Can you fly direct to your destination if you can cruise above FL450 regardless of airways?

If ATC allows a direct-to, then yes. However, what you will file is a flight plan based on published waypoints, but not airways. So pick and choose based on great circle and trade winds and so on.

  Airways

  The en route airspace structure of the National Airspace
  System (NAS) consists of three strata. The first stratum low
  altitude airways in the United States can be navigated
  using NAVAIDs, have names that start with the letter V, and
  are called Victor Airways. They cover altitudes
  from approximately 1,200 feet above ground level (AGL)
  up to, but not including 18,000 feet above mean sea level
  (MSL). The second stratum high altitude airways in the
  United States all have names that start with the letter J,
  and are called Jet Routes. These routes run
  from 18,000 feet to 45,000 feet. The third stratum allows
  random operations above flight level (FL) 450. The altitude
  separating the low and high airway structure varies from
  county to country. For example, in Switzerland it is 19,500
  feet and 25,000 feet in Egypt.

  (FAA Instrument Procedures Handbook - En Route Operations)

And from the FAA AIM:

  Operations above FL 450 − Use aids not
  more than 200 NM apart. These aids are depicted on
  enroute high altitude charts.

compared to

  Operation off established routes from
  18,000 feet MSL to FL 450 − Use aids not more than
  260 NM apart. These aids are depicted on enroute
  high altitude charts.

and finally

  Operation above FL 450 may be conducted on
  a point-to-point basis. Navigational guidance is
  provided on an area basis utilizing those facilities
  depicted on the enroute high altitude charts.

Special RNAV points can also be used, such as the HAR, see here: What are those 5-character alphanumeric waypoints? HAR allows up to 500 NM between waypoints.

The reason for the limitation in filing a huge distance without points is the air traffic optimization. The computers are limited by how far to look ahead for conflicts is one of the reasons. I don't have numbers at the moment but I'm mentioning it in case you were wondering. Also because the different sectors and FIR's prefer to have a complete leg(s) within their own airspace. However, they can coordinate together and shoot you direct-to the destination.


Is there a limit of how close a runway can be to the water?

FAA Advisory Circular (AC) 150/5300-13A covers "standards and recommendations for airport design." It does not include any restrictions on proximity to bodies of water, but it does make the following recommendation in paragraph 319(a):

  It is recommended that the entire RSA and RPZ be accessible to rescue and fire-fighting vehicles such that no part of the RSA or RPZ is more than 330 feet (100 m) from either an all-weather road or a paved operational surface. Where an airport is adjacent to a body of water where access by rescue personnel from airport property is desirable, it is recommended that boat launch ramps with appropriate access roads be provided.

The actual FARs (14 CFR 139, Certification and Operations: Land Airports) also do not state a limit. The only reference to bodies of water of any kind is in §139.325 (Airport emergency plan) paragraph (e):

  The plan required by this section
  shall contain provisions, to the extent
  practicable, for the rescue of aircraft
  accident victims from significant bodies
  of water or marsh lands adjacent to
  the airport which are crossed by the
  approach and departure flight paths of
  air carriers. A body of water or marsh
  land is significant if the area exceeds
  one-quarter square mile and cannot be
  traversed by conventional land rescue
  vehicles. To the extent practicable, the
  plan shall provide for rescue vehicles
  with a combined capacity for handling
  the maximum number of persons that
  can be carried on board the largest air
  carrier aircraft that the airport reasonably
  can be expected to serve.

So, bottom line: there is no limit, but airports are required to take water into due consideration when developing emergency plans, and the FAA looks at each airport and plan on a case-by-case basis during airport certification.

As for the rest of the world, I have no authoritative information; but as others have posted, it certainly seems like the situation is the same, there being numerous examples of airports worldwide built on natural or reclaimed land very close to water.


No, although they were used up into the 1990s. Wikipedia has an article on this - called the Fulton Recovery system. Your quoted paragraph is incorrect - U.S. Air Force Special Operations Command (AFSOC) did use the system, on modified MC-130s. Despite the danger, Wikipedia only mentions one death using the system, though given the clandestine nature of many of the missions it was used on, it would not be surprising if there were other as yet unrecorded instances of its use.

Modern special operations helicopters have a much greater range, and some, like the MH-53, MH-47, and MH-60, are actually air-refuelable, extending their range. Additionally, the CV-22 Osprey has a much greater range and speed than a traditional helicopter. These improvements in extraction vehicles made the 'skyhook' system obsolete.

Note that this article mentions the British used the system in 2001 to rescue an injured soldier behind enemy lines.


how long can this airplane stay in that airport?

The aircraft is "AOG" so it cannot leave. It needs to stay as long as it takes to complete the necessary repair.

  what is the airports role in this situation? Do they help them out or just charge the amount they stay on the ground?

The airport usually would charge the airline the parking fee. The parking fee is a small cost of not having an aircraft available in revenue service.


Can the divergence Mach be greater than 1?

The general perspective

I have so far seen multiple definitions for what "divergence Mach number" actually means (and worked with several of them), but it's usually tied to some empirical criterion with regards to drag increase with Mach number ($\frac{dc_D}{dM}$).

This means it's not telling you the Mach number at which shocks start to appear, but the Mach number at which somebody decided that the drag caused by those shocks is becoming "serious". It therefore stands to reason that this criterion will be different for different types of applications.

This means: For a given definition of divergence Mach number, and using suitably designed profiles, it may very well be possible to achieve divergence Mach numbers greater than 1 -- this means essentially that the shocks which form while accelerating towards and beyond the speed of sound are considered mild enough to not cause significantly more drag than would be expected if they did not occur -- again, for a given value of "significant".

The physics

The critical Mach number of a wing profile can, as you know, be increased by wing sweep. For an infinite, untapered wing at least, only the inflow component normal to the wing sweep line determines the profile pressure distribution. At 54° sweep, the effective Mach number is therefore just 58.8% (=cos(54°)) of the flight Mach number -- it'd be pretty easy to not even have shocks at M=1.0! However, real wings are never infinite (and rarely untapered), so there will be at least one shock at the tip/midsection/fuselage junction. That section at least will "see" the real Mach number, and "communicate" it at least some way to its neighbouring sections. That's one reason why Howe's equation has the exponent on the cosine.

Prelim design

Reality is a bit more complicated than the Howe's preliminary design equation, of course, because using the c/4 line assumes that that's roughly where the shock ends up forming. If you have e.g. a delta wing with an unswept trailing edge, the further downstream the shock ends up, the less swept it will be, and the stronger. So it is based not just on flow physics but also on some assumptions about the ability and methods of the people designing the wing profile (in turn probably based on previously-built and tested wings)


How is a turbine engine rotated for starting and inspections?

On the CFM56-7B engine powering the Boeing 737 NG family, the starter and the handcranking input are part of an accessory gearbox which role is to support components rotating with the high-pressure shaft. This gearbox is located outside of the engine core.

Other engines have a similar design, but the accessory gearbox location may vary, e.g. on the CFM56-5B powering A320 family and 5C powering A340, accessories are at the 6 o'clock position because clearance between nacelle and ground is sufficient.

Accessory gearbox on the CFM56-7B

The accessory gearbox (AGB) is located on the side of the fan containment case.

CFM56-7 exploded view. Source

It is a set of drive pads hosting accessories, including:

The handcranking mechanism used to turn the N2 shaft during borescope inspection (the N1 shaft can be rotated by moving the fan blades manually). The handcranking drive pad is visible on top on the picture below.
The starter, which is the large assembly at the bottom of the picture.

CFM56-7: Handcranking pad and starter, source Youtube

During borescope inspection, a square drive socket attached to a breaker bar is  inserted into the handcranking drive pad, or a pneumatic motor is used.

Handcranking drive pad (cover removed). Source: Youtube

Alternatively on other CFM56 engines the core can be turned directly from a pad on the TGB (see below).

AGB to core shaft

There is a gear train within the AGB with its input gear used to transmit movement between the AGB and the engine core.

The AGB is connected to the N2 shaft by two bevel gear gearboxes:

The transfer gearbox (TGB) fixed just aft of the AGB, on the fan frame case. A horizontal shaft links the AGB input gear and the TGB. A radial shaft is also connected to the TGB.
The inlet gearbox (IGB) fixed close to the No 3 bearing, in the fan frame hub. One bevel gear is coaxial to the HPC shaft, the other is coaxial to the radial drive shaft.

Let's remove some components to better see the link from AGB to high-pressure shaft:

CFM56-7B AGB, horizontal and radial shaft, TGB, IGB and engine shafts. Taken from this answer

The radial drive shaft runs within the 9 o'clock strut of the fan frame.

The described mechanism is bidirectional, the AGB is normally driven by the HPT shaft, but when using the starter or the handcranking mechanism, the pads rotate the AGB input gear using the gear train, and the input gear then drives the intermediate shafts and gearboxes.

Pad use

The accessories have allocated pads on the AGB, the ones mentioned have been highlighted in green:

Accessories and their allocated drive pads on the AGB. Source CFM56-7B manual

Rpm ratio of the gears

Data taken from the engine manual:

N2 is 14,460 rpm
Radial drive shaft spins at 1.343 N2 (19,418 rpm)
Horizontal drive shaft at 1.301 N2 (18,811 rpm)
Starter shaft at 1.002 N2 (14,494 rpm)
Handcranking shaft at 0.986 N2 (14,260 rpm)

Also: Actual photos of the gearboxes in this answer.


Why was a CFM56 conversion never offered for the short-body DC-8s?

I suspect it's because the business case just wasn't there. Every retrofit project I've been involved in boiled down to the money. Retrofits aren't cheap and ultimately the mods have to recoup those costs through improved revenue or decreased operating expenses.

Looking at your references, there was some structural changes to the wing and landing gear that came on the -55. I expect the earlier versions were ruled out of the mods due to the lack of those upgrades and the heavier CFM engines.

That doesn't explain why the -55 wasn't included. The Wiki article stated the -61 conversions did cost more than the -62 and -63 conversions because it had the shorter wing of the -55. So it boils down to the difference between the -55 and -61. Unmodified, the -61 had about 38% more payload capacity (72k lbs vs. 52k lbs). But the modified -71 lost almost 12k lbs of payload in the conversion due to the extra engine weight. So the -71 advantage over the -55 was only 20%.

The -72 and -73 didn't lose as much payload with the mods as they had the longer and stronger wing to start with. If you apply a weight penalty to the -55 similar to the -61 mods, it cuts the payload to approximately the same as the -43. That's about a 20% reduction in payload.

The other consideration is who was doing the mods.  I didn't do an exhaustive analysis, but the vast majority of the -7x conversions were for the big air cargo operators - Flying Tigers, UPS, and FedEx - or large leasing companies where the planes were in use in the US and Europe where noise was becoming an issue.

Many of the -6x aircraft that weren't converted (discounting those written off or broken up) were being operated in the countries where cheap trumps everything.

So most of the conversions were for cargo.  Another plus for the stretch aircraft is that cargo operations tend to max out on volume before weight. Obviously, that's not always the case, but the loads that max out weight tend to be special cargo (heavy equipment or machinery) not routine packages. The -71/-73 could carry almost 80% more volume than the short bodies.  Even the -72 had a 16% greater cargo volume. That's a big advantage in operational efficiency.

Since the long body could haul more cargo and generate a greater margin per flight, it made a worthwhile investment.


Are there any unmanned variants of Solar Impulse?

The raison d'être of Solar Impulse is to carry a single human being around for a long time. Of course an unmanned version would have better performance (I doubt it would be easier to design), but what would be the purpose of such a craft?

Solar Impulse is so fragile that it can only fly in unusually clement weather, so any scheduled service is out of the question. This would need a conventional backup, and if one is around anyway, why not use the conventional backup also on the few days of the year which would allow Solar Impulse to fly? It would also save the staff of meteorologists and ground support that Solar Impulse needs.

For high-altitude observation solar-powered drones have been tested (and found lacking) in the past. Helicopters have such high power demands that solar propulsion is not a viable option.


Why did my LGA-ORD flight make an S-shaped turn round the time it was passing a storm?

I find it hard to believe that this was a holding pattern of some sort.

Believe it. An hour before landing would be about the point at which the aircraft will start its descent to its destination. Almost certainly, air traffic control were delaying your flight for a few moments to ease insertion into the landing pattern at Chicago. Doing this at altitude burns less fuel than waiting until the aircraft is lower down.

The storms were incidental. Had the pilots been avoiding the weather they'd have diverted north or south and then resumed their route. A large S-bend wouldn't be necessary.


Why does the F-117 Nighthawk look different than other stealth planes?

Initial work on Radar Cross Section (RCS) reduction concentrated on absorbers and had started in Germany late in WW II. The Americans were not interested at the time, but British scientists documented the results and gained early insights in US RCS research when they pooled their results in the 1970s.

Lockheed started work on the systematical reduction of RCS when they discovered the academic papers of Petr Ufimtsev, a Russian mathematician who explained how to calculate the reflection of radio waves from the 1960s on. Their initial success with RCS reduction on the SR-71 was more luck than systematic work. At the same time, similar insights were gained in Germany where a manned prototype of an aircraft (MBB Lampyridae) similar to the Have Blue prototype proceeded up to wind tunnel tests. Then the program came to the attention of US authorities which quickly put an end to it.

In all those cases, the major idea was to restrict the surface to large, flat panels because the edges, not the total area, determine how much energy is radiated back. In that respect, the German design was much cleaner than both the Have Blue and the F-117, but I digress. Those designs can be called first-generation stealth aircraft.

When Northrop joined the RCS work, they found that even curved panels work well - after all, it is edge reduction and alignment which reduces RCS most. Their initial prototype was for a battlefield observation aircraft (in contrast to the Lockheed attack aircraft) which was called Tacit Blue.

When work on stealth prototypes was opened at the end of the Cold War, all engineers could pool their knowledge and combine the work on absorbers, edge reduction and edge alignment. This gave rise to the second generation of stealth designs which look indeed quite different to those of the first generation. What also influenced the designs was more understanding of the tactical value of stealth, so the second generation designs do not optimize RCS above all else but arrive at a compromise which combines low frontal RCS with good agility and multi-role capabilities.

Koyovis is right, but it was not only computer power but also the limitations of early RCS codes which were based - at least in case of Lockheed - on the ideas of Petr Ufimtsev, and he in turn used analytical methods which did not allow to investigate the RCS of curved surfaces. However, the computers at the time were already powerful enough to allow the F-117 to fly at all - in contrast to the MBB design, it is unstable and uncontrollable without artificial stabilization.


Can a TCAS be alerted when the intruder aircraft has a transponder in stand-by mode?

No. If the intruder's transponder is in standby it will not respond to interrogations and will be invisible to the TCAS. TCAS can't act on targets it can't interrogate.


What is this airplane with small wings at different angles seen at Paphos Airport?

Looks like a QAC Quickie Q2. It's a kit plane with over 2,000 produced.

(wikimedia.org)


Do airport fire departments have to have airstairs?

Sorry unfamiliar with FAA regs, but since Canada's regs are often just rewrites of US or ICAO rules:

In Canada, I cannot find any direct reference to airstairs as required minimum firefighting equipment : Canadian Aviation Regulations (SOR/96-433) section 303.09
there is however a requirement for holding an airport certificate in Canada requiring a safety management system be in place, this involves doing a detailed risk assessment.

logically having the ability to deplane any aircraft expected to land might be seen as a necessary risk management solution to a number of potential possible issues. There are similar requirements for "air operator certificates", meaning some of the accountability may be place on the airline. Like so much of Canadian law, we will probably not get a definite answer until a large number of people die and the courts get involved.


What is the tolerance of SSR against signal frequency shifts?

With respect to the radar frequency drift, I am afraid you are asking an impossible question, the interrogation frequency is continuously auto monitored, any drift tendance is electronically prevented. However should this occurs, the aircraft transponder has a sharp filter limited just to light Doppler effect, beyond that the transponder will not answer to the received signal.

I do understand a drift in the aircraft transponder, that is a frequency drift in the aircraft transponder answer, that’s not a problem; even though it is quartz generated, that is nearly impossible to drift, the ground radar accepts a frequency drift of + or - .5MHz, beyond that the received signal by the radar could be interpreted as a response to a lobesides  signal received by the aircraft transponder, and may get mutually eliminated.

However the radar memorizes all present mode A received information, if the received signal concerns an aircraft identification not received previously, the radar will accept the signal and not reject it as being a response to a lobesides signal.

If the frequency drift is important, this is equivalent to having lost the transponder. The total loss of transponder information may sometimes be mitigated by the availability of primary radar data. However, if false primary tracks appear too often, a “real” track may be considered to be fake. This is especially true when no other data is available (e.g. information from the previous sector).


How does an FMS shift after losing all external navaids?

Turns out indeed it's an issue affecting polar operations. It differs from type to type, but for the 737-600/-700/-800/-900 as an example, the message UNABLE REQD NAV PERF-RNP will be displayed.

For oceanic areas this will only happen if ANP shifts by over 10 NM, i.e., after losing the RNP-10 capability.

At an IRS drift rate of 650 metres per hour, it would take 28 hours of being airborne or a rather shifty IRS unit—no pun intended—for the message to be displayed.

So the answer is that the magenta line won't shift, unless the pilots choose an IRU over the rest by using the position shift function of the FMS.

For the 747-400:

  When no global positioning system (GPS) updating occurs, all position and velocity corrections gradually are phased out until the FMC navigation parameters equal the selected IRU position and velocity.

This logic is part of the RNP standards and regulations, to stop an auto flight system from chasing the course when navigational accuracy becomes questionable. Any loss of GPS (away from ground navaids) inhibits the FMS from applying any corrections without crew intervention.

Source: Polar Route Navigation


Why was the DC-9-80/MD-80 so successful despite being obsolete almost from birth?

It's simple.  Cheap (development costs amortized decades before) and reliable.  They made money for airlines.  Or, you know, they wouldn't have bought them.  There's more to operating costs than fuel burn, and in any case, fuel prices in the mid 90s were cheaper than at any time since the 20s in constant dollars.  Fuel was so cheap that Air Canada was bringing L1011s out of mothballs in the mid 90s because they could operate them Toronto to LA profitably.


Under what circumstances does a flying club need to do 100-hour inspections?

AOPA addresses this very matter in their question of the month found here

  A flying club aircraft normally would not need to receive 100-hour
  inspections.  FAR 91.409b requires a 100-hour inspection when a person
  receives instruction from a flight instructor who also provides the
  aircraft.  The FAA guidance further clarifies that the 100-hour is
  required when a person is providing flight instruction for hire in the
  instructor’s personal aircraft.

Your issues arise with these two points

  The students (Receiving dual instruction) may or may not be members themeselves.
  A club rule says that only approved club flight instructors may offer instruction in club aircraft.

As the answer goes on to state

  Some clubs require a flight instructor to be a member prior to giving
  instruction in club aircraft.  In this case, the FAA doesn’t view this
  as an issue as long as three conditions are met:

  There must be no contractual relationship between the member-instructor and the flying club for the provision of flight
  instruction.
  The member-instructor is not recommended or given preference by the flying club.
  The club members are free to choose instructors who are not club members.

  If any one of these conditions is not met, then a 100-hour inspection
  would be required for the club aircraft.


How to determine climb performance for various flight speeds?

Aircraft performance charts all work the same way. Unfortunately, this one only gives the climb speed at 85 knots indicated airspeed (KIAS).

To find the climb speed at different speeds needs more knowledge about the airframe. Then you can apply a simple approximation following this procedure.

The chart does not tell where on the polar the aircraft is. Will it climb better when flying faster or not? This is impossible to tell. Since you have only one speed and one power setting, but a range of masses, the aircraft will not be at its optimum climb setting for most points. We can make an assumption and declare the reference mass of 1700 kg as the point where the cited conditions are at the optimum. But then I would need at least the zero-lift drag and the aspect ratio to make further assumptions.

From the previous answer we take the climb speed equation $$v_z = \frac{v}{C}\cdot sin\gamma = \frac{v}{C}\cdot\frac{T-D}{m\cdot g}$$
and set the correction factor C = 1 for now. The resulting error is small at low speeds. Now we need drag and thrust.

First drag: The drag coefficient $c_D$ is approximately
$$c_D = c_{D0} + \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
with the known aspect ratio $AR$ and an assumed Oswald factor $\epsilon$ of 0.85. To arrive from here at the drag we need to multiply this with the dynamic pressure $q = ½\rho\cdot v^2$ and the reference area $S$:
$$D = ½\rho\cdot v^2\cdot S\cdot c_{D0} + \frac{(1700\cdot g)^2}{½\rho\cdot v^2\cdot S\cdot\pi\cdot AR\cdot\epsilon} = ½\rho\cdot v^2\cdot S\cdot c_{D0} + \frac{(1700\cdot g)^2}{½\rho\cdot v^2\cdot\pi\cdot b^2\cdot\epsilon}$$
when we substitute $AR = b^2/S$ with $b$ the span of your airplane. As I said before, induced drag depends on span, not on aspect ratio.

Now for the thrust. In a propeller aircraft power is constant and thrust is inverse with airspeed. Not indicated, but true airspeed, so we need to be careful. At sea level both are equal, and then thrust is straightforward: $$T = \left(½\rho\cdot v_{ref}^2\cdot S\cdot c_{D0} + \frac{(1700\cdot g)^2}{½\rho\cdot v_{ref}^2\cdot\pi\cdot b^2\cdot\epsilon} + \frac{5.5}{v_{ref}}\cdot1700\cdot g\right)\cdot\frac{v_{ref}}{v}$$

with $v_{ref}$ = 43.7278 m/s, which is 85 kts in sane units. The first two terms in the bracket look familiar: They are the drag contribution. The third term accounts for the climb speed of 5.5 m/s at the reference point in sea level altitude, so this accounts for the change in potential energy. If you need the thrust at higher altitudes, please correct $v_{ref}$ with the square root of the density ratio.

If those equations look daunting, continue solving for the climb speed:
$$v_z = \frac{v}{C}\cdot\frac{\left(D + \frac{v_{z_{ref}}}{v_{ref}}\cdot m\cdot g\right)\cdot\frac{v_{ref}}{v} - D}{m\cdot g}$$
$$v_z = \frac{1}{C}\cdot\left(\frac{D\cdot\left(v_{ref}-v\right)}{m\cdot g} + v_{z_{ref}}\right)$$


Why was the VC10 unusually prone to reverser-induced buffeting?

It may just be that other airframes mount their engines with sufficient clearance to avoid the buffeting issues that were seen on the early VC-10's. Ultimately it only took of a move of 11 inches to solve the issue

  ...testing was prolonged by the need to move each engine pair 11 in (27
  cm) outboard. This major redesign was needed to resolve tail-plane
  buffeting and fatigue issues due to thrust reverser operation. The two
  inboard engines could have thrust reversers installed at last,
  matching the 707.

So while it may appear in photos that other aircraft have similarly mounted engines you would need to look at actual technical drawings to truly compare mounting distances.

Its also worth noting that there is nothing saying other aircraft do not also see buffeting from their aft mounted thrust reversers, however they may not see enough to cause structural issues as was the case with the VC-10.


How much more economical are planes with retractable gears vs. those with fixed gears?

Consider the Piper Turbo Arrow IV vs. the Piper Turbo Dakota... Same max gross weight, same engine, same wing, but the Arrow (with retractable gear) is nearly 12% faster at full cruise power.  This would imply that, at the Dakota's cruise speed, the Arrow should burn roughly 14% less fuel (give or take a little; it's 75% vs. 65% power, but at different altitudes).  Given this, the Arrow will cost less to fly for a given trip ($/nm).  The trade-off is that the Arrow costs more to buy, maintain, and insure, while having a smaller useful load.

Note that I chose these models for a reason: The Turbo Dakota is literally a fixed-gear version of the Turbo Arrow IV with no other major changes.  In most cases where a model is available in both fixed and retract, the retract has a more powerful engine.  This makes comparisons much more difficult.  YMMV


Are transponder codes 7701 - 7777 ever used?

Yes these codes are used. Only 7700 is used to denote emergencies, and usually only if you aren't in contact with ATC, or can't get their attention(frequency is packed). Codes in this range are allocated according to the National Beacon Assignment Plan in the US. There are other codes that are assigned for various issues, 7777 as mentioned in the comments is assigned, and I've assigned others in that range before, same with the 7600 and 7500 ranges.

If you're already in contact with ATC, and they have you tagged, it is very easy to mark you as an emergency and have it light up on everyone in the facility's scope.


Why is Mode C helpful for ASDE-X systems?

Without knowing the altitude, it is very difficult (or impossible) to accurately calculate the position of a transponder by using multilateration (which is what ASDE-X uses). In addition, without knowing the altitude, ASDE-X would be unable to determine whether an aircraft is on the airport's surface, or passing overhead.


Why does Germany is not so advance in aircraft development?

May i suggest, you read the wikipedia artikle "History of Airbus".History of Airbus
There are also other big aerospace companies in germany, like MTU, DIEHL and LIEBHERR just to name a few. These companies don´t build their own planes, but manufacture major components for the aerospace industrie.


Does the co-pilot still remain in control of the plane if an engine fails during takeoff?

The operating procedures for the four airlines I worked for (2 commuters and two 747 carriers) all called for the flying pilot (which would be the first officer if it was their leg) to retain control of the airplane until all relevant checklists had been accomplished.

That said, it is, of course, the captain's prerogative to take control at any point. That would, I think, be very unwise to do in the case of an engine failure during takeoff unless the first officer was really screwing up.

The greater workload in the 747 during emergency/abnormal procedures lies with the non-flying pilot and the flight engineer (old 3 man cockpit 747-100s and -200s).

The recommended procedure at my last two airlines was, if the captain was flying at the time of the failure, to hand control to the first officer after all relevant checklists had been completed, to thus enable the captain to give his full attention to how best to proceed.

My personal and observational experience is that there is little difference between captains and first officers at the 747 level insofar as control manipulation during go/no go situations on the runway in simulators. In fact, I could point you to an accident resulting in the total loss of a 747 when the flying pilot was the Captain, and he elected to abort 30 knots after $V_1$, thus insuring the aircraft would leave the runway.


Do modern jet engines monitor and record exposure to particles of dust or sand?

As of now, there are no commercially available engine particle ingestion sensors, though a few are under development. One of the companies involved in development lays out the reasons for the absence of any such sensors:

  As of today, no commercial off-the-shelf particulate sensor is in use because of the special design and difficult requirements for operation and performance in this harsh environment, according to Dr. Hai Lin of Hal Technology in Fontana, California.

There are multiple sensors under development like the Dual Optical Embedded Dust Sensor which is used to determine the particle ingestion by the AGT1500 engine in M1 Abrams, where dust and sand is a bigger problem, if anything.

All of these sensors work on a similar principle- they measure the scattering of light by the particles using a optical sensor.

  The sensor detects light scattering from moving particles as optical pulsed signals whose amplitudes are proportional to size and whose number is proportional to concentration. This sensor technology can determine particle size, distribution, concentration and further be extended for composition.

In future most of these systems are expected to available commercially, as

  While continuing to advance this technology for particulate composition determination, Hal Technology is pursuing a licensing agreement or partnership with sensor or engine manufacturers to have the sensor integrated into engine heath management systems of the future.


On the A320 why do we follow this particular sequence of taking flaps and gear?

You would want to start with flaps/slats. The landing gear slows the aircraft down like an airbrake, and you'll need a higher lift coefficient to retain enough lift. Slats are a safety feature that allow for a higher angle of attack for the main wing, flaps provide a higher $C_L$ by themselves. So you start with a higher $C_L$ and the safety of the slats, then deploy the gear which slows you down, then delay more flap/slat at the lower velocity.

Deploying full flap/slat first and then deploying gear is also not a good idea: speed will be slow already at max flaps, gear deployment brings a significant further deceleration which may have an impact on safety, definitely on continuity throughout the landing process. You are in a queue with lots of others at a busy airport, and want to keep the array of craft flowing without sudden decelerations.


Why isn't the U-2 used for commercial purposes?

It is expensive to operate, and there is no economic value in what it does.

Apart from reconnaissance and espionage, the U-2 is used for high-altitude atmospheric research, but since it is operated by NASA and man-carrying, it is subject to an immense bureaucracy. When you want to fly your own scientific instrument on it, you need to go through years of certification procedures. The instruments which are rated to fly on the U-2 are ancient and much less precise than what can be built today. Therefore, most high altitude research is done by balloons, where the bureaucracy is much less suffocating.


Is it possible for a non-towered airport to have keyhole extensions Class E starting at the surface?

There was a control tower at SGH which closed. The FAA issued a rule which removed the Class D airspace as of December 10, 2015.

This leaves the class E airspace chunks. As you noted, the Chart Supplement for SGH has no information about the airspace, and FAA Order 7400.11A (the current version of airspace definitions) states only that, after an initial NOTAM announcing the effective dates and times, (p. E-183)

  The effective dates and times will thereafter be continuously published in the Airport/Facility Directory.

So, is the airspace between the surface and 700AGL in these two areas class E or G? I'm not a lawyer, but I think you could make a strong argument for the airspace being class G, unless the chart supplement gets an update or a NOTAM is issued.

Finally, to the question: why are these two areas there? Two thoughts come to mind.

The class E extensions existed alongside the class D airspace, and nobody thought to remove them. (This is the most likely, to me.)
There is some other operational reason for the class E airspace. There are instrument approaches to the field, though they terminate well inside the radius of the two airspace segments, so that's not very likely. Also, the class D airspace could be reactivated by NOTAM if a high-traffic event at SGH were to occur; the class E extensions could be part of that. However, both of these options are really stretches - my guess is that we've found airspace that someone just forgot.

2019 update: those extensions are no longer visible on the sectionals:

(skyvector.com)


How was the 747 in the China Airlines Flight 006 affected by the wing damage it sustained?

As you know the aircraft manufacturers keep tracking their aircrafts because any accident of these would damage their reputation. All automatic data transmissions are traced by the manufacturer whether the operator has a tracking contract with the manufacturer or not. Should it had an asymmetrical behavior causing any dangerous consequences the manufacturer would have made what is necessary to ground it.

In the website you refer to, it is written « After repairs were made to the plane, it returned to service on 25 April 1985. It continued in service for nearly 12 years »:

I may assume this aircraft has landed in Europe, or in USA, should it have been dangerous, it would have been grounded.

As far economical performances are concerned, that’s secondary compared to safety, it is the operator decision to evaluate to make it fly or not if it becomes less economical.


Do stealth designs have canard configuration?

So far, no operational stealth aircraft has had a canard wing as the canards do affect the radar cross section.

However, a few experimental and under development under development aircraft have canards, like the Chengdu J-20.

"J20 2" by V587wiki - Own work. Licensed under CC0 via Commons.

The Sukoi PAK-FA, on the other hand uses movable Leading Edge Root eXtensions(LERX), which are much more stealthy and are shown drooping down in the following figure.

Source: defenceindustrydaily.com

There are a few major drawbacks with the traditional canard designs:

Planform alignment Most of the canards are in aircraft for stability and aerodynamics requirements an as such are not amenable to planform alignment, as their characteristics are sensitive to their shapes and sizes. For example, compare the planform alignment in case of F-22 and Eurofighter Typhoon.

Source: forum.keypublishing.com

Some low observable aircraft, like the Boeing X-36 did  have planform alignment, it is simply that it is difficult to achieve.

"McDonnell Douglas X-36 planform" by NASA/Dryden Flight Research Center - http://www.dfrc.nasa.gov/gallery/photo/X-36/HTML/EC97-44165-151.html. Licensed under Public Domain via Commons.

Canard Angle Most (not all) of the canards have an anhedral or dihedral due to aerodynamics requirements, which means that they are not in the same plane as the wing and reflect radar waves in other directions, increasing RCS. The following image shows the (mis)alignment of canards with the aircraft.

Source: forum.keypublishing.com

More reflecting surfaces Having canards basically means there are two extra surfaces to reflect the radio waves and increase RCS.
Interaction with fuselage and wings The diffracted (radio) waves from the canards can impact on the wings and fuselage and get reflected back, which can increase the radar cross section.


Why do pilots announce the cruising altitude of a flight?

No real reason other than it keeps people from bugging the flight attendants by asking "how high are we??".

It also lets the flight attendants know that the aircraft is at cruise so won't be climbing and making the carts harder for them to push around.


You are a commercial airline pilot flying between two large US airports. Who do you talk to along the way on the radio and for what purpose?

This is a duplicate question, although this is actually asked much better than the other one is.

Generally, your picture of what goes on is pretty good.

As mentioned in a comment, there is Clearance Delivery, which issues your ATC (IFR) clearance.  Except... at most of the larger airports, that function is now automated and the clearance is passed via ACARS, which is essentially a closed e-mail system direct to the aircraft.  So it's actually common to NOT talk to Clearance Delivery now in airline operations.  You still do at smaller airports that don't have the PDC (Pre-Departure Clearance -- the automation that sends the clearance itself over the ACARS network) installed, and you'll call Clearance if you have a question about how you were cleared, and in a few other uncommon situations such as a reroute that's issued after you got your initial clearance.

Ramp Control exists at some airports, and it's essentially a "ground control" function for a separate, isolated area.  So in Atlanta, you actually have several of these, one for Ramp 1, which is the east side of the A terminal and the west side of the B terminal, another for Ramp 2 which is the west B gates and the east C gates, and so on.  They control the "in's" and "out's" of their respective ramps, including coordinating who will push back when.  As the aircraft leaves the Ramp Control area, it's handed off to Ground Control, and things proceed normally.  NOT all airports have this, and not necessarily every terminal (or gate) at a given airport will be controlled by Ramp Control.  Gates that aren't controlled by Ramp will typically call Ground to push.  SFO is like this.

Typically, controllers see most of what you've filed on your flight plan, so they know before a given flight is passed to them that SkyPig 23 is a 757 that departed JFK, is filed for FL 360, and is going to ATL with a routing of whatever set of airways, points, and STAR.  NOT every controller will see everything in the flightplan; I think the TRACON sees remarks but the Center may not, was one example I vaguely remember from a tour a while back.  But essentially they know who you are & what you're doing by the time you switch to their frequency.  Sometimes things get confused or the pilot requests a change (in altitude, routing, or whatever), and sometimes the controller has to change the plan up, but generally you check in at whatever altitude (and climbing/descending to whatever, if that's the case) and the controller acknowledges and that's that until he has a new clearance (further climb or descent, new routing, approach clearance, etc) to issue.

Mostly now, airlines are filed on both a SID (standard instrument departure) and a STAR (standard terminal arrival route) so  "requesting vectors" in pretty uncommon.  Could happen if your FMC (flight management computer) dumps your routing, but that's rare, and usually operator error when it does happen.  A departure or an arrival might INCLUDE vectors (i.e. fly heading 350, climb & maintain 5000', expect radar vectors to JEBBB), but in those cases it's expected.

Multiple approach controllers are pretty common, especially in the larger terminal areas.  Often you'll be switched from Center to one Approach Control frequency, who may be handling all arrivals from the east, with another handling everything from the west.  Then as you get close to the airport, they hand you off to "Final", which is still "XYZ Approach" but his job is sequencing everybody onto the base, dogleg, and final, clearing you for the approach, and then handing you off to tower.  If the first Approach controller owns airport to 30NM out surface to 17,000', the "Final" controller might own 7000' and below within 12 miles, and Tower owns 3000' and 5 miles.  Serious generalization there, but that's the idea... each successive layer of the onion owns a smaller but busier piece of airspace.  Letters of Agreement between the Center and the TRACON and then procedures within the TRACON will spell things out in great detail.

Hope that's helpful.  Good question asked well; hopefully this won't be lost to memory just because it was asked 2nd.


Are some countries' civil aviation authorities safer than others?

Lets take the EU for example. In the EU, there are 230 banned air carriers. The majority of these (228) are banned because the EU CAA has determined that the country in which these carriers operate do not have enough oversight to ensure the safe operation, regulation, and maintenance of the airlines.

Two of the air carriers are banned specifically because of poor maintenance standards, obsolete aircraft, or other reasons.

Similarly the US has the International Aviation Safety Assessment although a much shorter list because it really only evaluates airlines that are codeshare or operated by companies that serve flights to/from the US. For the EU, this is a larger list because it does not require crossing an ocean to get there...

Typically you'll find on these lists quite a few airlines that operate out of developing countries like the Congo or Angola. Its reasonable to draw the conclusion that countries that do not have regulatory oversight for much outside of running the government itself leaves the standards of safety to the operators themselves.

This isn't to say that the operators are automatically unsafe, they just lack government regulation and observation of safety standards.

So to mirror what vortaq7 said in his comment above, quantifying this is going to be difficult since the types of operations vary highly between countries. For example the US has a high accident rate looking at pure fatalities over the last 25 years compared to any other country, but this is because the US is biggest aviation market.

Looking at it in the context of incidents per million flight hours may be available, but it also groups a lot of different types of flights like cargo and commuter. I'm sure this type of data is available for more developed countries with reporting systems and formal accident investigations but may be difficult for countries that don't have that.

And now for a personal note... I know you're not interested in the personal aspect but Angola's air carriers are banned in the EU, so it gives a little credibility to what I say above, plus its a good story. :)

A part of my job is travelling the world and being flown out to oil rigs for work on the automation and safety systems. About 8 or 9 years ago I had to fly out to Luanda, Angola to be flown out to a rig a few hours off the Angolan coast. The flight there (and back) was on the Houston Express, a direct flight from Houston to Angola.

Upon arrival at the Luanda airport, I was taken to the heli-terminal for the flight out to the rig. Now understand that in the US Gulf of Mexico people travelling by helicopter to an oil rig are required to have egress training. In the EU, travelling out into the North Sea also must include cold water survival. In Luanda however, there were zero requirements (I know this because I did not have egress training, nor was I asked to prove I did).

After 3 or 4 equipment delays we were finally boarded on the helicopter, I sat across from the flight engineer and 3 or 4 other rig hands were on board. After take-off and after we flew over the coast, here is pretty much the actual words I spoke:

  ME->Flight Engineer: What is dripping on the back of my neck? Smells like fuel.
  FE->ME: It is fuel.
  ME->FE: Should I be concerned?
  FE->ME: Only if it stops dripping, that means we are out of fuel.

Be sure I spent the remainder of the flight studying very carefully how to pop out the egress window...

When we got back to Luanda the aircraft we were supposed to take back to Houston had "mechanical problems" which delayed my return by 3 days. I could see the aircraft on the tarmac and it was sitting on cinder blocks without any tires, literally like you would imagine leaving a nice car in a bad neighborhood overnight. I spent those 3 days in a compound run by the oil company that had 16 foot tall walls with barbed wire and a very hefty front gate.


Where can a civilian obtain centrifuge training/testing?

This is a tough one. I don't know of any civilian facilities (but it does not mean they don't exist). This is a bit of a shot in the dark but in my opinion you may want to contact NASA about the Ames Research Center 20-G centrifuge. If for no other reason than this is the only non military one that seems to exist. For what its worth high speed centrifuges are not that simple despite just being something that spins in a circle. The speeds that the unit spin at are extremely high to say the least, to do this with out ripping the whole thing apart requires careful balancing and construction so they are not exactly something you can build at home. Here is at least one company that is building them and installing them elsewhere in the world. They list a bunch of installs for other militaries that might be more open to a civilian coming in but who knows.


What is the difference between directs and shortcuts in the Route Availability Document?

A shortcut is a deviation from the filed flightplan given to an aircraft by ATC during the flight, if traffic and other factors permit. A flight crew cannot expect to get any shortcuts, so they cannot plan for it.

Routes in the RAD are flightplannable routes. If a direct route is available in the RAD, it can be used when filing the flightplan, prior to the flight. This allows airlines to plan for the shorter route, thus allowing them to bring less fuel and advertise a shorter flight time.


Why do some canard aircraft have dihedral on their canards?

If it is a canard, the assumption of a well thought out design is doubtful. Yes, dihedral will add to directional instability and require a bigger tail, but at least in case of the glider the vertical is sized for countering adverse yaw, so the bit of canard instability is easily compensated.

My direct response would be: To lift the core of the canard wake above the wing. But from looking at the Solitaire I wonder whether that is really true. At least on the Stagger EZ you can see that the designer tried his best to separate canard and main wing vertically.

Regarding flat spins: The spin axis normally runs through the forward fuselage, so there is not much horizontal airspeed at the position of the canard. The tail will help to dampen the yawing moment much more. A bit of canard dihedral will not make a difference.

But maybe wing dihedral was found to be lacking during flight test and changing dihedral on the canard seemed to be an easier fix? That would be my best guess, at least for the Solitaire.


Does contra-rotating vs regular propellers, have any effect on icing?

What are the parameters for icing on the wing?

temperature
air humidity
airspeed / pressure

The rotation direction of the propeller does not effect any of this parameters. Therefore the propellers rotation direction does not affect icing.


How do I calculate new minimal speed for a glider when I put water into the tank?

$v_2 = v_1 \cdot \sqrt{m_2/m_1}$ is the correct formula.

$v_2 = v_1 \cdot m_2/m_1 = 87km/h$ is simply wrong, possible that it is only a typing mistake, but it is wrong just the same.


What parts of Austrian airspace are not covered by primary radars?

The radar system in Austria is know by the name Goldhaube (Golden Hat). It is based on 3 fixed sites and several mobile stations. The coverage is this one:

Source

Another view:

Source

The three primary surveillance radars (PSR) are located at:

Kolomannsberg (Salzburg),
Großer Speikkogel (Koralpe)
Buschberg.

and are (or were) Selenia RAT-31 with a range of about 300 NM.

Source

Side notes

The difference between Austria and some incompletely covered areas is that Austria is not a large territory like China nor a water area like the Indian Ocean. It is relatively easy to get a full coverage.

In addition Austria is mountainous (famous ski resorts), so it's quite handy to use peaks for radar stations with increased range.

However, radio waves are mostly traveling in straight line. At low altitude in the valleys an aircraft is invisible. Military use this tactic under the name "ground hugging" or "nap-of-the-earth" to escape unfriendly eyes. Austrian army use mobile radars to make this possibility more complex:

Source

And to fuel imagination, there is this story of aircraft vanishing over Austria. Possibly a Bermuda triangle at the core of Europe.


Are general relationships between MTOW and OEW valid for novel configurations?

Many studies and presentations you will encounter about radically different configurations with much higher performance are the aviation equivalent of car commercials. Someone tries to get attention in order to get published, or she/he needs to convince investors to fork over their money.

Trust me, the aircraft designers of the last century were no idiots. They had the luck of living in a time when it took only a few years for aircraft designs to become obsolete, so they could go through the whole design process many times and apply what they had learned before.

Someone graduating from university today will be lucky if she/he gets the chance to go through every step of a major design process even once. I myself have brought three aircraft into the air and consider myself very lucky. I had colleagues who retired without ever having seen one of their many projects take off (literally).

The consequence of this is a very mature industry which has found an optimum configuration for most purposes already and is only tinkering with the details. Add to this an ever increasing thicket of regulations which have grown on the experience from existing designs. Sure, the progress in computer control is impressive, and engines get better all the time. Manufacturing precision is ever increasing, and materials still become better and more consistent. But overall, we still build aircraft like we did a generation ago, and I do not expect this to change radically in the future.

What impacts the design process most is certainly the incredible precision of simulation software, which allows to see details which remained hidden in a wind tunnel or a strength test. Things which had to be done consecutively can now be done in parallel, and the precision of knowledge at an early stage of a design is much higher than before. But at the same time aircraft become ever more complex, so the advantage of better simulation is eaten up by the increase in complexity. Add to that the fact that mostly beancounters will have the last word, where before engineers could determine how the work was done, and you will understand that the level of preparatory work is shockingly inadequate in modern aircraft companies. Many of the avoidable early mistakes will require late, expensive fixes (but by that time the stingy beancounter has left the company with a huge bonus for the money he bragged to have saved).

The design process is still the same, and where before the experience of a few people helped to find an overall optimum, large, integrated teams will together determine this optimum. The inexperience of the participants will only show up in delays, when the iterative design cycle needs to be repeated more often than anticipated, but the result will be of high quality - really bad designs are a thing of the past. But cutting corners will still have consequences, so small annoyances will still plague new designs. Consequently, most of the engineering work will involve ironing out these annoyances or retrofitting new systems to existing airframes.

To answer your specific question: Yes, the relation between OEW and MTOW will still hold in the future, and radically new configurations will show an advantage only on paper, before they have been thoroughly designed and test-flown. Better materials and methodologies will help to improve the ratio between OEW and MTOW, but this advantage risks to be eaten up by the desire to add bells and whistles everywhere.


What qualifications are required for an authorized flight instructor to teach IFR in AATD simulators, in the U.S.?

To provide instrument instruction the instructor must posses a valid CFI certificate with an "instrument airplane" rating.  This is irrespective of the type of training device or airplane used with the caveat the instructor needs to be rated for the airplane (either flown or being simulated).  In other words, if you cannot instruct in an airplane, you cannot instruct in a training device either.

The applicability of using the AATD is more of a program certification than an instructor pilot certification issue as there are different levels of training and special certifications for certain levels of training devices and simulators.  See 14 CFR 61, 141, 142 for details about training programs and AATD use.


Is the elevator really an 'angle of attack control' as described in Stick and Rudder?

Wolfgang Langewiesche is right to appropriate order of approximation. For every elevator position a statically stable airplane settles to a specific equilibrium angle of attack. That's how static stability works.
Airplane is statically stable if and only if increasing angle of attack causes higher increase in coefficient of lift on the aft airfoil (tail for normal layout). Then increasing angle of attack (by random fluctuation like turbulence) increases the lift aft more, the overall centre of pressure moves aft and the aircraft pitches nose down to return the angle of attack to the trimmed position.
By moving the elevator you adjust the coefficient of lift on the control surface, and the plane needs to assume a different angle of attack to shift the centre of pressure back to coincide with centre of gravity. Most aircraft are designed so this is quick enough that if you don't jerk the controls too much the angle of attack simply follows the elevator position.

isn't it true the Angle of Attack will increase because the relative wind is now coming from in front and above the plane?

The angle of attack is high when the relative wind is from below and low when it is from above.

If I then add power and climb (while holding the same attitude)

If you add power and leave the yoke as trimmed, the plane will start to accelerate, which increases the lift. That causes the plane to accelerate upward, which decreases the angle of attack. This decreases the lift more on the tail, so the tail sinks and the aircraft pitches up until it assumes the original angle of attack. At this point, the pitch angle is increased by the same amount as the flight path angle.
The aircraft is still moving faster than the original speed due to inertia, so the lift is still more than weight and the aircraft continues accelerating up and pitching up to maintain the angle of attack. When the speed returns to the trimmed, the aircraft is already pitched too much, so now it will slow down and pitch down again and repeat the cycle. This is called the Phugoid oscillation. In most planes it is damped, but still annoying if you don't counter it with a bit of elevator deflection. But if you don't touch the trim, just arrest the phugoid, the aircraft will settle in climb at the same speed.
It has some consequences:

Tendency of the plane to pitch down means it is losing airspeed.
If you are not pulling on the yoke, or trim aggressively nose up, you won't stall. Unfortunately pulling on the yoke to keep the nose up becomes too much of a muscle memory so it's easy to miss this clue.
It is how pitch for speed and power for descent rate works on descent.

See also How It Flies, specifically section 2.3 talks about trim and angle of attack, with more details further in chapter 6.


In a B737 NG, when a TO is flown with an Assumed Temperature N1, is the subsequent CLB N1 also adjusted (lowered) accordingly?

Possibly, but not necessarily.
The climb thrust can be selected on the FMC N1 Limit page. The choice is between CLB, CLB-1 and CLB-2. The climb thrust is then reduced according to the selection:

7 - Climb (CLB)
Push – selects full rated climb thrust limit. [...]
8 - Reduced Climb (CLB–1 and CLB–2)
Push – selects the associated reduced thrust climb mode.
CLB–1 provides a climb limit reduced by 3% N1 (approximately 10% thrust).
CLB–2 provides a climb limit reduced by 6% N1 (approximately 20% thrust).
Deletion results in the selection of CLB thrust.
Manual selection of a climb thrust rating overrides the automatic selection.

(Boeing 737 NG FCOMv2 11.40.47 - Flight Management, Navigation - FMC Preflight)
When a takeoff thrust derating or an assumed temperature is entered, the FMC automatically selects a corresponding climb derating. And yes, the climb derating is computed such that it is below or equal to the takeoff thrust:

Derated Thrust Climb
Two fixed climb thrust derates can be selected on the N1 LIMIT page. CLB–1
provides a climb limit reduced by 3% N1 (approximately 10% thrust). CLB–2
provides a climb limit reduced by 6% N1 (approximately 20% thrust). The
reduced climb setting gradually increases to full rated climb thrust by 15,000 feet.
In cruise, the thrust reference automatically changes to CRZ. The reference can be
manually selected on the N1 LIMIT page.
Use of an assumed temperature reduced thrust takeoff or takeoff derate affects the
FMCs climb derate computation. If a reduced thrust takeoff has been specified on
the TAKEOFF REF page, the FMC will re-compute CLB-1 and CLB-2 values as
required to avoid a climb N1 value greater than the reduced thrust takeoff N1
value.

(Boeing 737 NG FCOMv2 11.32.4 - Flight Management, Navigation - Flight Management Computer; emphasis mine)
However, if the pilots manually select CLB after the automatic selection of a derated climb thrust, then the climb thrust can actually increase over the TO thrust.


How is the aircraft stand vertical lux measured?

In 2m height, from two sides minimum, best if they are perpendicular to the centerline


Approach plate does not require DME, but DME used in the published missed?

DME can be used in the published missed, but does not have to be. There are other ways to identify the missed approach fix.

The missed approach instructions are:

  MISSED APPROACH: Climb to 1500 then climbing right turn to 3500 on ATL VORTAC R-005 to TROYS INT/ATL 15 DME and hold.

The missed approach procedure calls for a hold at the TROYS intersection. This can be identified by one of three means:

The intersection of the ATL R-005 and RMG R-115,
By 15 DME on the ATL R-005, or
By RNAV from a database.

These multiple methods of identification mean that DME is not required. If an RNAV or dual VOR receivers are used, DME is not needed.


What is the call for when an enemy air-to-air missile has been fired?

From an older NATO book on brevity words that I have, a hostile guided missile is VAMPIRE.

A hostile surface to air missile is, indeed, SAM.

Edit.
From the better list of brevity words

VAMPIRE  Hostile anti-ship missile

So VAMPIRE is not an air to air missile.
My old list did not specify the type of the hostile missile.


How to calculate the heading correction with a circular flight computer?

1 - First I calculate the track deviation angle:

To find the track angle:

outer scale: distance off track (NM) in this case 5 NM

divided by

inner scale: distance already travelled(NM) in this case 40 NM

To do this I divide 5NM per 40NM as per the picture below, the division is within the red circle and the result is pointed by the red triangle that says '60' on the other red circle with the arrow pointing to it.

the result is 7.5 as you can see on the picture below.

2 - Then I calculate the closing angle for the remainder of the journer:

To find the closing angle:

outer scale: distance off track (NM) in this case 5 NM

divided by

inner scale: distance to go (NM) in this case 80 NM

The remainder of the journey is (120NM - 40NM) = 80NM
The current deviation which is 5 NM.

To do this I divide 5NM per 80NM as per the picture below, the division is within the red circle and the result is pointed by the red triangle that says '60' on the other red circle with the arrow pointing to it.

the result is 3.77 rounded down to 3.7 as you can see on the picture below.

3 - Then I calculate the total heading correction:

total heading correction to reach the destination = track error + closing angle

that is:

7.7 + 3.7 = 11.2 degrees

so the heading must be corrected to 11.2 degrees left.


Are you required to disclose medical conditions to your flight instructor?

When it comes to the AME, you must disclose everything fully and completely.  Failure to do so may void any license and insurance and expose you to extraordinary civil and criminal risk.

When it comes to your flight instructor, who is not a medical professional, you do not need to disclose the specifics of your situation.  Saying, "I have concerns about passing a Class III Medical Exam due to certain conditions" is sufficient, and is not the same thing as lying.  Do not claim you are healthy when you know you are not.

Your instructor may decide not to continue training until a physical is passed, or he may decide just to be a little extra vigilant during training, and delay certain elements or maneuvers depending on the information you choose to provide.

For example: If you choose to disclose vertigo problems, he may avoid steep turns until medical clearance.  If you choose to disclose vision issues, he may avoid night-flight.

Regardless, you will need a medical before your first solo flight.

Do not lie to your instructor, but that is not the same thing as disclosing full details of your health with a non-medic.


Just like other aircraft flying VFR, see and avoid. Helicopters fly slower, which gives them more time to see and be seen.

They also have transponders and ADS-B requirements so it will be possible to see them electronically too (with TCAS today and ADS-B in in the near future).

While helicopters could technically have no transponder and hence no ADS-B requirement, operating inside big cities leads to the under class B veil, which ends up forcing transponder / ADS-B requirements anyway. What I really mean is there's little logic in owning a helicopter that can never go into the big city, those are usually expensive enough to warrant being able to go anywhere, unlike some old cheap piston planes.


When an emergency happens, why do pilots need to stay on the current ATC frequency?

This doesn't mean you won't change frequencies if you move into another controller's sector or there's another reason for a handoff, such as moving from Center to Approach or Approach to Tower; it's to say that if you're already talking to ATC at all (often optional for VFR), then you should report your emergency there rather than switching to 121.5.

121.5 is monitored at every ATC facility, so if you have an emergency and don't know the right frequency to use, you can always go there and someone will answer you--and presumably give you a better frequency as soon as they've figured out where you are. If you already know the right frequency, though, then it's better for everyone (including you) to use that instead.


777 small wing panel moving all the time during landing

That control surface is called a flaperon.

The flaperon functions as both a flap and an aileron to provide roll control, as with an aileron, and increased lift and drag, as with flaps. The flaperons on either wing move down together as flaps, and move up and down opposite each other as ailerons.

In the video, steady movement following that of the surrounding flaps from one position to another is an indication of operation in the role of a flap. If we could see the other wing we would see that flaperon moving in sequence. However, the short up and down movements, as opposed to the stationary flaps, is an indication of operation in the role of an aileron. If we could see the other wing we would see that flaperon moving opposite the flaperon in the video.


NASA uses them for pilot training and as chase planes for research aircraft.

  The two-seat F/A-18 support aircraft are normally used for photo or video chase. They are configured to transmit live video pictures from the air back to Dryden so engineers can visually monitor the mission as it is being flown. This feature greatly enhances flight safety.

There's an article from Armstrong Research Center with some more information, but that pretty much sums it up.

NASA also currently operates (and has operated) many other military aircraft types, either as chase planes or as subjects of research projects. Some examples off the top of my head include F-15s, F-16s, and of course their ubiquitous B-52s.

You say "obviously they are battle ready", but they are not – NASA aircraft are unarmed, and the ones in the photo certainly are carrying no missiles. They may have been fighters in a previous life, but the weaponry has been stripped. "Escort" doesn't mean "fighter escort" in this case!


Is it possible to re-engine aircraft with different engine options?

It's doable, but not easy. Unless the aircraft was designed with that in mind, even then it does pose challenges. An example would be the Boeing 787:

The two different engine models compatible with the 787 use a standard electrical interface to allow an aircraft to be fitted with either Rolls-Royce Trent 1000 or General Electric GEnx engines. This interchangeability aims to save time and cost when changing engine types; while previous aircraft could exchange engines for those of a different manufacturer, the high cost and time required made it rare.

The benefit of interchangeability makes leasing aircraft easier for the lessor, as their fleet would be compatible with all the airlines and their existing facilities.

[Once] a plane has one type of jet engine under its wings, it’ll always have that type of engine. It’s just too time-consuming and expensive to swap out a Rolls-Royce in favor of a new General Electric.
This complicated the sale and leasing of jets. If Airline A wants to lease a plane from Airline B, but the two didn’t use the same kinds of engines, that usually would sink the deal (Source).

Related and further reading:

How much would it cost for a large airline to switch engine manufacturer for their planes?
Why bother having different engine options on one aircraft?
Boeing still hasn’t solved engine swap ‘challenges’, 2007


Why are Low Cost Carriers ordering several hundred aircraft?

Volume Orders Discounts

These result in significant discounts to the airline. While discounts are commonplace in the industry, Ryanair ordered 737-800 for an estimated 40-50 million dollars as compared to the list price of around 90 million dollars. With an order of that size Boeing could not risk losing it to another manufacturer, and will be satisfied with less profit per aircraft. Source

Fleet strategy:

Some airlines sell their old aircraft after only a few years while their value is still high but the maintenance costs start to increase. Increased maintenance is bad when you try to squeeze out as many flights as possible and you have small profit margins on every flight. You can find some of Ryanair's old aircraft by the company code (AS) with other operators by searching 737-8AS.

Another suggestion is that the customers perception of Low-Cost airlines is generally negatively biased and having new aircraft counters this effectively.

Old Aircraft

Some operators (such as charter operators) will not have the same sensitivity to a slightly higher fuel consumption on their aircraft. They may not use their aircraft the same number of hours, so having an increasingly expensive jet sitting on the ground is not cost-efficient. The aircraft ordered by IndiGo are all new fuel efficient A320NEO.

Some of these ideas are emphasized in your link.

  Of its 530 orders from IndiGo, Airbus has so far delivered 99 aircraft. The airline currently has a fleet of 83 planes and has phased out 16 planes that were over six year old or among the first in its fleet.

A bit of Ryanair strategy is outlined in this document.


Have crash investigators ever used pilot cameras to help find the cause of a GA crash?

Absolutely: Here's one of many examples, and you can search the NTSB database for "GoPro" and find plenty more.

The NTSB will use anything and everything available to them in their investigation, though release of certain materials is prohibited by law (e.g. CVR contents are not released, only transcripts).
I believe the NTSB is observing a similar protocol for onboard video: A synopsis is released (including a transcript of conversations) when requested, but the actual video is kept confidential by the agency -- I am not certain in that though, and the NTSB press office could provide a more detailed answer on their rules surrounding cockpit video / audio in GA crashes.


How does ICAO differentiate between Commercial and Private flights?

According to ICAO Annex 6 Part 1 (PDF):

  The Standards and Recommended Practices contained in Annex 6, Part I,
  shall be applicable to the operation of aeroplanes by operators
  authorized to conduct international commercial air transport
  operations.

According to ICAO Annex 6 Part 2 (PDF):

  International general aviation operations with:

  a) aeroplanes with a maximum certificated take-off mass exceeding
  5,700 kg; or

  b) aeroplanes equipped with one or more turbojets engines.

The International Flight Plan form also requires flight type to be declared, but I am not sure that this would be ICAO's sole requirement.

Type of flight—Indicate which one:

S—Scheduled air transport
N—Non-scheduled air transport
G—General aviation
M—Military
X—Other

For a simpler explanation, this PDF lists civil aviation activities:

This page contains a table (at the bottom) classifying each type.


Do pilots keep light in the cockpit during long night flights?

White lights are usually off in the cockpit in night flights to protect pilots' night vision. Red lights are sometimes used as these do not impact night vision.
One of the challenges you'll run into is knowing when it's night, as the start of night varies by latitude and the exact time. Phones generally set their time from the mobile network, which may be absent on long flights, especially those over water. A pilot flying a jet over the pacific may may have a phone that is hours off the local time.
Putting my (albeit old and tattered) mobile developer hat on I would suggest you look for ways the phone can tell you whether it thinks it is night or day and use that, plus a manual selection for day/night mode. Look at the Android UIModeManager as a way this could be done native.


Telluride (KTEX): Why is the localizer antenna located where the glideslope should be?

The localizer for runway 09 is offset by 3°, almost certainly because of terrain. That would be a typical reason for a non-standard installation.

The approach plate for the LOC RWY 09 approach notes the offset (more than 3° and it would be an LDA approach):

The final approach course for the LOC 09 is 093°, whereas for the two RNAV (GPS) approaches it's 096°, which is also the current magnetic heading of the runway. The Chart Supplement has various notes indicating that terrain is an issue (and RWY 09 has a displaced threshold) so everything indicates that the localizer is offset slightly for that reason, presumably to avoid signal interference.

As for practical issues for pilots, correcting for a 3° offset shouldn't be a problem. A bigger consideration seems to be that the MDA on the LOC 09 approach is more than 2000' AGL so if the pilot breaks out late he'll very likely have to circle to land.


Why did this 737 not take off on first attempt?

With the help of the clearly visible livery (Royal Air Maroc), registration (CN-RNV) and approximate time (before August 2016, probably not by too much), I managed to find the specific Incident: Royal Maroc B737 at Frankfurt on Jul 23rd 2016, three takeoffs for the price of one on The Aviation Herald. It even links to the very same video that you do.

Unfortunately:

  On Aug 30th 2016 the BFU responded to an inquiry by The Aviation Herald of Aug 25th 2016 stating, the BFU had neither received any notification by the crew, airline or airport involved nor by the person taking the video (see below) and became aware of the occurrence only through the release of the video into the public more than a months after the occurrence. The BFU argued that as result it will not be possible to establish sufficient facts and evidence needed for a detailed investigation, hence the BFU decided to refrain from initiating an investigation.

So we won't have anything better than guesses anyway.

The article does speculate that the wake turbulence of the landing aircraft crossing above the runway just before might have affected it, but it was too close to the starting point and is unlikely to have this effect, so what remains is that the pilot flying started to rotate too early. There may be basically two reasons for that:

The pilot flying started rotating before appropriate speed was reached, or
they calculated lower rotation speed (Vr) than they actually needed.

The take-off procedure with the speed call-outs made by the pilot not flying is the same for every take-off, so the second reason seems more likely.

The rotation speed depends on weight, density altitude and flap setting. Inserting wrong weight is probably most common reason for this type of incident, but calculating for higher flap setting than they used is a believable option here too as they used rather low setting for the actual take-off.

It should be noted that the pilot realised their mistake and handled it correctly by lowering the nose back to let the aircraft gain enough speed first.


Why does strong shock wave-boundary-layer interaction produce a bubble reattachment?

After the rear shock leg, the subsonic flow inside the boundary layer decelerates further, which causes an expansion of the streamtubes and therefore reattachment. Note that with the presence of the supersonic tongue, the deceleration into the subsonic regime happens somewhat "slower" inside the boundary layer than outside (especially above the slip line).


Why was this Twin-Otter Take-Off unsuccessful?

Comments under the video say clearly:

According to Transportation Safety Board (Canada) report # AO7W0128,

Take-off weight did not meet performance capabilities of the Aircraft.
Calculations to clear 50ft obstacle were not performed.
Southeast end of runway, not clearly marked.
Take-off was attempted in an up slope direction with a slight tailwind which increased the necessary distance to clear a 50ft obstacle.
Center of gravity (CG) calculations were off and found to be too far forward.


What do the dashed extended green lines on this PFD mean?

Those are radials off of the HME navaid, which is tuned in both Nav receivers. The two radials displayed correspond to the courses set in the two course select windows.

Putting a navaid's identifier into the FMC "FIX" page can also generate similar bearing lines, although there would be a green circle around the navaid in that case.

An ILS (also the departure runway in the flightplan) extended centerline shows as white, not green, and appears when that ILS (or any other) approach is active in the route, rather than when the frequency is tuned.


Can pilots fly circling approaches at non-towered airports?

The way I understand that ATC order is that it is about "circling approach instructions" which is different than "(circling) approach clearance". They cannot tell you to enter a left downwind, do a right 360, or follow some other specific path to the runway. If they clear you to execute a circling approach to a given runway at a non-towered airport, then the path to the runway is for the pilot to determine, as necessary to separate yourself from other aircraft in the terminal area and land safely.


Why is a special certification needed to land at Paro Airport?

The approach to Paro is unbelievably complicated. It is flown visually through a valley with high mountains all around and no sight of the airport until the last moment. Here is a cut of a map with the approach paths:

Approach to runway 15, marked in red, is worse in this regard. The ridge is rather close to the airport, so the final turn usually ends over the runway threshold. The wings get level with 30–50 ft (10–15 m) remaining only (here's a video). The approach to runway 33, marked in blue, allows a bit more of a straight final, but not by much. In either case the aircraft must emerge from the turn with correct altitude, speed and rate of descent. So the pilot has to know landmarks in the valley and how to judge correct approach profile by them. The approaches also often involve turning around higher in the valleys which again must be done by landmarks at places where it is known to be possible. It is this knowledge pilots have to demonstrate before they can attempt the approach (as pilots in command).

There are other airports where pilots have to receive special training to be permitted to fly there, for example the Samedan Airport near St. Moritz in Switzerland, which is similar mix of high altitude, high mountains around and visual approach, though it's still a lot easier as the airport is visible from much greater distance.

There is however nothing similarly difficult on Princess Juliana Airport. It appears approaches to Princess Juliana are only flown to runway 10 and these are over flat sea and flat beach. The runway is visible from great distance and the approach is straight. The featureless water makes it slightly harder to judge height than solid ground, but that's what the approach lights (VASI/PAPI) and distance-altitude table are for (there is no ILS at TNCM, only VOR-DME). And there are many airports with approach over water, so it's nothing unusual for the pilots. If there was approach to runway 28, it would have to be off-axis to avoid the hills on the island, but it does not appear to be used at all.

The pilot, Marek Tůma, who ferried in and for first 3 months commanded the ATR-42-500 A5-RGH, wrote a 4-part report (2, 3, 4; unfortunately in Czech) about flying in Bhutan.

According to that the training involved:

Couple of hours on simulator (in Bangkok).
Then they were permitted to ferry the plane to Paro.
Flight as observers with the training captain who showed them all the relevant landmarks in reality.
Some practice circuits.

They couldn't fly with the training captain in the other seat, because they were ATR-42 pilots and the training captain flies A320-family (and possibly still has rating for the older BAe146, but not ATR-42).

He also wrote that while on early flights when temperatures are still low the performance is good, later in the day it becomes marginal and they often needed to follow the valley quite far before they managed to climb above the mountains. Careful planning and weight and balance calculation was always necessary.


Can I get a first class medical with eyesight of -4.25/-1.00 diopters?

From the FAA's website

The key line is "with or without correction". So as long as your vision is correctable to the standards given you are good to go. You can find the full AME guidelines here is you are curious.


How does security and baggage checking work in regards to a private jet?

Here in the US (you didn't specify where, and this is different in other countries), traveling domestically in your own private aircraft is much like traveling in your own private car.

Except in very specific situations, you are not generally required to go through security, and at many, many smaller general aviation airports airport security is almost non-existent, or at the very least they are not checking passengers and their luggage.

If the police have a reason to suspect that something illegal is taking place (they have reasonable cause) then they can search the airplane, but again, much like in your car, this doesn't usually happen.

International flights are a very different matter though, and the airplane, crew, passengers, and luggage must all clear customs at departure and arrival airports where they will be inspected.


What is the weight that is used to balance an aircraft called?

747s in everyday operation typically use fuel for ballast when needed. Ballast fuel is considered to be part of the zero fuel weight and you are not allowed to burn it, although obviously if you were about to run out of fuel, it's available.

Ballast fuel is carried in either the center tank or distributed evenly in the four main wing tanks. Individual carriers have different ideas insofar as their preference for either center tank or wing tank ballast fuel. Also, after the TWA 800 explosion back in the late 1990s, there were as I remember special rules for a time on carrying ballast fuel in the center tank.

Should you wish to explore the effects of ballast fuel on the CG of a 747-400, go to 747.terryliittschwager.com and select the first aircraft N402YY. When the aircraft comes up, you'll notice that the BALLAST FUEL radio buttons at top center have the Center Tank selected. If you put 100000 lbs of fuel in and then 1000 lbs of ballast, you'll see the zero fuel weight CG change from 30.6% MAC to 30.8% MAC.

Ballast fuel is more often necessary for 747s that were originally passenger airplanes and then converted to freighters than otherwise. The problem is that the heavy structure added for the large cargo door aft of the wing brings the basic operating weight CG farther aft then before the cargo conversion. 747s originally manufactured as freighters do not have this problem as they have additional structure for the nose cargo door in addition to the side cargo door structure.


What happens when changing the throttle on a PT-6 engine?

Pushing the power lever forward will command more power. Fuel flow will increase, so will the TIT and torque.

To maintain the same RPM, more torque is needed as the prop blades will increase their angle.

Pulling all the way back does not cut the fuel flow (FF). The minimum FF required to sustain operation will be managed by the fuel control unit (FCU).

Sidenote on terminology: throttle, power, and thrust levers are the controls for piston, turbine, and jet engines respectively.

RE: Torque limits

It depends on the engine, but generally:

  In cold weather conditions, torque limits can be exceeded while temperature limits are still within acceptable range. While in hot weather conditions, temperature limits may be exceeded without exceeding torque limits. In any weather, the maximum power setting of a turbine engine is usually obtained with the throttles positioned somewhat aft of the full forward position.

Related: Is turboshaft fuel efficiency affected by N2 loading?


How are GA aircraft ferried from factories?

As you've guessed, there are two options: a ferry flight, or shipping the aircraft in a container.

Ferry flights are quite common; the recent Cirrus ditching in the Pacific was a ferry flight to Hawaii. As well as planning a suitable route and dealing with permits and paperwork, refueling etc., the ferry company may install extra fuel tanks to give more range, and provide the pilot with specialized survival and communications gear. And an airline ticket home, of course :-) This might all seem expensive, but considering that a new top-of-the-range Cirrus SR22 has a list price of almost USD 800,000 you can imagine that ferry costs aren't necessarily a big deal in comparison.

The second option is to put the aircraft in a container and ship it, and there are some companies who specialize in this (the page has some small photos of aircraft in containers). The major concern in this case is removing the wings: gliders and many experimental (e.g. home-built) aircraft are designed to have their wings removed for storage and transportation (towing behind your car) but most typical Cessnas, Beechcraft etc. aren't. You need to have the aircraft professionally and carefully prepared and then re-assembled and checked after delivery.

Which option is best depends on the costs of each option and the value of the aircraft. There's also the consideration that if you buy a 60-year old aircraft from the other side of the world, ferry companies may decline to fly it to you because of the risks of subjecting it to the stresses and weather of a very long series of flights. Or their/your insurance company may refuse cover for a ferry flight for the same reason. Or perhaps the aircraft is certified for VFR only, which would make a long ferry journey much more difficult to plan and execute. In those cases, container shipping may be the only available option.


Is there a minimum number of people needed for an aircraft pushback?

Depends on the airline.  At minimum, you need one driving the tractor, and in unconfined areas with nothing to run into, this is sufficient.  In confined areas operators almost always require wing walkers to clear the tips, and someone at the tail if backing into a confined space or to make sure the pushback stays within any boundaries.

So the answer is, anywhere from 1 to 4, depending on the situation and the airline's internal policy.  Insurance requirements will have an influence on this in a lot of cases because the results of screw-ups are usually just insurance damage claims with nobody getting hurt.


What is the typical reaction time for most pilots?

Its a bit dated but here is a paper published by the Navy on visual reaction time you can find. Keep in mind these are navy pilots, often considered the best of the best and in peek physical condition. Based on the publish year I would suspect all subjects were male as well.

Here is another study by NATO on reaction times for pilots on low sleep.

This is a nice study comparing the reaction times of pilots to non pilots, might be of some help.

  An additional question I have related to this is, how can one design
  an aircraft to make it difficult for pilots to enter PIO's?

This is an interesting question and in some regards could be its own question here. One of the big debates (mainly between Boeing and Airbus) is if systems like this should exist and who has the final say in terms of control deflection. Airbus takes the approach that the computers should prevent the pilot of say pulling back on the stick and stalling the plane. While Boeing generally allows pilots to be the final say and while their systems will warn of a stall you can ultimately pill back the column until the plane stalls.

In terms of how you would design something like this you would have to limit control input after an approach to oscillation was detected.


How did aircraft in WW2 navigate to the carrier?

You are correct. US carriers did indeed have a homing beacon that enabled aircraft to find them.

The carrier transmitting units were called YE or YG, and the receiving units in the planes were designated ZB, and called "Zeebies". The transmitters consisted of rotating "superfrequency" beacons that broadcast different morse letters in different directions that could be decoded by the ZB units, but sounded like static to ordinary listeners. They were installed on all US carriers in WW2.

Here is an excellent summary of the system and its history. More information can be found here and here, and History SE already has a question about it.

The British also had a similar system, installed on a carrier in 1936 and used through the war.

Sources also indicate that the Japanese employed a radio homing system (Hirohito's War by Francis Pike), but I have been unable to locate any details.


Why hasn't Boeing updated the 747 with technology from the 787?

They did, in the 747-8:

Wikipedia:

  Similar in nature to the 747X, the stretched 747 Advanced used technology from the Boeing 787 Dreamliner to modernize the design and its systems. On November 14, 2005, Boeing announced that it was launching the 747 Advanced as the "Boeing 747-8"

(Emphasis mine)

The 747-8 includes technology in the cockpit, cabin, wings, and engines borrowed or learned from the 787 and 777 aircraft programs. Obviously you can't just pull the wings off of a 787 and stick them on a 747, but the wings were redesigned with aerodynamic information learned in the 777/787 program.


Why overhead bin was put on top of passengers head?

Because it is the most efficient use of space.

Due to the physics, specifically the way pressure differential is spread in a container as stress, a perfectly circular tube is the best shape for the body of an airplane, and a rectangular box is way, way, worse. Modern airlines have an oval cross-section, but it is still a lot closer to a tube than a box.

The question is than how do you allocate the space inside a tube. The widest floor area is in the middle vertically, so that is where the passengers go. Now we have roughly one to two meters of vertical space both above and below the passenger deck, not high enough to accommodate people but enough for cargo and storage.

Naturally you would want the heavy cargo to go below, and passenger storage to go above, for logistic reasons. Putting them on the same deck as the cabin would reduce the usable floor area for putting seats. You'd want maximum floor area to place the maximum number of passenger seats to increased revenue on the same flight.


Can someone please tell me all the units for the propeller thrust equations?

Any good formula (that is, the one without magic numbers baked in) will accept any units as long as they are used consistently.

If you use SI, then use every figure in SI, and you'll get the result in SI.

Force is measured in Newtons, which is different to the unit of mass (kg), specifically $N =  kg⋅m/s^2$. The factor is the gravity acceleration $≈9.81\ m/s^2$ (which comes from the original definition of kg). So your measured thrust is about 343 N.

Because people are so used to treating force (weight) as mass, the 'force' units like kilogram-force (kgf) or pound-force (lbf) are commonly used, often implicitly. But this only leads to traps like you experienced and should never be used scientifically.

Density is $kg/m^3$, which is numerically equivalent to $g/l$ you used.

(In the context of propellers, one needs to be careful about the units of rotation. Strictly speaking, the SI unit of angular velocity is $rad/s$. But in practice coefficients are defined for 'n' in revolutions per second, $1/s$ (or even revolutions per minute, rpm, which is a non-standard unit). Fundamentally, radian is a dimensionless ratio, so it does not affect the resulting units (over 1/s) when used directly in formulas, and the error is not always obvious).


Is it true an ILS CAT IIIc can automatically taxi-in an aircraft?

There is no provision in the ILS system to provide for an auto-taxi or runway vacate. IIIc is just zero-zero and roll-out control, not auto-vacate as the linked AvWeb article seems to suggest. Its a logical extension of the FAA definition, however auto-taxi is not part of the CAT IIIc definition or system requirements. The only requirement is to get the aircraft on the runway and stopped.

FAA Circular 120.28C provides for the definition of a CAT IIIc approach:

  c. Category IIIc. A precision instrument approach and landing with no DH and no runway visual range limitation.

Right now there is no airport approved for IIIc approaches because the aircraft would just sit on the runway, it has no way of taxiing in. Until an augmentation system like GPS with WAAS or LAAS, or the "Ground-Based Augmentation System" is developed further, automatic taxi is not there.

There is no provision in the existing ILS signals that allow for an aircraft to vacate the runway. GPS is as close as you can get, but that may be unreliable especially with larger aircraft like the Airbus A380 that doesn't have much play on either side, so GPS accuracy will have to be augmented with something. Additionally a system will have to be in place to avoid aircraft from colliding on adjacent taxiways or to manage traffic in and around the gate.

From a technical standpoint, this is a long way off, even with ground based radar systems, GBAS, and LAAS that are currently undergoing evaluation at several major airports world-wide.

Also see this FAA Document 8900.1 and Order 8400.13D


Is airframe heating a concern at subsonic speeds?

Yes, aerodynamic heating is observed even at speeds that are well below Mach 1.

The practical application of this heating is the difference between Total Air Temperature, TAT, and Static Air Temperature, or SAT.  In essence, SAT is the actual temperature of the air, while TAT is the temperature that the moving aircraft "feels" due to aerodynamic heating.  When climbing and descending at low and medium altitudes, ice can accumulate on an aircraft when the TAT gets close to or below freezing. A common rule is to turn engine anti-ice protection on when in visible moisture (rain, snow, cloud, etc) once the TAT is below +10 degrees Celsius, since some cooling may occur in the inlet and you want to have a margin of error.

It is common to be descending at, say, 300 knots, in IMC (i.e. in clouds) and observe a TAT above +10, then when slowing down to be below 250 KIAS below 10,000', the temperature drops several degrees so that anti-ice is now required -- the difference being the additional heating that is lost as the aircraft slows down from 300 knots to 250 knots.

At high altitudes, roughly 30,000' or slightly above, where the TAT is always well below zero (although still above the SAT), a different limit is noted: below -40 degrees Celsius, the air itself is too cold to have enough moisture to cause icing, so in climb & cruise below -40, the anti-ice can be turned off.  (In descent in IMC, the anti-ice is turned on regardless of the SAT, because descending into air that CAN support icing without your ice protection turned on could make your day far too exciting -- in a bad way!)

Also, at very high altitudes on a cold day, it's possible to have temperatures that are low enough that the freezing point of your jet fuel can be a concern.  Again, this is a matter of TAT, because that's what the structure of the aircraft feels.  One solution if the fuel tank temperature begins to approach the freezing point it to increase speed, which will raise the TAT somewhat.  If that's not enough, then descending to warmer air is about all that's left.

Bottom line, at sub-sonic conventional jet aircraft speeds, aerodynamic heating is very much a factor.


Could someone please explain what is thermal oxidation of the carbon brakes?

Catalytic oxidation of carbon occurs when a catalyst, such as an
  alkali metal(s), is present. When a catalyst is present, the
  temperature at which thermal oxidation occurs is lowered. Airplanes
  equipped with carbon brakes are susceptible to catalytic oxidation
  caused by exposure to alkali metal runway deicers. - Boeing Aero
  Magazine

Brake manufacturers produce Oxidation resistant brakes. The effects of can be obtained by using carbon brakes, or using a coating on the brake rotor and friction surfaces.

Best practices for carbon brake application according to Airbus.