What margin of error should one reasonably allow regarding aircraft performance? This question generated a lot of discussion around amateur pilots often making the mistake of calculating aircraft performance based on perfect conditions and not allowing for a 'safety factor' (i.e. they flew with the maximum possible payload and the passengers had not been honest or accurate about their weight).

The issue, as one commentator stated is that

  That’s fine assuming EVERYTHING works out just like the book ie no errors in calculating performance, aircraft and engine in peak condition, field atmospherics, perfect short field takeoff technique, etc.

So, what would be a more sensible approach to calculating aircraft performance and what margin for error should be allowed? This applies to all calculations, payload, runway length, (passenger weight!), airspeed etc. Instinctively I would guess 10% would be fine, but I don't know what I'm talking about :)

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

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

So given all of that, what are the margins?

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

Range in VMC conditions, non-sparse areas 30%

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

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

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

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

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

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

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

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

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

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

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


What does the NetJets "QS" stand for? Every NetJets aircraft that I've seen has a tail number ending in QS. Knowing aircraft operators, I'm sure it stands for something, but I don't know what.

What does the QS stand for in NetJets tail numbers?

The "QS" first stood for quarter share, according to the 1998 issue of Flying. Each aircraft will have multiple owners to help bring the cost down for the owner.


Pros and cons of a thin cambered wing? What are the pros and cons of a thin cambered wing?

Does a thin cambered wing suffer from a flow separation bubble on the lower side, at cruising speed/low AoA?

Very roundy leading edge, can air fill hole behind this,is flow attached at lower surface behind leading edge,during crusing flight/low AoA?

As that beautiful (but rather heavy) Andean condor, Vultur gryphus, is showing, this is the go to wing for maximum lift at the slowest possible airspeed.  Not quite as efficient as the high aspect albatross, but much slower.  These wings are all about combining slightly less efficient bottom lift with more efficient (air bending) top lift.  Perfect for catching thermals and riding them to higher altitudes.
The major con is they are so good at making lift that an increase in airspeed can create surplus lift.  Lowering AOA then creates major turbulence underneath the wing, as you surmised.  Now imagine bringing the leading and trailing edges up, making a thin flat wing.
This is exactly what airliners do when they want to go 3x faster.  Condors need not worry about this.
Thin wings also lack structural strength.  This becomes a major issue with scale.  Early air craft replaced these wings with solid thick wings as size and speed increased, but camber remains a valuable tool today to help slow an approaching aircraft to a safe landing speed.


Is communication with cabin crew or ATC included in emergency checklists? In a serious but non-catastrophic situation on a commercial flight (for example, a single engine failure on an A320), I understand that the pilots will follow a standard checklist (from the QRH) to put the aircraft into a safe condition.

My question is - will such a checklist generally include an explicit item to inform ATC, the cabin crew, and/or the passengers, or is this generally assumed to be done as a "standard procedure"?  If it is usually on the checklist, would it always come at the end, or are there situations where ATC might need to know about the incident as soon as possible?

In the case of A320, yes it does. Here’s an example of the emergency procedure for ditching. Note there are four instances where it tells the pilot to communicate with the cabin.


What is the A350's procedure for stained cockpit windows? Recently I read of this Ethiopian B737 incident at Dire Dawa on Jan 9th 2020. The aircraft flew through a swarm of locusts, which didn't cause any significant damage, but it rendered the cockpit windows completely opaque. So it clearly can happen.

Now on most aircraft, including B737 from that incident, the cockpit side windows can be opened and provide enough forward visibility to land the airplane from basically any available instrument approach.

However, A350 does not have any opening window that could be used, and Cat IIIB approaches that can be executed without any visibility are much rarer than just any instrument approach, so none may be available in range.

So what would the pilots do?

I am not sure if this applies to modern jets, but pilots of the past were sometimes landing "sideways" by using https://en.wikipedia.org/wiki/Slip_(aerodynamics). That provided some view from the side window.

I believe one example of that could be found in "Fate is the Hunter" by Ernest Gann.

Also general aviation pilots sometimes use this technique if the windshield is iced over.


Why are dirt and bugs on an aircraft so bad? It's noted in many POHs to keep your aircraft clean all the time, but is there a reason to this?  Dirt hardly add any sort of weight to the aircraft, bugs are extremely small and other things such as cars easily move even when dirty as a mud pig.

Does having dirt or bugs on your aircraft seriously affect the structure or performance signficantly?
If so, why?

For (modern) gliders with highly optimized laminar flow airfoils, bugs (or dirt) are a non-negligible factor, especially in competition gliding. There are some older laminar airfoils that are notoriously allergic to bugs (and rain), but all are to a certain degree. This is also the reason why any glider pilot worth his or her salt will painstakingly clean their ship each afternoon and before each competition flight.

Sufficient bugs will degrade your performance by a noticeable amount - most gliding computers even have a special "bug" factor to include that into glide path calculation (even though the measuring and correllation of that is quite subjective). I´ve had a few flights in somewhat biblically bug-infested conditions (summer, hot, low thermals) that more or less painted the leading edge black (like in this picture from an article on the DG Flugzeugbau website).

Bug wipers are quite common on high-end and competition gliders and can be found e.g. at http://www.storka.at/. Or try to google for "Mückenputzer". Of course bug wipers are not without drawbacks (concerning cost, installation, ease of use, drag etc.). A friend of mine once stuck a banana peel on his wing and tried to remove that with the wiper, resulting in banana and wiper being stuck in the middle of the wing. It took some creative maneuvers to clear that mess, by which time probably a lifetime aerodynamic benefit of cleaning had been spent.

As for the comparison with cars, their aerodynamics differ in a lot of ways. In comparison to a wing there is no laminar flow to talk of at higher speeds (most of it is turbulent), which drastically reduces the influence of the surface smoothness on the drag produced.


Are test pilots certified to fly all aircraft types? I just saw an hour long MIT lecture for no reason and the lecturer said he has flown over 70 kinds of aircraft.
Does that mean a test pilot is certified to fly almost anything?

Since you didn’t specify a jurisdiction, I’ll answer for the FAA. Others should be similar.
Pilots must be rated for the category, class and (if applicable) type of aircraft. Category is pretty broad, such as “Airplane”. Class is a bit more specific, such as “Multi-Engine Land”. Type is even more specific, such as “Boeing 737”.
A type rating is required for any type that:

has a Maximum Takeoff Weight (MTOW) of 12,500 pounds or greater, or
has one or more turbojet engines, or
has been designated by the FAA.

There is no limit to the number of ratings a pilot can have, aside from the time, money and skill required to pass a checkride for each one. However, type ratings are only available for certified aircraft.
For experimental (non-certified) aircraft, since no type ratings exist, the FAA can issue a Letter Of Authorization (LOA), which waives the type rating requirement for specific pilots in a specific plane for specific purposes, such as flight testing, training or demonstration.


Is a smartphone required to control a DJI Phantom 2 Vision+? Not sure if this is on-topic here, as the official guidance seems a bit vague.

Anyways, I've got a relatively simple question.  I'm considering purchasing a Phantom 2 Vision+, but am a little unclear about what options there are in terms of controlling it.  Their website makes a big deal about being able to set waypoints (using an iPad/mobile app) and have the quadcopter operate as an autonomous drone.  And that's useful for certain things, but it seems like it would be more fun to control it directly by remote.

Judging from the video here, it does appear that the quadcopter ships with a remote.  But it also looks like you're expected to stick an iPhone/smartphone onto the remote?  Is that a requirement or just an optional extra?

Is it possible to fly the quadcopter without using a smartphone/mobile app (using just what's included in the box)?

I'm pretty sure it works without the smart phone. If I understand correctly, the smart phone app simply relays the imagery from the camera, which can be useful for navigating especially if you do not have a clear line of sight.

Ars Technica ran a piece on this very model, which might interest you.


Aerodrome actual weather - METAR decode - 3 letters for this sky? How can I describe this sky, in 3 letters as per the Aerodrome actual weather - METAR  decode?

I found online a comprehensive list of Metar codes

This work sheet may be of use and generally the system of Okta is used to denote coverage in a Metar, but I would say

  L1 Clouds: Cumulus (Cu) with little vertical extent

but it could also be

  L5 Clouds: Stratocumulus (Sc) not from spreading out of Cumulus (Cu)

But I will agree with Ron on this one, its BKN (5-6 Okta based on the picture in my opinion)


Airplane longitudinal control: pitch or power? I recently came across some slides from a flight school teaching, for the initial climb after take-off and for the approach, the strategy of controlling/adjusting

  RoC/RoD with power

  Speed with attitude

I tried to inform myself a bit on the subject, because I am more familiar with the idea of controlling

  RoC/RoD with attitude

  Speed with power

I came to understand that this is mostly a difference between VFR vs IFR flight.
Is this true?
Does the first approach actually have benefits in terms of ability for the pilot to control the plane in VFR flight? If yes, how and which?

I was wondering how long that it would take for this question to come up.

It is the old "pitch -vs- power" airspeed control technique debate that rages throughout the aviation world.  There are strong proponents of both techniques (and they seem to view it almost as a religious debate in that the other side can never be right, no matter what), and both sides have good reasons for it!

Instead of saying that one is better than the other, let's just say that they are both techniques for managing the potential energy of the airplane (the airspeed that can be traded for altitude and vice-versa).  In fact, this is how I like to think about it (and don't pick a side):

If you change the pitch of the aircraft without changing power, the airspeed will stabilize out at a new value.

Pitch up and you lower the airspeed.
Pitch down and you raise the airspeed.

If you change the power setting of the aircraft without changing the pitch, the airspeed will stabilize out at a new value.

Add power and you raise the airspeed.
Reduce power and you lower the airspeed.

You can change both at the same time and get various results.

You can end up with the same airspeed that you had before.
You can end up with a lot more airspeed.
You can end up with a lot less airspeed.

Most often you need to change both at the same time in order to properly manage your airspeed.

So basically it comes down to what you want to accomplish.  If you need to change the airspeed you have two ways to do it, but used individually each comes with a side-effect.  In some situations this may be okay or even desirable, but you need to be aware of what your actions are going to accomplish.

Let's look at a specific example:

Sometimes, especially on an instrument approach, you want to maintain your current airspeed while changing your vertical speed.

Let's say that you are a little high on the glideslope.

If you simply pitch down to recapture the glideslope, you will gain airspeed but will recapture it quickly.
If you simply reduce the power to recapture the glideslope, you will lose airspeed but it will take longer than using pitch.
If you want to maintain your airspeed while recapturing the glideslope (typical on an instrument approach) then you would pitch down and reduce power at the same time, and when you recapture the glideslope you will pitch back up to maintain it and add power to maintain your current airspeed.


How does the relative wind on a propeller, strike the blade from behind (the non camber side)? This may be a stupid or simple question, although any help is appreciated! :)

If possible, please answer without mathematical terminology. So I understand the concept of the blade increasing air momentum at the front, thus creating lower pressure, and I also get that the blade acts as an airfoil, lower pressure at the top, and higher at the bottom thus pulling it forward, and producing thrust.

My main issue is that I can't visualize how the relative wind physically travels behind the camber side, and hit the back side of the airfoil like in the diagram? Wouldn't it hit directly on the camber side if it's moving forward, not travel below, and strike it from the back? If someone can explain, that would be amazing!

Plane moving forward plus blade moving down gives us a combined velocity vector, shown above in red.

Relative air(speed) is still coming from ahead—but this now no longer concerns the propeller as it has its own velocity vector.

Tilt your head (or check right image to avoid neck injury) and you'll see the blade's angle-of-attack. Remember, air (shown above in light blue) comes in from the direction opposite to the velocity vector.

Increase forward speed, velocity vector changes, angle-of-attack is now smaller, but the airfoil is also faster.


Why is an auditory alarm necessary when the autopilot disengages? The FAA gives one requirement for the autopilot in the following FAR...

  FAR §25.1329 Flight guidance system.

  (j) Following disengagement of the autopilot, a warning (visual
  and auditory) must be provided to each pilot and be timely and distinct from all other cockpit warnings.

Why is an auditory alarm necessary when the autopilot disengages?

Was there a particular accident where the pilots ignored visual warnings?

Yes, there have been several accidents caused when the autopilot has been inadvertently or automatically disconnected and the flight crew have failed to realise it happened. Even with the audible alert, it's reasonably common, but experiments in controlled conditions demonstrate that alerts provided in only one medium (just visual, or just auditory) are not reliably noticed in times of high workload.

Here's an interesting accident report I remember reading at the time, where the flight crew apparently failed to notice that they had deliberately disconnected the autopilot. For more on inattentional deafness, see the paper Failure to Detect Critical Auditory Alerts in the Cockpit: Evidence for Inattentional Deafness.


Stability and Control of an aircraft Why is the pitching moment coefficient of an airplane said to be constant about the aerodynamic centre of an aerofoil

Why is the pitching moment coefficient of an airplane said to be constant about the aerodynamic centre of an aerofoil?

Because the phrase "aerodynamic center" is defined as meaning "the point about which the pitching moment coefficient is constant."

That's it, that's the entire answer. If I've misunderstood the question, please let me know.


What is the longest range single-pilot certified (FAA and/or EASA) business jet? I suspect the single-pilot business jet with the longest range is the SyberJet SJ30x:

NBAA IFR Range with 100 nm Alternate
M 0.76 (1 pilot + 2 passengers; passenger/pilot at 90 kg each)
2,575 nmi (4,769 km).

But I am not sure; also, there are many negative reviews regarding SyberJet company and its aircraft of which, by the way, only a dozen have been produced for now. Are there any single-pilot certified jet with longer range in comparison with SyberJet SJ30x?

There aren't any civilian, current-production jets that come close to the range of the SJ30 for single pilot operations based on my research, although one or two turboprops have comparable ranges. I consulted Aviation Week's "Business Airplane's 2012" and the only other light jets listed with a long range are the Embraer Phenom 300 with a range of 1,954 nm, and the Cessna Citation CJ4 with a range of 1,913 nm.  The Cessna CJ3 comes in at a respectable 1,869 nm. The PC-24, which is still undergoing certification in 2016, is listed here with an NBAA range of 1,950 nm. All of these are (or will be) single-pilot certified in at least one cockpit configuration, to my knowledge.

Is there any reason you're restricting this to jets and not turboprops? (Speed is one of the biggest differences between the two categories.) The King Air 350IER has a range of 2,239 nm.  Several other turboprops have ranges that are comparable to average light business jets, like the PC-12 NG which has a  range of 1,544 nm.

Here's a graph of my own making to show these statistics:

For any readers unfamiliar with the restrictions regarding FAA approval for single-pilot operations, here's a good source: http://www.flyingmag.com/single-pilot-jets . The biggest stipulation is that transport category aircraft (12,500+ lb MTOW or not commuter category) are assumed to be two-pilot aircraft.

Note:  all ranges listed here except the PC-24's range are NBAA IFR max fuel ranges w/ 100 nm alternate as listed in Aviation Week's "Business Airplanes 2012"


Why don't commercial jet aircraft have a break-apart, parachute escape system? Imagine that the pilots on a jet aircraft determine that it will crash. Consider what would happen if the design of the craft allowed it to:

Break into four pieces
Each piece is pressurized independently
Each piece is attached to large parachutes, similar to how they bring down Soyuz or other space crafts returning to Earth

Would that not work so that passenger jets are brought down safely instead of crashing?

wouldnt that work for keeping a majority of passenger jets from crashing?

The majority of passenger jets don't crash.

Designing an aircraft like that would incur very substantial weight penalties. The Space Shuttle booster rocket parachutes weight 990kg, each (it needs 3) plus 550 kg for the drogue chute needed to pull out the main canopies. Plus another to pull out the 550kg drogue. Where are you going to put that much nylon?

Then there's regular maintenance of stuff that large and heavy - you will need an entire empty hangar to repack things along with a crew and a crane.

Also consider how you are going to break up a commercial airliner in an orderly manner. It would have to be designed for it and lined with explosives. That's going to be really popular.

Finally, parachutes need time to work. Large parachutes need considerable time. So this whole process only helps if there's a problem in cruise flight, and that's the phase with the lowest accident rate. Parachutes below 1000 feet are just excess weight.

Semi-related Addendum: After Challenger went boom the Space Shuttles were fitted with a crew escape system. It was intended to allow the crew to exit when the craft was under control but unable to reach a survivable landing site. Re-read that carefully: when the craft was under control. The crew exits at reasonable altitudes and the Shuttle crashes under remote control.

Parachutes simply haven't been a viable option for commercial air transportation since the DC-3 era.


What Are These Runway Lights For? I know that the strobe lights that flash in rapid succession of each other indicate the open end of the runway, to help guide pilots in at night. It's obvious the white lights indicating the edges of the runway. And I'm guessing the green lights at one end, indicate the open end, whereas red lights at the other end indicate you are approaching the end of the pavement.

But what are those lights at the ends of runways on (typically red) poles. Typically in large sets with one set on either end? Are these just to help the pilot line up? I would assume the actual runway edges and center lighting would assist with that?

As for what they are you can find that in the answer to the question here. In terms of how they work its an extension of the basic runway lighting system. There is a nice video discussing the various types here but effectively they help guide the pilot to the runway by providing them with an extended way to infer where the centerline is (beyond the runway its self) when making a low visibility approach. The system may also include a decision bar which helps a pilot by having a visual marker at a fixed distance from the threshold. Keep in mind that threshold lights lights count as runway in sight so the extended centerline can help a pilot lineup when they can not see the full length of the runway.

The colors will vary based on what the airport in question is equipped with but green is the runway threshold. Red is typically an area in front of the runway, it could be a displaced threshold or it could be an area off the runway all together. However these lights will appear on both ends of the runway and will be visible when approaching from that direction.

It should be noted that while certain lights are required for certain types of operations, lighting is not explicitly required by the FAA and there are plenty of unlit airports as well as a wide variety of lighting situations out there. The field I fly out of has REIL and 5 lights on each side of the runway which is far less than a class B airport would have but may be far more than your back country grass strip has.


What level of G-force does our body experience when we are traveling in a passenger plane? I have some understanding on g-force. But never come across how much g-force acts on a passenger who is traveling in a plane, especially when taking off.

I can't find solid references, hopefully someone will come along who can.

A 30 degree bank, the most you will normally experience, exerts a force of 1.15g, or 0.15 greater than normal acceleration you feel when motionless.  The autopilot is generally designed to begin descents and climbs with no more than 0.25g and are generally calibrated to manoeuvre in 0.25g increments.  A solid rotate or a firm landing might generate a bit more.

It's reasonable to work on a range of around 0.75 to 1.25gs. Anything more than that would be uncomfortable for many people.  You should only experience g outside that sort of range in heavy or severe turbulence.


Do wingtip vortices really only form when airplane wheels are separated from the ground? My GA theory textbook (which covers fixed wing up to and including EASA PPL) has some suggestions on taking off and landing light aircraft soon after large aircraft (besides avoiding it, if possible), intended to reduce the risk from wingtip vortices. These suggestions are to,

when taking off

...after a heavy aircraft taking off, to lift off at a point on the runway before the heavier aircraft lifted off
...after a heavy aircraft landing, to lift off at a point on the runway later than where the heavier aircraft's nose wheel touched the runway

when landing

...after a heavy aircraft taking off, to land as early as possible on the runway
...after a heavy aircraft landing, to land ahead of the point on the runway where the large aircraft touched down

When I asked about the why of these suggestions, the answer was that wingtip vortices form because the wings are generating lift, and when the aircraft's wheels are on the ground, the wings don't generate (or aren't generating) lift so no wingtip vortices form.

While that might be true in a "rule of thumb" sense, and a good generalization of these rules to serve as a memory aid, I want a bit more than that. The way I understand it,

Any airfoil will generate some amount of lift as long as there is ambient air movement around it; "lift" (as opposed to net positive vertical lift, which isn't being generated when landing anyway because the aircraft is descending) isn't something that suddenly starts being generated when one or more of the aircraft's wheels are separated from the ground
An aircraft can move at significant speed relative to the surrounding air even when all of its wheels are on the ground, causing likewise significant speed of movement of the wings through the ambient air

It appears to me that wingtip vortices should form at any time the aircraft (or rather its wings) is moving relative to the surrounding air; whether that's because the aircraft is standing still and there's a wind, or because there's no ambient air movement and the aircraft is moving, or a combination of the two. It also appears to me that the strength of the vortices should be in some way proportional to the amount of lift being generated.

Consquently, it seems to me that wingtip vortices should form at every point during the takeoff or landing roll (as well as taxiing and other movement on the ground) at which the aircraft is moving relative to the surrounding air, and increase in strength with (but not necessarily linearly with) the indicated airspeed of the aircraft.

It seems weird that the air flowing near the wingtips would somehow "know" anything about the position of the aircraft's wheels with respect to the ground, let alone that of any specific wheel (such as the nose wheel).

All that just as the lead-in to my question: am I missing something, or is this a case of the textbook (and teacher) presenting the simple case so as to not overwhelm students?

You are absolutely right. The vortices form whenever the wings produce lift. Even if the lift is not enough to let the aircraft fly.

Of course it is necessary to have a flow across the wing, and with very low speeds (like taxiing) the vortex is likely to be very small.

But,
it seems your textbook is trying to establish a save way to avoid the vortices of previous aircrafts. And since the strength of the vortex is related to the lift which is related to the air-speed and angle-of-attack this rule of thumb is quite practical. Especially since landing is a highly transient process which is very likely to result in a significant reduction of vortex strength.


Are there risks if the side joystick must be handled with a pilot's weaker hand? Suppose that a first officer were left-handed and a captain were right-handed. Both are NOT ambidextrous. Even after training, what if their weaker hands' control and  degree of versatility
remain worse than their dominant hands'?

In other words, in commercial (and not just military) cockpits, joysticks (on the side) must be grasped with only one hand. But does this fact presuppose or require perfect ambidexterity?

I can't speak for all pilots everywhere, but I've flown both sticks and yokes from both the right and left seat (as well as the front and the back seat in tandem aircraft) and found the adjustment process between switching from right to left hand to be very quick. I found getting used to sight picture differences to be a much bigger challenge and, like many others before me, sideloaded my first few landings (along with climbing/descending during turns) until I got the hang of it.

Other pilots I've spoken to about this have expressed the same feelings; there is a learning curve, but it is by no means insurmountable. At any rate, flying is far more of a mental activity, with masterful physical coordination being surprsingly far down the list of innate qualities a pilot needs.

And no, I am not nearly ambidextrous; in fact, my coordination abilities with my non-dominant hand are hilariously poor, as anyone who's ever watched my try to toss a tennis ball during a serve can attest.


If the Concorde had an engine fail at cruise altitude, would they enter the coffin corner? I know the coffin corner is only meant for subsonic aircraft, but if the Concorde is just cruising at Mach 1 and had an engine failure and also lost that afterburner, would it enter a coffin corner situation?

The Concorde doesn't need reheat to cruise supersonically, just to get there (the range would be pretty short if it did).  If it loses an engine it's not going to put the other 3 into reheat to hold altitude and speed (fuel burn) and it will do what just about all airliners have to do when at they lose an engine, descend to whatever its engine-out service ceiling is.  This is done at some speed near minimum drag that gives the flattest descent, called "driftdown" speed, whatever it is, and it will just pitch down as required to maintain that speed with the available military rating (non-afterburner) thrust. Obviously, it will come out of mach as it does so.

Also I should point out that being a supersonic aircraft, it doesn't really have a "coffin corner" in the normal sense.  That applies to subsonic airplanes that are limited to a speed just shy of Mach, and when they get so high they become hemmed in by stall speed on one side and trans-sonic related issues on the other.  The upper limit of a supersonic airplane's speed is aerodynamic heating related and is a function of the airframe material's ability to run at high temperature, which limits aluminum structures to below Mach 3.  This is why the SR71 is titanium.


Why are most runways laid out in a generally East-West direction? Runways are named by a number between 01 and 36, which is generally the magnetic azimuth of the runway's heading in decadegrees. From what I have read, most airport runways are aligned along an East-West corridor. Why is the North-South direction rarely used?

While there are many exceptions to east-west runways, generally speaking prevailing winds (which blow from a single direction) blow east-west rather than north-south. It happens because of Earth's rotation generates Coriolis effect.

There are other wind patterns besides prevailing winds. Trade winds occur near the equator and flow from either the north or south towards the equator. They curve towards the west due to the spin of the Earth. Polar easterlies blow close to the north and south poles. They blow away from the poles and curve east to west.

Hence, most of the runways are Eastish-Westish (not exactly East-West).


What are the pros and cons of scimitar propellers? I know scimitar propellers are used to reduce noise, but what is their downside? There has to be one, considering most propellers don't use that shape.

The biggest benefit of a scimitar propeller is the higher operating Mach number that can be achieved. Tip sweep delays the onset of shocks on the propeller and reduces drag at high subsonic speed. The noise reduction is achieved by reducing shocks on the blade tips at the same tip Mach number - supersonic props are known to be extremely loud.

The major disadvantage is the torsional moment created by the swept back tip. This can be somewhat mitigated by sweeping the inner blade forward which results in the typical scimitar shape. Still, in-blade torsion moments mean that the blade has to be built such that the deformation in flight will result in the desired blade twist. The use of stiff carbon fiber allows to keep this pre-twisting low.

That scimitar propellers have a high blade count is a result of their high operating speed: To keep the tip Mach number low, the diameter must be limited which increases the load on the single blade. Flying fast needs a lot of thrust, so the activity factor (power absorbed by the propeller per blade area) is high. To reduce the local Mach number on the blade, both chord and blade count are increased while the relative thickness of the blade's airfoil is reduced when compared to a conventional propeller. This results in a lower operating lift coefficient on the blades and lower supervelocities which again helps to increase the operating Mach number.


What does "ENG 2 REV PRESSURIZED" ECAM message mean in the Airbus A32F? What does "ENG 2 REV PRESSURIZED" ECAM message mean in the A32F (Airbus A320 Freighter)?

What are the possible consequences and actions the crew should take, on ground and during the flight?

In case of Airbus A320 (A318/319/320/321) models, ENG 2 REV PRESSURIZED means that the thrust reverser system is pressurized. From FCOM:

ENG 1(2) REV PRESSURIZED
Reverser system is pressurized, while rev doors are stowed and locked with no deploy order.

The crew are expected to reduce the engine thrust to idle when possible in flight (also on ground).

Reverse thrust system is pressurized with reverser doors stowed and locked.
THR LEVER 1 (2) .................................. IDLE
lf flight conditions permit, reduce the thrust of the affected engine to IDLE as a precautionary measure.

You can see a case where this warning came on.
Deployment of thrust reversers in flight could have fatal consequences as seen in a B767 Lauda Air Flight 004 (note that the warning is about reverser pressurization, not deployment).


Can you legally obtain Boeing maintenance documents? With the correct keywords on Google, it is possible to find Boeing MPDs (Maintenance Planning Documents), as well as Task Cards, and other technical documents.

I'm wondering, could a software vendor with the need to access these documents legally obtain them?

Everything is available for a price, and you don't need Google's help: You can get the Boeing Maintenance Performance Toolbox right from Boeing if you contact them.

You can also Google around and get PDFs of Boeing maintenance documents but these would be from unofficial/unauthorized sources (at least one Boeing maintenance manual made it onto Wikileaks).

As Boeing likely holds a copyright on their maintenance documents obtaining them from an unofficial/unauthorized source would be an infringement on that copyright.
More importantly you can't guarantee documents from an unofficial source are correct, current, and unmodified. If you intend to use the document for any aviation purposes (like performing maintenance on an aircraft) you would want to be absolutely certain they are the latest approved revision from Boeing.


What G forces does a pilot perceive in a "1 G" barrel roll? This is a follow on to an earlier discussion about pilot perception of G forces compared with actual aerodynamic loads on an airframe.  Years ago, the Boeing 707 prototype famously did not one, but two 1G barrel rolls to impress potential buyers. I would imagine the expert pilot just kept the airframe at 1G positive load through the entire maneuver, which would put him weightless at the top of the roll (plane inverted).  Is this what actually happened?  How is this done?

You can't do a barrel roll at 1G.  It's a loop pulled out into a coil, and you have to pull pitch to get it started so you are going to be 1.5 to 2 starting out, declining to 1G to .5 at the top, and pulling 1.5 to 2 on the pullout.

So the sensation at the start is like a hard climbing turn (which is what you're doing), pressed into your seat with about the force of a steep turn at the start, declining to normal gravity or bit less (giving a bit of that giddy becoming weightless sensation, but not coming out of your seat) as you ease off the pitch coming around the top, and about the same pressed into the seat force as at the start, or a little more, on the pullout.

A good barrel roll should be no more than 2Gs peak, but how much is a function of pilot skill and of the airplane's ability to keep up the energy through the first half.  A jet with oodles of power to keep the speed up in the steep rolling climb can get away with a very gentle pull and will see only about 1.5 or less on the pull up and pull out.

But it's always going to be more than 1 starting out and finishing off and when Tex Johnston said in an interview it was a "1G maneuver", he really meant "not much more than" as in less than 2 (and no worse than a steep turn, unless you screw it up and fall out).  Watch the film of the barrel roll and you see a firm pull up at the start with a fairly steep nose down attitude on the exit, which would have required a pull of at least 1.5 G in returning to level flight without over speeding.


Why do the MiG-15 and MiG-17 have a split air intake in their noses? MiG-15 and MiG-17 both have a split air intake in their nose. However, they have only one jet engine.

So why is the air intake split? Wouldn't it be a lot less drag to just let the intake flow cleanly into the engine?

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

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

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

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


How much time it will take a B787 to fuel completely when empty? When a big jet like B787 needs to be fueled with empty tanks, ideally how much time it will take to go full?

According to Boeing (via airliners.net), it takes 53 minutes to load 55,800 US gallons with two fuel trucks operating at 35 psi delivery pressure. The total fuel capacity of the 787-8 is 33,340 US gal, so fueling from empty to full should take about 31.6 minutes with two trucks.


How many planes do ATC controllers assist in taking off/landing each day? I know controllers have several short shifts each day with interval breaks but I was wondering how many planes they assist in taking off/landing depending on what type of controller they are each day? Locational wise perhaps LHR? (London Heathrow)

From the title of your question (taking off / landing planes), I assume you are asking about a tower controller. As you may know, most air traffic don't work in a control tower, but are en-route controllers working in an ACC (area control center).

The number of planes a tower controller handles each day is of course highly dependent on the airport traffic conditions (november, for example, is a quiet month). I work in an European single-runway airport, where the runway capacity is 40 flights / hour (landings and departures included) in optimal conditions. Controllers usually work around 5 effective hours per day, so the theoretical maximum number of planes would be 200 planes. In practice, it is very unlikely that a controller will actually control that number of aircraft, because the runway is used at maximum capacity only during peak hours (early morning, late afternoon and beginning of the evening). Also, a tower controller doesn't only work at the tower position, she will also be typically work a clearance delivery and an approach position.


What does gravity compensation do in flight control? In flight control designs for lateral directional movement, there is a block named "gravity compensation". This block changes yaw rate measurement from "$r$" to "$r-g/Vcos(\theta)sin(\phi)$" before it is sent to the controller. How does this block change the equation of motion?

That term is a feedforward.
It simply makes sure that during a turn the rudder will anticipate the need for that $r$ component and thus helps making the turn coordinated.
Since the term is complete (i.e. there is also the $\theta$ component) this will work also for climbing/descending turns.


Are there any special considerations involved in designing manual flight controls for supersonic/hypersonic aircraft? What things, if any, might need to be taken into account in the design of manual flight controls for supersonic or hypersonic aircraft that wouldn’t need to be taken into account with manual controls for subsonic aircraft?

In the transonic region, control forces may become too high for manual control (e.g. controls froze in WW2 planes diving at high speeds), so supersonic aircraft usually have powered controls rather than manual, cable-operated controls.

You also get CoG shift you have to compensate for. This is often done via a Mach trim system or by automatic fuel transfer.


How often do pilots fly drunk? AVweb reported: 2018.07.30 - A former pilot for Alaska Airlines was sentenced on
  Wednesday to a year and a day in federal prison, for flying two
  flights in 2014 with a blood alcohol level more than three times the
  legal limit.

  Arnston flew from San Diego to Portland on June 20, 2014, and then
  from Portland to John Wayne Airport, in Orange County. After landing,
  Arnston was selected for random drug and alcohol testing by airline
  personnel. Two breathalyzer tests showed Arnston had a blood alcohol
  concentration of 0.135 percent and 0.142 percent. The federal limit is
  0.04.
  BoardingArea reports: 2018.09.02
  Prosecutors allege he struggled with alcohol addiction over those two
  decades and routinely piloted commercial flights under the influence
  of alcohol.

Are there any published statistics on the percentage of pilots tested or otherwise gleamed for alcohol that failed?

How often do pilots fly drunk?

Youtube 1
Youtube 2
Youtube 3
Fox News

Its rare but it does happen. You can search the NTSB database here, the phrase "positive for alcohol" yields the best results as toxicology is fairly common in an accident so a lot of reports include "negative for alcohol" making "alcohol" alone a bad search term. I was able to find a few examples here, here, here, and here as well as some more report results.

according to this article

  ... Of over 10,000 pilots randomly tested for alcohol in 2010, only 12
  failed the test.

They don't cite any sources though.

This looks like it might be the original study and has slightly different numbers but this seems to include all "Aviation Employees" so pilots, crew, ATC and the related may have been included.

  Validity of Suspected Alcohol and Drug Violations in Aviation Employees

  Results:
  During the 11-year study period, a total of 2,284 alcohol tests and
  2,015 drug tests were performed under the reasonable-cause testing
  program. The PPV was 37.7% [95% confidence interval (CI), 35.7–39.7%]
  for suspected alcohol violations and 12.6% (95% CI, 11.2–14.1%) for
  suspected drug violations. Random testing revealed an overall
  prevalence of 0.09% (601/649,796) for alcohol violations and 0.6%
  (7,211/1,130,922) for drug violations. The LR+ was 653.6 (95% CI,
  581.7–734.3) for suspected alcohol violations and 22.5 (95% CI, 19.6–25.7) for suspected drug violations.

The FAA also has an interesting fact sheet you can find here quoting some accident numbers from the late 80's and early 90's as well as the pilots BAC.

Its worth noting that the regulations have changed a fair bit over the years. The current regulation for this is FAR 91.17 which establishes an 8 hour "bottle to throttle" time frame as well as a maximum .04 BAC.

  § 91.17 Alcohol or drugs.

  (1) Within 8 hours after the consumption of any alcoholic beverage;

  (2) While under the influence of alcohol;

  (3) While using any drug that affects the person's faculties in any
  way contrary to safety; or

  (4) While having an alcohol concentration of 0.04 or greater in a
  blood or breath specimen. Alcohol concentration means grams of alcohol
  per deciliter of blood or grams of alcohol per 210 liters of breath.

If you take a look at the original amendment creating 91.17 it reads

  Sec. 91.17 Liquor and drugs.
  (a) No person may act as a crewmember of a civil aircraft -

  (1) Within 8 hours after the consumption of any alcoholic beverage;

  (2) While under the influence of alcohol; or

  (3) While using any drug that affects his or her faculties in any way contrary to safety.

the important difference being that it does not establish a maximum BAC but leaves it open to the interpretation of "under the influence" which potentially left room for intoxicated pilots prior to the current verbiage.


Why weren't SA-On GPS units updated to become SA-Aware? SA = Selective Availability (gps.gov)

SA-On and SA-Aware are widely used in current air transport aircraft (...)

GPS that behave as if SA is still active (SA-On)
GPS that behave as if SA has been deactivated (SA-Aware)

I was under the impression a software update would turn SA-On to SA-Aware. But that's not the case. Why is that? I'm asking about transport aircraft. I wasn't able to find an answer, and to add a complication, ICAO says:

GPS system with SA activated ± 100 Metres (no longer relevant because SA is deactivated)

If it's "no longer relevant", then why is there a difference in the preflight check rule (shown below)?

Top quote and slide: FAA Briefing ADS-B Rules and Airspace, Sep 2017, via icao.int (PDF)

As the linked ICAO article on GPS accuracy states, the issue is not just the navigation accuracy but the reported accuracy which is critical when used for ADS-B.
From the report:

3.2.1 For GPS receivers which are not SA aware, the accuracy and integrity REPORTED and then used in ADS-B messages is based on an
ASSUMED value of UERE, corresponding to the period when SA was active.
This value is grossly larger than the accuracy of the positional data
delivered now that SA is inactive.
3.2.2 For SA off/ SA aware receivers, some report accuracy and integrity values based on the assumed UERE in the SA inactive
environment and some determine the UERE from the GPS message contents.
Thus SA aware systems report more realistic accuracy and integrity
values.

When SA was on it was implemented by dithering the satellite's clock and ephemeris data to create a UERE of approximately 32 meters. So there was no attempt in the SA On receivers to compute the UERE as it was basically fixed by the implementation of SA. Remember this was first implemented circa 1990 and ADS-B efforts were in draft form when SA was terminated.
Also GPS standards weren't revised just because SA went away. The changes were primarily driven by SBAS and GBAS development efforts not the need for ADS-B. SBAS was the basis for the TSO-C145/C146. The air transport market wasn't very interested in SBAS, they tended to lean towards GBAS (if they cared at all.) The TSO-C196 (SA Aware) is very much like the C145/C146 units but without SBAS. (I'm not really sure of all the history of this TSO as it was after my time working these products.)
Product changes around TSO changes are a fact of life. Trying to upgrade a product from one standard to a new one just doesn't happen as it is by definition a major change and requires a new certification. And even with a new GPS built to a new TSO, it can't be swapped into the aircraft without an STC and that's a major expense.
So, could the original TSO-C129 units be upgraded to be SA Aware (without going to the new TSO?) Theoretically they could, but not economically. Computing the real-time UERE has to be done within the GPS chipset which would require a complete redesign of the custom ASIC at which point it just worth moving to the new standard.
As for the preflight authorization requirement for the SA Aware (C196) units; it's because they don't have the SBAS integrity channel. They rely entirely on an aircraft based integrity process. This can cause periodic cases where the integrity is reported as unacceptable.

Glossary:

ICAO: International Civil Aviation Organization
GPS: Global Positioning System
ADS-B: Automatic Dependent Surveillance - Broadcast
SA: Selective Availability
UERE: User equivalent range error
SBAS: Satellite Based Augmentation System
GBAS: Ground Based Augmentation System
TSO: Technical Standard Order
ASIC: Application-Specific Integrated Circuit


What is the exact definition of a "crew duty day"? How do you define a crew duty day? When does it start and when does it end? Also what are the legal limits (in other words how long can a crew duty day last in terms of hours)?.

Edit: Here is a link I found, which basically defines what a Duty period is for the Australian Civil Aviation Safety Authority: https://www.casa.gov.au/standard-page/duty-time-flight-time-and-flight-duty-period.

My question: does each country define its own rules for what constitutes a duty day or do you have standardized set of rules. What happens when you fly say from the US to Australia? Which set of rules prevail?

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

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

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

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

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

  [Are there] standardized set of rules?

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

  does each country define its own rules?

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

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

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

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

  Let's start with the US.

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

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

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

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

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

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

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

And then...

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

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

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

So, finally, back to your question:

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

ALPA's FTDT Limitations and Requirements (May 2015)


Does Karman line depend on the wing area, and if not, why? The Karman line is the altitude at that the airspeed required to generate the sufficient lift to support itself exceeds the orbital speed. Looks like the Karman line is defined as some fixed value, equal to 100 Km. How this could possibly be?

In a usual flight, "the airspeed required to support itself" depends dramatically on the wing and can vary I think from 29 km/h for Gossamer Albatross till 389 km/h for X-15.

The calculation definitely does depend on wing loading. However, the Kármán line does not, because it is not actually defined by that calculation, it is defined by statement. The calculation, for a “typical” airplane, is just motivation for the value.


Is it legal for pilots to transport or use marijuana? More and more states are legalizing the recreational use of marijuana. What does that mean for pilots?

Is it legal for pilots to transport marijuana within states that have legalized it?
Can pilots use marijuana recreationally if their state allows it? Are there implications for medicals?

Is it legal for pilots to transport marijuana within states that have legalized it?

This I'm not sure about. I can't find any FAA regulation or guideline on it, so I think it would depend more on specific state statutes. The problem would lie in going over state lines, obviously, but intra-state transport is unclear. If you were ramp-checked by an FAA inspector and had marijuana on board, they would probably require you to get a drug test, and if failed (according to the next part of this question) you would lose your license (actually your medical, you would keep the license but be unable to use it). So it may be legal to transport it, but you certainly can't be the one using it.

  Can pilots use marijuana recreationally if their state allows it? Are there implications for medicals?

Negative. AME's have marijuana on the DNF/DNI (do not fly/do not issue) list:

  Controlled Substances (Schedules I - V). An open prescription for chronic or intermittent use of any drug or substance.
  This includes medical marijuana, even if legally allowed or prescribed under state law.

While the guidance just says medical marijuana, I would suppose that it includes legal recreational marijuana as well.

Since you would be using a controlled substance on the DNF list, you would not be eligible for flying under the BasicMed either:

  A diagnosis or medical history of substance dependence is disqualifying unless there is established clinical evidence, satisfactory to the Federal Air Surgeon, of recovery, including sustained total abstinence from the substance(s) for not less than the preceding 2 years. A history of substance abuse within the preceding 2 years is disqualifying. Substance includes alcohol and other drugs (i.e., PCP, sedatives and hypnotics, anxiolytics, marijuana, cocaine, opioids, amphetamines, hallucinogens, and other psychoactive drugs or chemicals)

Another way to look at it: Since pilots licenses are issued by a Federal authority, the Federal rules apply. According to Federal laws, marijuana is illegal and your license (or medical) is not valid even if the state you are in allows it legally. Marijuana is still a Schedule 1 substance (on the same level Federally with Heroin and LSD).


What is the relationship between power and fuel efficiency? We were having a discussion in our ground school that power will make the plane ascend or descend and that you use the stick for speed, forward for higher speed and back for slower speed. So does that mean as you fly higher, that means you increase power and ascend, and then fly from point A to point B, you will burn more fuel compared to if you went from point A to point B at reduced power, hence lower altitude?

Unfortunately, the cause and effect in this question is really muddled up. Peter Kampf's excellent answer should explain most of what you need, but it might be that you find his answer difficult to understand because you're still operating under the idea that the stick only manages speed and the throttle only manages altitude.

If this is the case, please consider this analogy: imagine that there are three buckets of energy available to any aircraft: chemical, potential, and kinetic.  (note for the pedantic: yes, chemical energy is potential energy.  Go away.)

Chemical energy is stored as fuel (dead dinosaurs).  It is released by the engine and can be converted into either altitude or airspeed or both.
Potential energy is altitude below you - the energy which is stored in the aircraft as altitude.  It can be converted into airspeed, but not back into dead dinosaurs.
Kinetic energy is airspeed - the momentum of the aircraft.  It can be converted into altitude, but not back into dead dinosaurs.

As long as the engines are operating, the chemical energy "bucket" is always pouring energy into the other two buckets.  The throttle determines how much energy is poured out per second.  The yoke (stick) determines the distribution of that energy - whether the kinetic bucket is pouring energy into the potential bucket, or vice versa, or neither.

What this means is that if you want to ascend, it's not enough to say that you simply have to pull back on the stick, or that you simply need to increase throttle.  Merely increasing throttle with the nose pointed at the ground does not help you ascend.  Merely pulling back on the stick with the airplane already at the critical angle of attack does not help you ascend.  To ascend, you need to "fill the altitude bucket", which (as Peter says) is always a combination of pitch and power.

As to your actual question regarding fuel efficiency, since it's based on false assumptions I will only say that it depends on the circumstances of the flight, but it is certainly not correct to say that increased fuel consumption is always the result of the greater throttle setting necessary to achieve a higher altitude.


Has there ever been a sideways H-tail on an airplane? I've seen several aircraft with 2 vertical stabilizers and 2 rudders. This could be an H-tail like the B-25 Mitchell or the A-10 Warthog, or something more sleek like the Su-27.

However, I got to thinking, are there any airplanes that have 2 sets of horizontal stabilizers and thus 2 pairs of elevators? This would be a sideways H-tail. I guess it would be sort of like a bi-plane, but in the tail only.

Do these exist somewhere? Why or why not?

Experimental planes are okay.

Most of the initial aircraft made by Wright brothers had the twin horizontal stabilizer setting. However, the elevators in these cases were set in the front, rather than back, as is the norm now.

By Wright brothers - OhioLINK Digital Media Center, Public Domain, Link

Quite a few of the early aircraft had a 'box' like configuration, notably the Santos-Dumont 14-bis, which made the first public powered flight. Again, though the pitch control was through the box like structure, it was more of a canard than a horizontal stabilizer.

Santos-Dumont 14-bis; image from Wikipedia

One of the earliest aircraft with a 'proper' twin horizontal (as well as vertical) stabilizer was the aptly named Bristol Boxkite

Bristol Boxkite; By Hpeterswald - Own work, CC BY-SA 3.0, Link

Another good example is its predecessor, the Farman III, which had two horizontal stabilizers and a single vertical tail right in the middle, forming a perfect sideways 'H'.

Farman III; By C.C. Pierce & Co. - http://digitallibrary.usc.edu/cdm/ref/collection/p15799coll65/id/12574, Public Domain, Link

You can see that most of these are early aircraft, which had structural limitations. As the aircraft design matured, the 'conventional' layout became the norm as a single stabilizer assembly can be used to achieve the necessary pitch control.


How does Air Traffic Control know a flight's route and destination? I am trying to find out in layman's terms how does ATC determine the direction a flight has to take after takeoff, or when should it start descending for the destination airport. I understand it has to do with the flight plan but Googling revealed lot of technical stuff that I couldn't understand. In my limited experience of listening to LiveATC and YouTube video, ATC never inquired about the destination - it felt like they already knew.

Is destination information always available on the screen to ATC or does the flight crew request changes based on their flight plan? How does it work when you cross international boundaries? Is the same flight plan available to ATC in all the countries the flight will be flying through?

For example, a flight taking off from SFO could be northbound towards Seattle or southbound to LA or eastbound. ATC has to make room for the proper direction of the flight and hence needs to know the destination.

To complicate matters, I have seen flights taking different routes while the destination is same e.g. one SFO-FRA flight hugged the west coast (magnificent views of the coastline) up to Canada before making a right turn, whereas other times - but with the same flight number - it kind of crosses the continental United States diagonally. So I feel it's not just about the destination, there are other factors involved.

Under instrument flight rules (which all scheduled passenger flights operate under), the pilot will file a flight plan with the local air traffic control authority (in the US, that is the FAA). This flight plan describes in fairly specific terms where the pilot intends to fly, by going from point to point. You can see flight plans on a site like https://flightaware.com.

These flight plans are entered (electronically, in most cases, but sometimes typed in) into the air traffic control system. So each controller who handles the flight knows where it is supposed to go next.

The details of the start and end of the flight isn't determined by the pilot, but by ATC when they set up the departure or arrival. These are done using instructions called SID (Standard Instrument Departure) and STAR (Standard Terminal Arrival Route). Depending on the traffic patterns around each airport, ATC may assign a particular SID or STAR. These instructions are like "fly at this altitude until this point, turn right, descend to this other altitude, fly until you get to this other point", and so on.

For international flights, the flight plans are transmitted from one country to another using AFTN (Aeronautical Fixed Telecommunications Network). So each country that the flight flies over knows where it is supposed to be going.

Other factors which can influence the actual route a flight takes can include:

Weather
Other air traffic
Military operations
International agreements (or more specifically, disagreements)


Drop the rope or drag the rope? I was the safety officer at a glider operation earlier this year and we had a new tow pilot who forgot to drop the rope. By radio, I instructed him to drop the rope before landing. The downsides of this is that it would temporarily leave the rope in the middle of the grass field where an aircraft might run over it, and also someone would have to golf cart out to retrieve the rope.

Later, when he found out about it, the chief tow pilot got angry about this and said the tow plane should have landed with the rope attached and dragged it back to the launch location. I thought this was unwise because this could damage the rope, or if the rope were to catch on something as the plane landed, it could have dangerous consequences for the tow pilot. Also, I have seen loose tow ropes whip around. Considering that there is a metal buckle at the end of the rope, imagine that thing whipping around. If the plane landed with the rope attached, I was picturing that buckle whipping into a bystander or a parked plane.

Of course, the third possibility is that he could do a go around, fly all the back and do the rope drop correctly. The disadvantage of this is that it would delay the return of the tow plane for another 10 minutes while he did the go around, and we had multiple people waiting for tows.

What is the best procedure?

To start: I flew gliders for 8 years at a field on the northern edge of KPHL's mode C veil and never saw a towplane (purposely) drop a rope for a non-emergency.  We operated out of a grass field surrounded by trees on most sides (maybe 10 miles south of KCKZ) and never had problems with towplanes landing with the rope attached.
There are some factors here that feed into this.  That particular field (http://www.pgcsoaring.com/) has generally well taken care of and is a completely turf field.  I think we added some lime markings to denote a landing box on our usual landing runway, but that's about it.  I have a picture of the runways used for normal operations below.  Takeoffs were started on the far right on runway 25 (picture has been rotated), and landings, typically, were facilitated on the runway marked by a dashed line.

Now, something that isn't quite clear from the overhead views are the trees.  At the far right hand side of 07-25, you have a stand of trees (and two hangers) that go up 40-50 feet.  Landing over these, particularly with a tow line, can put you out in the boonies if you want to make sure that the tow line isn't dragging through the trees.  The FAA Glider Flying Handbook (https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/media/gfh_ch12.pdf) indicates that a 200 ft tow rope can "fly" about 130 ft below a towplane, so clearance in that dimension is critical.  The pictured field actually has 3 operating runways (07-25, 01-19, and 13-31) and, on the approach to each (save 25), there are no trees near the runway threshold or the runway is situated at the top of a significant hill.
Insofar as ground abrasion goes, I'd see wear and tear on a towline over time, but it was relatively slow accumulation.  Slow enough that you could track it by rope checks at the weak link (if in use) and tow hook prior to each flight...which you are probably doing anyhow.  We always had a spare rope spliced and on a reel so that an in-use line could be quickly replaced during normal operations (maybe a minute or less during a regular takeoff if it was coordinated well).  But that's more or less semantics: the point is, for the turf field we had, which was well-cleared of rocks, branches, or man-made debris, there were no problems with dragging a rope over the ground provided that pilots and line crew were doing the routine safety checks that they would be doing regardless.  Not dropping a tow line also kept down non-airplane vehicle traffic on the field during operations (i.e., it eliminated the need for another runner to get the tow line, especially when aircraft are anticipated to be landing).
The Glider Flying Handbook has this much more to say about landing with a tow rope (GFH 12-10):

Landing with the tow line attached is not prohibited by
regulation; however, the following points should be considered:

Obstructions are cleared by more than the tow line
length (altimeter lag considered).

The field is well turfed. It is simply inviting early
tow line failure from abrasion to land with the tow
line on hard ground or paved runways. Landing with
the tow line should never be attempted unless the
field has clear approaches and is at least 2,500 feet
in length.

Other situations require the tow line to be dropped, normally
in the glider launch area, during short approach to the
runway. If the tow line is to be dropped, the tow pilot must
be constantly aware of the launch area situation. The tow
line drop area must be defined and ground personnel must be
briefed and aware of the drop area. Ground personnel must
stay clear of the drop area, and the presence of an individual
in the drop area requires an immediate go-around by the pilot
of the tow plane without dropping the tow line.


What is the significance of the "date designation expires" on a temporary airman certificate? I recently received my temporary airman certificate and it says that it expires in 120 days. However, there is a section that says "date designation expires". The date under "date designation expires" is not 120 days. So my question is, does it expire 120 days after the date of issuance or on the date under "date designation expires"? Thanks for any help!

"date designation expires"

Assuming your temporary certificate is issued in the United States.

Is the date that the Designated Examiner's designation expires (assuming it was a "Designated Examiner" who issued the temporary certificate).

A Designated examiner's authority has to be periodically renewed.

This is not the date your temporary certificate expires, which is 120 days from issuance.


Where can I find blueprints for the Wright Model HS? I'm looking for the Wright Model HS blueprints. Can someone help me?

You may want to reach out to the national archives they seem to have at least some of the Wright Brothers Blueprints. The Smithsonian may also be of help as they seem to have some stuff of theirs as well. This organization also has some of their early plans and seems to be knowledgeable on the topic you may want to reach out to them.


How to read the pressure diagram of an airfoil? According to most authors, "lift is the result of the difference of pressure on airfoil sides".

My question is not about how this difference is generated, but only about the representation of the pressure around the airfoil. In particular, diagrams like this are frequently seen when talking about airfoils:

From Bernoulli or Newton's Laws for Lift?

Being not an aerodynamics engineer, I'll like to understand what can be deduced from this diagram.

Does this diagram indeed shows the variation of pressure on the contour of the airfoil ? Will this vary if the angle of attack or the speed are changed?
Is it correct to deduce from this diagram that the points on the red portion undergo a pressure smaller than free airstream static pressure, and those on the blue portion undergo a pressure greater than free airstream static pressure?

What is the correct method to obtain the relative pressure at a given point p1? Is it to measure the length of the segment which is perpendicular to the airfoil surface at point p1? What is the scale?

On the figure above, is p2 absolute pressure indeed equal to free stream air?
Do point p2 and the similar one found on the trailing edge have specific names?
What other elements can be deduced from the graphic?

The drawing in your answer shows the contour of the tips of the local pressure vectors when they are plotted perpendicularly to the local airfoil contour. Yes, this will change with angle of attack. In potential flow theory, the local pressure can be calculated as the linear superposition of a contribution from camber and one from angle of attack. While the camber-related part is constant, the angle-of-attack related part varies linearly with this parameter.
Yes, since the diagram shows the pressure distribution at high angle of attack, the top surface shows mostly suction (= local pressure is smaller than ambient pressure) and all of the bottom surface pressure that is higher than ambient pressure. Static pressure is equivalent to potential energy and total energy is constant, so this means that flow speed is higher than the free flow speed over the red region and lower over the blue region.
Yes, measuring the perpendicular distance between the airfoil surface and the contour line will give you a pressure difference to the ambient pressure, but there is no scale, so all you can do is read relative pressures from that drawing. I recommend to use a different way of plotting pressure, see here for more.
Yes.
P2 has no specific name; here the flow accelerates through the free stream speed. The stagnation point is below the highest distance between airfoil and pressure contour near the nose (in the blue region). That the local pressure at the trailing edge is equal to free stream pressure is a coincidence - at lower angles of attack, the flow will decelerate below the free stream value near the trailing edge, so the blue region would wrap around the trailing edge. Here, flow separation at the trailing edge is imminent, and if the angle of attack is increased a bit, the pressure will turn to suction at the trailing edge.
I think this graph is not quite realistic but is meant to show the general tendency only. More can be seen when inviscid and viscous pressure are plotted together over chord in a cartesian coordinate system.


Why did this aircraft take off in the opposite direction compared to the one used by other flights right before/after it? I recently took a weekend trip to Naples and went to admire the city from above at the Certosa di San Martino panoramic viewpoint which, it turned out, was also offering a distant view at NAP operations that morning (June 15, 2019, around 12PM CEST). After taking a few pictures I couldn't help but spending a good 15 minutes tracking a few landings and departures with the FlightRadar app.

Runway 24 was in use at that time, except for a single departure in that timeframe which used runway 6.

Is this a common scenario - i.e. a single aircraft taking off from the runway opposite to the one currently in use?

I know the general factors taken into account when determining in which direction a runway is used, but what could be the reasons behind such a sudden and isolate (takeoffs and landings just 3 minutes before/after used runway 24) change in the airport operations?

The aircraft in question left NAP with more than 1 hour delay, leading me to think that it could have been pilot's request to spare a few minutes: probably positioning for 6 was faster from their gate?

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

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


How does IDENT work? In order to help ATC identify an aircraft on their screen, they may ask the aircraft to "ident." The pilot presses a button on their transponder, and the controller can verify that the aircraft they are talking to is the one they are looking at on the screen.

In what situations does ATC ask for ident, and is it ever required by procedure?
What does the transponder actually do in this mode?
What does the controller see on their screen?
Does it depend at all on either the code or the mode the transponder is currently set for?

(Note: This answer is tailored to the U.S. / FAA, because that is what I'm familiar with. All the citations and references are FAA materials. If anyone has any tips on possible international differences, please let me know and I'll edit them in. That said, I believe the descriptions I give are fairly consistent across the world, even if the FAA reg citations don't directly apply.)

  In what situations does ATC ask for ident, and is it ever required by procedure?

Generally, "ident" is used to help a controller identify an aircraft's secondary radar (transponder) return. By asking the pilot to "squawk ident," the controller can ensure that the aircraft he/she is talking to matches the radar target he thinks is that aircraft.

It can also be used for communication, to allow a pilot to respond if their radio transmitter has failed.

Specifically:

It is a method to allow a controller to identify an aircraft on radar, per section 5-3-3 of FAA Order 7110.65 (pdf):

  When using only Mode 3/A radar beacon to identify a target, use one of the following methods:

  a. Request the aircraft to activate the "IDENT" feature of the transponder and then observe the identification display.

For lost communication, per section 10-4-4 of 7110.65:

  Take the following actions, as appropriate, if two-way radio communications are lost with an aircraft:

  c. Attempt to re-establish communication by having the aircraft use its transponder or make turns to acknowledge clearances and answer questions. Request any of the following in using the transponder:

  1. Request the aircraft to reply Mode 3/A “IDENT.”

This last scenario is common when experiencing radio failures. If ATC suspects that you might be able to hear them but not to talk back, they might say something like "Cessna 12345, if you can hear me, squawk ident." If you reply by pressing the IDENT button, they can then issue you further instructions and ask you to acknowledge those instructions by pressing IDENT again.

  What does the transponder actually do in this mode?

In normal operation, every time the transponder receives an interrogation from a ground station, it replies with a data block containing certain pieces of information. This data block contains:

The encoded pressure altitude (for Mode C transponders)
A 12-bit identification code (this is the 4-digit code you select in the cockpit)
A single extra bit for the "ident" flag

When you push the IDENT button in the cockpit, the transponder sets that extra "ident" bit in its reply data. Anytime the transponder is interrogated while IDENT is active (for a set duration of time after you press the button in the cockpit), its reply data block will have the IDENT bit set. ATC computer systems notice this and cause the IDENT to be shown on the controller's radar display.

  What does the controller see on their screen?

It depends on the type of radar system in use. Generally the radar target will either blink, its symbol will change (or "blossom"), or an indication such as "ID" will blink in the aircraft's data block (where the callsign is shown).

The AIM has some schematic pictures that show what an IDENT looks like on an ARTS-III scope (an older system still in use at some TRACONs). See Figures 4-5-2 and 4-5-3.

I will try to find some pictures of other radar systems such as those used at ARTCCs and newer TRACONs.

  Does it depend at all on either the code or the mode the transponder is currently set for?

The code doesn't matter. The IDENT flag is an extra bit in the transponder's reply data that's independent of the 12 bits used for the code.

Obviously the IDENT will only be observed if the transponder is operating (not OFF or in a STANDBY mode). But the IDENT works in any mode used by normal civilian transponders (Modes A, C or S).


How are Victor airways defined and numbered? I am wondering how Victor airways get determined.

What determines how many 'segments' they are? For example some airways connect two VORs only, while other airways stretch across (or "connect the dots" of) many VORs as they snake across the map.

Also, is there a numbering scheme?

U.S. freeways have a numbering pattern. For example, odd numbered roads run North/South, with their names increasing in magnitude from West to East (I-5 runs from Seattle to San Diego; I-95 runs from Maine to Miami). Is there anything like that in Victor airway system?

The general rules for this are in FAA Joint Order 7400.2K, Procedures for Handling Airspace Matters. Chapter 20 describes when and how air routes are defined and designated, although it doesn't go into much detail about some things.

For example, the instructions on when to create a route are fairly general:

  20-1-3. WHEN TO DESIGNATE AIR NAVIGATION ROUTES

  ATS routes should be designated to serve en route operations when:

  a. The route is predicated upon NAVAIDs that are suitable for
  inclusion in the system.

  b. The benefits of the designation should outweigh any adverse effects
  to other airspace users, and:

  1. The route is a normal extension of an existing airway; or

  2. Users will benefit from charted information pertaining to navigational guidance, minimum en route altitudes, and changeover
  points.

Similarly, although there are some clear rules for NAVAID spacing, it doesn't tell you why a route would follow certain ones and not others:

  20-3-1. NAVAID SPACING

  a. VOR Federal airways are based on NAVAIDs which normally are spaced
  no farther apart than 80 NM. They may be based on more widely spaced
  NAVAIDs if a usable signal can be provided and frequency protection
  afforded for the distance required (see Order 9840.1, U.S. National
  Aviation Handbook for the VOR/DME/TACAN Systems).

The naming convention is in 20-1-5:

  20-1-5. ROUTE IDENTIFICATION

  Dual designation of ATS routes must be avoided. All alpha-numeric ATS
  route identifications must be assigned by Airspace Regulations and ATC
  Procedures Group as follows:

  a. Identify ATS routes based on L/MF NAVAIDs by color names (e.g.
  Amber, Blue, Green, and Red) followed by a number designation.

  1. Designate those routes extending east and west as Green or Red.

  2.  Designate those extending north and south as Amber or Blue.

  b. Identify ATS routes based on VOR NAVAIDs as follows:

  1. Route lettering must be as follows:

  (a) The letter “V" will prefix low altitude ATS routes below FL 180.

  (b) The letter “J" will prefix high altitude ATS routes at FL 180
  through FL 450.

  2. Route numbering must be as follows:

  (a) Assign even numbers for those ATS routes extending east and west.

  (b) Assign odd numbers for those ATS routes extending north and south.

  c. Identify advanced RNAV ATS routes as follows:

  1. The letter “T" will prefix low altitude RNAV ATS routes below FL 180, and the letter “Q" for RNAV routes FL 180 and above.

  2. Route numbering must follow the guidelines detailed in paragraph 20-1-5.b.1.(a) and b.2.

  d. Route segments must be listed from West to East for even numbered
  ATS routes, or South to North for odd numbered routes.

Many airways don't follow that numbering convention exactly, at least on certain segments. For example, V67 is more or less east-west between the GHM and SYI NAVAIDs although overall it's mostly north-south (from ENL to GQO). I assume that as the number of routes increased, they became longer and less consistent, possibly to avoid creating too many total routes: it looks like the lower-numbered routes are often more 'correct' than higher-numbered ones.

But just like with a road, even if it's clear why the road exists (I can see that people want to drive from A to B) it may not be clear why it follows the exact route it does (why does the road go north of that hill and not south of it?). All those 'small' decisions were made by the person who designed the route and there's probably no way to know them all.


What is the longest time after which plane crash survivors were rescued? I found:

Aviator Bob Gauchie retains the record for solo arctic survival by a downed airman, enduring 58 days of arctic weather before his rescue in Canada 1967.
After 72 days on the glacier, 16 of the 45 people on board the crashed Uruguayan Air Force Flight 571 were rescued alive.

Any longer ?

scope: For the purpose of this question only the initial rescue from the crash site shall be considered.

I have not found a period longer than the two you provided (quoted for completeness). It is unlikely that there is a longer period unreported, as that would be a major news item or historical note; it is possible but unverifiable there has been a person survive after a crash longer but was never rescued due to the aircraft never being recovered.

Aviator Bob Gauchie retains the record for solo arctic survival by a downed airman, enduring 58 days of arctic weather before his rescue in Canada 1967.

After 72 days on the glacier, 16 of the 45 people on board the crashed Uruguayan Air Force Flight 571 were rescued alive.

A couple notable contenders and interesting anecdotes:

Howard Snyder was shot down over Belgium during WWII and joined the Belgium resistance, staying with them for over 6 months until he was rescued by US Troops

Louis Zamperini's 47 days on the ocean after his B-24 crashed in the Pacific during WWII, likely an oceanic survival record after a plane crash, was depicted in the film and book Unbroken. Zamperini then spent another 28 months in Japanese prison camps before being repatriated

Roger Locher holds the USAF evasion record behind enemy lines, spending 23 days evading North Vietnamese troops during the Vietnam war after his F-4 was shot down

Juliane Koepecke's 11 days in the Peruvian jungle after falling from a disintegrating airplane

The record for desert survival, albeit with an unfortunate lack of rescue, the crew of Lady Be Good (WWII)

They survived for over a week in the desert with essentially no water, covering 115 miles...The remains of Moore are still lost in the Sahara’s Sand Sea of Calanscio. But he clearly broke all records for stamina and desert survival


What is the difference between Line-Replaceable Unit (LRU) and Integrated Modular Avionics (IMA)? I'm studying the Integrated Modular Avionics (IMA) and the Line-Replaceable Unit (LRU), but I don't get the difference.

A Line Replaceable Unit is a piece of hardware that can be exchanged for a replacement part in a relatively short time by only opening and closing fasteners and connectors. You will find the term LRU in avionics but also in ATC hardware. Examples are FMC, transponder, etc.
When you have a complex avionics system you tend to end up with a great variety of LRUs. All these LRU have a very specific function. To be able to quickly replace malfunctioning parts, maintenance needs to keep a large stock of spares for all these LRU's.
The Integrated Modular Avionics concept attempts to reduce the variety of LRU's by designing the avionics with common components. E.g. one type of power supply, one type of memory unit, one type of processing board and only a few variations of input/output modules. Instead of working with very function-specific LRUs, the IMU works with more generic Line Replaceable Modules (LRMs). This reduces the number of replacement parts that need to be kept on stock. The LRMs of IMA have more generic functions than in a traditional avionics system.


For supplemental oxygen, what is preferred between masks and cannulas? There are two main types of supplemental oxygen devices in light aircraft:

Cannula:

Oxygen mask:

What are the major differences between these two devices? Is one more suitable for specific siutations than another, or is it just a matter of personal preference?

Cannulas are not effective above medium altitudes, and the FAA prohibits their use above 18,000 feet (FAA brochure on Oxygen Equipment, PDF). Because they only place oxygen at your nose, you don't receive oxygen when talking or breathing through your mouth, while a mask covers both nose & mouth. This is, obviously, not great.

Cannulas are also less comfortable than a nice-quality mic/mask, but that's my personal opinion. A lot of pilots do prefer cannulas for comfort at lower altitudes, as they're easier to don and allow you to continue using your normal headset mic boom. For most pilots, especially those flying normally aspirated aircraft types, it's a matter of preference.


Why does this 757 have a propeller engine attached to the fuselage? I saw the following photo of a Honeywell Aviation Services Boeing 757-225:

If it's not a fake, the airplane has a propeller mounted on a pylon on one side.

What's the purpose of such strange design? Why does it need a propeller engine, if it already has two jet engines? Or is it a permanently deployed RAT?

From the description below the image you linked:

  The Honeywell, Boeing 757 test bed appeared on static display for a few days before departing half way through the event.

A testbed aircraft is an aircraft used for flight research or testing new equipment such as engines.

You can see other photos without engine or with a jet engine instead of a propeller one.

The engine is not needed to fly, but is being tested, and apparently that position has been deemed a good solution to the problem "where do we attach an extra engine we need to do tests on?".


Can seaplanes land on normal airfields or in a marsh or muddy area? I know there are some amphibious planes which can land on both water and land but how different is the their landing in comparison to that of a normal small aircraft?

Also, if seaplanes needs to go into some marsh, will that work for them?

Back in the early 1970s I belonged to a Civil Air Patrol (CAP) squadron that had a J-3 cub with an 85 horse engine on it. During the summer we would operate it on floats, during the winter on wheels. At the end of summer, we would land it on the grass alongside the runway at the Springfield, OR airport (no longer there, it's a big Walmart now) and replace the floats with wheels. In late spring, we'd replace the wheels with floats and take off from the grass.

The joke was that for takeoff you were supposed to line up all the cadets and have them pee in unison along the path the floats would take to aid in the takeoff. Actually, that wasn't necessary since western Oregon gets a lot of rain. Even with wet grass though, for the takeoff we'd get the initial movement by pushing, and we were always careful to ensure that the grass had nothing on the takeoff path that would damage the floats.

With the floats on, you could fly when the airspeed said 40 mph (yes, it was indicated in mph) which is about 35 knots. You could generally count on at least 5 knots of wind right down the runway when it was raining, so at 30 knots across the grass you were good to go.

You can go to YouTube and search "floatplane landings on grass" to see some examples of landing on grass. "Floatplane takeoffs on grass" will show some takeoffs, but a quick look showed using a dolly, which I think we did once or twice before my time with the group but then figured it was easier to just use the grass.


Can airplanes benefit from this "roughness" on bird wings? Why do birds have so much rough surface (overlapping feathers) compared to aircraft? Isn’t that cause additional skin friction drag?
Could planes maybe benefit from this?
link:
https://www.researchgate.net/publication/263394314_Gliding_Swifts_Attain_Laminar_Flow_over_Rough_Wings

It may seem counterintuitive, but by introducing a small amount of turbulence, this interrupts the slower boundary layer which is directly in contact with the wing, thereby delaying local airflow separation and aerodynamic stall. Essentially, at the expense of a small amount of parasitic drag, the stall performance and control effectiveness of the wing can be improved.
Aircraft add small fins called Vortex Generators to achieve this effect on otherwise smooth wings, flaps, ailerons, rudders, and elevators.

Here is a link to check out:
https://en.m.wikipedia.org/wiki/Vortex_generator