Has a "fight" ever happened in the cockpit?

I've never seen anything about pilots fighting during the flight but on Air India 611 they fought before the flight then proceeded to fly anyway. There are differing accounts of whether it was physical or just verbal. The captain claims he was punched for calling his older copilot "uncle."

On Express Jet 4453 apparently they got into such a heated argument that when they landed, the flight attendant made the passengers disembark. They continued on in a different plane with a different flight crew.

There are reports of a fight between pilots on a China United Airlines flight but finding out what actually happened will be difficult.

On JetBlue flight 191 the captain started ranting and raving to the point where flight attendants and passengers had to remove him and physically restrain him for the duration of the flight. There's video of the incident. He was charged with interfering with a flight crew but was found not guilty by reason of insanity.

And on Delta 2598 the pilots did an emergency landing when two flight attendants got into a brawl.


The EICAS will have the engine instruments and the crew alerting system in one display.  It is a vital instrument because it displays engine parameters, fuel, the crew alert system and other systems information depending on the specific airplane.

The CAS (crew alerting) functionality of the EICAS replaces the illuminated fault buttons in older airplanes.

YSSYguy CC-BY-SA 3.0

The electronic CAS that is part of an EICAS display is a superset of these old panels and can display a much bigger set of alerts.  The specific alerts that can be shown will cover most error and failure modes the airplane systems can reasonably encounter.  Cautions are yellow in color and will illuminate the master caution and sound an audible chime.  Warnings are red in color and will
illuminate the master warning and sound the triple chime (and the fire bell for certain conditions).  There may also be advisory messages displayed in another color, e.g. cyan, on the EICAS.

 EMB-145 EICAS.  The CAS is the upper right portion of the display

The messages themselves are terse and not detailed, though detail can be inferred from the pre-defined message text.  Warnings and cautions that are displayed can be addressed with memory immediate action items (memorized checklists) and/or the QRH (quick reference handbook) which defines the procedures for dealing with problems in a verbose checklist flowchart.  The QRH will be indexed by the messages on the CAS so they can be easily found and referenced.


How does one determine the elevation on a sectional?

The answer is A. The FAA chart user's guide is your friend here:

Simply check the scale, that already tells you it's 2000-3000 feet. Then look for contour lines, there aren't any, then it's 2000-2500 feet.


Looking for techniques to model resistance to roll rotation in a very simple, force-based flight model

The way this is commonly done in simulators is using linearized stability derivatives. For your example, one could calculate the rolling moment on the aircraft as the sum of such terms as:  rolling moment due to aileron deflection angle, rolling moment due to roll rate (roll damping), roll moment due to side slip angle, roll moment due to yaw rate, roll moment due to rudder.  For doing simulation each of these coefficients can be precalculated based on flight testing or CFD and then during simulation lookup tables can be used to find the current value.
My suggestion is that you take a look at JSBSim which is a cross platform opensource flight dynamics model that is used by FlightGear for example.  JSBSim allows one to build an aircraft model by defining the values in an XML file.  The website includes documentation, some links to papers and books, and example aircraft that are very useful.


How to calculate angular velocity and radius of a turn?

Your terminology is a little confusing, but I'm going to assume you're asking how to calculate turn radius and rate of turn based on airspeed and bank angle. These formulas can all be found in the FAA's Pilot's Handbook of Aeronautical Knowledge which is available for free online.
The Handbook gives the formulas for rate of turn and turning radius on page 4-34:
$$R=\frac{V^2}{11.26\tan\theta}$$
$$\omega=\frac{1,091\tan\theta}{V}$$
The variables used are:

$V$ = true airspeed in knots
$R$ = turning radius in feet
$\theta$ = bank angle in degrees
$\omega$ = rate of turn in degrees per second

For example, at 120 knots and a 30° bank angle, the turn radius and rate of turn are:
$$R=\frac{120^2}{11.26\tan30}=\frac{14,400}{11.26\times0.5773}=2,215 feet\approx\frac13nautical~mile$$
$$\omega=\frac{1,091\tan30}{120}=\frac{1,091\times0.5773}{120}=5.25°/sec$$
The "magic constants" in these formulas ($11.26$ and $1,091$) are conversion factors for the units involved (knots, feet, and degrees). Physicists would use unitless formulas involving $g$, acceleration due to gravity (roughly $9.8m/sec^2$).
You can also rearrange the formulas above using simple algebra to figure out the required bank angle given a desired rate of turn or turn radius.
Finally, note that things get a lot more complicated if you factor in winds aloft. Rate of turn will always be the same regardless of wind, but turning radius no longer applies because the aircraft will trace a spiral path along the ground, not a circle. The turn will be "sharper" on the upwind portion of the turn and "wider" on the downwind portion. This is why turns around a point is a complex maneuver taught in basic flight training: in order to fly a circular ground track, the pilot must constantly vary the aircraft's bank angle according to wind: lower bank angle upwind, higher bank angle downwind. The pilot must also use the rudder correctly to keep the turn coordinated at all times.
Other useful links:

Pilot's Handbook of Aeronautical Knowledge (quoted above)
Aviation Formulary has a section on turns
Standard rate turn article on Wikipedia
Banked turn article on Wikipedia

There are also some "Related Questions" over on the right-hand side of this page that might be useful.


Process for Compensator in Altitude Hold

A lag controller is basically an amplifier whose input is proportional of the present error, that is the difference between the current altitude and the target altitude

With low amplification the trouble is the lack of response as long the error is small.

With great amplification we have an overshoot effect with continuous oscillation around the target altitude.

The best simple low cost compensator consists of an PID

Please refer to this website:

https://en.m.wikipedia.org/wiki/PID_controller

The PID has 3 adjustable inputs:

A proportional input « P » somehow similar to a lag amplifier
An integral input « I » that is proportional to the error but also to the duration of the error, therefore an error as small it may be will be corrected with time and will decay
A derivative input »D » which is proportional to the slope of the error that is the error evolution, therefore it has a predictive value. Therefore the D input will neutralize the tendency of an error to appear or to increase.

The adjustment is done by small steps,

-you start by setting to minima the I and D inputs, and set the P input to get the best non overshooting response.

-In order to reduce the remaining error with the previous adjustment you increase the I input by steps and verifying you don’t get overshoots

-In order to avoid drifting error you act on the D input, increase the input so that you obtain a little overshoot that you correct by reducing the I input.

Trial and error adjustments could be useful


Why is the mammatus cloud formation so dangerous?

Nobody knows exactly how mammatus clouds are formed, it's been studied and there are several theories about it but none are accepted. They are most often seen below anvil clouds, ie cumulonimbus clouds with extremely powerful updrafts. One thing that the theories all agree on is that where they are formed on the underside of cumulonimbus clouds there are huge shifts in temperature, moisture and pressure within a short space of time. Although these clouds can form under other types of cloud they are mostly seen under the most powerful of storms.

So why are they dangerous?

They are usually made of ice: ice accretion is dangerous, especially for light aircraft without de-icing systems
They are almost always associated with severe low level wind shear. Wind shear is sudden changes in wind direction which is dangerous for aircraft. You can suddenly find that a 30kt headwind is a 30kt tailwind so you've lost 60kt of airspeed, this is especially dangerous during takeoff and landing
They are almost always associated with severe convective activity, ie very strong updrafts and downdrafts which are dangerous for aircraft. You could get sucked up thousands of feet or pushed down as well, and there's be nothing you could do about it
They are almost always associated with severe turbulence which is also dangerous for aircraft. Severe turbulence is at best extremely uncomfortable, at worst can cause a loss of structural integrity

So mammatus clouds are usually an excellent sign of an area to be avoided.


What's the difference between Stress and Strain?

Stress is the load divided by the cross section of the material bearing it, and is expressed in units of pressure.

Strain is deformation divided by the original dimension in the direction of the deformation, and therefore is dimensionless.


Why does this analysis show very high stress in a propeller?

The plots of your propellers seem to use a regular airfoil all the way to the root. Real propellers become almost cylindrical there, however. Also, aluminium propellers are hollow, so the outer part is only a thin shell, saving mass and reducing centrifugal loads significantly.

After all, real aluminium propellers work, so there must be a way to keep the stress in operation below the yield stress. FAR 23.907(c) even demands that a non-wooden propeller must be life-safe:

  The applicant must perform an evaluation of the propeller to show that
  failure due to fatigue will be avoided throughout the operational life
  of the propeller using the fatigue and structural data obtained in
  accordance with part 35 of this chapter and the vibration data
  obtained from compliance with paragraph (a) of this section.

Below is a drawing of a wooden propeller, but the outer shape of a metal propeller is not much different.

Drawing of a wooden propeller for the Fokker D VII (picture source)


Can old passenger airplanes be refitted with latest engines to extend their life and efficiency?

You are absolutely right - refitting new engines to older airplanes makes a lot of economical sense. After all, two thirds of fuel economy gains in the last 50 years were due to better engines.

However, some conditions conspire to make this harder than it might look:

The better efficiency was gained by increasing the bypass ratio of engines, which means that the new ones had more diameter for the same thrust. This makes them hard to fit to airframes designed for the smaller engines, and adding a longer landing gear would be too expensive - then it is indeed better to buy a new airframe.
Designs with tail-mounted engines would have center-of-gravity problems with newer, heavier engines. Tail-mounting engines was very popular after the Sud Aviation Caravelle pioneered this, but rules out those designs (BAC One-Eleven, Vickers VC-10, Boeing 727, Illyushin 62, DC-9, Tupolev 134 and 154) for refitting with more modern engines.

Add to this that airframes have a limited life time, and fitting new engines makes sense for only a limited number of aircraft.


What happens when an aircraft type is grounded while in flight?

The FAA is currently dealing with that on the 737 MAX.  They are allowing any airborne 737 MAX to continue to its destination or to an alternat or emergency landing site at the discretion of the crew  within the US thence flight ops are prohibited. Special airworthiness certificates and ferry flight permits may be issued by the FAA for moving the aircraft to a home base or maintenance depot as the discretion of the Administrator.


On the V2533 engine, what protections do the FADECs provide against uncommanded unstow?

Not from an FCOM, but from an A319/A320/A321 IAE V2530-A5 training manual, it's the same thing as the CFM:

  Inadvertent Stowage/Deployment

  In either case the LVDT [Linear Variable Differential Transformer] sensors would detect a movement the EEC
  would execute auto−restow or auto−redeploy.

  If the reverser travel exceeds 15% of its travel from the fully stowed position
  then the EEC will command idle.
  Following restow, full power is again obtainable.


It's the time taxiing without engines on, for example when under tow or during push back. As opposed to when you're taxiing under the aircraft's own power

The second is potentially subjective, but I'd personally count it as the moment the engine is actually running, post-start up procedure: that's the moment when I could use the engine as an actual engine with useful power.


Why are airliners not inherently "speed stable"?

Light aircraft and transport aircraft behave exactly the same regarding trimming for speed. Trim is for angle of attack, but power affects that trim and phugoid oscillation occurs in speed and pitch, because the feedback is second order.

The Boeing FBW has no trouble mimicking anything. It simply translates the control forces and position exactly as a hydro-mechanical link would, just in electric signals. The aircraft is still stable.

Airbus aircraft are also all stable, but their FBW relaxes the stability by auto-trimming for current speed. The result is that side-stick controls flight path angle and power controls speed.

The only exception to the stability are fighter jets (starting with F-16). Those are aerodynamically unstable to get faster control response and their FBW makes them neutral (that is, the yoke/stick again controls flight path angle).


(ICAO)

In cruise the wake turbulence levels off about 900 feet below the cruise level, which is just enough for another plane flying head-on 1,000 feet below to miss it or encounter the mild part of it. Encountered wake turbulence in RVSM should be reported to ATC, because the wind also affects it, and then the ATC will advise on a deviation for the remainder of your route and for the other aircraft behind you, for example.

Regarding the projected increase in travelers, new airways can be utilized, more use of free route airspace, using bigger (but not too big) planes, as well as improving the throughput of the runways using various technologies (NextGen and SESAR for example).


How can an airplane fly with single propeller without rolling over?

When it is slow, the two or three wheels should keep it from flipping over.

Once it is fast enough to fly, the wing will provide what we engineers call roll damping: Any tendency to roll† will cause an opposing moment which will stop the motion quickly. The rest is done by a differential deflection of the ailerons, so the wing creates an equal and opposite rolling moment to that of the propeller.

What is roll damping: Once the wing starts to roll, one side will go up while the other goes down. This will cause a change in local angle of attack and, consequently, local lift. The down-moving wing will see a higher angle of attack and a local lift increase, and the opposite happens on the other side. Total lift will remain unchanged, but now the change in the spanwise lift distribution will lift the down-moving wing back up and vice versa. The movement stops before it could pick up any speed.

With powerful engines, engine torque is a real problem and needs to be canceled with a few tricks:

Camber on the vertical tail: The vertical tail will create a side force and rolling moment which depends on the speed of the air flowing over the vertical. This helps to make the correction depend on the power setting of the engine. Just make sure that the vertical is in the slipstream of the propeller.
With contra-rotating propellers you can cancel the rolling moment of each propeller with that of the other. This needs a more complex gearbox, however.
In operation, apply power changes only slowly. With its narrow undercarriage, the Me-109 would become uncontrollable if the pilot went from idle to full power on the ground too quickly.
Watch the gyro forces of a spinning propeller: In taildraggers, the aircraft will yaw due to gyro forces once the tail is lifted during the ground run or the pitch attitude is changed in flight. Also, yawing (rotation around the vertical axis) will create a pitch moment (which acts around the spanwise axis).

† Roll: Movement around the longitudinal axis.


With positive passenger/bag matching rules, what happens to a bag that does not arrive with the passenger?

This is more a guess:

Think about the rationale behind the rule. A terrorist should not be able to send a bomb on a flight while staying at home. With this rule, a terrorist is forced to sacrifice himself by taking the same flight. Hopefully, most terrorists don't like this idea.

If the luggage wasn't put on board, or was put on another flight, the terrorist will notice this at the destination, and not before. Same effect, he had to be willing to sacrifice himself by boarding the aircraft.

So, the rule is not to never let luggage fly alone, it is about not letting it fly when the owner for some reason does  not take his flight.

If the luggage took another flight, it was for sure an error. The barcode scanner mis-read the barcode, the ID of the trays transporting the luggage was not read correctly, a computer error or whatever. Should not happen, but does from time to time.
If the luggage did not fly at all, it might simply have missed the flight due to technical / logistics problems. Or the barcode tag was ripped off etc.


Does the definition of visibility take object size into account?

The FAA gives the definition for "Flight Visibility" in 14 CFR 1.1:

  Flight visibility means the average forward horizontal distance, from the cockpit of an aircraft in flight, at which prominent unlighted objects may be seen and identified by day and prominent lighted objects may be seen and identified by night.

According to that definition, any mountain, geographical feature, structure, road, or other object could qualify for day visibility measurements, regardless of size. To identify the object in a way that is meaningful for measuring visibility, the object must be identified to a degree that the distance can be positively identified. If I see a mountain and positively identify it as a mountain that is at 150 NM distance, I can correctly state that I have at least 150 NM of flight visibility. Likewise, if I see a windmill and positively identify it as a windmill that is at 1 NM distance, I can correctly state that I have at least 1 NM of flight visibility.

The FAA also gives the definition for "Ground Visibility" in 14 CFR 1.1:

  Ground visibility means prevailing horizontal visibility near the earth's surface as reported by the United States National Weather Service or an accredited observer.

The term "prevailing horizontal visibility" is indefinite as seen here, so additional clarification is needed. In this case, that clarification is provided by the National Weather Service itself:

  Prevailing visibility is the value reported in non-automated surface observations. A human observer determines it by identifying objects and landmarks at known distances in a full 360 degree circle around the observation point. The greatest visibility observed over 50% or more of the 360 degree area is the prevailing visibility. If there is a sector of the 360 degree area that is significantly different from the prevailing visibility, the system may add a remark reflecting that difference. Pilots must realize, however, that nearly half the area around an airport may have lower conditions than the reported prevailing visibility.

Automated visibility sensors—such as those used with the Automated Weather Observing System (AWOS)—do not measure visibility over a distance. Instead, these systems sample a very small area for clarity of the air and use an algorithm to convert this value to a usable representative visibility value. For more information on these systems see the National Weather Service's Visibility Page.


How does a DC-10 flight engineer manually raise the cabin altitude?

Tip: accident investigation reports cover the system controls related to an accident. The one in question is here (ntsb.gov), from which:

  According to the March 20, 1994, edition of FedEx’s DC-10 Flight Manual, page 8-2-2/8-2-3:

    Cabin pressure is controlled and maintained by metered release of conditioned air in either an AUTO, SEMI-AUTO, or MANUAL mode…. The cabin pressure controller maintains the desired cabin pressure in relation to the altitude set…. In the AUTO mode, cabin pressurization is automatically controlled during takeoff, climb, cruise, and descent conditions to the lowest cabin altitude compatible with aircraft and flight requirement.

    When MANUAL control is selected, the control wheel engages a locking mechanism to secure the outflow valve in its existing position. After selection, manual control is achieved by pressing the control wheel inward (to disengage the control wheel locking device) and rotating the wheel to position the outflow valve to attain the desired cabin altitude. When the control wheel is released, the outflow valve is again locked in its existing position. Selecting the valve at more than two-thirds open can cause a negative pressure and create a noise in the cabin. At touchdown, the Second Officer [flight engineer] must manually depressurize the aircraft. [emphasis added]

Regarding the outflow valves, see:

What is this device below the door of a 737 (and other aircraft)?
What are these "portholes & panels" on the fuselage of the Omega Tanker DC-10?

And the aforementioned wheel and readout:

Source: wikimedia.org


What's is the difference among ECL, CFL, RFL, TFL messages in ATM?

In Air Traffic Control their is quite a few acronyms for levels at various stages in the flight. I am not sure what you meant by messages, or more importantly which messages, so I have kept the answer a little broader.

RFL

Requested Flight Level

The level that is requested in the flight plan before the flight. There can be multiple RFLs in a flight plan. Each time the aircraft wants to cruise at a different level, in the flight plan, an amended RFL is added.

The Pilot may also request an amended RFL mid flight but the RFL is not mentioned at the time just the request for a different level.

Speedbird 1 Request Climb FL360

CFL

Cleared Flight Level

This is the level that the aircraft is currently cleared at or cleared to.

This can be a level on the way to the RFL used as paperstop level for separation (a level the pilot is never expected to maintain but provides separation until conflict no longer exists);
The RFL when the aircraft is maintaining; or
Any other level that the aircraft is cleared to.

ECL

Enroute Cruising Level

Stole part of this one from the question: What is the difference between RFL and ECL in Air Traffic Control?, Thanks GgD for the resource.

From the EUROCONTROL SPECIFICATION FOR TRAJECTORY PREDICTION Edition: 1.0

Page 2:

  1.5. Definitions

  Enroute Cruising Level - The level that the flight is to maintain for a significant part of the flight after reaching TOC and prior to TOD.

Page 33:

  2.3.2  Enroute Cruising Level (ECL) (3.3.2)

  Domain Knowledge: The  ECL   is  a  notional
  level  that,  in  the  absence  of  constraints,  equates  to  the
  RFL .  In  the  case  where  a  flight  is  not  permitted  to  cruise
  at  its  RFL   for  any  or  a  part  of  its  route,  due  to  the
  presence of a  strategic constraint (level limit) which applies to
  flights between the  aerodromes of  departure and destination, the ECL
  will be limited  to the level defined by the constraint. The ECL may
  also  be  changed  by  instruction from  ATC where  the flight is to
  maintain a different cruising  level, typically due to the proximity
  of a flight at the  RFL  on the same  route.   As with the  RFL ,
  the  ECL  can be changed for different  segments  of the  route  and,
  if different in  the  cruise  phase,  is  changed  to  the  XFL   on
  passing  the  sector   boundary.  The  notion  of  ECL ceases to exist
  after the final  TOD  from cruising level.

So summarising the above passages, the ECL is the level that will be maintained from top of climb until top of descent. The ECL can be the same as the RFL if the aircraft can be cleared to fly the RFL.

So if there is a conflict at the level of the RFL and the aircraft is cleared to a level below the RFL, the ECL would be that level.

When the aircraft is cleared to fly the ECL the CFL and ECL are the same. So you can get the RFL, ECL and CFL as the same level.

TFL

Personally I have never heard of this level acronym so I am unable to respond on its relationship to the others. If someone else knows I would love to know also.

Additional Level Acronyms

I am also adding the major other level acronyms for ATC into the mix so they are all together. So the answer is as complete as I can get it.

XFL

Exit Flight Level

This is the level that the aircraft is going to cross an ATC sector boundary at. There are two different ways of using the XFL around the world:

In some ANSPs (Air Navigation Service Providers) it is the level that the aircraft will be cleared at when the aircraft calls the next sector. In this case the aircraft could be on Climb or on Descent to the XFL or could be maintaining the XFL all ready. This is used so that the controller knows the CFL when the aircraft calls.
In other ANSPs is is the level that the aircraft will cross the boundary regardless of the CFL issued at the time. This one is used for trajectory calculations inside the receiving ATC system.

PRL

Pilot Reported Level

This is the level the Pilot last reported at. In Procedural Environments this is the only way there is to find out the current level of the Aircraft.

MCL

Mode Charlie Level

There can be other names and acronyms for this level but they all have the same meaning.

This is the level received by the SSR radar or by the ADSB receiver. This has the the aircraft's current level usually embeded in a message with other details. This can be used to fill in the PRL on some systems or is a complete independent system from the PRL.

Sorry I found this question so late but thought it deserved an answer anyway.


The Michigan Alumnus written on Aug 13, 1938 refers to Clarence Johnson's experiences as a  Flight Test Engineer. He graduated with a MS in 1933 so presumably became an engineer at that time.


Are there different sub-types of a mayday call and do pilots use them when declaring emergencies?

The simple answer is no, there are no "subclassifications" of emergency or urgency calls in standard aviation phraseology. In terms of priority, they are all the same; however, in terms of actions taken, there can be differences based on what caused the aircraft in question to make the emergency or urgency call.

There's mayday (emergency), pan-pan (urgency), and everything else (routine traffic). Mayday trumps pan-pan, and pan-pan trumps everything else.

Broadly speaking:

mayday is used when the safety of the flight has been compromised and the pilot(s) require immediate assistance to recover.
pan-pan is used when the pilot(s) require assistance beyond that normally offered by air traffic control, or require priority handling, but the safety of the flight itself has not been compromised.

Compare When should the term “pan-pan” be used instead of “Mayday”? which discusses the difference between the two in more depth.

Yes, there is a bit of overlap between the two: it's possible to come up with situations where it is not entirely clear whether "mayday" or "pan-pan" is more appropriate. When in doubt, it becomes a judgement call. A pan-pan can escalate into a mayday as the situation develops, and even a mayday can be terminated if the situation that called for the original mayday call no longer exists. (The latter could, for example, happen if a GA VFR pilot becomes uncertain of their position, and are then able to identify their position in such a way that the flight can proceed safely; or if a non-instrument-rated pilot flies into IMC, and are able to return to VMC and proceed safely.)

The broad classification of emergency or urgency is then further specified by describing the type of emergency or urgency situation, using either standard phraseology or plain language, as appropriate. The purpose of this, however, isn't to prioritize such calls, but to identify to ATC (and other aircraft) what types of assistance is required.

Compare How does ATC handle different kinds of emergencies?, though that question is somewhat US-specific and specific details can vary between countries.

To mention a few examples, without in any way intending for this to be an exhaustive list:

mayday, VFR into IMC, negative instrument qualified — this one likely requires immediate help in returning to VMC, whatever that entails
mayday, decompression, emergency descent to ten-thousand — no immediate assistance required for that flight, but get everyone else out of their way now, then figure out how and where to get them onto the ground
pan-pan, fuel — this one needs landing priority, and may require vectors to the nearest suitable airport, but not much more than that
pan-pan, passenger ill — this most likely requires notifying someone on the ground so that the situation can be handled when they land, and might require this one flight to divert, but other than that, not a big problem from an ATC standpoint


Here's an answer for the B737, from own work compiled from several public sources. The A320 and other airliners are very similar.

The air conditioning packs are Air Cycle Machines (ACM) which remove heat from air through a reverse Brayton cycle. Hot compressed air is cooled and then expanded, which drops the outflow temperature to a temperature cold enough to provide cooling in hot environmental conditions.

The ACMs in the Boeing 737 are 3-wheel units consisting of a compressor, two heat exchangers, a turbine and an impeller fan. Bleed air is cooled in the primary heat exchanger, enters the ACM, is compressed further and cooled again in the secondary heat exchanger. The ACM compressor’s further temperature rise allows for more efficient cooling by the heat exchangers.

Cooling air for the heat exchanger is provided by ram air, via inlets underneath the fuselage, in front of the body/wing intersection. Water is extracted from the cool air, and sprayed into the ram air stream for more efficient cooling via the heat exchangers.

The impeller fan creates cooling air flow when airspeed is low. The impeller fan speed can be controlled independently from the ACM turbine/compressor axis, by the Turbofan Control Valve.


Can radar detect a small flying device with MEMS microengines?

Obviously the MEMS engine itself is not going to be detected: they're only a few millimetres across. The question entirely depends on what you attach it to.
Conventional radars have trouble detecting UAVs less than a couple of metres long, and replacing their power plants with micro turbines won't change that.

My neighbours at Aveillant already have a holographic radar system that can detect smaller targets such as UAVs more accurately. Again, changing the power plant technology won't change that.

Micro-turbines are not intended to replace propulsion systems, but to replace batteries, allowing them to use denser hydrogen, methane, or methanol fuel. As far as I've been able to find, they don't produce break-even power yet, but it's envisioned that they will become commercially relevant once they can produce more than 10 W (about .01 hp), in a few years' time. For comparison, a current, small, military UAV might generate tens of horsepower, and some experimental super-lightweight UAVs need as little as 5 hp, but with no payload or cargo.

TL;DR: (a) MEMS turbines aren't going to be relevant for UAVs for some years, and they'll have to be much bigger than they are now; (b) replacing the power plant won't make much difference to the radar signature.


What exactly do fighter jets and its pilots do during their peace time sorties?

As with any job, there will be some initial training to learn the basic skills needed, and that is typically done at a central location. But there will also be ongoing practice to maintain those skills and continue to improve them. Modern fighter jets are complicated machines and take a lot of knowledge and practice to operate. Simulators and classroom learning help but can't completely substitute flying and maintaining real aircraft. In the US, military aviators get about 20 hours per month of flying time. There's a saying in sports that "you play how you practice." When these pilots go into battle, lives are on the line, and they want to be able to recall skills they practiced recently, not years ago in basic training.


How does a constant pressure chart affect your preflight planning?

As others wrote, I don't think in and of itself the constant pressure chart will help with a go or no-go decision by itself.  However, I do believe it would help to get the big picture of what's happening with the weather; fronts, etc.  Knowing the big weather picture is more important depending on what kind of flying you do.  The constant pressure chart can help with that.  Regarding choosing a flight level or altitude to fly in I would use winds aloft, airspace charts like a sectional, anticipation of ATC given altitudes in the area you plan to fly in, etc.  Like many others have said: with regards to weather the more you know the better off your preflight planning will be and the constant pressure chart adds to your knowledge of the weather.


What margin of error should one reasonably allow regarding aircraft performance?

Aircraft POH and AFM utilize engineering data obtained from test flights, conducted by highly experienced test pilots who have a goal of presenting the best possible data for an aircraft.  Performance data is used to sell airplanes, long before the owner is working the numbers for his or her operations.  The subject aircraft have been primped, and the engines are working and in ideal condition.  So, if one flies with the same skill, and a finely tuned aircraft, with a ideally running engine, and can repeat a short field take off again and again, until their technique is highly polished, then perhaps one might consider using the book figure.

That doesn't often happen.  For most of us, the aircraft we fly have bug splat on the leading edge, tires that are not perfectly balanced, and other imperfections.  Furthermore, for the weekend flyer, and even for a research test pilot, all operations are not conducted with the degree of refinement which is done during the gathering of data for performance publication.

So given all of that, what are the margins?

I have not seen large scale studies, but I have had several hundred students, and several score of flight instructors who I have taught and prepared. To my knowledge none of them have had any serious accidents, and I have never scratched paint on an aircraft.  So here are my guidelines:

Range in VMC conditions, non-sparse areas 30%

Range in IMC, or night, or over sparsely populated areas 50%

Reduce margins by 10% for every 500 hours of operation in those conditions, down to 10% and 20% respectively.

For operations like take off from short fields, add 50%.  Reduce the margin by 10% for every 20 similar operation over a one month period, which you can verify book performance has been achieved. (Note this seldom happens, because we are seldom watching closely.) Maintain a minimum margin of 10%

Why 10% margins? Well, the windsock may change during your takeoff/landing, the tires might be a little under inflated. There might be bug splat on your leading edge and the airfilter on the engine may have a little dirt on it.  There is always something which is not perfect. So keep a margin.

Determine go/no-go points for TO and LNG.  Do the same for fuel burns on XC operations. If you are going to eat into your predetermined margin, divert.  Chances are the flight that is causing you to eat into your margins may be at night, with rime and clear ice, winds higher than forecast, and more turbulence than you are comfortable with. So with things less than perfect you are absolutely justified in being conservative.

If you are getting book figures, usually there is something not exact as the book.  For example, you may be under gross weight measuring climb.  So don't fool yourself.

One thing you should be able to duplicate is cruise performance.  Dip your tanks after every flight and compare the findings with your calculated figures.  If you can't duplicate the book figures, without margin, then something is wrong.  Climb performance is a bit harder to achieve the precise figures in the book. Even if you can duplicate fuel burn rates, keep a margin.

Making copies of the performance data, and marking the copies with your achieved results will help you recognize where you and your plane are performing.  Having friends spot you on takeoff and landings, perhaps when you are practicing specialty landings, and recording that data is also helpful to assess how you are doing.  Don't forget to record and factor in things like changes in gross weight, winds and even how wet and long the grass is.  They all impact performance.

In my own plane, I have dip sticks which I have calibrated for fuel level, I have a light weight digital bathroom scale, etc. as tools for conducting a flight, with verifiable performance.

In the professional world, I have had to optimize payloads with aircraft to get acceptable performance for low level survey operations. Repeating tests, with supplemental metrics (eg radar altimeter data) and then developing SOPs is something I have spent allot of time doing. All of us can work to refine our procedures and practices to enhance the safety of our operations, without imposing extreme and unjustified margins.

Over the years I have lost too many colleagues and friends to aviation accidents. Retrospectively, every one of them has made one or more judgment errors. Why cut it close, when a little more margin means you may fly again another day?


The mean camber line is the locus of points halfway between the top surface and the bottom surface (which are sometimes referred as upper and lower cambers). For a symmetrical airfoil, it is merged with the chord line.

This curve is described by a polynomial function at each point along the chord axis. An airfoil may have a camber line which changes direction at one or more point, and which possibly crosses the chord.

All measures are taken perpendicular to the chord which is considered having a length of 1 or 100%.

Adapted from Wikipedia.

What you ask for is the maximum camber, which is determined by the value of the maximum difference between chord and mean camber line, and the distance from the leading edge.

Adapted from Wikipedia.


What is an Enhanced surveillance system?

Enhanced Surveillance (EHS) is a variant of Mode S transponder protocol that includes Downlink Aircraft Parameters (DAP) in the information returned by the airborne Mode S transponder.

Mode S can be configured as Mode S Elementary Surveillance (ELS) or Enhanced Surveillance. EHS is the concept behind ELS, ELS being a limited implementation. ELS is deemed analog avionics aircraft oriented while aircraft with digital avionics should use EHS.

While ELS allows for selective interrogation of a Mode S transponder to obtain barometric altitude, EHS allows also to request DAP. These data are intended to be used by ATC to face the rapid traffic increase observed in Europe. With no surprise this initiative is driven by Eurocontrol.

The use of DAP is expected to limit voice communication between ATC and crews. DAP includes:

Source: Eurocontrol

In general, ATC automation tends to get all parameters providing information on current position, but also to anticipate short-term position. This is why roll angle or vertical rate are part of the DAP.

Mode S EHS takes benefit of Extended Squitter (1090 ES).

Related:

Transponder
Transponder interrogation modes
Mode S
ELS and EHS


What happens without trimming a statically stable aircraft?

Trimming or not trimming your aircraft should not change its inherent stability. It will, however, change the airspeed, vertical speed, and attitude of the aircraft based on power settings. Control input would have to be applied in order to maintain these parameters. The more out of trim the aircraft is, the more force/pressure will need to be applied to the controls.


Here's the difference in a nutshell:
When you change the number in Kollsman window to
bigger number and the atmosphere stays the same, the reading on your altimeter increases.
When you leave the number in the Kollsman window the same (let's say you have it set to 29.92 to see the pressure altitude) and the atmospheric conditions change so that the correct altimeter setting increases--i.e. the air pressure has increased-- then the reading on your altimeter decreases.
You increasing the setting in the Kollsman window is not the same thing as an increase in the prevailing correct altimeter setting.  They have the opposite effect on what you see on your altimeter dial.  The first thing makes the reading get higher, and the second thing makes the reading get lower.  When they both happen at the same time, the reading stays the same.
Clear as mud now?


What is the formula for the bank angle required for a turn in line-abreast formation?

Turning Rate

All planes flying a turn in line-abreast formation are turning at the same rate $\omega$.

A standard turn is commonly defined as $\omega_1 = 3°\frac{1}{\mathrm{s}}$.

Full Circle Time Period

If planes are turning at the same rate, the time period to complete a complete circle will be the same as well.

Time period: $$ T(\omega) = \frac{360°}{\omega}$$

The time period to complete a circle at this standard turn rate is $T_1 = \frac{360°}{3°}\mathrm{s} = 120\,\mathrm{s}$.

Air Speed

Since the outer planes have to travel a longer distance to complete their larger circle in the same perios, the outer planes have to fly at a higher airspeed then the inner planes.

Air speed: $$ v = \omega r$$

Bank angle

Turn rate: $$\omega = \frac{v}{r}$$

Banking angle:  $$\tan{\theta} = \frac{v^2}{rg} = \frac{\omega^2 r}{g}$$

Gravitational constant: $$ g = 9.81 \frac{\mathrm{m}}{\mathrm{s^2}}$$

That gives the banking angle as a function of turning radius: $$\theta(r) = \arctan{\frac{\omega^2 r}{g}}$$

See the purple curve in the graph below for the bank angle in a standard rate turn (3°/s):

This curve seems to imply that one can fly a standard turn (or any other given turn rate) at any radius from 0 to infinity. Therefore I added two more curves to indicate the physical limits:

air speed (green) must be in the operating range of the plane
g load (blue) must not exceed the maximum acceptable for plane and occupants. (The correct scale for the g load is the purple scale on the left divided by 10)

And finally, the same plot but for a double rate turn (6°/s):

Practical Relevance

Typical turn radii are in the order of 1000s of meters. Typical distance (wing span) of planes in a tight formation is in the order of a few 10 meters, that is a few percent of the turn radius.

If you compare the banking angles for two planes flying in tight line-abreast formation, the banking angle difference will have a similar relative difference, that is a few percent, or a fraction of 1° in absolute terms.

[I will calculate and insert an example here, when I have the time.]

For the practical purpose of actual formation flying, pilots will give the arcus tangens a break, and fly seemingly identical banking angles.


Blade inertia and rotor kinetic energy are NOT the same thing, but they are related.

Blade inertia is a characteristic of the blade. It is a quantity that shows how difficult it is to change the blade speed (either by acceleration or deceleration) The bigger the inertia of the blade, the harder it is to make it move or make it stop once it's moving. It has nothing to do with the speed/RPM of the blade, it has the same value regardless if the rotor is turning or not. It depends on the way the blade is built (how heavy it is and how is its weight distributed).

Rotor kinetic energy depends on inertia AND rotor speed (RPM). So, a rotor when it's stopped has inertia but has no kinetic energy.

Once you start turning the rotor you start building kinetic energy in it using power from the engine. If rotor inertia is big, the engine will work harder to accelerate the rotor BUT, if the engine fails in flight the bigger inertia will oppose RPM decay giving the pilot more time to perform the proper actions.


What is this hole at the front of the engine pylon on a Boeing 707?

This is because those engines have turbocompressors which are used to supply cabin air.

The engine bleed air drives the turbine of the turbocompressor, which in turn would drive a compressor which would pull in air from the atmosphere through the front hole, compress it, and send it down to the Environmental Control System for use as cabin air. The discharge outlet for this bleed air is the long teardrop shaped hole in the side.

The tubocompressor can be seen in the image below.

Norm King at work on the turbo-compressor on Number 3 engine on 17 August 2006. Photo: Karen Glass; image from 707.adastron.com


What is the theoretical maximum velocity of electric aircraft?

Since you seem not to be concerned about the usability of this hypothetical electric aircraft, let's make some simplifications:

The aerodynamics are so good that it does not create any drag. This is completely unrealistic but helps a lot to simplify things.
Structure, controls and propulsion are so advanced that they leave one third of the take-off mass for batteries. Who needs payload anyway?
Efficiency is 80%. Not even electric propulsion can be lossless.
Energy storage is the best current technology has to offer. This would be about 1.8 MJ per kg of battery for non-rechargeable lithium cells.

To accelerate a battery of the mass m to a speed v needs an amount of energy $$E_\text{kin} = \frac{m}{2}\cdot v^2$$
Flying Mach 2 at sea level is impractical; it helps to climb to at least 6.000 m (20.000 ft) to do so. This adds potential energy: $$E_\text{pot} = m\cdot g\cdot h$$
Conveniently, the result is independent of mass, so the potential maximum speed is $$v_\text{max} = \sqrt{2\cdot\frac{1}{3}\cdot0.8\cdot1{,}800{,}000\ \mathrm{m^2\ s^{-2}} - g\cdot h}$$
If we solve this for 6000 m, the speed at the end of the acceleration is 949.3 m/s, which is already Mach 2.966. If you prefer to use rechargeable batteries (1 MJ/kg), the maximum speed drops to Mach 2.15.

If you start to add a reasonable figure for drag, you won't even make it to the speed of sound before the batteries are empty. Currently, propellers are the most sensible way to convert electric energy into thrust, and large, low-speed propellers are the most efficient type. If you think to drive a conventional compressor with an electric motor, its subsonic efficiency is already far worse than the assumed 80%. Even its mass is not yet competitive with conventional gas turbines.


Is some sort of clearance, such as a clearance to enter nearby controlled airspace, required to legally fly in IMC in Class G airspace?

An FAA-appointed Designated Pilot Examiner has recently told me that it is legal to fly an airplane or glider in clouds in Class G airspace with no clearance, if the aircraft is appropriately equipped and the pilot has an instrument rating in airplanes.
On the other hand, here is a case, originally noted in an answer to a related question on ASE, where a pilot  who took off from
an uncontrolled airport into clouds without a clearance or
release from air traffic control (ATC) was found to not be in violation of FAR 91.155(a), the VFR cloud clearance and visibility requirements, but was found to be in violation of FAR 91.13(a), the prohibition against operating an aircraft "in a careless or reckless manner so as to endanger the life or property of another."  An interesting aspect of the pilot's defense in this case is his suggestion that by departing immediately after another aircraft which had received an ATC release and clearance, he assured himself that there would be no other IFR aircraft in the airspace above the airport 1.  Other aspects of the pilot's defense were the fact that  he broadcast his departure intentions on the Unicom frequency, and he monitored the ATC frequency for other traffic.
The FAA and NTSB did not find these arguments to be convincing.
There definitely seems to be a grey area here as to exactly what precautions, other than receiving an IFR clearance for adjacent controlled airspace, would satisfy the FAA as far as FAR 91.13 is concerned, in the context of operations in IMC in uncontrolled airspace.  Also, one can easily imagine situations that are clearly compliant with all regulations and all accepted practices, and yet clearly create significant risks, arguably more so than the case linked to in this answer.  For example, one could argue that any time any aircraft operates in IMC in uncontrolled airspace, this creates a significant risk of collision with VFR traffic which may be legally flying just outside the edges of clouds with no radio or transponder.  Yet IMC in uncontrolled airspace is an accepted practice-- many airports are located in airspace that is Class G up to at least 700' AGL, yet have established instrument approaches with minimum decision heights much lower than that.
Footnotes--
1-- Page 4 of the finding says that the respondent claimed that by following this procedure the respondent "assured himself that there would
be no other IFR aircraft in the controlled airspace above the
airport".  This may be a typo-- it should perhaps read "uncontrolled" rather than "controlled"-- since there seems to be no dispute that the respondent was able to observe the prescribed VFR minimums once he reached controlled airspace.


Why do the MiG-15 and MiG-17 have a split air intake in their noses?

The advent of (turbo)jet engines resulted in an important change in design of aircraft- the location of the engine, which can either be mounted on the fuselage  or in the wings (as in Me 262).

Also, the engine was shifted from the front (as in the case of a majority of piston engined fighters) to the rear in jet aircraft (as the exhaust has to be routed below the fuselage otherwise). In this case, the intakes can either be in the nose or in the sides (like in Hawker Hunter).

For the aircraft with nose intakes (a design which was eliminated by the ever increasing size of Radar equipment), the problem was how to get the air to the engine. In case of Mig-15, the Russians split the air in a central splitter, which then passed through two narrow air ducts passing through either side of the cockpit, avionics bay, fuel tanks and the nose landing gear bay. This inlet was quite complex, not to metion it made for a cramped cockpit, but on the other had, it was compact. Similar air intakes were used in aircraft like the Mig-21.

Another method was to put to simply put the cockpit above the air inlet duct, like the F-86 Sabre, which resulted in the raised stance of the cockpit (and better visibility).


What is the difference between a leading edge flap and a slat?

Slats are leading edge devices on aircraft that enable higher angles of attack. Flaps are devices on the leading (Krueger) and trailing edge which increase camber and the depth of the wing. Slats create a "slat" between the slat body and the wing leading edge so the air can pass from the bottom to the surface to hold off a stall to a higher AoA, flaps merely extend it fore and aft and direct the flow downwards for more lift. Both are mainly used in the low-speed situations of take-off and landing.


Why would an airport use crossing runways for takeoff and landings?

Any time the winds and traffic permit an airport may chose to use intersecting runways. You can read some interesting info on it here and here. In some cases when both runways are in use they may have the aircraft execute Land And Hold Short procedures. The pilot has the final say in a LAHSO situation and you can call no joy if you think you cant complete the maneuver as requested.

Some airports may only have 2 runways set up in an intersecting layout and may not have the luxury of parallel runways. Depending on terminal layout at commercial airports using both runways may aid in traffic flow on the ground as well as getting planes in the air.

Winds permitting generally have to do with the maximum cross wind component of a given airplane. Although generally speaking you will see this done in calm wind situations. The other cause I have seen for this is instrumentation, some airports may have intersecting runways that are not equipped the same or of the same length. As lets say the favorable runway is is 5000ft visual approach only strip and you need 6000ft to land. Luckily the airport has another intersecting runway that is a 7000ft strip (and has an ILS approach not that you need it (its nice out)). They may have you come into the other runway while they sequence small visual traffic on to the short strip (possibly having them land short if need be).


How does the Boeing 747 smoke evacuation work?

Looks like the smoke evacuation handle was used, but had little effect on the outcome. From the Final accident report of Boeing 747-44AF N571UP:

  The Captain called for the smoke evacuation handle to be pulled as the smoke accumulated in the cockpit. ... The smoke evacuation handle remained open for the remainder of the flight.

The report also has a note on its working:

  The smoke evacuation handle when pulled opens a port in the cockpit roof, which if the smoke is sustained and continuous, will draw smoke through the cockpit as the pressure is reduced by the open port ...

There is also a mention of it in the preliminary report:

  Smoke  Evacuation Handle –a  handle immediately  aft  of  the  P5  overhead panel that when pulled opens a circular, manually displaced vent in the  overhead fuselage section of the flight deck.

The final report also has an image of the exhaust port.

Smoke Evacuation Port (cockpit ceiling); image from Final accident report of Boeing 747-44AF N571UP


How can I get a ride in the jump seat as a non-professional pilot?

It's hugely unlikely. Almost vanishingly unlikely, with few exceptions perhaps for something a little smaller than a passenger-carrying A380 (like a private jet on a repositioning flight where you know the captain well)

You used to be able to go up and see the captain on the flight deck - I did it a few times as a kid. Even then asking to sit in the jump seat was usually met with a smirk.

And then 9-11 happened.

  With effect from 1 November 2003, ICAO Annex 6 was amended so that under Chapter 13.2.2 “all passenger-carrying aeroplanes of a maximum certificated take-off mass in excess of 45 500 kg or with a passenger seating capacity greater than 60 shall be equipped with an approved flight crew compartment door that is designed to resist penetration by small arms fire and grenade shrapnel, and to resist forcible intrusions by unauthorised persons. This door shall be capable of being locked and unlocked from either pilot’s station”.

And with that came locking of the cockpit door, and no more visits to the cockpit during flight (incidentally, if you ask nicely, the captain will often let kids take a peek when they're deplaning the passengers)

And then germanwings happened, and they had a rethink. But still no visits to the cockpit during flight at all for the average Joe.


Does ARINC 429 have any error correction methods?

You wouldn't correct the ARINC 429 label, but simply ignore that transmission and wait for the label to be resent again.
If the label isn't received properly within the defined period it would be considered timed out and the last valid label would no longer be used (timed out).


Who has authority to close a runway/airport?

Generally two groups have authority to close a runway (or airport) for an incident/emergency, and if either says it's closed, it's closed:

The airport owner/operator/management.
It's their facility, so if they say it's closed, it's closed.
Specifically it's the persons authorized to issue NOTAMs for the airport who can close a runway (by issuing the NOTAM saying it's closed), but the chain of command for making this decision may vary from airport to airport.
Runways may also be closed by airport administration without issuing a NOTAM (this happens frequently at Brookhaven airport (KHWV) - "Closed Runway" X's will be put out on the crosswind runway when the banner tow operators are set up for pick-up/release on that runway). Often there's a blanket NOTAM about "banner tow ops" or similar that sort-of covers this situation (basically "Expect strange things to be happening because the banner tow people are doing...whatever it is they do".)
The control tower (if one exists).
Whether or not they have the administrative authority to "close" a runway, they certainly have the practical authority to do so by denying anyone clearance to take off/land from it or to enter it, and by issuing NOTAMs indicating that a runway is closed/unusable for some reason.

At an airport like LaGuardia where you have both an FAA Control Tower and a robust airport operations/management group (The Port Authority of New York & New Jersey) a Memorandum of Understanding (MOU) or similar agreement is likely in place to ensure that everyone knows who is authorized to do what when, but in cases like this where an aircraft has a runway excursion the course of action is pretty obvious and nobody is going to want aircraft to be moving around on the ground until the situation is under control and safety can be assured.


Where can I find articles about Handley Page multi element segmented airfoils?

The images look a lot like the ones in:

A.M.O. Smith, “High-Lift Aerodynamics”, 37th Wright Brothers Lecture, Journal of Aircraft, Vol. 12, No. 6, June 1975

The  classic paper on multi element airfoils, great read!


What is the difference between an aeroscraft and an airship?

Aeroscraft is their brand name. It does not mean anything generally.

The general terms are:

"Aircraft" (but not "aerocraft") means any machine capable of sustained flight in the atmosphere.

"Aerostat" is a lighter-then-air aircraft. That is it has large shell filled with gas with lower density than air and uses buoyant force on that for lift. This includes balloons, hot-air or gas filled, tethered balloons and airships.

"Airship", or "dirigible" is an aerostat equipped with propulsion that allows it to move on it's own (as opposed to balloons that are tethered or carried by wind).


What is the maximum safe bank angle of a 747?

The descent angle helps to reduce the lift that the wing needs to provide, in two ways. It leads the aircraft into higher density air, where more absolute lift is possible at the same Mach number. That takes a while, but a more immediate effect comes from pointing the aircraft's nose downwards. Then, part of the gravity-induced forces can be counteracted by drag (D in the sketch below). This is similar to a glider, only with much lower aerodynamic efficiency and steeper angles. Terry reduces thrust and opens the speed brakes to avoid overspeeding, so he can dive as steeply as possible, thus reducing lift requirements.

Now more of the wing's lift L can be employed for turning the aircraft around. If he wants to achieve a constant sink rate, he still has to produce enough lift to balance weight, but reduced by the cosine of the glide path compared to the level flight condition. At 25° nose down, this is a reduction by 10%.

Now you are concerned about his roll angle. Please note that he wants to create as much sideways component of lift as possible, which will look like gravity to all onboard. At 60° roll angle (I think his 80° are a bit extreme), this works out to twice the normal vertical acceleration, and with the dive actually just 1.8 g, so everyone will feel almost twice the force of normal gravity. With the 80° roll, this will not be a stationary turn and not enough lift will remain to counteract gravity, so the aircraft will accelerate downwards during the turn. It will actually fall out of the sky. When already at Mach 0.85, I would be more careful than Terry, because things get ugly very quickly when Mach goes further up.

The term $m\cdot\frac{v^2}{R}$ is the centrifugal force which can be afforded by the horizontal component of the lift and which needs to be as big as possible for tight turns (a smaller radius R helps). This is the lift component that Terry needs to pull the aircraft around.

If we stay with stationary turns (without the "falling out of the sky" part), the maximum bank angle is given by the maximum load factor of the 747. At 400 KEAS, this is just 1.5g, so even with the 25° nose down attitude the maximum bank angle would be 53°. If you fly slightly slower, the load factor goes to 2g (equals 63° in a 25° descent) and tops out at 2.5g at 310 KEAS (68.7° in a 25° descent). Flying at Mach 0.85 in 30.000 ft will produce an equivalent airspeed of 306 kt in normal atmospheric conditions. The precise value varies with the actual flight speed, and the maximum safe bank angle is in the region of 60° to 70°.

I expanded my answer to the original question, and I hope in combination with this I can cover your questions. If not, please keep asking!

EDIT: I see, now you want to know the time to turn around. All I can do is calculate it under the assumption that enough lift is available, regardless of buffeting. In reality, I doubt that even the 48° case will give you a pleasant ride. All results are for the 30.000 ft case, because at 36.000 ft those higher bank angles will not be cleanly flyable due to compressibility effects.

At 60° the airplane flies with 2g, and with 25° nose down still at 1.8g. The turn rate would be 3.77°/s and 180° would be completed after 48 s.

At 70° it flies with almost 3g, and with 25° nose down at 2.65 g which is a little outside of the g limits. The turn rate would be 5.98°/s and 180° would be completed after 30 s (plus the time to roll to 70°, which now starts to become important).

The 80° case becomes really hypothetical, because even with the 25° nose down attitude the load factor will be 5.2g if flown without sideslip and enough lift to prevent overspeeding. The 747 will be close to breaking apart, but maybe a future aerobatic version can fly this maneuver safely. It will result in a turn rate of 12.35° and need 14.6 s for a 180° turn. I would add at least 4 seconds to bank to 80°, but the turn can be completed within 20 s. Hypothetically.

What Terry hinted to when he said he would bank to 80° is not the clean turns I am calculating here, but a dynamic dive where the plane accelerates because not enough lift is left to keep it from falling. To compute this, I would need more aerodynamic data on the 747 and need to employ at least a finite difference algorithm or a lot of paper and pencils.

Just that much: If the 747 is rolled to 80° but the pilot pulls only as many gs as the aircraft can sustain (due to buffeting I doubt that even 2.5 g are possible), the lift will almost exclusively serve to fly a tight turn, but not enough will be left to counteract gravity. Therefore, the aircraft will slip sideways, and directional stability will turn the nose downwards. This will take a while (I am guessing maybe 12 seconds, really a guess), but the aircraft will pick up speed from the beginning of the maneuver. I am a little more scared of flying faster than Mach 0.85 than Terry is, and the various reports of 747s going up to Mach 0.98 support his view that a little overspeeding is OK. It is hard for me to guess how much time it needs to become uncomfortably fast, and then a lot of lift will be needed to pull out of the dive. On the other hand, when the airplane is diving, all it needs is a roll and a pull-out to come out at 180° to the previous course. The pull-out will be performed at a much lower altitude, and creating the gs there will not be a problem.


Is it possible to eliminate induced drag completely?

The infinite span has nothing at all to do with having no ends.

The ratio of lift to induced drag increases with span. If you fix the lift, and vary span, the induced drag will tend to zero as the span tends to infinity. That means in limit a wing of infinite span generating finite lift (and therefore flying at zero coefficient of lift!) will have zero induced drag.

This is a highly abstract approach to things and I don't think it provides any useful insight.

Anyway, forget about the vortices. They only happen behind the wing anyway and therefore are obviously irrelevant! Instead, call upon the good old laws of motion. The lift is upward force of the air on the wing. By principle of action and reaction (Newton's 3. law) the wing must apply force of equal magnitude and opposite direction, that is downward, on the air. Now if the ambient pressure above and below the wing is the same, this force will accelerate the air downward, which will increase its kinetic energy. And by law of conservation of energy, this energy has to come from somewhere and the only way work can be done here is by drag.

This suggests the way to reduce it. If the pressure can be increased below the wing without accelerating the air, there won't be induced drag. Well, that's exactly how ground effect reduces drag. Normally it does not eliminate it, because the air can still move outward, but a wing flying in a trench could perhaps get quite close (though not to zero, because the air still needs to move at least a bit to maintain the pressure difference).


How does landing gear affect thrust on a light twin-engine airplane?

Thrust is not decreased.  The drag penalty means that more thrust is required to achieve a performance condition than without the drag penalty.  In level flight, more thrust is required to go the same speed.  When climbing, more thrust is required to achieve the same climb rate.  Your maximum thrust available is what the engine can produce, so the extra drag subtracts from whatever surplus thrust is available.

In a light twin the key thing is the surplus thrust margin available for climb at the most efficient speed for climbing while single engine (blue line speed).  To fly in level flight single engine at blue line speed, we'll say you need 500 lbs of thrust from the good engine.  To climb at that speed requires more than 500lbs, and to get a decent rate of climb, say 400 fpm, you might need 800 lbs (about what you'll get with a Lyc O-360 running flat out), which we'll say is what the engine makes at full power at sea level (a piston twin that can climb better than 300 fpm single engine at gross is a pretty good performer).

Add more drag by leaving the gear down, and the thrust required just for level flight goes up from 500 lbs to, say, 700 lbs because of the 200 lbs of drag of the gear sticking out.  Instead of 300 lbs of surplus thrust margin available for climb, you only have 100 lbs and it's a struggle to get any climb at all or to avoid descending, and only if you use perfect technique (on-speed, 5 degrees bank into the live engine).

So the proper answer for leaving the gear down is, surplus thrust available for climb is decreased and therefore climb performance at maximum thrust is decreased.  Which in a light twin at gross on a hot day means, as the old saying goes, "the remaining engine takes you directly to the scene of the crash".


What are the advantages of the B747-8 airfoil over B737's airfoil?

The airfoil profile you've shown is called a supercritical airfoil.

Typical airfoil sections are curved on the top and the bottom. The airflow over the top of the airfoil is accelerated i.e. the airspeed over the top of the airfoil is more compared to the free stream velocity. The associated reduced pressure helping to create lift.

Source: www.symscape.com

From the figure, two things can be inferred:

The pressure over the upper surface is lower compared to the lower surface
The pressure gradient is favorable in the forward section of the airfoil (where most of the lift is produced), while the gradient is adverse in the rear half, which can cause boundary layer transition and possibly separation, if the gradient is too severe.

Source: code7700.com

For low speeds (and low angles of attack), this causes no problem in lift generation. However, most of commercial airliners fly at in the transonic regime (with speeds ~ Mach 0.9), the flow over the top of the wing may reach supersonic speeds even when the aircraft itself is flying at subsonic speeds.

Source:fluid.mech.ntua.gr

The speed at which this happens (flow over wings becomes supersonic) is called the critical Mach number. The flow decelerates through a normal shock wave, resulting in a severe adverse pressure gradient over the rear of the airfoil.

Source: fluid.mech.ntua.gr

This causes serious problems like:

The adverse pressure gradient over the shock wave causes flow separation, decreasing lift and increasing drag. The speed above which the drag increases significantly is called the drag divergence Mach number

Source: history.nasa.gov

As the speed increases, the shock wave moves to the rear, as does the lift producing region. This causes a nose down pitching moment and stability issues.

"Transonic flow patterns" by U.S. Federal Aviation Administration - Airplane Flying Handbook. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration, p. 15-7. FAA-8083-3A.. Licensed under Public Domain via Commons.

The supercritical airfoils are designed to overcome (or delay) these problems. Designed by Richard Whitcomb, the main characteristics of these airfoils are,

'flattened' upper surface
highly cambered aft section
smaller leading edge radius compared to the traditional airfoils (that is why they are so thin)

Source: aerospaceweb.org

The main advantages of supercritical airfoils are,

It increases the drag divergence Mach number. For example, in the F-111, the drag divergence Mach number was increased from 0.76 to 0.88, a 16% increase.
The shock waves are developed further aft when compared to the normal airfoils
They greatly reduce the shock induced boundary layer separation, reducing drag

The figure below shows a supercritical airfoil in a transonic flow. Note the location of the normal shock compared to the 'normal' airfoil.

Source: space.bas.bg

The supercritical airfoils were not available when the Boeing 737 was first designed. However, the 737 NG airfoil incorporates elements of supercritical design,as does the Boeing 747-8 airfoil.

The supercritical airfoils reduce the fuel required, as they allow the aircraft to cruise at higher speeds with lesser drag. Additionally, the Boeing 747-8 has a wing span of ~68 m, which gives plenty of storage space for fuel. Also, improvements in engines and airfoils means that the 747-8 has nearly 50% more range compared to the original 747-100.


When are multiple hops more efficient than single leg?

In a broad sense, if the flight distance is nearly equal to the max range of the aircraft, the route with shorter legs is prefereable from the point of fuel economy. The reason is simple- more the fuel you carry more the aircraft you have more weight, which requires more fuel.

All other things being equal, the fuel caried is payload- one can see it as the aircraft carrying extra payload or as the fuel eating into the regular payload. Either way, the extra fuel carried impacts on the fuel effeciency of the aircraft negatively.

According to this document, payload burns fuel at the rate of 2.5-5 % of its weight in fuel per flight hour. For the longest non-stop routes in service, the travel time is in the upwards of 15 hours. Taking a value of 3% fuel burn, this means that a significant portion of fuel consumption is actually to carry the fuel itself. This is a significant issue, especially when the oil prices are high.
The increased take off weight will result in more thrust requirement, TO length and time to climb (or more thrust again), adversely affecting the fuel consumption, while increasing engine wear.
While it is true that the longer distance flights spend more time in altitudes with less drag, it is questionable whether that translates into any significant real world benifits. For example, the latest 777 ULR version has a higher aspect ratio to reduce drag, requiring the folding of wings.
Of course, fuel use is only a part of the story. The other significant factor is time- most of the ultra long range flights are targeted towards business flyers, for whom the addition of more than 25% due to shorter legs may be unacceptable. In the end, the deciding factor may be the percentage of seats filled per flight. When SA cancelled the Singapore-Newark flight, one analyst noted:

  “The plane burns a lot of fuel but carries very few passengers,” says Siyi Lim, an analyst at OCBC Investment Research in Singapore. “It didn’t make sense to continue.”

The ultra long distance flights also require additional facilities- extra crew for rotaion, extra food items carried etc. In general, the straight long distance routes have higher fares compared to the ones with stops in between.


What is the helicopter in the background of this image of the V-22 Osprey?

It's an MH-53 Pave Low.  In the Air Force Special Operations Command (AFSOC), the CV-22 replaced the MH-53, although there were several years when both were in the inventory.
From the look of the beach, this photo was taken near Hurlburt Field, Florida, which is where they were both based as the first CV-22's came on-line.  Hurlburt Field is also the headquarters of AFSOC.


What principle does the attitude indicator in the G1000 use?

G1000 is a multi-unit system. The attitude information comes from a specialised unit called AHRS (Attitude and Heading Reference System), typically GRS 77. AHRS uses two solid-state gyros (vertical and directional), plus a magnetometer, to obtain a complete attitude information.

In addition, AHRS does employ accelerometers and rate gyros. Their data is used for stabilisation, filtering, and as an input for autopilot and other systems.


Which civilian airport has the most runways (current and planned)?

Chicago O'Hare International Airport (ORD) today has 8 runways, which is more than any other current airport has. In 2015 14L/32R was closed and 10R/28L was opened, and further runway changes are foreseen.

Beijing Daxing International Airport will be Bejing's third airport (planned to open in September 2019). According to Centreforaviation it will have 9 runways. One runway will be reserved for military use. The ninth runway is not visible on public maps and illustrations at this moment.

Denver International Airport (DEN) currently has 6, but the long term master plan foresees 10 runways in total by 2030, and 12 beyond 2030. See Jonathan Walters' answer for images. (Fun fact: there are a plenty of conspiracy theories about the shape and size of DEN)
Additional runways are not necessarily used to increase (commercial) traffic. Runways maybe reserved for different wind directions, to separate different type of planes (military, general aviation), or for noise abatement. This was already discussed better in the other question that you mention.

As an example for the noise abatement,  this picture (from LVNL) shows a snapshot of active runways at Amsterdam Airport Schiphol. There are 6 runways, of which usually only 2 or 3 are used. The most distant runway (here in green) is almost always in use, causing very long taxi times in favour of reducing the noise exposure of nearby residential areas.


How do ATC radars know where to position a primary target?

Primary radar, even modern digital systems, do not give any possibility to the controller to determine altitude.  The digital system has that capability, but civil ATC does not.

In primary radar displays usually just the azimuth and range are plotted. So an aircraft at 15.000 ft 9.5 NM away will be plotted on 10 NM distance, just like an aircraft at 0 ft 10NM away. Usually the secondary radar is collocated with the primary so secondary targets can be displayed using the same projection (disregarding the altitude).

If you now apply horizontal separation based on this projection, you will never bust the separation minima. It is a conservative way of providing separation, but when there is no altitude information it is the best possible way.

Note that this does not only apply to primary targets, but also to Mode-A only targets


Why is the air traffic control profession so commonly perceived as "stressful"?

Some very spot-on comments, some comments that are totally ignorant of the job. I am a retired ATC, 32 years.  I worked at one of the world's busiest and most complex US facilities (as described by many independent sources).

Have you ever:

Heard a family on the other end of the radio screaming just moments before they were obliterated in the air by a military fighter flying VFR?
Tried in vain to find a way to contact the occupants of Payne Stewart's jet only to watch helplessly as it finally crashes after several hours of flight?
Had 30+ airliners in your sector which happens to be dotted with Level 5 thunderstorms?  The amount of airspace you now have has decreased substantially and the aircraft all need to deviate. They all want to either go in different directions, or they all want to head towards the few clear spots left. You sit there for 2 hours directing aircraft to basically thread a needle at 500mph and pulling out every trick in your book to ensure that there is enough space to ensure all 30+ aircraft (and more, because those aircraft never stop coming) make it through your airspace without encountering the dangers of severe weather or coming into physical contact with another aircraft. Aircraft that are often executing movements that they don't have clearance for, which requires quick and accurate reaction from the controller.
Dealt with one of the times when a corporate jet "flames out" at 43,000 feet and immediately descends through a dozen or more jets flying the same path, requiring the controller to immediately clear all of those aircraft out of the path of that corporate jet.
Had a small twin prop lose all electronics and be unable to navigate properly while in a thick cloud layer.  His portable radio is not working properly, so radio communications must be short and accurate. (Remember, you have another sector full of aircraft that you are also providing services to). Finally, his portable radio fail.  Right before that, you ask the pilot if he has a cell phone. He does.  You give him a phone number and you and he are able to communicate via telephone to finally guide him to a safe landing at Newport News Airport.

I could write a book about many specific events that controllers have experienced.  The "pucker factor" events.

But the real stress is the long term chronic stress that the job presents.
Certainly, there are facilities that are both low traffic and have uncomplicated operations. If you are lucky enough to work at one of these (and willing to accept the low end of the pay scale) then stress is probably much lower and stressful events infrequent.  But for the majority of controllers (who work at a number of very high traffic facilities; air traffic in the US is higher and more complicated than the next 29 countries' air traffic, combined) the stress is a chronic, continuous level (not the big adrenalin-pumping situations) from being attached to your position for several hours, trying to maintain a constant "big picture", maintaining situational awareness, issuing control instructions to ensure that SAFETY is always the first product of your efforts.  Many, if not most, controllers will most likely retire with high blood pressure, diabetes, sleep disorders, etc. that despite best efforts to exercise and live a healthy lifestyle will probably affect a controller for the remainder of their life.

Certainly, other jobs are stressful, and I would never try to compare one as "more stressful" than the other.  The top ones are all stressful.  But those that try to downplay the stress of air traffic control would only need to visit a busy air traffic control facility for a day and they would see and probably feel the stress themselves.

I have a very good friend that is an FBI field agent in Washington, DC.  He has worked on some very high-profile cases.  We were talking one day and he said something about the stress of air traffic control.  I chuckled saying that at least I wasn't being faced by some of the most dangerous people in the country. But his response was that in his job they have detailed plans for what they do.  His raids were in the middle of the night when these people were asleep and unsuspecting.  He had a well-trained team that each had specific responsibilities.  They had plenty of firepower and protective equipment.  He said that most of his operations were quite easy and they experienced little resistance. He did have moments of intensity, but he (who had visited an air traffic facility) did not think the stress he experienced was anywhere near to what he saw at the air traffic control facility.

But I still would not want to be a law enforcement officer, nor a school teacher for that matter!  My personality was a good match for the job of air traffic control.  But now that I am retired, I take blood pressure medicine, am borderline diabetic despite a regular exercise program and am within a healthy weight and eat very healthy.  I also still have sleep apnea and other sleep issues that I see a sleep doctor several times a year for.  All of my present health issues, which are well-controlled, are according to the doctors a direct effect of the stresses of being an air traffic controller.

Air traffic control IS stressful.  Is it more stressful than other jobs? I doubt it. And to argue about whose job is more stressful is a silly exercise. The trick is having a personality that meshes with the job.  If you are in a job that is not a good match, that is stressful.


Why do I get an overspeed warning at 250kts below 10,000ft in Microsoft Flight Simulator?

Most likely Cessna introduced a speed switch that is controlled by an aneroid.  Anytime you are below 10,000 FT MSL, the aneroid activates that switch.  If you go above 250 knots, the overspeed warning will sound.
As far as why that is the case, in the United States you are limited to a speed of 250 KIAS below 10,000 FT.  I would imagine this is also the case for most other countries.  The FAA realizes that most small airplanes with a much slower airspeed travel only below 10,000 FT MSL so the FAA is providing a safety margin to prevent in-flight collisions.
The structural limit of the airplane would not be a factor at 250 KIAS hence the red line at 300 KIAS.  I would imagine 300 KIAS deals more with structural stability than anything else.
My question... can a slow-tation go that fast?  :-)


How to modify an amateur kit build with wing hard points

You will most likely need a Supplemental Type Certificate from EASA

According to their FAQ, emphasis mine:

  My aircraft has been modified in the USA by Form 337 action. Can EASA accept this?

  Answer

  EASA accepts alterations on non-critical components that are substantiated via Form 337, as detailed in the EASA-FAA Technical Implementation Procedure (TIP) rev 5, paragraph 3.2.8.2 EASA Acceptance of FAA Alteration Data:

  “Except for alterations on critical components, FAA-approved or accepted alterations per 14 CFR Part 43 installed on a used aircraft exported from the U.S., regardless of the State of Design of the aircraft, are considered approved by EASA at the time of import to the European Union. EASA shall accept such FAA alteration data when substantiated via an appropriately executed FAA Form 8110-3, FAA Form 8100-9, FAA Form 337 or logbook entry.

  Alterations on critical components must be EASA-approved via STC, in accordance with TIP paragraph 2.2 (Design Approval Procedures for Supplemental Type Certificates (STCs)).

  An FAA STC whose installation is documented on a Form 337 must be approved by EASA in accordance with TIP paragraph 2.2.”

From the aforementioned TIP:

  2.2 Design Approval Procedures for Supplemental Type Certificates (STCs).

  2.2.1 Scope of STC Application Acceptance.

  2.2.1.2 EASA may accept applications
  for STCs for:

  (a) All STCs (Basic and Non-Basic) when the original STC application is made to the FAA:

  (1) On products for which EASA acts on behalf of the State of Design,

  (2) On U.S. State of Design products, and

  (3) On third country aircraft which have been type certificated by both EASA and the FAA.

So you should be able to apply per point 2.2.1.2.a.3, assuming of course, that the aircraft is certified by EASA and not operated within Europe as an experimental with a Permit-to-Fly.

In light of the above, and considering that a modification of the wing to carry an external load is not likely to be classed as non-critical, you should probably contact both EASA and the Design Organization for the type.

Alternatively, you could look into moving the aircraft into the experimental category

In this case you will need a Permit-to-fly, more info here:

  The European Aviation Safety Agency (EASA) is responsible for the approval of flight conditions. Such an approval is the basis on which a Permit to Fly (PtF) can be issued by the Competent Authority of the State of Registry, or of the State prescribing the identification marks of an aircraft.

  A PtF is generally issued when a certificate of airworthiness is temporarily invalid, or when a certificate of airworthiness cannot be granted, but the aircraft is nevertheless capable of performing a safe flight.

  Please use EASA Form FO.CERT.00037 (with EASA Form 18B in the annex) to apply for approval of flight conditions at EASA. With the approved flight conditions (EASA Form 18B) you can apply for a Permit to Fly at the local national aviation authority the aircraft is registered.


Could a person damage a jet airliner - from the outside - with their bare hands?

Yes, a few possibilities...

Brake hydraulic and electrical sensor lines located on some landing gear.
Putting foreign objects under or between the rotors of brake pads
Covering pitot system sensor holes
Pressing or hitting the pitot tube (on most airliners you will need a ladder)
Letting air or hydraulic fluid out - under inflating tires or cylinders
Bending or mis-adjusting bellcranks/control arms or changing the linkage geometry.
Damaging fuel vents

I am not sure of what your definition of "exposed" is but most airliners allow the E&E (electrical & equipment) bay usually located above or behind the nose gear and gear doors to be opened and closed from external control panels for ground crews. This allows access to most the computers, batteries and thousands of wire bundles. It may also give access to lines, cables, pumps, switches, and sensors.

Opening the gear doors of some airlines exposes the air-packs, generators, converters and aux turbine with it's associated mechanisms. Maintenance and inspection panels, engine cowls and fuel distribution panels expose or control critical systems.


What is the difference between LNAV/VNAV and LPV minimums on an RNAV approach?

There's an FAA paper on RNAV approaches that explains the differences between LP, LPV, LNAV and LNAV/RNAV approaches. I made a table for my own reference but since StackExchange doesn't allow tables (AFAIK) here's a summary:

LP: no vertical guidance; WAAS required; MDA for minimums
LPV: vertical guidance; WAAS required; DA for minimums
LNAV: no vertical guidance; WAAS not required; MDA for minimums; requires RAIM integrity if WAAS is not available
LNAV/VNAV: vertical guidance; WAAS or baro-VNAV required; DA for minimums; requires RAIM integrity if WAAS is not available (i.e. if using baro-VNAV); possible temperature restrictions if using baro-VNAV

The difference between LPV and LNAV/VNAV is that although they both have vertical guidance, LPV was intentionally designed to be very similar to an ILS approach with an increasingly sensitive glideslope whereas LNAV/VNAV was not. Other answers have additional comments about LNAV/VNAV having been designed earlier and for different equipment which would certainly make sense.


What are some Anti-icing solutions for small planes without an on-board system?

There are many things you can do to mitigate the risk of icing, but most involve prevention via avoidance of icing conditions.  For example, getting a good weather brief, knowing where the freezing level is, staying away from visible moisture, and finally, recognition and taking evasive action.

Pre-flight deicing liquids are not intended to prevent ice accumulation in flight.  As you noted, they will just blow off in the slip stream.  Anti-icing fluids such as TKS are very effective, but the aircraft must be equipped with a system to properly disperse it to be certified for flight into known icing conditions.

If you are not instrument rated it gets easier, because if you stay out of clouds you won’t ice up.  But if you want to fly IFR in the winter, (or any time you could be IFR in the  temperature zone where ice could form) your best method of increasing the safety margin is to arm yourself with knowledge, practice operational risk management, and exercise sound judgment to keep yourself out of icing.


In the US, will the tower likely think my aircraft has been hijacked if I taxi with the flaps down?

will the tower likely think my aircraft has been hijacked if I taxi with the flaps down?

No.
For the twenty-some-odd years I owned my plane, I only taxied with the flaps down (for important operational reasons), even at towered airports, and not once had anyone think I was being hijacked.
Indeed, it would be quite disconcerting (to say the least) for ATC to treat any behavior or condition not officially designated for the purpose as a signal that the aircraft has been hijacked.
For many airplane types, there are of course good reason not to leave the flaps down while taxiing. But worrying that ATC will think you've been hijacked isn't one of them.


It's a Russian internal city or airport identifier. Many small cities don't have IATA codes, but do have internal Russian codes.

This system is called CRT (Center for schedules and tariffs, ЦРТ, Центр Расписаний и Тарифов) named after a department in the organization that manages them (see below). Wikipedia article cited below claims it's also called "Sirena" code (named after Sirena -- a booking system for airline and railway tickets).

Here's a translation of a fragment from Russian Wikipedia:

  The internal city and airport coding system in the former USSR is structured analogous to IATA. [...]

  The airport code in this system consists of 3 letters of the Russian alphabet. As in IATA codes, the 3-letter combination is interpreted as atomic and has no internal structure. As in case with IATA, all 3-letter codes are unique.

  Like IATA, the codes were assigned to cities such that the code has something in common either with the name of the city or with its IATA code [...] Contrary to IATA, the internal codes were changed after cities were renamed in the 1990s: Saint Petersburg's internal code was changed from ЛЕД to СПТ, Samara (formerly Kuibyshev) -- from КУФ to СМШ, Ekaterinburg (formerly Sverdlovsk) -- from СВХ to ЕКБ.

  Many small cities and airports in the former USSR have an internal code only.

  In late 1990s foreign (non-Russian) cities were assigned internal codes because of the popularity of these destinations (e. g. Barcelona -- БЦН).

  As of April 2009, there are about three thousand internal codes that are actively used.

It appears that the codes are maintained by the Transport Clearing House. The section Coding Directories on their page Schedule & Tariffs  says:

  STC maintains the aggregated database of coding directories for the purpose of universal use of codes in information systems for passenger services reservation and sales, publication of timetables and fares, ticketing, settlement and other commercial issues related to passenger services.

  STC maintains the codifiers in pursuance of Provision on Assignment, Maintenance and Use of Internal Codes of Carriers, Organizations, Airports, Cities (points) and Civil Aviation Agencies (№ ДВ-63/и dated 12.05.94) and Directive "On Coding Directories Approval” (№ ДВ-109/и date 14.07.94).

  STC supports the following coding directories:

  Airlines
  Airports
  Cities

In Russian, STC is translated as CRT (ЦРТ) and I've heard people refer to the internal codes as "CRT codes".


Is there a list of what information different airlines track about their flights?

There is no particular list that provided by airlines company about their flights because it can be misused, but several statuses are provided:

(from http://www.flightstats.com/go/AirportTracker/airportTracker.do#1)

  Geographic Coverage - FlightStats provides definitive information for approximately 99.5% of U.S. flights, and better than 86% of flights worldwide.

  Completeness - FlightStats queries multiple sources to create a record for each flight enabling us to offer a broader range of information (for example, gate information).

  Accuracy - We have invested heavily in the areas of parsing, interpretation and error checking and developed the logic that enables handling of difficult issues such as cancellations, diversions and changing schedules.

  Codeshare Support - Our codeshare logic enables us to deliver flight information for both the operating and the marketing carriers, filling what is often a major gap in coverage.

  Real-time data sources include:

  FAA ASDI Data Feed
  European Data Feed
  GDS (Sabre, Amadeus, Apollo, Galileo)
  Direct Airport / Airline Data Feeds

  Batch data sources include:

  Innovata Schedules
  TSA Security Wait Times
  Security Information
  Health Information
  Consular Information


Is "Tally-Ho" used in ATC radio communication, specifically in the UK?

I have never heard "tally ho" used in civilian aviation and it not a recognised phrase so should not be used.  A civilian ATCO would not think positively about anyone using that phrase.

It used to be used in military comms in combat.  Its usage arose during WW1 when the Royal Flying Corps (and later the Royal Air Force) drew its crews mostly from the "officer classes" who, in general, were also fox hunters or supporters of the same.

"Tally ho" is the cry shouted out by a huntsman when the fox is spotted and the hunt is on.

I served in the RAF from 1976 to 1986. Then as a civilian in the military until 1993 and in that time never heard the phrase.  I suspect that it has died out since it is not standard phraseology and perpetuates stereotypes which have no place in modern, professional organisations.

A non-standard, but common phrase is a simple "visual", but the correct phrase in both civilian and military use is "traffic in sight".


I saw this pretty cool video a while ago:

It gives an intuitive discussion of gyroscopes.

On another level though, it boils down to the angular momentum of the spinning gyroscope, and the fact that in order to change that momentum's direction/magnitude, an external moment must be applied.


What happens when the surface ends at the laminar zone of the boundary layer?

Then you get a fully laminar boundary layer without transition. This can happen at very low Reynolds numbers, especially if no steep positive pressure gradients are encountered.

A steep pressure rise can lead to separation, and if the boundary layer does not change to a turbulent one, this separation can be final, with no re-attachment of the boundary layer. Then the attached flow ends before the body ends, but still the boundary layer is fully laminar.

It is not compulsory for transition to happen. If the flow is stable (either due to a negative, stabilising pressure gradient or due to very low Reynolds numbers), the boundary layer will stay laminar for its full length.


Does one-engine cruise consume less fuel than two-engine cruise?

For an A320, at FL 100 and weight 50 tonnes and ISA, the FF is 1028 kg/h per engine, so two engines is 2056 kg/h.

Now for the same but OEI: the FF is 1891 kg/h (just the one engine).

Scenario 1 is higher fuel flow rate. I'll explain why based on scenario 2.

In scenario 2, with one engine inoperative (OEI), the remaining engine will run at higher power setting, which improves the SFC (see image below), and therefore will improve the endurance (time in the air; how fast the fuel is used).

► It will diminish the range though, as range requires speed, which will be limited with OEI (and also due to the low altitude), i.e., don't mix the improved FF and endurance with why not always fly with one engine (ignoring the safety issues).

Source: Jet Transport Performance Methods, Boeing

(Don't miss the text left of the graph.) That's also why coast guard C-130s orbit with an engine deliberately turned off. Being a turboprop (gas turbine), the SFC relation holds.

Related: Why is max endurance different for jet and props?


What is the history of the "Superbay" at San Fransisco International?

Superbay Hangar is a maintenance facility at San Francisco Airport.

About previous tenants and when it was built, this forum mentions that:

  It is the large aircraft hangar built by AA in the 1970's to house the
  747. Both AA and TWA were the first tenants. Now it's UAL and AA. UAL uses it as a line maintenance hangar for the wide-body fleet.

  It sits all alone out towards the bay. When VIP's come to SFO, they
  park next to this hangar due to its isolated location.
  ...
  The SuperBay was built and is owned by the City of San Francisco. It
  is primarily used by UA/AA.

Going through the timeline on SFO's History, the vacant area of this hangar is visible in one of the pictures of 1960s. In later pictures (1981), it appears to be there (shown in the background)1.

Interestingly, more references are found about this hangar in the future development plans of the airport than the history. Examples can be seen here (PDF, p20 and 28) and here (PDF, p6). This site also talks about some future work for Superbay Hangar.

1: I am not 100% sure about direction of the camera, but it might be pointing towards that hangar.