How is passenger baggage transferred, and how does it happen so quickly? I've always wondered how airlines transfer bags between connecting flights. At a hub, bags must be moved to any number of connecting flights throughout the airport - some with very short connecting times. Seems like sorting them would take a lot of time. How does this process happen?

On big airliners, baggage is mostly stowed in containers, called Unit Load Devices. They are packed at the departure airport and pre-sorted to minimize the amount of sorting at a hub, but normally need to be emptied after arrival so the baggage can be re-sorted.

On regional jets and older aircraft which don't take ULDs, bags are still loaded individually and transported to and from the aircraft on open carts which are assembled to small trains (see picture below).

Airport baggage transportation (picture source)

Once the ULDs or the carts arrive inside the terminal, the bags are unloaded into the baggage handling system, a collection of conveyor belts, barcode readers and switch points. Since every bag received a sticker with a big barcode upon check-in, the reader can report the barcode of the next bag to a computer wich sets the switch point accordingly. Traditional systems employ humans with a portable barcode reader for putting the bags on the right belts.

Baggage tags (picture source)

The most recent systems put the bags on plastic trays which have RFID tags attached, and the RFID information is used for switching the conveyor belts. By loading the bags on standard size trays, the flow of bags is simplified. However, a baggage handling system is a complex piece of machinery, and some new airport terminals were delayed because the system did not work initially, or opened with lots of mis-routed or even mangled bags in their first months of operation. London's Terminal 5 and Denver airport, which went back to manual sorting after 10 painful years of trying to get their system working, come to mind.

When they are sorted, the bags are deposited either at a ULD packing station or an empty cart for transportation to their respective flight. At the end of their journey, they are routed onto baggage carousels for pick-up by their owners.

Baggage carousel (picture source)


Why did this commercial flight fly in circles while far from the destination? I was on the flight CX635 from Hong Kong to Singapore today, and I noticed the plane turning in a circle reminiscent of the holding pattern that planes often enter when they are queuing up to land.

However, this time I saw this flight pattern on the in-flight tracker while it was still in level flight, and once again when it was descending. When I got home, I saw that the pattern was also recorded on FlightRadar24.

Why did the pilot fly two circles in the middle of the ocean off the east coast of West Malaysia? I did not observe any obvious severe weather patterns, and the clouds were generally sparse (2 oktas or so) when it was doing the first roundabout, and there were no visible indicators of significant severe weather activity.

The first "circle" is a holding pattern. We discussed those here.
In particular, it seems that you were on hold at VINIL or VEPLI, according to the approach charts (page 5 of the PDF).

The second one is most likely for separation on final approach, the aircraft was probably early and ATC has asked them to perform a 360° to increase the separation between them and the aircraft in front.


How can ADS-B be secure when it is based on self-reporting? By all reports, ADS-B is the future of air navigation and ATC. In the simplest definition, ADS-B is aircraft self-reporting GPS position to benefit everyone.

How is this secure? Seems like someone could simply broadcast a false position for any number of nefarious purposes.

Maybe I am missing something obvious, but I have yet to see an explanation of ADS-B from a security perspective.

Yes, one can send deliberately wrong position reports. But why would anyone want to do that? We're assuming malicious intent, of course -- but even so?

Could an attacker cause a collision using fake position broadcasts? It is hard to see how. The core meaning of an ADS-B broadcast is basically, "Dear ATC, please don't clear anyone to fly too near such-and-such point in space, because that's where I am." Getting an unsuspecting other aircraft to avoid a particular point in space where in reality nobody is, will not in itself cause any accident. At most some distraction and swearing and "no sir, I reallly don't see that traffic" transmissions.

An attacker might mount a denial of service attack against the airspace by flooding an air traffic controller's monitor with dummy aircraft, so he can't find any safe way to route the real planes he's talking to. But for that effect it's not really necessary to send any fake position reports -- simply jamming the 1090 MHz downlink frequency would do just as well, and not be significantly more illegal or harder to detect.

You could try to convince ATC that someone else is in a different place than they really are. However, unless you jam the entire frequency, ATC would still be able to hear their real position reports, and their computers would be able to tell that they have several inconsistent reports from the same airframe address. It would be simple to handle that by separating traffic from both reported positions (which they need to be able to anyway, just in case someone accidentally misconfigures their transponder with a wrong address), and then we're back in the DoS scenario.

Could a suicidal attacker go up in an airplane of his own and get to ram into somebody else while faking his position as far as ATC sees it? If that's your goal, it would certainly seem helpful to stop broadcasting yoru true position, but that doesn't mean that broadcasting a false position would buy you anything that you don't also get simply by pulling the plug on your transponder so you don't broadcast anything. In both cases your problem would be that you're now a primary radar echo that doesn't correspond to any transponder reply. Depending on where you pull the trick that may or may not set alarm bells ringing -- but to the extent it does, broadcasting a different position wouldn't do anything to silence them.

One thing you can do is rig your ADS-B Out to transmit a wrong altitude and hope to get clearance to pass directly above or below someone which you might then try to ram without being seen -- because primary radar is generally bad at distinguishing altitudes. However, that is not a risk specific to ADS-B -- good old SSR also depends on airborne transponders to self-report their altitude in Mode C, and that can be tampered with just as easily.


Where can I find glide ratios for commercial aircraft? I know that light aircraft have poor glide ratios (typically 1:10) compared to commercial aircraft (typically 1:20 or above). I was wondering if there is a source where one can find the glide ratio by aircraft type.

I am particularly interested in the BA146 / RJ85 following the LaMia crash in Colombia.

The glide ratio is closely related to the lift/drag ratio; as lift/drag ratio is closely related to aerodynamic performance, aircraft manufacturers are very restrictive on such data and little reliable information is publicly available.
Some guesses can be made from incidences like Air Transat Flight 236. For the A330 this results somewhere around 24.

I'm not aware of any data on BA146/RJ85. As BA146/RJ85 focusses on short haul it may have a slightly lower glide ratio; 4 engines are also not favourable for a sailing plane. Still anything below 20 would be a surprise to me.

Edit: Seems I sort of mixed up the numbers. The A330 should be somewhere over 20 (quite a time since I worked on that...). Fopr the RJ85 on this forum the glide ratio is estimated as 15:1.

P.S.: Keep in mind that all these values are maximum values that can be reached under optimal conditions. Real values may be lower.


Are larger airplanes more likely to stall? Stalls happen when the boundary layer on top of a wing slows so much that it essentially becomes part of the airfoil.

My question is, as the wings on larger aircraft present a longer flow path for the boundary layer, they slow the layer more. Right? So, would they not be more have a lower stall angle? Isn't this what is hinted at by the use of slots on airliner flaps?

Even assuming the same airspeed, a larger chord would increase the free-stream Reynolds number. As a general trend, higher free-stream Reynolds number will delay the stall boundary due to earlier transition to a turbulent boundary layer, as can be seen below for a 2D section data from wind tunnel:

Image ref: NASA Contractor Report 4745

This answer has a different and equally good illustration of the effect in terms of lift curves.

Of course, things get more nuanced in 3D, whether the airfoil is optimized for natural laminar flow, and in transonic flow, where the maximum lift trend with Reynolds number can reverse at an intermediate Reynolds number.


Why is the coefficient of drag for straight wings at supersonic speeds lower than for swept wings? Why is the coefficient of drag of a straight wing lower than the coefficient of drag of a swept back wing at higher supersonic speeds (above, say, Mach 2)?

Mark is right when he says that there is no induced drag at supersonic speeds, but it is an invitation for misunderstandings. Induced drag is replaced by lift wave drag, and all what happens is that aerodynamicists choose to use two different names for basically the same effect: Air gets pushed down.

As usual when I post a long answer, I was not quite happy with the existing answer(s). Now I have some time and try to give a better answer.

First, why does the straight wing work better only at very high Mach numbers (> 2.0)? Because at lower supersonic speed a swept wing gives overall better performance. The sweep angle $\varphi_0$ must be high enough to allow for a subsonic leading edge (Mach < $\frac{1}{cos\varphi_0}$). Then the flow around the leading edge is subsonic and creates a suction area when accelerating around the nose contour. This suction helps to reduce drag - after all, this same suction is why a subsonic airfoil in inviscid flow has no drag. Edward C. Polhamus did a lot of research on this at NACA Langley and published several papers with equations for calculating the suction force.

Once you fly faster than Mach 2, the sweep angle for a subsonic leading edge rapidly gets too high for acceptable subsonic flight, and an unswept wing becomes the better alternative since you need to accept a supersonic leading edge. Examples are the wing of the F-104 or the canard of the XB-70.

Now for the airfoil drag at supersonic speed. Because it is easiest to explain, I select a rhombic cross section:

Rhombic airfoil in supersonic flow at zero angle of attack (own work). The plus sign denotes higher pressure, the minus sign lower pressure than ambient. By selecting a rhombic airfoil, the flow is very easy to determine because the pressure only changes when the local contour gradient changes. The two compression shocks create the typical sonic boom when arriving at the ground. Note that this airfoil already creates pressure drag even at zero lift. Any airfoil thickness greater than zero and any airfoil camber will cause this type of drag where the forward-facing areas see higher pressure and the rear-facing areas experience suction. This type of drag is called wave drag. It can only be minimized by minimizing the relative thickness of whatever is supposed fly at supersonic speed.

When the angle of attack is increased, this airfoil begins to create lift. Now the compression by the lower forward shock becomes stronger and that by the upper forward shock becomes weaker. The expansion fan is the same again on both sides, so the upper rear half experiences less pressure than the lower rear half. I tried to symbolize this by the amount of plus and minus signs:

Note that the pressure difference is constant over chord, so the center of pressure is at 50% of chord length. Note also that the lift vector is perpendicular to the chord line. Since lift is defined as the force perpendicular to the direction of the undisturbed air, supersonic lift always carries a drag component which is proportional to the angle of attack - there is no suction at the nose to alleviate this! The wave drag of the airfoil at zero angle of attack still comes on top, so we have a shape-dependent wave drag and a lift-dependent wave drag component. This lift-dependent wave drag replaces the induced drag of subsonic speeds. If we compare the magnitude of both, we find:

Subsonic: $c_{Di} = \frac{c^2_L}{\pi\cdot AR\cdot\epsilon}$

Supersonic formula for 2D flow: $c_{{DW}_L} = c_L\cdot\alpha$

This doesn't look so similar, so let's now express the angle of attack $\alpha$ by the lift coefficient divided by the lift curve slope:

$$\alpha = \frac{c_L}{c_{L\alpha}} = \frac{c_L}{\frac{4}{\sqrt{Ma^2-1}}\cdot\left(1 - \frac{\lambda}{2\cdot AR\cdot\sqrt{Ma^2-1}}\right)}$$

and the lift wave drag component becomes $c_{{DW}_L} = \frac{c^2_L}{\frac{4}{\sqrt{Ma^2-1}}\cdot\left(1 - \frac{\lambda}{2\cdot AR\cdot\sqrt{Ma^2-1}}\right)}$

Now let's compare the F-104 wing, which has an aspect ratio $AR$ of 2.45 and a taper ratio $\lambda$ of 0.385: If we plug in the parameters and adjust $\epsilon$ such that both sub- and supersonic lift-dependent drag coefficients agree, $\epsilon$ would need to be 0.89 at Mach 1.2, 0.58 at Mach 1.4 and 0.31 at Mach 2.0. The dramatic rise of lift wave drag over Mach is caused by the reduction in the lift curve slope over Mach.

For slender bodies the lift curve slope is $c_{L\alpha} = \frac{\pi\cdot AR}{2}$ and the lift wave drag component becomes $c_{{DW}_L} = 2\cdot\frac{c^2_L}{\pi\cdot AR}$. For slender bodies the supersonic $\epsilon$ is 0.5, regardless of Mach.

The important conclusions from this for wing selection are:

Sweep does no longer help once the leading edge is supersonic.
Lift wave drag continues where induced drag drops off. Lift always causes drag.
For a supersonic wing the aspect ratio is of minor importance.

Now back to the original question: Once the leading edge is supersonic, sweep is no longer helpful. Now the best wing is straight, because it will need the lowest wing area to create the required lift at subsonic speed. At supersonic speed its lower area will translate into lower friction drag, making it better than comparable delta or swept wings.


What methods are used for calculating maximum takeoff windspeed of a helicopter? I would like to calculate the maximum windspeed in which a helicopter may safely take off and safely land, assuming a theoretical wind environment with constant wind direction and no gusts.

I understand that Effective Translational Lift is generated when taking off into the wind, which increases the climb rate.

However, I would like to understand at what windspeed taking off and landing into the wind is theoretically no longer possible for a given main rotor RPM.

Some factors I have considered include:

while the main rotor is spinning at less than flight RPM, and nonrigid, that it may come in contact with the fuselage.
during takeoff or landing: if the vehicle must pitch forward to compensate for extremely strong headwinds while inches above the ground, the main rotor may strike the ground

While not relevant to the theoretical wind environment described above: if there are gusts, I have also considered:

during takeoff or landing: while hovering inches above the ground, a strong crosswind may roll the vehicle above a threshold which causes the main rotor to strike the ground.

What methods might I use to calculate these (and any other factors I have not considered) precisely?

The simple (and probably unsatisfying) answer would be:
The maximum headwind into which a helicopter can land will be somewhat less than it’s listed maximum operating speed.
Flying at Vmo into a headwind of equal speed should lead to a stationary velocity relative to the ground. In theory, the aircraft could gently lower itself all the way the ground like this (although, I certainly wouldn’t try it). The problem is, most helicopters will be in a very pitch-forward attitude at this point and the skids or landing gear may not be in the proper orientation to safely put the aircraft on the ground. This will vary from model to model and would need to be tested on a case-by-case basis.
It should be noted that landing and shutting the engine down are 2 separate problems. Many helis have a maximum wind speed for startup/shutdown, like this BK117 which has a listed limit of 50 knots in its POH.


Why do newer 737s use two different styles of split winglets? All new 737s use split-tip winglets, which are more efficient than the simpler blended winglets previously used.

However, for no clear reason, they use two different types of split-tip winglet:

New 737 Next Generations (the 737-700/-800/-900)1 use split-scimitar winglets, which have a main body shaped like a blended winglet, but with its upper tip hooked backwards, and also have an additional scimitar-shaped fin projecting outwards and backwards from the upbend in the winglet.

(Image by Mnts at Wikimedia Commons.)

The 737 MAX series uses the eponymous MAX winglets, which have a simpler shape than the split-scimitar winglet, looking essentially like if someone decided to put a winglet on the bottom of the wingtip in addition to the one at the top.

(Image by Aka The Beav at Flickr, via Helmy oved at Wikimedia Commons, modified by Altair78 at Wikimedia Commons.)

I don’t get it - why go to the trouble of producing two slightly different styles of winglet alongside each other for two mostly-similar families of the same aircraft?  Why not just go with the more efficient style of the two (be it the split-scimitar winglet or the MAX winglet), and use that on both the Next Generation and the MAX?

1: The 737-600 also belongs to the Next Generation family, but it left production long before the Next Generations switched from the blended to the split-scimitar winglet.

Since a winglet is basically a sail generating thrust (lift with a modest forward-tilted vector) from the circulating flow around the tip, extracting beneficial energy from the circulation (the thrust part) and producing an "outwash" that opposes and weakens the vortice flow in the process, it's just adding another sail beside the first one to extract more of the available energy from the flow.  From the NASA Dryden page:

  Winglets, which are airfoils operating just like a sailboat tacking upwind, produce a forward thrust inside the circulation field of the vortices and reduce their strength. Weaker vortices mean less drag at the wingtips and lift is restored. Improved wing efficiency translates to more payload, reduced fuel consumption, and a longer cruising range that can allow an air carrier to expand routes and destinations.

  To produce as much forward thrust as possible, the winglet's airfoil is designed with the same attention as the airfoil of the wings themselves. Performance improvements generated by winglets, however, depend on factors such as the basic design of the aircraft, engine efficiency, and even the weather in which an aircraft is operating.

In the case of the MAX, you can see that the lower winglet is at less than a 45 degree angle, so it's producing mostly vertical lift with a slight forward component because as you can also see its incidence is somewhat nose down relative to the main wing to optimize its AOA in the tip circulation.  It's kind of a half winglet, half tip extension.

Different engineering groups will do studies of different configurations and will say, "hey, if we do this, it'll be some little bit more efficient than if we do that, based on our particular analysis".

If you put different groups of engineers together to attack the problem, they are all going to come out with variations on what they think is the ideal configuration.  And so you see seemingly endless permutations that are, really, mostly nibbling at the margins of the major benefit that was achieved when you put one there in the first place.

Plus there is probably a bit of "styling" going on as well.  Just to be different.


Would a headwind result in a faster propeller rpm? A few weeks ago I did an experiment with a model aircraft that has a motorized propeller. I turned on the propeller and it turned at a constant speed. Then I turned on a desk fan and put it in front of the propeller (see the picture below) and I saw an increase in propeller rpm and an increase in noise.

Does this also happen to a propeller when a headwind hits it?

The problem is you're holding the aircraft with your hand.

Imagine a windmill. It has no power at all, it spins freely. What happens when wind is blowing at it? It turns.

Now imagine a propeller with no power connected to it, so it acts like a windmill. If wind is blowing at it, it will turn just the same. Why? Because a propeller pushes wind backward when it turns. When it is facing a headwind, the propeller wants to turn such that it is pushing air at the same speed as the arriving air.

In your case, I suppose the fan is blowing air at a faster speed, compared to the propeller is pushing air on its motor. Say the motor pushes air backward at 1 m/s. The fan blows air at 2 m/s. That's why it spins faster with the fan on.

But that's only true as long as you're holding the aircraft with your hand.

In flight, nothing is holding the aircraft at a constant ground speed. For example, assume in a no wind condition, an aircraft is flying at 80 knots. Suddenly it encounters a 10 knots headwind, and continues to fly into this headwind for the remainder of the flight. What happens?

At the moment of encountering the headwind, the airspeed indicator in the cockpit jumps from 80 to 90. The propeller rpm will also suddenly jump to a higher value. But that is not going to last. The aircraft is getting pushed backward by the wind, the airspeed is going to slowly drop back to 80. There is not enough power to keep the propeller at the higher rpm which pushes air at 90, it can only to 80. After a while, it is flying at 80 knots relative to the air, and 70 knots relative to the ground.


Why are the leading edges on the Boeing 787 made from aluminum? Why are the leading edges of the wings, horizontal stabiliser and vertical stabiliser and the engine's inlets made from Aluminium?

There are probably many factors in choosing aluminum vs. composites.

A big one is bird strikes. The leading edges are at the highest risk for this. Metal tends to absorb the impact better while retaining its strength, while composites would tend to delaminate and become much weaker. Resistance to in-flight hail must also be considered.

(Source Left, Right) Comparison of bird strike effect on aluminum and carbon fiber.

Anti ice was also mentioned. These areas are heated with bleed air (or, for the 787, electrical elements) to melt or prevent any ice formation. Metals do much better at high temperatures than composites, which would tend to melt or lose strength. Metals are also able to conduct the anti ice heat better than composites.

Another factor could be manufacturing. These surfaces have a lot of curvature. Composite panels are often reinforced with honeycomb core, which is best on relatively flat surfaces. Of course composites could be made into these shapes, but the shape would limit material and configuration options. Metal is also easier to work with or repair than composites.

As far as choosing aluminum over other metals, it tends to be very light and cheap for its strength, has decent temperature capability for anti-ice, and when properly used is fairly resistant to corrosion or fatigue.

The nose does not have anti ice and must serve as a cover for the weather radar. Composites can be made relatively transparent to radar, but metal would tend to block the waves.


Who has right of way on the ground? In the air, concept of right of way does exist.

Does it also exist for ground operation as well? Possible conflict might come from where taxi ways intersect each other. Do pilots have to agree with each other who goes first or ground controllers do this for them?

At a controlled airport, ground maneuvering, taxi routing and sequencing, etc., will be assigned to you by ground controllers after you make contact with them and enter the controlled areas of the field.  Even here the rules below will apply when aircraft are maneuvering in non-controlled areas of the field e.g. parking aprons, hangar spurs, refueling areas, etc.

Pilots are generally courteous and conscientious people and will usually try to be helpful to both parties.

At a uncontrolled airport or an uncontrolled area of a controlled field, the following right of way rules are going to apply to maneuvering on the ground:

  When two aircraft are approaching head on, or approximately so, each shall stop or where practicable alter its course to the right so as to keep well clear.
  When two aircraft are on a converging course, the one which has the other on its right shall give way.
  An aircraft which is being overtaken by another aircraft shall have the right-of-way and the overtaking aircraft shall keep well clear of the other aircraft.
  An aircraft taxiing on the manoeuvring area shall stop and hold at all runway-holding positions unless an explicit clearance to enter or cross the runway has been issued by the aerodrome control tower.
  Emergency vehicles proceeding to the assistance of an aircraft in distress shall be afforded priority over all other surface movement traffic.

Source: EASA (pdf pages 53-54)


Were there any successful flying machines that did not rely on Bernoulli's Principle? One of Leonardo da Vinci's flying machines appears to be a giant auger.  This design would not have exploited Bernoulli's Principle, but rather used the blade's rotation to push the air below it down to keep the craft airborne.

Image credit: Wikimedia

Were there any flying machines built like this that actually got off the ground?

EDIT: So maybe I have Bernoulli misunderstood, judging from the discussion.

How about all lighter-than-air vehicles:

Hot air balloons
Hydrogen- or helium-filled balloons
Airships

If you want to restrict the choice to heavier-than-air vehicles, rockets should still qualify.

You may also include VTOL aircraft which do not rely on their wings during hover, their internal turbo machinery would still use Bernoulli's principle, however, so for me they do not qualify.


Can a non FAA CFI (EASA for eg) sign off a high performance endorsement on an FAA PPL certificate? I have an FAA PPL cert, flying in the UK. Can a qualified EASA CFI sign off a high performance endorsement on my FAA certificate.
Thanks

No, the problem is that the endorsement must come from an "authorized instructor" which is defined in 61.1(b):

  Authorized instructor means -

  (i) A person who holds a ground instructor certificate issued under part 61 of this chapter and is in compliance with § 61.217, when conducting ground training in accordance with the privileges and limitations of his or her ground instructor certificate;

  (ii) A person who holds a flight instructor certificate issued under part 61 of this chapter and is in compliance with § 61.197, when conducting ground training or flight training in accordance with the privileges and limitations of his or her flight instructor certificate; or

  (iii) A person authorized by the Administrator to provide ground training or flight training under part 61, 121, 135, or 142 of this chapter when conducting ground training or flight training in accordance with that authority.

The requirement for an "authorized instructor" comes from 61.31:

  (f)Additional training required for operating high-performance airplanes.

  (1) Except as provided in paragraph (f)(2) of this section, no person may act as pilot in command of a high-performance airplane (an airplane with an engine of more than 200 horsepower), unless the person has -

  (i) Received and logged ground and flight training from an authorized instructor in a high-performance airplane, or in a flight simulator or flight training device that is representative of a high-performance airplane, and has been found proficient in the operation and systems of the airplane; and

  (ii) Received a one-time endorsement in the pilot's logbook from an authorized instructor who certifies the person is proficient to operate a high-performance airplane.

So you can't get an endorsement from a "CFI" who is not authorized under Part 61.


What are the correct names of the parking spaces for turn-around? A plane can be parked at the terminal and the passengers can board through a jet bridge. Also it can be parked somewhere else, far away from the terminal and the passengers would need to take the bus to get there.

What is the correct name of those parking spaces?

They are referred to as aircraft stands.

ICAO Definition:

  Aircraft stand.
  A designated area on an apron intended to be used for parking an aircraft.

Stands at the terminal building are commonly referred to as gates, while stands further away may be referred to as remote stands or remote gates. The aircraft stand term covers both types.


What do these polygons mean on VFR charts? There are a lot of blue polygons on this VFR chart:

What do they mean?
Source

To add a little to @abelenky's answer, you'll notice that each area has a identifier in it: SBR-522, SBP-505 etc. Those identifiers are made up of the ICAO country prefix, the airspace type, and a unique code. The airspace type can be Prohibited (P), Restricted (R) or Danger (D).

Since SB is the ICAO code for Brazil, SBR-522 is Brazil Restricted area #522; SBP-505 is Brazil Prohibited area#505 etc. I couldn't quickly see any nearby danger areas, but here's one in South Africa: FAD-193, near Port Elizabeth.

You can look up those codes in each country's Aeronautical Information Publication (AIP) or local equivalent to get more information about what each area is, what altitude it goes up to, any special rules etc.


Can I become a pilot if I am under treatment for Attention Deficit Disorder? I know that before you even begin training in flight school, you are required to get a physical examination from a doctor to determine if you are fit to fly. Online articles stressed the importance of being completely honest with the doctor about any existing conditions.

I was just recently diagnosed with ADD (or rather, I described my issues to my regular physician and simply started receiving medication to treat it) and this is something I would naturally disclose at the physical examination.

Does FAA disqualify someone from getting their pilot's license on the basis of ADD?

I take medication for this once a day and it resolves any issues I face from it.

I'm going to assume you're asking about US/FAA requirements - If not what's below may not be particularly helpful.

ADD is not a disqualifying condition, however if you have a formal diagnosis of ADD or ADHD you may need to undergo additional testing in order to receive a medical certificate.
Also some of the medications used to treat ADD/ADHD may be disqualifying (I know that Adderall, Focalin, and Ritalin were all on the FAA's "No Fly" list - I'm not sure if they're still an absolute NO or if you can get approval for them).

AOPA has a pretty decent drug list that you can search to see if what you've been prescribed is permitted - it's a little easier to search/cross-reference than the official FAA "Do Not Issue/Do Not Fly" list and they do a good job keeping it up to date, and a brief article on ADD/ADHD & medical certification.
They also have a service to assist you with getting your medical (as part of Pilot Protection Services) which can be helpful.


Why do some Mach trimmers move the elevator? A pop-up rod on a the FO's control column on a DC-9 that shows the Mach trim position. (YouTube)
Regarding the title, I'm not sure if it's just some or all jetliners (I tried to research it). On the DC-9, MD-80, and 737NG,* it is stated clearly in the FCOMs that the Mach trim moves the elevator to counter the Mach tuck. On the 737 the system starts operating above Mach 0.615 (See FCOM 9.20). And below is part of the text from the MD-80 FCOM:

Operating on a Mach schedule, the Mach trim compensator pulls the First Officer’s control column aft as Mach number increases. As the control column moves aft, an indicator rod on the left side of the First Officer’s control column extends, giving visual indication of Mach trim operation.

Why don't the mentioned Mach trimmers use the stabilizer? I always thought the stabilizer had more fine control, not to mention the drag penalty of an offset elevator. There must be a reason for moving the control column aft and not just trim the stabilizer.
Update
It is not an era's technology limitation. The Boeing 707 moved the stabilizer for its Mach trim according to both an accident investigation report and a Cambridge University book. And like the DC-9, the 707 did not have hydraulics for its elevators.
* The MD-90** and B717 move their stabilizer according to their FCOMs.
** Unlike the rest of the DC-9 family, the MD-90 uses a powered-elevator.
My current working hypothesis is that the answer relates to stick forces, but I can't find any reliable sources on the design reasoning.

I checked these posts where Mach tuck was discussed:

Why does aircraft stability increase when it transitions from subsonic to supersonic flight?
What are the advantages of a Trimmable Horizontal Stabilizer?

I think it's because the 9 uses free floating elevators with servo tabs to move them.  The columns just move the servo tabs which means the actual input forces are really low and there is feel spring unit in the system.   For mach trim they just have a servo motor that applies a little pull to the column via the feel spring unit, and the rod extends to tell you the motor is pulling on the column.

There is a trimmable stab for pitch trim, but it will have a fairly primitive controller (figuring pre-microprocessor 1965 electronics) and to incorporate a mach trim mode into the stab control system was probably much more expensive than the simple setup they came up with.

The more modern setup, with hydraulic elevators that are always faired with the stab when not displaced by a control input, and a stab controller that is fully integrated into the autopilot and air data systems is way less drag.


Are radar bars centered around the horizon or do they move with aircraft pitch? Say I am in a military aircraft with a non-AESA radar.
The radar is set to scan 4 elevation bars, so when I fly level, 2 above and 2 below the horizon.

If I pitch 20 degs up, will it continue to scan around the horizon or will the bars move up with the aircraft pitch?

If i understand your question, you are asking whether the vertical elevation direction of the radar antenna lobe is corrected for when the aircraft is in a pitched up position as compared to a level position. (Whether this correction would be done mechanically in older radars or electronically with AESA radars is secondary)

It probably depends on the particular aircraft and version.
But to my knowledge it is generally not. The antenna will keep its direction within the host aircraft and thus scan a higher altitude volume when the aircraft is pitched up.

Note that the pilot can change the vertical elevation range of the antenna by tilting it up or down manually at any time (if it is not locked on a target) and will probably do so in order to compensate for longer phases of pitch up flight.

As an example, this document is a description of the AN/APG-66 and -68 radar systems of the F-16 Fighting Falcon.
(It is a documentation for a general public simulator game, but you can be confident that it describes the function of the real aircraft very accurately)
See page 11, section "Elevation".
In the case of the F-16, the antenna tilt interface is part of the HOTAS controls, on the throttle:
http://falcon4.wikidot.com/avionics:hotas, see "Antenna Elevation Knob"

When a target is "tracked" or "locked" this is another matter. In that case, the antenna will generally move autonomously in order to keep the target within the center of its detection lobe as long as possible, both vertically and horizontally (azimuth), within what is physically possible taking into account the attitude of the host aircraft versus the target. (See the doc for this also)


What is the difference between “affirm” and “acknowledged”? Recently, I've watched Air Force One and I heard ATC and the pilots say "Acknowledged." instead of "affirm" or "affirmative" as I've learned..
Is it common to say both? Or might "Acknowledged." just throw the controller / pilot off?

"Acknowledged" means I heard you & understood what you said & I take responsibility for the information you just gave me.
"Affirm" and its opposite, "negative," are answers to a yes/no question.
They aren't really interchangeable, although Hollywood script writers are notorious for getting details like that wrong.
An example of correct usage would be, "Callsign 123, is your ride smooth at FL350?" "Callsign 123, affirm." (Answers the question, yes the ride here is smooth.") Then, "Callsign 123, we've had reports of light turbulence at your 12 o'clock and 100 miles." "Callsign 123, acknowledged." (Or, "roger" is more common, but same meaning... either way, I've received & understood the turbulence report.)
To reply "roger" or "acknowledged" to the question "is your ride smooth" is incorrect, because all you'd be saying is, I heard your question. There isn't any "yes" or "no" component to either of those replies. Likewise, to reply "affirm" to the "turbulence ahead" call is wrong because there was no question being asked there. The controller just needs to know that you heard the information so that it doesn't have to be repeated.
Interestingly, the FAA Pilot-Controller Glossary doesn't list "acknowledged" at all, but lists "acknowledge" as a directive: tell me that you heard me.
It also lists "affirmative" and not "affirm" -- that may be more used elsewhere. Also, with the quality of modern radios, the risk of the initial syllable(s) getting lost & the receiver left puzzling over "...ative" has probably diminished over time.


Do aircraft have radar or other forms of traffic sensing? Quicky question.

Do modern commercial aircraft include radar to detect traffic in their vicinity or perhaps have some mechanism to receive transponder signals.

I know they have forward facing weather radar but the ability to detect and be warned of other traffic on a collision course would seem to be a good idea.

I'm particularly reminded of the Proteus Airlines Flight 706 incident where a mid-air collision occurred because of visual blind-spots and the ATC not knowing the other aircraft was even out there. I am also aware in this case a transponder monitor would not have helped either...

EDIT:

I suppose TCAS does do the transponder bit, but wont detect aircraft without the necessary device turned on. I'm more thinking of a short range RADAR or even LIDAR, something akin to, though longer range than, the things they are hooking up to cars these days.

By far, most civil aircraft lack radar to display conflicting traffic, and certainly to enhance traffic situational awareness.  TCAS and the use of ADS-B are the most effective tools for traffic conflict and situational awareness information.

Lidar is not presently utilized on civil aircraft for traffic avoidance.

Keep in mind that TCAS essentially uses the same mechanisms as secondary ATC radar.


Can ADS-B DF-17 messages with a non-zero remainder after CRC check be used? For fun I've been using an AirSPy SDR (Software Defined Radio) to receive and decode ADS-B packets, primarily DF-11 and DF-17 messages.

The code is written in C++ and works reasonably well. It performs IQ processing / demodulation, packet extraction, CRC checking etc. As its output it generates AVR formatted message strings that are then served via a Listen Socket / Socket based interface. I then use Virtual Radar as a client to decode and display the data.

With regard to the DF-17 and DF-11 packets, I'm currently only forwarding the ones that have an Interrogator ID of zero, the so called "unsolicited squitters". i.e. Complete packets that have a zero remainder after CRCing.

I also receive / decode plenty of packets that have non-zero Interrogator IDs.

Can I use these for anything useful?

In other words, could I extract any useful information, positions, velocities etc. If so I could then re-write them as unsolicited DF-17 messages and pass them to Virtual Radar.

I am researching this to the best of my ability, but currently drowning in specs and documentation as there appears to be so much of it!

Apologies if I've miss used any of the jargon, I'm only a week into my project.

Messages with Downlink Format 17 are, as you know, ADS-B messages that do not require interrogation. As such the interrogator ID will be zero.

Frequently you will see that, after applying the CRC check, the CRC remainder is non-zero. This is caused by corruption of the ADS-B message between the transmitter (see note) and the receiver. This is partly because transmissions of multiple aircraft are unsynchronised so that they may overlap an become difficult to untangle. This overlapping is called garbling.

Since you have IQ information available, you may be able to de-garble overlapping message with some success. Also, you could try to do error correction using the CRC algorithm. Up to two rogue bits can usually be corrected, more than that becomes difficult.

To improve the performance of the CRC error correction you can again use information from the IQ sampling, by giving each bit a confidence value based on the shape of the received radio data.

If you are not able to correct the error bits (i.e. you have a non-zero remainder after correction), you should consider that ADS-B message as useless.

Note: there are a couple of aircraft flying with rogue transponders that transmit garbage DF-17 messages with non-zero remainder. They will be phased out in the next couple of years.


Are answers posted to the FAA Sample Knowledge Exams? I'm studying for the private pilot knowledge exam, and wondering if the answers to the sample test are posted anywhere. Here is the exam: https://www.faa.gov/training_testing/testing/test_questions/media/PARSampleExam.pdf

Let me answer your question by first quoting from the 2017 Gleim Instrument Pilot Knowledge Test book.

The FAA no longer releases the complete database of test questions to the public. Instead, sample questions are released on the Airman Testing page of the FAA website on a quarterly basis.…
Gleim utilizes customer feedback and FAA publications to create additional sample questions that closely represent the topical coverage of each FAA knowledge test.

The rewrite removed questions that are no longer relevant to most pilots, e.g. NDBs, Colored airways, and added new questions on things like GPS, PFDs, CRM.

In addition, they now shuffle the answers for each tester, so you can’t just do things like remember that most of the answers to a group of questions is 'A'.

They supposedly cleaned up the answers on some of the calculation questions so that minor differences in measurement do not result in getting an answer that is not one of the choices. For example, in previous exams some of the charts were reproduced at 98% scale. If you didn’t correct for that you would get an answer that was midway between two selections.

They also cleaned up the questions that had two right answers but one was more right than the other.

Since the exams are testing for the same content, and draw the questions from known publications, understanding past questions will give you the knowledge to pass the current exam.

Purchasing a test book from GLeim, ASA, or Sporty’s is probably worth the money for most people. With your purchase, most booklet makers also give you on-line tests so you can go into the test well-prepared.

According to Gleim, 85% of test takers pass on the first try, so don’t make too big a deal out of the test. If you are prepared, you’ll pass.


Do ducted fans eliminate induced drag? It has often been said on this site that induced drag on wings is the inevitable result of producing lift over a finite length. Converting this to the realm of propulsion, I assume that propellers have "induced drag" or something similar, as they produce thrust over a finite length.

With a ducted fan, the airstreams above and below the airfoil can't just "slip around the side," because they're blocked by the duct. My intuition thus suggests that ducted fans would not have induced drag (or its equivalent), assuming that the space between the blades and the duct is negligible.

Is this accurate?

EDIT: I'll add this ahead of the answer because it will necessarily come up: This answer is based on the model described by Prandtl, which is only that: A model, a simplified description for what happens that works to explain some phenomena. There is some disagreement about this model, so a separate explanation using a differen theory might help. The problem is that an explanation with pressure differences doesn't help much here, at least I wouldn't know how to answer the question without working with Helmholtz/Prandtl.

Fundamentally, what we are talking about are vortex rings that are created because air is moved in some direction somewhere and not moved everywhere else. That's independent of how you move it, and fundamentally, a duct or winglet or something similar can't change that. You can look at the vortex itself as the thing that actually creates lift or thrust, so you want and need that vortex.

Then there's Helmholtz's theorems. Quick quote from that article:

Helmholtz’s first theorem:
The strength of a vortex filament is constant along its length.
Helmholtz’s second theorem:
A vortex filament cannot end in a fluid; it must extend to the
boundaries of the fluid or form a closed path.

In the case of a normal wing, the vortex ring ("closed path") consists of one side along the length of the wing, two sides trailing behind the wingtips and the fourth side is somewhat lost, or far enought away that it can mostly be ignored. The three sides that are not along the wing itself are the problem, they are what the term "induced drag" refers to. Because there is no surface at the end of the wing for the vortex to end at, it has to continue into infinity. And there is some friction involved in creating long fast-spinning vortices, so you get drag. (Any help in explaining this part more eloquently is appreciated)

Because the amount of lift/thrust that you want is given, the vortex strength isn't something that can be changed either. What can be changed, however, is the distribution/speed/radius. If the lift distribution is elliptical (see: Spitfire), the lift gradient is minimal across the wing so there is no strong and fast vortex at the end, it is gradually created along the whole wingspan and the induced drag is minimal. Winglets do something similar by forcing the vortex to go all the way around the winglet.

In the case of a propeller, the inner side of the vortex ends at the spinner or shaft, so the ring is broken and you are only left with a linear vortex, but it is still trailing infinitely into the air at the tips of the blades. You can look at a wing in the same way if you interrupt the ring at the fuselage.

In the case of a ducted fan, you have two fluid boundaries, both on the inside and on the outside, which appears to solve the problem. You can have a vortex around the blade only and no vortices trailing into infinity creating drag. The problem is that the fluid doesn't really end at the duct because the duct has a finite length. So what you get is a large vortex around the whole duct. Air is moving in at the front and out at the back, and somewhere, that air moves back to the front far away from the engine.

In the case of a ducted fan, the vortex ring is created in the place where the moving air meets the static air at the beginning and end of the duct. Instead of a very small vortex around the tip of the wing (and along the wing, to not mess up Helmholtz's theorems), you get a larger one around the whole duct.

Therefore, I wouldn't say that the duct can eliminate induced drag. The effect is fundamentally comparable to a wingtip device: It increases the inner radius of the vortex and thereby reduces the induced drag significantly. It's far more effective at that than a wingtip device, but it has to be because ducted fans are usually relatively small so the drag would otherwise be enormous.


Why did the Daimler-Benz DB 605 compression ratio vary between cylinder banks? The Daimler-Benz DB 605 was an inverted V12. The compression ratio of the 2 banks varied slightly. Why did the designers do this?

  Compression ratio: 1:7.3 right bank, 1:7.5 left bank (museomotori.unipa.it)

The 605 (601E above) used a "wild" valve timing. This valve overlap would start letting in the air/fuel mixture, while the exhaust valve was still open. So the intake would help push out the exhaust. This hurts the low RPM performance, so a special low-speed intake was also added.*

This overlap, the rotation direction, the compressor (supercharger) being closer to the left bank, are some of the reasons that resulted in the right bank having a lower compression ratio than the left. This affected the 603 and 605, but not the 601 because it didn't have such a wild timing overlap.**

But isn't compression ratio constant due to the fixed volume (a reply to a comment):

No, dynamic compression ratio is a thing that is affected by valve timing. An example (not 605 related) is given as:

  However: intake valve closure (sealing the cylinder) always takes place after BDC (bottom dead centre), which may cause some of the intake charge to be compressed backwards out of the cylinder by the rising piston at very low speeds (...)

* enginehistory.org

** ww2aircraft.net (translated from another link)


Do any UK universities include PPL/Commercial flight training as part of an aviation degree? I recently became interested in becoming a commercial pilot after buying Flight Simulator X and a Saitek Yoke system. I'm still studying my GCSE's, and I am now debating between computer science and a career as a pilot.

I currently don't have the money to get my private pilot license, and very much doubt that I'll have the money for commercial training in the future. Therefore, I am curious as to whether or not some universities offer both PPL and commercial flight training as part of an aviation degree program.

One UK list is here, it mentions several universities that include PPL and/or ATPL training in the degree course, but they appear to cover only the theory part of the courses with actual flight training being optional. Where a full PPL is included, they mention extra costs of around GBP 7000 on top of regular tuition.

If you look directly at the university sites they seem to confirm this: Leeds includes only 10 flight hours for the PPL; Brunel and Salford both include a UK NPPL but at extra cost.

You might be able to get a scholarship of some kind to cover all or part of your tuition, but that depends very heavily on your personal situation and what the individual university offers. Finally, you could consider the RAF as an alternative route to paid flight training but I have no idea if that's of any interest to you and I imagine that competition for cockpit places is very tough.


Can I fly a paramotor after learning on a paraglider? This video has inspired me to spend next week doing a 6 day paragliding course. The only downside is the school near me don't teach paramotoring.

Could I buy (and safely use/self-teach) a paramotor after learning to paraglide?

It's never safe to teach oneself to fly anything. Aviation pioneers did that out of necessity, but many died or got badly hurt doing it. Training gives you the benefit of decades of hard-won experience without the underpants soiling moments and broken bones.

You are talking about going from being an inexperienced paraglider pilot to a complete novice powered paramotor pilot without the benefit of any mentoring or coaching.

It's a bad idea™


How to simulate magnetometer used on navigation system? Magnetometer is used to measure yaw angle which will be used on AHRS system.When I simulate the magnetometer in matlab, I feel confused about what unit should be used for measurements magnetometer?Should I use μT(microtesla),rad or degree?
I know in real world, the magnetometer is to measure earth magnetic field, so it should be μT. the reason that I feel confused is that:In some papers, their simulation says $B_{i}$(earth's magnetic field) is given by $[\frac{1}{\sqrt{2}},0,\frac{1}{\sqrt{2}}]$ or $[1;0;1]$,symmetry-preserving observer.page11 and they didn't give the unit of above vector. I also find a book, called Small Unmanned Aircraft: Theory and Practice, it introduced how to simulate IMU sensors and says the standard deviation and bias error of Magnetometer could be 0.3 degrees and 1 degree.
So I am totally confused about the unit and value of the earth's magnetic field or Magnetometer measurements.

The unit does not really matter if you measure the right quantity. But obviously angle magnetic induction and angle are different quantities. Typically—but it might depends on the type of magnetometer used and is not true e.g. of mechanical compass—there will be two or three magnetometers detecting components of the magnetic induction vector, and then you calculate the bearing to magnetic north, and if you have three components the inclination from those.
The raw output of an electric vector magnetometer, measuring one axis of the magnetic induction vector, will be a voltage. You can convert it to the inductance in μT or whatever unit, but for navigation you only care about the direction and the units cancel out when you calculate that so you don't have to.
For magnetometers intended for nagivation, the required accuracy is only specified for the angle, in degrees, because the magnitude is not used.


Would it be a viable option to make the engine generate lift? I was thinking that if you made the engines generate lift it might help a tiny bit with the amount of time to takeoff, and thus lowering runway lengths.

Good thought, and it does happen. Tilt the jet exhaust or propeller downwards at a shallow angle $\phi$, and there is lift created at sin $\phi$ while thrust is reduced by cos $\phi$. If we take small angles, let's say 3 degrees:

$\Delta L$ = T $\cdot$ sin(3°) = 0.052 T
$\Delta T$ = T $\cdot$ cos(3°) = 0.9986 T

So 5.2% of engine thrust is converted into lift, for a loss of 0.14% of horizontal thrust. Free lift! Slight angles like this are found in aircraft installations, for instance in tail mounted jet engines which are angled horizontally to reduce yawing angle with a failed engine.

With engines mounted underneath the wing,the downwards pointed thrust would help a tiny bit in lift and reduce the take-off length. As @mins points out, with tail mounted engines the nose down pitching moment may counteract the lift benefits.


Was the F4F-1 Wildcat ever built? The original design for the F4F Wildcat was as a biplane, but with the -2 model, it was redesigned as a monoplane. I am wondering if the -1 model was ever actually built, or did it remain as a blueprint only?

According to aviation-history.com the design never left the drawing board.

In 1935, the US Navy ordered the XF4F-1 as a backup to the US Navy’s first monoplane fighter, the F2A-1 Brewster Buffalo. However, data from the Buffalo demonstrated that the biplane fighters could no longer match the performance of the monoplane. It was now apparent that biplane fighter's days were numbered as the XF4F-1 performed no better than the re-engined F3F.
The design never went further than the drawing board and the Navy’s thinking had finally reached the conclusion that the navy fighters were lagging far behind land-based fighters. The biplane design was scrapped in favor of a new prototype, designated the XF4F-2 (G-18).


What is the authority of the Air Boss at an airshow? Regular ATC operates under regulations like FAA Order 7110.65 when they control traffic. At an air show, there is typically an "air boss" that manages aircraft within the air show area.

Is the air boss required to have the same training and certification as a regular controller?

Does the air boss operate under the same regulations as regular controllers?

Does the air boss have the same authority as regular controllers?

Air bosses who orchestrate air shows do not receive special training or certification . Infact FAA also lacks the resources to inspect all aircraft that participate in air shows

FAA doesn't have certification standards for air bosses . Waivers for customary flight standards are provided to air shows, which then hire people to direct planes in flight.

There is no training in place right now for an air boss

http://www.rgj.com/story/news/2014/03/23/ntsb-hearing-addresses-distance-between-race-course-and-spectators-other-issues/6587627/

However,  typically former air-traffic controllers with a great deal of aviation experience are hired as Air Bosses at Air Shows .

The air boss implements the standards on the FAA waiver

Firms like ICAS provide Air Boss training


Could a tilt quadcopter use turbofan engines? I was wondering whether having a quad tiltrotor would allow for the use of turbofan engine rather than turbo prop. I read on another question that the V-22 uses turbo prop as it is easier to balance, but if there were 4 turbofans then it could surely balance and with the engines closer. Could a turbofan tilt rotor be possible for supersonic speeds and VTOL? And would tilt rotor or tilt wing be better in this application? Also wouldn't turbo fan mean there isn't the stream to worry about between sets of motors?

In a way, this has been done already half a century ago.

When NATO decided to try a VTOL strategy, the Harrier was not the only result. There was even a supersonic VTOL fighter, and it used swivelling engine pods at its wingtips, much like the V-22 does today. It was the VJ-101C, developed in Germany and first flown in 1963.

VJ-101C in flight. Note the opened intake door aft of the cockpit where two additional lift engines were complementing the thrust from the wingtip engines (picture source)

While the VJ-101C used six Rolls-Royce RB145 turbojets, a later production version was planned to use turbofan engines. NATO changed it's mind before the turbofan-powered version was built, however.


if center of pressure moves forward with angle of attack, then does it move forward of center of gravity also at a particular angle? Consider an aircraft where-

Center of gravity lies forward of Center of Pressure in CRUISE.

Now as angle of attack increases,

CP moves forward,

then for particular angle, it must move forward of CG.

In that case, wouldn't longitudinal stability be lost?
As , now the CP would be making nose pitch up moment, the tail plane will also make nose pitch up moment ( as it acts downwards)

Longitudinal stability is related to Neutral Point (NP) rather than CP. Exactly because CP moves around, it is not a convenient reference point.

There is no strict requirement for the tail to create downforce for a stable airplane, even though this is a common arrangement.

It may well happen that CP may move ahead of CG and the aircraft remains stable. But it won't keep doing it indefinitely: at some point the wing will stall, CP will move back (this will depend on the wing plan form though), and NP will cease to exist as such. Stability analysis is difficult in such regimes.


What is the proper procedure to change VFR altitude when changing heading from east to west? When you fly from west to east, sometimes your route heads west to avoid obstacles or to clear class B or C airspace.

According to hemispheric rule, let's pretend I selected 7500 feet for VFR to the east. En route to a destination with flight following, when I change heading to the west and the route to the west takes about 30 mins, can I remain the altitude until I get a new instruction from ATC? Or, should I request descent/climb and follow the hemispheric rule?

The destination and the post-take-off route are to the east, but when most of the route is to the west, it makes me confusing to select a proper altitude.

If you are on VFR Flight Following you usually don’t need to ask permission to change altitudes. The exception would be if you are given an altitude to fly from ATC. For example, last week I was flying west from Corona and approaching Burbank’s airspace. While climbing through 4,000' I was given an altitude restriction of “At or below 5,000'”. ATC had me fly over Burbank’s Class C altitude (4,800') but wanted to keep me below the departing traffic. I could see a big jet pass me and once it did I was told to “resume own navigation”. On my initial call I had indicated that I was going to fly home at 6,500' so I climbed to that altitude. I could fly at any appropriate altitude, e.g. 4,500', 6,500', 8,500' etc. but given how busy the airspace is and the expectation of ATC that I would remain at 6,500' I would not change altitude unless I first arranged to do so with ATC.

On the flight into Corona, at around 15 miles from the airport, I was given instructions to fly at or below 3,000'—presumably to avoid traffic departing Ontario. There was no need to inform ATC that I was leaving 3,000' when I had the airport in sight and began my descent.

On the other hand, once I got past Ventura, the traffic volume was much lower so I wouldn’t necessarily talk to ATC if I wanted to climb to go over a mountain or avoid a cloud.

As a general rule, when you begin your descent to land ATC can figure it out. In many cases the beginning of the descent corresponds with picking up the ATIS. Since ATC likes to know that you have the ATIS I will usually combine the descent and ATIS call in one transmission.

In your specific example, since you will be flying at the wrong altitude for 30 minutes, you should either climb or descend—unless your current altitude was assigned by ATC.

FYI, in SoCal when ATC says  “At or below 5,000'” they really mean “at exactly 5,000'”.


How are composite materials on aircraft joined? Answer for the question Why are planes using rivets & not welded construction? describes why rivets are preferred for joining aluminium alloy components. But how are carbon-fibre-reinforced plastic components in new aircraft joined?

Ideally, fiber composites are bonded and connected by a scarf joint. The scarf ratio is determined by the ratio of fiber tensile strength and the shear strength of the resin. If your fiber takes 3000 N/mm², the resin transmits 20 N/mm² and the fiber content is 60%, the ratio is 1:90, so a 1 mm thick composite layer would need to be joined over a length of 90 mm. In reality, such a ratio is impractical to achieve, so lap joints are used when accepted by the certification authorities. This is the case for for composite gliders, where you will find both scarf and lap joints.

In the early days of powered composite aircraft, fiber composites were seen with the experience of aluminium in mind, and treated with the same methods. Therefore, the Lear Fan and its contemporaries had to use rivet joints throughout the structure. The idea was that by riveting the airframe could be more easily disassembled for inspection and repairs. Riveting carbon fiber composites is quite problematic: You need to use expensive titanium fasteners because aluminium rivets would quickly corrode when in electrical contact to the electrochemically much nobler carbon fibers. Drilling and countersinking holes cuts the very fibers which you try to connect, so you have to double up on wall thickness what is destroyed by the riveting. But the FAA still insisted on rivets - even stringers on panels were riveted, when bonding would had been the most sensible solution.

Aircraft engineers have an expression for composites that are treated like metal: Black Aluminum. The LearFan was pure Black Aluminum. Many of the engineers in this project ended up with Beech when they produced the Starship, so many of the same techniques were transferred as well. At least, the Starship had a fuselage shell which was laid up on a mandrel and then cut just aft of the cockpit section to get the mandrel out. The splicing of the two fuselage sections was then done by a tapered lap joint; if you want, a practical way of making a not-quite scarf joint.

Today we have a new generation of engineers who slowly accept that the nature of composite structures requires their own methods of treatment. But you will still find riveted joints even in modern composites structures. Old habits are hard to break.

A good reason for riveting is to avoid peeling at the edges of a bonded joint. Engineers with no experience rivet their composites, once they gain some experience they switch to bonding and with lots of experience they add rivets again.


Could reduced-lift wingtips allow an airplane to generate less wake turbulence? Would it be possible to weaken the wake vortices generated by a large aircraft (which can be dangerous to smaller aircraft behind the large aircraft, and are the limiting factor determining how closely aircraft can be safely spaced in the air) by shaping the tips of its wings so that the lift generated (and, thus, the amount of air deflected downwards) by the outermost portion of the wing drops off gradually to zero, instead of abruptly transitioning at the wingtip from “lots of lift, lots of downward-deflected air” to “no lift, no downward deflection of air”?

Diagram of what I’ve got in mind:

This would come with a slight efficiency penalty (equivalent to slightly decreasing the length of the wing), but could still be useful in some situations despite this (such as high-frequency operations by a mix of heavy and less-heavy aircraft in heavily-congested airspace, or large numbers of takeoffs and landings by both heavy and light aircraft on closely-spaced parallel runways), and the reduction in lift generated by the wingtip would offset some of this penalty by reducing the upwards bending force on the outer portions of the wing (and thereby reducing the amount of material needed for stiffening this part of the wing).

Lift already does taper off gradually towards the tips, even on rectangular wings without any washout. That effect becomes stronger with tapered wings, of course. The reason is the pressure equalization resulting from flow around the wingtips, like you show in the lower picture. And like in that picture, the wake is spread over span in reality. Your upper picture is unrealistic and a gross oversimplification.

However, the eventual strength of the wing wake will be little affected by this. The resulting vortices are caused by wake rollup and do not come directly from the tips. The tip vortices are only a small part of the overall wake.

Regarding efficiency: Tapering lift towards the tips will make the wing more efficient. Lift far away from the wing root causes high root bending moments and requires a heavier structure. Lift near the root costs less structural weight and the net lift of the wing (lift minus wing weight) will be higher with a near-triangular lift distribution. This insight was published as early as 1933 by Ludwig Prandtl and rediscovered by R. T. Jones in 1950.


Who has the responsibility to make altimeter corrections in cold temperatures? I work as air traffic controller in Asia and we refer to both ICAO and FAA regulations. As winter is coming, there is a debate on altitude correction (or altimeter correction?) for cold temperatures. Some insist that we (ATC) don't have the responsibility to make altitude correction, and the others insist that we have, when ATC performs radar vectoring. (We know that the pilots have responsibility when IAP.)

In related to this, ICAO DOC 8168 states (Vol 1, Chap 4 Altimeter correction):

  The pilot is responsible for these corrections, except when under radar vectoring. In that case, the radar controller issues clearances such that the prescribed obstacle clearance will exist at all times, taking the cold temperature correction into account.

So, I've tried to find references about this but failed.

Here're my questions.

1) Is there a document or manual for ATC about how to make altitude corrections when radar vectoring?

2) Why is there no altitude correction for hot temperatures that make for a steep angle of descent?

3) Should ATC-issued altitudes take into account temperature-induced altimeter error, or does should ATC issue the true altitude and leave the responsibility on the pilot for making the correction?

I don't have enough points to make a comment so I'll just leave this one...
http://code7700.com/altimeter_temperature_correction.htm

All throughout, it's
Pilot In Command...
Pilot In Command...
Pilot In Command...
Pilot In Command...

  4.1.4 Air traffic control (ATC). If an aircraft is cleared by ATC to an altitude which the pilot-in-command finds unacceptable due to low temperature, then the pilot-in-command should request a higher altitude. If such a request is not received, ATC will consider that the clearance has been accepted and will be complied with. See Annex 2 and the PANS-ATM (Doc 4444), Chapter 6.


Where can I find records of old FAA registrations? I know where to find details for FAA N-Number registrations. But where can I find records and details on older FAA NC, NR, NL, and NX numbers?

NC, NR, NL or NX are not necessarily older aircraft. Any aircraft more than 30 years old can use NC instead of just N.

So, to find the a/c registration you just take out the C.

I own a glider that was built in 1965 so my numbers are NC and 5 digits.

It should be the same for R, L, and X, which are any aircraft that has a restricted, limited or experimental airworthiness certificate can use those letters after the N. See FAR Part 45.22.


How to get data from Aeronautical Fixed Telecommunication Network? I would like to download some NOTAMs and I know they can be obtained from the AFTN (Aeronautical Fixed Telecommunication Network)
.

Do you know a way to access such network and request obtain the data from it?

So the AFTN is essentially one of the first e-mail systems, before email was even a thing. If you want to pass a flight plan, you'd select the AFTN addresses for the owners/ managers of every FIR along the route, as well as all the different offices at your destination airfield that would need to know you're coming. Unfortunately (or fortunately, depending on your perspective) unless you have access to an AFTN terminal and your AFTN address was included in the To: column, you'd have to hack the system to gain access.

And when I say "Hack", it's not necessarily in the traditional sense. The AFTN dates back to the 1950's, and maybe earlier. It is unencrypted and built on good ole' fashioned copper wire! Whilst I'm not a hacker, I believe one needs to gain physical access to the system in order to exploit it.

Nations which are considered "developed" have mostly transitioned to a digital version of the system called Aeronautical Message Handling System (AMHS). Because the AFTN copper wires are still in use in many developing nations, "bridges" are in place to digitize the analog signals allowing for interoperability between the two systems.

So the long of the short, no, you cannot legitimately access any and all AFTN messages whilly nilly.


What is the meaning of T/O Thrust => TRQ / N1 in a flight log? I work at a software company which builds record-keeping software for aviation.

What is the meaning of TRQ / N1 in a flight log, under a T/O Thrust header? I imagine it refers to torque at N1 (but in my limited experience, I have rarely encountered instantaneous torque as a relevant measure in aviation so I'm suspicious).

What is the meaning of TRQ / N1? Is this, like N1, expressed as a percentage?

(Indeed, we have a close relationship with out clients and can ask them, but answers sometimes take time and I prefer to be proactive and know more than the bare minimum.)

Jet engines use N1, EPR, or lately (Airbus A350) Thrust % values for takeoff power.

Turboprop aircraft use torque. So it's either N1 or torque for your software depending on which aircraft is used for the flight.


Is it common for carriers to have separate certification for analog versus glass cockpits? Is it common for carriers to have separate certification for Analog cockpits versus Glass (digital) cockpits?

Pilot type ratings are usually same for both versions (analog and digital cockpits) of the same aircraft as far as regulations are concerned. For transition to glass cockpit, you may have to take a Electronic Flight Instrumentation Course (or differences training course).

In some cases of transition (for example, EASA  ATR 42/72 (glass cockpit, non
ECL) to any other ATR 42/72 'classic'), a full type rating training course is required; however, the type rating is still the same.

For example, see the FAA and EASA type rating lists.


What is the name of centre of mass speed of an aircraft? I have a list of positions (X [NM], Y[NM], Z[NM]) of an aircraft. Every coordinate is given every 1 second.

I calculate the speed [knots] between two consecutive coordinates in the following way:

$S_{i+1}=\frac{\sqrt{(X_{i+1}-X_{i})^2 + (Y_{i+1}-Y_{i})^2 + (Z_{i+1}-Z_{i})^2}}{1s}3600\frac{s}{h}$

It's basically space over time.

Does this 3D speed have a specific name?

It describes what the velocity vector of the aircraft centre of gravity is in relation to the surface of the earth. Ground speed is the 2-D projection of your speed on the ground, climb speed is the vertical component.

Both ground speed and climb speed are very useful parameters as such: ground speed to figure out when the aircraft arrives, climb speed to adjust engine settings etc for reaching cruise altitude with a minimum amount of fuel used. The 3-D vector sum of the two has little practical use, that is probably why it has no separate name as far as I know.

The integrated signal is of more use: what is the position in 3D of the centre of gravity of the aircraft relative to earth? Pretty useful for navigation.


Staying oriented in VFR This is something I have been questioning more and more often on how pilots do it. So, let's say we are flying on a new location and know very little about it. When flying around and keeping the location of the aerodrome we took off to later return back to it, how do we plan to consider which points to reference and which points represent what when flying?

Might be worth to mention VFR is in practice. Let us assume we do not have a GPS.

As an example where I have been flying I got references like a prison and a stadium that indicates a fly path back to the aerodrome, but I got to know those thanks to my instructor and become more aware of them. But when I think about it, at the start I had no idea. And when I consider way ahead once I have the ability to fly alone, I often think of how will I be able to understand which points references what, how can I quickly understand where I am and what is best for me to try and plan ahead to stay located when in flight.

Apologies if it is really obvious it is still something very recent to me and I have this worry recently. Just though it could be something I could start gain awareness, the sooner the better?

Thank you in advance!

Many of the features marked on your sectional chart are there precisely because they're things a VFR pilot should be able to see from the air and use as landmarks for navigation using "pilotage".

If you're preparing for a cross-country trip, you start with a straight line from origin to destination than then adjust it slightly so that it passes over these features as checkpoints every 10-15nm, and you'd put each of those points in your nav log as your flight path.  Then you do the additional calculations (wind, time, etc.) to turn that into something you could, if necessary, follow via "dead reckoning".

Even if you don't have GPS, you may have a VOR receiver (or ADF, if in a really old plane) that could be used as well.  DPEs here require that you be able to use VORs to fix your location on a PPL checkride; I don't know if that's everywhere, but IMHO it's a good idea regardless.

If all else fails, or any time you are in immediate danger, you can always call ATC and ask for help.  But until you've had the training on all the above options and demonstrated reasonable competency with them, your instructor shouldn't be allowing you to get yourself into such situations.


Could Falcon 9 fairing become glidable / flyable? Reading and thinking about this and this questions on space exploration stackexchange, I was wondering if the fairing could shape itself, so that it becomes one stable and steerable gliding element able to land safely, fully replacing the parachute / paragliding wing.

The idea is to hinge both halves longitudinally, and convert (by actuating & hinging) the tapered conic root part into trailing edge control surfaces or V-tail elevons, making the whole system flyable and steerable, eliminating conflicts between wind, paragliding wing and fairing large surfaces.

Is this concept practical in any way, could this thing fly and if not, why?

(let's assume both halves open for separation with payload, close for entry, open again in "glide mode" once subsonic)

Currently the fairing is separated at about 100 km altitude, when the aero-thermal flux drops below 1135 W/m2. So it's not separated outside the atmosphere, the fairing still experiences noticeable drag.

That means the fairing has to be separated from the stage quickly, to prevent it crashing into the payload. With 2 fairing halves this is easy: the two halves can push against each other (using simple pneumatic cylinders or pyrotechnics), and both will move away from the stage in a straight line. By pushing with slightly more force at the top of the fairing, the halves are pushed in a direction where the wind will make sure halves are pushed farther apart.

If you were to hinge the fairing, you can't do that any more. You get two events:

open the fairing. One half hinges open while the other one has to stay in place.
once it's opened far enough, apply thrust to get the fairing away from the payload.

You can't do this under aerodynamic load:

the wind will exert a force on the fairing. One wobble in the wrong direction and the fairing will be pushed closed again.
the half-open fairing is not stable. The nose cones will be pushed inward by the wind.

So you'd have to separate the fairing at a much higher altitude, which reduces the payload of your rocket by a significant amount. It also means the fairing is separated at a higher speed and becomes more difficult to recover.

Mechanical actions are always a risk. A hinged fairing adds to that risk: the timing is critical, and the actions have to be carried out under load from acceleration.

JWST deployment and Shuttle robotic arms have fewer time constraints, and the actions are carried out without a load.


What is Flexible Gunnery in the US Air Force? I read many times in English Wikipedia that some servicemen were trained in Flexible Gunnery schools, but I don't get what that exactly means.

Example:

  In January 1942, the 2d Air Force was withdrawn from the Western Defense Command and assigned the operational training of units, crews, and replacements for bombardment, fighter, and reconnaissance operations. It received graduates from Army Air Forces Training Command flight schools; navigator training; flexible gunnery schools and various technical schools, organized them into newly activated combat groups and squadrons, and conducted operational unit training (OTU) and replacement training (RTU) to prepare groups and replacements for deployment overseas to combat theaters.

flexible gunnery - the firing of swivel guns (as in an airplane)
fixed gunnery - the firing of a gun having no traverse so that the entire gun platform or aircraft must be maneuvered for aiming

(flickr.com) Swivel guns on a B-17 (underside and waist).

From Wikipedia: "Flexible Gunnery" training developed diverse skills for various aircraft and differing positions within bombers, e.g., waist gunner, rear gunner, etc.

From a 13-minute declassified US Army Air Forces training film, Flexible Aerial Gunnery: Making a Gunner, from 1943 about that gunnery course, the course included but was not limited to:

learning the machine gun types inside out
learning bullets trajectory and aiming
train on moving objects using a BB gun
train in the air by shooting at a trailing dummy attached to another aircraft
learn the different shapes (silhouettes) of enemy aircraft and learn to judge their distance through the sight to judge whether to fire
learn the different positions, including the ball turret and how it functions
train in a ball turret simulator
train at night by utilizing tracer ammo
the course took a few weeks to complete.


Air Traffic Control System management I'm having a class about Database management system, and the professor gave us a project regarding Air traffic control system. The exact assignment is to "Design and create a system which can manage informations of Air Traffic Control System, summarize entities and how system works".

I'm not asking you to do this for me, what I would like to know is

what should i know about air traffic control systems?
how does it work?
what are the entities involved in it?
what is an air traffic control system?

Air traffic control system is the computer system that air traffic controllers use to keep track of the aircraft they are controlling.

The system processes data from the primary and especially a secondary radar and displays them in suitable fashion for easy understanding by the controllers. The radar processing itself is not interesting for database class. But there is a bunch of information about each aircraft that needs to be remembered and associated with it's radar image:

The assigned transponder 4 octal digit code (usually called "squawk"). This is a code the secondary radar receives from the aircraft used to associate the data to the correct radar return.
Identification, also used as callsign. It is registration number or flight number (sometimes internal company flight number that is different from what they show in time tables)
Aircraft type

The aircraft type is needed so the controller knows the performance of the aircraft, so it needs associated performance data like maximum speed, approach speed, maximum altitude etc.

Flight plan. This needs to contain:

Start and destination airports
Preferred cruise altitude and speed
List of waypoints

You may consider current clearance limit (altitude and waypoint); I am not sure whether the current systems include it or not.


Is there a minimum separation between a landing aircraft and another crossing its runway? I have just seen this video of what has been called a runway incursion at LEBL (my hometown airport). A russian jet initiates a go-around after seeing an argentinian plane crossing runway 02:

https://www.youtube.com/watch?v=1N5THRSp4hM

It's not clear (as of 2014-07-07 1400L) whether ATC gave clearance to cross the runway. Anyway, my understanding is that even with ATC clearance you are required to check for incoming traffic and hold short of the runway if such traffic exists.

Seems like the taxiing crew either didn't look for incoming aircraft or they estimated they had enough separation to cross the runway.

So, is there any regulated separation distance (time/space) that can be used to tell who was responsible for this conflict? It's solely based on pilots' criteria?

When an aircraft has been given a clearance to land on a runway, that runway is exclusively reserved for the landing aircraft. (Except for LAHSO and "land after" operations, where only part of the runway is reserved for the landing aircraft).

That means that no other aircraft or vehicle should be on that runway. In this case, clearly something went unplanned. Either the crossing aircraft was not given permission to cross, the landing aircraft no clearance to land, or ATC mistakenly cleared both the landing aircraft and the crossing aircraft to access the runway.

Pilots should always check if the runway they are accessing is safe, and in this case the crew of the landing aircraft did apparently observe the incursion and aborted their landing. The crew of the crossing aircraft noticed the landing aircraft a bit late, but you hear their engines spool up as well as they cross. The sound of the go-around thrust arrives second later due to the difference in distance.

The crossing aircraft seems to be taxiing toward the rising sun so they may have been blinded and missed the fact that they were crossing a runway.


Variable versus fixed costs in the airline industry I want to list the costs airlines have to sustain by distinguishing them between variable and fixed. Variable costs change in proportion to aircraft usage. Fixed costs show little or no change in proportion to changes in activity.
This is an incomplete list I took from the FAA website (here)
Variable costs:

Fuel and oil.
Maintenance (e.g., maintenance labor, parts airframe/engine/avionics, engine restoration, thrust reverser overhaul, propeller Overhaul).
In-ground and in-flight crew salaries (can also be thought as fixed costs).

Fixed costs:

Parking and hangar fees.
Insurance.
Aircraft modernisation.
Computerised maintenance management program.
Weather service.

Question:
(1) In which category should I put

Landing fees (ATC, runways, taxiways, parking at stand or apron for a certain time (e.g. 2 hours), use of gates / fingers / terminal for disembarking).

Lounges fees.

Scheduling coordination.

Surcharges or rebates in addition of landing fees (for noise, peak-hour operations)

Passenger charges

Administrative cost (managing/issuing tickets, etc.)

Overflight fees

(2) I'm fundamentally confused about the distinction between fixed and variable costs. For instance, landing fees increase with the number of flights and, hence, with the demand of tickets for a given route. Should they be classified as variable costs for this reason? Is this the same reason why fuel and oil, maintenance, and crew salaries are classified as variable costs?

I’ll address your second question first.

I'm fundamentally confused about the distinction between fixed and variable costs.

Simply put, variable costs are ones that go away if you cancel a flight (or, more likely, a pair of out-and-back flights) while fixed costs are ones you still have to pay.
A challenge is that many “fixed” costs are actually step-variable costs. For instance, if you cancel enough flights, you might be able to reduce how many aircraft or gates you need. But with the black and white dichotomy given, we classify those as fixed.

Landing fees (ATC, runways, taxiways, parking at stand or apron for a certain time (e.g. 2 hours), use of gates / fingers / terminal for disembarking).
Surcharges or rebates in addition of landing fees (for noise, peak-hour operations)
Passenger charges
Overflight fees

If you don’t land, there is no landing fee, so that’s variable. Ditto for gate fees, noise fees, peak-hour fees, passenger fees and overflight fees.
Space to park an unused plane isn’t usually an issue when it’s just one or two flights canceled; that will be included in some other fixed cost.

Lounges fees.
Scheduling coordination.
Administrative cost (managing/issuing tickets, etc.)

These are fixed (or step-variable), since canceling one or two flights won’t meaningfully change them.


Why there is a 'MACH' in this Compressibility Correction Chart? I couldn't find what 'Mach 1.0' and 'Mach 0.8' are trying to indicate in the middle of the chart.

Can anybody explain about this please?

As I read it, the upper arch pointed to by Mach 1.0 represents the correction necessary at the different pressure altitudes when flying at Mach 1.0, while the lower arch pointed to by Mach 0.8 represent the correction necessary at those pressure altitudes when flying at Mach 0.8.

i.e. the correction necessary at 30,000 feet at Mach 1.0 is roughly -30, while the correction at that same altitude but Mach 0.8 is only roughly -15.


How fast can pushback tugs actually go? (maximum possible speed) For school, I'm doing a project where we choose a topic about anything, ask questions, and learn about it. I chose my topic as fuel efficiency of airplanes, and one of the things I want to research as part of that topic is fuel efficiency of planes on the ground and see if we can cut down fuel burn at airports. While I was exploring that sub-topic, I thought about tugs and if they are capable of going faster than 30 kts. If they are, we can use them more than just for pushback and potentially cut down on aircraft fuel use.

This AC covers a lot of the regulations around towing aircraft and according to the regulations

  Towing Speed. Towing speed should not exceed that of walking team
  members. Towing speed should not exceed the safe operating speed for
  the conditions or the published speeds established by the TLTV
  operators published procedures.

In other words you can do either as fast as your operator says you can or as fast as the tug manufacturer says you "safely" can. The AC goes on to discuss a lot of other things but also mentions this tug in their section on tow-bar-less tugs. According to their website:

  Unique hydrostatic drive for moving aircraft on the ground at up to 32
  km/h [~20 MPH] – without compromising safety

This is about the same speed that Terry discusses is the maximum taxi speed in this answer so you don't really gain any speed. Depending on the aircraft and airport in question you don't want to cut down taxi time to much as that may be an important time during which the engines come up to temp.


What if a flight, transporting a recorder from an aviation accident, crashes? Are there any correctives or countermeasures against the rare irony, that objects essential to a flight accident (eg recovered flight data recorder and cockpit voice recorders) are damaged or destroyed on a subsequent flight carrying them? The worst case is if this freight flight crashes.

Context: As in many other Air Crash Investigation episodes, Season 14 Episode 4 (available on Youtube) concerns Copa Airlines Flight 201. Due to a lack of facilities in Panama or Colombia, the recovered FDR and CVR and other parts (including the cockpit instruments) had to be transported to the NTSB's labs in Washington, DC, USA. I presume that for want of expediency, they were freighted by air?

If the Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) need to be transported by airfreight, to expedite extraction of the recorded data and analysis of the accident, the probability of the aircraft used to ferry the devices crashing is rather low, as aircraft accidents do not happen as frequently compared to the total of movements per day/week/month/year.

Nevertheless, in the event of the aircraft used to ferry the devices crashing, the FDR and CVR are built to survive crashes and impact, so the probability of the first pair of FDR and CVR being still usable for data extraction after a second crash is quite high.

Since the FDR and CVR record not only data but also timestamps along with the data, the distinction between the FDR/CVR from the first crash and the FDR/CVR from the second crash is not a problem. Upon data extraction, the investigating party would recognize which flight parameters belong to which flight. Additionally, if the FDR and CVR on both flights were identical models, the serial number of each device would help identification.


Does ATC handle non-regular widebody flights differently? Six weeks ago, roughly, a Corsair charter flight landed at Lamezia Terme International Airport (SUF), in Southern Italy. It was a Boeing 747-422, registration F-HSEA. It carried 500 tourists from Liege Airport (LGG), Belgium.

My question: when a flight like this is headed to an airport which is not an usual landing spot for wide-bodies, how does the ATC figure out a wide-body is coming? Do they figure this out by just communicating with the pilots when airborne or do they receive an official note beforehand?

No, ATC does not handle these flights differently from regularly scheduled ops
ATC isn't concerned with why an airplane wants to go to an airport or whether they regularly operate there or even if there are ground services available for them at the destination.
Whether the flight is regularly scheduled or not may fall under different regulations but ATC services do not vary.  The charter flight will be operated under instrument flight rules (IFR) and will have a flight plan filed with ATC prior to departure.  The controllers at the departure airport will receive information about the flight prior to that planes departure and will service the flight to its filed destination.  This works exactly the same way as normal scheduled service by that same (or any other) airline.


Does a full set of legible structural engineering drawings for the Hughes H-4 Hercules still exist? I am not looking for unreadable images or pictures of images, but a fully legible copy or print.

I would contact the Evergreen Air and Space Museum in McMinville, OR.  They currently have the actual H-4 prototype and their curators may be able to help.


How much hydraulic fluid is in a jet airliner? Hopefully the title is self-explanatory. I am wondering how much hydraulic fluid - in mass and volume - is carried in normal operations for a jet (the bigger the aircraft in your answer the better).

FCOM for the A320 describes 3 independent hydraulic systems, with accumulation reservoirs for each at 6.5L,12.5L & 14.5L (1.7USG,3.3USG& 3.8USG) respectively, so +33.5 liters is a good bet, which translate to 26-33 kgs depending on fluid type.

Note that more fluid will be available in the system, but how much exactly you will need a mechanic to answer.


Do Jabiru aircraft have a long history of engine failures or other technical issues? I heard that a friend of mine experienced an engine failure in a Jabiru 2200. Does this happen very often and are there other common failures in the Jabiru family of aircraft?

I don't know about a "long history", but the Australian aviation authorities (Jabiru is an Australian company) did introduce operating restrictions because of what they considered to be a high rate of engine failures. Note that Jabiru makes their own engines, unlike most other aircraft manufacturers, and as well as using them in their own aircraft they sell them for use in LSAs.

CASA mentioned 45 incidents in one year:

  These precautionary limitations follow a high number of Jabiru engine
  failures and power loss incidents, some of which resulted in aircraft
  forced landings.

  More than 45 Jabiru engine failures or in-flight engine incidents have
  been reported in 2014, with CASA recently becoming aware of incidents
  in previous years.

  Problems with Jabiru engines include failures of through bolts,
  flywheel bolts and valve train assemblies, as well as cylinder
  cracking.

  The failures affect a range of Jabiru engine models and have occurred
  in aircraft used in different flying activities, although many have
  been reported in aircraft used for flying training.

By itself, the number 45 doesn't mean much without considering more information about the number of aircraft, the number of hours flown, maintenance performed etc. and Wikipedia says that Jabiru didn't agree with CASA's decision (which isn't surprising). But presumably CASA did think about those things and still decided that there should be restrictions in place.


Does the F-4 Phantom use (have) differential horizontal tail deflection? Is differential horizontal tail deflection used to roll the aircraft around the longitudinal axis along with the ailerons / spoilers and a bit of rudder?

No, the two sides of the Stabilator are connected to one another and move in unison.
The following is from the USAF F-4E flight manual, page 1-21.


What are various specifications of Engine oil used in Piston and Turbine engine aircraft? I only know of two types MIL-O-7808 and -23699. Is there anything else ?

Here is a general answer for a general question.

Function of oil is three-fold for both piston and turbine engines:

Lubrication - reduction of friction;
Cooling - carrying away of heat; and
Cleaning - carrying away of contamination.

Oils used in jet engines must be able to withstand temperatures that are much hotter than piston engines.

Here is a link to some of the lubricating oils used in navy jet aircraft and the various specifications.

Jet Aircraft Engine Lubrication Systems

Piston aircraft engines tend to be air-cooled and are therefore manufactured with larger tolerances. This results in an engine that uses up oil (burns it). Most POH of piston aircraft that I've seen call for ashless dispersant oil, which refers to an oil that has non-metallic additives and has the ability to suspend combustion particles.

Here is an article that describes piston aviation oils.


How do pilots detect fuel contamination in flight? According to the Aviation Herald, an Alitalia Airbus A330-200 diverted en route "reporting fuel contamination".  How can the pilots detect fuel contamination in flight?

If fuel contamination is suspected (because of engine control system fault indications, slow engine responses or rapid engine pressure ratio (EPR) fluctuations), there is an associated checklist procedure to followed which can confirm the contamination:

Fuel contamination checklist as posted by "330 skipper" at Nov 24th 2017 13:47Z on Avherald:

  If ENG 1(2) CTL SYS FAULT alert triggered associated with AVOID RAPID THR CHANGES or ENG 1(2) SLOW RESPONSE, and with rapid and
  continuous EPR fluctuation indications on both engines:
  A/THR.........................................................................................................OFF
  If EPR fluctuations stop on both engines: ECAM PROC..........................................................................................APPLY
  A/THR.........................................................................................KEEP
  OFF
  If EPR fluctuations continue on both engines: FUEL CONTAMINATION CONFIRMED Apply condition: If fuel contamination confirmed
  If ENG 1 CTL SYS FAULT and ENG 2 CTL SYS FAULT alerts triggered with AVOID RAPID THR CHANGES or ENG 1(2) SLOW RESPONSE:
  A/THR.....................................................................................................OFF
  FUEL CONTAMINATION CONFIRMED Apply condition: If fuel contamination
  confirmed
  If fuel contamination confirmed: LAND ASAP

In addition, the Flight Crew Operating Manual (FCOM) has the following procedure to be followed if fuel contamination is confirmed:

Special thanks to @mins for providing the images of the procedure and the FCOM