What is the least expensive way to become a commercial pilot in the UK? Besides the RAF is there a way of becoming a pilot without spending tens of thousands of pounds on flight training? I'm finishing university and looking to go into a career in flying, I can't join the RAF since I am partially colourblind so I would not be allowed to train as a pilot in the Air Force.

There's a finite minimum set of requirements you must meet to get that ATPL and type ratings, and there's a finite minimum cost associated with that.
Nothing's going to change that. The only thing you can possibly, maybe, change is who is going to pay that money.

So don't fail any of the tests. The ONLY way to reduce the cost is to complete the training in as short a time as possible. Which means minimising flight hours, simulator hours, and retaking of courses. All of which boils down to passing every test first try.

And it will still take tens of thousands of pounds.

Going the Air Force route is also takes tens of thousands of pounds, except the air force (and thus other people, taxpayers) pick up part of the bill.
Same with every other scenario in which you're not paying everything yourself. Someone, somewhere, is paying for it.
Used to be (and maybe still is, but it's unlikely given the glut of unemployed pilots) some airlines would take on people and train them from scratch. But that's now rare. Most at the very least require you to have your PPL already, and many won't hire you unless you are qualified on at least some aircraft in their fleet.


What is the top speed of the twin seat Hawker Hunter? Recently I learnt that the Hawker Hunter had a side-by-side twin seat trainer version. This is unusual, since more often the tandem configuration is used. I'm sure the engineers had a good reason to choose this solution, but it got me wondering: how much is the top speed impacted by the resulting increase in frontal area?

From what I've found online, the specs are the same for both trainer and single-seat versions but that doesn't seem right; if nothing else, the empty weight should be different. Is there a former Hawker Hunter pilot here who trained on the twin seater and can tell us the truth?

The manufacturer
lists over half a dozen variants of Hunter two-seaters.
You probably mean the T.7.

For a fair comparison, its closest single seat variant is the F.6,
maximum speed Mach 0.94
(715 mph) at sea level.

The T.7A, a T.7 with different instruments, has a maximum speed of
Mach 0.92 (690 mph) at 36,000 ft.

So the T.7 is a few per cent slower than the F.6.
But it's no slowpoke: in 1959 it even won
the flying leg of a complicated race against 200 other entries.

Your empty-weight test suggests that these numbers are trustworthy:  the weights posted there say that the T.7 is 762 pounds (5 per cent) heavier.


What is the Specific Fuel Consumption of CFM56-7B24/26/27 engines? I think the title completely says what I need. I use FSX (Flight Simulator X) to simulate flights and while flying the B738 I saw that it consumes much more fuel than the estimated amount, which is calculated by the software. By doing some research in the airplane folder I figured out that the problem is because the wrong Specific Fuel Consumption (SFC) is  entered there. And by some research on the net I also found the type of engine that B738 uses. So, right now, I need to know the SFC of the CFM56-7B24/26/27 engine so that I can enter the correct value in FSX.

SFC for CFM56-7B is 0.5lb/lbf/hr. As an aside, the LeapX is 16% better at 0.42lb/lbf/hr.


Why do intermeshing helicopters use asymmetric airfoils? I am referring to the Kaman K-max and the Kaman Huskie here. They both use NACA 23012, which is an asymmetric airfoil. Any reason as to why this is? Is there a different mechanic in play when intermeshing rotors are considered? Does Reynold's number change due to factors that don't affect normal helicopters?

Edit - I can see how my question can become very broad. My question would be answered if somebody could explain what factors come into play in intermeshing rotors that affect the choice of airfoil.

Helicopters in general use asymmetric aerofoils because they are not required to fly inverted or produce negative lift. Intermeshing helicopters are no different in this regard.

The exception would be aerobatic model helicopters, which use symmetrical aerofoils because they are designed for similar performance either way up.


Are there examples of passengers' Micro SD cards or USB flash drives surviving crashes? Are there any well-documented cases of Micro SD cards or USB flash drives surviving 100% hull loss crashes? I'm asking about cards held by passengers, not ones that are part of the aircraft's systems.

Yes. Some videos where recovered from the germanwings crash. See this article talking about it: link

The video can now easily be found online. I recommend against it tho.


What technologies exist to find an aircraft position after it crashed out of line of sight? What is the best way in the manner of products to find an aircraft after it crashed out of line of sight. Are there defined standards, and what are the selection criteria?

It depends on the UAV.  Many consumer UAVs eg DJI, etc. track the position of the drone via GPS and log it so you can find the crash site quickly.  Others emit beeping noises so you can locate it by sound.


Are there any airliners capable of vertical climb with engine thrust only by pointing the nose up? So, sort of inspired by this question, I was wondering if there were any passenger airliners with enough thrust to fly straight up, supported purely through the thrust of their engines rather than the aerodynamic lift generated by their wings - so that once it's flying along, it can just point its nose at the sky and go straight up; if you think about the launch of the Space Shuttle, you’ve got the right general idea. According to some of my comments, this is apparently called a "zoom climb". Note that I'm not asking about VTOL, since some aircraft that are capable of this may not be capable of VTOL due to a lack of thrust vectoring.

I know that some military fighter aircraft are capable of this, but based on some research with Wikipedia, it appears that the Boeing 747, Boeing 787, and the Airbus A380 can't - though the 787 would almost be able to do it if it had four engines rather than two.

Are there any passenger aircraft that are capable of doing this? Obviously they wouldn't do so while passengers were on board, but I'm just interested in the ratio between Operating Empty Weight and Maximum Thrust.

No, there are few planes that can do this at all. In order to be able to climb out straight up you need a thrust-to-weight ratio greater than 1. In other words you need enough thrust to propel the full weight of the aircraft up without the wings generating lift.

Wiki provides a brief list of aircraft and associated thrust to weight ratios, the Concorde comes in on top at 0.372 with full afterburner but this is at max weight. Although at its empty weight it was pushing a 0.877 ratio. Even running on fumes would not have done it at full afterburner in the Concorde. For comparison the 757-33 has a ratio of 0.6 at Operational Empty Weight assuming a maximum thrust of 42,600 lbf per engine.


Which part of aircraft is contributing the most weight of airplane? Which part of the aircraft contributes the highest portion of weight?

Note: we had argument that, wires connecting the avionics systems are the major contributors of aircraft weight. Due to some issues with optical fibre technology this is not been used in aviation yet. So my question arises as mentioned above.

Aerospace Engineering e-Mega Reference shows the following table for two aircraft (the large commercial jet, the B747-100, and the military jet, the C-5A). You can see that it differs quite a lot between the B747 and the C-5 already, so it's hard to give a definitive answer for all aircraft in general.

Also, it depends a lot on how you break down the components, for example, here the Nacelle and Propulsion system are shown separately, but if you combine the two (and some others as is done in the dry engine weight, I think) things could change.
The Aerospace Engineering e-Mega Reference points to Beltramo as the source for the numbers. Perhaps you could find some information there about what belongs to which group.

However for both aircraft, it can be seen that the Wing and the Airframe are significant contributors (and for the B747 furnishing is also a large part of the weight)

I think they included all the wiring in the Avionics part (that would make sense to me), but still it is a relatively small part of the total weight.


Which official document lists active airport identifiers? Is there an official FAA document with which I can find an airport by its identifier code if I do not have a name or location? In the Chart Supplement I can find the airport if I know the city and state. However, I can’t seem to find any sort of reverse lookup document that lets me find it by code only.

I know I can search on SkyVector/ForeFlight/etc. but I am specifically asking if there is a government published “index document” for this.

The FAA JO 7350.9L - Location Identifiers contains complete lists under decode subsections organized alphabetically. Example:


Where can a PDF of the TPP legend and supplemental materials be found? When you buy a book of government approach plates, or a Terminal Procedures Publication (TPP) it comes with a legend and other supplemental documents along with it. Now that a lot of pilots are using digital flight bags like ForeFlight it's easy to overlook this stuff.

What I need is a PDF of these materials, but after a lot of searching I'm just not finding it. Does anyone know if the FAA publishes this digitally? This page mentions that it's available, but I don't see the download for it.

Apparently the file you are looking for is FRNTMATTER.PDF, located in the "D" download file.   DDTPPD_201603.zip

(but it still looks like you have to download the 900MB ZIP file just to get that one important file)

The file that @JonathanWalters referenced has very similar information in a much smaller download and a different format.  But there are differences between the two.

I recommend downloading both the Chart Users guide at the FRNTMATTER.PDF file, and judging for yourself which one (or both) best has the info you are after.


Why do Western aircraft manufacturers use FPS system while Russian aircraft manufacturers use MKS system for flight instruments? Why is there a variation in aircraft flight instruments of aircraft from Western & Russian origin?

Foot–pound–second system (FPS)
Meter-kilogram-second (MKS)

The short version is that "Western" countries (nearly all countries, in fact) use knots and such because that's what we started with and, once that became entrenched, the cost of retraining every pilot and reequipping every plane--and the inevitable confusion and crashes during that transition period--greatly exceeds the benefits.

The USSR, PRC and a few others were able to use metric units because they didn't need to care about compatibility with the rest of the world--or perhaps saw the lack of compatibility as a good thing, helping to keep them isolated.


What airline academies are available to US citizens? It seems that EU/Asian/Middle Eastern citizens have the opportunity to apply for several self-funded programs which (upon acceptance and completion) guarantee a job as a first officer on small twin engine aircraft flown by the sponsoring airline. Is there any such program available to US citizens? And if so, what makes an applicant competitive?

Many of the Asian ones are only open to their own nationals, to give them the opportunity to become a pilot as well. Pilots are in demand, and particularly captains are hard to find. For the funding, many F/Os are now self funded, low cost airlines do usually not fund initial pilot education.

An outfit like Stella Aviation in The Netherlands did offer bank loans to fund the license, guaranteed until the student found a job.

Unfortunately, we don't see many USA citizens working as expats: they are often very expensive due to having to pay double taxes when working abroad, USA has historically had few tax agreements with other countries.


In F/A-18, where the servo-loop closure is accomplished? In the flight control system of F/A-18, where is the servo-loop closed? I mean which of these two scenarios happen: 1-The position of the actuator and servo-valve ram are sent to the flight control computer and the servo-loop is closed there in the software, 2-the servo-loop is closed near actuator that means the actuator has an interface that receives a command and compares it with the actual position. If the second scenario is what happens, the interface is digital or analog?

Ram position feedback is sent back to the relevant channel in one of the two flight control computers via wire carrying an analogue signal. If it is a leading edge flap, aileron or rudder it is done twice. The big surfaces (Trailing Edge Flap and Horizontal Stab) are quad redundant. The signal is processed on a printed circuit board inside the box. There is negative feedback occurring via an operational amplifier type circuit.


How do "fundamentally unstable" aircraft deal with the risk of computer failure? As technology becomes more advance airplanes are becoming less and less stable.  In flight school I learned that it's dangerous to load a Cessna out of it's CG range, and now in college (for aerospace engineering) I'm learning about modern fighters and their fundamentally unstable designs.

A lot of these unstable aircraft are supermaneuverable but rely on computers to fly them more than the human pilot in the cockpit.

I'm sure that these airplanes are thoroughly checked before every flight to make sure the computer systems will perform accordingly, but in the event of a failure what kind of side affects might a pilot experience?

The two conditions I can think of are

No computer aid, but the control surfaces are still "responsive"
The pilot loses all control of the aircraft and none of the inputs work.

"fundamentally unstable" but über-responsive aircraft have multiple computers that take a vote on everything the pilot wants to do. If one computer fails the others will take over. There is often no direct connection between the control column and the flight surfaces so the "no computer aid" situation would be the same as #2.

If everything fails, the checklist is rather short: eject immediately.


When were commercial pilots first allowed to use glasses? Currently, pilots with defective (but correctable) vision are allowed to pilot airliners if they have at least two pairs of their corrective lenses (typically glasses) with them on board.

Was there a specific moment in time when this was first allowed by law and regulations (prior to which persons with defective vision would have been prohibited from piloting an aircraft, even with corrective lenses)? Or has flying with corrective lenses been allowed since the earliest moments of airliners' history?

In the US, the department of commerce had an Aeronautics Branch. It was first responsible for civil aviation safety. On February 28, 1927 it published a list of the first physicians, who were qualified to give medical examinations for pilot licenses.

On December 31, 1926, the Aeronautics Branch issued the first air commerce regulations, that included medical standards. These standards discerned three levels of physical standards one for each class of pilot : private, industrial and transport. The standards included regulations for visual acuity. Private and industrial class pilots were allow to wear corrective glasses.


What is Density Altitude? I'm trying to get a deep understanding of the term: Density Altitude.

So I have read the explanations in my instruction book, and online articles.
One source explained it differently then the other which confused me.

Wikipedia defines Density Altitude as:

  The density altitude is the altitude relative to standard atmospheric
  conditions at which the air density would be equal to the indicated
  air density at the place of observation. In other words, the density
  altitude is the air density given as a height above mean sea level..".

https://en.wikipedia.org/wiki/Density_altitude

So if I would believe Wikipedia then I could look at the ISA table to find the altitude by using the pressure.

Here is an ISA table:

My instruction book (Aerodynamica, prestatieleer en vliegtuigtechniek by Bas Vrijhof on page 112, written in Dutch) claims this:

  in de ISA is de dichtheidshoogte altijd gelijk aan de drukhoogte

Translated to English: in the ISA the density altitude is equal to the pressure altitude.

So, let's say I'm flying in an aircraft, the pressure is "22.22 Hg", and the outside air temperature is -0.9°C. The altitude in the ISA would be 8000 ft. The Density Altitude would also be 8000 ft.

Skybrary defines Density Altitude as:

  Density altitude is pressure altitude corrected for temperature.

Link: https://www.skybrary.aero/index.php/Density_Altitude

This explanation contradicts with the Wikipedia explanation:

  the air density would be equal to the indicated air density at the
  place of observation

On another wikipedia article I found this:

  De relatie tussen temperatuur, hoogte en luchtdichtheid kan worden
  uitgedrukt in density altitude.

Translated to English:
The relationship between temperature, altitude and air density can be represented as density altitude.
Link: https://nl.wikipedia.org/wiki/Opstijgen#Benodigde_snelheid

So in short, each source explains Density Altitude in their own manner, some contradict the other which confuse me.

So my question is:

What is Density Altitude?

The concept of 'density altitude' is kind of like the concept of 'wind chill'.
Stick with me here, I'm going somewhere with this.
Cold weather is dangerous for the human body, and wind (because of increased heat loss on human skin) makes it worse. But how much worse? Is it worse to be outside in -10C temperatures with a 20 knot wind, or -15C temperatures with a 12 knot wind? The concept of 'wind chill' resolves those two values into a single easy number.
Density altitude works the same way. It's difficult and tedious to compare and contrast how an airplane will perform on a 25C day with a pressure of 29.80 at an elevation of 600 MSL, versus a 20C day with a pressure of 30.17 at an elevation of 1250 MSL. We need a way to mash all of these variables into one easy-to-use number. That number is density altitude.
So just as I can say "The wind chill is -10C" and it doesn't matter whether it's warm but windy or cold and calm, I can say "The density altitude is 2,000" and everyone will have the same idea of the expected performance of the airplane, no matter what combination of factors led to that result.
Once you start thinking of (and using!) density altitude as a simplification tool, its value becomes a lot more obvious.


What is the Dimension of Equilibrium Space in Longitudinal Space? Full untrimmed Flight Dynamics model of an Airplane is separated into two separate systems: Longitudinal and Lateral.

When the untrimmed model in Longitudinal direction, which is six dimensional, is trimmed (f(x,u) = 0), what is the dimension of the equilibrium space? Is it two dimensional? If yes, then why?

x = state vector for longitudinal direction
u = control vector in longitudinal direction

I never heard of the term "Equilibirum Space" in flight dynamics and I can't find references in a quick google search.

However, I assume you are talking about describing the flight dynamics of an aircraft as a linear state-space model. When linearising, you can indeed separate the equations of motion in the plane symmetry (longitudinal) from the assymetric (lateral) motions.

$\dot{ \vec{x}}=\mathbf{A} \vec{x} + \mathbf{B} \vec{u} $

The dimension of the state vector $\vec{x}$ is usually 4 (velocity, flight path angle, pitch angle and pitch rate), in your case the dimension of the control vector  $\vec{u}$ is 2 (thrust and elevator deflection).

You linearise the equations of motion around an equilibrium point; the state and control vectors describe the deviation from that equilibrium point. The dimension of the equilibrium points is 6 (4 state variable, 2 control variables).

One could say that the equilibrium point is in the space spanned by the 6 independent state and control variables. If that is what you mean, then dimension of the equilibrium space is 6.


What is the FAA definition of solo flight? If I'm a student pilot (for commercial), and I flew for pleasure with friends one night, do I log those hours as solo? Does solo mean, only pilot in the aircraft? Or does it literally mean only person?

According to FAA, it means that the pilot should be the only person in the aircraft. According to 14 CFR § 61.51 - Pilot logbooks,

  (d) Logging of solo flight time. Except for a student pilot performing the duties of pilot in command of an airship requiring more than one pilot flight crewmember, a pilot may log as solo flight time only that flight time when the pilot is the sole occupant of the aircraft.

14 CFR § 61.8761.87 - Solo requirements for student pilots also says pretty much the same thing:

  (a) General. A student pilot may not operate an aircraft in solo flight unless that student has met the requirements of this section. The term “solo flight” as used in this subpart means that flight time during which a student pilot is the sole occupant of the aircraft or that flight time during which the student performs the duties of a pilot in command of a gas balloon or an airship requiring more than one pilot flight crewmember.


Can a plane land on an aircraft carrier without support from its crew? Imagine a scenario where a carrier was dead in the water. No-one inside. Could a plane land on the carrier? What would such a procedure look like potentially?

The Nimitz Class aircraft carriers are the largest warships ever built. With over 6,000 personnel (crew and aircrew), the carrier has a displacement of 102,000t, and a flight deck length of 332.9m.

From: Nimitz Class Aircraft Carrier - Naval Technology
https://www.naval-technology.com/projects/nimitz/

332.9m * 39 in/m * 1 ft/12in = 1081.9 ft.  I think many small (2-4 seat) aircraft could land & stop in that distance. I'm pretty sure I could in my Cessna 177B, fixed gear, with micro-vortex generators for slower landings. Even without any headwind to help slow down.

From the 177B Pilot Operating Handbook:

  LANDING PERFORMANCE:
  Ground Roll    ---------------------------------------------------- 600 FT

And that was before the micro VGs, so it should be even shorter now.


In reference to airspace, what does the FAA mean by "within the lateral boundaries of"? Is this construed to also imply a vertical limit? Several FARs use the phrase "within the lateral boundaries of" (x airspace).  What does the FAA interpret this phrase to mean?  Specifically, what is the vertical extent of the airspace encompassed by this phrase?

The common-sense interpretation of this phrase would appear to include any airspace whose latitude-longitude coordinates fall within the boundaries of said airspace, regardless of altitude, from the earth's surface all the way to outer space, or at least to the upper limit of the airspace which the FAA has any regulatory authority over.

Otherwise, it would seem to serve just as well to dispense with the "within the lateral boundaries" phrase and simply say "within" (x airspace).

Is there any evidence that the FAA interprets "within the lateral boundaries of" differently than the meaning noted above?

The answer to this question affects the interpretations of certain FARs, describing, among other things, airspace where ADS-B-out is required, airspace where 3 miles visibility is required to enter a traffic pattern under Visual Flight Rules with no special VFR clearance, airspace within which aerobatic flight is prohibited, airspace where prior authorization is required to operate unmanned free balloons, and airspace in which an ultralight aircraft may not be flown without prior authorization from ATC.

The FAA normally interprets the phrase "within the lateral boundaries of" (x airspace) to mean any airspace whose lat-lon coordinates fall within said boundaries, regardless of altitude, from the earth's surface all the way to outer space, or at least to the upper limits of the airspace which the FAA has any regulatory authority over.

Pilots would be wise to follow this common-sense understanding of the meaning of "within the lateral boundaries of".

However, the FAA is not a monolithic entity, nor is it immune to making the occasional blunder.  On a few occasions, some subset of the FAA has adopted a very different understanding of the meaning of "within the lateral boundaries of".

For example, in the text of a spectacularly misguided Final Rule published on page 51966 of the October 5, 1993 edition of the Federal Register, the FAA implied that the phrase "within the lateral boundaries of the surface areas of ... Class E airspace designated for an airport" would not encompass any Class E airspace higher than the floor of the 700' or 1200' AGL "transition area" that invariably overlies a Class-E-to-surface airspace.

To correct this imaginary problem, the FAA changed the wording of FAR 91.157 from the existing wording

  91.157 Special VFR weather minimums Except as provided in appendix D, section 3 of this part, the following special weather minimums and
  requirements apply to operations conducted to or from an airport in
  controlled airspace:  (a) Operations may be conducted only under an
  ATC clearance-- (1) Within the lateral boundaries of the surface areas
  of Class B, Class C, Class D, or Class E airspace designated for an
  airport; and ...

To the new wording

  91.157  Special VFR weather minimums ( a ) Except as provided in appendix D,
  section 3, of this part, special VFR operations may be conducted under
  the weather minimums and requirements of this section, instead of
  those contained in 91.155, below 10,000' feet MSL within the airspace
  contained by the upward extension of the lateral boundaries of the
  controlled airspace designated to the surface for an airport. (b)
  Special VFR operations may only be conducted--(1) With an ATC
  clearance...

However, the FAA failed to also change the similar wording of FARs 45.22(a)(3)(ii), 91.155(d), 91.303(c), 91.309(a)(4), 93.152, 101.33(a), 103.17, 107.41, 135.205(b), and 137.43(a), thus implying that none of these FARs should be understood to apply to any Class E airspace above 700' AGL in most cases, or above 1200' AGL in the remaining cases.

This blunder has never been officially corrected-- the text published in the October 5, 1993 edition of the Federal Register has never been officially retracted.


When flying on a glide slope, does the G meter show 1G or less? If your angle of attack in landing pattern is 14 degrees but your vertical velocity is 600 feet/minute, does the HUD show you 1G or not? Why?

I presume, an implicit assumption in your question is that we are flying a perfect glideslope, that is, a straight line with a constant speed, and without disturbances.
If this is the case, the acceleration will be zero by definition, and the only effect we (and an accelerometer) will feel is gravity.
The 'G-meter' shows the acceleration (incl. gravity) with respect to a calibrated standard 1G. Now, the question is, will gravity be the same from the point of view of the device/pilot?
The answer is: almost, but not quite.
First of all, the 'G-meter' typically shows the normal acceleration: that is, along the body Z axis. It is 'vertical' for the pilot, but not necessarily vertical for the Earth. This is the critical acceleration component, the greatest one (because the wing can produce by far the greatest force on an airplane), the one that is always specified in the flight manual and the one that you might exceed in normal manoeuvring. This is why the device shows it and not the 'total' combined acceleration.
Thus, the gravity component as measured by the 'normal' accelerometer will depend on the airplane attitude. In terms of G, the factor will be $cos(pitch) \cdot cos(roll)$. For the given example, if we assume the glideslope angle -3°, pitch will be $14-3 = 11°$, and with zero roll, the measured G will be $cos(11°) \approx 0.98$. Very small difference indeed.
However, in a more extreme example of a vertical dive, the accelerometer will show zero (0G).
But that's not all. If we want to be really pedantic and measure beyond 1%, we'll need to take into account that the apparent gravity changes depending on the location. Given that the accelerometer shows, essentially, weight of a calibrated mass, it will indicate different G even if the aircraft is standing on the ground.
I'm not talking about gravity anomalies, which are truly miniscule. The biggest contributor is Earth rotation, which adds some centripetal acceleration, the more of it the closer to the equator you get. At the equator, it reduces your weight by almost $0.4$% with respect to the pole.
A further $0.1$% can be accounted by the fact that Earth radius is greater at the equator than at the poles - by about 21 km. This is typically a bigger contributor than the aircraft's own altitude (esp. given that glideslopes are usually near the ground).
Altogether, if we calibrated at a pole and then make an approach near the equator in the stated conditions, we can expect almost $2.5$% reduction of the indicated G-force.
In truth, the calibration is usually done for middle latitudes (and digital AHRS may calibrate before takeoff on the actual location), so the difference will be even smaller. But anyway, the biggest contributor - attitude - is unaffected by these small changes. Yet, it is still small by itself, often below the accuracy of the G-meter.


What is the difference between SUA (Special Use Airspace) and FUA (Flexible Use Airspace)? The EUROCONTROL Concept of the Flexible Use of Airspace (FUA) is that:

  an ASM concept currently applied in the ECAC area and based on the fundamental principle that airspace should no longer be designated as
  either pure civil or military airspace, but rather be considered as
  one continuum in which all airspace user requirements have to be
  accommodated
  an airspace management concept applied in the European Civil Aviation Conference area on the basis of the “Airspace management
  handbook for the application of the concept of the flexible use of
  airspace” issued by Eurocontrol

EUROCONTROL also defines Special Use Airspace (SUA) as:

  Airspace of defined dimensions identified by an area on the surface of
  the earth wherein activities must be confined because of their nature
  and/or wherein limitations may be imposed upon aircraft operations
  that are not a part of those activities.

Question: what is the relationship exists between SUA and FUA? Can they be considered as the same thing? Is SUA a special type of FUA or vice-versa?
What is the difference essentially?

Flexible Use of Airspace is a concept rather than a part of airspace (which SUA is), where the whole airspace is used for both restricted and unrestricted (civil) activities. According to FAA:

• The FAA version of Flexible Use of Airspace (FUA) is called “Joint Use Airspace”
• Although not defined as such, the domestic United States could be labeled as being completely FUA airspace.

The Special Use Airspace (SUA) is a portion of the Flexible Use Airspace (FUA), in which unrelated activities have been restricted:

In accordance with the FUA concept, Special Use Airspace is a defined portion of airspace which may be temporarily reserved for specific activities which require the restriction or segregation of other traffic.

Basically, in a FUA, SUA will be a temporary restriction (rather than a permanent one). Eurocontrol also says the same thing:

The EUROCONTROL Concept of the Flexible Use of Airspace (FUA) is that:
Airspace is no longer designated as purely "civil" or "military" airspace, but considered as one continuum and allocated according to user requirements.
Any necessary airspace segregation is temporary, based on real-time usage within a specific time period.

Related concept is Advanced Flexible Use of Airspace in which SUA is allotted in real time.

An airspace management concept in which airspace is managed as a single entity and in which there are no fixed structures and airspace reservations for special airspace activity are allocated in real time.


Can a private pilot placard an inoperative instrument? For certificated small aircraft that are not required to have a minimum equipment list. If you have an instrument break while on a cross country flight and it is not a legally required instrument for the type of flight. You are on the ground at a distant airfield and would like to return to your home-base mechanic rather than hiring an A&P in the middle of the trip.(or if the airport has no local services)
Can the pilot legally label the instrument as inoperative for the duration of the trip without hiring an A&P to officially "deactivate" and placard the item?

The answer to your question is probably. The rule governing this is

  §91.213   Inoperative instruments and equipment. (a) Except as provided in paragraph (d) of this section, no person may take off an
  aircraft with inoperative instruments or equipment installed unless
  the following conditions are met:

and if you skip past the MEL section (which, as you noted, doesn’t apply to most small general aviation aircraft) you see the conditions that must be met.

  (3) The inoperative instruments and equipment are—

  (i) Removed from the aircraft, the cockpit control placarded, and the
  maintenance recorded in accordance with §43.9 of this chapter; or

  (ii) Deactivated and placarded “Inoperative.” If deactivation of the
  inoperative instrument or equipment involves maintenance, it must be
  accomplished and recorded in accordance with part 43 of this chapter;
  and

  (4) A determination is made by a pilot, who is certificated and
  appropriately rated under part 61 of this chapter, or by a person, who
  is certificated and appropriately rated to perform maintenance on the
  aircraft, that the inoperative instrument or equipment does not
  constitute a hazard to the aircraft.

Suppose your landing light burns out. A landing light is not required unless you are flying for hire, so you can put a piece of tape under the switch and label it Inoperative and you are good to go.

If your transponder fails, turn it off and mark it Inoperative. If you are going to fly in airspace that requires a transponder, you have to jump through some hoops per §91.215, but you are still good.

If there is something that requires removal or disabling—and it is not something you are allowed to do in Part 43—then you need an A&P to remove or disable it and make a logbook entry. I’m having a hard time thinking of something that would need disabled and yet you could still legally fly the airplane. The best I can come up with right now is a stuck push-to-talk button. That’s not listed in Part 43 as something that you can perform maintenance on, so an A&P would have to disable it and make a logbook entry.

By the way, you can fly forever with inoperative equipment. There is a LORAN in plane I fly that has been marked inop since they decommissioned LORAN. When I put a new radio in my plane 10 years ago, I kept the old one in case something happened to the new one, and marked the nav portion inop.


What does "synoptic" mean in avionics? I came across a mention of a display of "graphical aircraft system synoptics" on this page.  I think in context that it means "status display" or "summary page"- the page that shows flap position, hydraulic pressure, etc.

However, synoptic isn't even a noun in some dictionaries. Google searches for the word turned up only passing references to the term, not a solid definition. The actual word usage seems very aviation-specific.  What does the term actually mean and how does it differ from "system status" or "summary page?"

Synoptic refers to the active system diagrams that are selectable, usually on one of the middle displays above the center console.  If you want to know what the hydraulic system  is up to, you can select the Hydraulic Synoptic and an active diagram of the hydraulic system appears, showing what's pressurized and what's not, valves open and closed, the pressure values, quantities, etc.  There will be one for most of the major systems, hyper simplified compared to a normal system schematic because only the essential information is presented.


Why did WWII prop aircraft have colored prop tips? Why do propeller aircraft from World War II and similar planes sometimes have the tips of the props colored? I see it on single engine planes like the P-51 as well as bigger, multi-engine planes such as the B-17.

The prop tips are painted for visibility, to show that the prop is turning. This is especially important when the aircraft engine will be running in close proximity to people on the ground, but is also helpful in alerting the crew of other aircraft that the engine is running, and the aircraft might be moving soon.

For visibility, the tip color should be in high contrast to the blade, typically white on black.

Some operators paint the prop tips in an alternating pattern for a strobe effect for heightened visibility. This is especially helpful when operating in areas where people on the ground may be unused to being around aircraft; the strobe effect is an attention-getter. A three bladed prop painted in this way might use a pattern of one, two, and three stripes, or two, three, and four stripes.

Here is an example of what this pattern would look like on a 206:

Source: own work

This is what the pattern on a Quest Kodiak looks like in motion:

Source: excerpt from original photo by Dave Forney


Can commercial airliners fly over hurricanes? When Patricia was making landfall yesterday I opened up Flight Radar 24 to see if there were any planes flying around or near it.  As I had expected, there were a couple of storm watching planes near the hurricane, but what surprised me is that there were some commercial flights that seemed to be going over portions of the hurricane...

So, I'm curious, can commercial aircraft go high enough to simply fly over a hurricane, assuming they take off and land at airports that are not effected by the storm?  Or perhaps they can only safely fly over the fringes and need to stay away from the eye?

Basically, can airliners fly over hurricanes, and if so can they fly over all of it, or just parts?

In general, no- except in emergencies or 'small' hurricanes.

Commercial aircraft usually fly around bad weather (like hurricanes), not over it.
Some of the hurricanes can reach upto 50,000+ ft height, making it all but impossible for most modern commercial aircraft to fly over them (except maybe you're flying a Concorde). Even for smaller storms, the convective process over the hurricane will cause severe turbulence, affecting overflying flights.
Even for hurricanes where the  aircraft can fly over, there is the problem of safety- What will happen is something happens (for example engine failure) and the aircraft has to descend to lower altitudes? Obviously no one wants to descend into the storm.
There are some aircraft that do fly into hurricanes for scientific experiments. These are crewed by trained (and experienced) specialists and involve a lot of detailed planning. For example, the aircraft are equipped with radar that helps in avoiding the worst parts of the storm. Still, it is risky and the aircraft is exposed to significant loads and vibrations not usually exposed in commercial service.


What is the criteria for selecting BNR or BCD as data encoding in ARINC429 I was going through ARINC429 part1-18 and found all the labels that are defined along with transmission bit and data encoding. What is the criteria for choosing BNR or BCD for data encoding ? Why are some BNR while rest are BCD ?

The general ARINC guideline for publishing data is to publish both BCD and BNR values when both types are defined. That allows the receiver of the data decide which to use. If only one form exists, then that's the way it's coded. It ultimately comes down to what the ARINC committee decided made the most sense.

Typically, BNR coded data is used by computational functions -- things that process the data value and expect the greatest precision in the number. They don't really care whether the number is easily readable.

BCD coded data is typically used by display systems as pilots like to read decimal numbers the numbers can easily be scaled to a readable display, e.g. DME range in NM rounded to the nearest 0.1 NM or bearing to the nearest 1 degree.

BCD is also used in control panels where the data is discrete decimal data (radio frequencies) and the crew enters a decimal value.


Could abrupt flight controls input cause damage in these circumstances? I went flying yesterday with a friend in my 1972 Grumman AA-5. She's a good copilot for someone who doesn't know much about flying. I showed her how you can pitch up and down, cause 0G, and float, which is fun. I did that when she was stretching in an awkward position to surprise her, but she took revenge and did it quite hard and abruptly while in cruise around 105 MPH without turbulence, which made us hit our heads on the canopy.

We probably didn't have our seatbelts tight enough. But could this have structurally damaged the plane? Should I tell my mechanic? It behaved  normally afterward.

Now you know what a terrible idea it is to do "fool around" stuff with a passenger.

The AA-5's maneuvering speed is 122 MPH so you can't overstress it at 105; it will stall first (and you'd have likely snap rolled it) so you should be fine.

When in doubt, the rule of thumb is, when it's metal, if it's not permanently bent, it's good to go.  The metal structure is a big spring (elastic deformation under load and returns to its original shape below the "yield" threshold) and if you don't go past its elastic limit into the plastic range (the yield limit - permanent set to a new shape after bending) it just springs back and Bob's your uncle.  A single application of a near overload to a metal structure has no significant effect fatigue wise if you stayed in the elastic range.

If you think you might have over stressed it past the metal's yield point so there is a permanent set, there will be telltale wrinkles in the skins of the wings or tail that weren't there before. If you know what to look for, I wouldn't call for a mechanic, but if not sure what you're looking at, you should have an expert take a look.

But, like I said, a pull or push on the AA-5 at 105 mph can't overstress the airframe in the first place, so if you were really going that speed, I wouldn't worry about it.  I would just resolve to be more careful about passenger briefings and "horseplay".


What's exactly meant by the "slippery when wet" report on ATIS? I read this discussion and discovered the definition of "slippery when wet" from this advisory circular but I'm still having a hard time understanding why the runway condition is expressed as "slippery when wet" rather than just as "slippery." My guess is that the wet runway normally doesn't bring a slippery runway condition but it sometimes does and in that case it's expressed as "slippery when wet" rather than just "slippery." Is my guess correct?

why the runway condition is expressed as "slippery when wet" rather than just as "slippery."

Because the runway is normally not slippery, and thus it cannot be described simply as "slippery", but it must be specified when this occurs, particularly when it is wet it is slippery.

Saying only "slippery" would mean that the runway is always slippery, and is not the case.

Saying only "wet" does not convey the information that it is also slippery in that condition. (and you want to specify this because not all runways are slippery when wet)

It is not said "slippery when icy" because "when icy" everything is slippery, so that does not need specification, "icy" is sufficient.

"slippery when snowy" I never heard of it, generally because either the runway gets snowploughed fast enough, or because when there is too much snow the runway gets closed.


Why do the C-141 and C-5 have T-tails? Both the C-141 Starlifter and C-5 Galaxy have T-tails, where the horizontal stabilizers and elevators are mounted on top of the vertical fin rather than on the sides of the aft fuselage.  T-tails are usually only found on aircraft where the real estate on the sides of the aft fuselage is taken up by engines (Il-62, 727, DC-9, Tu-154, etc.), as the T-tail configuration has the serious disadvantages of

needing a vertical stabilizer strong enough to carry the entire weight of the horizontal tail plus the considerable downward aerodynamic forces generated by same, making for a considerably heavier (and, thus, less fuel-efficient) airframe,
causing maintenance difficulties, as it's harder for the mechanics to inspect and repair something that high up (this was an indirect cause of the crash of Alaska Airlines Flight 261), and
being susceptible to an extremely dangerous "deep stall" condition, where, at an angle of attack slightly past the stall point, the disturbed wake from the aircraft's wings blanks out the horizontal tail, causing a total loss of pitch control and making recovery essentially impossible.

The C-141 and C-5 have conventional wing-mounted engines, yet both have the tail configuration of an aircraft with fuselage-mounted engines; why is this?

It comes down to a matter of philosophy. Or, if you are less generous, it’s a matter of fashion. Note that the Russian equivalent to the C-141, the Il-76, uses a T-tail, too, while the An-124 uses a conventional tail.

T-tails were in fashion in the early jet age. They were widespread, first in fighters and later in transport aircraft, too, because they:

Have a longer lever arm when placed on top of a swept vertical, reducing tail size and mass,
Allow for a smaller vertical tail due to the endplate effect, which lowers the requirement for hangar doors and ceilings. In case of the A400M, the T-tail allowed for a height reduction of approximately 2 meters.
Stay in undisturbed flow during stall. With wing-mounted engines resulting in a more forward wing position, the danger of a deep stall is reduced when compared to a configuration with tail-mounted engines.
Allow for less interference drag, especially when combined with a Küchemann body in the intersection between vertical and horizontal tail.

Therefore, if your conceptual design team is dominated by aerodynamicists, it will tend to favor the T-tail version. Only when second-order effects are considered will the conventional tail win. And those second-order effects will only become known by experience.

What are those effects?

Flutter! The rear loading ramp requires cutting the rear fuselage open, reducing its torsional stiffness. Add to that a mass on a long lever arm (the horizontal tail) and you get a structure with a very low eigenfrequency. In order to get that frequency out of the usable speed range, you need to stiffen the fuselage,
which adds structural mass. Both tail surfaces might be smaller for a T-tail, but the whole aircraft will be quite a bit heavier. During flight test of the C-141 it was found that the antimetric wing bending mode would nicely couple with the torsional Eigenmode of the the tail, resulting in some scary footage. Also, a coupling between elevator rotation and horizontal tail torsion required to generously add mass balance to the tail.
And then there still is this lingering suspicion that you might get into a deep stall. However, with the long distance between wing and tail of a configuration with wing mounted engines this is less of a threat than it might seem.
A real problem, however, is the tendency of a T-tail to produce a strong nose-down pitching moment in a sideslip. A low tail will eliminate this effect.


What would FAA controllers be referring to when mentioning "code 0027?" In the second video on "You Need To Hear These FAA Tapes From That Oregon UFO Incident That Sent F-15s Scrambling," you hear controllers mention a code 0027. If the target in question had a transponder, the content of the article is misleading. Does anyone know if code 0027 refers to something specific in ATC terms, or are they just referring to a transponder code?

Here's the full link to the article. http://www.thedrive.com/the-war-zone/18473/faa-recordings-deepen-mystery-surrounding-ufo-over-oregon-that-sent-f-15s-scrambling

In the video the controller states that the target was a "code" 0027, which would indicate a transponder code.  Using ATC radar (in this case ARTCC) the controller can see what a secondary radar return (transponder) is squawking.  In this case apparently it's "0027" and displaying an altitude of 37,000 ft.

According to FAA Order 7110.66E entitled "National Beacon Code Allocation Plan (NBCAP)" code 0027 is assigned to ZAU (Chicago ARTCC) and is listed as IS-3 (code category) IS= Internal Departures - Special Use.

Here is the link 7110.66e

I have no clue as to why that transponder code is attached to that target in Oakland Center's airspace.


Would a de-aerating fuel tank have any benefits? I know turbine engines (bearings) are cooled by oil jets and that when oil is scavenged from the bearings it is more of a mist than a liquid, hence the need for various types of de-aerating this mist to produce oil once again. So is there a need for fuel de-aerating? Especially in fighter jets, because they maneuver a lot, will this cause the fuel to churn in its wing, causing the fuel pump to suck in a lot of air?

As an add on, I read from multiple sources tanks in wings can operate in high-g situations simply by having multiple fuel ports leading out of them. I find this a little confusing. Let's say a fighter is dashing, so all the fuel in its tank is rushing to the rearmost part of the tank. If this tank has a front and a back fuel port, and they are being sucked by the same pump, will this result in something like a 50/50 fuel/air mixture? This has to be dealt with, or the combustor will hiccup, or even worse the flame will back travel into the fuel line and bust it open, am I right?

PS: I know all about baffling, so please don't include this in your answer, thanks!

There are ways of preventing air from being pulled into fuel lines due to change in speed,
direction, or orientation.  On of the simplest is called a "clunk" line, which is a flexible hose with a weighted fuel inlet at the end. The inlet and fuel simply fall to the "lowest" level G forces take it.

As far as fuel entraining air by agitation, important factors are viscosity and the chemical
make up of the fuel.  Fuel is generally "thinner" than oil so air can escape more easily.
Chemically, fuel does not have the tendency to form bubbles as a mixture of soap and water would.  Air entrainment simply is not an issue with flight maneuvers.  No doubt the oil
companies have a good number of chemists to keep it that way.


Why do the outer parts of wings generate less lift? In this Wikipedia page it says:

  Constant chord: parallel leading & trailing edges. Simplest to make, and common where low cost is important, e.g. in the Piper J-3 Cub but inefficient as the outer section generates little lift while adding both weight and drag.

Why does the outer section generate less lift?

The outer wing section generates less lift because flow around the wingtips reduces the pressure difference between both sides. This effect dies down quickly when moving inboard, but will still reduce lift somewhat at the wing root.

Screenshot of the Stanford Aero wingcalc page. This is a Java page for which you need to add http://aero.stanford.edu/wingcalc.html to the exceptions list in Java. Then you can change aspect ratio, wing sweep, taper ratio and twist. Here the lift distribution for an unswept, untwisted rectangular wing is shown which has a local lift coefficient of almost 1 at the center. Due to the low aspect ratio, wing efficiency is still at 99%

A rectangular wing can be optimal if stall characteristics and ease of construction are included:

The lower lift coefficient at the tip ensures that the stall starts at the wing root, resulting in a docile stall behavior without a sudden rolling motion.
The constant chord allows to use one single jig for building all ribs of a wooden wing.
The shorter root chord of a rectangular wing requires a heavier spar, but when wings are braced and the root bending moment is low, the weight impact is negligible.

If the goal is a simple to build aircraft with forgiving stall characteristics, the rectangular wing will be an efficient choice, especially when bracing is used. Only when performance is most important will a rectangular wing be less efficient than a trapezoidal wing.


What is the difference between CAMO and CAME? Could someone explain the difference between a Continuing Airworthiness Management Exposition CAME and a Continuing Airworthiness Management Organization CAMO?

CAMO is the organisation and CAME is a "book" that need to write.

This "book" contain procedure to explain how you will work (how you communicate with aircraft customers, how you manage your docs, etc...).


How long does it take to get your official FAA certificate in the mail? I'm asking this question because the only answer on the web right now is pretty old and I assume this is a common question. The above link refers to an FAA page that says:

  We are currently processing permanent Airmen Certificates for
  temporary certificates that were issued approximately May 3, 2015.

The above quote hasn't been updated in weeks.

How long does it normally take to get a new certificate in the mail?

Does it vary substantially?

Is there a better place than the above link to get an idea of how long a certificate will take to be processed?

The Airmen Certification page you linked to is the best place to get a quick status update - the little note at the top gets updated when they move into a new batch of certificates. You can also search for yourself in the airmen certification database: When your new certificate or rating shows up there your certificate is probably in the mail.

How long it takes to get your permanent certificate depends mainly on how many they have in the queue ahead of you - Mine took about 60 days, but I've heard as little as 30 and as long as 100+.
If you're getting close to the expiration of your temporary certificate you can request an extension either online or at your local FSDO (more details over on this answer)


Why do the 737-100/200’s thrust reversers blow fully open if hydraulic pressure is removed while the reversers are partly open? If the thrust reversers on an Original-series 737 (the 737-100 and -200) are 2 inches or more from the stowed position, and hydraulic pressure is removed from the reverser actuators, the reversers will travel to the fully-extended position under aerodynamic loads at airspeeds down to below 130 KEAS (knots equivalent airspeed), as was discovered during the investigation into the crash of Pacific Western Airlines Flight 314.  To quote the official accident report:

... It was found that the air loads on the reversers were insufficient to deploy them further if they were freed with the leading edges 1 inch out from the closed position. If the initial deflection was increased to 2 inches, they invariably deployed fully under the air loads. At intermediate settings, deployments only occasionally occurred. ...  [p. 17-18 of the report; p. 23-24 of its PDF file]
... The ground runs showed that partially opened thrust reversers deployed at various speeds during taxi tests with manually controlled airlground logic. The rate of deployment varied with the amount of the initial open condition of the reverser doors and also varied with speed. In all cases partially opened doors deployed fully before 130 Kts.  [p. 18/24]

However, the 737 Originals use target-type reversers (you know, the kind with the two buckets that close behind the engine’s tailpipe, the ones that everyone immediately thinks of when they hear the phrase “thrust reverser”); I can easily see how they would be blown to the full-open position if the engine(s) aren’t operating, but, if they are running, then, without hydraulic pressure holding the reverser buckets in position, shouldn’t the engine(s)’ jet blast force the buckets apart and open a path between them for the engine efflux to exit?

If the buckets could be opened by engine thrust, they would be ineffective to reduce speed. By the same token, you want airflow to help them deploy when needed. The controlling force then is the hydraulic actuators. Without hydraulic power it would be very difficult to achieve positive control over the buckets' position.


What is the point of having lots of different flaps settings? This question is about the number of flaps settings on different airliners. One can notice that this varies greatly between models and manufacturers. On a Cessna 172, you usually only have 4 or 5 settings.
But on airliners you have usually more, especially on Boeing.

So I did a quick search and found the following (links point on the image I used):

B777: 7 settings: 0-1-5-15-20-25-30
B737-900: 9 settings: 0-1-2-5-10-15-25-30-40
B787-8: 7 settings: 0-1-5-15-20-25-30
B787-9: 10 (!) settings: 0-1-5-10-15-17-18-20-25-30

On the other hand, Airbus seems to stick to the same scheme for its models:
 the A320/A330/A350/A380/A330 all have 5 settings: 0-1-2-3-full

The questions are:

When you have 9 or 10 different settings, what is the point of having so much ? Is that really useful ? Does the crew really incrementally uses all of them on approach and landing ?
I mean, if they only step, say from 0 to 5 on approach, then  5 to 15 on long final, and then 15 to 30 on short final, then the manufacturer could have saved some metal.
Boeing planes have more settings than Airbus. Is there any particular design reason behind that ?
Airbus doesn't designate the different positions as angles, but as incremental numbers. Anybody knows why they did that design choice?

1a. On take off, with a light airplane you may select less flaps to reduce the additional drag and save some fuel. Max takeoff flaps are reserved only for short runways and high loads. Fuel savings are very important nowadays.

1b. On approach, less flaps produce less noise and may also allow a higher approach speed (VFE is the maximum flaps extended speed and may be different for different flap settings). Maximum flaps are set only later in the approach when the plane has stabilized at the final approach speed.

1c. The flap setting has an effect on the airplane's pitch angle. A certain flap setting may help to minimize the tailstrike risk. The longer B787-9 has nine settings, while the shorter 787-8 has six.

I learned the Boeing numbers are not true angles either. For example, settings 1 and 5 may only affect the leading edge slats. At higher settings they approximate the actual angles (which are anyway somewhat misleading in the case of today's multi-part Fowler flaps, which move both down and backwards).

https://www.flightglobal.com/news/articles/farnborough-aero-secrets-of-boeings-new-dreamliner-401784/

http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_08/pdfs/AERO_Q408_article05.pdf


What do I request when contacting tower of an airspace I'm transiting over? I'm a student pilot who has just begun dual cross-country with my instructor. However, he has not been explicit when I've asked him about radio comm with tower/approach/radio during the flight. If I enter an airspace (say, Class D) and contact the tower, but I do not intend to land there, what would my initial call to the tower be? And what are the differences in requests for approach/departure and tower?

This will vary for every airspace so lets go over them in descending order.
Class B (Bravo): First off, keep in mind for your future solos that as a student pilot you are not allowed to fly solo in class B airspace unless your instructor has given you training and a logbook endorsement for that specific class B (see 14 CFR 61.95). But if your instructor is in the plane then technically they are accepting the clearance, not you. For Bravo airspace a clearance is explicitly required and a typical exchange will go something like this:

PIC: "1234XY 5 miles south west of KPHL at 4000 heading to KPNE requesting transition through the airspace."
ATC: "1234XY squak 3425 and ident, altimeter 29.92"
PIC: "1234xy 3425 29.92"
ATC: "Ident received, you are cleared through to KPNE on your current heading at 4000"

En route you may get traffic advisories or other instructions while in the space so you need to stay on the frequency.
Class C (Charlie): For Charlie airspace you only need to establish 2-way radio communication. A response containing your call sign will allow you into the space. Lets look at an example

PIC: "Allentown approach 1234XY 20 miles to the southeast of Queen City at 3000 in bound for landing at Queen City"
ATC: "1234XY standby"

Anytime you hear your call sign, it is considered to be the establishment of 2-way radio communication, if you hear "aircraft calling Allentown, standby", you have not established 2-way communication and must remain out of the space since they did not respond with your call sign. Likewise you may be explicitly instructed that you must remain out of the space.
Class D (Delta): Delta airspace typically  extends up to 2500AGL, and you can often climb over it flying VFR. You do not need to hail the tower when doing so but many people do so out of courtesy. If you intend to enter Class D, follow the same procedure as Class C.
You can find the whole breakdown here
Flight Following: Where available and workload permitting you may be able to pick up flight following while in route. You can also coordinate a hand off from them to the airspace you are entering.


To what extent is the HOST system still in use? The Host Computer System (HOST) used to be the backbone of the US air traffic control centers (ARTCCs). There was a lot of publicity early in 2015 about the En-Route Automation Modernization (ERAM) fully replacing it, as the FAA announced they were finally finished implementing ERAM. However, deep in the FAA website, the HOST system still seems fairly active.

I just want to clarify if it is fully out now. Is it still available as a backup? Do certain ATC systems still draw from HOST systems? Do controllers still use certain HOST systems?

Overall this is a pretty technical question, but any information is helpful.

From this news article dated April 30, 2015:

  "As of today, Host is history," FAA Administrator Michael Huerta declared during a press conference.

From the latest NextGen report dated June 2016:

  In March 2015, the 20 planned ERAM sites achieved operational readiness, which signified the full commissioning of ERAM into the NAS and allowed the FAA to begin decommissioning the legacy HOST system.

So, it is fully out, it is not available as back-up, and no ATC system uses Host.


What are dimensions of the B-17 propellers? I'm curious about the aerodynamics of the Boeing B-17 propeller, as the proportions looks perfect for a project I'm working up. Does anyone out there know where to find the specs/dimensions/models for the B-17 prop?

According to the maintenance manuals from here about halfway down the page (part 1 page 3) the B-17 was equipped with:

  PROPELLER.

  Type: Three-bladed, hydromatic, WEE50-473 or 505,
  full feathering.
  Mfgr.: Hamilton Standard.
  Hub: 23E50-473.
  Blade: 6477A-6.
  Diam.: 11 ft. 7 in.

Part two of the manual has all the installation and setup instructions instructions if you are looking for those as well.

Hamilton Standard seems to have been acquired by (or turned into) UTC Aerospace which appears to still make propellers. You may want to reach out to them as they may have more info on hand. There are quite a few B-17's lurking around and there may even be one near you that you can go take a look at and possibly even measure.


What are the measurements for a "Black Box"? I was wondering as to the measurements of  "black box" recorders. I have a new invention involving the "Black Box" and I need to know the measurements of the recorder.

The two main "black boxes" are the Flight Data Recorder (FDR) and the Cockpit Voice Recorder (CVR). These units are available from various manufacturers and therefore sizes vary. Many units can be used as either CVR or FDR, or as both.

A quick search provides a few examples:

etep Sentinel ED-112: CVR/FDR
Height: 3.929 in (9.980 cm)
Width: 4.970 in (12.624 cm)
Depth: 6.907 in (17.545 cm)

L3 F1000: FDR
Height: 7.62 in (19.4 cm)
Width: 4.88 in (12.4 cm)
Depth: 19.56 in (49.7 cm)

Universal Avionics Systems CVFDR: CVR/FDR
Height 6.1 in (15.5 cm)
Width 4.9 in (12.4 cm)
Depth 8.0 in (20.3 cm)

L3 SRVIVR: CVR/FDR
standard configuration:
Height: 3.25 in (8.26 cm)
Width 5.55 in (14.1 cm)
Depth: 6.55 in (16.6 cm)
extended configuration:
Height: 3.25 in (8.26 cm)
Width: 5.55 in (14.1 cm)
Depth: 7.2 in (18.3 cm)

L3 FA2100: CVR
Height 5.5 in. (14.00 cm)
Width 5.0 in. (12.70 cm)
Depth 12.6 in. (32.00 cm)

If you were asking something else, see:

How much data do FDR and CVR generate on commercial jets?

Or other questions already asked here.


How large are the CF-100 Canuck wingtip fuel tanks? How big are the CF-100 Canuck's wingtip fuel tanks and what is the maximum fuel capacity they can carry?

This diagram from the RCAF Canuck Aircraft Operating Instructions states the wingtip tanks could each hold up to 292 imperial gallons or 350 US gallons.


What is the function of the lower vertical fin on a MIG-23? I would like to ask about the function of the lower vertical fin in Mig 23 .

Directional stability at supersonic speed.

The air above the aircraft is less dense at supersonic speed, and elasticity reduces the effectivity of the fin - it bends and twists from the air loads. Conversely, the lower fin operates in denser air and creates more side force per area.

Also, the lower fin shifts the aerodynamic center of the empennage downwards, which is improving the handling characteristics. Adding area below the centerline helps to reduce the roll contribution of the vertical tail in a sideslip, which improves handling characteristics (more directional stability AND lower yaw-induced roll).

As long as the vertical tail surface sits above the centerline (more precisely the longitudinal axis of inertia - for now we can assume both fall together), any side force will also create a rolling moment.  This is undesirable because now a yaw command will not only create the intended yawing moment, but also a rolling moment.

If you want to yaw in order to turn, the vertical tail above the centerline will even roll the aircraft in the wrong direction, so you need more coordinated aileron command than with a symmetrical vertical tail.

The MiG-23 is not alone: Many supersonic combat aircraft use ventral fins. See the picture below for an example where the effects of additional vertical tail area are compared to the effects of a ventral fin of the same area.

(Source: Ray Whitford: Fundamentals of fighter design)

At supersonic speeds, the stiff, low aspect ratio ventral fin has a nearly constant contribution to directional stability, whereas the wing-like vertical tail loses effectivity in proportion to the Prandtl-Glauert factor $\frac{1}{\sqrt{Ma^2-1}}$ because it bends and twists more due to its higher aspect ratio. The small ventral fin of the F-104 raised directional stability by 30% at Mach 2.

(Source: Ray Whitford: Fundamentals of fighter design)

At high angles of attack, the vertical tail is in the wake of the fuselage which reduces local dynamic pressure and, consequently, effectivity. The ventral fin then is in ideal flow conditions, so it can help to stabilize the aircraft at high angle of attack, just when the fuselage contribution to instability is largest.


What exactly is trim? Although I have a rough idea of what it is...

In my mind from growing up watching hundreds of hours of Seconds from Disaster / Air Crash Investigation, trimming an aircraft is turning a dial that changes the airplanes "forward" direction. So maybe it changes the control surfaces so that the plane is flying straight forward even though the rudder for example is at some deflection angle that isn't 0.

However if I was asked to define trim I couldn't exactly say what it is, what situations I would use it for or how it's achieved.

If the aircraft is trimmed, the flight controls are in a state where no force needs to be exerted in order to continue straight and level flight. Aerodynamic and gravitational moments about all three axes are nulled out.

Changing the trim of the aircraft in pitch could happen in the following ways:

a shift in centre of gravity, for instance by shifting fuel from centre tanks to tail tanks, or payload shifting position;
a change in thrust of an engine that is located above or below the centre of gravity;
a change in horizontal tail angle or trim tab;
a deflection of the elevator.

If the aircraft was in straight and level flight and the trim changes because of a change in any of the above, it can be compensated for by the other factors. Elevator deflection is fastest but requires a pilot force which is uncomfortable for longer periods, that is why the forces can be trimmed out to make the new stick position the neutral force one.


What is "detonation" in a piston engine? Recently, I saw this question, which included a rather alarming quote:

  Full throttle operation with carburetor heat on can cause detonation.

Woah! That doesn't sound good. In fact, I would have figured aviation engine manufacturers would have worked hard to prevent their engines from exploding, and possibly destroying the rest of the aircraft and/or killing the pilot in the process.

I also found this question, with a rather calm quote:

  What if I have a noise cancelling headset on, and the engine undergoes detonation?

It seems like there should be other cues that your engine just blew itself to bits...

I'm figuring that perhaps "detonation" in this context doesn't actually mean that your engine block turns into shrapnel. I also figure that it doesn't refer to the normal process of piston engines, where fuel is injected and mixed with fuel before detonating. So what does it mean?

Detonation, as the name suggests, is an explosion of the fuel-air mixture inside the cylinder. Under normal operation, the spark plugs each ignite a point in the fuel/air charge, which then propagate through the cylinder and provides a consistent, regulated burn in a process called deflagration. This extends the time that the burning fuel pushes on the cylinder, providing a gentle power stroke.

During detonation, the fuel/air charge (or pockets within the charge) explodes rather than burning smoothly. Because of this explosion, the charge exerts a much higher force on the piston and cylinder, leading to increased noise, vibration, and cylinder head temperatures. The violence of detonation also causes a reduction in power. Mild detonation may increase engine wear, though some engines can operate with mild detonation regularly. However, severe detonation can cause engine failure in minutes. Because of the noise that it makes, detonation is called "engine knock" or "pinging" in cars.

(Source: FAA PHAK, page 6-18)

Detonation can be caused by a number of factors, but generally they relate to a situation outside of the engine's design. Using the wrong fuel can cause detonation: the octane rating of a fuel is basically the amount of pressure it can take before it detonates. Similarly, high cylinder temperatures can cause detonation(1). This is why mixture is set very rich when at high power levels: the excess fuel cools the cylinders, preventing detonation. As noted above, full power with carburetor heat on can cause detonation, as the increased temperature mimics the effect of high cylinder temperatures. Full carburetor heat is required to provide at least a 90 degree F increase in intake air temperature.

Further reading:

Page 6-19 of the Pilot's Handbook of Aeronautical Knowledge.
An article at Savvy Analysis

1) Detonation is distinct from pre-ignition, where the fuel/air charge is ignited by something other than the spark plug. Notably, detonation and pre-ignition often cause each other, as a detonating engine will have a very high CHT (potentially enough to cause pre-ignition), and if the charge pre-ignites as the cylinder is still rising, the continued compression may cause the charge to detonate.


How much lift is lost by wing dihedral, and can it be fixed? The loss of lift, though negligible, was mentioned in another thread regarding the angle of dihedral wings. Not knowing the coreect name but will external "ribs" on the wing surface reduce that loss? Also, is that lift loss less or greater with forward swept wings than straight or rear swept? And is that loss due to the dihedral angle of the wings increase with a greater angle?

The amount of lift lost to dihedral is because of a trigonometrical condition, and cannot be fixed by ribs.

Lift is always perpendicular to the local surface, and each wing half develops lift at the dihedral angle. Only the vertical bit is useful for suspending the aeroplane weight.

In order to quantify:

Cos 5° = 0.9962, so less than 0.4% of lift is not useful.
Cos 10° = 0.9848, meaning a 1.5 % loss.

Wing sweep has the same roll/sideslip stabilising effect as dihedral does (this answer), so less or no dihedral is required if the wing is swept. But there are many other considerations related to lift and drag with a swept wing.


What are the equation linking static air temperature with true airspeed & altitude? If I want to calculate static air temperature (OAT), but I'm only given an altitude and a true airspeed. Is there such an equation that relates these principles together. I've had a look at wikipedia and to calculate OAT, the total air temperature is required. Problem is, I don't have a Mach number to solve the equation. Is there another way to solve this problem

Provided that your calculations take place for a standard day, below 11 km altitude the Outside Air Temperature is simply a linear function of altitude. From the wikipedia article for Standard Atmosphere:

So OAT = 15 - 1.98 * Altitude, with OAT in °C and Altitude in 1,000 ft. Airspeed data is superfluous.


What are the limitations to adding wings with engines to a helicopter? I've probably seen this in science fiction and cartoons but never in real life. Rotor wing aircraft (helicopters) have numerous advantages over their fixed wing counterparts, and vice versa. For example, helicopters can take off and land vertically and do this almost anywhere. But fixed wing aircraft can fly further, faster and are more fuel efficient than helicopters of similar weight.

What are the limitations to adding folding wings to a helicopter, each equipped with a turboprop or turbofan whose shafts connects with the helicopter fan blade for vertical take off?

Once enough speed is gained from the vertical takeoff helicopter phase, the gearbox connects the turboprop or turbofan, they power it enough for it to generate lift at the fixed wings and when the wings are generating lift, the gear box disconnects the helicopter blades and they fold and are housed in the fuselage (like landing gear) to reduce drag. The fixed wing part of the flight takes over for faster speed, more efficient cruise and better range. The same process applies for landing.

I know there are turbofan aircraft that are a cross, their advantages of fixed wing over rotorwing are limited and their wings do not fold.

A very promising British design from the 1950s used both, a rotor at low speed and a conventional wing at high speed for lift creation. This was the Fairey Rotodyne, a prototype for a flying bus to connect remote locations with a VTOL aircraft. Its rotor was tip-jet-powered and burned a mixture of fuel and compressed air bled from two wing-mounted Napier Eland turboprops. After take-off, power was switched to the propellers and the rotor was unloaded to minimize its drag at high speed. This way, both lift-creating means could be optimized for their speed domain.

You will notice that the wing is unusually  small while the rotor is unusually large. This allowed both to operate at higher efficiency than wings or rotors which are designed to work over the full speed range. However, the combination of the two weighs more than either a rotor or a wing, which reduced the possible payload of the Rotodyne. Neither was meant to fold away because that would had increased weight even more.

Fairey Rotodyne (picture source Ed Coates collection)

In the end, it was wavering British government support rather than any technical issues which limited the Rotodyne to a single prototype.

Today, the most promising solution seems to be a coaxial rotor with a separate source of thrust; either a propeller or jet engines. The coaxial rotor is slowed down at high flight speed in order to keep tip Mach numbers below 0.9 and the lift asymmetry of conventional helicopters is no problem for a coaxial rotor design, allowing much higher flight speeds.

Folding a wing would not help much: When the wing is not needed (which is at low speed), its friction drag is low. Folding the rotor, on the other hand, makes more sense but so far is limited to a helicopter on the ground in order to reduce its storage space on aircraft carriers. Folding in flight has only been studied conceptually.

Illustration 1B from US patent application 2015/0474290 A1 by Bell Helicopter Textron Inc.


Compute great-circle track from longitude The Aviation Formulary defines Clairut's formula to compute the intermediate track  (bearing) for a GC based upon latitude, but any given GC (ignoring one passing through the poles), crosses a given latitude twice (below the maximum latitude where track = 270 or 90).

For my application I'd easier compute the intermediate track based on longitude, since this will have only one solution, but I'm insufficiently capable at spherical triangle math to re-arrange the available formulae to give that result. Any hints on computing immediate GC tracks based on longitude, or modifying the computation based on latitude to select the 'rising' or 'falling' solution, would be welcome.

For context, this is for a navigation device emulation in a simulator, to show the desired track along a leg. All the other values (eg, cross track error) are provided by existing formulae.

@James Turner: considering the date of the question, you've surely moved on. If you found a solution elsewhere, you can post it here and get some bonus points for answering your own question. Anyhow, the Aviation Formulary has the answer to your question: it's not Clairaut's Formula. You can find the latitude of ownship position by entering its longitude and the coordinates of the GC endpoints into the "Latitude of point on GC" formula. Then, knowing lat and long of both current position and destination, you can determine the heading to use leaving that point from the "Course between points" formula.


Is it really cost effective to put a motion system underneath a Full Flight Simulator? Civil full flight simulators are mounted on top of a motion system. It is an expensive system, requires higher and therefore more costly buildings, and requires greater structural integrity of the simulator itself. A cost driver of considerable proportions.

Why do we have to have motion systems on simulators? We get motion information from our central and peripheral vision, right?

While a simulator with motion simulation is more expensive to own/operate than a simulator without motion simulation it is still cheap compared to a real airliner

So if the regs say a particular type of training can be done on either a real airliner or a full motion simulator then it is likely to be cost-effective to use the full-motion simulator.

And as a bonus you can run scenarios with a high level of realism that would be too dangerous to run on a real airliner. Emergency training in real aircraft has to strike a balance between training pilots to deal with adverse conditions and avoiding accidents during training.

  Why do we have to have motion systems on simulators? We get motion information from our central and peripheral vision, right?

A pilot gets motion information from 3 different sources.

His body
His vision
His instruments.

Unfortunately item 2 on that list is sometimes unavailable and item 1 has terrible medium to long term accuracy.

In normal life our brain uses a combination of our bodies motion sensitivity and our perhiperal vision to build up a picture of where we are. In the absense of visual information it will continue to try buliding up a picture of where we are but the accuracy of that picture will quickly degrade.

It's one thing for a pilot to be able to make correct decisions when his only source of motion information is his instruments. It's quite another to make correct decisions when his body and his instruments are apparently in conflict and he has no visual references.


Is the A-10's cannon effective against tanks? Perhaps this isn't on-topic, but is the A-10 effective against tanks (tank armour) when using its cannon?

For example, this page claims:

  Using the cannon, the A-10 is capable of disabling a main battle tank from a range of over 6,500 m.

Is that true?

If that were so, why does a "main battle tank" (e.g. an M1 Abrams) have a 120 mm gun -- contrast that with the A-10's 30 mm cannon?

I thought that in WW2 you needed something like a 75 mm or 88 mm gun to be effective against the then-heavy tank armour. And the gun on a "main battle tank" has if anything increased in size since then -- or converted to missile instead of projectile -- is a 30 mm cannon effective?

Is the armour-penetration of an A-10 exaggerated (if it is effective against only e.g. softer armour than main battle tanks)? Does the cannon being mounted in a plane make it especially effective (I'd guess not, the muzzle velocity of a GAU-8 is 1000 m/s and and A-10's airspeed only adds 200 m/s to that)? If it is effective then why isn't that the primary armament of a main battle tank?

Well it depends....
It depends on the tank, where you hit it, what angle you hit it, how far the A-10 was from the tank when it fired, and what kind of ammunition was used.
Wikipedia quotes that a GAU-8/A firing the PGU-14/B depleted uranium API ammunition offers the following armor penetration capability.

Armor penetration of Armor-Piercing Incendiary ammunition, BHN-300 RHA, attack angle 30 degrees from vertical:

76 mm at 300 meters
69 mm at 600 m
64 mm at 800 m
59 mm at 1,000 m
55 mm at 1,220 m

Whether that's a declassified spec with all other known values a secret or a realistic representation is unknown. I'd say it sounds reasonable. Tanks tend to have heavy armor on the front and sides but lighter on the top. Certainly the PGU-14/B could defeat armor on APCs and older generation MBTs. Modern MBTs with advanced composite/reactive armor may be more difficult to crack. While it might not be able to penetrate the chobham hull of an M1A2, it can certainly take out fuel tanks, destroy the engine, etc.
Keep in mind that a GAU-8/A can hammer a 5-mil Circle with 70 such rounds with a 1 second burst, provided the pilot has a steady trigger hand. This also can have a cumulative destructive effect on armor plating.
While the gun can be employed against armor, the preferred method is to attack tanks using standoff weapons like the AGM-65 Maverick missile. Getting close enough to tank columns to use the gun can be hazardous, especially if the group has mobile AAA/SAM escorts.


What are the names of these aircraft? I need help to identify a group of planes, can someone help me?

The top image is a Bellanca Skyrocket.

The second image looks like the Fairchild FC-1, one was built as a prototype, followed by the FC-2 which was powered by a radial engine.

Not sure about the last, found a few similar but nothing exact.


Do French, Spanish, Italian, and Greek controllers still speak to their native pilots in their native language? At the time of my retirement in 1999, controllers in France, Spain, Italy, and Greece typically spoke to their native pilots in their native language in spite of the fact that English was/is the international language of aviation and is specified as such by ICAO. Not following the ICAO convention deprived non-native speaking pilots of valuable situational information.

Does anyone know if any of the aforementioned countries have come around to having their controllers always speak English?

Well, I just pulled up LEMD on LiveATC and heard some Spanish there. So Madrid clearly speaks Spanish sometimes, although it's probably not very busy right now (5:30 AM there). Archives from midday for LFPO and LFBD (Orly and Bordeaux) have plenty of French. Archives from midday for LGAV (Athens) approach has something definitely non-English (I can't tell if it's Greek or not, but I can't imagine anything else it'd be); LGAV has heavy use of English, but it's not exclusively English. And LiveATC has no feeds for Italy. So, for three of them the answer is definitely "yes, they still speak not-English;" for the last, LiveATC can't answer.


Can Air Traffic Controllers participate in Q&A? While asking the question in chat How do we get controllers on the site? @egid suggested there may be FAA or union restrictions on participating in Q&A. That would be sad since pilots and controllers communicating with each other improves safety and efficiency... but certainly doesn't mean it isn't true.

Does anyone know of specific restrictions placed on controllers by the FAA or NATCA (National Air Traffic Controllers Association) which would prevent them from answering questions on this site?

I realize this blurs the line slightly between the main site and meta, but I'm asking about legal reasons, not speculation about why we haven't attracted any controllers yet (that I'm aware of).

I am not aware of any legal limitation for air trafic controllers to speak out on a public website, but there could be one.

StuckMic.com is however an ATC forum in which FAA ATCo's seem to participate actively. This leads me to believe that they are allowed to speak out on a public website. There are very likely restrictions on what they can share.


Where can I find the information from the back of a TAC if I don't have a physical copy? The Atlanta TAC has a note that says "See back of this chart for procedural information within the Atlanta Class B Airspace":

If I don't have a physical copy of the TAC - because I'm using a flight planning app, for example - where else can I find the information?

If you are using Fore Flight you can Turn On Legends which will show you the legend information for the map. You may also be able to download the information somewhere else in the application. It will help if you inform us of which app you are using.

In the documents section of Fore Flight there are some other Atlanta area documents. Im not sure what the back of the cart looks like so I'm not sure if any of them are correct but there is the Atlanta FLY chart and the Atlanta Class B diagram.


How does pulling back provide better steering during rollout for light GA planes? I had requested clarification on an answer to the question, How do I keep a C172 straight on the centerline during landing/rollout? I did not comprehend how pulling back after touch down provides better steering, the reply to my comment was:

The nose gear won't be off the ground, it will just have less pressure/force on it. The oleo strut won't be compressed, and the wheel will have an easier time turning side-to-side smoothly.

But,

Isn't an uncompressed strut (or lightly compressed) limit/lock the steering because of the nose gear centering cam mating?

AFAIK, at least for cars, better steering happens when the front axle is loaded more, whether mechanically or aerodynamically (front-end downforce).

In jet-liners, pushing forward on the control column after landing (or during takeoff roll till about 80 knots) to firmly stick the nose gear is in many SOPs for better control (type dependent; degree of pushing varies). Boeing 777 example:

On touchdown, take positive action to lower the nose gear to the runway and maintain moderate forward pressure on the control column to assist in directional control.

So what am I missing? I don't presume to know more than the above 3 points, after all suspension engineering is not an easy field (with the big shots working for the big racing teams).
Let's limit the scope to light GA planes (in tricycle configuration, of course).
I'm not questioning the validity of the technique, rather inquiring about the physics involved, perhaps there's more to it than the strut?

Pulling back on the yoke does not improve nosewheel steering.  If there is enough elevator effectiveness to hold the nose off then there will be plenty of rudder authority for directional control.

Not all airplanes are the same of course, but the Cessna 172 you specifically mentioned has a tendency for the nosewheel to shimmy at high speeds.  Holding the nose off as long as possible reduces the annoying vibration and stress on the nose strut.  It also prevents the pilot from over controlling.

As the elevator looses effectiveness so too does the rudder, and once the nose falls through direction control is maintained through nosewheel steering.  Ideally this transition is smooth and virtually transparent to the pilot since rudder pedals are used for both.


What was Boeing's competitor to the C-5? Doing some of my airplane learning, I have come across a point many times that the engines for the Boeing 747 (at least partially) came from Boeing's competitor to the C-5 Galaxy. What was this plane that Boeing had made to compete with the C-5?

In 1964 the US Air Force awarded study contracts for a new cargo aircraft to Boeing, Douglas and Lockheed. The aircraft was called CX-HLS. ( cargo experimental - heavy logistics system)

Lockheed won with the C-5A design. Boeing's design was never built but would have looked like this:

source: Widebody Aircraft Chronology

Source: Boeing archives

Source:TDPRI.COM


I have a FAA Private VFR SE license based on my foreign license, and added IFR in my home country; how to upgrade the FAA license? I already validated my non-US licence and got a FAA Private VFR SE Licence based on my foreign licence. I recently completed my IFR rating in my home country and was wondering how to 'upgrade' my FAA licence and add the IFR privileges?!

I tried my best to find something on google but I only found references to a "FAA Instrument Knowledge Test Foreign Pilots" without any details.

Any experience or pointers for me?

I assume that your FAA private license was issued under 14 CFR 61.75, and that section also includes the requirements for adding instrument privileges:

  (d) Instrument ratings issued. A person who holds an instrument rating
  on the foreign pilot license issued by a contracting State to the
  Convention on International Civil Aviation may be issued an instrument
  rating on a U.S. pilot certificate provided:

  (1) The person's foreign pilot license authorizes instrument
  privileges;

  (2) Within 24 months preceding the month in which the person applies
  for the instrument rating, the person passes the appropriate knowledge
  test; and

  (3) The person is able to read, speak, write, and understand the
  English language. If the applicant is unable to meet one of these
  requirements due to medical reasons, then the Administrator may place
  such operating limitations on that applicant's pilot certificate as
  are necessary for the safe operation of the aircraft.

The "appropriate knowledge test" in this case is the Instrument Rating - Foreign Pilot test, it's described here with a few sample questions. Some more information is here, including the point that you don't need any prior authorization to take the test:

  • Requires NO instructor endorsement or other form of written
  authorization.

I'm not sure about the exact process involved (I guess you just do the test and send the certificate to the FAA) but the FSDO that validated your foreign license for VFR should be able to give you all the details.


Could a terrorist hack the ILS? I'm reading all these reasons why consumer electronics can't be on during takeoffs and landings and one specific reference that is made over and over again is the sensitivity of the ILS equipment. I understand that isn't a Die Hard 2 scenario, but what about simply throwing random interference on those frequencies hoping to disrupt navigation? I know very little about RF or the power levels involved, but a generator inside a hotel room in or around the airport property sounds like a feasible scenario.

There are numerous unclassified papers talking about LOC, GS, MLS and other navaid jamming. There are also instances of that happening, both intentionally and unintentionally.  The issue with consumer electronics is made worse is that local consumer electronics on the plane can have local oscillators in the receivers.  They are small signals, but they are close to the antenna, hence the greater risk.

Jamming LOC (lateral ILS guidance) and VOR are similar. GS interference is a bit more difficult to provide false readings that make sense to a pilot, when the transmitter is off airport.

The reality is that even GPS can be jammed, faked with stronger signals, etc. Numerous companies make GPS-GNSS simulators, and it is not rocket science to integrate those into jamming systems.  Some of the countermeasures are documented in open literature, and other countermeasures and methods are not.  GPS jamming becomes an issue with various weapons delivery systems, and creating effective countermeasure packages with limited size-weight and power (SWAP) is a constant challenge.

I concur with @STWilson, that if faced with the possibility of interference, it would be good practice to monitor your approach with GPS, NDB, OM and other navaids.  For example, one can always start a timer crossing the OM, even if doing an ILS. Certainly in a war or terrorism situation, additional cross-checks are good investments of effort.


What organisation owns intersection names? I understand that five letter intersection codes (such as WARPI, PAPPI, KUBBS, ROSLY, ZALPO, ...) are unique in the world.

However, their names don't comprise a national prefix (as aircraft tail number do, or airport codes do), which would allow to delegate name bookkeeping to the individual countries's aviation authorities by prefix.

Therefore, a single, international organization has to somehow own and disambiguate all the intersection names. I would expect the ICAO to be that organization, but I haven't been able to find any resource mentioning that.

Help?

The allocation of waypoint names is actually handled by each country's individual aviation authority. This means that there are actually duplicates in different countries or regions. The ICAO has made at least two attempts to remove the duplicates and make the names globally unique, one in 2010 and another in 2018. Despite these efforts, there are still over 1000 duplicate waypoints in the ICARD database.


How much does an airliner cabin elongate at altitude? How much (about) is a commercial plane's cabin elongated at cruising altitude, due to interior-exterior pressure difference?
Of course there should be a slight shrinkage because of temp difference, but I estimate that overall a 30m cabin  should be elongated by few centimeters.

We can identify three effects that have an effect on cabin length:

Stretching due to the bulkhead pulling on the end of the fuselage;
Shortening due to the fuselage expanding in diameter (Poisson effect)
Shrinkage due to temperature

These are simple solid mechanics problems. Given an airplane with length $l$, diameter $d$, wall thickness $t$ made with a material with Young's modulus $E$ and Poisson ratio $\nu$ and linear expansion coefficient $\alpha$ pressurised to a pressure differential $p$, cooled to a temperature differential $\Delta T$....
$$\Delta L = \dfrac{d p L}{ 4 t E} - \dfrac{\nu d p L}{2 t E} - \alpha \Delta T l$$
$$\Delta L = \dfrac{d p L(1-2\nu)}{ 4 t E} - \alpha \Delta T l$$
Let's have a wall thickness of 3mm, diameter of 4m, length of 40m subjected to 0.5bar and 70°C temperature difference. Aluminium $E=$70GPa, $\nu=0.33$, $\alpha=25\mu m/m°C$. Filling in the numbers, we obtain $$\Delta L=3.2mm-70mm\approx-67mm$$
So thermal expansion definitely has the upper hand here, shrinking the fuselage by a few centimetres in total, whereas pressurising the fuselage can only expand it by a few millimetres. The numbers here are very much approximate but the order of magnitude will not change much with "real" numbers.


What does "Constant wind condition during flight" mean? What is constant wind condition during flight? Is it zero wind velocity at an instant (say at level flight) or wind with constant speed, say 20 m/sec (at steady level flight or whatever it is) Which statement is correct?

It means constant, or unchanging wind magnitude and direction.  It could be still air or just a constant upper level wind.  That can happen on local flights but is rare on long cross country flights.