What would cause an aircraft (j3 piper cub) to slide backwards when going into a stall?

This is called a "tail slide" or "whip stall". It is an aerobatic maneuver when performed on purpose, but can be dangerous if done by accident because it causes damaging forces to control surfaces. Some aircraft if the CG is in the wrong location, will tend to tail slide before they fully stall (my C-177 is prone to this). – Ron Beyer

Aerobatically, to enter a tail slide you would enter from level flight at full speed (maneuvering speed) and pull straight up (1/4 loop) and wait for your airspeed to bleed off to zero. The aircraft will then slide backwards and eventually the nose will drop. You stay in the dive until you have enough airspeed to recover.

Doing this on accident is a little more complicated, and is surprising that the J-3 could even do it. What happens is that you pull up while adding power just as you would be practicing a power-on stall, only the tail stalls before the wings do. The tail drops and the aircraft slides backwards. This is especially dangerous at low altitude because the only way to recover from a full tail-slide is to allow the nose to drop and gain airspeed in the dive.

The recovery action for an incipient tail-slide is similar to recovering from a stall. Nose down to the horizon and full power. Newer training requirements don't let the student go into a full stall, it teaches to recover the aircraft as soon as the aircraft begins to buffet, or at stall speed + 10kts. I'm not sure I agree with the new requirements but that is a topic for another question.


What are the requirements to get your private pilot certificate?

In the US, you'll need to be 16 old to start training and 17 to get your Private Pilot's license in a piston-powered aircraft. To get your license you'll have to have a minimum of 40 hours total time, including at least 20 with an instructor and 10 solo. You will also have to pass a written test, and get a Medical certificate.

Details:

If you're pursuing a Private Pilot license, per 14 CFR §61.83(a) or (b) you must be 16 years old to get a student pilot certificate (or 14 years old if you're going to train in a balloon or glider.)

NOTE: 14 CFR mean Code of Federal Regulations, Title 14 - Aeronautics & Space.  §61.## means "Part 61" which covers Certification of Pilots and Instructors.

To start training you will also have to pass a medical exam for a 3rd Class Medical Certificate, per 14 CFR §61.23(a)(3). If you're generally healthy, getting a 3rd Class Medical isn't terribly difficult.

Assuming you successfully complete the training, per 14 CFR §61.103(a) or (b) you can get your Private Pilot license for an airplane at 17 years old (or 16 years old for a balloon or glider.)

Per 14 CFR §61.109(a) to get your license you will need to have completed at least 40 hours of flight time, including at least 20 hours of time with an instructor and 10 hours of solo time.

However, many pilots take more than the required minimum 40 hours to get their license. My suggestion is to try to complete your training in as short a calendar time as is possible. By taking lessons frequently (more than once per week) you will minimize the amount of "repeat" lessons, which will help you get your license with fewer hours. If you're only taking a lesson every few weeks, you will end up repeating topics and spending more than the required 40 hour minimum.

Per 14 CFR §61.35, you will have to complete a ground school program (can be with an instructor, or a "home study" course) before you take the Knowledge test (aka: written exam.)

Per 14 CFR §61.109(a)(3), you will need at least 3 hours of "Instrument" flight training to get your Private Pilot license. That's really not intended to be enough for you to fly safely on instruments, but to give you a basic set of skills to get out of a low-visibility situation. If you keep up with your flying, getting in Instrument rating is a GREAT idea, once you have enough hours.

You can look up the specific wording of all of the rules at http://www.ecfr.gov/

Another good resource for student pilots is the Aircraft Owner's and Pilot's Association's Learn to Fly page http://www.aopa.org/Pilot-Resources/Learn-to-Fly.aspx.


If the static port get blocked, and no alternate static air source is fitted, will the transponder keep provide mode C?

It will stop reporting correctly as it is connected to the same static air line as the altimeter

  The transponder depends on an external altitude encoder to provide the digitized pressure altitude that the transponder needs for its Mode C replies. The encoder is connected the same static air line as the altimeter and is wired electrically to the transponder

However the transponder may not know the port is blocked and will still report the erroneous information it is receiving. If the port is blocked it’s pertinent to shut off altitude reporting manually.


You're probably fine.  File a ASRS form all the same though.

The feds tend to focus on safety of flight issues or gross violations that indicate general incompetence.  Some guy flying below a B shelf doesn't rise to the level of incompetence (because it's not).  Worst case, you caused a resolution advisory for an airliner which, in the grand scheme, is not a huge deal (for you, legally) if you were following the rules (sounds like you were).

If you get a letter, call an aviation attorney.  I doubt it will come to that though.

Keep on flying.


How is the A320neo engine different from the A320ceo engine?

It is a very large question and it will be difficult (even with all information) to give a strict answer.

Both LEAP-1A (A320neo family) and CFM56-5B (A320ceo family) are turbofan engines which means they have two cores (HP and LP core) and two flows, and where total airflow is created by a Fan. As you said, LEAP-1A has a larger diameter allowing higher by-pass ratio (efficiency improvement) and lower rotational Fan speed (noise reduction). Besides, OPR (Overall Pressure Ratio) is greater (~40:1 vs. ~33:1) and lead to a performance improvement too.

Nevertheless, even if LEAP-1A has a slightly greater max thrust (~155kN vs. ~140kN), we cannot affirm there is "a range improvement" since they do not operates on same aircraft. If it's true here, it is more appropriate to compare aircraft range than engine range. Moreover, thrust is calculated for an aircraft flight mission (by Airbus, Boeing, etc.) and then generally given to engine manufacturers as input for conception.

Now, to answer more specifically your questions, LEAP-1A service entry was in 2016, more than 20 years after CFM56-5B first flight. Therefore LEAP engines gather a lot of improvements resulting from years of research and maturity tests. So yes, there is others differences between these engines (you can find public characteristics on manufacturers or specialised websites - even wikipedia get a lot of information actually).

1. Are the engines lighter than its predecessor (are they made of lighter alloys?)

Material is probably one of the field where you can find best improvements in aeronautics the last decades, for both aircraft and engines. In particular, many advances have been made with composite materials.

When comparing CFM56-5B and LEAP-1A, the most significant (and literally the most viewable) point is about Fan material. For a CFM56-5, fans are probably made of steel or nickel alloy (I don't know exactly but these are common for old generation engines). In a LEAP engine, composites are used for fans with titanium at leading edge. This allow, amongst others, a lower number of blade (18 blades) and larger chord: fan mass reduction despite larger diameter, aerodynamic efficiency, etc.

But is LEAP-1A really lighter than its predecessor CFM56 ? Not sure, remember that the diameter is larger. A quick search on google give 2900kg for LEAP-1A and 2400kg for CFM56-5B, but I don't know if it was calculating in the same way.

Note that other improvements are made in high temperature parts (like HP turbine) both in cooling and material resistance resulting in a higher combustion temperature (again there is an efficiency improvement).

2. Do the new engines have the reduction gearbox which lacks in the ceo engines?

No, both LEAP-1A and CFM56 do not include gearbox. CFM international has never developed an engine with it. This is a manufacturer choice as the gearbox lead to an extra mass and often extra maintenance costs. In the other hands, gearbox give advantages by decoupling LP turbine / booster and fan speed and remove one constraint to optimise each component.

As @Bianfable said in comments, it is a little bit awkward to talk about ceo and neo engines as Airbus manufacture these aircrafts with 2 different engines. For example, Pratt & Whitney PW1000G turbofan on A320neo include a reduction gearbox..

3. And what is TAPS II combustor technology?

TAPS (Twin Anular Premixing Swirler) is a combustor technology developed by GE aviation. While CFM56-5B used SAC (Single Annular Combustor) or DAC (Double Annular Combustor),  TAPS is a newer type of combustor used for GEnX engine (Boeing 747-8 and 787). The version II is the scaling version for LEAP engine. The main idea is to limit rich combustion zone (mainly responsible for NOx).

Take a look to this FAA report for interesting details.


Are there specific engine TBO requirements for aircraft used in flight instruction?

§91.409   Inspections. (b) Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person
(other than a crewmember) for hire, and no person may give flight
instruction for hire in an aircraft which that person provides,
unless within the preceding 100 hours of time in service the aircraft
has received an annual or 100-hour inspection…

You can rent out your airplane without complying with 100 hour inspections provided that you don’t provide both the pilot and the airplane. Insurance will be a lot more, probably 3-4 times as much. If you are renting it out you might have more than 100 hours in a year so you need to make sure you  comply with 100 hour ADs.
I do it with my Cherokee from time to time when I know people who want to learn to fly. The students can use any CFI they want and pay them separately from renting. Depending on how many people want to learn, I have an open pilot policy with only some CFIs and me as named insureds or if there are only a few students, everyone is a named insured.
Edit: The only maintenance requirement for Part 91 operators is 91.409 discussed above. TBO is not specifically mentioned in the FARs so you won’t find a rule saying that you don’t have to comply with manufacturer’s TBOs. I have a folder of 116 Legal Interpretations and NTSB opinions. A search of them finds no mentions of TBOs.
As you point out there are lots of articles that mention it. I'd trust them. This AVWebarticle by maintenance guru Mike Busch says,

Both Lycoming and TCM publish engine TBOs in the form of non-mandatory
service bulletins. Some Part 121/135 operators have Operations
Specifications that require them to comply with all manufacturer’s
service bulletins (even non-mandatory ones), while others have Op
Specs that require compliance only with mandatory service bulletins.


The life (Low Cycle Fatigue life) on the Civil airliners is generally talked abut in terms of number of cycles i.e. number of flights. And since airliners undertake quite predictable flights in terms of loads and stresses, and typically a very limited variations among these parameters for their entire life (since any aircraft would be designed for certain type of range and payload and would be used for that particular purpose mainly, for economic reasons), its easy to talk in terms of number cycles, since variations from flight to flight are limited.

But this issue of keeping track of actual mission profile is very critical for fighter (actually any military jet but I would restrict myself to only Fighters because its easier to point out the things for this case) jets which have quite unpredictable usage profile. Any fighter jet is typically designed for a certain mission mix i.e. mixture of a bunch of mission profiles that the fighter is expected to carry with the expected relative frequency (which comes from the past experience of an Air Force). But still in real life, the actual missions flown end up being quite different that this assumed mission mix. Now it is possible to utilize the airframe structural life to best possible extent by keeping track of actual mission profiles flown and debiting life for each mission from the designed number of hours. Obviously one needs to calculate the life debit for actual mission flown in terms of the equivalent hours for assumed designed mission mix. Say a fighter is designed for 8000hrs assuming it will fly 10 times of missions with certain frequency, and it recently flew a mission for which we know the parameter, then what would be the number of hours of equivalent life that was utilized from this 8000hrs..?

To calculate this we need the loading parameters of each mission such as how many Gs were pulled for how long time intervals, how many rolls performed with what roll rate and so on. Every aircraft has system which collects this information (measured by various sensors) for entire mission. Once on the ground, this information is fed to what is called as "Life Tracking System". It analyses the data, calculates how many hours of debit this mission took on the airframe and then decides what is remaining life.

This can be done at component level as well and one can keep track of available life of each component and accordingly schedule maintenance for each component individually. I am not sure how this is exactly done for entire aircraft (Looking for Patents by Aircraft OEMs would be a good way to start digging in), but I know for the Jet engines. The methodology should be the same in principle. Specifics might change. I suggest you read about Volvo Aero RM12 Life Tracking System (LTS) which finds its origin in GE's LTS for F404. (A good starting point to read) and another one. Essentially all OEMs have similar systems now. RM12 has improved utility of the engine by ~30% i.e. the engine is used for 30% more time now as compared to the case where LTS was not used and differences in missions were not accounted for. Because many missions do not take as much toll on the structural life as it was expected during design (or more number of less stressful missions are flown in actual practice than it was assumed for design).

Most popular technique used to calculate the equivalent LCF life debit for each mission considering variations in loads and stresses for each mission specifically is known as Rain Flow Counting Algorithm. The process essentially looks like this:

You apply the actual measured loads and see what stresses the analysis predicts for each mission. Then apply Rain flow Counting to calculate accumulated structural fatigue damage and residual life remaining. Rain drop counting is the model which helps you covert the irregular fatigue loading (i.e. varying missions) to equivalent cyclic loading and thereby coming up with a life debit number which is equivalent to the design mission mix and which you can subtract from the designed life hours. That's how you can take care of variation in the missions and loadings in each mission.


What is the real difference between aerospace and aeronautical?

Aeronautics is a subset of aerospace.

  Aerospace is the human effort in science, engineering, and business to fly in the atmosphere of Earth (aeronautics) and surrounding space (astronautics).
  source: https://en.wikipedia.org/wiki/Aerospace

They are, somewhat incorrectly, used interchangeably - to colloquially refer to the broad subject of "flight".


Why does a turbine helicopter need to spin a tail rotor?

Well, that’s complex. Where should I begin?

The main job of the tail rotor is to use its long lever arm and directed force/thrust (horizontal lift) to counteract the torque of the spinning main rotor. The exhaust gas of a Turboshaft engine does not produce a large amount of thrust for the very large amount of torque the rotor-powertrain combination produces. See the previous topic: Does a turboshaft's exhaust provide any thrust?.
Energy is finite. In simplest terms, any energy taken out of the engine before the exhaust gasses reach the exhaust nozzle will be energy taken out of the thrust generated. Turbofans generate less thrust with their hot-side core exhaust than Turbojets. Turboprops generate a lot less thrust with their exhaust than Turbofans. And, Turboshafts generate less thrust than that. The most important contribution the exhaust has in a Turboshaft is to dispel heat and waste from combustion.
NOTAR (No Tail Rotor) helicopters already exist that use Coandă Slots and ducted thrust instead of a tail rotor. An internal fan is used instead of the exhaust, though.
The anti-torque thrust a helicopter creates must be variable with the ability to fine tune.
If the engine fails, you still need yaw control until you land.
As complex, damage-prone, maintenance-dependent, and expensive the typical tail rotor system is, if it were possible to use your idea with today’s engine technology, it would have already been done.
I am sure there are other reasons. But, great question. Way to think out of the box.


What is this object in the cockpit of an ultralight?

It's an airspeed indicator for ultralights.  The pitot inlet is at the bottom and the pitot air pushes a little red plastic disc up and down on a central rod, with a calibrated clearance between the edge of the disc and the walls of the tube.  They are very sensitive and are good down to 10 MPH or less.  You'll also see them on hang gliders.

See here:
https://www.aircraftspruce.com/catalog/inpages/hallwindmeter.php?clickkey=5468


How to determine the direction of rotation of components inside a gas turbine engine using the blade profile?

If you know the direction of gas flow, you can determine the direction of rotation of axial flow components (like the fan and turbine in the example) by the angle of attack of the blades. Think of it intuitively--if you were to blow air through the engine in the same direction it flows during operation, which way would the blades windmill? The direction of windmilling is the same as the direction of powered operation, as long as the airflow is in the same direction.

Because their angle of attack, of the blades of the fan would deflect air flowing into the engine counterclockwise when viewed from the front, meaning the fan rotates clockwise when viewed from the front (or counterclockwise from the rear looking forward, which is the conventional way of expressing rotation).

For this particular engine, all other turbomechanical components rotate in the opposite direction as the fan, indicating that the low pressure shaft is connected to the fan using a gearbox that reverses the rotation direction.

This is the low pressure turbine and shaft:

The compressor rotates in the same direction as the high and low pressure turbines, and is attached directly to the high pressure turbine shaft with no gearbox. The high pressure turbine is axial flow and looks like a smaller version of the low pressure turbine, but the compressor is not an axial flow component, which makes the analysis slightly different.

Unlike in axial flow components, in radial flow components like this compressor (a synonym for a radial flow compressor is a centrifugal compressor), the airflow enters and exits in a different direction. The direction of flow also differs between energy-absorbing (turbine) and energy-dissipating (compressor) components. Gas enters radial flow turbines at the edge and flows inward, exiting at the center. In radial flow compressors, gas enters at the center and exits at the edge. You can determine the direction of rotation by imagining the forces the air would exert as it changes direction, similar to the windmilling axial flow components:


Could a hybrid electric steam plane be more efficient at altitude than at sea-level, and how to optimise it to frigid air?

Forget the electric stage - when using steam, you will most likely already have mechanical energy and when ducting that steam through a turbine, even rotational energy to turn your propellers. What advantage do you expect from converting that rotational to electrical and directly again to rotational energy?

That design could be simplified even more: Instead of heating water, the fuel could heat compressed air and let that run through a turbine. That is how any modern jet engine works.

In order to keep mass down, the steam would need to be condensed in a cooling circuit. While the wing surface could be used for this, the required piping would add a substantial weight penalty. In an open circuit where the relaxed steam is simply dumped overboard (like on the Besler biplane or most steam engines), range would be rather limited.

There was to my knowledge a single attempt at building a steam-powered airplane with steam condensation. This was a version of the Messerschmitt 264 bomber which was supposed to run on a mixture of coal powder and heavy oil instead of gasoline. It was never completed.


Why is this plane flying a circular track?

A recent article in Aviation Week showed a modified Bombardier Global 6000 with a "canoe" type fairing underneath the fuselage which typically houses a variety of radar or electronic intelligence (ELINT) equipment (link (free registration req'd) with pic) (alternate). The UK's RAF flies the Sentinel aircraft which is based on a prior Bombardier model, the Global 5000. So it's certainly possible that the track is a valid orbit path for surveillance in that area.

The USAF E11A is based on a Global 6000. It carries the BACN battlefield communication relay system which allows integrated, real-time communication across several, sometimes incompatible platforms. It is designed to operate at high altitudes to allow coms over mountainous terrain.

Since the Jalalabad airport is currently controlled by US armed forces from the adjacent Forward Operating Base Fenty, it would make sense that a communications aircraft would loiter over the area.

If it is a military flight, it looks from the flight path that it may have originated from Kandahar, where the USAF has a base.

(Source)


What is the purpose of the box between the engines of an A-10?

It is the intake/exhaust duct of the cooling system.

Basically, the front side consists of the ram air duct, which feeds air into the ECU precooler, with the (heated) exhaust air vented out through the rear. The image below shows a closeup of the duct.

Image description: Kenneth Thompson, 576th Aerospace Maintenance and Regeneration Squadron aircraft mechanic, aligns a portion of the pre-cooler ram air duct onto the top of an A-10A Thunderbolt on Davis-Monthan Air Force Base, Ariz., Jan. 23, 2013. Source: warthognews.blogspot.in

Here's another image that shows a cross-section of the system. The cooling system (without the box) could be seen above the APU.

Image from pintrest.


Can commercial aircraft dump luggage or cargo mid-air?

No they can't. The cargo doors are secured and will not open mid-flight.

Cargo holds are usually pressurized so opening the door anyway would cause depressurization.

Also if the weight was too high the pilot should never have lifted off in the first place.

Then after you theoretically throw the stuff off board think about what happens after to the stuff. It will drop down hard probably on someone's roof.

Only some military cargo planes with a back hatch are designed to jettison cargo.


What is the typical space allocated to first class vs. economy class passengers?

Width and pitch give you the space that is allocated to you and your seat. First Class seats are more bulky than Economy seats, so the actually usable space is a smaller fraction than in Economy. I wonder how the square meters would convey more information; generally, in Economy you are boxed in by your neighbors, while in First you can outstretch without reaching the limits of the cabin space allocated to you.

The aisles are wider in First, but it will be hard to make a concrete claim on "your" part of the aisle. Cabin crew in First will be more tolerant of eccentric behavior, so your mileage varies. Also note that in First on wide-bodied Aircraft every seat will have direct access to the aisle, so you will not need to step over the feet of your neighbor.

You also get more space for your baggage (luggage). On narrow-bodied aircraft two people sit in First Class where six would sit in Economy, so you get three times more space in the overhead bins. On wide-bodied aircraft this difference is even more pronounced, count on having in First the space of 5 ore more Economy seats. The bins are smaller, though.

Also, the steward will take care of your coat in First, so your space requirement is reduced as compared to Economy.


What winglet airfoils are used on the Boeing B737?

Aviation Partners Boeing, a joint venture between the two companies, developed the winglets for 737NG, 757 and 767 aircraft.  They are offered in two varieties, a "blended" version, which is where the wingtip is upturned to near vertical and a newer, "split scimitar" version which adds a downward pointing tip as well.  They are made of a composite material with aluminium leading and trailing edges.

Their purpose is not to generate lift, but rather, prevent wingtip vortices (which generate a significant amount of induced drag) from spilling onto the top of the wing.

The design characteristics of the blended winglet are described in US Patent 5,348,253.


Are remarks in the Chart Supplement (A/FD) "regulatory" or "advisory"?

A required rule in the airport/facility directory is required. It is a very good idea to check the AFD entry online (or on paper) before you fly to a new airport. It just takes a second and you can learn important things, such as "NO DEPS AFT 2230" or "PPR FOR TKOF ON RY 15. CTC FBO 970-920-2016" (Aspen).


Can I act as SIC with these specific type ratings?

The single B-737 type rating includes all variants of it, from the -100 through the Max; if you were typed in a -200, you have the type, so there is nothing else required in that regard to be Second In Command (SIC) on a 737 NG. (Source... my experience, having flown the -200, classics, NG's, and the Max, all with the one "B-737" type on my certificate.)
The DC-9 family is similar; I don't think there is a separate type for the MD-80.
That all said, there are other requirements pertaining to recency of experience and training. The other answer by @wbeard52 covered these. The pilot would also need a current medical. But as far as required ratings, those mentioned in the original question are sufficient.


How much does each engine on a Boeing 747 weigh?

Boeing 747 can be operated with different types of engines (and in general a specific model has multiple models of engines compatible with it due to competition between different engine manufacturers). Here are some of the engines that are compatible with B747 and their weights:

GE CF6-50: 8,825–9,047 lb
Rolls Royce RB211-524G/H : 12,540–12,764 lb
Pratt & Whitney PW4000-94: 9420 lb

So as you see, from model to model the engine weight might differ and all these engines have been used on B747 at some point.


Where can I find ATC Guidelines for handling Airport Incidents?

I'll answer from US ATC perspective having worked ATC at 3 different airports. First, I'll describe the alerts, then I'll describe training

As with all things, each airport has different procedures for how they handle emergencies or accidents. For each airport, the airport operator and the ATC Tower will come up with numerous Letter's of Agreement for how they want to handle things from lighting to emergency services. My first airport had 2 alert conditions, Orange and Red. Orange was go to standby positions, something is inbound requesting emergency services to be ready in case something happens. These are relatively common. Red was an actual accident/crash.

The more common alerts are broken up into 3 categories I, II, and III. Alert I alerts are usually, a heads up to the crews to just be ready, but not go to the runway. Alert II are go to the standby positions, somebody's inbound with an issue and services are needing to go there. When this alert is declared, often as soon as the plane lands the runway is closed automatically until the airport inspects it(making sure no debris fell off the aircraft on landing). And Alert III is an actual crash. Most of the times, this is an immediate closure of the airport. This is due to the emergency services focusing on the accident and can't be available if something else were to happen on the field. Note, super large airports can have enough spare capacity to keep portions of the field still operating, depending on what all they have and how their command/control works.

Training wise, it's often just on the job training and usually the light emergencies, where people just need to get back or gear stuck or similar non-crash emergencies. Usually in the course of a controller's training at their facility they'll get a couple of these and know how to react. There are discussions of past issues as well, when there's time and resources available to do these types of discussions. Full on crashes, as stated are rare, so likely the first time a controller has to deal with it, they'll have seen small issues in the past to help prepare them.


Is a French PAC skydiving license equivalent to an AFF license?

If you mean you are learning to skydive and will be taking PAC instead of AFF, then the differences are minor. IIRC, in PAC the last jump is number 8, whereas in AFF and PFF it's jump 7.

There's also the Canadian version, PFF, and I assume other variations as well. Generally, schools do not follow any of these exactly and add their own variations.


What is the meaning of "altimeter three-zero-one-one"?

That is a QNH altimeter setting in inches of mercury, with the decimal omitted.  So in the case given, that is a QNH of 30.11 inHg or about 1020 hPa.


Why does the wing root of the A330 have a pronounced twist?

Short answer:
To create a funnel for all the air streaming towards the fuselage.
Slightly longer answer:
Air approaching a swept wing will be accelerated towards the area with the lowest pressure and, therefore, will be sucked towards the wing's center. The center itself will show a markedly different pressure distribution over chord than the two-dimensional flow over the same airfoil would because here the acceleration is much lower while the deceleration length at the end of the airfoil is compressed. If the swept wing has no twist and the same airfoil over span, a flow pattern similar to that pictured below will result:

The blue lines on the wing surface are lines of equal pressure (isobars) and in the plots denote the pressure coefficient on the upper side of the wing section. The red lines show the pressure coefficient on the lower side.
In order to maximize the achievable lift at transsonic speed it is desirable to modify this wing such that the isobars will run along lines of equal chord percentage over the full span. To achieve this, several tricks must be combined:

Make the root airfoil thicker at the front and thinner at the rear part.
Do the reverse for the tip airfoil: It must be made thinner at the front and thicker at the rear part.
Use negative camber at the wing root.
In order to compensate for the much higher zero-lift angle of attack of the modified root airfoil, increase its incidence.

The last step is what causes the kink in the trailing edge. Of course, increasing the wing chord at the center increases this effect. In case of the A330 and A340, the incidence changes from +4.5° at the root to 0° between 30% and 70% span and -2° at the tip when on the ground and -2° at 70% span and -5° at the tip in flight.
Thanks to @ymb1 who found a very illustrative picture of the A330 (shown below, source) the root twist becomes obvious: The root airfoil has visibly much less forward camber (negative camber, actually) and, consequently, a higher zero-lift angle. In order to produce a similar lift coefficient, the center wing needs a higher incidence to compensate for this change in airfoil shape.

Another find by @ymb1 is this picture of Airbus root airfoils (source). The thick nose is easy to spot; it is needed to shift the suction area on the swept wing root forward so that the pressure distribution becomes more similar to the one of the airfoil at mid-span. Also, while the top has a long straight stretch, the bottom is rounded which in combination produces negative camber. The rounded bottom helps to maximize relative thickness. Since the chord at the center wing is increased, the local lift coefficient can be smaller than on the mid and outer wing and still carry the same circulation for low induced drag. What is saved in lift is added in thickness for structural efficiency and for stowing the landing gear. The lack of rear loading (= high local camber in the rear airfoil section) helps to gain the needed volume for the landing gear bays.

Here is another one, this time an English Electric Lightning F.1. The reflections on the leading edge show nicely how it is pulled down at the root with plenty of nose camber there. This being a design from the early Fifties, this nose camber is used to give the wing better stall behavior and isobar shaping was not yet practised. Note that the local incidence has not been increased at the root.

EE Lightning F.1, Imperial War Museum, Duxford (Edited), CC BY-SA 2.0 (picture by Roland Turner from Birmingham, Great Britain; source)


What are the lateral sensitivities of GPS approaches?

Check out AIM 1-1-9 for localizer information. Basically, the localizer is positioned so to have a course width of 700' at the threshold. So full deflection to either side is 350'. A CDI has 5 dots on each side, so at the threshold each dot is 70'. Near the Middle Marker, one dot means you’re off course by 150 ft. Near the Outer Marker, a one-dot deviation puts you about 500 ft. from the centerline.

GPS (non-WAAS) approaches have a constant full scale deflection of .3 NM after the final approach fix.

  AIM 1−1−17 5 (e) (5) When within 2 NM of the Final Approach Waypoint (FAWP) with the
  approach mode armed, the approach mode will switch to active, which
  results in RAIM and CDI changing to approach sensitivity. Beginning 2
  NM prior to the FAWP, the full scale CDI sensitivity will smoothly
  change from ±1 NM to ±0.3 NM at the FAWP. As sensitivity changes from
  ±1 NM to ±0.3 NM approaching the FAWP,…

WAAS on the other hand is similar to the localizer.

  AIM 1-1-18 (d) 4 Both lateral and vertical scaling for the LNAV/VNAV and LPV approach procedures are different than the linear scaling of basic
  GPS. When the complete published procedure is flown, ±1 NM linear
  scaling is provided until two (2) NM prior to the FAF, where the
  sensitivity increases to be similar to the angular scaling of an ILS.
  There are two differ- ences in the WAAS scaling and ILS: 1) on long
  final approach segments, the initial scaling will be ±0.3 NM to
  achieve equivalent performance to GPS (and better than ILS, which is
  less sensitive far from the runway); 2) close to the runway threshold,
  the scaling changes to linear instead of continuing to become more
  sensitive. The width of the final approach course is tailored so that
  the total width is usually 700 feet at the runway threshold. Since the
  origin point of the lateral splay for the angular portion of the final
  is not fixed due to antenna placement like localizer, the splay angle
  can remain fixed, making a consistent width of final for aircraft
  being vectored onto the final approach course on different length
  runways. When the complete published procedure is not flown, and
  instead the aircraft needs to capture the extended final approach
  course similar to ILS, the vector to final (VTF) mode is used. Under
  VTF, the scaling is linear at ±1 NM until the point where the ILS
  angular splay reaches a width of ±1 NM regardless of the distance from
  the FAWP.


Where can I listen online to live VOLMET broadcasts?

The Globaltuners site will allow you to tune their UK radios (subject to them being online) to the UK VOLMET frequencies if you really wanted. Whether this is technically "legal" or not is for you to decide ... it's not in the UK, but it's not enforced either.


Is pumping the control column an acceptable technique during flare?

He’s not pumping the yoke per se;  rather the pilot is making a series of quick, precise corrections to the yoke in order to track a precise glideslope to an aimpoint while on short final.  This process can be exacerbated by gusty winds on final, poor throttle control, etc.

Here’s a better example from the cockpit of a C-2 Greyhound CODS aircraft making a Case 1 trap aboard Carl Vinson (CVN-70).  Note the hundreds of minute inputs the pilot makes to the yoke, rudder pedals and throttle on lineup, in close and at the ramp.  He’s applying pitch inputs to correct for deviations from glideslope, throttle inputs to correct for airspeed deviations from Vref+5 kts, aileron and rudder inputs to correct for deviations from lineup on the groove, and rudder inputs to correct for yawing brought on by changes in power.  It looks exhausting.


What is the correct definition of "spanwise" and "chordwise" with a swept wing?

b) is a correct description of both .
"Spanwise" is perpendicular to the aircraft's longitudinal axis because it does not relate to the width of the wings, but to the span of the aircraft. which includes both the wings and the fuselage. Consider that the wings of most aircraft and all birds, don't really have a clear "root" where  the wing ends and the torso/fuselage begins.
"Chordwise" is parallel to the aircraft's longitudinal axis because that is the way the air flows. Any other angle would not make sense. It might be of interest on some specific airplanes, but otherwise the only thing that matters is the general airflow, which is parallel to the aircraft's longitudinal axis for cruise flight in most any aircraft.
Swept wings, be they aiming forward or aiming back, have a characteristic that can't be defined by either span or chord. The same goes for delta wings for which every chord over the span of the wing is different.


Why "Throttle...Open 1/2 travel" on engine troubleshoot checklist?

Revised following update to OP:
If the engine quits and you're gliding along with it windmilling and the throttle pulled back to idle, if it comes to life at some point, you may not even be aware of it because you can barely tell the difference between off and idling when it's windmilling in a glide.  On the other hand, pushing it full forward isn't such a good idea either.
You want it set to a power setting that makes it obvious it's come back to life, but you don't want to set it to full throttle because you don't want it going full bore instantly, which is generally not helpful to the engine because the oil pump may only be making 20 or 30 psi while windmilling, or none at all if it stops windmilling, and full power before the oil pressure can catch up is murder on the plain bearings of the crank journals that depend on oil pressure to keep crank journal and bearing separated from physical contact.
So half throttle makes a nice compromise.


Would the Concorde have been better off using a tailed delta wing?

The beauty of the pure delta configuration was you could get a reasonably low supersonic drag configuration in a planform with a lot of wing area, essential for really high altitude cruise and for reasonable landing speeds without high lift devices.  It was a good overall compromise for Concorde's mission.

The Avro Arrow, produced then scrapped in Canada in the late 50s, also used a large pure delta plan form (which is thought to have had some influence on Concorde, a lot of Avro's engineers having joined the Concorde program when Avro Canada vanished).  This allowed it to meet the RCAF's specification that required M2+ while being capable of sustaining a 2G turn at 50,000 feet, something no interceptor could do at the time.


Difference in lift generation for a swept wing and straight wing in subsonic condition

Since both the lift curve slope and the effective angle of attack are reduced by the cosine of the sweep angle at quarter chord, the lift coefficient of a swept wing at the same geometric angle of attack is reduced by the square of the cosine of the sweep angle.
Also, the pressure distribution over chord differs between straight and swept wings, especially near the center and the tips. All this makes swept wings less attractive, were it not for their ability to delay compressibility effects, basically for the same reasons which reduce their efficiency.
However, lift is generated in the same way: By pushing air down or by a pressure difference between upper and lower wing. Both are equivalent explanations of lift.
Only at high sweep angles and high angle of attack will vortex lift kick in and produce this pressure difference by means of a strong vortex on the upper side of the wing.
Since you ask about "subsonic condition … lower than Mach 3", I wonder whether you actually ask about supersonic flight with a subsonic leading edge. Now things are rather different between a swept and an unswept wing: While the sufficiently swept wing with a subsonic leading edge will still exhibit a pressure distribution similar to that at subsonic speed, the supersonic straight wing will create a shock, resulting in a slowing down of the flow where at subsonic speed an acceleration could be observed, and vice versa. Also, the center of pressure will move back in supersonic flight.


You might also consider evaluating Hydrogen-powered aircraft and Biofuel as ways to operate aircraft with combustion engines on alternative fuels that can be produced in a more sustainable manner.


Which aircraft have made notable use of lateral asymmetry?

There are quite a few asymmetric aircraft, most of which are,

experimental
engine test beds

A good example of experimental aircraft is the NASA F-16XL

F-16XL with supersonic laminar flow control experiment (black area on left wing, front) or "glove." Image from nasa.gov

Aircraft used as engine test beds are usually asymmetric. The following image shows a B-47 Stratojet used as engine test bed for the the Orenda engine earmarked for Avro Arrow program.

Image from silverhawkauthor.com

A closeup of the rear:

Image from google

English Electric Canberra PR9s had offset canopies.

By MilborneOne - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=13266605

So did the de Havilland Sea Vixens.

By Yeovilton_Vixen_2009-001.tif: Nigel Ishderivative work: Cobatfor - This file was derived from  Yeovilton Vixen 2009-001.tif: , CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19477903

Of course, all 'conventional' helicopters (with tail rotors on one side) are asymmetric, but I don't think that's what you're after here.

Also, see this page and the Wikipedia page on asymmetric aircraft. As a disclaimer, I wouldn't call any of these aircraft 'ugly'.


Are any online resources available for ATC recordings?

LiveATC is probably your best shot. The quality you'll get on the stream depends on where the receiver is setup. Since aircraft communications are in VHF or UHF (military) reception is basically within line-of-sight range. This is why often you'll hear the aircraft side of the conversation without hearing ATC.

I would just browse the various streams on LiveATC until you find a good one. OR, if you're near an airport, set up your own receiver!


Is it legal for a balloon to land at a US international airport?

Assuming the winds directed a hot air balloon near a US international
  airport

By this I assume you mean a major airport in class B or C (possibly even D) airspace. An "international" airport is simply one that is an airport of entry and maintains customs officials and processing ability and may or may not be a "large/major" airport.

  would they face legal trouble/fines

This depends on how the balloon is equipped. As mentioned in the comments you need a transponder and a 2 way radio to enter certain controlled airspaces (usually those surrounding big airports) and if the balloon is properly equipped it would be allowed to enter and utilize public resources such as airports and landing areas. This advisory circular on ballooning would indicate it is legal to enter all airspaces in a balloon.

There are of course some practical problems here such as the fact that as a balloon you can't really divert around an airspace if you are not granted clearance. If there is no safe landing space and the wind is blowing such that your only option is to enter the class B you may be stuck declaring an emergency, or at least getting back on the radio and explain whats going on. Some FAA officials may consider this poor/dangerous flight planning (since you should have looked at the wind prior to departure) and you may end up in some trouble for that.

From the Balloon Hand Book

  As a general rule, balloons do not freely operate within Class B
  airspace. Equipment requirements are the same as for Class C airspace;
  however, due to air traffic congestion, the balloon pilot requesting
  entry to Class B airspace will likely be denied entry, as ballooning
  operations inside the Class B airspace constitute a potential traffic
  conflict....

But legally you can and the FAA prefers you coordinate before hand,

  Should it become necessary for operational reasons to fly through
  Class B airspace, that flight should be coordinated at least one hour
  prior, as provided for by 14 CFR section
  91.215. It is permissible, and perfectly legal, to operate a balloon under the lateral limits of the Class B airspace.

Same applies for class C,

  Balloon operations in Class C airspace, while technically feasible,
  are usually not advisable


Based on the unique 6x pusher-prop configuration, this looks like a derivative of the Convair B-36 Peacemaker. Looking up the Wikipedia article for the B-36 and scrolling down to the variants section, this seems like an XC-99 (or, more aptly, the XC-99):

Public domain image via United States Air Force - USAF photo via, Joaobsen, Wagner, Greer (1980), B-36 Peacemaker in action - Aircraft No. 42, Squadron/Signal Publications; 1st edition, ISBN-10: 0897471016

This was to be a passenger variant of the airframe, with a passenger capacity of up to 400 people. Beyond the prototype, it didn't enter service.


How do I execute this instrument approach at Larnaca (LCLK)?

If you're course 200 then you are more than 30 degrees off the initial outbound track of the approach, therefore you should join the hold prior to commencing.

In more practical terms, if you're VMC at any point and your happy with your terrain clearance, then there would be nothing to preclude a request for a straight in, although from experience, LCA can get busy!


What information is recorded in aircraft sensor and maintenance logs?

For the F-35, it captures possibly too much. Not just every aspect of the physical operation of the jet, but all the other things the jet can do.
Capturing details on all the radar and sensors that may be trying to track it, route, speed, altitude, G's etc, etc.
The specific details of what is captured and available for download is not generally public info.
The Autonomic Logistics Information System (ALIS) system is going away, to be replaced by Operational Data Integrated Network (ODIN) in late 2020.
https://www.thedrive.com/the-war-zone/31861/replacement-for-f-35s-troubled-alis-cloud-based-brain-rebranded-odin-and-is-still-years-away

The Pentagon says that a replacement for the F-35 Joint Strike
Fighter's long-troubled cloud-based computer brain is finally coming.
The U.S. Air Force, Marine Corps, and Navy have said that the existing
system is one of, if not the most significant factor in the abysmal
mission capable rates for their respective F-35 variants and a major
contributor to the growing sustainment costs for the aircraft.
Unfortunately, the upgraded system is not expected to be in widespread
use until 2022 at the earliest.


Is there a minimum start altitude for autorotation landings?

What you're looking for is the height/velocity curve, some times called the 'dead man's curve'. This shows the altitude and speed requirements for a safe autorotation, plus the height and altitude conditions under which an autorotation is probably not possible.

A lot of variables go into this, and the h/v curve is specific to the particular helicopter, and in particular, whether the helicopter has a high inertia rotor system or low inertia rotor system.

For example, the Robinson R22 has a low inertia rotor system, meaning that the rotor blades are fairly light, and thus don't have a lot of inertia to remain spinning in the case of engine failure. A similar size helicopter, the Enstrom F28, has a high inertia rotor system, so the h/v curve for the Enstrom looks quite different from the Robinson, but is somewhat similar to another popular high inertia helicopter: the Bell 206 JetRanger.

As the article notes, Robinson doesn't recommend a climb out under 45 knots speed, while Enstrom allows it at 17 knots. This limitation is governed by the h/v curve, not performance. While the Robinson could climb out at lower airspeeds, it wouldn't be safe in the event of engine failure.

Disadvantages of a high inertia system are that it uses more fuel, and is slower to accelerate under power in low rotor speed conditions (which are also potentially deadly).


Why did the turbojet replace the piston engine?

Two more reasons the gas turbine supplanted the piston engine for aircraft use:

Power output. Aircraft piston engines have a practical limit on how much power they can put out, before becoming inefficient. This worked out to be around 3000hp. Two of the largest and most powerful piston aircraft engines that were also reliable enough for aircraft use are the Napier Sabre and P&W R4360, at around 3000hp, developed at the end of WW2. Yes, more power has been obtained from piston engines on land based vehicles, but they're either racing engines whose reliability is too low for aircraft use, or they're far too heavy for aircraft use, such as the 20k+ HP diesel engines that power cruise ships.

Gas turbines don't have those limits, one contributing factor being the lack of a reciprocating action. With a piston engine, each full stroke results in the piston accelerating to top speed, then coming to an abrupt halt and accelerating in the opposite direction... twice. Gas turbines that just spin can be made substantially larger while maintaining the reliability and efficiency that aircraft use demands.

Also, gas turbines tend to have a very high power to weight ratio, making them ideal for large aircraft use, where weight is very important.

Equating HP to thrust isn't simple as HP is raw power, while thrust includes altitude, velocity, and propeller/fan efficiency.

A simplified example was published on Aerospaceweb:

  Luckily, we do have access to data from a NASA report that does
  provide all the data we need to illustrate a sample case. The data is
  provided for a Boeing 747-200 cruising at Mach 0.9 at 40,000 ft
  (12,190 m). In this example, the aircraft's engines produce 55,145 lb
  (245,295 N) of thrust, only a quarter of its rated static thrust, to
  cruise at a velocity of 871 ft/s (265 m/s). Using the equations
  provided above, we calculate the power generated by the 747 to be
  87,325 hp (65,100 kW).

Using that very simplified example, a GE90 producing 115,000 pounds of thrust would be putting out the equivalent of around 160,000 horsepower.

Also, the maintenance requirements on gas turbines are substantially lower, especially for the high output engines. For example, the very large RR Trent series turbofans have a TBO (Time Between Overhaul) of around 15,000 hours. On the large piston engines such as the R4360, the TBO was more like 1500 hours, and the very large piston engines, especially the radial engines, had a prodigious appetite for engine oil. Plus intermediate maintenance on piston engines that gas turbines don't need, like changing spark plugs, that had to be done frequently. The Convair B36, which had six R4360's, required 336 spark plugs. Not something you could do in your driveway in an hour.

Some of the gas turbine's reliability comes from it's lack of vibration. Large piston engines, with their reciprocating action, tend to vibrate a lot, which reduces the life of engine and auxiliary components, like fuel pumps and spark plug wires.

Thus, not only did the turbojet, turboshaft, and turbofan make possible aircraft that wouldn't be practical at all with piston engines, such as large airliners flying at 30k+ feet, they also lowered the cost of maintenance and the frequency of maintenance substantially.

There is one area where the piston engine for aircraft use is still the better solution, and that is when the engine gets small, below around 500hp. Gas turbines don't scale down all that well. The small ones are not fuel efficient, nor does the cost get substantially lower.

As an example of this, consider one of my pet daydreams - a single seat Mosquito helicopter. Aside from the ultralight version, two versions with larger engines (and requiring a FAA helicopter license) are made, the XE285, with an 85hp snowmobile engine, and the XET with a 90hp gas turbine engine derived from a backup power generator. The piston engine sells for maybe 2k USD and burns around 5gph, while the gas turbine sells for 10k and burns 8.5 gph.


Do different planes (category) aim differently in the 'final stages before flaring'?

Because of the downrange offset between the PAPI and the GS antenna, only a P3 (jumbo jet size) PAPI (14 meters eye to wheels) gives a more or less parallel path between the ILS glide slope and the pilot's eye so that they are both aligned on short final.  The other PAPI categories all have a deviation between the ILS slope angle and the PAPI slope angle, so that if you stay on the ILS glideslope all the way down, at some point the eye height becomes too high for the PAPI and you will see three whites even though you are right on the ILS.

You take this into account in training to learn to resist the urge to dive to correct because the last thing you want is to increase sink rate close to the ground. So really, once you are really close in, inside the airport boundary, you don't rely on the PAPI lights.  If you were on-slope in a stabilized approach configuration at Vref at decision altitude, you just have to hold the pitch attitude and speed with maybe a few small pitch tweaks based on the runway sight picture and you will cross more or less at a wheel height of 50 ft. The goal is to hear "50" from the GPWS just as the threshold is passing below, and the speed tape pointer is right at Vref.  From there the touchdown point takes care of itself using the normal flare/thrust reduction procedure you use for that airplane.

This Transport Canada Staff Instruction regarding the design of PAPI installations and issues with harmonizing them with ILS approaches gives some useful background: https://www.tc.gc.ca/media/documents/ca-opssvs/AC_302-009.pdf


Helicopter retreating blade stall: Increasing the fwd speed decreases the tip speed on retreating side and angle of attack. So why limit on V_n.e?

For the same reason aircraft have $V_{S}$ — you don't want to get into stalled condition, because while recovery is possible, it is difficult and far from certain.
Due to the gyroscopic effect, the rotor blades reach the lowest point 90° behind the point of minimum lift. As the helicopter accelerates, the lift would decrease on the retreating side, which would push the aft side of the rotor down, pitching the helicopter up, and reducing the speed again (that is, unlike hover the helicopter is stable in forward flight).
Except the pilot wants to accelerate, so they keep pushing the cyclic forward, which increases the angle of attack on the retreating side (90° ahead of the desired tilt to compensate for the gyroscopic effect), compensating the loss of lift due to the lower air stream velocity.
So the angle of attack is higher on the retreating side because of pilot input, not inherent property of the rotor.
Now when the helicopter reaches the point of stall, the tendency to pitch up will increase, and it won't be possible to compensate it with more forward cyclic, since the retreating side is not able to generate more lift. In this sense, the condition is actually self-correcting as the helicopter will start climbing and losing speed. However

the accompanying vibrations from the repeated stalling and unstalling of the blades as they rotate will stress them significantly and might cause structural damage and
the violent pitch up accompanied with some roll to the retreating side (which it is depends on type) might lead to the pilot losing spatial orientation and consequently control over the usually low flying vehicle.

So you still want to avoid getting into the retreating blade stall condition in the first place.


Which aircraft have elevators (lifts)? How do they work?

After researching myself and asking a colleauge I found out that the L-1011(one of my favorites)

and the DC-10 (thanks to @UnrecognizedFallingObject for the comment)

had persons elevator.

On the Tristar and the DC-10
The purpose are to connect the Main Deck with the personnel-cabin or the Lounge.
.

The Mechanism as "@ratchet freak" stated in the comment is an "rack and pinion gears" elevator with 1 electric motor with 1 outer shaft (primary) and 1 inner shaft, as stated in an report of an incident with one of these elevators.

On the A380 there is an elevator to connect the 2 main decks, but this one is only for trolleys.

Edit:

Additional Information on mechanism of elevator:

  Drive System

  Each lift is operated by an independent drive unit. Each drive 400-cycle, three-phase,
  alternating current (AC) motors. Each motor is connected to a gearbox with
  counter-rotating drive shafts and sprockets for a chain drive. The drive shafts are
  operated by a common worm gear within the gearbox. In the
  event of one motor failure, the other motor will drive the lift at
  half-speed. Two, independent, continuous loop, bicycle-type chains taking power from the
  dual-output sprockets on the drive units actively drive each lift.

  Limit Switches

  The range of travel of the lifts is controlled by limit switches installed
  within the wire duct attached to the forward side of one of the vertical lift
  tracks. There are two sets of two limit switches for each lift:
  one set located in the service center and one set in the lower galley.
  One switch is a normal stop switch and the other limit switch is for
  overtravel in the event the normal switch fails to operate.
  The limit switches are actuated by a cam plate mounted on the side of the lift.
  The cam plate has a machined offset to prevent actuation of the
  overtravel limit switch unless the normal switch fails to operate. In
  addition to the limit switches, mechanical stops are installed in the
  vertical lift tracks to stall and shut off the gear motors if both
  limit switches malfunction.

Further and detailed Information can be found here in this Incident.


Can airline pilots communicate with dispatchers?

Yes, and it is a regulatory requirement that it is so.

§121.99   Communications facilities—domestic and flag operations.
(a) Each certificate holder conducting domestic or flag operations must show that a two-way communication system, or other means of communication approved by the FAA certificate holding district office, is available over the entire route. The communications may be direct links or via an approved communication link that will provide reliable and rapid communications under normal operating conditions between each airplane and the appropriate dispatch office, and between each airplane and the appropriate air traffic control unit.

The typical way to contact dispatch is through SELCAL which allows two way communications between two specific parties over HF or VHF radio.  To contact a dispatcher we would tune the COM associated with SELCAL to the proper frequency (these were charted on company airport pages and you would use one from an airport nearby that you are overflying) and then use our handheld microphone (with keypad) to dial a code for our dispatcher, which is noted on our release paperwork.
As long as you are monitoring a SELCAL frequency and dispatch (or someone else with your aircraft code) calls you, the airplane will announce "SELCAL" and typically a light or some other visual notification will come on.
Once connected, you talk to your dispatcher over that com radio the same as you would talk to ATC.  From there your dispatcher can connect you to maintenance, med link, or anyone else you might need to talk to.
For larger airplanes typically used on overwater routes you will probably also find a satellite phone in the cockpit that can be used as an alternative way to call dispatch.
Textual communications to and from dispatch are also possible using ACARS.


What happens to incoming flights when the airport shuts down?

If a "terrorist takeover" like this were to happen in the real world...

...and the tower still had communication capability:

The tower controllers would advise pilots of the situation, and likely instruct them to return to the Approach frequency to coordinate their next steps (probably a landing at an alternate airport).
Presumably the tower would still have telephone communication as well, and be able to let Approach know to expect the planes to come back because of the emergency, otherwise the pilots would certainly inform the approach controllers of what's going on when they switch back to that frequency.

...and the tower has no communication capability:

With no response from the tower the usual thing for pilots to do is return to the Approach frequency to find out what's going on. The pilots could elect to attempt a landing anyway, treating the airport as an untowered field (this somewhat famously happened at KDCA, for somewhat different reasons), or proceed to an alternate airport.
If the weather required an instrument approach and the ILS radio signals are not transmitting this would be something the pilots could detect pretty easily (similarly if they were turned off while flying the approach there would be indications in the cockpit that the signal was lost and the pilot would execute the missed-approach procedure), and they would proceed to an alternate airport, again coordinating with the approach controllers.

...in any case:

No matter what the situation the aircraft would divert to their alternate airports long before they were in danger of running out of fuel. They would notify ATC of the situation and proceed to an alternate airport. (If not cleared by ATC to proceed to an alternate at some point any sane pilot will declare an emergency for low fuel and proceed on their emergency authority to make a safe landing somewhere.)

So basically there's some "artistic liberties" taken in Die Hard 2 in the interest of making it a movie you'd want to sit through.
A movie where a bunch of terrorists take over an airport and a bunch of flights divert to alternate airports (mildly inconveniencing the passengers) while the National Guard surrounds the airport and deals with the terrorists wouldn't sell nearly as many tickets!


Impact of centre of gravity position on stall recovery

It sure does, and that is the reason we don't abuse aft CG limits.
An excessively aft CG shortens the torque arm of the tail pitch down forces and lengthens the torque arm of pitch up forces ahead of CG, including more of the wing.
As a full stall develops, the nose of the fuselage will also generate lift in addition to its area drag as the plane sinks, making it harder to "bring the nose down" and unstall the wing by reducing its AOA to the relative wind.
By design, a larger tail adds safety if one is foolish enough to test aft CG limits. A speed brake or parachute is another line of defense.
The effect of forward set CG on stall speed may arise from the need to generate a bit more lift with the wing to counteract increased tail downforce but remember most tail "downforce" is used to set wing AOA, only a little more is needed for forward CG.
Forward set CG will also make it harder to lift the nose in slow flight, which may actually drop the nose before it stalls if elevator is small or travel is limited and the horizontal stabilizer is large.  The B-52 was designed in this manner for obvious reasons.
Each plane is different, and even a docile trainer like the Cessna 152 can be dangerous if aft CG limit is exceeded.


According to the Jeppeson chart legend[pdf] those are database identifiers. I'm presuming that's what would show on a menu in the FMS.


Is there an ARINC label/data that can be associated with a gyroscope's precession?

Short answer: No easy way. It may be possible for a crew to detect some drift by comparing the IRS mag heading to the magnetic compass.  This does have problems though as the IRS doesn't really 'measure' mag heading.  It works in true heading and calculates mag heading by applying a magvar correction from a table.
Modern aircraft do not have free gyros that output data. They have inertial reference systems (IRS). The IRS has multiple gyros and accelerometers and outputs a complete navigation solution.  They also have an internal GPS (or an input from an external GPS) to improve their accuracy.  So there's not a lot of 'drift' in the output solution.
These units have internal integrity monitors and will report a fault to the crew if the nav solution exceeds limits.  In some failure modes the IRS will revert to an attitude only mode (ATT) that just outputs raw rates and accelerations (free-gyro mode).  In this case, the crew can provide a heading update to set a heading.  This will drift just like a stand-alone directional gyro.  The crew will have to check it regularly against the mag compass and update as necessary (~ every 10 minutes).


Why did most WWII Allied piston engines not use fuel injection?

Those engines didn't use carburetors as in gravity operated float carburetors.  They used "pressure carburetors".  Pressure carbs are mechanical fuel injection systems that inject the fuel from a single point at the start of the manifold instead of injecting fuel at the intake port via a distribution system.  Not quite as theoretically efficient as point fuel injection, but it has all the other advantages including automatic mixture control and no G sensitivity, as well as being less sensitive to damage by not having small high pressure fuel lines running to each cylinder.

On cars in recent years you had a similar system called "throttle body fuel injection", more or less an electronically controlled pressure carb.


How comes lift is less than weight on take-off?

Indeed, what puzzles a lot of people is that excess lift (excess as in more than we need for weight) it not what makes an aircraft climb.

Of course, a take-off is a dynamic situation which doesn't really call for a balance of forces and momentum, so the situation is a bit more complicated to explain, but let's try a thought:

Imagine it this way: If lift > weight you will accelerate 'up-'wards (ie. balloon style). Air will come not only from the front moving backwards, but also from above moving below. The relative air moving past your wing is now coming from front and slightly above. This decreases your angle of attack and thus decreases lift, usually up to the point where lift = weight again.

If lift< weight, the opposite happens (ie. accelerate downwards) and air will move from below the wing towards up. This increases the angle of attack, increases the lift, and again lift will match the weight.

It's basically a statically stable system, where the only really stable position ,if you think about, is when lift equals weight (in straight-level flight, mind you. For climbing and descending you have the formula stated in your question).

If you want to climb, increasing lift is not the way to go !


What's the relationship between drag divergence Mach number and maximum operating limit Mach number?

They are unrelated definitions. Mmo is set by the designer with input from actual flight testing, Mmo is a maximum safe speed and is only concerned with practical operation and structural integrity. Mach divergence is a physics phenomena. Mmo can be much lower or higher than the Mach divergence from one aircraft to the next. Mmo has a similar purpose to Vne but Mmo is a more useful measure for high performance aircraft.
It just happens that most commercial and large business jets are designed for high subsonic cruise so the design goal is to push divergence to higher speeds for more efficiency and Mmo ends up very close to Mach divergence.


Those are Learjet 35's. In USAF service, they're called C-21's.

Source


Material alternatives for aircraft leading edge

If we're talking about transport category airplanes, the options depend to some extent on the wing.  Wings with hard leading edges (no slats) and supercritical airfoils with poor stall characteristics are not very tolerant of what is called "runback ice"; ice that melts or is prevented from freezing by a warm but not hot leading edge and can run back and re-freeze just aft of the leading edge, forming a ridge, creating a dangerous risk of premature stall in the approach configuration.
These wings may require "evaporative" anti icing, which heats the leading edge to above the boiling point, so that supercooled drops that strike immediately turn to steam and can't flow back onto the wing plank as water.
Such a leading edge will run at about 110 degC when anti-ice is on and you will burn yourself pretty nicely if you touch one.  The leading edges can be aluminum since the aluminum's heat treat state isn't affected until over 200C. So a composite material would have to have a transition temperature above 200C to have some margin to be tolerant of overheat cases.
If your wing has slats, runback icing isn't a concern in the approach configuration with slats extended, so the slats themselves may only need to be heated to about 50-60 degC, and the composite options become wider.
If you're not finding any high temperature composites on the web, try searching just for high temperature Epoxy laminating resins.  There are all sorts of resins that can handle temperatures almost as high as aluminum and some that are higher.
In any case, the biggest reason composites aren't used for heat-anti-iced leading edges is poor conductivity. If you heat the leading edge with bleed air blown inside (typically) or with electrical elements bonded on the back of the skin (I think that's how Boeing does in in the 787), you need the heat to transfer to the outer surface immediately with almost no temperature loss (so that a sensor mounted on the inside surface is reading very close to the actual temperature on the outer surface) and you generally want a smooth surface, so aluminum is the ideal material.
Of course you could go with rubber boots and make the leading edge out of whatever you want, if you're willing to live with the inferior performance at ice shedding. Airplanes typically use boots because their engines don't make enough surplus bleed to heat a leading edge. Just about all turboprops and some small corporate jets like the earlier Citations are like that - and some are able to heat the leading edges but have to use boots on the tail, or, make the tail big enough to handle the ice so you don't have to anti-ice it at all (the CRJs do this).


What are the repercussions of flying an aircraft with an invalid N number on the side?

As a controller, if it's a correctly constructed N-number, I'd know nothing. and wouldn't do anything. If you file a flight plan, however, the N-number you use will go into the FAA's database. Keep in mind that if you ask a controller for flight following, a Mode C check, etc., there will be a record, even if it's only "on the tape".
I have no idea whether they would flag an unregistered number, but I can give you some history on an aircraft that flew with an INVALID N-number.
In 2006 (or so, why is this stuff so long ago?), I was working the high altitude sector in the LBF (North Platte, NE) area. I received a handoff on an aircraft with a call sign similar to, but not exactly "N1EP2D", which is an illegal construct (see https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/forming_nnumber/)
I alerted my supervisor, who directed me to question the pilot. As it turned out, the pilot had filed this deliberately, and on a whim.
The FAA does not do "whimsical".
I instructed the pilot to submit the correct N-number, which he did, and I amended the flight plan. I also instructed the pilot to NOT use the invalid number, and to call our Operations Manager for further instructions.
I heard it was a six-month suspension, although I had no official follow-up.


How are conflicts between pilot flying and pilot not-flying over aircraft control resolved?

The whole idea behind the policies and procedures for transferring control of the aircraft between the pilots is so that everybody is always on the same page.  Somebody always needs to be flying the aircraft.

If I want to hand control over to the other pilot, and he doesn't want it/can't take it, he would simply explain why not.  I have never seen standard operating procedures (SOP's) that explain how to refuse, as simply saying no or unable should let the other pilot know that there is a problem and should be the beginning of a conversation about it.  On the other hand, the SOP's do cover the scenario where the other pilot doesn't respond.

This is why there is always a challenge/response as part of handing off control.  If the other pilot were incapacitated and I didn't realize it, I would say "You have the flight controls" (or whatever phrase that the SOP's require) and wait for his response.  If they didn't respond, I wouldn't just blindly stop flying the airplane and assume that they are.  Instead, I could say it again or look over at them to see what was going on and figure out what the problem was while continuing to fly the airplane.

Now, to request control from the other pilot (rather than requesting them to take control), I would simply skip the first part and say "I have the flight controls" and they should respond with "You have the flight controls."  Again, it's a challenge/response situation so that everybody is on the same page.

In either case, the captain is the final authority and can always override a request.  Airline policies are all very clear that if there is a disagreement, the captain has the "tie breaking" vote.


Why is Thunderbird 5's number upside down?

This is because Thunderbird 5 is the opposing solo, and spends almost all of its time inverted.

Apparently though, this plane's number was not always painted upside down:

Just guesswork on my part, but maybe the Thunderbirds did not fly inverted maneuvers before the F-16s?


Is it negligent to depart with one thrust reverser inoperative?

No, it is not negligent.  Landing performance data assumes no thrust reverser usage and thrust reversers can be dispatched inoperative per the Minimum Equipment List (MEL) with a logbook entry and possibly the inoperative reverser mechanically locked/disabled.  With a single thrust reverse operative, depending on the aircraft and airline ops, the other one may or may not be used.  If it is used, caution in maintaining directional control during landing is advised.  Any such stipulations will be part of the MEL verbiage.

A proper MEL action will consist of a logbook entry by the pilots or maintenance, a logbook sign-off by maintenance and dispatch notification of the MEL.  Thus, the pilots, maintenance and dispatch are all aware of the issue.  Lastly, and special requirements of the MEL will be noted by the crew when they consult the MEL book after noticing the MEL in the logbook and in the dispatch paperwork.   In the airplane I am familiar with you could visually note the thrust reverser locking bolt during the walk-around inspection to verify that maintenance had done its job properly.  This also presented a nice opportunity to query the First Officer and see how well they were paying attention during the inspection.

The situation would only be negligent if proper procedures were ignored.


What are the differences between the different types of TCAS?

The Traffic Collision Avoidance System TCAS (also called ACAS - Automated Collision Avoidance System) is used in aircraft to alert the pilots about possible collision.

The basic system in all the levels are the same. As per the FAA what differs is the type of warning issued to the pilots. As per FAA:

  TCAS is a family of airborne devices that function independently of the ground-based air traffic control (ATC) system, and provide collision avoidance protection for a broad spectrum of aircraft types.  All TCAS
  systems provide some degree of collision threat alerting, and a traffic display.  TCAS I and II differ primarily by their alerting capability.

TCAS I issues 'traffic advisories' (TAs) to the pilot, alerting him to the impending collision.

TCAS II provides the pilots with resolution advisories(RAs) in addition to TAs. Basically the TCAS provides the pilot with the required escape manevores in th vertical direction.

TCAS III and IV were supposed to provide horizontal resolution RAs, but development was stopped due to limitations of the available TCAS antennae.

TCAS is expected to be replaced by automatic dependent surveillance – broadcast (ADS–B)


A321 Two unsuccessful strong crosswind landing attempts. What was actually going on?

Based on the provide date, I looked up weather history and the METAR (weather report for pilots) was:

CYUL 110700Z 24033G49KT 15SM -SHSN OVC033 M02/M08 A2937 RMK SC8 SLP948

Which translates, in English, to:
CYUL weather report at 11th day of the month, 0700 UTC time: Winds at 240 degrees at 33 knots gusting to 49 knots, visibility 15 statue miles, little snow, overcast clouds at 3300 feet, temperature -2C, dew point -8C, altimeter 29.37 inches of mercury; Remarks: scattered clouds at 800 feet, sea level pressure 948 milibars
49 knots would be equivalent to 90 km/h, but it is possible that the wind report by the ATC tower was higher at the time of landing.
How much crosswind was there?
Assuming the pilots attempt to land at 24L / 24R, there would be little or no crosswind. However the high wind speed + high variation of wind speed would be a problem: the fluctuation is 16 knots. For a small airliner like a A321, 16 knots of airspeed gain / loss is a lot. The pilot did not feel comfortable putting it down, so he chose to divert. The decision was a wise one: he tried enough (2 attempts) and concluded he'd better get back while there is still fuel left.
(Side story: I once heard a GA pilot who go-around 9 times on the same runway because of high wind. On his 10th approach he crashed)
Was it wise to takeoff?
Yes. Scrolling back the clock a few hours to the time when the pilots would prepare their flight, the weather forecast was:

(...) FM110400 24030G40KT P6SM BKN025 OVC050 (...)

Which translates to: from 0400 UTC time onwards, wind would be 240 degrees at 30 knots gusting to 40. Well, not good, but this was 9 knots below the reported gust when they actually arrived. Moreover, an alternate airport which was within reach and with better winds was chosen. This flight was short, and it is not surprising that on such short flights the alternate is return to the departure airport.
Was it wise to abort the landing and apply full power?
Absolutely! Forcing the plane onto the runway is the exact opposite of what a pilot should do. I will tell you, most (I don't have a number, but a fair guess would be >80%) of the landing accidents occur because the pilots failed to recognize that the aircraft was not fully prepared for landing (gusting winds, too high on approach, flaps not configured etc.). If those pilots chose to apply full power, go around and give it another shot, many lives would have been saved. Many people perceive aborting a landing as "dangerous"; in fact, it's the best thing to do in those situations.


How is the fuselage of the Boeing 787 produced?

There is a YouTube video showing the method for creating the structure:

YouTube: 787 Composite Construction

This video from British Airways shows the joining process:

Fuselage Section Joining Process which you can see is not welded, but riveted together. The sections are lined up and riveted together using joining plates.

  Since it is not fabricated as a single piece there are bound to be stresses on the joints. Will it effect/endanger the passengers?

No, not more than any other conventionally constructed fuselage. The joining plates are metal and the structure around them is a metal bulkhead. The 787 fuselage is not a 100% composite construction.

  Are the same methods used to join the wings?

Yes, if you watch the second linked video in full, you can see the composite wings being bolted to the fuselage structure. The entire wing support structure looks to be a conventional metal structure.

  Last but not least, are there problems due to the joints before and if so, what has been done to rectify these problems?

There are new challenges with any type of new construction technique, here are a few articles that outline the challenges:

NY Times: New Challenges for the Fixers of Boeing’s 787
MIT Technology Review: Boeing's Composite Problem

Boeing has said that the 787 is as easy to repair as traditional aluminum skin aircraft. One case in point is the Ethiopian Airlines aircraft ET-AOP damaged by fire. The procedure to fix it is to cut out the carbon fiber material and put a "cure in place" patch over the hole. In this case other structure had to be replaced or repaired like stringers and bulkheads. This was the first major airframe repair that Boeing had to undertake. ET-AOP took 18 months to repair before being returned to service.


What is the typical voltage and frequency of the electrical generator in an airliner?

A constant speed drive (CSD) converts the rotation from the accessory gearbox to a predetermined constant rotation rate.  The rate of the accessory gearbox is directly related to the high pressure spool (N2) rate and changes with power adjustments.

The CSD will ensure its rotation rate is constant.  The Challenger 604 CSD rotates at 12,000 RPM and outputs 115 VAC @ 400 hertz.  Its max output is something like 30 kVA or kilovolts-amps.  Since we are talking AC power, it is not appropriate to call that watts.  The AC power is converted to 28 VDC by the way of transformers called transformer rectifier units (TRU).


Can you fly 2000 miles on an engine that costs less than $500k? If so, what type of engine?

Your best bet would be an airplane/drone that is built from carbon composite and graphlite rod (pull-truded carbon rod with incredible strength - widely used in sailplane spars) powered by a couple of aviation diesels like the Austro Engine E4.

The Specific Fuel Consumption of the E4 is .336 lbs/hp/hr.  Except for similar competing diesels, nothing in any traditional aircraft engine configuration comes close except the old tubro-compound mechanical-monstrosity radials like the R3350 that could get into the high 3s (normal gas piston engines are around .45 lb/hp/hr and turboprops well above that, around .5-.6 lbs/hp/hr).

The E4 is 168 Hp so two would give you 336 HP for take off, and the engine burns 5 US Gal per side at 60% cruise, or 30 lbs per side, so to go 2000 nm, if you can get the thing to cruise at 150kt, you need 130 US Gal capacity plus a VFR reserve, say 140 gal total, or 840 lbs of fuel.

So design an airframe that can haul, say, a thousand pounds of payload with those two engines and 840 lbs of kerosene, and is clean enough to go 150kt, and there you have it.


Can I do a VFR climb-out on IFR flight plan?

KTUS doesn't have a VCOA, but I can think of a couple of alternatives (other people may have more). First, file a composite (VFR to IFR) flight plan. See the AIM section 5-1-7:

  Flight plans which specify VFR operation for one portion of a flight,
  and IFR for another portion, will be accepted by the FSS at the point
  of departure. If VFR flight is conducted for the first portion of the
  flight, pilots should report their departure time to the FSS with whom
  the VFR/IFR flight plan was filed; and, subsequently, close the VFR
  portion and request ATC clearance from the FSS nearest the point at
  which change from VFR to IFR is proposed.

Second, depart VFR and ask for a pop-up IFR clearance when you need it. But this isn't ideal if you know that you'll be in IMC (or in the flight levels) at some point and you want to make sure your clearance isn't delayed.

Third, depart IFR and just ask ATC for whatever handling and routing you want. If weather conditions are good and there isn't much traffic, there's a good chance they'll let you do what you want. Considering the terrain, though, I wouldn't do it unless you're familiar with the area. And of course there's a chance that ATC won't allow it anyway.

Finally, although this doesn't answer the question you could just fly the ODP. I've never been to Tucson but the airport elevation is 2643' and right now the temperature is 32C and the altimeter setting is 30.10, that means the density altitude is about 5000'. And since you're departing to the east (more or less) it looks like you'll need to get to at least 11000' (IFR altitude) because of terrain, so you have to climb 8000' with limited space to do it and with reduced performance because of the high DA.

I don't know what you fly, but climb performance in those conditions isn't great in many light piston aircraft - at least if they're normally aspirated - and a climb in the hold seems like a good way to get up there safely. Of course, if you know the area well and your aircraft is up to it, then things would look different.


How long does it take to restart a turbofan engine inflight?

It can take from a few seconds to eternity. If the core cools down, the engine might lock up.

Windmilling starts are only possible if the aircraft is flying fast and low enough. It will assist the startup process, but needs additional help from the starter or bleed air, typically below 300 knots and above 20,000 ft. Details vary from type to type. If everything works as designed, a windmilling assisted restart is faster than a regular engine start.

The ability to restart in flight must be proven as part of the certification process. However, right after takeoff the speed is too low for a pure windmilling start, and an additional energy source is needed.


How to correct these garbled tail numbers?

Having just N71 could be a valid tail #, but airlines almost always use all 5 characters. Most likely, the "@" characters are masking the actual characters in the full tail number.
A site like PlaneSpotters dot net may help, but the search on
https://www.planespotters.net/photo/search?tag=N405
gives both 405DX (Delta) and 405WN (Southwest). Further research may reveal if either of those was only active outside your target dates, but there will probably be cases where neither can be ruled out.
In this case, the current N405DX is pretty new, while N405WN first flew in 2001 (link), so that's probably it. But there could have been a different Delta jet flying in 2001 using that registration, so again, more research required to rule that out entirely. Searching Google on the full tail number is often useful that way.
Anything with three masked characters is probably beyond resolving, but with only one or two it may be possible.


What are the general problems faced for maintenance in fuel inerting systems?

As far as commercial airliners go, the inerting system is relatively simple and lightweight; see the below diagram from Airbus for a relatively representative architecture (most systems also have some kind of compressor to inert the tanks more quickly in certain situations).

With a total weight of just a few hundred pounds and the ability for most of the architecture to be colocated near the fuel tanks, the inerting system is far less complex and heavy than, say, the air-conditioning system. The air separation module (ASM) is practically the only unique component; most other maintenance issues with inerting systems are similar to those of other systems: mechanical/thermal fatigue and failure, software bugs, accidental damage, etc.

However, there have been some issues with the reliability of the ASMs, which is currently the biggest concern of aircraft operators. I can't find any public information on why so many ASMs are failing at half their predicted service life, but I imagine it has something to do with their being a relatively new mechanical technology on commercial aircraft.


Would it be beneficial to have rotors AND propellers instead of a tiltrotor?

There are 2 major problems. First is the weight you'd incur from:

Extra rotors/propellers
Transmission components (the V22 already has a transmission in case of an engine failure, it's already more complex than you'd ideally want but it's necessary for safety)
Structural components to support the forces from the propellers and extra transmission

It's lighter to turn the engine and rotor together, and probably more reliable.
More importantly the rotors have aerodyamic issues at higher speeds. Remember the rotors are still up there, and they must be dealt with. You could:

Fold them away or back: you'd need a mechanism capable of stowing and unfolding the rotors in an airstream, which means weight
Have them produce no lift: this means they will be dead weight so they will take away from payload
Use them for lift: this would be similar to a gyrocopter, where a rotor is unpowered but produces lift from forward flight. There's aerodynamic limitations due to the differences in lift from advancing and retreating blades which would limit your top speed


Do military aircraft overflying other countries' airspace require special clearance?

In general, a diplomatic clearance is required for overflight of military aircraft over other countries. The aircraft are considered state aircraft and prior clearance has to be obtained through diplomatic channels. Note that the clearance is usually issued by the defence ministry of the concerned country.
The mode of clearance and monitoring varies from country to country. In case of US:

Foreign governments seeking diplomatic clearance for state aircraft to transit U.S. territorial airspace or land in the United States must obtain a diplomatic clearance number (DCN) issued in advance by the Office of International Security Operations, Bureau of Political Military Affairs (PM/ISO), Department of State. The DCN authorizes the aircraft to transit or land in the United States and/or its territories, in accordance with the approved itinerary.

The overflight permissions are also dependent on agreement between various countries, like India-Pakistan. In some cases, like some EU countries, military transport aircraft can operate without diplomatic clearance.
Some other countries, like Canada give blanket clearance for military aircraft from some countries:

3.2.3 Blanket Diplomatic Clearances to Foreign Military Aircraft

By order-in-council, United States, United Kingdom, and New Zealand military aircraft are exempted from the requirement to have a formal diplomatic clearance (see 3.2.1 above) prior to overflying and/or landing in Canada.

Military aircraft from North Atlantic Treaty Organization countries other than the United States and the United Kingdom are granted clearances on an annual basis. These clearances do not apply to aircraft carrying armed soldiers, armaments and/or other dangerous goods, nor do they apply to aircraft carrying government personnel.

The procedure is usually the same in most of the countries- the overflight request is given through diplomatic channels to the countries' defence ministry, which then evaluates it and approves (or rejects it). The procedure for Canada is given here:

The state of origin will provide full flight details, as outlined in Annex A, in a diplomatic note from its embassy to Foreign Affairs and International Trade Canada (DFAIT). DFAIT will consult with the Department of National Defence (DND) Operations Centre and, if the foreign military aircraft is landing at a civilian airport, with the Foreign Inspection Division to determine whether any pre-conditions should be imposed. After this consultation, DFAIT will reply to the requesting embassy by a return diplomatic note. On advice from DFAIT, the DND Operations Centre officer will then issue the appropriate flight clearance and distribute copies to the interested parties.

In case of India:

For clearance of flights by foreign military aircraft, the concerned diplomatic mission in India or abroad are required to apply to the Ministry of External Affairs with copy to Air Headquaters/Naval Headquaters forclearance of such flights. After clearance given by Ministry of External Affairs, Air Hqrs/Naval Headquaters will issue necessary AOR number for operation of such aircraft, whether it is overflying Indian air space or landing at any Indian airport (civil or defence).

The monitoring of overflying aircraft depends on the country. Civil ATC usually monitors the aircraft carrying transponders, while the military radars (where available), monitor all air traffic and scramble fighters when the aircraft is not identified/responding properly. Overflight without permission may at the very least result in the aircraft being forced to land by authorities.


How (and when) does Heathrow alternate arrival paths?

Heathrow has an extraordinarily elaborate runway alternation programme, designed to spread out noise as evenly between its different neighbours as possible.

Daytime runway alternation follows a daily cycle and a fortnightly cycle. Alternation starts at 6am and continues till the last aircraft departs at the end of the day.

In the morning we use one runway for take-offs and the other for landings. At 3pm – roughly halfway through Heathrow's working day – we swap over
We continue this morning and evening pattern of runway use for the rest of the week
The following week we switch completely. What we did in the evening during the previous week, we now do in the morning. And vice versa

Regarding planes over Richmond (which is situated under the approach path to runway 27L):
During the week starting 8th of April, the programme states that 27L was used for landings from 6:00 until 15:00, resulting in a lot of traffic over Richmond during the morning, but little to none in the evening.
During the week starting 15th of April, the programme states that 27L is used for landings from 15:00 until the end of the day.
During the week starting 22nd of April, they will switch over again to land on 27L from 6:00 to 15:00.
You can read much more about the programme here.


What is the cost per hour of a Gulfstream V?

The Gulfstream G550 is a variant of the Gulfstream V.

From aopa.org (November 16, 2015) for the G550, it costs $4,731.05 per hour, give or take. (Assuming the plane is paid for already.)

Adjusted for inflation that's $4,825.11.

Note that the GV is older than the G550, and would generally cost more to operate.

  This figure includes fuel, maintenance (parts and labor), engine reserves, auxiliary power units if applicable, and miscellaneous expenses to include crew travel, catering and cabin supplies, landing and parking fees—all boiled down to a single number.


What is the difference between active tip clearance control system and passive tip clearance control system in turbine?

This is kind of half an answer, but the difference between active tip clearance control and passive tip clearance control is in the definition of “active” and “passive”. An active system has some way of determining the clearance, and then making adjustments to achieve a desired gap. So, it has a feedback loop in the control system. A passive system has no feedback, it just operates “blind”.

Turbine blade tip clearance is usually achieved by blowing cool or hot air onto the turbine casing, to make it contract, and move closer to the blade tips (when cool air is being used), or expand (when using hot air). A passive system will just blow x amount of air at temperature y, during a given portion of the mission (say the climb), without actually knowing what the actual clearance is.  It was up to the designers to make sure the values for x and y result in the right tip clearance. In comparison, l expect an active system has some feedback so it modulates the flow to achieve a desired clearance.

Here is a scientific paper that describes a concept for active tip clearance. The paper uses the term “open loop” to describe a passive system. An active system would be “closed loop”, because there is a signal going back to the controller, telling it how well it is achieving its target tip clearance. It appears in this paper, this signal is not an actual measure of the tip clearance, but rather a prediction from a thermal model of the casing & blade.


Have landing gear collapsed at the gate?

A good landing gear design locks it into the extended position under the aircraft's weight. This makes it physically impossible to retract it at the gate, but when the switch is in the wrong position the gear starts to retract during liftoff, when the wings take over the duty of carrying the weight.

This doesn't mean that careless operation or maintenance procedures can't make it retract, however. When the aircraft is poorly balanced, say during loading and unloading, the weight on the nose gear might not suffice to lock it, so a wrong switch position can cause an unintended retraction.


There are several reasons:

A helmet provides head protection. A fighter airplane can make many sudden turns and a helmet provides reduction of the risk of a head injury.
If the pilot needs to eject the airplane, helmet is needed to protect from wind blast, in addition to what I mentioned #1.
Helmets play an important role in noise attenuation.
The mic and headphones are mounted in the helmet.
Many helmets contain a sun visor, hence the pilot does not require to use sunglasses.
Modern helmets have a mounted display, night vision support. The latest ones help to see the pilot in any direction they desire, and even through the airplane.
Oxygen supply mask can be directly mounted to the helmet.