Is a license required to transmit in the designated aviation band? Is an FCC license required for people to operate a radio in the aviation band?

The FCC does not presently require a license for Aviation Radio installations in aircraft, where those are VHF and UHF (as I recall).  These are covered in Part 87 of the FCC regulations.

Travel outside the US requires a station license, and I believe HF transmissions require a license.

Similarly the operator (pilot) needs a permit when traveling outside the US, but does not need the permit within the US, to answer your question about the operator.


Flightradar24.com track info What is the meaning of the track info found on Flightradar24, as seen below?

Would be the angle between the route and the equator?

That is the angle between true north and the current ground track. FR24 is slightly different to (most) aviation in that it uses true north instead of magnetic north as the datum.


What is the relation between drag and weight? Given an aircraft type and fixing its wing configuration (flaps, slats) and fixing its speed and altitude and assuming it flies horizontally, what is the relationship between the aerodynamic drag and weight of the aircraft?

Of course this relationship depends on the aircraft itself and on many other things, but what is more or less the power-law?

Say we compare two A320s, the one heavier by a factor of 1.3. Of course the heavier one will fly with a higher angle of attack, because it needs more lift. This will create more drag and the engines will run with higher power to achieve the same speed. How much more drag will it be? If the behaviour is approximated as power-law, what would be the exponent? The cross section increases when we "pitch" the aircraft. Is the aerodynamics in the design process optimised for "half-loaded" aircrafts? Also, how does this translate to fuel consumption, say on 40000 feet with the usual speeds?

If you allow to make a few simplifications, the answer is easy:

Friction drag is not affected by the angle of attack change. That means no onset of flow separation on the heavier aircraft.
The wing's optimum L/D is reached with the same flap setting in both cases.
Lift changes linearly with angle of attack, so the lift coefficient $c_L$ can be expressed by the product of lift curve slope $c_{L\alpha}$ and angle of attack $\alpha$.
We neglect the changed lift contribution of engine thrust when the angle of attack is increased.

Now the drag $D$ can be expressed by this equation:
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\left(c_{D0}+\frac{(c_{L\alpha}\cdot\alpha)^2}{\pi\cdot AR\cdot\epsilon}\right)$$
Per the definition above the term $c_{D0}$ is constant, so the change in drag between the lighter aircraft (index 1) and the heavier aircraft (index 2) will be
$$\Delta D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\frac{c_{L\alpha}^2\cdot\left(\alpha_2^2-\alpha_1^2\right)}{\pi\cdot AR\cdot\epsilon}$$
In order to express this drag difference $\Delta D$ in terms of the aircraft's mass, write the lift coefficient $c_L$ as $\frac{2\cdot m\cdot g}{\rho\cdot v^2\cdot S}$:
$$\Delta D = \frac{g\cdot\left(m_2^2-m_1^2\right)}{\pi\cdot AR\cdot\epsilon}$$

The other symbols are:
$\kern{5mm} \rho\:\:\:\:\:$ air density
$\kern{5mm} v\:\:\:\:\:$ velocity
$\kern{5mm} S\:\:\:\:\:$ wing surface area
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's Oswald factor
$\kern{5mm} g \:\:\:\:\;$  gravitational acceleration

Now we can answer your questions:

  How much more drag will it be?

The drag will increase with the square of the mass increase. The gradient of that increase depends on the span loading of the aircraft.

  what would be the exponent?

2

  Is the aerodynamics in the design process optimised for "half-loaded" aircraft?

No, always for the fully loaded aircraft, as lighter loads can be tolerated much better than higher loads. However, since fuel burn will cause a change in aircraft mass over time, the aerodynamics must work over a range of altitudes.

  how does this translate to fuel consumption, say on 40000 feet with the usual speeds?

Drag is compensated by thrust, so you need more thrust to overcome the higher drag. Fuel consumption goes up linearly, but since cruise at 40.000 ft means that the aircraft is light and the engines are running at close to their maximum sustained thrust, a mass increase by 30% is impossible. For a practical result, the heavier aircraft would fly at the same angle of attack and speed but at a lower altitude where both the increased lift and the increased engine thrust can be provided by the higher air density.

If you need to calculate the trip fuel at different weights: We had a similar question before, so please follow the link for an explanation.


Why does speed lose out to capacity? The Concorde had a maximum speed of 2.05 Mach, carrying about 96-128 passengers. The Airbus A380 can achieve a top speed of 0.95 Mach with more than 500 passengers on board. This means roughly 5 times more passengers can be accommodated by compromising half of the top speed. So, why does speed lose out so much to capacity that it ultimately becomes unfeasible to operate a supersonic airliner?

Which means, roughly 5 times more passengers can be accommodated by compromising half of the top speed. So, why does speed loses out so much to capacity that it ultimately becomes unfeasible to operate a supersonic airliner?

I think you are asking, "why do supersonic aircraft have such low capacity"?

To travel faster than the speed of sound you need to have a very sharp nose and minimal area exposed to the forward direction, to minimize the generation of shockwaves. Shockwaves are bad for people on the ground (the 'sonic boom' effect) and they are terrible for fuel efficiency. Second you really do not want to trap air on flat surfaces facing forwards, because the air will get squashed in the supersonic flow and heat up a lot (like when you blow up a bicycle tyre or a football it is warm afterwards, or when the space shuttle re-enters the atmosphere). Again this is an enormous drag and having hot air flowing around your aircraft causes problems with the structure (Concorde used to grow by 300 mm during flight because of the heat).

Since you cannot be wide and you cannot be tall (without being aerodynamically inefficient), you need to be very long if you want lots of people. And then you have other problems.

The design and construction of Concorde was never a commercial project, it was funded by two governments almost as a vanity project, as a prototype or as an experiment. Then it was given for free to two airlines to use as they wanted.

So unlike the A380 and the B747, no one has ever said "now we try to maximize the economics and the capacity of our design": that never happened. All they ever asked was "How do we make this work!?"

Whereas the subsonic aircraft get a lot of time, money and thought spent on how to make them more economical to use by filling them with more passengers.

For more information I recommend this interview with a former Concorde pilot: http://omegataupodcast.net/2015/02/166-flying-the-concorde/

  Also, Concorde was developed 40 years ago. Are some more efficient supersonic Airliners possible today?

I am sure that these days a far more fuel efficient supersonic engine could be built for passenger operations. And I do believe there would be a market for it on say LON-NYC or even maybe LON-DXB. But designing supersonic aircraft is quite different to designing subsonic ones; and then you have all the difficulty of modern safety regulations without being able to demonstrate you are relying on old, proven designs; and then there are very few routes where it could work profitably so you have very high development and maintenance costs spread over a small number of airframes.

Basically, it isn't worth the risk to anyone to make it.


Is the altimeter setting corrected for temperature? In an ATIS or AWOS/ASOS recording, is the reported altimeter setting corrected for temperature?

I think it must be, because on a hot day, the altimeter should still show correct field elevation. If it wasn’t corrected for temperature, then the reported field elevation could be badly wrong on a really hot or really cold day.

(This and other questions describe pressure and density more generally.)

The reported altimeter setting, QNH, is 'somewhat' corrected for temperature, in that it corrects for temperature error at the aerodrome elevation. This is the main difference between the more-meteorologicaly-inclined QFF which does not contain this temperature correction.

You will still get altimeter errors because of the high/low temperature while being above (or below) the aerodrome  (about 40 ft for each 1000ft for each 10 degrees C), but the actual temperature error at aerodrome level will be 0.


Are gliders susceptible to bird strikes? Gliders don't travel at the high speeds that make bird strikes so devastating in airliners. However, they are also smaller, lighter and softer, and can still move pretty swiftly.

Are they also vulnerable to bird strikes? What happens when a large bird collides with a glider?

Gliders, as every other aircraft, are susceptible to bird strikes. This is a detached glider's tail after hitting a 10 kg vulture:

  The  accident  was  caused  when  the  crew  lost  control  of  the  airplane  following  the  loss
  of a part of the tail assembly after the vertical stabilizer on the airplane struck a griffon
  vulture head-on.

Some countries are more susceptible to this kind of accidents than others. In Spain, which has a large population of vultures, I routinely hear about fatal accidents due to bird strikes.


How much is a used airliner worth? The second hand airliner market is active. Some airlines prefer to sell their aircraft within 5 years of purchase, like Ryanair. On the other hand, some airlines prefer to use second hand planes.

What criteria are considered to evaluate second hand airliners for purchase?
How are the used airliners sold to another operator?

HOURS/CYCLES

The single most important factor in the value of an aircraft (generally speaking) is hours. This will almost single handedly define what the plane is worth. When a plane is built all the parts on it have a life time. This is traced through a series of logs for the plane. When a part is at or approaching its life time it must either be rebuilt or replaced. If you are looking at a plane that has high hours/cycles chances are parts on it will need replacing soon. This is costly to the new buyer and will often reflect in a lower sale price. Here in the US commercial aircraft require more frequent inspections than general aviation planes. These inspections are not cheap and a plane that needs inspection when compared to a plane that just came out of inspection will be reflected in the price as well.

There are of course other factors like wear and tear, corrosion (which can be very costly to fix) and interior condition but generally speaking when large planes change hands they are at least partially repainted with the new companies livery and the interiors are often redone.

For some airlines it may be advantageous to buy second hand planes if they are already flying that make/model. Lets say smallTimeAir flies almost exclusively 727-200's this means they have a nice store of parts for that plane and a crew well experienced in fixing them. It will be easier for them to add another 727-200 to the fleet than say an A320 for which they will need new mechanics and parts they don't have. This makes some used airframes desirable to some people.


Why is engine No.2 started first, instead of No.1? I realized that some Boeing manuals recommend that the engine number 2 must be started first, is there any special reason for this?

The isolation valve in Open or Auto ensures that the Auxiliary Power Unit (APU) bleed air reaches the engine number 2 starter. Engine number 2 start Exhaust Gas Temperatures (EGT) are generally higher.

http://www.lt-vacc.org/images/mesti/Boeing%20737-300-400-500%20Operations%20Manual.pdf

Engine number 2 is started first because it's on the opposite side of the air bridge. When starting with external air or power it is normal to start Engine number 1 because it is further away from the carts.

http://theflyingengineer.com/projects/airbus-tech/hydraulic-systems/

According to Flight Crew Operations Manual (FCOM) 3 Standard Operating Procedures (SOP):

  Engine 2 is normally started first. It powers the yellow hydraulic system, which pressurizes the parking brake

Looking at the electrical schematic that Boeing provides, we see that Transformer-Rectifier (TR) 3 is powered from the R/H AC Bus. TR 3 is an important TR from which significant avionics are powered. Ergo, you would want to have this TR powered up and running first in case you lose AC power to the aircraft during start.


What is the history of glass cockpits? All glass cockpits seem to have the same basic setup for the primary instruments. Altitude tape on the right, air speed tape on the left, turn coordinator on top and an artificial horizon in the background. I can't find any good information on how the glass cockpit came to be and more specifically, how this layout was developed and adopted. I'm curious about:

Who developed the first glass cockpits?
Which planes first used these glass cockpits?
How was the current layout developed, were other layouts in use beforehand?
Was there any resistance or difficulty in getting these systems adopted amongst pilots or their companies?

I can't find any good information on ... how this layout was developed

The glass cockpit arrangement for the primary flight display copies the defacto standard analog instrument minimal T arrangement that pilots are/were used to.

Airspeed     Attitude   Altimeter        Airspeed       Attitude     Altimeter

 .........

              Heading                                  Heading

From Wikipedia


What are the aerodynamic design principles behind the "supersonic" propeller of Luigi Colani's C-309 racing plane? One of Luigi Colani's designs that is particularly confusing to me is the second design iteration of the C-309 propeller racing airplane. Allegedly, its two propellers are designed to be supersonic and they have a very peculiar shape, as shown in the photo below.

The leading edge of the C-309 propellers is both forward-swept and twisted in a circular fashion, given the propeller blades a helical appearance.
This is a very different approach from real-world supersonic propellers found in e.g. the Republic XF-84H Thunderscreech.

Assuming the propeller material to be indestructible for a moment, and that the propeller design is not guided by aesthetics alone, what would be the aerodynamic reasoning behind creating a propeller of such an absurd shape? Is it equivalent to a forward-swept wing that takes into account the relative velocity from the propeller rotation?

Looks like the Colani Museum has picked up my question on Twitter and posted a response later with an archive photo of an advertising article:

The English part of the article says about the propellers:

  Since 1976 we have been investigating sharply cambered pusher and tractor propellers which maintain supersonic flow over part of their top surfaces.

In contrast, the German translation says:

  Since 1976 we have been investigating strongly forward-swept pusher and tractor propellers.

So this sounds to me like they were simply looking to develop strongly forward-swept propellers with a supercritical airfoil. Aesthetics almost certainly also played a role in the design.


What is the maximum speed of all the stages of a geared bypass tubojet engine? What is the maximum speed of all the stages of a geared bypass tubojet engine before they start losing efficiency.

The maximum rotational speed of turbofan blades follows from compressibility effects, just like those for helicopter rotors and for propellers.

Image source

On most high bypass turbofans the fan tips can get to slightly supersonic speeds. A Rolls Royce engineer at the Singapore Airshow mentioned Mach 1.05 for the fan tips, that is why the blades have swept back tip shapes.

All other stages are designed such that blade tip speed remains subsonic: compressibility effects cause a rise in blade drag before the speed of sound is reached. It then drops again, but:

There is a large region of high drag that needs to be overcome, where torque will be waisted on compressibility for no gain in thrust.
Blade root stress is proportional to rpm squared, and it is best to stay in the subsonic region.

For the blades in all stages of the turbofan, three main design considerations are:

tip speed;
blade mass;
operating temperature.

Image source

Blade rotational speed follows from blade radius and tip speed limit. For the fan, a slow turning long blade is best, since it works just like a rotor or propeller does. The compressor blades become smaller at each stage due to the smaller air volume to be compressed, the turbine blades reverse this trend. Rotational speed of the compressor and turbine stages is chosen such that tip speeds stay below the compressibility drag, as confirmed verbally by a Rolls Royce engineer.

Benefit of the gearing can be seen from the shape of the engine: the low pressure turbine blades have a smaller radius than the fan blades, an un-geared engine would turn the LP turbine too slow. With a geared turbofan, the fan tip speed will stay at around the same tip speed, but the RPM of the LP turbine will be brought to a higher value. Below drag divergence number for the hot exhaust gases.


What is this part which is mounted on the wing of Embraer ERJ-145? Take a look at the yellow parts which are mounted on the wing of an Embraer ERJ-145. What is it?

Two closer images:

From bottom:

They are called vortilons. They can induce a vortex to the upper surface of the wing at high angles of attack, which allows flying at higher angles of attack before stalling.

Additionally, four vortilons were installed on
the lower surface leading edge of the outboard wing panel. Their interaction with the wing sidewash at high angles of attack produce
strong vortices that are convected to the upper surface, where they
modify the pressure distribution and boundary layer development,
postponing flow separation and increasing maximum lift. Their
shape and position were defined using the 3D panel program. The
combined effect of the leading edge droop and vortilons allowed an
improved take-off and landing performance without resorting to
more complex variable geometry leading edge devices (such as
slats), for a small cruise performance penalty. Figure 22 shows a
schematic representation of the ERJ145 droop and vortilon.

(The evolution of the aerodynamic design tools and transport aircraft wings at Embraer)
They were first used on the Douglas DC9. The original patent shows the vortex on the upper side of the wing:


Is it possible to fly backward if you have really strong headwind? Is it possible to fly a plane backwards if you have a really really strong headwind? I mean when you are aloft, you have positive airspeed and airflow over the wings but you have negative ground speed.

Yes, certainly! If your airspeed is lower than the speed of the headwind, the aircraft will fly backwards relative to the ground.

Example videos:

from ground (noisy, better turn down your volume)
from cockpit

However, note that headwind cannot cause a plane to fly backwards through the surrounding air. Constant wind does not affect airspeed.


How to correct a roll due to turbulence? I fly a Piper Cherokee 180 (PA-28-180) in an area that has frequent turbulence. When turbulence causes the aircraft to roll to one side I usually try to correct by using aileron and rudder in the opposite direction of the roll.

However my flight instructor says that I should use rudder only to correct for the roll. I can get the wings level by using only rudder but it seems to me that using aileron and rudder would be the most effective method. Can someone please explain to me why I should use only rudder in this instance?

Your instructor needs some... instruction.  Inducing roll using rudder alone is something you do when you are right on the edge of a stall because a downgoing aileron can potentially induce a stall when right on the edge.   In a normal climb, using rudder alone is totally nuts.

Apply only the rudder required to keep the ball centered with the application of whatever aileron is necessary.   If you needed all the roll power you can possibly get, you would apply full aileron and full rudder to use the resulting skidding to increase the roll rate.


Has the construction team of the Northrop Grumann B-2 Spirit made use of the features of the German Horten Ho 229? 1)
 2)
In the first picture, we can see the German-made Horten Ho 229. See also this video.
The second picture shows the American-made Northrop Grumman B-2 Spirit. See also this video
Clearly, both air wings show a remarkable similarity. The German plane looks much smoother though than the quite linear and edgy American one (is there a reason for this? Hasn't a smoothly formed plane less resistance?).
The Horten brothers, who supervised the construction and came up with the design, had no computers at their disposal like plane designers have these days. Every time some adjustments had to be made to make it fly better. In this BBC article one can read the plane was its time far ahead.
The designers and constructors of the NG B-2 Spirit did have computers and more advanced technology at their disposal to construct a working flying wing which clearly shows much resemblance with the wing developed decades before (maybe in a more "instinctive" way?).
My question is simple (I couldn't find this on the internet}:
Did the people who made the NG B-2 Spirit make use of the information of the Horten Brothers. Did they use the blueprints of the HH Ho 229?
Extra question: Why does the Northrop Grumann have such an "edgy", straight form, while the Horten has a smooth, curved form? Isn't curvature and smoothness better for the aerodynamics?

If the objective is very similar, good engineers will independently arrive at a very similar solution.
Yes, the Northrop engineers knew of the Go-229 / Ho-IX. But Jack Northrop has also played with flying wings before – witness the YB-35 and YB-49. Unfortunately, those designs "did not fly" with the conservative bureaucracy of the Air Force. While the Ho-IX was a very advanced concept, there was no "secret" in its design, so how a low RCS airplane should look like was quite obvious to the Northrop engineers.
That the B-2 looks more "edgy" is caused by more insights into stealth technology. While the Horten IX tried to minimize frontal area, used wings of wooden construction (which are transparent to radar energy) and Reimar Horten had planned to use radar absorbing charcoal, the B-2 uses edge alignment in order to reflect radar energy at specific angles, besides using radar absorbent material. When Northrop was designing the plane, it had a rhombic inner section with rectangular wings, much like what is now shown of the new B-21 design, but the small chord at the wing root created a structural weakness when the Air Force added a low level flying requirement. That only was overcome after Boeing got involved. Boeing engineers changed the planform to the current shape by adding more chord at the inner wing which resulted in the typical "W"-shaped trailing edge of the B-2.

B-2 design evolution and its Lokheed competitor (picture source)
After the B-2 production run had ended and after Grumman had merged with Northrop, a full-scale RCS model of the Horten jet was fabricated by Grumman engineers with modern techniques to simulate the aircraft as it would appear to electromagnetic energy. It was tested at a RCS test facility, using similar frequencies as those used in WW II. While the design did show a markedly lower RCS than comparable airplanes of the time, this can be fully attributed to its shape and the use of wood.

Horten IX replica on a sting at the RCS test range (picture source)
Reimar Horten was a bit dogmatic about his designs and insisted that they only use a wing and not even a vertical tail, even though this would had benefited its flight stability. As it turns out, a straight vertical tail produces in combination with a wing or the horizontal tail a nearly perfect corner reflector. While this dogmatism helped to reduce the airplane's RCS, it resulted in marginal lateral stability.


Is it possible to drive into Gibraltar Airport's runway? The runway of Gibraltar Airport crosses an active 4 lane highway

Example Video.
My question is are there any security measures which prevent normal traffic from entering the airport through the runway when the runway is not in use?
How much security risk does such a runway intersecting with a civilian road entail?
Edit: To make the situation more realistic, assume that some very hostile elements are heading towards the airport, and maybe they need only 5 minutes to throw a grenade at an aircraft, or open fire or cause some other similar destruction.
I am specifically looking at how fast would the response of airport security at Gibraltar Airport would be in such a situation, especially given that it's a small airport with only around 15 departures a day. And simply if there are any measures to prevent normal traffic from entering the airport boundary in the first place?

There are no physical restraints to entering the runway when the road is open.

You can see from this video of the crossing that Gibraltar police and the base for the Royal Air Force are present. The runway is owned by the Ministry of Defence. Anyone attempting to drive on the runway will probably be intercepted in seconds, although I am not aware of any reported attempts.

They also have a street sweeper to take care of FOD (foreign object debris).1

There are plans to build a new four-lane diversion road and tunnel section. Construction started in 2008 but it still hasn't been completed as of 2018. The crossing across the runway will be kept for exceptional, specific, or emergency use but pedestrians will still be able to use the crossing.


Why don’t airliners use stabilizer movement to assist with large pitch control inputs? Most large airliners not only have elevators for pitch control, but also moveable horizontal stabilizers.  The elevators are used for primary pitch control, with the stabilizers being used to trim the aircraft, and, for some airliners, as an alternate method of emergency pitch control in the event of a loss of elevator control (due to, for instance, a failure of the hydraulic systems powering the elevators, an elevator actuator hardover, or the physical separation of one or both elevators from the aircraft).  Due to their much larger size, the stabilizers have a vastly greater maximum control authority than the elevators (which is why large modern airliners can be trimmed throughout very wide center-of-mass longitudinal-position ranges without having to defair the elevators, and why a stabilizer trim failure is generally somewhat inconvenient); however, despite this, few, if any, large airliners use the stabilizers to assist the elevators when making large longitudinal control inputs (for instance, when taking evasive action to avoid a MAC, or when recovering the aircraft from an upset).

Why is this?  Airliners can and do use secondary flight controls to augment the primaries in other situations; with roll control, for instance, small inputs are handled by the ailerons alone on most aircraft, while the spoilerons1 jump in to help the ailerons with larger changes.  So why aren’t the horizontal stabilizers called on to assist the elevators when large, sudden changes in pitch are necessary?

1: A spoileron is the technical term for a spoiler that is also used for roll control in flight (these are usually the same spoilers as those that can be extended symmetrically in flight to slow the aircraft).  Essentially all large aircraft, and many smaller aircraft, have them to help with large roll inputs; a few aircraft, such as the Mitsubishi MU-2, have only spoilerons, with no conventional ailerons.

The elevators hydraulic actuators are quick response devices, the THS is screw operated and therefore is slower to response.
Therefore it’s normal to use the elevators for short term action and theTHS for long term action.

For safety you can’t rely only on elevators or only on THS. One system should be able to neutralize the other in case of failure.


What call sign does Marine One use when the President is not on board? How would the pilot of Marine One identify himself to air traffic control without the President on board? Does it have an N-number? If anyone knows, I would like a specific call sign/N-number of any of the Sea Kings. In particular, how would a Sea King pilot flying alone identify themselves to air traffic control?

Marine one is the call sign of any of the (300+) United States Marine Corps aircraft carrying the President of the United States. So, if he's not on board, the aircraft reverts back to its original radio call sign.

In case you are asking about the Marine Helicopter Squadron One, you can find the ID from helis.com. HMX-1 uses the call sign 'NIGHTHAWK' usually, but this is prone to change depending on the circumstances. From the site:

  In Korea, call signs changed on a regular basis; during the Vietnam War, squadrons might use the same call sign for more than a year. Today, squadrons deploying to a combat zone,i.e. Iraq and Afghanistan, are assigned a "theater" call sign for use during that deployment only.


Can anyone identify this biplane? This biplane from the 1930s is from an English airshow. Can anyone identify it?

Maybe it is one step before the Gladiator: The Gloster Gauntlet. Here the number of wing struts and the landing gear are a better match.

Gloster Gauntlet (picture source)

It must be noted that a lot of experimentation went on with those aircraft. The one in the picture above has guns added on both wings which made the aircraft too heavy and were removed later.

The type in your picture clearly has a different engine with a smaller and deeper NACA cowling - maybe it was used for testing the Bristol Mercury engine of the Gladiator.


As a commercial pilot, can I fly my spouse for her work? So I hold a commercial license and have a 2nd class medical.  My wife is an engineer and a product she works on needs to be altitude tested (unrelated to aviation). She was suggesting that we could rent the plane from the flying club I am a member of and she could submit the receipt and get reimbursed for the flight cost. If she wasn't my spouse and was a friend asking me to rent a plane and give her the bill I'm pretty sure this is pretty clearly not OK.

We talked about doing a "pro-rata share" but wasn't sure how that's defined cause... it's my wife - shared finances and all that.  Any experts have any feedback on whether or not we're okay to do this?  Or if we really want to do it do we just eat the cost of the flight ourselves?

EDIT: Clarifying based on comments - This is USA (CPL) and my wife and/or company wouldn't be on the bill. It would be my name because it's a flying club and they would only rent the plane to me.  So it would get charged to a credit card in my name (joint account with my wife) and she'd turn around and get it reimbursed.  I agree, I'm not "holding out" in my opinion... but just trying to make sure I keep things above board.

The prohibition you're worried about as a CPL is "holding out" flight services to the general public, which can be summarized as providing both plane and pilot as a package to strangers.

In this case, you would be providing both plane and pilot, so your concern is understandable.  However, there is a clear personal link from you to your wife and via your wife to her employer, i.e. they're not the "general public", so you're okay.  It would even be okay if your customer were a bona fide friend, rather than your wife or her employer.

If the company could rent (or otherwise provide) the plane and separately pay you to fly it, you wouldn't need that personal link.  Given you're renting from a flying club, that's not possible, but it's something to keep in mind for future scenarios.  Do check with the flying club to make sure it's okay with them and their insurer.  I assume you have the appropriate insurance for yourself.

The pro-rata stuff only applies to a PPL, and given the FAA's policy that flight time and even employer goodwill can count as "compensation" even if no money changes hands, a PPL could still get busted even if they "eat the costs" as you propose.  As a CPL, though, you don't have to worry about that, just the "holding out" rule.


Why does a T-tail produce a pitch-down moment in sideslip? Here is something which I did not find in any book, but confirmed in several wind tunnel and flight tests: A T-tail causes a strong nose-down moment in sideslip. This can even be observed in a potential flow analysis, so no fancy viscous effects should be required for an explanation. But I have never understood why it happens. I would even have an explanation for a pitch-up, but the pitch-down really has me puzzled. Does someone here know more?

I've found some useful research here: E.C. Polhamus. Some factors affecting the variation of pitching moment with sideslip of
aircraft configurations. Technical report, NACA T.N. 4016, 1958.

The image shows the situation for high angles of $\beta$:

  At large angles of sideslip with swept horizontal
  tails, the loading will probably not be antisymmetrical mainly because
  of the difference in lift effectiveness of the leading and trailing portions
  of the horizontal tail caused by the difference in their effective
  sweep angles. This would result in a net lift induced on the horizontal
  tail which is a function of sideslip and tail height. This possible
  effect of tail height is illustrated in sketch 9 for large positive sideslip
  angles:

Interesting to see is that the model has no wings, so we can rule out any causes related to wings, in case people were thinking in this direction.

I putsome more thought into it, and I drew these diagrams, which helped me understand the things being said in the paper.

The blue pluses and minuses are the resulting velocities caused by the horizontal velocity as a function of the sideslip ($V_{\beta}$).
The red distributions are the forces on the elevator as consequence of this $V_{\beta}$.

This component creates an increased velocity over the left side of the rudder, and a decreased velocity over the right side of the rudder.
If there's no sweep, the effects are equally strong, and no effect on the lift is present (denoted by the top two images)

However, if there's sweep, the effect on the left side is less strong, whereas it is stronger on the right side (indicated by the two tails in the bottom row).

In a T-tail, this stronger influence is acting on the lower side of the tail. As it is a minus (meaning a relative reduction in velocity), it will lead to a reduction in suction on the lower side, or an upward force, causing a pitch down.

In a normal tail, the minus will act over the upper surface. It causes a deceleration of the flow over the elevator, thereby reducing the lift it generates. This causes a pitch up movement.


What does Lion Air faking the repair of the AoA vane mean for the Florida repair shop that ceased operations? This is a lengthy read, but worth it. I'll quote the main piece I am speaking of.

  At the Bali airport, a vane, known as an angle of attack sensor, was replaced. Crash investigators were presented with photographs supposedly showing that a mandatory test was done after the vane had been replaced. But upon further inspection, investigators concluded the photos were from a different aircraft. “This is a test that Lion Air was required to do, and they didn’t,” said John Cox, an aviation safety consultant. If the test had been done, engineers likely would have realized the vane was calibrated incorrectly by 21 degrees

Source: nytimes.com

On Friday, October 25th, 2019, the FAA revoked the repair station certificate of the Florida repair shop that had sold the second-hand part to Lion Air.

  The FAA revocation order said Xtra “recklessly and systemically” failed to comply with federal safety requirements.

Source: Seattle Times

Would the finding in the first article imply the Florida repair shop can reopen for business? Or, did they sell Lion Air the AoA and was miscalibrated by them, and therefore the business will remain closed?

AoA = angle-of-attack

The FAA action, while supposedly not directly related Lion Air but more to Xtra's problems with working on parts they were not authorized to work on because they hadn't demonstrated that had everything in place, is obviously politically related to the event because the crash put the spotlight on Xtra and the FAA had to do something once having lifted that particular rock.

So from a strictly legal standpoint, Lion Air's maintenance actions don't help Xtra and what will happen is Xtra will have to make reforms and then go back to the FAA to try to get their repair cert reinstated independently of any Lion Air actions.

Normally what happens is a part goes to a repair facility, and the repair shop puts it though an Acceptance Test Procedure (ATP) as per the manufacturer's Component Maintenance Manual (CMM). There is usually some kind of test rig that has to be made (instructions for making it in the CMM), that runs the specified functional tests on both ingoing and outgoing parts.

So the part goes in, and gets an incoming ATP. If it passes the incoming ATP, it's considered serviceable and gets tagged NFF (No Fault Found) and sent back to the airline as serviceable.  If it fails ATP, it gets broken down and repaired as required.  It then gets an outgoing ATP (the same test normally) to validate function before it is tagged repaired/serviceable.

I can't really tell from the article if the mis-calibration was inherent to the vane as received or was something screwed up when the airline installed it.  Notwithstanding the likelihood that Xtra was turning parts around that they don't appear to be approved to repair, it's not uncommon for parts to come back to an airline NFF, or repaired, and still fail when it's installed on the plane.

So either Xtra had the proper manual, test rig, parts and tools, training etc. for fixing these vanes or they didn't.  The FAA's action makes it sound like they didn't and were maybe just receiving units and doing some other test they made up themselves, or maybe just smiled at it and sent it back out. Hard to say.

In any case, receiving a part back with a serviceable tag is no ironclad guarantee that it will work in service, and "bad from spares stock" happens from time to time.  No system is perfect.  The business depends to some degree on the redundancy of having two and three of everything to cater to random failures no matter the background causes, except in this instance Boeing decided to let that single-point-of-failure spot in the system architecture get through cert, and here we are.


How does a pilots license of cluster ballooning differ from other ballooning or unpowered flight? John Ninomiya discusses his experience with developing this new style of ballooning on his Cluster Ballooning website.

Many of the site's links are now broken, but on there he formerly attested that he was granted a pilots' license by the FAA for this style of flight.

I remember the wording clearly suggesting that this license was different than other flight license. Does anyone know how it did, or could have, differed?

Any other relevant history about cluster ballooning is also appreciated.

The license required for operating a manned free balloon would be a "Lighter-than-air, Balloon" license (as opposed to a "regular" license, which is usually thought of as being for "regular" Airplanes - the kind that take off and land using runways, as opposed to lakes).
Cluster balloons are, for all regulatory purposes, just "balloons" - the only difference is rather than having one monolithic envelope filed with hot air like the balloons most of us are used to seeing they have a bunch of smaller envelopes, usually filled with helium.

An Airman Registry Search shows that there is one "John Ninomiya", with a commercial pilot's license for lighter-than-air balloons, which is consistent with what I'd expect.

A lot of the requirements for a private pilot license in balloons are similar to what you need to do to get a private pilot license in an airplane - for example you still need to learn the same regulatory environment, you'll learn to read the same charts, you'll cover flight planning and weather, etc.

The differences are that you'll be learning balloon systems rather than aircraft systems, and the experience requirements under FAR 61.109 are pretty radically different because of the fact that balloon flying is pretty radically different from flying around in an airplane.

You can peruse Part 61 of the FARs for all the specific details on training requirements for lighter-than-air balloon pilot certificates - Subpart E  (Private Pilots) is probably where you want to look.


Is it negligent to depart with one thrust reverser inoperative? [Source:] The aircraft had departed with one thrust reverser (on the left wing) inoperative, and the pilots knew of incidents in the craft's maintenance log where the auto-brakes had failed to activate during landings.

Why not fix and then recheck the defective parts? Were these pilots deliquent and remiss?

Footnote: I learned of  this flight accident first after watching Mayday, Season 14, Episode 5.

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

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

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


Why are turbofan inlets circular- or oval-shaped instead of square-shaped? Source: materialsengineeringconsultant.com and initious.blogspot.com.

Most of the engines are circular except for some that are oval. The oval shape provides a better ground clearance.

Why aren't the intakes square-shaped? Is there some aerodynamic reason for the circular / oval intake shape?

Airliner jet intakes are round because the engines are round, and for subsonic flight that's all you need - it's easy and cheap to engineer, provides a clean airflow for the engine and unlike some other shape doesn't present unnecessary frontal area that will only cause drag. You've already identified ground clearance as the reason for a flattened shape on some installations.

Ah, you say, what about Concorde or the Tu144?

Source: http://www.hitechweb.genezis.eu

Notice that I specified 'subsonic'. Once one reaches supersonic speeds the requirements change. The intake is crucial in controlling airflow into the engine, reducing it's speed to a subsonic level so that the engine can operate efficiently. It's far easier to engineer the required flaps and baffles around a rectangular intake than to do the same with a circular one.

These are the different intake configurations for Concorde at (A) Take-off, (B) Supersonic cruise and (C) Reverse Thrust

(By Nubifer (Own work) [CC0], via Wikimedia Commons)

This is just as true of air intakes on supersonic military aircraft. You'll notice that almost all supersonic military aircraft use some variation of rectangular intakes for this reason.

As with all things aeronautical, there are exceptions. The English Electric Lightning,  Mig-21 and the SR-71 (and numerous others) use circular intakes with the geometry adjusted by a movable inlet cone.

You'll find a more detailed discussion of supersonic intakes in this answer

"MiG-21 RB23". Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:MiG-21_RB23.JPG#/media/File:MiG-21_RB23.JPG

"Lockheed SR-71 Blackbird" by Judson Brohmer/USAF - NASA Website Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Lockheed_SR-71_Blackbird.jpg#/media/File:Lockheed_SR-71_Blackbird.jpg


What is the typical pilot to aircraft ratio in military squadrons? On aviation.SE, we already find this question addressing the pilot to aircraft ratio in airlines. It states that typical big airlines have roughly between 15 and 20 pilots per aircraft.

Military aircraft may require less pilots per aircraft:

airliners are in flight almost all day long every day
a typical airliner flight requires between 2 and 3 pilots (the 3rd one for very long steps or as an instructer)
a typical fighter is a one-seater
a fighter flight less time than an airliner
military cargo may flight more than fighters, but I hardly see a cargo used as much as a passenger aircraft (I may be mistaken)
HALE UAV may require several crew per flights but I don't know how long are those flight neither how many UAV can be operated simultaneously by one crew

When searching the number of each type of pilots (fighters, cargo/airliners, UAV) per air force (whatever the country), it is easy to come across recruiting websites (with requirement to become a military pilot and salary) but I fail to find anything about the number of pilot an air force has.

My question is : What is a typical ratio of pilots to aircraft in a typical military squadron? Does it differ between fighter squadron, transport squadron and UAV squadron?

As has been said, there is no one exact rule, but a broad estimate can be easily produced.

There are 12,500 active duty pilots in the USAF, and the service counts just over 5,000 manned aircraft. This will give an overall, rough, ballpark figure of 2.5 pilots per aircraft across the entire force.

Counting aircraft types by pilot seats, one can calculate the total number of pilot seats at around 8,350. About a thousand comes from training aircraft, however.

This gives an overall approximate figure of 1.5 pilots per seat, across the entire USAF.

This is not distributed equally. As mentioned in the comments above, combat units tend to run relatively low ratios. With the recent shortage of pilots, especially ones rated for combat aircraft, it has sometimes fallen below 1:1 in some units. For transport and utility aircraft, there are more crews.


Why are primary and supportive instruments in instrument flying different depending on the phase of flight? For example, in straight-and-level flight, the power's primary instrument is the Air Speed Indicator (ASI), and the supportive are the engine instruments.

In another example, straight constant-airspeed climb, the primary are engine instruments, and the supportive is the ASI.

Why does the primary instrument change?

Because during certain maneuvers, certain instruments provide more relevant information to a pilot than do others.

In straight and level flight, the heading indicator provides more relevant bank information as it tells you whether your current bank attitude is maintaining the desired heading.  The altimeter is providing the most relevant pitch information as it’s telling you whether your current pitch will maintain the correct altitude.  The airspeed indicator is the best indication for your required power as it’s telling you if the current power settings will maintain the desired airspeed.  Other instruments provide supporting information.  Here in straight and level flight the attitude indicator provides good supporting bank and pitch indications, the VSI provides supporting pitch information, etc.  Supporting instruments change to primary instruments in certain maneuvers and vice versa.

And, incidentally, in a established constant airspeed climb, your primary for bank is the heading indicator and your primary for pitch is the airspeed indicator.  Primary for power is either the tachometer, manifold pressure, torque, or fan speed gauges, depending on the aircraft you are flying.  Typically you would set to maximum continuous power in a light airplane for this situation.


What component of an aircraft generates its electric power? What component of an aircraft generates the electric power to start the aircraft's engine?

For a Rotax 912 engine, I think the magneto generates the electricity, but I'm not sure; I also think about the ignition coil or electronic ignition.

For most small planes, it is the battery, which turns the electric starter motor. A generator driven by the engine or by a small propeller in the slipstream then charges up the battery while the plane is flying.
Some history:
a few older and small planes had a pull cord in the cockpit with which the pilot could pull-start the engine, like a lawn mower. For engines with no starter at all, the pilot or their assistant would grab the propeller and swing it around by muscle power to start the engine (be careful!).
Some very old planes had starters operated by a crank that you stuck into a hole in the engine cowling, and turned by arm power. This worked for small engines but was too hard to do for bigger engines. In that case, the crank turned a small flywheel up to great speed and then the engine was geared into the flywheel through a reduction gear drive, and the energy stored in the rotating flywheel turned the engine to start it. This was used in the P-26 "Peashooter" plane.
In later years, a small electric motor spun the flywheel up to speed instead of a hand crank. The Antonov An-2 still uses this type of starter, called an inertia starter, as does the Dromader crop duster with the radial engine.
Another method of starting an airplane engine was to explode a blank shotgun shell in a closed chamber and send the hot gas through a tube to a special cylinder geared onto the crankshaft, which thereby turned the crankshaft to start the engine. This is called a Coffman starter and it plays a key role in the old movie "The Flight Of The Phoenix". In some versions of this principle, the gases from the shotgun shell were sent right into one of the cylinders of the engine itself, forcing the piston down and turning the crankshaft.
This idea saw use in more modern times, where a jet engine could be started by burning a charge of solid rocket motor fuel called a cartridge inside a sealed chamber and using the hot gas to spin up the exhaust turbine. F-4 Phantom jet fighters could be started with cartridges like this in just a few minutes even in Alaskan winters- without the use of a start cart.


For IFR flights that require two alternates, is there a regulation that requires enough fuel to reach the furthest one? For flights that have two alternate destinations, I'm looking for a reference - either EASA or ICAO - that states that you need enough fuel to reach whichever alternate would require the most fuel to get to.

I think this is common sense, but I need a reference if anyone has it?

EASA OPS 1.255, appendix 1, 1.4 b).

I don't have the text in English here, sorry.


What is that device on an Su-27 pilot's helmet? While watching a YouTube video (2.5hrs), I noticed this device on the top of most Russian Su-27 combat pilot's helmet. A google search only shows it for a Su-27 and MiG-29, but apparently no other aircraft. It was not on any Chinese, Syria, Ukraine or Russian aerobatic pilots flying the Su-27. It appears to be at the wrong angle and has a metal plate that seems to exclude it from being some type of illumination.

What is this on a Su-27 helmet?

That is the mounting point for night vision goggles. The following image shows a helmet with NVG mounted.

Helmet mounted NVG; image from lemt.by

The USAF has helmets with different mounting and some of the modern pilot helmets (like BAE Striker II, for example) have an integrated night vision device.


Could an aircraft be tied down, then throttle up and release for takeoff in order to use a shorter runway? Could airplanes, in theory, be designed to takeoff by first tying the tail to a post, throttling the motors to full power, and then letting loose?

Could it even take off while tied, if the cable is attached to a point that's higher than the tail of the aircraft?

As already mentioned, aircraft cannot take off without moving through the air, because it is the airflow around the wing that generates the lift required for take-off, and the only practical way of generating sufficient airflow around the wing is to move the wing through the air. This is typically done by moving the wing, and thus also the fuselage it is attached to, forward.

There is, of course, another way to look at that: aircraft can take off without moving relative to the ground, if exposed to a strong enough wind from the front of the aircraft.

That said, keeping the aircraft stationary, "throttling the motors full power, and then letting lose" is a very common short-field take-off technique at least for propeller aircraft; there's nothing theoretical about that. The aircraft is, however, typically kept stationary by applying full brakes while applying full engine power, rather than by using an external tie-down.

The tail likely isn't designed to take the force of holding the aircraft stationary while the engine is running at full whallop, although there's no reason why such an anchor point couldn't in theory be installed (see motor aircraft towing gliders to altitude, scale up somewhat, and you're close).

Since the brakes are already there and need to be powerful enough to at the very least hold the aircraft stationary during the engine run-up prior to take-off, which happens at a significant fraction of full power and can quite well happen at a hold short point just before the runway, there's no reason to spend weight on reinforcing the tail section to that point. Instead, just use the brakes for the few seconds needed.


What happens at the wings when the yoke is pulled backwards? What happens at the wings and vertical stabilizers when the yoke is pulled backwards or forward on typical airliners like the Boeing 747-800.  Is it any different for smaller similarly shaped aircraft like private jets?

Most aircraft have control surfaces that work in a similar manner from a little Piper up through a 747. Forward and back movement of the yoke or stick typically results in actuation of the elevator. For aircraft that have the common style empennage the wing remains unchanged. For aircraft that have elevons they move accordingly.

Pulling away from the front of the aircraft on the control column causes the aft end of elevator to move upwards relative to the airframe. This action causes the aircraft to pitch nose up.

Pushing towards the front of the aircraft on the control column causes the aft end of the elevator to move down relative to the airframe. This action causes the aircraft to pitch nose down.

Take a look at this GIF for a nice animation or this video.


Is it possible to control the direction during auto-rotation? Is it possible to control the direction during auto-rotation, and how does it work?

It's entirely possible.

Attitude control works the same way during autorotation as it does during normal powered flight. It's a good thing, too... during an autorotation you want to target your descent toward a suitable landing spot :-)

To (say) roll right, moving the cyclic causes the swashplate to move in such a way that the rotor blade's pitch (angle of attack) is greater during the left-side portion of the blade's travel, and lower during the right-side portion. This produces more lift on the left side, which causes a right-rolling moment on the helicopter.

The fact that the collective is all the way down and that the rotor's RPM is being maintained by airflow through the rotor does not change the way the cyclic produces attitude changes.

The anti-torque pedals still work too, although during an autorotation the pilot will promptly apply full right pedal, since lowering the collective will essentially eliminate torque from the rotor. Pedals can still be used for yaw though, as the tail rotor is still spinning (it is linked to the main rotor).

The "180° turning autorotation" is a common maneuver taught in basic training, where the pilot must set up the autorotative descent and then complete a 180° turn toward a landing spot.

For more information about autorotations in general, I recommend the FAA's (free online) Helicopter Flying Handbook. See page 2-24 for a general description, and page 11-2 for procedures/technique.

There are also lots of autorotation demonstration videos on YouTube that show maneuvering to a landing spot / 180° turns during the auto.


How do flaps deploy and stow with very large wing flex? On large airliners, the wings are generally of the high aspect ratio types and hence very flexible. Now the flaps are attached to wing only through a series of tracks, and as the wings flex, these tracks change relative positions to one another as well. How is the flap designed so that it can ride on these tracks regardless of their positions? I scoured the internet for answers and the only vague one I got is this description

  One of the flap tracks positions the flap and all others absorb horizontal displacement.

Intuitively this is like designing a door that can open and close with a doorframe that is sometimes straight and sometimes crooked. Is the door also flexible itself?

This question applies to not just flaps, but to spoilers, speed brakes and leading edge slots or drooping leading edges as well. How are they designed?

If the flap is on 3 tracks, it flexes with the wing and there is compliance built into track system.  If the flap is on two tracks, it'll stay straight as the wing in front of it curves.  But in a two track system, the panel is short enough that the wing curvature is negligible to the flap.

What that statement means is that with a 3 track panel, as the flap flexes with the wing, the total distance between the 3 tracks gets longer and shorter by some value, say an eighth or quarter of an inch or whatever.   To accommodate this the center track is used to control the lateral position of the panel, while the inner and outer track has lateral side play built in to the roller system so the change in distance doesn't cause binding in the outer tracks.

Slat systems are the same. The center track has guide rollers that locate the slat and the outer ones are "floating" laterally by having larger roller clearances.  Other panels on the wings like spoilers that are much shorter are able to get away with just using spherical bearings that allow some compliance as everything moves.


Why do some flights make turns shortly after takeoff? I have seen that flights will make a turn, after traveling some large distance (say after some kilometers), but that can be done before.

Why not flying directly like in 2?

I am not expecting a passenger flight to do like fighter jets and perform nearly vertical take-offs, or some other manoeuvrers.

Are these flights restricted to do so, or is there any reason to behave so? Or did I misunderstand something?

It is mostly standardized procedures.

I take as example Amsterdam airport (AMS), but the following is applicable to most, if not all, major commercial airports.

Let's look at the departure charts, in particular this one:

as you can see, if an airplane is departing via that runway, it MUST follow one of the two specified paths to exit the airspace of the airport through the "ANDIK" waypoint. It has different paths for the other exit waypoints, but they are similarly defined and limited in number.

In the link you will find similar charts for each of the runways.

Within restrictions due to factors like terrain, noise abatement over populated areas (as Dan's mentions in his answer), areas restricted due to security and safety (over city centres, government and military installations, nuclear power plants and such) or used for other purposes (military operations, space launch and such), these routes are defined so they don't intersect (much).

This ensures arriving and departing aircraft don't come close to each other, which greatly reduces the risk of collision and allows responsibility for different routes to be split among several controllers who can each handle their assigned routes mostly independently of the others.

Weather conditions and other factors will dictate which runways are used, but the runway will dictate how the airplane will exit the airport's airspace, after the appropriate exit waypoint has been selected (you generally would not use a waypoint on the north side if you have to go south).

So, to summarize:

you have a limited amount of exit waypoints
you have a limited amount of runways
weather will restrict your choice (well, the airport's tower will do this for you) of runway
your destination will restrict your choice of exit waypoint
for each runway-waypoint pair you will have one or two possible routes

This results in the kind of behaviour you have observed.


Is it standard procedure to unlatch the cockpit door before an emergency landing in a small aircraft? I was watching an Air Safety Institute video called "Real Pilot Story: Cemetery Crash – A near-death experience with valuable lessons for all pilots." It discusses a situation where a 1958 Bonanza crash landed in cemetery due to an engine failure.

At the 2:23 minute mark they are discussing the lessons learned and the pilot states that "I should’ve reached across and unlatched the entry door because that could jam in a landing, and in a Bonanza it’s very difficult to get out if you jam that door."

Is that really the proper procedure in the case of a crash landing? It seems a little strange to suggest that, while trying to land safely, the pilot should pop the cockpit door open.

As always check your POH for procedures, however most light aircraft call for unlatching the door in the event of an emergency landing or ditching.  Two principle reasons: 1. It aids egress, which can be difficult with a jammed door. 2. It allows better energy absorption of the front part of the fuselage, by permitting it to crumple better.


What is the difference between MEL and CDL? I know the MEL and CDL are the minimum equipment list is provided by the manufacturer, if component missing or damaged means the aircraft must pass the MEL and CDL, I need some suggestions how it was actually working in aircraft maintenance

The MEL lists the limitations of the aircraft when some equipment (autopilot, transponder...) are inoperative.
The CDL deals only with non-structural external parts (wheel fairing...) that may be missing without grounding the aircraft.

From this website, emphasis mine:

  The CDL is a listing of regulator-approved non-structural external parts that may be missing but the airplane remains airworthy.

  To qualify an item onto the CDL, a restrictive set of conditions must be met, e.g.:

  The effect of the missing part upon adjacent structure and systems must be evaluated.
  The effect upon airplane performance must be measured.
  The combined effect upon the aircraft when more than one CDL item is present must be determined (i.e. the effect of a combination of items missing).

  [...]

  The CDL should not be confused with the MEL (MEL). While the MEL describes the limitations of aircraft operation in case of a system being inoperative/having malfunctioned (e.g. transponder failure), the CDL deals with situations where external parts of an aircraft are missing/fallen off (e.g. fairings, aerodynamic seals or panels).


What is the minimum speed at which the Antonov An-2 can maintain level flight? The An-2 famously has "no stall speed", as control can be maintained in descent at arbitrarily low airspeed. As wikipedia says:

The An-2 has no stall speed, a fact which is quoted in the operating handbook. A note from the pilot's handbook reads: "If the engine quits in instrument conditions or at night, the pilot should pull the control column full aft and keep the wings level. The leading-edge slats will snap out at about 64 km/h (40 mph) and when the airplane slows to a forward speed of about 40 km/h (25 mph), the airplane will sink at about a parachute descent rate until the aircraft hits the ground."[4] As such, pilots of the An-2 have stated that they are capable of flying the aircraft in full control at 48 km/h (30 mph) (as a contrast, a modern Cessna four-seater light aircraft has a stall speed of around 80 km/h (50 mph)). This slow stall speed makes it possible for the aircraft to fly backwards relative to the ground: if the aircraft is pointed into a headwind of roughly 56 km/h (35 mph), it will travel backwards at 8.0 km/h (5 mph) whilst under full control.

But there has to be some minimum speed at which it can generate just enough lift to counteract gravity, what is this speed (and does it have a general name)?

"No stall speed" just means no stall break in the traditional sense.  The AN-2's slatted wing's maximum AOA is very high (typically about 10+ degrees higher than un-slatted, or mid-high 20s vs mid teens) and there isn't enough tail power to get the AOA high enough to get any kind of break.
Stall speed is normally published as the speed at which the wing is at maximum lift coefficient.  A typical wing makes a Clmax of about 1.5, slats raise that to about 2.5, and a slotted flap raises that again to about 3.5-ish. The AN-2 has full span slats and flap-flaperons so you can assume that just about all of its 770 sqf of wing area is producing a Clmax of mid 3s with slats out and flaps down.
You can use the handy calculator on this page (click on the "Stall Speed Calculator" link) to work out what the speed is at which this is achieved. For the AN-2 you could assume with 770 sqf of wing area, with, for argument's sake, a Clmax of 3.5 for the entire wing, and operating at, say, a relatively light 9000lbs, you get a "stall" speed of 32.8 kts (37 mph), the speed that the wing is making maximum lift based on those assumptions and technically, this is the answer to your question.
With a slatted wing, the lift curve has a more rounded top; this is, lift declines fairly gently after the peak, so you can continue raising AOA and all that happens is sink rate goes up, until the tail runs out of downforce authority.
With power, thanks to the slats, you get both more tail downforce with the slipstream blowing on it, and because you can reach very high deck angles, you start to get a significant boost from the vertical component of engine thrust itself when the thrust line is canted up at, say 25 degrees.  And on top of that you get added lift from the slipstream itself passing the wings..
If the engine is making, for argument's sake, 4000 lbs of thrust when at full power (you get roughly 4 lbs/hp) and the thrust line is canted up 25 degrees, there is a vertical thrust component of about 1700 lbs.  This has the effect of reducing your weight by 1700 lbs, and plugging in a 1700 lb weight reduction into the calculator gets you down to about 29 kts (or 33 mph).  Add in the additional lift from slipstream passing part of the wings dropping the minimum speed a few more mph, and you can see how you can get to the point of the plane being able to back up at 5 mph in a 35 mph headwind using power in the slow-flight regime, at a relatively light weight at least.
So, the AN-2, at a relatively light 9000 lbs, using the standard formula and using typical assumptions, should be able to fly at a minimum speed of 37 mph power off and about 30 mph or a little less power on without sinking, which agrees more or less with the article's statements.
Plus, there is enough tail power with power on to increase AOA a little more, getting speed down to 25 mph, but while it's under control, total lift will be declining and the airplane will be sinking while doing so.
None of this is particularly special.  The AN-2 achieves its performance with lots of wing area and full span slats and flaperons.  Other STOL aircraft with full span flaps and slats can do the same thing.


Why is the minimum runway length non-linear in relation to the landing weight? The graph below shows the landing runway length requirements for a Boeing 747-8.

(taken from the Boeing 747-8 Airplane Characteristics for Airport Planning)

Considering the fact that the kinetic energy and impulse are directly proportional to the mass, I would have expected this graph to be linear – but clearly that's not the case. What is causing the non-linearity here?

While the kinetic energy is proportional to mass, it is not proportional to velocity.

The heavier the aircraft is, the higher the landing speed. So the stopping distance increases mainly because of the higher landing speed.

Comparing two landings, first at mass = $m_1$, the second at mass = $m_2 =1.1 \cdot m_1$, the landing speed will be $\sqrt{\frac{m_2}{m_1}}$ higher during the second landing.

The kinetic energy during the landing will scale proportional to the square of the mass.


What factors are considered when a runway is planned? What environmental factors are considered when a new runway construction is planned (e.g. winds, weather, sun direction, etc.)?

First, wind rose data, unless you built the airport in the early 20th century without weather data.

By BREEZE Software (http://www.breeze-software.com/) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

It's nice to check old airports and see how they evolved over time. In the past they usually built three runways, each separated by 60 degrees in direction, to cover the compass. Over time some are lengthened, others demolished, more are added in the favorable direction, and so on. Nice example is KORD if you want to hunt the history on your own.

Example of runway closure: Why did the north / south runways close at Daugherty Field (KLGB)?

For a commercial airport expecting long haul jets, you need a long runway, to bring down civil works cost you need to find a place with a relatively flat terrain that would house said long runway.

Airport's elevation also plays a factor to runway length. The higher the airport, the longer the runways need to be. Surrounding terrain also is important. Unless you can build an island: VHHH.

For sun direction, engineers recommend Ray Bans, since the Earth spins.


What is an approved weather source for flying an instrument approach into an airport with no working ATIS? What can you use as viable weather information landing at an airport with ATIS inoperative due to the tower being closed after hours? Let's assume the approach secondary weather source is also unavailable but the ADS-B weather information is current.

My real question is: can you use ADS-B weather legally in this situation to shoot an approach if needed?

How is the ADS-b weather derived? If the ATIS is inop, it will usually be because the sensor equipment is inop. If that is the case, how would ADS-b get the data for that airfield? If the sensors are working and the transmitter is inop, you would get the weather directly from ATC. If you were in IMC and/or IFR, your Approach plate would list an alternate source of weather info, and/or minimums adjustments when the weather is not available.

Saying that, having the weather is not a requirement to land at a Class G or E airport in VMC. Most airports will revert to one of these when the tower closes. A pressure sensitive altimeter is not necessary in VMC. Title 14 CFR, Part 91.205(b) just says “Altimeter”.

In all other cases, follow the regs below:

  91.121 Altimeter settings
  (a) Each person operating an aircraft shall maintain the cruising altitude or flight level of that aircraft, as the case may be, by reference to an altimeter that is set, when operating—
  (1) Below 18,000 feet MSL, to—
  (i) The current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft;
  (ii) If there is no station within the area prescribed in paragraph (a)(1)(i) of this section, the current reported altimeter setting of an appropriate available station; or
  (iii) In the case of an aircraft not equipped with a radio, the elevation of the departure airport or an appropriate altimeter setting available before departure; or.
  (2) At or above 18,000 feet MSL, to 29.92” Hg.


What is the meaning of HOT-1, HOT-2, CAM, etc., in cockpit voice recorder transcripts? When reading the the written down recordings of CVR like here, for instance, it is common to see abbreviations like HOT-1, HOT-2 or CAM. I guess that CVR records multiple channels and the codes indicate the microphone that is believed to be closest to the source of the sound. But what exactly these abbreviations mean? Which others are possible?

They may vary from report to report, and the abbreviations used will be laid out in the report before the transcript, for flight 1549 (NTSB, .pdf) they are as follows:

  ATIS Radio transmission from the Automated Terminal Information System
  RDO Radio transmission from accident aircraft, US Airways 1549
  CAM Cockpit area microphone voice or sound source
  PA Voice or sound heard on the public address system channel
  HOT Hot microphone voice or sound source
  INTR Interphone communication to or from ground crew

  For RDO, CAM, PA, HOT and INTR comments:

  -1 Voice identified as the Captain
  -2 Voice identified as the First Officer
  -3 Voice identified as cabin crewmember
  -4 Voice identified as groundcrew
  -? Voice unidentified

  FWC Automated callout or sound from the Flight Warning Computer
  TCAS Automated callout or sound from the Traffic Collision Avoidance System
  PWS Automated callout or sound from the Predictive Windshear System
  GPWS Automated callout or sound from the Ground Proximity Warning System
  EGPWS Automated callout or sound from the Enhanced Ground Proximity Warning system
  RMP Radio transmission from ramp control at LaGuardia
  GND Radio transmission from ground control at LaGuardia
  CLC Radio transmission from clearance delivery at LaGuardia
  TWR Radio transmission from the Air Traffic Control Tower at LaGuardia
  DEP Radio transmission from LaGuardia departure control
  4718 Radio transmission from another airplane (Eagle flight 4718)
  CH[1234] CVR Channel identifier 1=Captain 2= First Officer 3= PA 4= Cockpit Area Microphone
  * Unintelligible word
  @ Non-Pertinent word
  & Third party personal name (see note 5 below)
  # Expletive
  -, - - - Break in continuity or interruption in comment
  ( ) Questionable insertion
  [ ] Editorial insertion

HOT vs. CAM:

  This recording contained audio from Hot microphones used by the flightcrew. The voices or sounds on these channels were also, at times, heard by the CVR group on the CAM channel and vice versa. In these cases, comments are generally annotated as coming from the source (either HOT or CAM) from which the comment was easiest to hear and discern.


Can turboprops use a recuperator? A recuperator is a device which extracts heat from the exhaust of a turbine and transfers it to the front air. This heats the air, which means the turbine uses less fuel to heat the combustion chamber to its max operating temperature.
They are used in gas turbines for power generation, because they can supposedly double the fuel economy.
Is this viable in a turboprop? Basically you need 2 heat exchangers per recuperator, so I could understand if they're too heavy. The other thing is potentially blocking airflow too much at the intake, causing too much drag.
Are these problems surmountable in aircraft engines? Is there a way to make them light enough and streamligned enough for aircraft?

The related question doesn't really answer this for turboprops. For jet engines, that related question does explain why it's no good---extracting heat from the exhaust means less jet speed. For turboprops however, it's all about shaft power, just like a electrical generator (before applying power to a prop instead of pure generator).

An aircraft engine is a thermodynamic device, that converts heat to mechanical power. A 'virtual' air parcel entering the engine goes through a thermodynamic cycle, which determines the bulk of the power plant efficiency, which include quite a big chuck of irreversibele air friction, with a minor role for bearing losses.
The engineering optimisation process however includes a lot more than just power plant efficiency. At the bottom line, the optimisation is tailored towards generating the most dollars of profit per unit of time, but a more optimistic view is that the engineer will optimise the aircraft fuel efficiency as a whole. In practice, this results in finding a balance between power-to-weight ratio and fuel efficiency, as additional weight increases the power required.
A recuperator is a heat exchanger between the compressor discharge air and the engine exhaust air*. Its goal is to replace part of the energy required from combustion of fuel by energy extracted from the exhaust, and does not modify the thermodynamic cycle in any way. I looked up some (approximated) data from a PT-6 turboprop at 850shp: [source, copied from training manual]

Ambient: 300K
Compressor discharge: 600K
Turbine inlet: 1200K
Exhaust: 800K

A recuperator could in theory cool the exhaust to 600K and heat the compressed air to 800K (ideal infinitely long counterflow heat exchanger) for a delta of 200K. The total desired temperature increase from compressor discharge to turbine inlet is 600K (1200K-600K), so we can reduce the fuel flow required by 1/3rd (only 400K delta still required). That seems excellent!
In practice, heat exchangers are bulky (air is a terrible fluid to transport heat). Furthermore, it's only operating on a 200K difference. The real question then is whether a real-world air-to-air heat exchanger (likely of cross-flow type, like an automotive intercooler, so less efficient than a counter flow heat exchanger) can be made so efficient that it does not introduce more losses than gains. Historic evidence suggest this is unlikely, especially if cost is considered (the material must be able to withstand 800K).
Furthermore, if we're going down the road of heat exchangers, different options are available. For example, an intercooler (cooling between compressor stages, which actually improves the thermodynamic cycle) could work on a higher temperature differential as well as lower absolute temperature, and would only present a single flow obstruction when the air is still nicely compact (power required is volume flow times pressure drop!) inside the engine. However, historic evidence again suggests that this is not cost-efficient, and instead seems to favour increasing the combustion chamber temperature and pressure.
*You may wonder, why not heat the intake air with exhaust air? We would work on a much larger temperature difference! In fact, this would be counterproductive, as the thermodynamic cycle operates on the difference between high and low temperature. Increasing the temperature at the inlet disproportionately increases the power required to compress the air, and does not result in an increase in turbine power (which in the end operates on a pressure differential, and cannot extract work from hot air at ambient pressure). There's a reason we use intercoolers, not inter-heaters in compressors.


What is the ATC protocol for hijackings? If a commercial aircraft is successfully hijacked, by a competent pilot / pilots, and they make contact with ATC for regular requests (i.e. weather updates, flight path information or clearing air traffic), will ATC still aid the (new) pilots, or do they have some other procedure, like trying to persuade them to hand control back to the original pilots?

I'm just wondering if there is a formal procedure for such an event, as I'm guessing it's rather unlikely that they would contact ATC like that. But always possible, of course.

In the US, the ATC protocol for hijackings is classified for reasons of national security.

  10-2-6 Hijacked aircraft

  Hijack attempts or actual events are a matter of
  national security and require special handling. Policy
  and procedures for hijack situations are detailed in
  FAAO JO 7610.4, Special Operations.‡ FAAO
  JO 7610.4 describes reporting requirements, air crew
  procedures, air traffic procedures and escort or
  interceptor procedures for hijack situations

Air Traffic Organization Policy, FAA, 2015-12-10.

‡This document's content can only be accessed from within the FAA network.


What are the requirements for grass height around runways and taxiways? I am looking for the requirements for grass heights around runway and taxiway edges, signs and lights?

The faa limits grass height around 12 inches in the United States. http://bettervm.basf.us/frequently-asked-questions/case-studies/small-airport-with-big-history-cuts-cost,-time-&-mowing-with-vegetation-management.html


Why isn't the course fixed along an airway? Why does in some cases magnetic course (not magnetic variation) change between navaids along a same airway? Isn't it supposed that a straight line in an aeronautical chart representing an airway has always the same magnetic course between navaids? Apparently that isn't so, but I don't understand why isn't so.

Isn't it supposed that an airway has always the same magnetic course between navaids?

No. The course depends on where you plot it from.

That's a random RNAV airway I picked, it has two headings, 114° and 298°, and the difference is not 180°, it's 184°, so over the course of 112 nm there is a 4° shift.

That's due to the curvature of the Earth.

Consider the following image carefully, notice the North-South needles, how they look on a 2D projection and on the actual globe.

Source: Wikipedia

That's the shortest path connecting those two points in South Africa and Australia.

If I'm in South Africa, looking at Australia, I'll look toward 141° (not 90°), as I get closer, this converges on 42°. If I look back from Australia, I'll face 222°. The difference between 222° and 141° isn't 180°.

If your airway exceeds 150 nm, this becomes noticeable. It becomes even more noticeable if you are flying between distant RNAV waypoints (e.g. NAT route), your heading (track to be more precise) will keep changing.

If you chase a true heading, and keep it constant over a long distance, this happens:

Source: Wikipedia

That's a very long turn, not straight-and-level flying.

Flying a great circle route, or staying on an airway between two navaids, requires flying a course, not a heading/track. The course's heading is only valid from where you plot it / start it. Along that course (i.e. route), the track keeps changing as the first image illustrates, and you're not turning.

An advanced autopilot follows the route computationally; a pilot hand flying would intercept the course, keep the selected course unchanged, and fly the deviation. If no factors (e.g. wind) push the plane off course, no turn inputs will be needed and the actual course will shift as the plane flies straight-and-level. The Course Deviation Indicator won't show any deviation because there isn't any.

Where It Starts

To further clarify why the course depends on where it starts, it's the fact that a VOR station—for example—transmits the radials in straight lines, those straight lines translate to a curved line on a 2D projection. They don't appear curved on a chart because the distances aren't big, even for the most powerful high altitude VOR station.

Hypothetically, if VHF had a huge range and wasn't limited by line-of-sight, VOR navigation would have become a bit confusing the farther out you are from a station.

Speaking of VOR

Just for the sake of completion, you'll notice I focused on RNAV waypoints. There's another factor affecting VOR stations. Two nearby VOR stations may have different alignments to the magnetic north. It depends on when they were built. One could be 20 years older than the other.

Once they're built and aligned, they are in most cases never re-aligned when the magnetic declination changes. It has to do with the cost and the redrawing of airways.

That can amplify the shift further.

So, think of a radial's heading as a highway marker.


What exactly is considered "instrument time" for an instrument rating? I have read in several sources that you are supposed to log instrument time when you cannot orientate the airplane by outside, visual cues alone. This seems clear enough. But I've also read that roughly 10% of flight time should be on instruments. Now, the instrument rating requires 40 hrs on instruments or in poor visibility conditions, so can we infer that pilots would receive their rating after approximately 40x400 = 16,000 hrs? Is this estimate approximately correct? Also, does all of this time require an instructor?

I think you are conflating two different things. Most IFR rated pilots have very little actual instrument time. Even airline pilots who fly in all kinds of weather have a low percentage of their time in the clouds. A lot of it has to do with where they fly—at over 30,000' they are often above the clouds. I would imagine that it varies a lot with the type of flying that the commercial pilot does. A freight hauler in the Northeast probably has a lot more instrument time than one in Arizona. Likewise, someone who flies their small aircraft a lot on business might have relatively more actual instrument time simply because they will be flying in the weather rather than above it.

If you look at the instrument requirements in CFR Part 61, the training requirements for the Instrument say "…hours of instrument training using a view-limiting device…". So it is possible to get your instrument rating with 40 hours of flying "under the hood" and never fly in actual instrument conditions. (You can also get some hours in a flight simulator.)  And when you take your practical test for these ratings, you will be flying under the hood and not in actual instrument conditions.

The same language is used in the Commercial rating as well. In fact, you could have a CFI who has never flown in actual instrument conditions teach you how to fly IFR!

To get an instrument rating you need 40 hours of hood time. Only 15 hours of this is required to be with an instructor. Lots of people save money on their rating by flying with a pilot friend or fellow student.

Once you have your instrument rating, you need to maintain currency by flying 6 approaches, holding patterns, and tracking courses in actual instrument conditions or with a view-limiting device. If you listen to the radio on a nice weekend, you will hear lots of pilots requesting practice approaches to maintain currency. Usually they are flying with a friend rather than an instructor.


How can I renew my non-current Indian CPL? I have not renewed my Indian CPL since 2001 and would like to renew it. what is the procedure as the CAR says nothing about renewing licence below 5700 kgs category.
Since there is no rule what can be done. I am flying regularly on my FAA licence.

This is for CAA , each country might have a different rule but in general this is the rule . If you haven't flown in India since 2001 then your license has been expired. So I assume that if you have any other license valid , you have to go to Indian civil aviation with your current  log book and they will request a confirmation from the country that you have got your license from to be sure that your license is still valid in that country.Then you have to do the conversion requirements which generally are 4 exams (for most countries are Law,HP,Nav, Met) and then you also have to go to any ATO in India and you must undergo sufficient ground and flight training for the same category aircraft that you have your other license on , and then do a oral exam and flight test .

If you haven't flown in the last 10 years , you have to do all CPL exams again .
Good luck.


How to programmatically access AIP data, METAR, TAF, NOTAMs? I'm looking at developing an app where one of the functions I would like to implement needs to use data which is normally available in AIP, like:

Aerodrome names, ICAO codes, GPS location, elevation
VFR reporting point names, GPS location
Nav points (names, locations)

In addition, I may want to display or use data from NOTAMs, METARs, TAFs, etc in my app.

Does anyone know the official sources for this data, ideally published by CAAs (FAA in the US, Eurocontrol in the EU and similar)? Please note I'm really only interested in programmatic access (e.g. a JSON, XML or similar feed available through a web API or similar), as opposed to document based data in the form of PDF or HTML files.

It goes without saying that I would ideally like this access for free, but a commercial arrangement is also I would look at - provided it's not outrageously expensive.

ICAO is offering a very nice API for retrieval of, for example, aerodrome names/ICAO codes and NOTAM's. It is currently in public beta, which means that it is free to use. Once they finish testing it, there will be some kind of cost involved, but they have not published any pricing details yet. You can find it here: https://www.icao.int/safety/iStars/Pages/API-Data-Service.aspx

NOAA offers API access to weather information such as METAR's and TAF's: https://aviationweather.gov/adds/dataserver

You can find waypoints and navaids, including names and locations, via EUROCONTROL EAD: https://eadbasic.ead-it.com/fwf-eadbasic/restricted/reporting/reporting.faces (register first, then return to that link). However, what they seem to offer is a one time search/database dump, more than an actual API.


How do I select an appropriate controller gain for this roll control autopilot? I'm trying to select a suitable K value for this roll control autopilot, based on:

Instead of the Gyro, I've also just considered a negative unity proportional gain feedback. How do I select the appropriate controller gain K for the system? (I'm feeding a step impulse into the system). I know that for each aircraft it would be different, for a fighter jet you want quick response times, but maybe not so much on a commercial airliner. What I'm trying to find out/understand is there design criteria/a method to selecting this value?

Is there a overshoot(%) I should aim for?
Is there a required damping ratio set?
Or do I eyeball it, and find a balance between the time to settle and overshoot(%)?

You want fast response, but not any overshoot. The perfect response to a step input in this case would be a critically damped one. Matlab/Simulink are your friends here.

Things to consider in your feedback loop:

Aircraft dynamics - is the initial inertia response modelled? Meaning, does the aircraft roll spool up to its final roll rate upon aileron deflection?
Is aerodynamic resistance to roll modelled?
Is it a digital loop, and if so what integrators are you using? If Euler your loop rates need to be high.

I've seen a similar design for a helicopter with a controller gain of 20 and an additional roll compensator $\frac {s + 1}{s}$ in the forward loop, and a negative unity feedback.

You could eyeball the response, use different settings for the feedback gain, and find the fastest response without overshoot. You'd have to testcase it for several extremes. You do need some form of damping feedback as well, I reckon your first task would be to find a response that is not oscillating.


Is prior clearance into Class B airspace revokable? I was piloting outside of Class B airspace in an area well known for being difficult from which to contact ATC via radio because of mountainous terrain. When I did get cleared into Class B, I was only about a mile outside of Class B airspace. Immediately, another controller took over (different gender / same frequency), revoked the clearance, and said to stay clear of Class B and scolded me for only being one mile outside of Class B. (I complied with that request, never entering Class B – so there was no violation.)

Question: Can you legally be “uncleared” into Class B after receiving a clearance into Class B?
Could you speculate on what may have happened?

Every clearance can be cancelled or revoked, irrespective of the type of clearance.


ASTERIX category 240 fields placement in a UDP packet I searched the placement of ASTERIX Category 240 radar video data fields in a UDP packet. But I cannot find any useful info. Is there a standard for this work?

The Asterix structure is explained in detail on this document on the Eurocontrol site.

Wireshark.org has a page explaining the protocol as well.


Where can I find this transonic prop airfoil? I am interested in identifying this prop airfoil due to its uncommon high .92% efficiency (the best metal props are closer to 83-87%). I have done an exhaustive search for it. It is labeled "NACA RML 9 G 06a". I do not know where I originally got this plot and therefore have no way to know what "ref 3" is.

It does not appear to be a airfoil number and a google search doe not return any "NACA RML" however I have a library of about 2000 "NACA RM" which refers to NACA Research Memos; perhaps the additional "L" means "Letter(s)".

I can find NACA reports starting with "RM G-10" but no G-9. I have also searched for derivatives of "06a" in an airfoil number. I would appreciate any assistance in identifying this airfoil.

The label you seek is not an airfoil, it is a research memorandum produced at Langley. (RM Lxxxx) The subject airfoil is NACA 4-(5)(08)-03 and the maximum efficiency from the test as reported in the conclusion was 88% at m0.71, partway down the curve where compressibility effects become adverse.


At what altitude did Concorde go supersonic? At what point during flight would Concorde go supersonic? Would it climb to cruising altitude first? Does altitude affect the transsonic difficulties (buffet, need for extra thrust, etc.)?

Concorde went supersonic during its climb phase to the cruising altitude.

The altitude at which the Concorde can go supersonic was limited by the regulations. For example, the aircraft was only allowed to go at 400 knots during the climb phase between 6,000 and 32,000 ft; also, the aircraft was allowed to go supersonic only after it has crossed the coastline.

As the air gets thinner during climb, the Mach number increases for same IAS, reaching around 0.93 at 25,000 ft and 0.95 at 28,000 ft. After this, the afterburners are engaged and autopilot is set to the cruising altitude (~ 60,000 ft). During this climb phase to the cruising altitude, the aircraft goes supersonic, settling at around Mach 2 at over 50,000 ft.

The flight envelope limitations of Concorde (at one configuration) is shown in this image:

Source: pprune.org

The altitude affected the thrust requirements, as more thrust is required for the same speed at lower altitudes due to density. This is one of the reasons for Concorde flying at altitude far above that of subsonic airliners.


How do I log simulator time in my logbook as a CFI? I'm a CFII at a 141 flight school, and when I give instrument instruction in our AATD flight simulator I'm kind of confused on how to log it. Should I log "As Flight Instructor" time even though it's not a flight? (My logbook has no "Dual Given" column which would make more sense.

Also, am I able to log "Flight Simulator" time? Even though there's only 1 yoke in the simulator, which I am not manipulating.

Buy a second logbook
Here's one that costs $11
As a CFII who had exactly the same problem that you did, I can tell you that this is the easiest and simplest way to keep your simulator dual given and your airplane dual given separate.  You just log all of your simulator time as if it was airplane time, but in a simulator.  So, flying a sim that emulates a multi-engine airplane? Airplane Multi-Engine Land column!  Put the student in the soup?  Actual instrument column! Record the serial number of the AATD in the "Aircraft ID" column and you're all set!
But it would be simpler to have just one logbook...
In that case, see if there's an unused column in your logbook that you can cross out and relabel as "simulator dual given".  Airplane Single-Engine Sea works well for this.
Isn't there some kind of technology that could solve this problem?
Sure is!  Electronic logbooks are the bee's knees.  Try Zululog, I don't use it but it's free so if you hate it all you've lost is some time.  Foreflight has a logbook option too. I don't like it (it seems lightweight to me) but you might.
Can I log flight simulator time?
Technically you can log anything you want, including passenger time, chair flying time, and time spent in the hangar arguing about taking off from a treadmill.  The question is whether or not that time is valuable toward future certificates, ratings, or employment.  Dual given as an instructor in a simulator is, sadly, not at all valuable.  No one really cares and you can't use it toward any certificate or rating that I'm aware of.
Which is why you want to log your simulator instruction in a separate logbook; assuming you're not planning to instruct for the rest of your life like me, when you go in for interviews you'll be able to just bring your aircraft logbook and leave the simulator one at home.


If a CDI needle is deflected to the right, why is the aircraft off track to the left? Consider a CDI as shown below. If the CDI is set to FROM and the selected course is north, but the needle indicates three dots to the right (each dot signifying a 2 degree deviation from the selected course, i.e. 6 degrees in total), then why is the aircraft's radial at 354 degrees?

I associate a right movement of the needle with a "positive deviation", which would correspond to the aircraft's radial being at 006 degrees.

The CDI indicates your desired course. The white circle in the center of the instrument represents your position. If the desired course is to the right of your position, you need to move to your right to rejoin your course.