Why aren't 757 scimitar winglets flush with the ailerons? Over my many past flights aboard 757s, I have seen changes being implemented with their design. One of which was notably their refit of scimitar winglets. Although one of their most notable characteristics is the extended pointy edge on their tip, I have noticed that the inner edge of the winglet (past the wing position light) does not run flush with the aileron, unlike that of the older 757 winglets.

What is the reason behind this design exactly?

Thanks!

*Please note that the first 3 photos below are of the scimitar winglet and the last is of the original older design

Photo credits: First 3 photos are taken by me personally. Last one is from: https://www.flickr.com/photos/33415137@N06/6151948806

No prior knowledge of this design choice, but the design direction seems pretty clear here.
The original design reduces load towards the wingtip for efficiency. The textbook spanwise loading for maximum efficiency is the elliptical loading, however when tip devices, as in the original design, are employed, the tip load should not be zero. With a tip device, it is possible to maintain a pressure surface <> suction surface pressure differential. Therefore at the wing tip (just before the tip device), there is still significant lift being generated.
The scimitar winglet design that you have shown must be more efficient than the original design (otherwise why else would they retrofit it?), which therefore means that it can isolate a greater pressure differential from the outboard pressure surface to the outboard suction surface. Because this tip device is designed for a greater pressure <> suction surface pressure differential, but the original design was designed for a lesser differential, more load can now be generated outboard for the same drag penalty. As can be seen in the picture, the chord extension is at an incline to the trailing edge. This gives more camber to the outboard section of the wing, and therefore more lift on this portion and nearby.
Of course, the designer could have just tilted the trailing edge down for the same chord length as the inboard section of the wing. This would create the increase in outboard wing loading, but due to the abrupt change in camber from the aileron to the cambered outboard section, there would be a significant vortex formed. To decrease the effect of the vortex formation (it will still generate, but will be weaker), the surface follows the original design, but is extended with significantly more camber after the original wings trailing edge. The trailing edge camber (extra downwards curve) is very apparent in the first and second images. This device therefore allows an increase in outboard load without having to affect the inboard section geometry.
Obviously just creating more lift outboard, and therefore more overall lift, doesn't necessarily help an aircraft. During cruise, we only need sufficient lift to overcome the weight force. Because the new tip device creates more lift for the same amount of drag at a particular incidence, and because the drag polar is relatively unaffected, this means that we can create the same lift at a slightly different incidence angle, and therefore can cruise at a lower drag penalty.


Is there a public database for annual flights by aircraft type? I am doing research about the number of flights and distance flown performed by aircraft types, in a given year. For example:

There were X A320-200 flights, flying an average distance of Y nautical miles, in the year Z.

I know that these records are kept for all registered flights, so I am wondering if there is a database where one can find such info?

I am looking for data of as many regional flight airliners as possible.

Short answer is "no". There is no such thing as a "registered" flight.

In cases where pilots have filed flight plans, you could aggregate that data. It would be a BIG programming project. There are commercial services that analyze flight plan data. They might be willing to help you for a price that would be in the 10's of thousands of dollars.

Flight plan data would only be good for US information. Other countries would require other data collection.

Small planes usually don't file flight plans, but you may not care about this.

Aircraft manufacturers estimate how much their planes fly around. Whether they would be willing to share this data with you, I don't know.


Could TCAS be overwhelmed by multiple conflicting traffic and "give up"? I understand that TCAS can handle several "targets" simultaneously. However, I'm interested in the (highly hypothetical) scenario where TCAS would need to deal with multiple conflicts in a dense environment.

Is there a point where TCAS goes into some sort of "cannot resolve" mode becoming effectively inoperable, or does it try to cope with everything thrown at it, even if it leads to impossible solutions (defined here as maneuvers outside the flight envelope or the ability of crews to follow in a timely manner)?

From my general knowledge about TCAS (that is, not from actual simulations of such scenarios), I'd say that yes, it can be overwhelmed, but not in the sense that it will give up.

First, TCAS can demand a very limited range of resolution advisories (RAs). They are only vertical. The standard "Climb" or "Descend" RA assume the rate 1500-2000 fpm. TCAS can ask to increase it to up to 4400 fpm. (Or it can ask not to manoeuvre). In most installations, it will also not produce some RAs depending on the aircraft configuration; for example, it will not ask to climb at all if the airplane has flaps down past certain point.

Second, TCAS doesn't think too strategically. It can handle many targets ("intruders"), but in the end it will sort them according to their severity (primarily using the time-to-encounter factor) and will handle the most immediate ones in RAs.

It may well happen that after a short time, another intruder will become more severe. TCAS will then recalculate RA accordingly. (It takes into account the current climb rate and is generally reluctant to change the direction or even to choose a so called "crossing" RA, where the aircraft must cross the current path of the intruder, but it will do that if it determines this necessary. It also takes into account the typical (but clearly defined) pilot's reaction to the first and subsequent RAs).

So, at each point of time TCAS will "try its best" to handle immediate threats. It will (generally) not demand impossible manoeuvres nor superhuman abilities: all it can demand is known and accounted for. Yet, in theory I bet it is possible to create a scenario where TCAS would lead to very close encounters, or will select a sub-optimal strategy - even if we assume that all the aircraft obey their RAs precisely, which in itself is not given. In aviation, the engineers (so far) generally favour clear deterministic algorithms over something very clever but unpredictable and hard-to-test.


Is it legal to bring your own survival gear aboard an airliner? Is it legal to bring your own survival gear aboard an airliner?

Considering the sobering article by William Langewiesche that is appearing in the July 2019 edition of "The Atlantic", one might want to consider bringing:

Oxygen canister with regulator and pressure breathing mask
Parachute

Yes, it's legal to bring a parachute, if you can fit it within the permitted carry-on limits. It has been done.

No, it's not going to save you. You are not going to be able to jump out of an airliner. Unless your name is D.B.Cooper, and you're hijacking the last flying 727 with a rear exit door, that is. Again.

No, it's not legal to bring a pressurized container onboard a passenger jet. When you want to fly with a pressurized tank (say, a pony or deco bottle for tec diving), you have to unscrew the valve and bring it separately. This is to ensure you can't bring explosives or poisons inside the tank.

Yes, if you could bring an oxygen or nitrox container (less fire hazard than pure O2), combined with a firefighter SCBA, it could improve your odds of survival in the very marginal event of a fire-related accident, in which the plane manages to land intact enough for you to don it.

No, none of these are practical measures. If you want to somewhat improve your odds without impractical means, wear comfortable leather shoes without heels, cotton clothing, and a fanny pack for your papers, so that you're not tempted to reach for your luggage in an emergency.

One specialized item that has been considered for inclusion on airliners as safety equipment is fire hoods. There are portable smoke hoods that can give you a couple minutes' protection for evacuation. They don't include air or oxygen, only a simplistic filter, which is still a solid step above just holding your breath.


Is rate of turn information (both Turn Coordinator and Turn Indicator) accurate only in balanced turns? I was studying the difference between the TC and TI, and I thought I heard or read somewhere before that the turn rate information on the TC or TI are only accurate when the ball is in the middle.
Let's say I'm in a left turn and the TC shows I'm on the rate one mark, but the inclinometer is showing a slip (left ball).
A slip means I will need less bank or more rudder to be coordinated.
In this situation am I still getting a rate one turn despite being in an uncoordinated turn? And is there any difference here between the TC and TI?
My guess is the turn rate information is independent from the inclinometer, and so I am still turning at a standard rate but uncoordinated.
Is there any truth to the statement that the turn rate information is only accurate when the ball is in the middle?

The physics of turn coordinators, and turn rate indicators, are complex.
The since the gyro axis is not usually not perfectly horizontal, the instrument shows some response to pitch rate, as well as to turn rate.  In a coordinated turn at some particular turn rate, the calibrated markings can only be perfectly accurate at one specific pitch rate.  This means we have to specify either the bank angle or the True airspeed when we calibrate the instrument for a given turn rate.  In practice, the True airspeed is specified and assumed to be constant regardless of turn rate, while the bank angle, naturally, varies with turn rate.
Errors from flying at a different True airspeed than the instrument was calibrated for may be small enough to generally ignore in actual practice, but they do exist.
This is explored in more detail in the following ASE answers to related questions--
May turn rate indicators (and turn coordinators) be calibrated to be accurate at all airspeeds, or only for one?
Are turn rate indicators calibrated to a certain speed? If so, what speed?
In some "turn coordinators", does the gyro spin opposite to the direction it spins in a "turn rate indicator"?
If the aircraft is slipping or skidding, then the relationship between True airspeed, bank angle, pitch rate, and turn rate is altered, so the calibrated markings will no longer be accurate even if the True airspeed is the one that the instrument is calibrated for.  For example, in a wings-level skidding turn, the pitch rate is zero.  For the reasons explored in the above links, this will create some change in the turn rate indication.  The indicated turn rate will be different than if we were flying at the same True airspeed but in a fully coordinated turn.
Another way to look at it is that all turn rate indicators, and some if not at all turn coordinators, are designed so that the gimbal axis of the gyro stays approximately horizontal relative to the earth during any given coordinated turn.  If the aircraft is not banked at all, then any turn will tilt the gimbal axis of the gyro away from horizontal, which will affect the sensed turn rate.
Of course, it could happen that a change in indication due to slipping or skidding could exactly offset a change in indication due to flying at some True airspeed that is different from the True airspeed that our instrument is calibrated for.  So the full answer to the question is "Generally, yes, but it's complicated."
The details discussed in the third link above suggest that there may be fundamental differences in the way that a skid, or a slip, affects the reading of a turn rate indicator versus a turn coordinator--i.e. whether the indicated turn rate is increased or decreased-- and furthermore that there may be differences in behavior between different makes of turn coordinator, because they may not all share the same direction of spin of the gyro wheel.
This would be fertile ground for some actual in-flight experiments to make some real-world observations as to how the turn rate displayed by a given instrument is altered by slipping or skidding.  Keep the airspeed and the indicated turn rate constant, and make the aircraft slip or skid through one or more full 360-degree turns, and measure the actual time to complete 360 degrees of turn in each case.  For completeness, repeat the experiment at a different airspeed, or a different indicated turn rate, or a different amount of deflection of the slip-skid ball.  Be sure to include the extreme case of a wings-level skidding turn.  Finally-- especially if flying with a turn coordinator rather than with a turn rate indicator-- do some basic tests to see if, starting from a standard-rate turn, moving the stick or yoke aft to "pull" some extra G's tends to boost, or to reduce, the indicated turn rate.  Similarly, starting from a standard-rate turn, test whether moving the stick or yoke forward to "unload" the wing to a lower G-load tends to boost, or to reduce, the indicated turn rate.  These tests will help show which direction the gyro wheel is spinning in that particular instrument, which is relevant to understanding what is going on in the slipping or skidding situations.


Is there an online source for European Instrument Approach Procedures? The FAA offers instrument approach procedures on their website free of charge (FAA Charts).  Is there a similar site provided by EASA or the EU?

Eurocontrol has an online repository of European Aeronatical Information Services.

You'll need to register, but the basic service is free.

By default, the application is JAVA applet based, which works not in the best way. After logging on, you can change the default behaviour to HTML based, which makes it more user friendly.

Then clicking "Enter Application" will bring to the next level.

Here you'll find several reporting options, but what you are interested in is located under "PAMS Light [AIP]"

Select the country you are interested in, "Charts" for AIP type and "AD" for Aerodrome and there you have the charts.


Why are turbine blades not made out of titanium, only compressor blades? According to this video on jet engine blades, titanium is never used for the turbine, because it "melts and burns at the temperature of the flame". Only the blades of the compressor are made of this material.

However, the melting temperature of titanium is higher than that of any steel alloys I could find, and titanium produces a protective layer of oxides on the surface. What other properties of titanium make using it impossible?

Titanium is unsuitable because it will react with oxygen and carbon at high temperature, well below its melting point, making it very hard and brittle. Welding titanium is very complicated because it needs to be shielded extremely well from any oxygen when hot. Ti$_3$O will form above 500°C, and Ti$_2$O above 600°C.

Initially turbine blades were made of steel alloys, but they have been displaced by nickel alloys.

Also, they operate in an environment which requires constant cooling, so they can be 200 - 300°C cooler than the turbine entry temperature of the gas coming from the combustor(s). Modern turbine blades are hollow and have a perforation at their leading edge. Pressurized, relatively cool air is forced through the blades and the perforation and flows around the blade's surface, creating a cool sheet of air to shield the blade from the hot gas. Also, before entering the turbine the gas is accelerated, which already lowers its temperature. See the plot below of parameters inside an older engine taken from this source.

Shortly past the fuel injectors the maximum gas temperature of approx. 1800°C is reached, which drops to 1100°C at the entry to the first turbine stage. Note that this temperature has been raised to 1500°C in modern military engines! At the same time, the highest temperature is connected with the lowest speed (30 m/s), and the flow accelerates to 200 m/s directly before entering the first turbine stage.

Titanium in contact with oxygen would lose a lot of its strength at these temperatures, even though its melting point is at 1650°C.


Which FAA or EASA regulation does prevent a high wing to cross the passenger compartment? I'm looking for reference subpart and eventually chapter in either FAA or EASA regulation where it is stated that for passenger aircraft with high wing passenger compartment can not be interrupted by fuselage-passing wing, so the wing must be placed above the fuselage (with additional fairing thus increasing drag and weight - eg. ATR-42).

I know this is quite obvious but I need a regulation reference for a report.

There is no reference to such a regulation in the design reference books that I have. As I remember, in the F27 the high wing did make the passengers tuck their head in when walking to the rear seats: the wing does cross the fuselage, which makes for a much lighter construction than when placing the wing on top of the fuselage.

Image source

There is also no regulation stating a minimum height between floor and ceiling.
There is statistical data on average passenger length, and design departments of aircraft manufacturers are very much concerned with passenger appeal. So they may be instructing the construction department that the wing must be placed on top of the fuselage, despite the weight penalty, in order to increase market share. Populations are getting taller over time.


How does the glide ratio change with velocity in a glider with air brakes deployed? I'm interested in how the glide ratio steepens when increasing velocity, starting from the best slope (best L/D) velocity, in a high drag configuration (air brakes fully extended on a glider).

I've seen several graphs of how L/D changes with AOA for various powered aircraft (and not in a high drag configuration), but couldn't find a relevant one.

Will be happy to see a L/D vs AOA graph and/or a sample polar in clean vs dirty configuration.

This can be easily answered with a spreadsheet. Start with speed $v$ going from 20 m/s to 50 m/s. Add a column for the zero-lift drag coefficient and keep in mind that the increasing Reynolds number will change that value over speed, like that: $$c_{D0}=c_{D0_{Ref.}}\cdot\left(\frac{v_{Ref.}}{v}\right)^{-0.3}$$
I picked as reference values $c_{D0_{Ref.}}$ = 0.01 and $v_{Ref.}$ = 25 m/s. Adjust as required.
Next, add a column for the zero-lift drag coefficient with speed brakes deployed and add a constant value. I picked 0.015 for the example plot below.

Now we need to add induced drag and start with a new column for the lift coefficient $c_L$. Since weight does not change with speed brake setting, one will do for both configurations:$$c_L=\frac{2\cdot m\cdot g}{\rho\cdot v^2\cdot S}$$
I used 350 kg for the mass $m$, 1.225 for air density $\rho$ and 10 m² for wing area $S$. The induced drag coefficient $c_{Di}$ will be $$c_{Di}=\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
My sample glider has an aspect ratio $AR$ of 20 and an Oswald factor $\epsilon$ of 0.98. Again, adjust as required. For extra correctness you might want to add an extra column for the real-life lift coefficient with beginning stall. Keep the "clean" lift coefficient for induced drag but plot all drag coefficients over that extra column where the lift coefficient grows less than the linear value once it is above the threshold where flow separation starts on the wing, say 1.25. Now your speed will not be correct for lift coefficients above that threshold, but your induced drag will become very realistic.

Now add another column for induced drag with speed brakes deployed. In oder to model the distorted lift distribution over span with speed brakes, reduce the Oswald factor to maybe 0.7. Add both drag coefficients for the total drag coefficient: $$c_D=c_{D0}+c{Di}$$

The result should look something like that. The index wF is for the configuration with speed brakes deployed:

The glide ratio E is the ratio $\frac{c_L}{c_D}$ and plotted on the right Y axis. Note that the best glide is cut almost in half and moves from $c_L$ = 0.7 to about $c_L$ = 1.0 for speed brakes deployed. I did not add the extra drag at high lift, so your result might look slightly different.


Why don't airplanes have smoking cabins? Is there any airplane model that has a small lavatory-like cabin just for smoking? I have never seen any such planes and that made me wonder why this is?
It would not take much more room than a normal lavatory, make it much less likely that someone will smoke in the lavatory regardless of the ban and provide smokers a way to satisfy their need.
I will have to add that I am not a smoker, just a person with weird ideas/questions.

Related Questions:
• Are there any airlines that still allow smoking on-board flights
• Was smoking banned because of passenger safety or occupational safety?

Just off the top of my head,

It would take up space that could be used for three or four paying passengers. This would result in increased ticket prices for everybody and the non-smoking majority have no incentive to subsidise a smoking cubicle.
It would require a ventilation system that would prevent smoky air from getting into the rest of the cabin, which would add weight and complexity.
It's a fire risk and a small fire from some idiot disposing of paper in the ashtray could spread; it would be hard to detect such a fire early because you couldn't just put a smoke detector in the smoking cubicle.  (I guess an infra-red detector would work.)
Almost nobody tries to smoke in the lavatory so reducing the occurrence of an event that hardly ever happens isn't worth much.
Rates of smoking are decreasing in most Western countries, so demand for such a cubicle is already falling.
Anti-smoking legislation is often aimed at worker protection: who's going to clean the smoking cubicle and what equipment will they need?
I doubt there's significant pressure, even from smokers, for such a service to be provided.


Throttle friction lock - what is it? Referring to a general aviation airplane, what is the throttle friction lock and what do I need it for?

It's a device that makes the throttle harder to move. You need it to keep the engine vibrations from slowly moving the throttle away from where you left it during cruise.


What would happen if a helicopters rotor hit the [in-air] refueling probe? My first guess is that they would catastrophically fail - but I also read the Eurocopter Cougar has propeller blades that will withstand the impact of a 20mm round (I'm guessing other military helicopters are similar).

Is it likely that the probe could bounce off or is it a pretty much guaranteed byebye scenario?

Also could the rotor become entangled in the hose or would it simply slice it?

It would chop it right off.

Watch the video. It's fun. When the helicopter pitches up right after refueling, the rotor disc cannot follow the movement (its hinges allow the blades to pitch up and down, and inertia makes it change its plane of rotation only slowly). The refueling probe is cut cleanly in half.

However, I would not try this on purpose. The risk of damaging a blade is considerable. I am sure the rotor blades needed to be replaced after that incident.


What causes the average speed difference between the JFK to DEN flights and the JFK to LAX flights? I just realized shortest JFK - DEN flights are ~4h40m (280 min) and shortest JFK - LAX flights are ~6h (360 min). I'm talking about currently available commercial flights.

NY - DEN (straight line) distance is ~1625 mi, NY - LA distance is ~2450 mi (approximate measures using Google Maps' Measure Distance). So NY - DEN is about 0.663 of NY - LA distance-wise, while JFK- DEN flight takes about 0.777 of JFK - LAX flight time-wise.

In other words, going by distance, I would have expected JFK - DEN flight to be about 42 minutes shorter, or slightly under 4h. Any idea where the ~15% increase in flight time from what I expected comes from?

There is certainly a difference, but most of it definitely has a good explanation. Most of it is overhead such as taxi time that applies to both flights (almost) equally. This has a relative big impact on short flights.

The taxi out time for both flights will be about 27 minutes; JFK is not exactly known for its quiet taxiways. Both flights will add about 30 nautical mile for their departure route.

Both flights will fly approximately great circle routes, probably less than 2% extra distance during cruise.

The LAX flight will typically do a straight in arrival, almost no extra distance there.

The DEN flight will typically do a full arrival, 30 NM extra distance there.

The taxi in at LAX is 13 minutes on average, and 9 minutes at DEN.

Let's assume that both aircraft fly 460 knot true airspeed with 20 knots headwind during cruise, so 440 knots ground speed.

My estimates for the total flight times are then:

JFK-LAX

GC distance 2150 n.m
Departure detour 30 n.m
Arrival detour 0 n.m (straight in)
Cruise detour 25 n.m
Total distance 2205 n.m
Taxi out: 27 minutes
Climb out: 60 n.m. @ 300 kts = 12 minutes
Cruise: 2085 n.m. @440 kts = 4 hour 44 minutes
Descent/Landing: 60 n.m @ 240 kts = 15 minutes
Taxi in: 12 minutes
Total time: 5h50 minutes
Margin: 10 minutes

JFK-DEN

GC distance 1400 n.m.
Departure detour 30 n.m.
Arrival detour 30 n.m.
Cruise detour 15 n.m.
Total distance 1475 n.m.
Taxi out: 27 minutes
Climb out: 60 n.m. @ 300 kts = 12 minutes
Cruise: 1355 n.m. @440 kts = 3 hour 05 minutes
Descent/Landing: 60 n.m @ 240 kts = 15 minutes
Taxi in: 9 minutes
Total time: 4h07 minutes
Margin: 33 minutes


Can the divergence Mach be greater than 1? I know that by decreasing t/c and increasing the sweep angle it is possible to increase the divergence Mach, but what is the limit?

I am calculating the Mach for a wing with a quarter chord sweep angle $\Lambda_{1/4}=54 ^\circ$. According to Denish Howe (Aircraft Conceptual Design) the “two-dimensional” divergence Mach can be found with Korn equation and then converted in a "three-dimensional" Mach considering the sweep with the following equation:

$$ \frac{M_{3d}}{M_{2d}}=\frac{1}{(\cos\Lambda_{1/4})^{0.6}} $$
 This led me to a divergence Mach of 1.19 which doesn't seem reasonable at all.

However, if the assumption that only Mach perpendicular flow affects the shock is maintained, this might be possible with very high sweep angles. What is the limit of this assumption?

The general perspective

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

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

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

The physics

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

Prelim design

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


Was smoking banned because of passenger safety or occupational safety? Federal regulation CFR 252.3 notes that:

  Air carriers shall prohibit smoking on all scheduled passenger
  flights.

Was this because of: 1) passenger safety concerns (the airplane may catch on fire from an unextinguished cigarette); 2) consumer demand (passengers demanded all-non-smoking flights); or, 3) for occupational safety concerns (the flight attendants were breathing in cigarette smoke all day)?

I've posted my own answer but am happy to be proven incorrect.

Related questions:

• When did inflight smoking become (widely) prohibited?

• Is it legal to smoke in your own plane?

If you look at the part of the Federal code (49 U.S. Code § 41706) that actually instantiates this :

  (a) Smoking Prohibition in Interstate and Intrastate Air
  Transportation.— An individual may not smoke— (1) in an aircraft in
  scheduled passenger interstate or intrastate air transportation; or
  (2) in an aircraft in nonscheduled passenger interstate or intrastate
  air transportation, if a flight attendant is a required crewmember on
  the aircraft (as determined by the Administrator of the Federal
  Aviation Administration). (b) Smoking Prohibition in Foreign Air
  Transportation.— The Secretary of Transportation shall require all air
  carriers and foreign air carriers to prohibit smoking— (1) in an
  aircraft in scheduled passenger foreign air transportation; and (2) in
  an aircraft in nonscheduled passenger foreign air transportation, if a
  flight attendant is a required crewmember on the aircraft (as
  determined by the Administrator or a foreign government).

It is the presence of a flight attendant that triggers the non-smoking requirement. Thus, one can safely assume that it is an occupational safety concern (sidestream smoke) that forced the regulation change.


Why don't airplane turbo piston engines have boost control? Why is it possible to over-boost piston aircraft engines? All turbo car engines have a wastegate that just vents pressure back to the intake, whereas in an airplane the pilot has to look at the manifold pressure gauge to protect the engine.

The majority of piston airplane engines are based on very old technology, before computerization was available. The vast majority of airplane piston engines are carbureted with manual mixture control, prop control and turbo control and the pilot has to manage all that plus carb heat manually.

New engine technology has been very slow to come into the piston market because certification costs are so high, and the market is so small. It would cost engine manufacturers millions to develop and certify new turbo-normalizing systems for these old engines and as there are probably only a few thousand turbo-normalized avgas piston airplanes in the world they would never recoup the costs.

There are modernized engines on the market with electronic fuel injection, computerized engine management with turbo-control, and single-level operation. These are slowly making inroads into the market but it's going to take time.


Where is the control loop of the actuator closed? When electro-hydraulic servo-actuators are used for the actuation of control surfaces in aircraft, linear variable differential transformers (LVDTs) are used for position or velocity feedback. There is a control loop that compares the actual position with the commanded position.

Where is the loop closed? In the flight control computer or in a module near the actuator? By this, I mean where this comparison is taken place?
What are the pros and cons of each of these methods and which one is usually used in modern aircraft?

Different aircraft and manufacturers take very different approaches.

1. Boeing 777

The B777 has three Primary Flight Computers (PFC) that are responsible for flight control laws computation and four Actuator Control Units (ACE) that are responsible for the closed-loop control of their responsible flight control surfaces.

The ACE is primarily an analog device, including the actuator control portion. Note that analog here refers to any control system that is not a general-purpose computer. Analog devices have a finite number of possible failure modes. For this reason, it is enticing from a common-mode/generic failure perspective that bedevils digital computers. The main disadvantage is that it is less flexible and powerful than a digital computer.

Ref: http://www.davi.ws/avionics/TheAvionicsHandbook_Cap_11.pdf

2. Airbus A320

The A320 closes the actuator loop directly on the five flight control computers: 2 Elevator and Aileron Computers (ELAC) and 3 Spoiler Elevator Computers (SEC), plus 2 Flight Augmentation Computers (FAC) for rudder controls.

In order to combat against common-mode failures, SEC, ELAC and FAC are designed to have completely different architectures by different design teams. Software is also designed to ensure dissimilarity across the command and monitoring channel of each computer.

An in-depth discussion on common-mode failures can be found in this paper, which cites software, and in extension, general-purpose computing, as a major source of common mode failures.

Ref: http://www.davi.ws/avionics/TheAvionicsHandbook_Cap_12.pdf

3. Airbus/Bombardier A220

The A220 accomplishes the closed-loop servo control in Remote Electronic Units (REU) located fairly close to the control surfaces and their actuators. For this reason, a total of 10 REUs are located across the aircraft.

The Primary Flight Control Computers (PFCC) normally compute the flight control laws. Since REU is a digital computer, in the scenario where all PFCCs fail (for example, a generic failure) and if sufficient number of REUs remain operational, the REUs can take up the slack to run Direct Mode control laws.

The primary advantage of this setup is the reduced wiring weight compared to centrally located servo-loop controllers, as well as higher failure tolerance in the case of single servo-loop failures.

The primary disadvantage, once again, is the common-mode failure across the REUs. Due to the high number of REUs, it becomes prohibitively expensive to design sufficient dissimilarities into them. For this reason, a third backup control loop, in the form of an analog Alternate Flight Control Unit (AFCU) is needed to cater for this remote failure mode.

Ref: https://quizlet.com/421493192/a220-lod-ch9-flight-controls-flash-cards/


Is a fighter pilot allowed to fly two different model fighters? Does a fighter pilot who flies the F/A-18E have permission to fly the F/A-18F for training a new pilot? Or does an F/A-18E pilot fly with an F/A-18F for night bombardment?

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


What to do when you accidentally land on a runway thats borderline long enough to land on? I was reading another question earlier when I noticed a story about a 737-700 that landed at M. Graham Clark Downtown Airport in downtown Branson Missouri.  The runway is only 3738 ft, long, which is a bit short for that particular kind of aircraft.

Apparently the pilots set the aircraft down hard and immediately did everything in their power to bring the craft to a halt, stopping about 500ft short of the far end of the runway (which, btw, ends in a cliff.  Just to heighten the suspense).

I'm sure they had their reason, so I'm not going to question them.  I just wanted to use it as a set up for this question:

If you accidentally touch down on a runway that is borderline long enough to stop your aircraft on, how would you determine if you wanted to either stop or just do a touch and go?  Is it too late once you've already touched the ground?

In terms of safety, the key mistake was made as soon as the pilot made the decision to land on that runway. The corrective emphasis should be on determining why this mistake was made and taking whatever steps are necessary to prevent that mistake in the future. Especially in transport category airplanes, the crew should always calculate the required landing/rollout distance for the current landing weight, wind, atmospheric (temperature/pressure) and runway surface conditions, and this should be compared against the approach plate / airport diagram / A/FD. In most transport category airplanes this can all be computed by the FMS and it is standard procedure to do this on every single flight.

The question of what to do after the key mistake is still valid, though. I would say it depends on when the pilot recognizes that the runway is too short.

If recognized on approach, a simple go around is clearly called for and perfectly safe.
Once the wheels touch the ground, the decision gets a lot more complicated. The pilot must choose whether to reject the landing or commit to it. If you recognize it as soon as you touch down, you would probably be able to apply takeoff power and get airborne again safely. Once you've started to brake and decelerate, there will quickly come a point-of-no-return. Since you're starting at high speed, you're using up a lot of runway early in the landing rollout. Also note that in many airplanes it can take a significant amount of time to retract spoilers, stow thrust reversers, and spool the engines back up to takeoff thrust. You'll be consuming a lot of runway during this time. (At a constant 120 knots, you'll use up 2,000 feet of runway in just 10 seconds.)

In my opinion it's far better to commit to a landing. If I'm going to overrun the runway, I'd rather it happen at low speed. If you try to take off again and don't make it, your overrun will be at much higher speed, and destructive energy in a crash is proportional to the square of your ground speed.

So there's a gray area... you could attempt to take off again if you were dead certain you were going to make it. Otherwise, it's most likely best to "cut your losses" and get the airplane as slow as possible when you run out of runway, in order to minimize damage & injury. If you can get it down to, say, 30 or 40 knots, you're likely to escape without any serious injuries (the plane may take a bit of a beating, though, depending on what's beyond the end of the runway). If you do it at 120 knots, all bets are off. And you did mention a specific runway with a cliff at the end; obviously that would have to factor into the decision-making process. It may be that you simply realized your mistake too late and there is nothing you can do about it.

This leads me back to the original point, which is that the key mistake was made as soon as the pilot decided to set up an approach to that runway. The best bet is to make sure that never happens.

EDIT: After reading about the specific incident you referred to, it seems that the pilots simply mistook the airport itself for a different one with a longer runway. So it's not necessarily that they failed to calculate their required landing distance; rather they just landed at the wrong place. This is a different, but equally bad (or worse) mistake, discussed to some extent in the comments below.


When sizing a powerplant for a GA aircraft, how do you estimate the power required for other electrical systems? When designing a GA aircraft, I have sized a powerplant (in kW) needed to run the plane on its mission. However, this does not consider the power needed for avionics, de-icing, etc. How do I approach finding the numbers for these systems? Are they significant?

For de-icing, this study from Hamburg University shows some example power consumptions from 23 KW/m^2 to 44 KW/m^2. For sizing an engine, should I just assume the thrust will have to be decreased in order  to accommodate de-icing?

This depends heavily on how the plane is set up especially these days with the prevalence of glass in the cockpit even in GA planes. For a point of reference most small GA planes like the Piper Cherokee run 60-100 amp alternators which usually have a bit of headroom in them but power everything and charge the battery just fine. If you want to fly in most airspace you are going to need to power at least a transponder and a radio (more than likely two radios).

The Garmin GTX330 is a 250 Watt transponder and is fairly common in the Archers I fly.

Your run of the mill Garmin GTR 225 radio comes in 10 and 16 watt versions.

To get the total requirement just add up all of your components draw. Most manufacturers list power requirements (or voltage and current draw requirements) for any given piece of equipment and you will have your required power.

As for De-Ice requirements this depends on the type of system you implement. A weeping wing will only require power to drive the fluid pump and the windshield heater where as a boot style system will require enough power to drive the compressor that inflates the boots. Although its becoming increasingly more common to see FIKI on GA planes the majority of the small aircraft fleet still lacks FIKI capability.


How does gust affect a swept wing I have a basic question that I cannot seem to find a solid answer for:

How does a gust affect a swept wing?

Sorry our experts did not weigh in on this one in more detail.

Sweeping the wing increases the "dihedral effect" of tending to create a greater roll force when struck with a side gust, as the windward wing is angled towards the gust, and the leeward away.  This is exactly the same effect as what happens in a side slip.

Swept wings also improve yaw stability.
Of course, a very sharply swept wing presents a shorter torque arm to a rolling gust than a less swept wing of equal length but greater span.

The "dihedral effect" of swept wings can be aerodynamicly countered with side area under the CG, particularly fuselage side area or landing gear spats.  Ventral fins offer another alternative.

A gust from the direction of flight will affect a swept wing similarly to a straight wing, producing a momentary increase in lift.

The venerable Tiger Moth biplane has slightly swept wings.


Why are months (e.g. December) used to notate a runway? I'm writing a report on runway quality and I've stumbled onto a weird qualifier in the data. I understand that runway 17/35 indicates which direction the runway is facing based on magnetic heading.

  RWY_ID 17/35 17/35 26-Aug 14/32 30-Dec 28-Oct 21-Mar 13/31

What does 21-March mean for example?

Very likely, whatever data source you're using has been mangled by Excel (or some other spreadsheet or data processing system that tries to convert everything that might be a date into a date format).

26-Aug is actually runway 26/08, 30-Dec is actually runway 30/12, etc. (See "How are runways numbered?")

Some computer system saw those numbers, assumed that they were dates, and presented them that way. The other runways aren't valid as dates, so it left them alone. It wouldn't be the first time that people used Excel without fully understanding its default date-parsing settings and thereby causing problems for people trying to use their data afterward.


In an Airbus, if the AOA sensor fails and the computer pitches the plane down, can the computer still only pitch down 10 degrees maximum? For example, something similar to Qantas Flight 72.

Assuming the Angle of Attack sensors are faulty and give bogus data - for example, that the Angle of Attack is 20 degrees, or the maximum Angle of Attack when the plane is flying normally and in no danger of stalling.

The flight protection systems are going to kick in and try and pitch the plane down because the computers will think the plane is stalling or about to stall because of the (bogus) Angle of Attack readings.

Would the computer still be restricted in how far it can pitch the nose down? For example would it suddenly angle down but stop at 10 degrees nose down, or would it go into a ballistic, unrestricted and dangerously steep dive?

I read a pilot in an Airbus cannot make the plane pitch down more than 10 or so degrees in ''Normal Law'', would this apply if the plane's computers are trying to pitch the plane down due to faulty AOA sensor data?

The answer below is for the A320, as this is the only Airbus manual I have access to.

  would it go into a ballistic, unrestricted and dangerously steep dive

It'd likely stop somewhere before that. "Abnormal attitude law" engages when:

Bank angle above 125°
Pitch above 50° nose up or below 30° nose down
KIAS below 60 to 90, or above 440
Mach above 0.91
AoA above 30° to 40°, or below -10°

I believe the FAC will also give up at some point as the computed KIAS is so far away from what is measured. If it is a double ADR failure or double FAC failure it will go down to Alternate Law. If it is a triple failure it would go to Direct Law, as was the case of GXL888T.


Should I put yesterday's date for destination date/time on a flight plan if the flight is to go east bound across Zulu +-12 time zone? The international date line runs across the middle of Pacific Ocean opposite (12 hour ahead or before Greenwich mean time (zulu)) Zulu time.  It is the boundary where 24 hours elapses and the date changes.  I am trying to clear the fog in my mind how pilots account for the date on their flight plan when the flights cross Zulu+-12.

When you file a flight plan, you don't enter an arrival date or time. You just enter proposed UTC departure time and estimated length of time enroute. For aircraft or pilot logbooks we only use UTC date and time for departure, and UTC date and time for arrival. The local arrival date or time does not matter. The international date line has no bearing on UTC date or time.


Would it be feasible to develop a dirigible-based refueling station for fighter aircraft? The impossibly bad 2005 film Stealth featured a dirigible-based, mid-air refueling tanker station for the stealth fighters to use.

At first, this seemed like it might have been the singular good idea in the film as a dirigible would have a very long loiter time making it ideal for fighter refueling.

But I don't think it's possible, right? What is the maximum known air speed of a dirigible vs. the lowest possible air speed for a tactical fighter?

(Note: I do think it'd be possible for helicopters and osprey to use a dirigible tanker, right, as their stall speeds can be essentially zero?)

What is the maximum known air speed of a dirigible vs. the lowest possible air speed for a [stealth] fighter?

Airship fastest speeds

According to Guinness the world record speed for an airship was 70 mph by Steve Fosset in 2004.

Guinness also say

  The large rigid airships built by the USA and Germany in the 1920s and 30s could reach higher speeds (up to 140 km/h or 87 mph according to some sources), but these were never officially measured to FAI standards.

Stealth aircraft slowest speeds

The F-117 has a landing speed of 180 mph.

The F-35B is stealthy and can hover.


Jokes only pilots would get in Airplane In the 1980 comedy movie Airplane!  Are there some jokes that only pilots would get?  I always thought there was sight gag with the runway when they are taking off.  The runway look likes it has exit ramp like an interstate highway.

Not really.  That movie had more gags associated with everyday objects eg Capt. Oveur initiates taxiing the 707 by shifting it into gear, like a car, etc.  I don’t really recall any aviation specific elements - aside from that it took place on a commercial airline flight - that only pilots or someone with a deep knowledge of aviation would get.  One aviation item which gets a little overlooked was names of the flight crew - Captain Clarence Oveur (Clearance, Over), FO Roger Murdoch, and FE Victor Boston, being plays on common radio terms “Roger, Roger.  What’s out vector, Victor?”  Another one I recall was a minor scene between Lloyd Bridges and Robert Stack where they argue the pros and cons of letting Stryker do a normal landing vs foaming the runway and letting him land wheels up.  Of course what made that scene funny was the slapstick use of a water cooler.  Bridges had another scene with Stack where Stack remarks “That’s impossible!  They’re on instruments!” which cuts to a scene with Stryker, Elaine, and Dr Rumak playing jazz using musical instruments in the cockpit.  Most of the film’s jokes had to be more relatable to the man on the street’s concept of air travel eg “the White Zone, Red Zone” recordings they used to play, being pestered by religious irritants for money in terminals, etc.  I don’t think Airplane! would’ve have had nearly the appeal if it’s humor was based on a deep knowledge of aviation.


Does a system exist that can bulk process satellite data to find a plane lost over ocean? The case of the lost Malaysian Airlines plane is tragic for all those involved.

In the case of such a plane lost over the ocean, hypothetically (and described very simplistically), it would seem that the fastest way to search for wreckage would be:

to define an area to be searched
wait for the latest satellite images for that area at high-resolution to be available (given appropriate positioning and programming of the satellites)
then search the captured imagery for deviations from ocean blue

Presumably this could be done reasonably quickly by a computer, and that satellite imagery is taken after a suspected crash, and exceptions (e.g. spots of white amongst the blue) are able to be verified by a human.

Does such a system exist? Are imaging satellites able to be configured to take such imagery on demand over a large area? And do such batch-image processing systems exist for this purpose?

Update: Satellites were eventually used in the search for MA370, see this article.

This question might be better answered by the folks at space exploration but here's a shot:

Oil slicks are not uncommon at sea, so finding one from the aircraft is not too easy.
It's an incredibly large area pulling a lot of processing power. You're going to need pretty good resolution imagery over several square kilometers and then run image recognition on it. Look at this image which has a scale of 25 miles which is still a fraction of what you would need to get an idea:

The fragments you're looking for are very small in regards to waves. I suspect depending on where you are there's a large amount of noise from other rubbish which is hard to filter out, such as a white plastic sheet to a door. You might even go confusing big aircraft parts to other white boats. Yes, you can continue the search but it takes time to go through all of these and dismiss them.
A lot of volunteers searched for Steve Fossett when he went missing, and there was some attempts to locate him by satellite imagery from google maps, which was not successful.
Aircraft, while not fast, can be over the side within a few hours, while I think you have to wait until the satellites have caught all the imagery you would like.

While I think it could be done as you say, you would need to develop software and I don't think the market for it exists, but that's just my guess. Reading up it appears that satellites are used against drug cartels along the USA-Mexico border and against illegal immigrants elsewhere in the world.


How is combustion directed in one direction in a jet engine? The answer here explains how jet engines work. During the BOOM phase air expands, however, the expansion would be in both direction, say toward the turbine blades as well as towards the compressor blades. Why is it that the compressor blades are not affected by this, because the blow could actually cause the compressor blades to rotate in the reverse direction?

The shape of combustion chamber does the trick. It's expanding towards the turbine. Pressure is highest when the air leaves the last compressor disk. Fuel is added to keep pressure from dropping. The pressure it's just a bit lower but the amount and temperature of the air is much greater so the air can be used to turn turbine. To increase efficiency pressure drop is kept to minimum. If something wrong happens or throttle is advanced very fast compressor blades can be effected. The surge happens and flow direction reverses.
Look at the cutout picture of a real jet engine. It will be obvious. There are very simplified pictures of the jet engine that can make understanding confusing as they can be just wrong.


Where is the best center of gravity? I'm designing a plane, and I have a question. What is the best place for the center of gravity, relative to the center of lift? I've heard that it's best put just behind the center of lift, but I would like a second opinion.

The center of gravity (cg) should be right above or below the center of lift. Otherwise the airplane will start to pitch and never stabilize.

But you do not select the position of the cg, instead, you adjust the center of lift such that lift will act along the same axis as weight. This is called trimming the aircraft and is done by adjusting the elevator deflection (or the incidence of the stabilizer). Of course, you should select the cg position such that the available elevator deflection range will not only shift the center of lift to the cg, but leave enough margin for manoeuvring.

The next condition is to ensure proper natural stability. Once the tail surface produces more lift per area than the forward surface, the aircraft will be instable, so that any angle of attack deviation from the desired state will quickly increase. Therefore, the cg should be placed slightly ahead of the neutral point of the airplane. The neutral point is the cg location at which angle of attack changes will not cause a change in pitching moment. The neutral point of a single wing is near its quarter chord point (it moves forward from the quarter chord point with decreasing aspect ratio), and the neutral point of the whole aircraft is the mean of the neutral points of all components, adjusted for their lift curve slope.

A good first position for the cg is at the quarter chord point of the wing. This ensures that the tail surface will be only lightly loaded, but it might be that stability at this position is not satisfactory. To increase stability (and reduce pitch agility), move the cg further forward, and vice versa. If you want to optimize the aircraft's lift-to-drag ratio (and minimize trim drag), select the most backward cg position with still acceptable stability.

GA aircraft are normally very stable, and their cg position might even be close to the leading edge of the wing. Details depend on tail size, aspect ratios of all surfaces and the desired agility.


Why is a sweeping second hand required for IFR? The reasons why a clock is necessary for IFR have been explained elsewhere, but I haven't seen the reason that the clock has to have a sweeping second hand.

It seems like when timing things it would be more useful to have a ticking second hand, why is it expressly required that it be a sweep?

As @fooot mentions in the comments it means that the hand must be concentric with the hour and minute hands, it is not a reference between the difference of deadbeat and sweep seconds as many watch brands commonly reference now. This is a regulation that is intended to clarify the difference between a second hand that references the main dial and one that is on a sub dial. Historically planes may have had more complicated nav clocks like this hamilton where the large second hand is for the chronometer and not the elapsed time clock.

(source)

You can find what looks like one of the early AC's on digital clocks here. It references FAR 91.33 (which seems to no longer be in place) you can find the original verbiage here. I can not find any FAA legal interpretation that further defines "sweeping seconds".

On a bit of a side note, wrist watches (in any form) are not a legal substitute for a mounted clock.


Cp, Cg and Np location of a tandem wing configuration, both have positive lift? I understand that in a tandem layout( 1 wing at front of plane, 1 wing at rear, both have positive lift) , the Cp has to be ahead of the Cg, and the Np behind the Cg.

Is there a rule of thumb how far forward the Cp has to be in front of Cg?, like 17% to 33% of MAC, etc.

Should Cm vs alpha, still have a negative slope?

Is it possible to have a 50% lift split between rear and front wings, just have a higher incidence in front wing, so it stalls first.

Any help would be appreciated

I understand that in a tandem layout, the Cp has to be ahead of the
  Cg, and the Np behind the Cg.

No. Yes.

For a true tandem (without horizontal tail), it makes little sense to talk about an isolated wing. The combined CP will always coincide with CG (in a static flight). Otherwise, as Jan already noted, the airplane will pitch up.

For NP (neutral point), see below.

  Is there a rule of thumb how far forward the Cp has to be in front of Cg?, like 17% to 33% of MAC, etc.

Forget about CP. It's useful in aerodynamics (and somewhat in structural design), but for the dynamics and stability analysis only NP matters. CP is very inconvenient, it moves all the time.

All these 'rules of thumb' apply to NP, not CP. In particular, the distance from CG to NP (CG being ahead) in terms of MAC is your 'static stability margin', and is the main contributor to static stability.

The rule is roughly the same regardless of the aerodynamic configuration. Some minor effects will be different (for example, damping will probably be lower), which may require some minor adjustments.

  Should Cm vs alpha, still have a negative slope?

For static stability, yes. This is essentially the definition of static stability; how you achieve this slope is another matter.

  Is it possible to have a 50% lift split between rear and front wings, just have a higher incidence in front wing, so it stalls first.

Yes. You'll normally need a somewhat smaller front wing for that. Or you can have a swept front wing and straight rear. Note that if you want a stable aircraft, at a higher angle of attack by definition the lift on the rear wing must rise more than on the front one. If you want to keep this AoA (e.g. at a lower speed), you'll need to dump this extra gain via re-trimming.


What are early/inside and late/outside turns (see, e.g., PBN Manual Order 8260.58A) and when do pilots perform them? While studying FAA's PBN Manual (Order 8260.58A), I came across the concept of early/inside and late/outside turn construction (Section 5-3. Turning Departures).

For each of the possible cases, it provides instructions for constructing different Obstacle Clearance Areas.

Here are some examples:

  a.) Early and inside turn construction

  1. Turn following VA leg.

  2. Turn follow VI leg.

  3. Turn-at-fix (FO or FB).

  b.) Late and outside turn construction

  1. Wind spiral application

My question is, what are these kind of turns exactly? Are they special cases of a "normal" (expected) turn? In addition, how do pilots know when they have to perform such turns?

What also confuses me is the fact that the PBN manual, which describes the design of IFPs, covers such cases that have to do with a pilot's/ATC's "on the spot" decision. When designing, for example, a SID, shouldn't you end up with one (multi-branched or not) Departure Procedure, with specific waypoints selected after the evaluation of specific Obstacle Clearance Areas covering "normal" turns and not special cases?

I think what you're talking about are what pilots refer to as "fly-past" and "fly-over" waypoints.
Up until recently, all waypoints in the world were "fly-past", ie you could cut the corner from one leg to the next and not actually fly over the waypoint itself. This is still the standard, unless otherwise stated.
But then some SIDs and STARs needed people to actually fly OVER the waypoint before turning onto the next leg, and so coding was included in FMCs etc to get the autopilot to not start the turn until AFTER the waypoint. The difficulty is that there's usually not any differentiation in the presentation on the CDU between "fly-over" and "fly-past" - you have to look at the produced track on the ND to then see whether you're cutting the corner or turning after the waypoint.


Amazon Atlas nose-down elevator deflection? In this link I read about the crashed aircraft:

  The airplane then pitched nose down over the next 18 seconds to about 49° in response to nose-down elevator deflection.

I feel that this is a common mechanism, unknown to non-expert, like me. What does it mean?

Interested in a rather intuitive, relaxed explanation, rather than an analytical one.

"Nose-down elevator deflection" is a long winded way to say the elevators moved in the direction that would push the aircraft into a dive.  It's phrased this way because it isn't always clear from flight data recorders whether this was a commanded (pilot input) movement, or uncommanded.

In either case, the elevators were deflected downward, which pushes the tail up and the nose down, and over a fairly long time (in terms of a crash in progress) the aircraft was nosed down by 49 degrees.


Is it possible for a plane to use cameras and screens instead of a clear windshield? I was just wondering: is it possible to have a commercial plane with no cockpit windshield, just external cameras and video screens?

The question come in my mind after reading the nth occurrence of laser in pilot's eyes. Moreover, a structure without windscreen is surely lighter: when there are not passenger, we avoid to put windows! Which are the limits and the opportunities to this solution?

With "ever" I don't mean "in centuries" but in 30/40 years.

It's entirely possible to do this now, it's simply not a good idea. The drawbacks to safety outweigh the benefits of doing so. If you have no cockpit windows an electrical or systems failure would leave pilots totally blind, without any references whatsoever. The "mark I eyeball" works in a wide variety of conditions and does not require electrical power of any kind. Plus, there's usually 4 of them in the cockpit, and chances are at least one of them will work.


Where are the communications antennas normally located on general aviation aircraft? In the past I have had instructors suggest that I use COM1 in the air and COM2 on the ground. The rationale was that most aircraft have the COM1 antenna on the belly making it favorable for air to ground when in the air and COM2 on the roof making it favorable for ground to ground when on the ground.

It can definitely be helpful to use the top antenna for ground communications and the belly antenna for air.

I frequently fly a late model PA-32 and I haven't found documentation on which communications antenna is which.

I also frequently fly Cessna aircraft which usually have all comms antennas on the roof.

I sometimes fly an SR-22 and my instructor suggested using COM1 on the ground and COM2 in the air. This is reverse from what I thought was usual, but indeed the SR-22 AMM shows that the COM1 antenna is on the roof with COM2 on the belly.

Is there really a rule of thumb here or does it vary so much from one aircraft to another that no rule of thumb is possible to say?

Honestly? That AOPA article overstates the issue of airframe shadowing (at least for light GA singles): Both antennas will usually work fine on the ground, and will probably work without any issues in the air as well.

Airframe shadowing can cause issues, but if it were as big an issue as people like to make of it there would be no aircraft with single-radio installations (because they would either not be able to talk to people on the ground, or not be able to talk to people in the air).
There are plenty of aircraft flying around with only one radio.

If you're concerned about whether your transmissions are readable pick a nice quiet time of the day and ask the tower for a radio check on Com #1, then repeat the process on Com #2. (Because we're talking about AM radio the results of this test are valid for your aircraft's position and heading when you did the test, and in weather conditions similar to those the test was conducted.)

The general rule of thumb is that each radio will be connected to a separate antenna (this is necessary if you want them to work independently). Some avionics shops have a preference of which way they wire things, and I'm sure manufacturers have a standard they use in their shops (either the POH or the maintenance manual for your aircraft MAY tell you what the manufacturer's standard is; it may also be noted on the FAA Form 337 for the avionics installation if one was filed).

I've seen varying combinations of which radio is connected to which antenna ("Single radio - Antenna on top" ; "Single radio - Antenna on bottom" ; "#1 Left Wing, #2 Right Wing" ; "#1 Top-Front, #2 Top-Rear", "#1 Top/Ground, #2 Bottom/Air" ; "#1 Bottom/Air, #2 Top/Ground").


What is the call sign for the US president's private helicopter? The Air Force VC-25's are Air Force One, Marine aircraft are Marine 1, a private jet is Executive 1. What about when the president is using one a private helicopter?

The callsign of a civil aircraft transporting the President of the USA is Executive One, as you already mentioned yourself. An aircraft owned by a corporation which happens to share the name of the president is not any different. (According to a comment by Dan Sheppard, Vice President Nelson Rockefeller used his personal plane, whose callsign was Executive Two – this would be the closest thing to the situation you ask about that has actually happened.)

However, as was already mentioned in another answer, it is highly unlikely in this day and age that the Secret Service would allow transporting the President on anything other than one of the VC-25s, VH-60Ns, SH-3s, or "The Beast", publicity stunts such as George W. Bushs flight with the Lockheed US-3A notwithstanding. Note that this was the only time so far that the callsign Navy One was used, which tells you something about how often something like this (POTUS using an aircraft other than one of the VC-25s, VH-60Ns, or SH-3s) happens.


Why has the folding wing option of the Boeing 777 never been ordered? The Boeing 777 has an optional folding wing mechanism to fit into tighter spaces, but it has never been ordered by airlines, according to Wikipedia. Why is this option so unpopular?

Now with the Boeing 777X, Boeing is again offering a smaller, less complex wing folding option. Has this been ordered, and are other airliner models planned to incorporate folding wingtips?

The folding wingtips are found mostly in naval aviation. The reason is the space constraint inside the hangar of the aircraft carrier.

"US Navy 070128-N-9712C-003 Aircraft fill the hanger bays on board USS Ronald Reagan (CVN 76) after recently embarking Carrier Air Wing One Four (CVW- 14)" by U.S. Navy Photo by Mass Communication Specialist 2nd Class John P. Curtis.

As can be seen from the photo, folding the wings offers the only practical way of fitting fighter aircraft inside the cramped hangar space. For example, the F/A-18C/D had a wing span of 11.43m; this was reduced to 8.38m with the wings folded, a 26% reduction.

However, the price to pay is an increase in complexity, weight, price and increased maintenance. The figure shows the wing folding mechanism of a F 18.

Source:polepositionimagery.com.au

The major drawbacks of folding wings are,

The increased weight and complexity due to the folding mechanism. The folding mechanism takes time to operate and there are safety concerns if they get stuck in a position.
The folding of wings limits the fuel capacity and as a result, the range of the aircraft, as fuel is usually not carried on the folding part of the wings.

Source: zarco-macross.wikidot.com

As can be seen, the F/A doesn't carry fuel in the folding part of the wing. In fact, after the airlines didn't take up its folding concept in 777, Boeing added fuel tanks to that area and increased range of the 777-200/300.

There has previously been no reason for airliners to fold their wings, as airports offered enough space for operations and ground movement. However, as the size of aircraft and their aspect ratios grow (to reduce drag), designers are finding it more and more difficult to keep the wingspan below the 80m 'box' which airlines believe is the maximum they can cope up economically.

The first major program to be affected by this limitation was the A380, which limited the wingspan of the aircraft to less than 80m and reduced its aspect ratio.

"Giant planes comparison" by Clem Tillier (clem AT tillier.net) - Original Work. Licensed under CC BY-SA 2.5 via Commons.

Basically, Boeing is facing the same problem. The proposed 777x is the largest-wingspan aircraft Boeing has ever produced. However, in the case of the A380, Airbus managed to reduce induced drag through the use of wingtip fences, among other design decisions. The 777x is expected to have a raked wingtip, which is not as space effective as the wingtip fence.

Source: Flightglobal.com

As a result, Boeing is considering folding wingtips. However, there are important differences between the original plan in 777 and the proposed plan in 777x.

In the original plan, Boeing proposed to fold 21' of the wingtip. However,the new plans call for folding only 10'.

Original Wing folding plan in Boeing 777. Source:www.seattletimes.com

Image:Boeing

As can be seen from the figure, the folding plan is much more modest. This is not expected to have the drawbacks associated with the the original plan, as,

The end of the wing will not house controls.
As the size of the wing to be folded is smaller, the folding mechanism will not be as heavy and complicated.
That part probably will not carry fuel.
Advances in actuation systems since the original 777 will reduce the weight penalty.

To put things into perspective, the 747-400's winglets were 6' feet tall.

Airlines have already placed orders for 777x and it is their operational record that will determine if other aviation manufacturers (Airbus, that is.) will follow suit.


Do airlines black-list certain movies on their inflight entertainment system? Do airlines trust the common sense of the responsible employee, when it comes down to NOT making certain movies available?

Besides excluding movies not appropriate for minors, are movies like United 93, Snakes on a plane or Alive officially a no-no?

Otherwise, without an official directive against these movies, aren't airlines risking a blunder and sparking an Internet storm?

The specific policies relating to in-flight entertainment are a matter for individual airlines. They will tailor content to the demographic of their typical passengers.

Air crashes and similar themes are almost universally avoided, but there are significant regional differences leading to films being more or less heavily censored, or simply not offered.

For example - airlines based in Muslim countries will censor references to pork and pork products, either by deleting the scenes, or editing the dialog, or both.

Europeans are tolerant of some nudity, but dislike excessive violence, while the Middle East will censor all sexual language and bare skin, but permit a much higher level of blood and gore.

Other, lower-level censorship may also occur. Logos of competing airlines can be pixelated or deleted.

This is important to airlines. In February 2013 a United Airlines flight was diverted because of a 'passenger incident' originating when parents complained about 'inappropriate content' for their young children (http://www.telegraph.co.uk/travel/travelnews/9973766/Sexually-explicit-in-flight-film-causes-plane-diversion.html)

Much of this information was sourced from CNN. Apply your own judgement when assessing the veracity of such a source.


What effects to controllability are there when the rear doors are opened on a KC-130? Many years ago, I was part of a LRRP drop taking photos from inside a KC-130 aircraft. The rear doors are (relatively speaking) huge. The top half pivots up and into the craft, while the bottom half descends down and (I assume) into the airstream.

When the main doors are opened like that, how does that affect the stability and controllability of the airplane? Would the pilot have to trim down or up, or do nothing?

While my personal experience is that plane, I wonder of any plane that opens large portals into the airstream.

Answer based on information found on-line. Related documentation:

USAF C-130 Operations Procedures
C-130T Flight Manual
Lockheed News Service, 1957
KC-130 Specifications
KC-130J Specifications
C-130 HALO Practices

C-130J Hercules
Source: Flight Global

The KC-130 Hercules is the tanker variant of the C-130 Hercules. The cargo opening consists of a door, and a ramp which can be operated separately.

The door is opened by rotating up and inwards the top panel.
The ramp is opened by rotating down and outwards the lower panel

Source: CQ Planes Spotting

KC-130 / C-130 have a good maneuverability at low speed.

From the the C-130 flight manual:

Door and loading ramp are operated at a speed of 150 KIAS, with flaps down at 50%.
Same conditions for flying with door and/or loading ramp open.

Low speed adjustments:

Reducing speed from 300 kt to 150 kt requires nose up trimming.
The center of gravity may be adjusted by ballasting fuel in the tanks (refueling tank and aircraft tanks).

Opening the ramp will change the aerodynamic shape of the aircraft:

The ramp will not be moved past the horizontal position (only need for full down position is to load cargo on the ground).
Moves the nose down.
Balanced by some trim accordingly.

If loads are dropped (pallets, paratroopers) or fuel is delivered, the center of gravity will roll back, with a significant nose-down tendency, and trimming will be required.

Opening the door will be less of an issue as seen on the image below:

The aircraft is near level.

Above: KC-130J Hercules (source: Military.com).
Note that the attitude is not so far from level, in spite the door is open.


How did the gyro gunsights of WW2 get the range and lead of a target? I just read this article on the gyro gunsight, but I don't understand how it computed range/position to the target and then calculated how much lead is needed.

Surely it must have had radar to get range to the target? But I could only find one mention of radar in the article, and it only pertained to one particular model of the gyro gunsight. Even if so, I don't understand how a radar return is integrated with a gyro instrument.

I understand that a gyro can tell you your roll angle and rate of turn in any or all axes, but the main thing I'm missing is how did it know range and position of the target? It seems only radar can do such a thing and I don't know how radar data could be integrated with a gyro way back in the 1940's. The wiki article even says that these gyro gunsights were developed "just before the Second World War". But I also noticed the article is not that well-cited.

You are seriously over estimating the technical capabilities of the time.

The gun-sight is not much more than an intricate slide-rule. You had to feed it information about the target size/aircraft type and it used the gyro information from your own aircrafts turn rates to project a reticule circle on the glass.

The position of the projection is offset from the guns aiming point according to the gyro factors, the set range, and the fall rate of the ammo. When the reticule circle lines up with the wingtips of the target you are at the right distance and angle to the target and you push the trigger.

It assumes you are following the same flight pattern as the aircraft in front of you. That is.. chasing it in a dog fight. That makes it fairly limited in use and effectiveness and would be no replacement for a seasoned pilot.

Additional Reference Links:

Aviators Database

Axis History Forum

Video: Gyro Gunsight Mk IID

CORRECTION:

Upon watching the video it is apparent that the implication that the aircraft must be following the same flight pattern as the target is misleading. In reality the target reticule, and in effect the pilot's aircraft, needs to be turning at a rate to track the target's flight pattern. Further, the range can be adjusted while continuing to track the target. That all sounds a bit like rubbing your head while patting your tummy and I am sure took quite a bit of practice and an accommodating target that maintained a constant heading or turn rate in front of you.


Did Solar Impulse flight in commercial airspace and have kind of type 23 certification? I read that the amazing Solar Impulse back in 2015 had circulated around the globe for 500 hours. It flew with speed 70 km/h and altitude of cruising 28000 ft. My questions are below

Did it fly in the commercial airspace? if yes then did it have kind of type 23 certification for small aircraft?
I have searched about the system of it such as flight control system and autoflight, but found nothing. What kind of the system was used in solar impulse? Did it have typical system with small aircraft such as Dassault Falcon or Pilatus?
Maybe anyone has detailed information related to solar impulse system such as flight control, autoflight, etc?

Thank you

To answer the question presented in the title, I looked to Wikipedia for details on the flight(s) of Solar Impulse. According to Wikipedia, Solar Impulse 2 (HB-SIB) circumnavigated the Earth’s Northern Hemisphere in 17 legs/flights. Of those 17 legs, 14 legs had maximum altitudes above 18,000 feet MSL. In the U.S., Class A airspace is between 18,000 and 60,000 feet MSL. It is not considered “commercial” airspace. It is accessible to any aircraft with a Mode C transponder and ADS-b, including experimental aircraft. And, even this requirement can be waived with prior approval.

  91.135 Operations in Class A airspace.

  Except as provided in paragraph (d) of this section, each person operating an aircraft in Class A airspace must conduct that operation under instrument flight rules (IFR) and in compliance with the following:

  (a) Clearance. Operations may be conducted only under an ATC clearance received prior to entering the airspace.

  (b) Communications. Unless otherwise authorized by ATC, each aircraft operating in Class A airspace must be equipped with a two-way radio capable of communicating with ATC on a frequency assigned by ATC. Each pilot must maintain two-way radio communications with ATC while operating in Class A airspace.

  (c) Equipment requirements. Unless otherwise authorized by ATC, no person may operate an aircraft within Class A airspace unless that aircraft is equipped with the applicable equipment specified in §91.215, and after January 1, 2020, §91.225.

  (d) ATC authorizations. An operator may deviate from any provision of this section under the provisions of an ATC authorization issued by the ATC facility having jurisdiction of the airspace concerned. In the case of an inoperative transponder, ATC may immediately approve an operation within a Class A airspace area allowing flight to continue, if desired, to the airport of ultimate destination, including any intermediate stops, or to proceed to a place where suitable repairs can be made, or both. Requests for deviation from any provision of this section must be submitted in writing, at least 4 days before the proposed operation. ATC may authorize a deviation on a continuing basis or for an individual flight.

For further details about the aircraft, it’s custom autopilot and flight controls, and the actual flight Itself, visit https://aroundtheworld.solarimpulse.com/adventure .


What's the point of using T-38 to instill flight proficiency in Space Shuttle pilots? As discussed in this Q&A, NASA pilots had to fly 15 hours a month on T-38 to maintain flight proficiency.

NASA Dryden's T-38 Talon trainer jet in flight over the main base complex at Edwards Air Force Base. Source

As a newbie, this seems rather weird - from all little I know about the Shuttle, its flying characteristics in no way resemble T-38.

So why use T-38? (or any normal jet at all)?

What the T-38 airplane provides NASA is currency and proficiency in high performance aircraft operations in a jet which has many of the same characteristics as the shuttle in this respect ie high wing loading, high approach and landing speeds, similar glide descent ratios.  The White Rocket is a temperamental and challenging little jet to land and will not tolerate sloppiness from her flight crew here.  She requires the pilot to stay well ahead of it while making an approach, plan out and execute small corrections very precisely while maintaining airspeed, glide path and angle of attack.  Maintaining good proficiency in these aspects of high performance aircraft flight and keeping sharp on that high speed mindset comes in handy in an astronaut's line of work.

And T-38s make excellent chase aircraft, capable of keeping up with the shuttle during the final phases of its descent and approach, and can provide an extra set of Mk 01 eyeballs to verify external functioning of systems, eg landing gear, speedbrakes, hydraulic leaks, etc.

Actually, outside of the shuttle sims, landing approach practice was done in a modified Gulfstream II which included a replica of the shuttle flight deck for the left seat guy.  It apparently was remarkably similar to the shuttle in a deadstick landing.


Do any aircraft carry boats? A small boat could be part of general cargo, but that would typically just mean it's unloaded at an airport and transported to the nearest body of water by land infrastructure. This is not what I'm looking for.

Instead, is there any aircraft that can directly deploy a boat to (or retrieve one from) water?

I would imagine there are cases when moving a boat by plane could be useful, especially when there's little or no infrastructure available on land.

Does such an aircraft exist?

Yes. During and after WW2 several aircraft were converted to serve as "Dumbo" aircraft, dropping boats or rafts near people in distress. Other models were used as well, but the B-17 were among the most prominent. Most were retired when the helicopter gradually took over rescue operations.


If the "Fuel Shutoff Valve" is ON, wouldn't fuel be cut off? Ok, so this may be more of an english lanugage question, and I can confirm from context that when the fuel shutoff valve is ON fuel does indeed flow to the engine, but wouldn't that just make more sense to call that valve the fuel valve?

If the component that shuts fuel off is on, operational, in use, functioning, etc., shouln't fuel be shut off, as the name implies?

I realize this could be seen as a quibble, but confusion causes accidents and IMO this is wildly confusing.

EDIT

Looking at the Cessna 152 checklist today I noticed this interesting quirk. On the regular checklist side (pre-takeoff, maneuver, etc.) the checklist reads "Fuel Shuttof Valve - ON", but on the emergency checklist for an engine fire it merely states "Fuel Valve - OFF".

I can see where that can be confusing, but it comes down to perspective.

From a maintenance and engineering perspective, you are actuating the fuel shutoff valve which controls the fuel to the engine.  The actual terminology when referring specifically to the valve would be opened or closed, which would result in the fuel being on or off.

From a pilot perspective you are simply turning the fuel selector on and off, which happens to be connected to the fuel shutoff valve.  The pilot doesn't even need to know about the valve, so they placard it from the operational perspective in the cockpit and say whether the fuel is on or off.

Note that these are placarded as a fuel selector and fuel off both of which seem pretty clear to me.


What is an easy format for giving pilot reports? Is there a technique anyone has to make it easier to give PIREPs (mnemonics, etc?)  I'd like to be able to give them while I fly but I can never find the expected format handy, so it ends up being a hassle.  If there's a trick anyone has to make it easy to give one, please share!

Who you are:
Cherokee 1234A, a P28A
Where you are:
10 miles north of La Belle VOR, altitude 6000 feet
Build your own "METAR":
Five minutes ago (time) wind aloft 230 @ 24 (wind) imc (visibility) medium turbulence (weather phenomena) broken clouds at my altitude, clear below (cloud cover) temperature 10 degrees (temperature)

That's it!
There might be a way to exactly meet the form the controller needs to write it down, but this works fine and you have a fluent and well structured report.


How does climb-rate vary with density/pressure altitude? I'm seeking to write a little web or phone app which can help me choose the best cruising altitude based upon winds aloft. I know Garmin Pilot (and probably Foreflight) have a cruising altitude selector, but they don't seem to take into account the extra time/fuel required to get to the higher altitudes. I'm looking to make a calculator which factors that in.

I realize that the actual formulae for climb-rate, take-off distance, landing distance, etc are quite complex, but I don't need to generate them from scratch. What I plan to do is start with the charts in the performance section of the POH for a particular aircraft...

...and find some known values for climb-rate for given pressures/temps/weights and use curve-fitting to come up with simple formulae which are still within a few percent of what I would get with these charts.

Of course, to be as accurate as possible, it would be better to know, roughly, how climb-rate varies with pressure-altitude, density-altitude, weight, etc. Some of the adjustments (eg. for weight) seem to be fairly linear (at least over the domain of values of interest to us), while some others seem to have some curve... so maybe they vary as $b^{-x}$, $\frac{1}{x}$, $x^2$, $log(x)$...?

Does anybody know the general way in which climb-rate varies with these factors? (Bonus round: can you do the same for take-off and landing distances, in case I wanted to make a calculator for those?)

For propeller aircraft, the climb rate is a function of

available power
demanded power
weight
air density
wing lift

Five variables, and wing lift is itself a function of Mach number, Reynolds number, wing AoA, wing area. Available power is a function of air density, throttle setting, propeller incidence - demanded power a function of air speed, air density, angle of attack, Mach & Reynolds numbers. So in total a very large matrix of independent variables - in order to find equations via an analysis, we'll have to make some assumptions and simplifications. For instance that the aircraft thrust vector stays reasonably horizontal so that $T \cdot sin(\Gamma)$ is close to zero and can be disregarded. Also, that lift = weight during the climb.

For the steady climb, the weight equation then becomes $$W = C_L \cdot \frac{1}{2} \rho V^2 \cdot S \Rightarrow V = \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{1}{C_L}} \tag{1}$$

For the drag in horizontal flight:

$$ D_h = C_D \cdot \frac{1}{2}\rho V^2 \cdot S = \frac{C_D}{C_L} \cdot W \tag{2}$$

and the required power in horizontal flight $(P_r)_h$ becomes:

$$ (P_r)_h = D_h \cdot V = W \cdot \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} \tag{3}$$

The power required to maintain climb speed $C$ is $W \cdot C$ and available power $P_a = (P_r)_h + W \cdot C$, hence:

$$ C = \frac{P_a - (P_r)_h}{W} = \frac{P_C}{W} \tag{4}$$
Combine (3) and (4):

$$ C = \frac{P_a - (P_r)_h}{W} = \frac{P_a}{W} - \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} = \frac{\eta \cdot P_{br}}{W} - \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} \tag{5}$$

Above picture shows a graph of $P_{br}$ of the P&W Wasp: function of manifold pressure and altitude. This engine had a turbo-charger for improved altitude performance, the engines of GA aircraft may not have these. Plots of variable pitch propellers show a propeller efficiency $\eta$ of about 0.8.

How this ties into the graph shown in OP:

The equations feature air density $\rho$. This is a function of static pressure and of temperature: an equation to convert to static pressure and vice versa can be found here.
Available power for a normally aspirated piston engine decreases as a function of altitude, approximately according to $\frac{({P_{br}})_h}{({P_{br}})_o} = (1 + c) \frac{\rho_h}{\rho_o}$. Tests on some American piston engines showed that for many of them a value of $C$ = 0.132 would be appropriate, refer to figure below which also shows the altitude-power function of a piston engine with supercharger.

All references and pictures from a university lecture book, paper copy only.


Is it possible to perform a spin recovery in IMC? In other words, after some training, is it possible to recovery a spin solely by relying on instruments?

If using a vacuum-pump traditional attitude indicator, I assume the answer is no, since there are limitations for its pitch and bank indication. What about an AHRS-based attitude indicator? Is it capable of matching 360° attitude changes in all directions, and catching up (without delay) with fast rolls? Can it filter out vibration well enough, so that a pilot is able to perform a spin recovery maneuver?

I do not want to speak for civilian training here, and I do know that each aircraft has its own set of emergency procedures. Those procedures will depend upon the instrumentation that you have available to you. In my case I had full IFR instrumentation with a state of the art inertial navigation system. Spin recovery should be in the set of immediate action emergency procedures that you have memorized, and you should be able to perform them in your sleep. Can you recover from a spin while in IMC? Most definitely, and I speak from experience.

I flew high performance tactical jets for the US Navy. This included the T2, the A4, and the A7E. We only did spin recovery training in the T2. It was a lot of fun. High performance jets are often flying on the edge of their performance envelope. Consider air combat maneuvering where you can easily find yourself in uncontrolled flight, departing the aircraft in a high-g turn, or even nose high at 0 airspeed. I was told it was quite difficult to spin the A7E, which is what I flew in the fleet.

In the Navy we were trained never to look out the cockpit if we thought we were in a spin. There was unusual attitude recovery training under the hood, as well as learning how to recover from departed flight (approach turn stall), and spins. It was drilled into us from day one to come in to your instruments for spin recovery. It would not have mattered to me whether I was IFR or VFR, the decision on recovery was strictly based on instruments. We were told if you look outside the cockpit during a spin you might misinterpret the visual cues, and while not actually in a spin, place the aircraft in one by applying spin recovery techniques. The procedures were something like:

Altitude: below 10,000 feet eject
Angle of attack: oscillating above 23 units of attack
Airspeed: oscillating between 110-140 knots
Turn needle: pegged
All four conditions met: apply spin recovery procedures

I flew over 30 years ago and I still remember these procedures. You might enjoy how I came to appreciate the seriousness of spin recovery. I had a decorated Skipper who had flown all through Vietnam in the A4 as an attack pilot. He stood up one day in the ready room and told us young'uns, "I don't care what you do out there, just make sure you brief it before you do it. Too many of us die because we impulsively decide to do something without thinking it through completely. Know your emergency procedures."

One night I was out at 25,000 feet tooling around after completing my mission, waiting to recover at the ship. A bit bored I had the thought, "I do loops in the simulator where it is blacker then this back home all the time. I have plenty of altitude to get the airspeed I need ... Why not?" And down I went. Unloading the aircraft to negative 1 or 2 G's I picked up airspeed well above what I needed and started pulling back up into the loop. It was dark out, no moon, with a solid cloud layer at 5,000 feet. I remember having an uncomfortable, anxious feeling at some point. Something wasn't right. I started paying attention. It was quiet. There wasn't the usual engine and wind noise! I came into the cockpit and the first thing that caught my eye was the full white of my rather large attitude indicator located in the middle of the instrument cluster. I had relaxed back pressure on the stick at some point. Oh my God. Not what you wanted to see in an A7: nose pointed straight up. Quickly glanced at my airspeed indicator to the left and watched it drop like a rock to the peg at 0 knots. Then the aircraft dropped backwards pushing the tail, and then entering a roll. I was along for the ride though. I wasn't thinking. I wasn't present. Spin recovery didn't enter my thoughts. Never checked my altitude. The aircraft dropped like a leaf for a bit and then settled in a descending roll. I put in opposite aileron and came out of it. Whew! Of course my gyros were toast and the inertial navigation system useless. I ended up coming through the solid overcast and doing my instrument approach to the ship on pressure instruments. I always followed my Skippers advice after that.

Eventually we came ashore and I found myself doing regular emergency procedure training in our simulators. Towards the end of one of these sessions I decided to practice spin recovery. I knew we couldn't get the simulator into a spin, but I thought it might be useful nonetheless. So every time I got to the simulator I made sure I practiced.

The next time I found myself at sea I had finished my flight, and was getting together with a section to practice air combat maneuvering: 1-v-2. We had agreed to meet at a point over the ocean, at a given time, with an altitude separation between flights. I had everything below 15,000 with 5,000 as the hard deck. they had 16,000 an above. You could get there early, or late depending on how you wanted to try to set up the fight. Eventually we set up radio comms. The rule was that we had to talk to one another until one of the flights had gained sight and could then maintain separation.

As I came in to the fight I decided to make a gamble. I unloaded the aircraft with 2 negative G's and descended quick to 5,000 feet. They wouldn't be looking for me that low and so I would be outside their scan for bogies. The top of my aircraft was painted this dull off gray and it blended in with the haze and blue-gray of the ocean underneath. The sky above was clear blue. The tactic payed off and I saw the flight at around 18,000 feet. They knew they were in trouble when I stopped answering their radio calls. I pulled up into an Immellman, but had bled off a lot of airspeed from the dive as I was level at 5,000 feet in the denser atmosphere. As I got to 18,000 feet I was directly behind the two airplanes and I saw my airspeed hit the peg. I quickly called 2 Aim-9 missile shots to win the fight. Then on my back at zero airspeed the automatic flight control kicked the rudder inadvertently, and the A7 entered a spin. How do I know? Well, the AOA was above 23, the airspeed was between 110-140, and the turn indicator was pegged. It was second nature and I was in full control of the situation. As I was assessing the situation I got a call from the other flight lead asking, "Hey where are you?" I replied calmly, "I am a bit busy hold on ..." After recovering from the spin we headed home.