Do aircraft technicians need additional certifications to work in other countries? Professional technicians, who work in aircraft maintenance, usually obtain some sort of national certification, right?

Let's suppose someone got training and certification in one country, and wants to migrate to another country. Does he require some certification to work there as an aircraft technician? How is it achieved?

I don't have personal experience, but this is absolutely something you can do.

Unfortunately many countries do not have the exact same standards or licensing scheme, so often your licence is not automatically converted, but you rarely need to start from scratch.

For example, if you wanted to come to Australia, you would need to attend a CASA approved Part 147 training organisation, which are located around the world. They will assess you, possibly provide you with some extra training, following which you can apply for an Australian Part 66 engineer licence. Once you get that licence you shouldn't have too much difficulty migrating, but that's a discussion outside of my league. More details on this conversion process are on the CASA website.


Statistics - Does the majority of new pilot training occur at controlled or uncontrolled airports? Is there any data available on where pilots undertake their training?

I'm interested to know whether most (USA) pilots complete their training at a controlled airport, or at a uncontrolled field.

I'm interested in this because it would likely give an indication of the relative level of comfort of new pilots operating in both controlled and uncontrolled airport environments.

I assume that it's likely that a Designated Pilot Examiner would be more likely to operate out of a controlled field just due to traffic volume, so the location of issuance of a pilot's certificate isn't necessarily a good proxy for where training hours are undertaken.

No one really tracks these stats and they would be tough to track on any note. The latter half of my training was out of an uncontrolled field but lots of touch and gos occurred at controlled fields so I had lots of experience talking to the tower even though I was not flying out of a towered field.

  I'm interested in this because it would likely give an indication of
  the relative level of comfort of new pilots operating in both
  controlled and uncontrolled airport environments.

As a pilot you are responsible (as per the ACS) for understanding the regulations and procedures for both situations and in todays day and age it would be foolish for an instructor to not at least present both situations in your training. That being said, you can technically get your PPL in an airplane that does not even have a radio but you are still responsible for understanding the regulations and may be asked to explain them on your check ride.

  I assume that it's likely that a Designated Pilot Examiner would be
  more likely to operate out of a controlled field just due to traffic

The DPE that I went to was at an uncontrolled field (as are the other 2 in my area). Im not sure this is an accurate generalization.

Keep in mind the DPE will go over your logbook and may look at the airports you landed at. If you dont have sufficient towered experience they may ask extra questions about that but you may not be required to demonstrate it on your check ride.


How is the length of a leg calculated? Here are few facts:

A flight is basically climbing, staying high, then descending toward a runway

Changes in altitude increase the distance an aircraft flies. Given the climb/descent angle, this increase may be insignificant, but it still exists.

The path followed by an airliner may not be direct

Given many elements (TSA, other traffic,...) I imagine an airliner can almost never take a direct route. Not to mention the path leading to the approach.

An airport may have several runways whose length may not be the same

The departure point may be the parking position, the beginning of the runway, the end of the runway, the point where the aircraft reaches $V_2$,...
The same goes for the arriving point.

The precision of the maximum range of an aircraft is really precise

When looking at ailiners' performances, one key figure seems quite strange: the range. It seems quite precise (few miles). Lets take the ERJ-140ER as example. Its maximum range is 1250nm. Given this number, I imagine the precision is less than 10nm (3 significant digit), i.e. about 3 to 4 times an international airport's runway length (4km for dubai international airport).

Given all those elements, how is a leg length (distance of 1 flight between 2 airports) calculated for an airliner?

Many of the 'variables' you mention, are in fact fixed, and in large determined by dispatch (the smart folks at the company). For commercial flight, the flight plan will be filed in advance (generally by the company dispatch), and will contain all the waypoints en route, including expected flight levels. Dispatch makes the calculation for the most efficient flight in close collaboration with ATC authorities, for example by reserving slots on certain airways.

Deviations from the flight plan are not common - you won't hear ATC tell an airplane mid-flight to suddenly take the long way round - instead, any route alterations are communicated to the pilots when they are still on the ground, and if necessary, extra fuel is taken on board.

This flight plan is then given to the pilots, and programmed into the FMC. The FMC is a very sophisticated piece of software, and can in fact calculate the required fuel for this leg all by itself - you can even program it to calculate the best trade-off between efficiency and speed (see this KLM video at 1:40). I'm not entirely sure about the details, but you can probably program the SID and STAR of the departure and destination airports respectively as well.

On top of this, extra fuel is taken on board for things like taxi, expected holding patterns (your dispatcher will know how busy you can expect it to be at your destination airport; e.g., Heathrow is generally very busy and you might want to take some extra fuel on board), and enough fuel to at least be able to perform a few go-arounds or a diversion if circumstances call for it. In the end, the pilot is responsible for taking enough fuel on board, but will rely on the FMC and dispatch to make an educated guess.


Why is the gear handle shaped the way it is? In the aircraft cockpits I've seen, the gear handles all seem to have the same general shape (they look like a little wheel). Is there a reason for this beyond simply making it absolutely obvious that it's the gear handle?

It's required by law, at least in the US. 14 CFR 23.781, Cockpit control knob shape specifies these shapes for the flap and gear controls on smaller aircraft:

For larger (transport category) aircraft, 25.781 specifies the same thing:

As for why those shapes are specified, it's for at least two reasons:

The shape resembles the thing it controls, so it's an obvious memory aid
The controls are all shaped differently, therefore you can distinguish them by touch alone, without needing to look at them

As others have noted, there have been accidents in the past caused by pilots using the wrong controls, and this is one reason why the FAA decided to do something to standardize them. Parts 23 and 25 also state where the controls should be placed, for the same reason.

The FAA's Airplane Handbook says:

  There have been many cases of the pilot mistakenly grasping the wrong
  handle and retracting the landing gear, instead of the flaps, due to
  improper division of attention while the airplane was moving.

They recommend - and I was taught - leaving the flaps alone after landing until clear of the runway (unless you have a good reason for retracting them earlier, like a short-field landing), then check and retract them with the statement "flaps identified and retracted". "Identified" in this case simply means that you're sure you have the right control in your hand. Some instructors even avoid touch-and-goes in complex aircraft (i.e. with retractable gear) because they feel the risk of retracting the gear rather than the flaps during the maneuver is too high; they stop and go instead, even if that means taxiing back for takeoff.


How are range violations during a launch countdown handled? I was watching the ULA Atlas V IBIRS countdown tonight but the launch was scrubbed (after some technical issues) ultimately because of a range violation: an airplane was in the restricted area.

I've seen this happen because of boats before, but I know it also sometimes happens because of wayward planes. Specifically: Is this just a standard airspace violation? Or is it treated differently since this particular launch was military-related? Whose job is it to keep the airspace clear, how do pilots know to stay clear of the area, and what happens to the pilot(s), if anything?

(Here's a more detailed tweet thread that has some interesting discussion.)

As far as the FAA is concerned, it's just an airspace violation.  There is a restricted area over the center/base that extends up to 5000 feet.  This is active continuously.  There are other restricted areas that extend up to 'unlimited' that are "Intermittent by NOTAM normally 24 HRS in advance."

So high altitude traffic is not impacted by the continuous restriction and when there is a launch the restriction is published by NOTAM in advance.  This gives ATC the ability to route traffic around the area without any significant impact.  Since the safety area extends out into international airspace, the FAA can't control it as restricted airspace.  They have been defined as FAR 91.143 airspace, which states:

  §91.143   Flight limitation in the proximity of space flight
  operations. When a Notice to Airmen (NOTAM) is issued in accordance
  with this section, no person may operate any aircraft of U.S.
  registry, or pilot any aircraft under the authority of an airman
  certificate issued by the Federal Aviation Administration, within
  areas designated in a NOTAM for space flight operation except when
  authorized by ATC.

So violation of the NOTAMed airspace is a violation of 91.143.

In my experience (5 years working launch ops) the issue usually arises with GA aircraft that want to watch.  If someone enters the area, ATC will try to contact them by radio.  There are also helicopters and or plane that can intercept and escort the aircraft clear.  Space Shuttle launches had the largest contingent of aircraft.  Some small booster ops might have one helo or a King Air to deal with intruders.

The aircraft can also be used to get the attention of boats in the area.

Whether you scrub a launch or not depend on the launch window. I've seen them range from a few minutes to several hours.  A violator at the wrong time will cause a scrub with a short window, while you can handle the delay with a larger window.


How to calculate the fuselage geometrical parameters? How I can calculate the fuselage midsection having a constraint length? Also, if I want a cross section shaped like an Antonov that on top of it have a lower ratio than the bottom, as that is part or can do the calculations to determine the area in front.

There is no straight answer or a formula for this one. In real life you first think of what you want to fit inside the fuselage and then design the rest of the plane. For airliners that would be space for passengers and luggage as well. Different fuselage shapes come straight in line from the requirements that the airplane is supposed to meet. Antonov has the shape you described, because it needs a lot of space inside and should stay low to the ground, so it's wings are mounted on top. It also has a huge weight, so a strong set of wheels is required - hence the shape at the bottom (to create enough space for the landing gear to hide without taking the loading space)

Apart from functional requirements, designing a fuselage must take many different aspects into consideration (starting from the most important - but of course the hierarchy depends on many factors):

mass
drag - the frontal area is not all, it is also the nose shape, wing connection and overal area wchich results in friction loses
stress caused by wing's lift and drag, momentums of wing and stabilizers and pressure difference
fatigue safety
doors, windows, landing gear


What airplane is this? and why the strange inlets? Why does it have such strange intakes?

That's a Polish Air Force MiG-29 "Fulcrum".  The strange intakes are to decrease the risk of foreign object damage during rough-field operations.

Edit to clarify: Normally, when the MiG-29 is in flight, the large ramp intakes below the wings are open, providing all the air for the engines, and the louvered intakes on top of the wings are closed.  However, if the aircraft is going to be operating from rough fields or flying at very low altitude, the pilot can close the main air intakes.  When the main intakes are closed, the louvered auxiliary intakes automatically pop open, so that the air going into the MiG-29's engines comes from above the aircraft, rather than below it; this greatly decreases the risk of the engine eating loose objects on the runway (that, and the fact that the opening a foreign object would have to pass through to enter the engine via an auxiliary intake is much smaller than the opening for the main intakes).  As the auxiliary intakes are smaller and at an angle to the airstream, the engines can't get as much air (and, consequently, can't produce as much thrust) when using the louvers as they can when using the main ramps; Mikoyan apparently decided that, for rough-field operations, decreased performance was an acceptable price to pay for a decreased rate of engine object ingestion.


Can I save money on becoming a helicopter pilot in the US if I do flight hours in Mexico? Flight hours costs approximately $285 per hour. Below is a screenshot from a local (Newport Beach, CA) school regarding what it takes to become a private pilot.

So I was hoping that maybe there might be a school in a local country like Mexico where I could do that for less money. If so, are there any things that I need to take into consideration. Or how do I make sure that those hours will be applicable to my license to be able to fly in the US?

As far as I can tell from the FARs as long as your training is performed by an FAA-certificated flight instructor and complies with the appropriate requirements of part 61 of the FARs you could theoretically do parts of your (primary/private) training anywhere you want, get all your endorsements, then come back to the USA to take your checkride and get a regular US (FAA) pilot's license for the appropriate category/class of aircraft.

From a practical standpoint I think this may be more work than the money you save.
If you do your pre-solo training in Mexico any instructor you come to in the US is going to want to fly with you a bit before they endorse you to solo.
If you try to do the whole thing in Mexico you would have to comply with Mexico's flight training requirements (Medical, student pilot certification, solo endorsements, etc. - about which I know basically nothing) as well the US FAA's requirements (like holding a US student pilot certificate with appropriate endorsements prior to taking your checkride).

Note that the procedure is a little different if you want to get a Mexican pilot's certificate and then convert it to a US/FAA certificate (that's all detailed in FAR 61.75 if you're interested. It doesn't sound like that's what you want to do, but at least as far as the regulations go that seems to be a more well-traveled path and something your local FSDO could probably advise you on - at the very least it would involve paperwork, possibly also a checkride).

I'd like to say a couple of words on Primacy since we're talking about training: Where you learn and the procedures you learn first will form the foundation of your aviation knowledge.
What that ultimately means for you depends on how different the regulations are where you do your training versus where you will do most of your flying. The FAA has been moving to standardize our procedures to be more in line with ICAO standards for a number of years now, but there are still differences and you may have to re-learn some of the regulatory bits of aviation if you did the bulk of your training elsewhere.

It makes sense to me to learn to fly where you intend to fly -- ideally in the same region (a sleepy corner of the midwest versus lower New York's airspace can be a culture shock!) but if cost is a factor find the best bang for your training buck in the airspace system you'll be spending most of your time in.


Are there US guidelines on how aviation is handled during an emergency situation? Suppose that we find that a meteor is headed for, say, Dallas, TX, and it's too late to prevent the impact. The USA has 3 days to evacuate the area before the impact. The impact is one of the size of Tunguska: it will inflict massive damage in an area about the size of London, and we will notice the impact, but it will be mostly localized damage, so there's no global climate change or widespread damage.

Naturally, if you need to evacuate 1.26 million people in 3 days, you want to speed up the evacuation as much as possible, so you want to use all the possible methods of evacuation, be it through air, on water or on the ground, as efficient as possible.

Is there an American Federal authority like FEMA, the TSA or the FAA that has guidelines on how to handle the aviation part of such an emergency evacuation? The example of a meteorite is just that, an example. The meteor itself is not that relevant, what is relevant is how they'd handle the aviation part of the evacuation.

To clarify: I'm specifically talking about the aviation related parts, so anything related to the airspace over the area, how it would affect regional passenger traffic, to what extent local airports and pilots would be involved,... I realize there are other related actions, like evacuations through the highway and route system and through waterways and canals. Those are not what I'm interested in, insofar as they're not related to air traffic and aviation.

Given the scenario described, this is highly speculative but I'll have a go anyway.

I assume that FEMA would be responsible for the overall evacuation and indeed their transportation annex says that the FAA's main responsibility in an emergency is limited to airspace management:

  DOT/Federal Aviation Administration (FAA) is responsible for the
  operation and regulation of the  U.S. National Airspace System,
  including during emergencies.

The same document appears to rule out military control of US airspace (my emphasis):

  Under certain conditions, DOT/FAA may delegate  use of specified
  airspace for national defense, homeland security, law enforcement, and
  response (e.g., search and rescue) missions, but retains control of
  the airspace at all times.  DOT/FAA may also implement air traffic and
  airspace management measures such as  temporary flight restrictions in
  conjunction with these missions.

In practice, the main thing the FAA would do is to set up one or more (possibly very large) Temporary Flight Restrictions to ensure that only emergency and evacuation aircraft could use the airspace around the affected area (see 14 CFR 91.137). In the catastrophic scenario you described, it might be serious enough for the FAA to close the entire national airspace system to non-emergency traffic - as they did on 9/11 - because the refugees would presumably have to be taken all over the US and the evacuation would be a genuinely national crisis.

Apart from that, the FAA could provide extra ATC services by calling in controllers from vacation and/or making them work overtime; they would probably also have to implement some quick procedures to manage the increased air traffic in the area. They could waive or suspend rules on crew working hours, required aircraft maintenance or anything else that would reduce the amount of time that evacuation aircraft could spend in the air. Of course all these things would increase the risks involved in operating the aircraft, but in the face of an unavoidable disaster that would presumably be acceptable. Anyway, I guess no one would prosecute a pilot for flying overtime to save lives in such an extreme situation.

Mobilizing GA aircraft for the evacuation is another possibility (an aviation equivalent of the Dunkirk evacuation) and the FAA could help there by setting up temporary ATC procedures, creating ad hoc control towers at smaller airports and so on.

The FEMA document linked above implies at least some planning has been done with the FAA on disaster response:

  DOT/FAA Response Cells: FAA activates specialized response cells to
  manage and  coordinate air navigation services and other
  aviation-related efforts.

But what FEMA and the FAA would really do in a specific situation is very speculative and has much more to do with disaster response than aviation: the aircraft are just there to move people and things around, and the real challenge is deciding how to use them.


What does X on a private runway mean? Does an X at the ends of a private runway mean it's inoperable or does it mean its restricted to the public?

One of the reasons why a private runway owner would "X" it would be to indicate that the runway is not in good condition or closed. This can be for a genuine concern or to avoid liability concerns.


Why was the Bristol Brabazon scrapped? According to Wikipedia, 6 million pounds were spent developing the Bristol Brabazon, and the only prototype was scrapped for 10,000 pounds, that is a 0.17% loss recoup. There was a lot more value in keeping that plane intact than scrapping it, maybe for future projects, or special assignments, or further testing, like an An-225. It held more value as a museum piece, or a "sculpture" in Bristol, than the value from the scrap metal.

Was there a reason for being scrapped, other than the 10k in scrapped metal?

You're right, as an exhibition piece it would had been quite an attraction. But it was not up to the Bristol company to decide her fate.

During and after the war, most British aviation development was managed by the government. The Brabazon was the result of a committee which set the goal to develop a transatlantic airliner with 1943 technology, not by a company and its technological visionaries. If you had asked people like Willy Messerschmitt in 1943 how the future airliner would look like, he would had basically described a Boeing 707: Swept wings, turbojet engines, pressurized cabin for about 100 passengers. But Government bureaucrats put the goal for the Brabazon quite differently, and the result was technically obsolete by the time it took to the air. Even before the Brabazon flew first on September 4, 1949, the de Havilland Comet had already flown on July 27, 1949 and was on its way to revolutionize air travel. Its development had started later and was directed by engineers, not bureaucrats.

When that became obvious, the bureaucracy felt too embarrassed to keep the Brabazon around. The situation was similar to Beechcraft and the Starship: Burt Rutan's 85% scale prototype was cut into pieces out of spite when it became eventually clear even for Beechcraft's board just what a turkey it was. The same fate befell the Brabazon.

But its legacy for Bristol is still very positive - without the Brabazon, it would certainly not employ as many people in aerospace as it does up to this day.


For aircraft with variable-sweep wings, how unstable is it to have each wing in a different position? Wikipedia presents this photograph of an F-14 Tomcat, with one variable-sweep wing swept forward and the other back:

I was surprised to see that this configuration was possible; much less feasible or safe to fly with. My idle assumption, not being an aviator of any kind, was that this would be extremely unstable and difficult to handle. I would have assumed, given the prior assumption that the aircraft would be unstable, that the wings would have interlocks requiring them to be swept symmetrically, as a safety feature.

Is this photograph of a maneuver that is manageable and safe enough to perform routinely, or would doing this with the wings be an exceptional event or done only for testing? What kind of impact would this have on the aircraft's handling, given a forewarned, experienced pilot?

This was an intentional test run by Grumman in response to US Navy concerns about asymmetric wing sweep.

From The story of F-14A, Aircraft No. 3, BuNo. 157982

  One of these [flight tests] was in response to concerns raised by the US Navy regarding asymmetrical wing sweep. No. 3 is best remembered for photo shown at right. A series of flight tests were conducted from December 19, 1985 to February 28, 1986. Grumman's Chief Test Pilot, Chuck Sewell, conducted several trials with the right wing locked in the forward position of 20 degrees, and positioned the left wing at 35, 50, 60 and 68 degrees of sweep in flight. 60 degrees was determined as the maximum for landing. In the event of an operational in-flight malfunction, Sewell found the aircraft to be acceptable for carrier landings in this configuration.

Evidently it was manageable, and safe enough that carrier landings were permitted with asymmetric sweep.  There's no control available for the pilot of the Tomcat to intentionally asymmetrically-sweep the wings in flight, though.

How the handling qualities change I haven't seen reported anywhere.  I agree with Robert DiGiovanni that you'd expect additional drag on the side with the extended wing, but the Tomcat has additional options on how to move spoilers and other control surfaces and it isn't clear to me if it can detect and respond to asymmetric sweep or if it's just up to the pilot to do so.


Where can I find data tables for lift and drag coefficients of airliners? I'm teaching an introductory course in fluid dynamics and I'd like to show some "real" data regarding drag and lift forces on an airfoil. It is easy to find data on the geometry of typical airfoils, but I was not so lucky with $C_L = f(airfoil, Re, i)$ and $C_D = f(airfoil, Re, i)$ ($Re$ is the Reynolds number and $i$ the angle of attack). I'm looking for that kind of diagram or data :

Data for commonly known aircraft would be great (B737, B747, A320, A380).

Thanks.

My first thought was: Abbott-Doenhoff. They wrote a book with lots of measurement data, and you can find it here. Of course, this was all long ago, but public data for the airfoils of today's airliners are not published.

A lot of data is also freely available in old NACA and NASA reports, however, you need to know what data you want to search for it efficiently.

If you want to focus on glider airfoils, the Stuttgarter Profilekatalog would be my next source, but unfortunately there are still people who want to make money from it even though the work was financed with public money. This is also quite old, and more modern airfoils from Delft University are similarly restricted.

Another great source is the UIUC airfoil database, but here the focus is on section data and not on polars. But it contains many useful links with airfoil data.

And then there is always XFOIL: Feed it with the coordinates, and you get very good simulations of what a wind tunnel would measure, at least as long as most of the flow is still attached. Lots of plotting functions will help to uncover what is going on in much more detail than any wind tunnel data could ever hope to do.


How realistic is atc-sim.com as an ATC simulator? I was wondering how realistic https://atc-sim.com/ is.  I only play for fun, not for training, but I want to play as accurately as possible.

Not very realistic.

it's text-based; no readbacks.
there are no approach clearances. You can assign speed, altitudes, and headings, but there is no way to instruct an aircraft to execute a specific approach.
there aren't, really, any missed approaches or go arounds
no emergencies

Basically, it' just a game of "keep the aircraft separated", but it doesn't properly simulate how ATC works.


Are all EGPWS-equipped aircraft using the same underlying system? All modern transport-category aircraft and many other aircraft are equipped with enhanced ground proximity warning system (EGPWS). When this EGPWS acronym is used, is it always referring to the same system which has been integrated into the aircraft? Or is it a general term which refers to a system of various manufacturers?

To take it a step further, is there only a single system which allows aircraft to comply with the requirements to have this system integrated?

Yes and no.  When you say EGPWS that is a trademark of Honeywell, so all EGPWS systems are made by Honeywell.  The fine print is the the requirement TSO-C151c is for a Terrain Awareness and Warning System (TAWS).

The TSO functionally describes the Honeywell system. (Honeywell actually designed it before the FAA decided it was a necessary addition to the rules.)  Since implementing the standard would most likely require the use of Honeywell proprietary information (patents), Honeywell is legally required to provide the product it to all customers on a non-discriminatory basis.

As a result, even though Rockwell Collins provides the Integrated Surveillance System (ISS) for the B787, the TAWS component of the ISS is sourced by Collins from Honeywell.

That said, Thales was able to patent a similar system in France about the same time.  There were lawsuits, and in the end they agreed to let each other exist.  ACSS (a joint venture between L-3 Comm and Thales) sells TAWS units in the US that is based on the Thales system, so there is an alternative to Honeywell. Thales does sell their system outside the US.

Some of the primary Honeywell patents for the EGPWS have recently expired or are about to expire. So there may be some new alternatives soon.  Of course Honeywell has been making 'upgrades' beyond the regulatory requirements which they have been patenting.  These may help them hold their market share.

So no, there is not a single system to meet the requirement.  OTOH, there's not much competition either.


What are these bars on an F-16's nose? I've always wondered what the purpose of these "bars" on the nose of the F-16 (and some other military aircraft) are. Are they sensors (if so, what kind)? Are they lightning strips? I can't seem to figure out how to word my search query to find an answer, so I figured I'd ask here!

Source: af.mil

These are antennae for the IFF (Identification Friend or Foe) system.  IFF is a system to help distinguish friendly aircraft from unfriendly ones.

This particular antenna arrangement is used on only a couple of F-16 models. The first was the F-16 Air Defense Fighter (ADF) version. This model was converted from the F-16 Block 15 for use as a fighter interceptor for the US Air National Guard. A total of 271 F-16A and F-16B aircraft were upgraded to this standard between 1989 and 1992. One of the modifications made during the conversion process was installation of the Teledyne/E Systems Mk.XII Advanced IFF system, given the designation APX-109. This system included four antennas, often nicknamed "bird slicers," placed in front of the cockpit canopy with additional antennas on the bottom of the inlet.

From: http://www.aerospaceweb.org/question/planes/q0286b.shtml


How far ahead will ATC issue runway crossing clearances at controlled FAA airport? In past years it was common to get a taxi clearance that would include all required runway crossings. This was true even if there were several runway crossings over a long distance.

Now it seems that ATC has limits on how far ahead they can issue runway crossings. What are the ATC limits on taxi clearances that include runway crossings?

I suspect that you're thinking of this procedural change that took effect from June 30th, 2010. Before the change, a taxi clearance could indeed allow you to cross multiple runways, but now you can only be cleared to cross one runway at a time:

  This change establishes the requirement that an explicit runway
  crossing clearance be issued for each runway (active/inactive or
  closed) crossing and requires an aircraft/vehicle to have crossed the
  previous runway before another runway crossing clearance may be
  issued. At airports where the taxi route between runway centerlines is
  less than 1,000 feet apart, multiple runway crossings may be issued
  after receiving approval by the Terminal Services Director of
  Operations.

It was a big change at the time (according to what I've read) and it was widely publicized by the FAA and other organizations. The relevant ATC instructions are in the ATC orders 3-7-2:

  Aircraft/vehicles must receive a clearance for each runway their route
  crosses. An aircraft/vehicle must have crossed a previous runway
  before another runway crossing clearance may be issued.

The orders have several examples and the corresponding phraseology.


As a US citizen living in Europe, must I use a trust as the owner of an N-reg aircraft? I have found lots of information online about European pilots owning and flying N-reg aircraft using trusts set up in the US. I live in Europe, but I'm a US citizen, so must I also set up a trust because I don't live in the US? I cannot seem to find a definitive answer on this with references to supporting regulation.

As a US citizen you can own an N-reg aircraft directly, regardless of where you live. The regulations on aircraft registration are in 14 CFR Part 47. They say who can register an N-reg aircraft, but they don't say anything about where that person must be. 47.3(a)(1) simply says:

§47.3   Registration required.
(a) An aircraft may be registered under 49 U.S.C. 44103 only when the
aircraft is not registered under the laws of a foreign country and is—
(1) Owned by a citizen of the United States;

The regulations are summarized in a more readable way on this FAA site. A trust allows a non-US citizen (or non-resident alien) to own an N-reg aircraft provided they have no more than 25% of the voting rights in the trust, per 47.7(c)(2)(iii).


Are there any aircraft with a nose wheel braking system? I'm pretty sure that there are no aircraft equipped with a brake on its nose wheel, however two of my colleagues think there might have been.  Are there?

Aircraft with retractable gear of course have devices to stop the wheels from spinning when retracted,  but I'm asking about brakes used to stop or slow down the aircraft. Please don't consider aircraft with a tail wheel, gliders, experimental aircraft, or aircraft used for flight testing (certified aircraft only).

There are quite a few 727 that actually had nose wheel braking, however they utilized it only for maximum braking power. (Also they were proven to be ineffective and unreliable, so a service bulletin was written to remove the system).

Saab Gripens use nose wheel brakes to stop as well, the main gear sits farther aft than most planes, so there is quite a bit of weight on the nose gear, which makes it effective for stopping.


How can a designer maximize the glide ratio of an aircraft with low aspect ratio wings, other than by increasing the aspect ratio? As I understand it, the gliding range is given by a lift to drag ratio—hence to increase the gliding range, I would want to increase the lift and reduce the drag as much as possible.

To that end, apparently, it seems that high AR fits both the bills. However, does that mean that I will not able to enhance the gliding range with low AR wings at all?

With a given wing span, everything that reduces drag will increase the gliding range. Aspect ratio is less of a factor here because induced drag depends on wing span, not aspect ratio. But increasing the aspect ratio with a given wing span will reduce the wetted surface and, consequently, friction drag.

What can be done to increase gliding range outside of increasing span?

retract the landing gear,
avoid struts or bracing wires,
minimize friction drag by allowing for more laminar flow and minimum surface area.
minimize pressure drag by streamlining everything

Generally, a low aspect ratio shifts the polar point of best gliding range to lower lift coefficients, so reducing all that parasitic drag becomes more important the stubbier the wings are.

The most effective way, however, to increase gliding range is indeed a larger wing span if all other parameters are held constant. Increasing span while keeping wing area constant will:

increase aspect ratio and reduce wing chord,
reduce induced drag at the same lift coefficient,
and, as a consequence, lower the optimum gliding speed, so the parasitic drag is lower as well.


Is falling a mode of flying? I frequently observe people arguing (on this very web site) about the question if falling is a mode of flying or not. It appears to me that the majority of people have a strong opinion that it is not.

Surely it is a matter of definition. I made the effort to look it up in a number of online dictionaries. Most sources provide many possible options to define flight, like Merriam-Webster:

  1a : an act or instance of passing through the air by the use of
  wings

but it continues with

  2a : a passing through the air or through space outside the earth's
  atmosphere

Wikipedia tried to put everything into one paragraph:

   Flight is the process by which an object moves through an atmosphere (or beyond it, as in the case of spaceflight) without contact with the surface. This can be achieved by generating aerodynamic lift associated with propulsive thrust, aerostatically using buoyancy, or by ballistic movement.

Flight may be aerodynamic, propulsive, aerostatic, or ballistic.

When one throws a ball, the ball is flying. It flies until it hits anything else than air. Why would it be different if the ball is thrown upwards, or pushed downwards, or just dropped?

In my understanding, falling is just a very special case of flying. Is this correct?

Since falling is just the final result of a ballistic arc if you let it go long enough, and ballistic arcs are considered "flight" per the Oxford Dictionary (as in the ballistic arcs of balls, spacecraft, arrows, etc being considered "flights"), then technically, a falling object is in flight.

You could give it just the tiniest lateral push when you drop it so it goes down with a slight ballistic curve;  in the end, no different from driving it laterally so it has horizontal energy/inertia with a high velocity that exactly counteracts gravitational pull, and give it a vacuum so it can do that indefinitely - a satellite - , the only difference being that and the ball being the location in or out of the atmosphere and energy put into it.

In other words, orbital vehicles, baseballs, bullets, are all "falling" and are technically in flight, and so is a ball you drop straight down... if the Oxford Dictionary definition is what you want to use.

In my own airplane, if I push over with just the right elevator input, and go zero G, my plane is now in a ballistic arc.  The wings are superfluous, for a few seconds anyway, and my plane is "falling", just not straight down.  So if you accept that in that condition it is still "flying", the falling is flight.


Why does a clean configuration lead to the generation of greater wingtip vortices? "Slow, heavy, clean" are the three major conditions generating stronger wing vortices. It's very clear how "slow and heavy" aircraft create stronger vortices, but why a "clean" configuration generates stronger wake turbulence is less clear.

I did some digging on this, and found some people saying "use of the flaps reduces the AoA and thus leads to weaker wake turbulence" and others claiming "use of flaps moves the center of lift toward the root of the wing and that leads to less lift around the tip of the wings and thus less wingtip turbulence.

Which explanation is correct?

Edit) I checked the answer given here What is the relationship between angle of attack and wake turbulence?, but I'm not really sure "not really" is the right answer to this. The AIM (Aeronautical Informational Manual) is very clear about this, designating "clear" (along with "heavy," and "slow") as one of the three factors that increase wake turbulence.

I would actually assume the opposite to be true.

Let us assume the vortex intensity and the induced drag are directly correlated. The induced drag coefficient can be expressed as:

$c_{Di}=\frac{c_L^2}{\pi\cdot AR \cdot e}$

$c_L$: Lift coefficient
$AR$: Wing aspect ratio
$e$: The so-called Oswald factor, a number which equals one for elliptic lift distributions. It decreases for distributions that deviate from the elliptic one.

Most wing designs aim to achieve an elliptic-like lift distribution in order to minimise induced drag in clean configuration.

As flaps, spoilers, air-breaks and so on are deployed the lift distribution will deviate substantially from the elliptic one (see diagram), hence reducing the $e$ factor and increasing the induced drag. If the first assumption still holds, an increase in induced drag will have been caused by an increase in vortex intensity.

Additionally, significantly higher lift coefficients can be achieved with deployed high-lift devices, which also contribute to increase vortex intensity.


What is this airport outside of Cairo, Egypt? Out to the east of Cairo, Egypt, is a large two-runway airport that Google Maps calls "Capital Cairo Airport" or "Capital International Airport". Here's a link. However, I can't find any information about this airport or what it's used for. Cairo has a major international airport within the city, here, so I'm confused as to what this large airport only 30-40 minutes away is.

As far as I can tell, it doesn't appear on Wikipedia's List of airports in Egypt, and satellite view shows no planes parked at this airport. Satellite view history in Google Earth shows that two years ago, the airport only had one runway, but since then the second runway was added. So apparently this airport was important enough to merit two runways, both over 10,000 ft. Why? What is it used for? Does anyone know?

30°02'52.55" N  31°49'55.05" E

The two runways to the east form an existing air force base called Wadi Al Jandali AFB. The new western runway and terminal form a new civilian airport called Katameya/Al-Qatameya Airport. It is also known as Capital International Airport.

(Source)

The airport is set to serve a new administrative capital that is yet to be completed.

Another new airport, Sphinx Airport, is west of Cairo. It is also adjacent to an existing AFB called Cairo West.

  Al-Qatameya will serve the new administrative capital project and the Cairo West airport will receive charter flights, along with Cairo International Airport to ease pressure.

They are not operational in the sense of scheduled air traffic. Google Earth shows what can only be the new Sphinx Airport (west of Cairo West AFB):

30°06'15.42" N  30°54'03.38" E


How much thrust is lost due to the bleed air system? I've read that bleeding air for the pneumatic system from the engine core can produce important losses in thrust, and also rising the fuel consumption too. Today this problem is worse, with the more uses of high-bypass turbofans engines, which have less air passing through the engine core.

How much engine thrust is lost due to bleed air?

For the Boeing 737-800:
Bleeds off:

If bleed air is turned off, it gives ~1% N1 increase. This higher N1 also means a 1 or 2 knot faster $V_1$ and/or $V_{mcg}$. Bleeds on adds about a 2.5-tonne correction to the gross weight.

For the various anti-ice:

The penalty can be as high as 5% N1. Note the single- and dual-sources figures. Dual means APU is running and is providing bleed air.
Exact loss in thrust (force)
That will be very hard to calculate without test bed data from the engine maker. Not to mention it varies with the different elements: pressure altitude, temperature, forward speed, etc. That's why I included the V1 and weight impacts.
Based on the graph below, 1% N1 at high takeoff power equates to about 2.4% of total thrust. That should be treated as a ballpark figure.
(Source)
In cruise however, having all anti-ice on might warrant flying lower due to the decreased thrust.
Other uses and alternatives
Bleed air used for cooling the turbine blades for example, helps increase thrust, not decrease, as the burners can run hotter without damaging the turbines.
The "all-electric" Boeing 787 uses bleed air for engine anti-ice. Using the generator to run the other anti-ice elements also reduces the thrust due to the shaft off-take. But, there is the benefit of weight reduction.


How does cabin pressure vary with respect to ambient pressure during descent? I came across this statement in a book -
"During a descent, the cabin pressure in a pressurized aircraft usually climbs at as lesser rate than ambient pressure".

Could someone explain this statement in simple words?

During descent, the rate of change of pressure inside the cabin of a pressurized aircraft is lower than outside (ambient).

Inside the aircraft, under active control the  cabin pressure increases from equivalent ~8000ft above sea level to ground level. In the meantime, the aircraft descends from cruising altitude which is typically much higher, also to ground level.

Assuming the pressurization and descent start and end roughly at roughly the same time, the cabin is necessarily pressurized slower than the increase of air pressure outside in absolute terms  (e.g. psi per minute) assuming a steady pressurization profile .

Corner cases arise when the airport is at an elevation above 8000ft or so since the cabin will be further depressurized during descent. So while the relation holds in absolute magnitude , they will be of opposite sign. (until there is an airport  24,000 ft or so....)


Why do piston engines have a lower fuel consumption with higher temperatures? It is very common to find in the AFM/POH, Section 5 of most piston engine airplanes (C152, C172, PA28, BE76, etc) charts that indicate the fuel consumption for cruise/economy power settings.

You will notice that in all cases, for a given set of pressure altitude, RPM and manifold pressure (if constant speed propeller) the fuel consumption will depend on the OAT. The question is: why does the fuel flow (in PPH or GPH) decrease for higher temperatures?

I should make sense to me that higher temperatures (hot atmosphere) would decrease the overall performance of the engine, as we all know, since the air is less dense which directly impacts in the engine's operation. If the engine's performance is degraded in a hot day, why does it burn less fuel?

All manufacturers publish similar results, but I can't figure out a physical explanation to it. If you could point out an official reference in any textbook I would really appreciate.

I don't have a reference, but the physics behind is not that complicated.

The key is that you have constant RPM, constant pressure altitude and constant manifold pressure.

A motor sucks in lots of air, but since the throttle restricts the air flow in the intake, the air pressure between throttle and motor is low. This is the manifold pressure1. At idle, i.e. almost closed throttle, the pressure is very low, while at full throttle, it ideally equals ambient pressure. And in turbocharged motors, it is even higher than ambient pressure.

Finally, manifold pressure together with RPM and displacement of the motor is a measure of how much air volume is aspirated by the motor per time interval.

Since you keep everything constant, this volume also is constant. But warmer air is less dense and contains less oxygen molecules per volume.
Less oxygen molecules means less fuel can be burned. This is why fuel consumption is lower.
But it also means less power. To compensate, the throttle could be opened a little more to let in a little more air volume. This would also increase the manifold pressure.
But if the throttle is already fully opened to get max. power, you can't open it further. So, max. power is lower at higher temperature.

1) NOTE: For simplicity, I'm speaking about absolute pressure here. The gauge in the cockpit displays the under-pressure with respect to ambient pressure, so a high displayed value means a low absolute pressure. And since ambient pressure changes with altitude, manifold pressure does, too, even if the displayed value is constant. The benefit of this is that the displayed value is a good measure of the power with respect to the max. power achievable at that altitude.


What is the maximum height of USAF fighter pilot? In response to this comment:

  Three days later I happened to meet a commercial pilot at school who has flown
  F4s during Vietnam. He gave me the worst news of my life. My 6'3" ass was too
  tall to ever fly a fighter.

Is this actually true? A cursory search seems to contradict what he was
told:

  To become a Jet fighter Navigator, you have to have [...] a vertical standing
  height of between 64 inches (5 foot 4 inches) and 77 inches (6 foot 5 inches)
  tall.

It would appear his height is within range. Was he told wrong or am I missing
something?

To become an Air Force pilot, you have to be a commissioned officer, there are few ways you can do that. First you can go through the Air Force Academy, which is probably the most common. Another way is to be in an ROTC program through your college of choice. The last way I know of is to graduate college and join the Air Force through the officer candidate school (OCS).

Regardless of the method you choose, there are certain requirements you must meet:

Be a U.S. Citizen
Have any 4 year college degree or be within 365 days of attaining it
Minimum 2.5 GPA (although I'd be surprised if they took you that low)
Under the age of 28 by the board convening date
Have a standing height of 64-77 inches and a sitting height of 34-40 inches
Have no history of hay fever, asthma, or allergies after the age of 12
Meet USAF weight and physical conditioning requirements
Normal color vision
Meet refraction, accommodation, and astigmatism requirements
Distance vision cannot exceed 20/20 uncorrected or must be corrected to 20/20 or better
Near vision cannot exceed 20/40 uncorrected or must be corrected to 20/20 or better

If you've met those requirements you can then go through the Air Force Officer Qualifying Test (AFOQT) and through Military Entrance Processing Station (MEPS) for your intellectual and physical evaluation. If you pass those tests, you may be selected for the Officer Candidate School (if not joining through ROTC or Academy).

After that you go into undergraduate pilot training (UPT) where you spend a year learning to fly through academic and hands-on training. Depending on how you perform at UPT you will receive a seat assignment. Higher scores are selected for fighter training while lower scores move towards transport aircraft. You can voice your opinion on what you want to fly, but ultimately the decision is driven by the needs of the Air Force at the time you graduate UPT.

After UPT, you will move to Advanced Flight Training (AFT) which is between 6 months and a year long depending on the aircraft you've been assigned. After AFT you'll be assigned a squadron and location.

If you don't meet height requirements

There is a waiver process, although getting a waiver for height requirements is extremely rare (if not completely unheard of). The issue is that the ejection systems are designed for a specific height. This process starts by appealing a medical review board which you are allowed to write a letter to argue your position, however even with a waiver you would probably not be assigned a fighter aircraft. You would probably be assigned an aircraft that does not have an ejection system like transport or mid-air refueling aircraft.  As RhinoDriver mentions in the comments, the T6 training aircraft is also equipped with an ejection seat and if you can't fly the trainer, you can't progress on.

The only other alternative to be a US Air Force pilot outside of height requirements is to be an unmanned aircraft pilot.

Source 1: U.S. Air Force ROTC Website
Source 2: Department of Defense Article


Compressor-Turbine: Why a shaft and not kind of a "rotating drum"? I'm studying the fundamentals of jet propulsion and its applications. I really have this next question and haven't found an answer yet: why do jets use a shaft (or more) to connect the turbine(s) to the compressor device(s), but not a "rotating drum" instead?

What I call a "rotating drum" (I sketched it below) is a thin, rotating cylinder that has built-in rotor blades at the beginning and exit.

I'd like to know if this is a feasible arrangement, and what would be the disadvantages of it. I think this might be unfeasible because:

There would be a lot of thermal stress at the middle of the drum.

But if we were to overcome this drawback somehow, I think we would benefit in the following ways:

Less weight, I think, with respect the traditional shaft system.
More internal space (no hollow) for other demanding components, like the combustor. The combustor could be made a bit larger, thus increasing the burning efficiency (more reaction time for reactants, ...).

I don't know how correct/wrong I am. This is a question out of pure curiosity and I wanted to get some feedback on it. Should I go ahead and start working on a small scale prototype of it? Hope my question here is not too basic.

PS: The sketch I made is just that: a sketch. Therefore, important things like the relative number of stages compressor-turbine, or the increasing/decreasing areas for each of those two components, do not appear.

There are a few very practical reasons why turbine engines use inner shafts/spools.

First, jet engine spools are very high speed rotating parts, this means they are subjected to high amounts of centripetal force. Centripetal force is calculated by $F=mr\omega ^2$ were F is Force, m is mass, r is radius of gyration and $\omega$ is angular velocity. So obviously the larger the radius of gyration the higher the forces that the rotors must carry. To reduce the radius of gyration manufacturers try to push the mass of the rotors as close to the centerline of the engine as possible. In the picture below (source) I have circled the HPC, HPT and LPT rotors. You can see how they are very thin under the blades and then have a large bulb very close to the engine centerline. Moving all of this mass towards the centerline, lowers the radius of gyration, and thus reduces the centripetal force. By reducing the centripetal force, you can reduce the strength of the rotors as well, since they don't have to carry as much load. This allows you to remove mass from the rotors, further reducing the centripetal force and overall weight of the engine.

Next, you want the bearings to be as small as possible. This is because as the radius of a bearing increases the linear velocity of it also increases, via this equation: $v=\omega r$. The faster the linear velocity the higher the wear, the greater the friction and greater the heat generation. So there is a push to make the bearings as small as possible given other constraints. In the image below I have circled the bearings, the red circles are on the low pressure spool bearings, while the blue circles are the high pressure spool bearings. This isn't always done, but it is becoming very common for the aft high pressure bearing to actual ride on the low pressure shaft. Typically these shafts spin in the same direction, so the bearing speed is reduced by this equation $\omega_{AftHPbearing}=\omega_{HP}-\omega_{LP}$. Bearing friction reduces the efficiency of the engine, and bearing wear is a significant maintenance driver.

(This is getting long so I am going to truncate the rest) There would be many other issues as well, such of blade mounting (dovetails in compression instead of tension), blade design (compression instead of tension), possible increase in leakage paths, containment, stator structure design (now all of your stators are attached to a stationary shaft that can only be supported at the ends), control of variable stator vanes, getting the fuel into the combustor, how do mount the engine, etc.

Edit: Just reread the question and realized you were also talking about making the combustor bigger. Modern combustors are getting smaller and are much smaller than they were in the original jet engines. You can also see in the pictures above, they already don't use all of the space available to them and if they needed more space the arm (shaft) connecting the HPT and HPC could be lowered some more.


Why is the aerodynamic center for most airfoils located at the quarter chord location? I've been reading several sources on the location of the aerodynamic center

https://web.mit.edu/16.unified/www/FALL/fluids/Lectures/f03.pdf
https://en.wikipedia.org/wiki/Aerodynamic_center
John Anderson Jr., Fundamentals of aerodynamics

Many (such as for example Wikipedia) determine the aerodynamic center by writing out the equation for the moment for an arbitrary point, and then apply some definitions to get to the end result: the aerodynamic center lies at the quarter chord, see below:

However, I'm looking for a more physically intuitive explanation, probably starting from thin airfoil theory. The way I understand it, ultimately the aerodynamic center is determined by how the distribution of lift changes with angle of attack.  Thus, the distance the center of lift moves w.r.t. the aerodynamic center cancels out the resulting moment due to the change in lift with angle in attack.
Can we explain why this point ends up to be at the quarter chord location?

It has to do with the Birnbaum distribution. The center of its area is at one quarter.
In potential flow theory, lift can be calculated as the linear superposition of a contribution from camber and one from angle of attack. While the camber-related part of lift is constant, the angle-of-attack related part varies linearly with this parameter. This means that changing the angle of attack adds or subtracts circulation, the chordwise distribution of which is described by the Birnbaum distribution. The important part is the self-similarity of the angle of attack dependent lift resulting from this addition or subtraction of the same chordwise distribution.
The center of pressure of the resulting angle-of-attack dependent part is constant and at 25% of chord for 2D flow and wings of large aspect ratio, at least as long as flow remains attached and viscous effects are negligible.
The pictures below (own work) show the circulation over chord produced by camber alone (so AoA is 0°) on the left and the Birnbaum distribution alone on the right (so using a symmetric airfoil). Total circulation is simply the sum of both. Copied over from this answer thanks to the helpful suggestion of ROIMaison.

ultimately the aerodynamic center is determined by how the distribution of lift changes with angle of attack

That is precisely right: The aerodynamic center (a better word for it is "neutral point", btw.) is the point where the additional lift force from a change in angle of attack can be summed up. Do not look at the lift distribution per se (that is what determines the center of pressure), but at its change over angle of attack, because that is what determines the neutral point and what shifts the center of pressure back and forth. The constant part caused by camber does not change with angle of attack and the part caused by angle of attack has its center always at 25% (under the conditions mentioned above) and its magnitude grows with angle of attack. This growing contribution of the angle-of-attack-dependent force is what shifts the center of pressure forward (on airfoils with positive camber) rsp. backwards (on airfoils with negative camber) towards the 25% point.
BTW, I wish we had more people like Aaron Swartz. That article is now 97 years old and these monopolists still want 42 € from me for a copy. Sorry, no details from it – I could not find any online.


If the push was accidentally started with the brakes on, what will happen since these towbars don't have shearpins? The push was started accidentally before the brakes was released. What will happen since it doesnt have shearpins?

While it isn't desirable to try to push an airplane with the brakes set, nothing much happens if you try. Nothing moves, and the tow bar is so strong in straight compression/tension that it isn't likely to be damaged.

Problems are much more likely once momentum and moving tugs/airplanes get involved; that is when a sudden brake application is more likely to "break a towbar" (actually, a shear pin or coupling -- designed to let go before you damage the aircraft landing gear). But even that is a side-to-side failure mode, rather than pure compression.

To answer the edit to the question about "without shear pins": pushing straight back, same, nothing happens. If the aircraft applies brakes while being turned and the towbar can't break, then either the tug gets slammed to a halt, or else something gets damaged - probably at or near the point where the towbar connects to the aircraft. (Or possibly both happen.) That's bad... aircraft out of service, seriously expensive repairs, etc. Which is why shear pins ARE used in towbars. Repairing damaged towbars is far cheaper that repairing damaged aircraft.


Is there any difference in landing minima between ICAO and FAA? The FAA IFR Landing Minima Chart has both ceiling and visibility minima regardless of approach type (straight-in or circling). I believe it means that a pilot should meet the both ceiling and visibility minima although he conducts straight-in approach procedure.

But in my country (not USA, we follow ICAO regulations), landing minima for straight-in approach procedure consists of only 'visibility'.

So I guess there is difference on landing minima between ICAO and FAA. But I couldn't find that information.

In most cases, FAA approach charts do not provide a requirement for a ceiling as you say, but rather provide the minimum altitude that a pilot may descend to without having the runway environment in sight (the DH/MDA) and the minimum required visibility.1
In fact, as described in the FAA Instrument Procedures Handbook, Page 4-7 and in the AIM, section 5-4-20(e), air carrier pilots, who are restricted from even beginning an approach if the reported weather is below minimums, are only restricted by the visibility and may fly the approach  when the reported ceiling is lower than the minimum altitude on the approach plate (note that this does not apply to Part 91 operations).
The main reason for this is that a ceiling does not necessarily cover 100% of the sky over the airport environment, and it is quite possible to see the runway even when there is a reported ceiling.

References
FAA Instrument Procedures Handbook, Page 4-7 says:

14 CFR Part 135, section 135.225 states that pilots may not begin an
instrument approach unless the latest weather report indicates that
the weather conditions are at or above the authorized IFR landing
minimums for that procedure. 14 CFR Part 135, section 135.225 provides
relief from this rule if the aircraft has already passed the final
approach fix (FAF) when the weather report is received. It should be
noted that the controlling factor for determining whether or not the
aircraft can proceed is reported visibility. RVR, if available, is the
controlling visibility report for determining that the requirements of
this section are met. The runway visibility value (RVV), reported in
statute miles (SM), takes precedent over prevailing visibility. There
is no required timeframe for receiving current weather prior to
initiating the approach.

AIM, section 5-4-20(e) says:

e. Published Approach Minimums. Approach minimums are published for
different aircraft categories and consist of a minimum altitude (DA,
DH, MDA) and required visibility. These minimums are determined by
applying the appropriate TERPS criteria. When a fix is incorporated in
a nonprecision final segment, two sets of minimums may be published:
one for the pilot that is able to identify the fix, and a second for
the pilot that cannot. Two sets of minimums may also be published when
a second altimeter source is used in the procedure. When a
nonprecision procedure incorporates both a stepdown fix in the final
segment and a second altimeter source, two sets of minimums are
published to account for the stepdown fix and a note addresses
minimums for the second altimeter source.

Notes
1 Under relatively rare conditions, TERPS specifies that a ceiling is required for a specific approach, but this will be notated on the approach chart with the words CEILING REQUIRED.


Is an increase in induced drag always caused by an increase in the angle of attack? In this video at 2:57 they increase the AoA to maintain lift, which normally also increases the drag. Now, imagine that we don't increase the AoA: the drag will not increase but we will not have enough lift to maintain level flight. If we want to keep the same lift and fly in level flight we must increase the AoA and only then will the drag increase.

So induced drag is just caused by a larger AoA, so basically this is a type of pressure drag.

Do you agree that if we don't increase the AoA as described in the video then the drag will not increase as well?

At 2:58, the video says "To replace the lift lost by the increased upwash and downwash, the wing must be flown at a higher-angle-of-attack than would otherwise be necessary."

This statement is true no matter what angle-of-attack the wing is "feeling" and no matter how much lift it is making, as long as the amount of lift it is making is not zero.

For example, let's say at a given instant in time, with a given angle-of-attack and airspeed, when the instantaneous flight path is horizontal, the wing would be making Lift equal to Weight if it weren't for the upwash and downwash effect, but because of the upwash and downwash effect, the wing is only making a force equal to 90% of Weight.

Forces are not in balance, and the flight path is curving downward.  In the next instant in time the flight time will no longer be horizontal.  Yet despite the fact that we aren't actually replacing the "missing" lift, it is still true that that "To replace the lift lost by the increased upwash and downwash, the wing must be flown at a higher-angle-of-attack than would otherwise be necessary."  If we were happy to settle for a lift force equal to 90% of weight at that instant in time, and the upwash and downwash effect were not there, we could fly at an even lower angle-of-attack.

More practically, we normally don't want to allow the flight path to curve (accelerate) downward, so we do keep lift close to weight, or very close to it, except during the brief transition (pushover) from a climb to level flight or from level flight to a descent.  The reduction of lift that happens in a steady-state descent (or climb), compared to in level flight, is very small for moderate climb or descent angles.  For more, see a What produces thrust along the line of flight in a glider? and Does lift equal weight in a climb? .

Only if the wing is mounted inside a wind tunnel, where the connection between Lift and Weight is completely severed, does it really make any sense to ask "What happens if we decide not to replace the missing lift?".  In that case, indeed, the upwash/downwash effect does not force the wing to be flown at a higher angle-of-attack than would otherwise be necessary.


Is the Airbus A380 a viable shorthaul airliner? What is the technical, mechanical and economic feasibility of using the Airbus A380 for short haul flights of under 4 hours in its 800 plus seat configuration?  I'm talking about cost and economies of scale, frequency of repairs and service etc.

I can't say if anyone has looked at a short-haul version of the A380, but we can look to the Boeing 747-400D for comparison.

In addition to removing the wingtip extensions and winglets as described in the Wikipedia article, a friend at Boeing described to me other changes needed. Boeing beefed up the wing box due to the increased landing cycles. There were also some changes to the brakes to improve cooling as the short flights didn't provide adequate time to cool the brakes passively.

It should be noted that ANA was the only customer with 19 aircraft built. They retired the last of them 3 years ago. So it would appear that there isn't much of a market for a short haul jumbo.


Do any aircraft automatically test that the pitot-static system is functioning properly before liftoff? Given that a properly-functioning pitot-static system is absolutely essential for flight (a plane cannot be flown without valid airspeed data, or at least not for long), are there aircraft that automatically check the functioning of the pitot-static system before liftoff?  This seems like it would be quite easy to do; during takeoff, compare the airspeed measured by the pitot-static system against the groundspeed (which could be read from speed transducers mounted on the landing gear), and sound an alarm (“INVALID AIRSPEED” or something similar) if the rates of change of the two fail to match within a certain tolerance (indicating either a failure of the pitot-static system or severe windshear along the length of the runway, both of which necessitate rejecting the takeoff).

First of all, ground speed is already determined by the IRU’s. No need for landing gear sensors although most airplanes do have WHEEL SPEED transducers for anti-skid currently installed. Wheel speed is not always equal to groundspeed but can be at times. For example, wheel speed right after takeoff is different than ground speed because the wheel begins slowing the second it leaves the ground.

Second, airspeed changes with altitude. So, the higher you are the faster your airspeed. This means that taking off in Death Valley might show a different airspeed RELATIVE to groundspeed than in La Paz El Alto.

Third, most of the time, airspeed doesn’t register correctly until about 60 knots. You’ll see that most airspeed indicators have 60 knots as the lowest indication mark. This is because if the airplane is pointed into the wind, it could register spurious readings. So, before any checking gets done, the plane needs to be moving above 60 knots.... Like during takeoff.

Fourth, airspeeds are cross checked during takeoff roll. The vast majority of airspeed splits on a new flight leg occur on takeoff roll and result in a rejected takeoff - your premise anyway. Occasionally it’s not noticed until takeoff. This is rare. The other instances (which I work on more frequently) are in flight malfunctions usually related to inadequate pitot heating.

Fifth, the current system works very well. No need to reinvent the wheel.


Is special permission required to take off from a field within restricted airspace? I had a question about restricted airspace that I wanted to clear up before resuming my training Sunday; you know, to maximize time in the air.

The airport I am training at is KMRH and it's surrounded by lots of restricted/military airspace/MOAs. From what I have read, restricted airspace requires permission to fly in; however we have never done that, we just call up on Unicom and state our intentions to other pilots.

If someone here could look at an online sectional of the area and get an idea of what I am saying and attempt to explain this to me it would be very helpful. If nobody can crack through my thick skull, I can always ask my CFI!

The most obvious point to make here is that KMRH is not in restricted airspace: the sectional shows that it's in uncontrolled class G airspace, with class E at 700' AGL. But having said that, there is indeed a lot of special use airspace nearby:

W-122 is a warning area
R5306A and R-5306D are restricted areas
A-530 is an alert area

You can't enter the restricted areas without permission from the controlling authority, but you can enter the warning and alert areas if you want. More details of each area are on the sectional chart, the FAA's SUA site and JO 7400.8X.

Looking at the sectional, it looks to me like A-530 is a 'gap' in the restricted areas to give access to KMRH and the three private airfields nearby. R-5306 A and D are from the ground to 18,000 MSL (up to but not including FL180, to be precise) and operate continuously. If the A-530 airspace were the same then there would be no way in or out of KMRH (over land, at least) without getting permission every time. Because A-530 is sandwiched between two restricted areas, I guess there's probably a lot of military traffic around and that's why it's an alert area rather than normal class E airspace.


How does aircraft design affect carburetor ice? The Cessna 172 and Piper Warrior are similar in many ways, including their engines: for most of their production history (1968-1998 for the 172; the entire history for the Warrior) both were equipped with a Lycoming O-320 engine of 150 or 160 horsepower.

One significant difference between the two is in their before-landing checklists: the 172 instructs the pilot to turn carburetor heat on before closing the throttle (p. 4-19):

  Carburetor heat should be applied prior to any significant reduction or closing of the throttle.

Conversely, the Warrior recommends carburetor heat "if required", and even recommends against it unless necessary (p. 4-23):

  Carburetor heat should not be applied unless there is an indication of carburetor icing, since the use of carburetor heat causes a reduction in power which may be critical in case of a go-around. Full throttle operation with carburetor heat on can cause detonation.

Considering that these two aircraft have very similar engines, what would explain such a drastically different approach to the potential danger of carburetor icing?

I've downvoted the answer from Habu because it ignores a major difference in engine design.

For small GA planes, the Lycoming engines have the carburetor bolted to the bottom of the crankcase where it gets some heat from the hot oil.  Fuel/air exits the top of the carb where it is routed through pipes inside the crankcase where the hot oil further increases its temperature. This makes the Lyc generally resistant to induction icing.

In Continentals, the updraft carburetor is not mounted on the hot crankcase but on part of the manifold assembly, insulating the carb itself from the heat of the crankcase, and the fuel/air mixture is routed directly to the intake manifold and not through the engine crankcase which holds the hot oil.  The result is that the TCM O-300 engine has earned the reputation of being an icemaker. The difference in the POH instructions as to how to fly each engine is directly attributable to engine design and it has absolutely nothing to do with the weather in Vero Beach versus Wichita.

I'm going to post line drawing images of the two engines to illustrate the point. First: Lycoming.  Second: Continental

What the original poster is missing is that for most of its history, the Cessna design used Continental engines.  Now that it has switched to Lycoming engines, the difference in the engines is probably zero, but they have not abandoned the former POH instructions as that might be confusing to the pilots that fly these planes.  After all, using carb heat more often as a default procedure for the Lyc powered Cessnas is a safe procedure.


How did the 9/11 hijackers find their way to New York City? It is quite well known that the airplane hijackers on 9/11 were not professional pilots. So, my question is how some people who didn't have any experience of navigating the airplanes could find their way, for example from Boston to New York City?

I read somewhere that some natural signs like the Hudson River (for example) helped them to find their way through New York City. But I'm still looking to find a more convincing answer if it is available.

Several of the hijackers, including Mohamed Atta, held at least private pilot certificates and had undergone ATP level jet training in DC9 and 737 full motion simulators in December of 2000. Atta himself held a commercial license with instrument and multi engine ratings. They were well versed in aerial navigation techniques and more than capable of navigating the aircraft in question back to New York City and Washington DC after it was hijacked and secured.

A basic scenario that any private or commercial pilot could have done:  the hijackers knew the flights they were booked on and the rough routes they would take to their destinations. A little basic planning amongst themselves would have produced the approximate position the aircraft would be at at the time it was hijacked.

Once seized and the flight crew liquidated, they could quickly determine their positions either from their headings and next waypoints or with a simple VOR fix (any competent private pilot can do this). The autopilots could quickly be disengaged and the airplanes hand flown using basic pilotage (good weather prevailed over the east coast that morning) or radio navaids to return to their targets. The navigation and flying they did that day was relatively simple.

As an update, I know these kinds of questions float around with “9/11 truthers” and other conspiracy fanatics as some sort of proof that the official explanation is incorrect. Quite often they cherry pick quotes and ignore any other evidence that won’t fit their narrative. Combine that with the public that’s largely ignorant about aviation, it allows these kinds of ideas to fester very well without challenge.


Are there legal limits associated with the use of the autopilot in the US? A lot of new avionics basically fly small planes for you. Looking at a Beechcraft with a pretty cool glass cockpit, it claims to do everything for you except within 50 feet of the ground. Basically you takeoff and land and nothing else according to the advertising.

I'm planning on doing more than that, but it made me curious, is the "within 50 feet of the ground" non-autopilot part because it's a legal requirement or because it's just the trickiest part and they don't want to deal with that?

Is there a legal requirement in the US for part of the flight to be piloted manually, whether that be percentage or just takeoff and landing or is that just the hardest part to automate? If so, can it be remotely piloted?

This varies based on if you are VFR or IFR certified.

Basic currency requirements for general aviation flying under part 91 which I presume is the target of this question. The comments to the answer outline the commercial implications, can be found in

  §61.57   Recent flight experience: Pilot in command.

  (a) General experience. (1) Except as provided in paragraph (e) of
  this section, no person may act as a pilot in command of an aircraft
  carrying passengers or of an aircraft certificated for more than one
  pilot flight crewmember unless that person has made at least three
  takeoffs and three landings within the preceding 90 days, and—

  (i) The person acted as the sole manipulator of the flight controls;
  and

  (ii) The required takeoffs and landings were performed in an aircraft
  of the same category, class, and type (if a type rating is required),
  and, if the aircraft to be flown is an airplane with a tailwheel, the
  takeoffs and landings must have been made to a full stop in an
  airplane with a tailwheel.

  .... [read on for IFR and night currency]

However the FAA actually views using the auto-pilot as manipulating the controls. You can find the full legal interpretation here. But in short,

  The FAA considers a pilot's use and management of the autopilot to be
  the equivalent of manipulating the controls, just as one manages other
  flight control systems, such as trim or a yaw dampener. The autopilot
  system's sophistication does not affect a pilot's responsibility to
  manipulate and manage all control systems, including an autopilot,
  appropriately. Therefore, a pilot may log PIC flight time as the sole
  manipulator of the controls for the time in which he or she engages an
  autopilot.

With that in mind you can maintain your currency using only auto-pilot and in theory if your plane and the desired airport was equipped for auto-land (which, as far as I know, no GA planes are) you could maintain your currency without physically manipulating the yoke aside from takeoff and climb to autopilot altitude. So no there is no legal obligation to physically touch the controls to maintain currency if your plane is capable of some kind of completely programmable flight (I don't think any are currently).

There is however one notable exception to this regulation. On an IFR checkride you must fly a manual approach,

  From the ACS...

  • The applicant must accomplish at least two nonprecision approaches in simulated or actual weather conditions.

  At least one must be flown without the use of autopilot and without
  the assistance of radar vectors. The yaw damper and flight director
  are not considered parts of the autopilot for purposes of this Task.

  It claims to do everything for you within 50 feet of the ground.

This is a bit misleading. First off, most, if not all GA planes lack auto-throttle so power management is in the hands of the pilot and is fully manual in most cases. Some more modern airplanes like the DA-42 have FADEC which loops prop and throttle controls to one lever minimizing but not eliminating manual control.

There are lots of autopilots out there and function varies heavily: some only have a single axis (heading hold and adjust capability). Some have 2 axes which can hold altitude and headings and some which have the ability to follow GPS courses, fly approaches down to different minimums etc. It should be noted that some units can be set to create situations that can stall the aircraft or otherwise put it in a dangerous flight scenario, the auto in autopilot does not mean absolute protection or full automation.

  If so, can it be remotely piloted?

This is actually a completely separate question if you are asking "do I need to physically be inside the aircraft" i.e. "can I maintain currency with a drone if it's properly equipped". I don't think the FAA has fully fledged regulations on this yet. If by remote you mean by use of autopilot, see above.


What is the meaning of this information provided by Air Traffic Control? Air traffic controllers seem to broadcast this information, is anyone able to tell me what this is or what its use is for?

LTBA 162120Z 03008KT 360V080 9999 BKN035 06/02 Q1028 NOSIG

Especially the last part, what does NOSIG mean?

This is a METAR, a weather report. From the Wikipedia article:

  METAR is a format for reporting weather information. A METAR weather
  report is predominantly used by pilots in fulfillment of a part of a
  pre-flight weather briefing, and by meteorologists, who use aggregated
  METAR information to assist in weather forecasting.

The meaning of this METAR is:

Location: LTBA
Day of month: 16
Time: 21:20 UTC
Wind:  True direction = 030 degrees, Speed: 8 knots
Wind direction is variable between 360 and 080
Visibility: 10 km or more
Clouds: Broken sky , at 3500 feet above aerodrome level
Temperature: 06 degrees Celsius
Dewpoint: 02 degrees Celsius
QNH (Sea-level pressure): 1028 hPa
No significant changes expected in the near future

NOSIG means: No significant changes expected in the near future.

See this METAR-TAF decoder.


When can I proceed inbound in a hold in lieu of a procedure turn when cleared for the approach? Let’s say I am holding on a published hold in lieu of a procedure turn but not yet cleared for the approach. Upon receiving approach clearance (say on the outbound leg of the hold) would I have to cross the fix an additional time before proceeding inbound?
I have attached a picture as an example and a red X where the approach clearance is received.

You don't need to do a full turn around the holding pattern, you can just cross the IAF and proceed inbound. This is from the AIM 5-4-9(a)(5):

The holding pattern maneuver is completed when the aircraft is
established on the inbound course after executing the appropriate
entry. If cleared for the approach prior to returning to the holding
fix, and the aircraft is at the prescribed altitude, additional
circuits of the holding pattern are not necessary nor expected by ATC.


Benefit of a deswirl vane for a turboshaft helicopter engine I am trying to understand the benefit of deswirl vanes on a turboshaft helicopter engine. For these type of engines, the kinetic energy of the exhaust stream is essentially wasted energy. Also, raising the static pressure at the exit plane by deswirling will reduce the shaft output power. So, why bother?

This is a very good question. However, there is a slight error in your question, which is causing the confusion.

Turbine power, is determined by the ratio of total pressure across the turbine (and other factors). See the formula here on NASA’s website.

$$ W_{Turbine} = \eta \cdot c_p \cdot T_{t_4} \cdot \left( 1-TPR^{\frac{\gamma-1}{\gamma}} \right) $$

Where $$ \gamma = \frac{c_p}{c_v}$$

and TPR is the total pressure ratio across the turbine:
$$TPR =\frac{P_{t_5}}{P_{t_4}}$$

In comparison, thrust is determined by the static pressure. See the “engine thrust equation” (the second formula) on this page here. The thrust is given by two terms; one due to the increase in velocity of the mass, the other is the “pressure thrust” term, which is due the the nozzle area x the difference in ambient static pressure and the nozzle exit static pressure.

In simple form;

$$F_{N} = \dot{m} \cdot (v_e - v_i) + A_j \cdot (p_{s_{exit}} - p_{s_{ambient}})$$

(Ignoring the mass of the fuel, which is very small compared to the air mass flow, $\dot{m}$).

So, increasing the exhaust nozzle static pressure at its exit increases the thrust from the exhaust gas, but will not reduce (or change) the power provided by the turbine, because that’s a function of total pressure.

That’s not to say the amount of thrust you will get is very large, and worth the weight of nozzle guide vanes at the exit. Some turboshaft engines have them, some don’t.


What would be the minimum number of engines required to climb in a 747? There was a really good Air Crash Investigation by Nat Geo which showed the British Airways Speedbird 9 issue where volcanic ash swept over all four engines and through the air vents inside the cabin. As a result, all engines stopped working.

After around fifty attempts to restart the engines, engine four roared back to life. Although this did bring good news to all onboard, one engine would still not have given them enough power to clear the mountains that were in their path around Jakarta. Due to this, the Captain turned back to sea.

Nat Geo Flight 9. All engines stopped.

I don't think National Geographic would be super accurate but this looks like one engine could have cleared this mountain.

Anyway, this got me thinking.

A 747 can fly on one engine but can't climb? This does make sense, one engine can make a 747 fly for longer but it cannot climb with just one. What then would be the minimum number of engines required for the jet to clear the mountains? Two?

@Michael Hall said it best, in the first sentence of item 1 of his answer:

  There are simply too many variables for a definitive answer.

Here are two extremes to illustrate the range of answers insofar as altitude is concerned:

Let's say you have a 747 at it's optimum altitude in cruise with all four engines operating, say 37,000 just for the heck of it. Now let's say you lose one engine. Can you now climb on three engines? No, in fact you won't even be able to keep the altitude you have. You will start drifting down.

Now let's say that same 747 with the same load (actually heavier because it would still have the fuel on board that it used to get to its 37,000 foot cruise) lost an engine while on the takeoff roll but after V1. Will it climb? Yes, even with the drag from the gear and takeoff flaps you will be able to lift off the runway and climb.

But back to the one-engine scenario. My gut level feeling is that any 747, if carrying no passengers or cargo and only, say, 30,000 lbs of fuel and down low (5,000 ft?) and in a clean configuration could eke out a little climb. Can't prove it though.

But start adding weight or drag and the answer would change. The first model to not be able to do it with weight and drag being added would be the 747-100. The first -100s I flew had a max takeoff weight of 735,000 lbs as I remember. The next model to fail would be the -200. 825,000 lbs was the highest max takeoff for the -200s I flew. The highest max takeoff that I have for a -400 on the DOS weight & balance software I wrote was 910,000 lbs.

The biggest difference performance-wise is due to engine size. The more power the one engine has, the more it can keep aloft.

And there are other variables. What was the nature of the failures of the three engines? Are they windmilling or seized? Even whether the remaining engine is an inboard engine (2 or 3) or an outboard engine (1 or 4) is a factor. When it comes to performance, even how many insects are splattered against the leading engine of the wing can make a difference.


Why does the length of the 737 vary so much? The longest version is almost 50% longer than the shortest, and even within the "next generation" models, the difference is almost 40%.  Why such a big difference in lengths?

Airlines want to have different sizes of aircraft to match their passenger loads as well as possible. The different loads may be for different routes, times, or airlines. It is more efficient to fly a smaller plane if extra space isn't needed.

Aircraft manufacturers have some options for how to meet this demand. They can create a whole new airplane for each size, but this is expensive for everyone involved. Each plane would have to be certified separately, requiring much more time and testing. They may not be alike, requiring pilots to be trained on each individual one. And airlines would have to maintain all the different types of airplane.

Instead, aircraft manufacturers choose to stretch the fuselage to fit in more passengers. This can allow most other things on the plane to remain the same, with generally just minor modifications. This greatly decreases the amount of design and testing required to create the new size of aircraft. The same pilots and mechanics can work on any of the sizes, since most parts and features are common to all of them. There will be some inefficiency, in that parts on the small versions are designed to withstand higher loads of the bigger versions, but this is more than offset in the cost savings of having common parts.

Most aircraft come in different versions with different lengths, but it can be most noticeable on the smaller planes like the 737.

The manufacturers also market their products based on their coverage of different seat capacity. Each manufacturer is able to cover a wide range of seat capacity by offering different sizes of 3 basic models.

Source


Am I allowed to replace my own Model A-30 Altitude Digitizer? My Transponder Mode C (Altitude Reporting) function quit working.  The position reporting function is working fine.  I believe the failed component is the self contained Model A-30 Altitude Digitizer "box" that is bolted to the interior of the fire wall.  It has a connector cable to the transponder and a rubber pitot tube connection.  I am an Aerospace engineer with 32 years experience designing and testing Space Shuttle Main Engines and components.  I have done my own annuals and had my local FBO mechanic inspect the work and sign it off.  The replacement of the Altitude Digitizer box does not require the removal of the transponder - just bolt on the new box and re-connect the air tube and plug in the "D" connector to the transponder.

As the aircraft owner would that be approved for me to do as a non-complex assembly/maintenance?  I know the calibration would have to be done by my certified avionics shop personnel, but can I do the R & R of the box?  Having my avionics shop do it adds another \$200.00 to the calibration cost of $175.

Per 14 CFR 43.3(d):

  A person working under the supervision of a holder of a mechanic
  or repairman certificate may perform the maintenance, preventive
  maintenance, and alterations that his supervisor is authorized to
  perform, if the supervisor personally observes the work being done to
  the extent necessary to ensure that it is being done properly and if
  the supervisor is readily available, in person, for consultation.
  However, this paragraph does not authorize the performance of any
  inspection required by Part 91 or Part 125 of this chapter or any
  inspection performed after a major repair or alteration.

This means if you are not a mechanic yourself, you can still perform this work as long as it is supervised by someone who is authorized to perform the work. Based on your question, I assume that you actually want to perform this work yourself.  Further down in 14 CFR 43.3(g), the FARs state the type of work you can perform without supervision:

  Except for holders of a sport pilot certificate, the holder of a pilot
  certificate issued under part 61 may perform preventive maintenance on
  any aircraft owned or operated by that pilot which is not used under
  part 121, 129, or 135 of this chapter. The holder of a sport pilot
  certificate may perform preventive maintenance on an aircraft owned or
  operated by that pilot and issued a special airworthiness certificate
  in the light-sport category.

Preventive maintenance is defined in  Appendix A to 14 CFR 43, paragraph C. If a function does not appear in this list, it is not preventive maintenance, and as such must be performed by personnel authorized to perform repair work. The only item in this list that is even remotely relevant to your situation is item 31:

  Removing and replacing self-contained, front instrument panel-mounted
  navigation and communication devices that employ tray-mounted
  connectors that connect the unit when the unit is installed into the
  instrument panel, (excluding automatic flight control systems,
  transponders, and microwave frequency distance measuring equipment
  (DME)). The approved unit must be designed to be readily and
  repeatedly removed and replaced, and pertinent instructions must be
  provided. Prior to the unit's intended use, and operational check must
  be performed in accordance with the applicable sections of part 91 of
  this chapter.

Note that your situation does not appear to qualify, because the item you are replacing is not part of a self-contained, tray-mounted device.  Even if it were, you would still not be authorized to perform the work because this item specifically excludes work on transponders.

Of course, I am not an attorney nor do I perform aircraft repairs, so my interpretation is completely non-qualified. For the best answer, I would suggest contacting your local Flight Standards District Office for guidance.


What is the effect of thrust vectoring effect on the rate of turn? I just got a question after reading my old Principles of Flight book. The equation for the rate of turn is $\textrm{ROT} = 1,091 \cdot \frac{\tan(\phi)}{V}$,
with $\phi$ denoting bank angle and $V$ denoting airspeed
How would that change when the airplane is equipped with thrust vectoring like the F22 or SU35? Is there an equation for that?

The standard equation applies to any coordinated level turn (so that the G felt is "straight down" to an occupant of the aircraft, in an aircraft frame of reference). Matters not how it's all achieved - flaps, high-lift devices, helo rotor, thrust vectoring, whatever... a coordinated level turn at "this" bank will take "this" much radius. And it will have a calculable G load.
Actually achieving (and sustaining) that G load may take all sorts of interesting effects, such as thrust vectoring. But once you're there, the standard equations apply.
And, if you choose to fly an un-coordinated turn, with some amount of side-loaded G force (example, a car turning at high speed... no appreciable "bank angle" so the G force pushes you toward the outside of the turn), then all the standard assumptions are out the window. At that point, your radius would be a function of G & not bank... and it'd get uncomfortable really fast!


Does engine oil have a shelf life? Suppose that I buy a case of oil.  For some reason I stop flying and the oil sits in storage for a sufficiently long time.  After that, I decide I want to put it in my engine.

Is there a point after which (reciprocating) engine oil should no longer be used after being kept in storage?

If the answer is "Yes", what sort of time range is it?  Months, years, decades?

Engine oil in quart plastic bottles is considered to be good for 10 years unopened.

The Exxon document here lists a 10-year shelf life for each of the oil products listed when stored in unopened, undamaged quart containers between 0 and 40 degrees C (32-104 degrees F).


Why did an iPad software failure cause a return to the gate? I was amazed to read this which implies that a software failure on iPads caused departing flights to return to the gate.
I used to be an avionics engineer up until a point before the current generation of consumer electronics and now develop "field" apps for phones and tablets.  I know two things to be true.

Consumer phones and tablets of all persuasions used in field applications have nowhere near the reliability of certified avionics.  I own an iPad, amongst many
other devices, and it does not get close to six nines reliability (as do
none of my other consumer devices).  In particular, since the latest iPad updates over the last year or two, it's been quite buggy.

The hardware is not designed and built to the standards required for avionics and, without appropriate hardware, the
software cannot be to aviation standards either.

I know that these devices have been certified for use and I know why and what they are used for but I thought they were only convenience devices.  It seems that they have become part of the safety chain.
Are they MEL items?  Does anyone know what's really going on here?

iPads are used so the flight charts and manuals are electronic instead of the old phonebook that had to be printed and distributed every few months.

This means that without it the pilot has no up-to-date copy of the flight chart of the airport where he is trying to land which is a safety issue.