Azores after it ran out of fuel. The captain was an experience glider pilot. That is really about the limit.

Keep in mind that there's nothing ordinary about 1000km in a glider! 1000km is a very long distance and you'd need a very good glider and a very experienced pilot in just the right conditions.


Flutter is a phenomenon that can occur when a structure is subjected to aerodynamic forces. It occurs not only in aircraft but also for example in buildings, power lines, road signs and bridges. Flutter is an oscillation caused by interaction of aerodynamic forces, structural elasticity and inertial effects.

Perhaps the best known example of flutter is the bridge over the Tacoma Narrows ('Gallopin' Gertie')  that collapsed due to flutter in gale force winds.

Flutter in aircraft causes the wings and / or stabilizers to oscillate.
When the airspeed increases the energy added in each oscillation to the structure by the aerodynamic forces increases. At some speed the damping of the structure may be insufficient to absorb the energy increase from the aerodynamic loads and the amplitude of the harmonic oscillations will grow until the structure breaks.

A flutter test is performed to determine what speed flutter occurs yet is still damped. Theoretically an aircraft should be able to stay structurally intact up to the design dive speed ($V_d$) which is at least 1.4 times the design cruise speed. In flight tests, the $V_d$ is not always demonstrated as this is very risky since there would not be any margin from breaking up. The maximum speed is slowly increased in subsequent flight tests with careful data analyses in between up to a point where the test team decides that it is no longer safe to continue. This establishes the maximum demonstrated dive speed ($V_{df}$); the published maximum operating speed ($V_{mo}$) and never-exceed speed ($V_{ne}$) are well below $V_{df}$ to give margin from disaster.

This video shows flutter in a Hawker 800. The incident occurred not during testing but was caused by inadequate fitting of the ailerons(FAA PDF).


Why don't all flights use the North Atlantic Tracks (NATs)?

The answer doesn't state that half of the flights between western Europe and North America use the North Atlantic Oceanic Track System (OTS). It states that half of the flights over the North Atlantic use the OTS.

Part of the flights over the North Atlantic don't cross between western Europe and North America and they don't use the tracks. Examples are flights to/from Iceland or the Azores. Also flights crossing between Ireland and the North Western point of Spain are entering the North Atlantic Region.

Also part of the flights that do cross between western Europe and North America and vice versa may use random routing for various reason.

On some days the winds are such that favourable tracks to North America are within the Reykjavik control area, which allows for random routings.

Some combinations of origin / destination are better served by avoiding the OTS area at all. For example flights between the Iberian peninsula and Florida are generally South of the OTS.


From own experience some years ago an empty B737-300 with ~2500kg fuel in the tanks can be moved by crosswinds as low as 55kt. Surface was a regular dry concrete apron with no slope. That's why my companys GOM (ground operation manual) required ballasting the aircraft with max fuel in high winds and chocks on the main wheels both sides.


How many significant digits should I use for simulating aircraft equations of motion?

From your description, it's not an issue with the aerodynamic coefficients. If as you have described previously that you're modeling F-18, then the airframe should be unstable longitudinally. A 1e-10 deviation (assuming it applies to body rates, body speeds, etc. as well) is well-within typical trim error bound; in fact, a deviation is unavoidable when dealing with computational floating point. But if it's longitudinally unstable, any deviation will magnify over time exponentially.


How was I able to just plug in my headphones and listen to ATC and pilot chatter?

This is a feature offered on some United Airlines aircraft and flights. It's an interesting way to hear what's going on in the cockpit. You can find lots of information by searching for United channel 9.


Can pilots take multitools on board in Canada?

pilots are never allowed to have any kind of weapon on board. when pilots go to work they have to go security just like the passengers.

there has been accidents because of this.
https://en.wikipedia.org/wiki/Federal_Express_Flight_705#Flight_crew_and_hijacker

its maybe allowed when the total length is smaller then your hand but i`m not sure if this rule applies to pilots.


Can helicopter or aircraft intro flight hours count towards a private pilot license?

Yes, these hours can be counted towards PPL, if you fly with a flight instructor next to you, which is generally the case if you go to a flight school and ask for "introductory flights" anyway.

In my case, they provided me with a tiny logbook for free so I can log my hours.


How to calculate the drag on an airfoil from momentum equation (Fundamental of Aerodynamics 5th edition, J.D.Anderson)?

those are some great questions. I will try to be very concise.

Firstly, regarding to the line ‘bh’, there is no fixed length you can calculate. Ideally you want to make sure you get measurements of the entire region where there is a momentum loss. Therefore, you seek to take measurements until you reach a point far enough so $u_1=u_2$.

Note that this momentum loss is directly related to the size of the wake, thus the length of ‘bh’ would be determined by the Reynolds number, separation point, incidence, etc. One common problem, especially at high AoA, is that the rake is so large that the wake rake does not cover this ‘bh’ line. This would mean that the momentum loss measured, and therefore the drag, is smaller than it is physically.

With regards to the distance from the trailing edge: You must avoid being too close since phenomena like recirculation bubbles or the pressure difference between the upper and lower part of the aerofoil would basically ruin your measurements (the velocity is not normal to the probes , etc). On the other hand, the flow in the rake induces an additional momentum loss, thus if you take the measurements farther aft, you would be also measuring this contribution, apart from the drag of the aerofoil. In addition, the size of the wake increases, leading to the problems mentioned in the first question. Typically, a distance of approximately one chord is used for the experiments.

The next question is related to a different topic, wind tunnel corrections. From the picture, due to the momentum loss, using the equation of continuity, you will always have $ai<bh$. What is defined as ‘”streamlines far away from the body”, lines ab and hi, are assuming constant pressure and velocity. If you add the wind tunnel boundaries, imposing the streamlines to be parallel to the surface of the tunnel, there would be an acceleration of the flow, $u_1<u_2$, thus this p=p_infinity will no longer be achieved.

This change in the velocity profile will affect the measurements at the rake, therefore some corrections are needed. The bigger the wind tunnel is, the smaller the corrections are. In the book you will find a nice chapter about this.

Regarding to the last question, unfortunately I don’t have the book anymore… But this method has indeed some drawbacks (in addition to the ones aforementioned). Firstly, the pressure drag is almost neglected. Moreover, measuring the turbulent flow at the wake is difficult and leads to errors  if the velocity is not normal to the probe (this happens especially at high AoA).

Hope this has helped!


What's the wisdom of attaching an aircraft lift strut to a wing spar utilizing a single eye bolt vs the common two plate or strap method?

Vertical bolt = less optimal.  The reason is the tube walls in the 12:00 and 6:00 locations (top and bottom areas) are effectively the primary tension and compression members of the tube, and the 9 - 3:00 areas are the shear zones.

In other words, if the tube was an I beam, you'd be putting holes right in the cap strip flange of the I beam where the tension and compression loads are highest.  You're like the plumber who drills holes in floor joists too close to the edge and severely weakens the joists.

The horizontal bolt is much better because the holes are in the neutral axis of the tube, the middle of the shear zone, and the bolt/nut serve to prevent the tube from ovalizing (squashing flat) under bending load. So the horizontal bolt actually strengthens the tube overall, because the hole has little effect on the upper surface's compression strength and the lower surface's tensile strength, and the bolt and nut support braces the tube against flattening (by preventing the sides from spreading), so the upper and lower surfaces can get closer to their actual stress limit potential.

So the middle picture, pound for pound structure wise, is the best method. However you can do it the other way if you size the material to compensate for the strength lost to the holes at the top and bottom, so either way will work.

And in fact, on something like an ultralight with wire braced wings and a spar supported at multiple points along the span, a designer may find a vertical eye bolt like the top sketch to be the most elegant solution in the greater scheme of things, and it's worth while to do it that way and compensate as required with heavier meat adjacent to the holes than would be needed with a horizontal hole.

But if you tested the single vertical bolt configuration against the single horizontal bolt configuration, with identical hole sizes and material thicknesses, the vertical one would almost certainly fail first.


Do crosswinds affect which pilot lands the plane?

Never ask a question with "ever" in it - because the answer will very rarely be no!

For example - if one pilot is training, then while they may have planned to do the landing reality might dictate that they have to hand over the controls to the instructor. I'm sure the same will apply to type ratings or differences training - nobody is going to let you have a crack at a severe crosswind landing during your first front-seat flight in an A380.

Additionally, flying schools will often have strict crosswind limits and some may not grant you full "As Pilot Operating Handbook" privileges until you have [x] number of hours AFTER your test.

In other words - you may have two qualified pilots, but only one of which is allowed to land the plane!

But I'm being deliberately pedantic - I suspect you're focussing more on commercial, multi-crew operations rather than two pilots who happen to be in one aircraft and I'm not qualified to answer that bit!

I'm not aware of any requirement to take seat position into account, however.


How can Ryanair offer flights for a penny?

Besides @Sebass van Boxel's answer, I'd like to add the following:

I was talking to a Fastjet pilot (ex easyJet) and he was telling me that obviously not all seats are available for a cheap price.

If you book early you will get a special price but try booking a day before and you will see.

As has been said, a lot of money is made on all the extra services such as luggage, food, etc.

From what he told me, the profit on each flight for easyJet is minimum \$400 per flight at 96% full — which is not much, but consider that easyJet has something like 1,000 flights a day and that means \$400,000/day profit. Not bad...

That how the money is made.


Is there something like a table of aircraft required runway lengths?

Such table would not be useful at all. As the required runway length varies with the aircraft weight, pressure altitude, temperature, aircraft configuration, runway slope, condition (wet, dry), wind, etc.

Examples:

A 7000-foot runway can handle a 747, but listing the 747 under aircraft that can takeoff from 7000' runways does not say how big the weight penalty will be.
A 7000' runway at sea-level is longer than 7000' at a high altitude airport.

I'm afraid you won't find such list.

Related:

For designing a runway, what are the largest cargo airplanes in use?
How can a Boeing 747 takeoff from Princess Juliana 7,546 ft runway?


When does an instrument approach "begin" per §135.225(a)

Beginning an instrument approach would mean being established on any segment of that approach, whether the initial, intermediate, or final approach segments, and they have received ATC clearance to do so.


What does "E" stand for in a polar curve?

E is used as the symbol for L/D in German. Normally, a symbol description will call it "Gleitzahl" (glide ratio).


What is the purpose of this loop in a taxiway?

In the US, this is called a "run up area". It is used by small piston powered airplanes to test their engine prior to takeoff.

The circular design allows several aircraft to full throttle their engines without the prop blast hitting the aircraft behind it. It also allows other aircraft like a business jet, to pass the testing aircraft and takeoff immediately.

Larger aircraft or turbine powered aircraft don't usually test their engines near taxi-ways and other aircraft (or aren't allowed). If they need to test their engines, a special blast "pen" or blast "barrier" is used.

Youtube video of a FedEx engine test.

This Youtube video of a airplane landing shows a ground view of the significance of the hills and mountains off the departure end of 36.

Why the run-up is at this end - Google Earth 3D


For a teardrop shape, which orientation has the least drag?

The design looks similar to the wheel fairings found on many Cessna-type aircraft. They lead curve-first.

If it was going tip-first, you could have a nice laminar airflow initially, but once it reaches the curve, the airflow will separate from the surface and produce a big wake with associated drag. By leading with the curve you can have a laminar flow right to the tip, with only a little bit of drag.


Does taxiing time gets considered in a pilot's flying hours?

In the US, taxi time can be logged. 14 CFR 61.51 says the pilot must log (emphasis mine):

  Total flight time or lesson time.

And 14 CFR 1.1 says (emphasis mine):

  Flight time means:

  (1) Pilot time that commences when an aircraft moves under its own
  power for the purpose of flight and ends when the aircraft comes to
  rest after landing; or

  (2) For a glider without self-launch capability, pilot time that
  commences when the glider is towed for the purpose of flight and ends
  when the glider comes to rest after landing.

Note that in reality, general aviation pilots (I don't know about airline pilots) usually just log whatever is on the Hobbs meter, which may include some time sitting still on the ramp doing post-startup checks, setting up avionics etc. That might not be strictly correct per the regulations, but absolutely no one cares.

This question is closely related.


What is the difference between a POH and an AFM?

Both a POH and an AFM meet the "Operating Limitations" requirement in the ARROW acronym.

The difference between the two is mainly in length and content: an AFM is usually a thinner document, satisfying the requirements of FAR 23.1581 and not much else, while a POH contains these required items plus other information like system diagrams (The contents & format of a POH are standardized in GAMA's Specification 1).

Parts of the POH (like the Limitations section) are FAA-Approved, and serve as the AFM, and both documents are typically associated with a specific airframe (by serial number).

A better explanation might be this:
The AFM is a regulatory document (it's contents are prescribed under the section of the regulations the aircraft was certificated under - Part 23, Part 25, etc). The POH is a GAMA-defined document whose contents meet the regulatory requirements of an AFM, and present other information in a standardized way so that a pilot can go from a Cessna to a Piper to a Mooney to a Socata and browse the book to learn about the airplane they're about to fly with all the information presented the same way no matter who the manufacturer is.

The other two types of documents you may encounter are an "Owner's Manual" (which usually goes along with a thinner AFM & provides some of the information found in the newer-style POH) and a Pilot Information Manual (PIM) which is a "generic" version of the POH which many pilots buy so they can study the procedures without removing the regulatory document from the aircraft.

Chapter 9 of the Pilot's Handbook of Aeronautical Knowledge talks a little about the differences between the two documents (and a whole lot of other flight documents).


A tailwind provides a faster groundspeed.

The aircraft moves through the air so whether the ground is moving relative to the mass of air has no relevance to the aerodynamics of an aircraft at cruising altitude.

  a British Airways passenger jet approached supersonic speed this week as it rode a surging jet stream from New York to London.

from The Telegraph, 10 Jan 2015

They mean groundspeed - so the term supersonic is moot.

  The Boeing 777-200 jet reached a ground speed of 745mph as it rode winds of more than 200mph across the Atlantic. At ground level, the speed of sound is 761mph.

Aircraft often use the predominantly westerly† jetstream when flying from the USA to Europe, From Japan to California or across the USA. Flying the other way they pick an altitude to avoid it.
 Wikipedia

The Jetstream is a high speed, high altitude, wind that blows moderately reliably in one direction.

 Metcheck

† Westerly means "blowing from the west" - towards the east.


Why do airlines split themselves into domestic and international subsidiaries?

Sometimes it can be for the purpose of recruiting pilots and cabin crew at lower pay. The airline may have pay agreements, possibly union collective agreements or else just formal agreements with non-union "associations", which set pay, working hours, and other conditions. This can be a barrier to offering ultra-low-cost tickets on the discount brand. If they structure the low-cost brand as a nominally separate entity, those agreements won't extend to it. See, for example, this news story on Westjet's new low-cost brand.

But there are lots of other brand-management reasons they might do this. They may want the big brand associated with reliable, high-service business travel for which they can charge full fare; and the new brand associated with cheap fares at the expense of everything else. Look at how the car companies spawn different brands so they can focus their marketing on luxury (Infiniti) mass-market (Toyota) and fun-and-cheap (Scion, now rolled into Toyota).


Why do we use pylons to mount the engines on jetliners?

Engine placement was a tricky question when jets were introduced, and much has been learned since then. The initial idea was to mount them inside the fuselage or wing root. When they grew too big, they were closely mounted to the wing ("underslung" position, like in the Me-262, the Il-28 or the early Boeing 737).

However, the underslung position has two disadvantages:

More of the leading and trailing edges is obstructed, blocking space that would otherwise be used for slats and flaps. Consequently, an underslung position reduces maximum lift.
The center of gravity of the engine is too far back. Moving it more forward helps to place the center of gravity of the wing ahead of its elastic line. Bending will now create an opposing inertial moment, which is very helpful to dampen flutter.

Starting to move the engine downwards away from the wing initially increases drag, because now a narrow slot opens between both with a tendency to separated flow. Only when the engine is moved downwards enough, the drag of the wing-engine arrangement reaches its minimum. This placement was chosen in the next generation of jets like the B-52 or the Boeing 707.

Moving it still further down makes the pylon longer and thus increases the total drag again.

The big diameters of modern high-bypass ratio engines make it impractical to move it down enough to reach the drag minimum, but by moving it forward, the engine can again be lifted up, so a shorter landing gear becomes possible. Vortex generators are added if that pesky separation between engine and nacelle cannot be avoided.


Is there any way to stop a pilot from crashing an airliner?

COULD you do that?  Sure.  The relevant question, though, is if the tradeoffs involved would be worth it.

How could you do that?  Essentially, a trusted 3rd party could have the ability to disable all controls that the demented pilot has access to and assume all control over the aircraft.  If you're willing for somebody in the network operations center to have the ability to "turn off" every switch & control in the cockpit and remotely pilot the airliner to its landing, then you're set.  The pilot is now every bit as much a passenger in the aircraft as everyone sitting behind him is, and short of taking the crash ax and causing a depressurization, he can't affect things that much.  (And even if he did that, the airplane still won't crash.)

The problem with that plan is obviously that if the remote control function gets taken over by hackers or a demented individual at the operations center, the pilots are helpless to intervene.  After all, for the demented PILOT to be rendered harmless, you have to remove ALL ability to override the remote control, all ability to pull circuit breakers, all ability to affect everything.

So, where is the greatest threat?  A demented pilot that overcomes the other pilot (by force, by locking him out of the cockpit, whatever), or problems at the operations center or in the remote control process?  The track record of airline pilots is unmatched by nearly anything else for reliability and resilience, and we aren't nearly as vulnerable to being hacked as any remote control datalink would be!

The general understanding is that the best solution is to keep the pilots in control of the aircraft, and have measures in place so that if one of them loses it, the other pilot can keep things going.  Things like having a flight attendant in the cockpit to let the other pilot back in (would have changed the course of the Germanwings flight) can go a long way.  Or if there is a struggle for control, a pilot could summon the flight attendants over the PA to get help restraining the madman.

Perfect solutions? No.  But better than allowing the aircraft to be taken over by somebody outside!

After all, while "pilot goes nuts" is a vivid headline, the extent of the actual risk is quite limited.  Millions & millions of commercial flights happen without incident every year, and introducing a slew of new risks in the form of remote control that can't be over-ridden, seems like a severe over-reaction to what is in fact an incredibly remote scenario.  There are better ways to deal with the extremely rare & unlikely "crazy pilot" possibility than that.


how can i help the air force at this age if I'm only 13 years old?

As stated by Crossroads, AFROTC is an option. So is the Civil Air Patrol. Both will give you a taste of armed uniformed services life. Otherwise, look into volunteer opportunities locally to support the armed forces. Military.com may be a good start on researching charity organizations. Just be respectful in the forums, please.


Why are some airplane wings not painted?

Fuselage present a large vertical surface with greater length than height. Wings are a large horizontal surface that is shorter in the direction of travel. So...

The fuselage paint job is clearly visible on the ground, painting on the wings only if you are above or below the plane. This is probably the main reason. Simple geometry. It would be waste of money.

Sun will heat a large horizontal surface more than a large vertical surface, so making the wings white is more useful than making the fuselage white. While I am not sure that wings would be structurally weaker if heated, the heat would cause thermal expansion, which would indirectly result in increased drag by making maintaining optimal shape more difficult.

Paint has significant effect on drag, more specifically it affects when the boundary layer transitions from laminar to turbulent. In the very long fuselage the difference is probably insignificant and you can paint them as you wish, but for wings the paint should be as smooth as you can make it. While I doubt white paint is smoother than paint of any other color, keeping it simple is probably a good idea.


Have pilots encountered a UFO, and what to do if you have?

Pilots do encounter UFOs all the time. I just want to emphasize that UFO means "Unidentified Flying Object" - something which is flying, and which the pilot cannot identify. It does not mean an alien craft.

The guidelines for pilots are as follows (AIM 7-6-4):

  7-6-4. Unidentified Flying Object (UFO) Reports

  a. Persons wanting to report UFO/unexplained phenomena activity should contact a UFO/unexplained phenomena reporting data collection center, such as Bigelow Aerospace Advanced Space Studies (BAASS) (voice: 1-877-979-7444 or e-mail: Reporting@baass.org), the National UFO Reporting Center, etc.

  b. If concern is expressed that life or property might be endangered, report the activity to the local law enforcement department.

Air traffic controllers have the following guidance under FAA Order 7110.65 section 9-8-1:

  9-8-1. GENERAL

  a. Persons wanting to report UFO/unexplained phenomena activity should contact a UFO/ unexplained phenomena reporting data collection center, such  the National UFO Reporting Center, etc.

  b. If concern is expressed that life or property might be endangered, report the activity to the local law enforcement department.

The question "Was it of the E.T. kind" is beyond the scope of this site. This subject is, let's just say, suitably covered by other sites on the Internet at large.

One notable example of a UFO report is the 2006 O'Hare UFO sighting. For other examples, a Google search for "pilot UFO anecdotes" offers some decent results. "ATC UFO report" even links to some recordings of pilot UFO reports to ATC.

Some objects commonly reported (genuinely) as UFOs are spacecraft, fast or high-flying military aircraft like the U-2 or the SR-71 when it was in service, rocket launches, weather balloons, kites, errant helium balloons from kids' birthday parties, flocks of birds, con trails, and lightning storms. Any of these and more can easily look, under the right circumstances, to a pilot like a "UFO."

The closest experience I've had in my flying history to a "UFO" happened at night, during a landing approach in the midwest U.S. I was on a downwind leg when a very bright light appeared above me in the center of the windscreen, and rapidly moved downward toward the horizon. It scared me half to death; my instinctual thought was that it was the landing light of another plane descending on top of me. It turned out to be a meteorite. It only took me a second or two to figure it out, but boy did it get my adrenaline up! There was no need to report it though.

Culturally, pilots are generally apprehensive about reporting UFOs, out of fear of sounding like a lunatic or unhinged conspiracy theorist and being laughed at. Nonetheless, reports are not uncommon.


Can planes still land during a regionally-diverse ATC malfunction?

During a control tower malfunction, can planes still land?

Yes.

If one tower goes down, the other layers of ATC will still be functioning, and they'll divert the aircraft elsewhere: if LAX goes down, national level ATC would work with the SoCal Tracon (Southern California Terminal Radar Approach Control -- i.e. "Approach") and perhaps the airline dispatchers to send the airplanes elsewhere: San Diego, Ontario, Long Beach, Burbank.  Those farther out would be diverted elsewhere just to avoid having too many airplanes piled up in one place: land in the Bay Area, or LAS or PHX, for instance.

Okay, let's assume that all the towers in the LA Basin are all down.  And let's assume that SoCal is down too.  And just to make the scenario complete, we'll assume that LA Center has lost all of their radios too.  (This is like the scenario that happened several months ago when Chicago Center lost their radios due to sabotage, except we're assuming LOTS of facilities all have the same problem at the same time.  Straining the limits of "willing suspension of disbelief" pretty hard here, but let's do it to make the point.)  What happens?

The pilots talk to each other on the usual frequencies and land.

There are plenty of uncontrolled airports out there, and they function just fine with pilots using what's known as CTAF -- the Common Traffic Advisory Frequency, where everybody broadcasts their position & intentions.  "Whozit Traffic, Cessna 1234A, left base, touch & go Whozit."  "Whozit Traffic, Piper 9876B, left downwind, full stop Whozit."  Based on those transmissions, you can build a good picture of who's where, who's closest to me & where I need to be looking to find him, and what (if anything) I need to do differently to not get too close.

And nobody needs ANY assistance from the tower in order to put the aircraft safely on the runway, stop, and exit.  We talk to them to keep the flow of traffic neat & orderly (they can be more efficient than just working it out on our own -- particularly when you start alternating departures with arrivals), but they have zero role in the actual act of landing.

Now in the scenario posited above where every ATC radio in all of the southern half of the state of California has failed, there would be complications, particularly if there was weather involved.  (See Die Hard 2, where weather had shut down EVERY airport in North America, apparently, save one, and the bad guys had shut down the ILS to that airport... we're well beyond "willing suspension of disbelief" there.)  But you'd also have a couple of things in your favor: no departures, and the runways normally used FOR departures would be available for landings as well.  Also, the goal is no longer a smooth & efficient flow of aircraft in & out; it's simply to get everybody on the ground safely.

Would it be a mess once you got on the ground & wanted to get to a gate?  Sure.  Visions of gridlocked LAX are easy enough to imagine.  But could everybody get on the ground safely?  Absolutely.


What is the purpose of thinner airfoils used near wing tips?

There are two main reasons for thinning the wing towards the tips:

Thinner airfoil sections cause less drag simply because they disturb airflow less.
Thinner sections down to 10% have a higher maximum lift coefficient, which helps both near stall and during maneuvering: A section with a higher maximum lift coefficient will show more aileron effectiveness, too.


Question about federal airways in Class E airspace going from 5500 MSL(USA)

Likely at the floor of the Class E airspace.  A Federal Airway coinciding with a Class E floor higher than 1200' AGL would normally only exist in mountainous terrain.

A definitive example could be found by looking in the FAA's "Airspace Designations And Reporting Points" document, available on-line.


Is drag the only aerodynamic force that acts upon an asymmetric body (a glider in particular) travelling through the air?

You are right, lift and drag are just convention. But the aerodynamic forces are usually grouped into one total force named "total aerodynamic force" ("résultante aérodynamique" in french).

As explain in how it flies:

  drag is a component of the aerodynamic force, namely the projection onto the direction parallel to the relative wind.
  lift is another component of the aerodynamic force, namely the projection onto the two directions perpendicular to the relative wind.

This convention applies to any aircraft.

For further reading, see the section about forces of how it flies.


What is this aircraft with a crew member in an exposed nose compartment?

I believe this is a Dornier Do 18 flying boat / patrol bomber. The cockpit with its central piece of glass is quite distinctive. It entered service in 1938, and doesn't appear to have been involved in the Spanish Civil War.

There is a short film on YouTube which has the same sequence as the documentary you saw. Looks like it was part of a movie which featured the Do.18; the cockpit fills with smoke and the "bloke in the nose" (the gunner) starts to look for somewhere to land is what I think is going on.

The Dornier 18 has the distinction of being the first German aircraft to fall to British gunfire in WW2: on September 26th 1939 a Do.18 was felled by a Blackburn Skua.

Since there is some astonishment at the position of the forward position, it's worth noting that it was extremely common for inter-war military flying boats to allow someone to be stationed up front in this manner, for both reconnaissance and gunnery, and for ropes and other maritime uses. For instance most of the designs for medium and large seaplanes from Short Brothers and Supermarine have such a front station in this period.

There are too many to list, but since you mention Studio Ghibli you may want to reference Italian seaplane designs by CANT (e.g. Model 25, Z.501), Macchi (e.g. M.18, M.24) and Savoia-Marchetti (e.g. SM.62, SM.78) from where a lot of inspiration was derived.

I took a look at the documentary you saw, the aircraft registration is 6L+E05. So this was a Do 18D-1 which entered service in June 1938 in Travemünde and ended its days two years later in Putzig (Puck, Poland) after an engine fire on takeoff.

source


It seems I've asked a question that has no answer. From the explanation below provided by a Diamond Aircraft representative, it is clarified that the intent of the AFM's caution is not to always run the electric fuel pump at high altitude, but to use it as needed to clear the symptoms - which are more likely to occur as altitude increases.

  The IO 360 with the Precision Fuel Injection System does not have a
  vapor separation and return line to the tank(s). Vapor in the fuel
  system will travel through the fuel system including flow and pressure
  transducers, into the injection system. Vapor can form under higher
  ambient temperatures and low ambient pressures. Fuel gravity fed
  through the system (electric pump off) from the tanks is “lifted” by
  the mechanical pump. The suction of the mechanical pump can cause some
  cavitations (vapor formation), especially as the fuel flows through
  resistances such as elbow fittings. Vapor bubbles will cause momentary
  low pressure indications and may also cause momentary erratic or high
  flow readings as the flow transducer turbine spools up with the loss
  of fluid resistance. These momentary occurrences can be suppressed
  with the electric pump. The electric pump activation increases system
  pressure to compress or return to liquid, the formed fuel vapor
  bubbles.

  [...]

  The intention of the steps for electrical pump selection, above each
  of the Cautions in the AFM is not for continuous operation of the
  pump, as this could potentially mask a defective mechanical pump and
  eliminate the redundancy of the fuel delivery system. If the abnormal
  fuel pressure or flow indications do not stabilize with the electric
  pump on, emergency procedures and maintenance action may be required.


Does the air resistance of a jet engine air intake count towards the jet's total air resistance?

This is a very tricky topic. Basically, you need a clear definition of what is part of the engine-related drag and what is counted towards airframe drag. Splitting up drag between components will always produce an arbitrary result.

An intake can generate thrust as well as drag. In case of the SR-71 at Mach 3, the intake contributed 54% of overall thrust, if you just look at the pressure distribution over the intake walls.

Generally, the job of the intake is to feed air to the engine compressor at just the right speed and as homogeneously as possible. This requires it to suck in air when at rest from all around the aircraft, and to ingest only the core of the stream of air flowing towards it at high speed. What is not ingested needs to flow around the intake lips and the engine fairing, and the drag caused by this process even has its own name, being called spill drag.

At high speed the intake needs to slow down the oncoming air and does so already ahead of the intake lip at subsonic speed. At supersonic speed this slowing down is accomplished by shocks, which adds another source of drag. This can be easily counted as part of the airframe drag, but done right this slowing down will compress the air, which in turn will increase thrust. Apart from viscous losses, this compression pays for itself and is almost drag-neutral in a good design and at ideal conditions.

Next is the flow around the intake. Just throttling the engine will change the airflow through it and thus the flow pattern around the intake. You can imagine that some configurations show marked changes in aerodynamic drag depending on the throttle setting. In case of the Eurofighter, the vicinity of the canard will even cause throttle changes to result in notable pitch moment changes.

To answer your question: Yes, the intake will produce drag, and how much it does depends on how you define drag. It is certainly wrong to think that the stream tube hitting the intake will just disappear into it and not add any drag.


How is a confusion possible between Western and Russian Attitude Indicators?

It's so easy to sit in our comfy lounge chairs and wonder how on Earth pilots get things wrong.

The error didn't happen without context. It was dark. There was little to no external visual reference due to cloud. The pilots were manually flying in a busy phase of flight. And the captain was probably adversely influenced by a medication/opioid.

Even without the artificial horizon mixup, the conditions were ripe for spatial disorientation.

This image is taken from this short video (yellow arrows were added). It demonstrates how a left turn on the Soviet display is similar to a right turn in a Western display.

The captain was used to the left display, where if the main line of focus was angled to the left, that would mean he needs to make a right control input to go back to wings level. In the accident flight, he saw that the most predominant line - the horizon on the Western display - was angled to the left. Due to the context I've mentioned, he went back to his basic knowledge - that a left angle means I need to make a right control input.

Of course, if he was on top of his game, he would have remembered that even on the Soviet indicator, the artificial horizon should have been level. But by this point he was already disoriented and confused, with the first officer's instructions ambiguous and worsening his dilemma.


With a fully deflected rudder the airplane will fly with substantial sideslip, and by dropping the windward wing it can be held on a straight course. This is usually done intentionally with gliders and light aircraft when they want to lose altitude quickly, because the high sideslip angle will increase drag substantially. If $\zeta$ is your rudder deflection angle, the slip will normally have a sideslip angle $\beta$ of between -$0.5\cdot\zeta$ and -$\zeta$, depending on the details of the aircraft.

If the hardover happens at high speed, the resulting aerodynamic forces will certainly overstress the fuselage and tail structure, and the aircraft will break apart and crash. No amount of pilot skill can prevent this!

If the aircraft survives the hardover incident, the best the pilot can hope for is a controlled crash: The sideslip angle will cause the landing gear to be torn off, and the dropped windward wing will provoke a ground loop - if the pilot tries to level the wings during the flare, the resulting yawing motion will ground loop the plane in the other direction.

I once had the chance to fly the prototype of the Swift S-1, an excellent Polish aerobatic glider. During one maneuver my left pedal got stuck, and I saw myself already sideslipping the plane into the ground. In the remaining minutes I tried to get the pedals unstuck and got lucky, ending the flight with an uneventful landing. Afterwards, I found out that the pedal mechanism had caught the wire from the battery, and my maneuvering had freed it up again. This was the closest I ever came to land with a rudder hardover, and I am not eager to ever try this out for real.


Are there a toilet and (small) kitchen in the Su-34?

Yes, the Su-34 does technically include a food ration warmer, a "sanitary container", and some room that allows for sleeping.

However, all three are much less impressive than the terms might suggest:

The food ration warmer is not a microwave. It's just a small can heater:

There is also some dedicated room for extra cans.

The "sleeping room" is just a bit of room where one could fit a sleeping sack.

One can lay down their head and torso on the entry hatch and fit their legs between the seats. This may come in handy for really long missions, likely with in-air refueling. This is more of a side effect of having an entry ladder and a hatch than a deliberate amenity.

The "toilet", or "sanitary can" as it's called, is exactly as illustrated in your question. Its interface technically supports both methods, but there's no record or hint of anyone ever using any but the first.

The reason for these is that the Su-34 is meant to be a long-range bomber with enough air-to-air capability to fly unescorted. So, even though based on a modified fighter platform, it was fitted with minimal amenities. However, these amenities are more of a "tick the box" type.

P.S. To correct some premises, ~8,000 kg is the payload limit for most of the Su-27 family, but not the -34. The Su-34 is significantly above that, with a maximum payload of 10,400 kg with maximum fuel or 12,500 kg with reduced fuel. In practical usage, it's an attack aircraft/bomber that can defend itself and operate against extensive air defenses.

To have an idea of where such a concept comes from, look at the Tu-22M. While a strategic bomber by role, it's rated up to Mach 2 and 2.5 g, has basic defensive armament, and is meant to engage aircraft carriers. So the VVS idea of a bomber from the 1970s on has been less of a bomb truck and more of an enlarged fighter with a large payload of guided munitions.

The Su-34 is a further development towards a fighter-like bomber direction. It's a heavy fighter platform with added wing area, range and payload to match older bombers. To narrow down its role, consider the F/A-18 for a comparison as an exemplary fighter-bomber that you'd see deployed on A2A missions as easily as A2G. The Su-34, OTOH, is more of a fighter-based bomber that doesn't need a fighter escort, but complements the base models for A2G and leaves A2A missions to Su-30/Su-35 variants.

P.P.S. I've taken the liberty of editing out your 2nd image, as it's from a space station.


That's a reflexed trailing edge airfoil. Its center of pressure moves forward with decreasing AOA giving it an almost constant pitching moment. It is often used for flying wings.


What do the gyroscopes used in commercial aircraft actually look like?

The first gyros were mechanical: A spinning wheel with gimbal mount and driven by air pressure. The picture below shows the innards of one which was used in the Supermarine Spitfire (picture source). The black disk on the right is the instrument background and the arm on top moves the vertical needle sideways in accordance with the turn rate of the aircraft. The white coating on the needle is phosphor to make it glow in the dark.

State of the art is to use a ring laser gyro. This is an optical device which sends a laser beam around a triangular or square track in both directions. Rotations will make the light path shorter in one direction and longer in the opposite direction, so the interference between the two beams shifts the place where the waves cancel each other. This shift is registered and interpreted as a rotation. An alternative design uses optical grade glass fibers for the light path.

The placement is important because flexing of the fuselage will give different results for different mounting positions. To my knowledge, in airliners gyros are mostly part of the avionics suite below the cockpit.

See here for a list of sample applications.

Ring laser gyro assembly with three gyros, one for each spatial axis (picture source).

More modern MEMS sensors are on the advance but mostly to be found in backup systems or on unmanned aircraft. They are much more compact and use less power, but their accuracy is lower than that of ring laser gyros.

Silicon Sensing CRS03 MEMS gyro (picture source).


Degree of motion terminology for special aviation movements

The opposite of climb is "descend" (that's an easy one).
The second one can be "translate" or possibly "slew" but I think the most appropriate word is "slip" as in sideslip.
Translate is a controlled movement from one place to another, and slew is an uncontrolled one according to Oxford, but when you work the "slew" switch for a directional gyro system, it's a controlled action, so there you go.
However, those terms apply to a stationary object that starts to move sideways, "slip" describes lateral non-turning movement of an airplane sideways when it's already moving forward, so this is probably the best definition.


Can you use a mode 3AC interrogator in EU airspace?

Partial answer:

  Is the backwards compatibility seamless and simultaneous?

Yes.

  Able to reply to both mode S and mode 3 interrogators in real time?

Yes.

  Or a toggle switch between modes, in which when mode S is selected mode 3 interrogations will be ignored?

No - a Mode S transponder will respond to interrogations by a "pure" mode 3 interrogator. Mode S interrogators have a special interrogation format that allows them to interrogate "pure" mode 3 transponders without triggering replies from mode S transponders even though those transponders do support mode 3 interrogations.

  Do European standards allow mode 3A/C interrogators to operate within their airspace?

Don't know.

  Could this cause interference with local mode S infrastructure?

Yes, in principle, for the same reason (FRUIT) that mode S was introduced in the first place - "overcrowding" of the airwaves. It won't be catastrophic. There are already plenty of airborne mode 3 interrogators operating (TCAS and AWACS).

  Are there any other potential concerns with operating a mode 3 interrogator in EU airspace?

Consider both radio communication regulations and aviation regulations.


Is freezing of windows normal in airlines?

Was it anything to be concerned

No

  Should I have brought it to the notice of the airline crew?

Yes, but not because it is a safety issue. Tell them so they can deal with it to give the next passenger a nicer experience.

What is happening is no different than a glass of ice water sitting on your kitchen counter. The warmer side of the glass (the outside) becomes cooler because of the cold on the inside and it transfers that coolness to the surrounding air. That surrounding air cools enough to cause the moisture it contained to condense into liquid that sticks to your glass. If the glass were cold enough, it would freeze that condensation. The window on the aircraft is that cold so the condensation freezes.

There is a mechanism under the window to keep this from happening. It is a jar of desiccant that absorbs all moisture (dries the air) in the window area so that there is no moisture to condense in the first place. Often, there is a tiny bit still.

As the desiccant absorbs moisture from the air, it retains it. So periodically, it gets saturated to the point it can't absorb anymore and the desiccant needs to be changed.

Either the desiccant in your window needed to be changed or moist air is bypassing the desiccant on its way to the inside surface of the window. Normally there is a seal between the outside window and that thin plastic window you can touch and the only way for air to get in or out of that inter-window area is through the desiccant. Your window may have a broken seal allowing moist air to bypass the desiccant.

Either way, it is a system designed only to keep the window from forming ice so the passengers can look out the window, it has no safety or structural consequences.


Is the nose cone of the MiG-21 adjustable in-flight?

Yes, it moves forward as the speed increases. Its purpose is "to slow the flow of air from supersonic flight speed to a subsonic speed before it enters the engine."
From Wikipedia:

The air flow to the engine is regulated by an inlet cone in the air intake. On early model MiG-21s, the cone has three positions. For speeds up to Mach 1.5 the cone is fully retracted to the maximum aft position. For speeds between Mach 1.5 and Mach 1.9 the cone moves to the middle position. For speeds higher than Mach 1.9 the cone moves to the maximum forward position.
On the later model MiG-21PF, the intake cone moves to a position based on the actual speed. The cone position for a given speed is calculated by the UVD-2M system using air pressures from in front and behind the compressor of the engine. On both sides of the nose there are gills to supply the engine with more air while on the ground and during takeoff.

You can watch it move on YouTube.
(Source) The aforementioned gills.

Related: What are the merits of an inlet cone/spike/centerbody vs. a 2D inlet?


What means do airline ground staff have to converse with pilots in flight?

There are numerous methods for air-to-ground communications.  I may be missing a few, but off the top of my head, here are the ones I can remember:

normal VHF comms
Operational staff at the airport maintain an operations frequency that you can use just as you would would ATC.  The limiting factor here is the requirement of line-of-sight with the ground antenna and this limits range.  We could normally raise ops about 30-40 minutes out, at altitude, if someone was actually listening.  This is similar to a GA pilot calling unicom to arrange ground services.  This method is also used for maintenance at some stations and for talking to fuelers and deicing operators.
SELCAL
This is a selective calling protocol that operates over HF and VHF frequencies.  Each participating airplane and ground station (typically a dispatcher or ATC) has a code and if you know the code you want to communicate with, you can establish two-way communications with them.  To use this in the air required tuning a specific frequency and using a hand-mic with a keypad to dial the ground station code.  On the ground I'm not sure the exact method they use (phone patch?) but when they called us we'd get an aural "SELCAL" announced by the airplane along with a light to alert us.
AIRINC phone patch
This service provides VHF-to-PSTN patches and allows you to call your dispatchers actual phone, medlink, or anyone with a phone you feel like calling.  This worked by calling an operator over the normal radios and having them dial a number and connecting us together.
Satellite phone
Works just like any other satellite phone and use the Iridium network.
ACARS
This works just like text messaging.  Select your recipient, type a message and hit send.  You get alerts when messages arrive.  The interface I'm familiar with in the airplane is a program in the FMS with limited pre-set recipients you could contact (dispatch and perhaps a few others).  The ACARS software can also be setup to send specific messages to specific stations, e.g. an "In-Range" message which is routed to operations at your destination.  From the ground side, this is usually baked into the dispatch flight-following software.  Our dispatchers could right click on an airplane, get a menu, pick "text message" and type a message that would be sent to that airplane.


How do people smuggle stuff with private airplanes?

There are lots of ways to smuggle goods with planes and it depends what you are smuggling and the aircraft on which you are smuggling it. Smugglers often bank on the fact that most countries do not have or allocate the resources to search every aircraft throughly enough from top to bottom before every flight as that is simply impractical on some level. Some times all you need is a good audio equipment road case.

Generally you need to get past customs which happens on the ground and is its own set of issues. In the USA the Customs And Border Protection takes care of a lot of the searching. Smuggling sometimes happens on commercial aircraft and there is plenty of info on it here on the CBP website. In this case the goods are smuggled on aircraft that are very much on radar and flying at assigned ATC speeds. Sometimes they are even loaded by official personal. On occasion even the head honcho is involved, moving some strange things.

It is possible to "fly under the radar" but that also depends on where you are going and what their radar coverage is. Steps have been taken over the years to combat this issue. It seems that some of the smugglers have once again resorted to small aircraft.

Barry Seal, the inspiration for the movie American Made was historically a pretty prolific smuggler. The movie takes some poetic license but is based on some facts.

  Seal used his knowledge of aviation to become the infamous smuggler he
  was. Once in U.S. airspace, Seal would drop to 500 feet and slowed to
  120 knots to mimic, on radar screens, helicopters which frequently
  flew from oil rigs to the coast.

  Within U.S. airspace, Seal would have people on the ground monitor for
  any signs his planes were being tailed. If they were, the mission was
  aborted. If not, they would continue on to drop sites over the
  Louisiana bayou, where duffel bags full of cocaine were dropped into
  the swamp. Helicopters would pick up the contraband and take them to
  off-loading sites, and then on to Ochoa distributors in Miami by car
  or truck.

Smugglers are still attempting to move product in older, but fast, biz jets with fake or missing registrations. To avoid being discovered they are apparently destroying the planes after they use them sometimes.

There is a great article on some of the history of air smuggling here. Which dates back to the early days of aviation.

This is a fairly interesting story...

Just remember, aviation smuggling is Illegal very illegal


How could a PA-28 be made to fly higher?

The Turbo Dakota (PA-28-201T) is very close to what you seem to be describing and is likely much less expensive to buy outright vs. the time and materials required to modify a lowly PA-28-1xx.  The published ceiling is FL200 with its TSIO-360 but at light weights* I'm sure a determined pilot could coax it to FL230 or FL250.

So, the answer is: a big TSIO engine.  The 260hp TSIO-470-B (only TSIO-470 made to my knowledge) would probably do the trick.  A TSIO-520 has taken me to FL250 in a T210 so I know it would probably take a Cherokee at least that high assuming that you successfully attach the engine to the plane (approvals, engineering, mechanical, W&B, etc).

*The Dakota is one of the few small single engine planes with a gross weight of more than twice its empty weight leaving plenty of wiggle room for a pilot seeking to extract better than book performance from the plane.

**Answer assumes you have an O2 system that will do the job at FL250.


What physical and mental attributes do I need to become a pilot?

Shhhhhh, here is the biggest secret of aviation: It's actually quite easy to become a pilot.  You can actually get your private certificate before you are allowed to drive!

The FAA has a nice page that tells you what is required to become a private pilot.  When most people think of piloting small general aviation aircraft, they are thinking about the Private Pilot certificate.  Part 141 is the most common route for that.  The hardest part is being able to pass the FAA physical, but keep in mind that as a private (or even recreational) pilot, you don't need to get a Class I, just a Class III.

To become an airline (ATP) or military pilot does require a great deal more work and training, but I think that may be beyond the scope of your question.

The best advice is to go to the local airfield or FBO and find a flight school.  Good luck.


Is a fighter pilot allowed to fly two different model fighters?

Typically yes, but they generally won't be training a new pilot one day and flying a night bombing sortie the next.
Two seat trainers are intentionally very similar to their single seat counterparts.  (for obvious reasons!)  A pilot training in a squadron to replace front line fleet F/A-18E pilots will likely conduct early stage familiarization flights in the F model, but later solos will be in the E model.  And once training is complete the operational squadron he/she is assigned to will only fly the E model.
After an operational tour, if a pilot is assigned to an instructor tour there might be a refamiliarization flight in the F model as part of the IUT (Instructor Under Training) syllabus, plus a written test on any procedural or limitations differences.  Since the front seat of the two seat trainer is in the same location as the seat in the single seat model, the student will sit in front for most flights, with the instructor in back.  The IUT syllabus would emphasize the change in perspective when flying formation, and performing or observing other maneuvers while sitting in the rear seat.
In summary, a pilot would be cleared to fly either model as part of the training process for being designated as a qualified instructor.
They then might fly the F model for early stage flights, and the E model as formation lead for flights later in the syllabus.  But they wouldn't go on a night bombing mission as a shore-based instructor, unless of course it was a training flight.


When you look at FAA publications the criteria for a "stabilized approach" is pretty simple:

  A stabilized approach is one in which the pilot establishes and maintains a constant angle glidepath towards a predetermined point on the landing runway.

When pilots talk about stabilized approaches we generally mean a little more than that though - for example the SKYbrary description of a stabilized approach, the Flight Safety Foundation, and Airbus all include more than just the constant-angle glide path in their recommendations for what makes an approach "stabilized".

Criteria that are commonly included in a "stabilized approach" are:

Maintaining a constant-angle glidepath toward a predetermined aiming point on the runway.
Maintaining a specified descent rate
Maintaining a specified airspeed (Vapp)
(Generally being slightly above Vapp is OK, but below is unacceptable.)
Having the aircraft configured for landing (gear, flaps, etc.)
All required checklists completed
The approach can be maintained with only "small corrections" to pitch, heading, or power.

An approach is "stabilized" if all the required criteria are met by a specific altitude (Airbus calls them "Stabilization Heights", and recommends 500 feet for approaches in VMC, and 1000 feet for approaches in IMC).
If the approach is not stabilized by the appropriate stabilization height (or conditions cause the approach to become "destabilized" - a sudden change in winds for example) the approach is abandoned (a "go-around").

So what makes stabilized approaches safer?
The theory is that a stabilized approach reduces the pilot's workload as they're getting closer to the ground: If the aircraft is configured for landing and all the checklists have been completed all the pilot has to do is gently nudge the controls to keep the plane going where they want it, and they can concentrate all of their attention on a nice, safe, (hopefully) smooth landing.

Are stabilized approaches always safer?
From a workload perspective, yes. It's hard to argue with "The pilot has less work to do".
From a "What if my one-and-only engine dies?" perspective, maybe not.

Stabilized approaches generally require partial power to be maintained throughout the approach, and although the engines in modern single-engine piston/jet aircraft have a pretty good track record of reliability there are good arguments for "non-stabilized" approaches (or approaches that are effectively "stabilized" at idle power) in single-engine aircraft.

Even if you're not flying a "stabilized approach" the way the airline folks define it you're well-served by incorporating some of the elements though - going around if your checklists aren't completed by a certain altitude, abandoning the approach if you have to manhandle the controls to try to keep things together, etc.


Could a rear center of gravity position cause an airliner to lose control when a pitch-up is commanded?

On virtually any swept-wing design, "wingtip stalls" are a danger. Most light aircraft are designed with a straight wing and a leading-edge contour such that the inside of the wing stalls first. This has two advantages for light craft; first, aileron control is available as long as possible into stall entry, allowing roll control and thus the ability to stay coordinated. Second, the departure of airflow over the top inside of the wing will reduce or eliminate the downwash of air over the horizontal stabilizer, which normally corrects for a slight nose-heavy CG. With the balancing force gone, the normal response of the aircraft will be to nose down, restoring a lower AOA and building forward airspeed to let the pilot recover quickly.

With a swept wing as is seen on modern jet airliners, the wingtips tend to stall first instead, because the airflow over the swept wing lowers the stagnation point and thus the effective angle of attack of rearward sections of the wing, so the wingtips at the rear will exceed the critical AOA first.

When the wingtip stalls first on a swept wing, two things happen. First, aileron control is severely affected, making it harder to stay wings-level and avoid entering a slip or even a spin. Second, the center of lift from the unstalled portion of the wing moves forward, placing the CG further behind it. An aft CG works against pilot efforts to nose the aircraft back down to recover, and in an uncoordinated stall the aft CG will keep the tail of the airplane "outwards" from the center of the spin, hindering or preventing efforts to cancel out the rotation with the rudder as the vertical stabilizer will be stalled due to the extreme "sideslip".

This is a potential problem in any airliner, where the weight is distributed along the majority of the fuselage. Any significant deviation from mean values for per-passenger or per-bag weights can place the CG too far aft. Tail trim tanks can further exacerbate this.

However, Air France 447's crash, in my amateur analysis, was not caused by trim characteristics. It was primarily caused by the pitot tube icing. This had several detrimental effects on the flight crew's situational awareness:

The disagreement of the plane's two pitot-static systems cause the flight director to unexpectedly disengage the autopilot, setting the flight crew on their heels.
This same disagreement in the pitot-static data also caused the flight director to switch from "normal law" to "alternate law 2" which among other things disabled roll and pitch/AOA limiters, as the data used to calculate those limits is no longer reliable.
Lastly, the lack of reliable pitot-static data was reflected in cockpit instrument displays. We don't know exactly what they saw because information on the status of the right side pitot system is unavailable (it was not recorded by the black boxes). However, we do know the disagreement of data caused the red-flagging of practically all information reliant on such data, including the airspeed and altimeter tapes, the flight director, velocity vector, and all secondary indicators including AOA readouts, the stall horn, etc. The flight crew would have been totally reliant on external visible references to determine the aircraft was stalled.

A secondary instrumental cause was the stall indicator system itself. Counter-intuitively, the stall warning was issued when the aircraft was nosed down, and stopped when the aircraft nosed up. This was due to the flight computer treating the extreme AOA calculations (in excess of 40 degrees) as unreliable. Nosing down brought the AOA back into the "reliable" band, but the resulting alarms were counter-intuitive to the pilots; applying a control input and hearing an audible warning is usually a signal to back off that control input.

Finally, the flight crew themselves demonstrated a lack of familiarity with the behavior of the aircraft in exceptional circumstances; the loss of pitch/roll limiters and the counter-intuitive stall horn behavior caused the flight crew, in the absence of the captain, to make a series of critical and ultimately fatal overcorrections and inactions.


Can you do your PPL solo time in an ultralight?

Nope.

Your solo time must be done in the category and class of aircraft for which you are seeking a pilot certificate (the FAA doesn't come out and say it in those words, but that's what the "aeronautical experience" requirements basically boil down to). You must also pass a pre-solo knowledge exam and receive instruction in the particular make and model of aircraft you will be solo-ing in (the second of which is impossible in an ultralight: You cannot receive dual instruction in that aircraft as by regulation it can only have one seat).

As you don't need a pilot certificate to fly an ultralight you could just get one, get some basic instruction on flying it (from someone who has flown them before), and go fly. Some ultralights are pretty fine basic aircraft thanks to modern materials and construction techniques.

Your private pilot training & solo experience would be helpful in flying certain types of ultralight aircraft, but it's not required as long as you abide by the regulations applicable to ultralights.
Similarly experience in the more "airplane-like" ultralights may help you out in the rest of your private pilot training, but that experience isn't required (and not really "loggable" toward your training, through you can put it in your logbook if you wish -- just log the time as "Ultralight Flying" or something similar.)


What is the exact definition of a "crew duty day"?

How do you define a crew duty day? When does it start and when does it end?

In the most simplistic terms, a crew's duty day can be defined in two parts: the "flight duty period" (FDP) and the "flight time".

The FDP begins when the crew "clocks in" for their shift. There might be administrative duties to accomplish prior to flying, so "flight time" has not yet started. The FDP ends when the last flight that they operate blocks in. The Flight Time begins and ends with each Block Out to Block In, and there might be several individual flights within a single FDP. Once the FDP is over, they might still be required to attend to admin duties, but their FDP "clock" has stopped ticking. Their "rest" clock has not yet started, just because their FDP has ended. (Some of these terms and definitions will be expanded upon later.)

  Also what are the legal limits (in other words how long can a crew duty day last in terms of hours)?

This is an extremely complicated question, and the rest of this answer will be devoted to this, in conjunction with your other sub-questions.

  [Are there] standardized set of rules?

Not necessarily rules, per se... but the ICAO does have a lot of documentation about duty/rest, fatigue management, and the effects on safety. Although the ICAO cannot publish laws, most of it's member nations write their aviation laws in close conjunction with ICAO's recommendations. These nations have ratified treaties stating that they will "abide by" most of the ICAO's recommendations.

  does each country define its own rules?

Yes, each regulatory body has its own laws for determining duty/rest requirements. Most are very similar, and based on the ICAO's body of documentation and research.

Narrowing this down even further, each carrier develops it's own policies and procedures that are based on (and approved by) it's parent nation's regulatory body.

  What happens when you fly say from the US to Australia? Which set of
  rules prevail?

You will follow the policies of your air carrier, which are enforced by your carrier's country of registration.

  Let's start with the US.

Ok, within the US, most of the rules regarding duty/rest for Part 121 Air Carriers are enumerated in Part 117: Flight and Duty Time limitations and Rest Requirements: Flightcrew Members.

There are some "All Cargo" duty/rest requirements under Part 121 Subpart Q (Domestic), Subpart R (Flag), and Subpart S (Supplemental); however, carriers can chose to use these 121 Subparts OR Part 117, but not both. Once they make that choice (listed in their GOM/OpSpecs and approved by the FAA), they are stuck with it.

  What is the exact definition of a “crew duty day”?

As noted in the comments of the question, this is not a legal term within the US FARs. Under Part 117, we find the definition for these related terms:

Calendar day means a 24-hour period from 0000 through 2359 using
Coordinated Universal Time or local time.
Duty means any task that a flightcrew member performs as required by the certificate holder, including but not limited to flight duty period, flight duty, pre- and post-flight duties, administrative work, training, deadhead transportation, aircraft positioning on the ground, aircraft loading, and aircraft servicing.
Flight duty period (FDP) means a period that begins when a flightcrew member is required to report for duty with the intention of conducting a flight, a series of flights, or positioning or ferrying flights, and ends when the aircraft is parked after the last flight and there is no intention for further aircraft movement by the same flightcrew member. A flight duty period includes the duties performed by the flightcrew member on behalf of the certificate holder that occur before a flight segment or between flight segments without a required intervening rest period. Examples of tasks that are part of the flight duty period include deadhead transportation, training conducted in an aircraft or flight simulator, and airport/standby reserve, if the above tasks occur before a flight segment or between flight segments without an intervening required rest period.
Rest period means a continuous period determined prospectively during which the flightcrew member is free from all restraint by the certificate holder, including freedom from present responsibility for work should the occasion arise.

From there, it can get extremely complicated and an airline's crew scheduler probably could not do their job without the aid of a computer. Flight crewmembers are restricted to a certain number of hours in a duty period, and there are limits to cumulative hours as well:

total Flight Time cannot exceed:
-- 100 hours in any 672 consecutive hours or
-- 1,000 hours in any 365 consecutive calendar day period.

And then...

total Flight Duty Period cannot exceed:
60 flight duty period hours in any 168 consecutive hours or
190 flight duty period hours in any 672 consecutive hours.

They are required to have a certain number of hours of "rest" in between these duty periods, and those rest hours are required to be in a certain type of facility (if they are not at home).

The amount of time in the cockpit for a flight is also determined by what time of day you start, whether or not there is an on-board relief crew, whether or not you have crossed more than 60 degrees of longitude (and if you HAVE, how long have you been within the new "theater"), and several other factors.

So, finally, back to your question:

What is a crew's "duty day", and what are the legal limits? The answer is so complicated, that the Air Line Pilot's Association has published a 60-page document (updated several times) with 128 scenario-based Q&As just to help "clear it up".

ALPA's FTDT Limitations and Requirements (May 2015)