How does hydraulic actuator servo valve feedback work? The book Aircraft Systems uses the following diagram for a mechanically controlled hydraulic linear actuator (for moving a control surface e.g. an aileron):

The following explanation is given about its operation:

  As the pilot feeds a mechanical input to the flight control actuator, the summing link will rotate about the bottom pivot, thus applying an input to the servo valve. Hydraulic fluid will then flow into one side of the ram while exiting the opposite side resulting in movement of the ram in a direction dependent upon the direction of the pilot’s command. As the ram moves, the feedback link will rotate the summing link about the upper pivot returning the servo valve input to the null position as the commanded position is achieved.

However, I fail to understand this explanation given the diagram. If the mechanical signal is to the right, the summing link will slant to the right (i.e. /). I assume this is a command for the cylinder to move to the right. When the cylinder moves to the right, the feedback link causes the summing link to eventually return to the upright position (i.e. |). But when this position is achieved, the Servo Valve (SV) input is now more extended than it was before (the whole summing link is now upright but with a net shift to the right). How is this the null position that would cause the SV to close?

In search for an answer, I came across a better diagram which makes sense with a sliding sleeve of the SV (but this diagram is in my opinion not what the first figure illustrates):

]]

Is the first figure simply a poor explanation and the second figure is more representative of how these hydraulic linear actuators work?

The actuator in the first picture is a position follower system and only works as intended if the servo valve is closed as a consequence of the resulting piston displacement. The system in the picture works if the cylinder end is connected to the flight control surface (the left eyelet with the cross in it) and the piston end is connected to the structure frame. The key for understanding is the shift in the centre of rotation:

The servo valve is closed when the summing bar is vertical.
At first, the cylinder is stationary and the pilot deflects the stick, rotating the summing bar about the lower hinge and opening the servo valve. (Black dotted line).
While the pilot keeps the stick stationary, the cylinder moves in response of the servo valve opening. If the initial deflection was to the right, the piston moves to the right. The centre of rotation is now the top hinge (mechanical input).
When the summing bar becomes vertical again at the point where the pilot now holds the stick, the servo valve closes. (Red dotted line).

The second diagram does not show how the cylinder is attached and where the mechanical input is connceted to at the botttom. It could be a position follower system or a simple velocity output where input deflects the servo valve, oil starts to flow as long as the input is open, and the output end moves with a speed proportional to the input deflection. If the lower "First Mechanical Connection" is attached to the moving surface and the cylinder is free to move, we get a mechanical position follower again.

The mechanical feedback provided by the summing link was how the first generations of hydraulically operated systems worked. Nowadays controllers are electronic, not mechanical: a position transducer measures cylinder output, and adjusts servo valve input in response to the control laws programmed in the controller.


Is it allowed and/or safe to place objects on the dash in a PA28? I am told by my maintenance engineer that NOTHING is to be put on the dashboard area above the instrument panel - this is where I keep my DUAL GPS to have an unobstructed view of the sky. It was asserted that it could block one of the vacuum vents that are on the top of the dash.

I follow rules to the 'T' but similarly to make up rules 'on the go' is also not appropriate - I could not find a single word about this in the POH?

Can someone tell me if it's allowed and/or safe to place objects there?

Next time you go flying just stick your hand up there and see if you can feel any suction at those holes when the engine is running. I doubt it. The holes in the coaming panel (the flat panel on top of the dash) near the base of the windshield are defroster outlets.

The vacuum pump on the engine accessory case sucks air through the air driven gyros on the instrument panel through rubber hoses interconnected to the vacuum instruments (on the Cherokee there is a regulating valve/manifold between the pump and the instruments).  On the upstream side of the instruments there is an intake hose with a cylindrical filter to filter the cabin air before the pump pulls it through the gyros.

The filter is mounted in the open below the instrument panel somewhere in the jungle of wires and tubes, on a bracket of some kind.  If you slide on your back and get your head under the panel, you should be able to spot a cylinder about the size of a small can of beans with a wire mesh around it and pleats like a car air filter.  That's the vacuum system filter.

The main thing to be wary about when putting electronic devices on top the panel is they may or may not alter the wet compass when turned on.  Better to have an external antenna you can stick there and keep the GPS unit on a control wheel clip or something like that.


Why does XKCD say that autogyros will crash if the pilot reacts to a stall as in a normal airplane? This recent XKCD comic is all about autogyros.

Image is copyright XKCD, licensed under CC 2.5 BY-NC

The note at the bottom is what got my attention

  Extremely safe, unless you do the one thing you instinctively do to escape a stall in a normal airplane, in which case it will crash immediately

So what is that one thing, and why does it not work in autogyros?

That one thing is to unload the rotor too much (i.e. "push on the stick"):
From explainxkcd:

... Unfortunately, as soon as the rotor stops spinning, the whole aircraft falls like a brick and the rotor may be impossible to restart in flight. This is a situation that should be avoided at all costs.
Normally it is not a problem since the weight of the aircraft keeps the rotor spinning. However, if the weight becomes too low or even negative, the angle of attack will become negative, and the rotor will slow down and eventually stop. It can happen when the pilot "pushes on the stick" and dives.
Unfortunately, "pushing on the stick" is also how you escape a stall in a fixed wing (normal) airplane as it is a way to regain airspeed. This is actually a counter-intuitive maneuver but because a stall is an emergency, pilots are trained to do it instinctively. It can trick a pilot trained in fixed wing aircraft into doing the one thing that shouldn't be done on a gyro.


How can a modified ramjet produce static thrust without a turbine? A big selling point of the ramjet is its absence of moving parts (hence why it can be translated as "statojet" from other languages). However, an even bigger drawback is that a ramjet cannot produce static thrust, thus a ramjet-powered aircraft cannot take off by itself.

The early Leduc 0.22 and Griffon prototypes solved this by adding a coaxial turbojet. This was further refined with the Pratt & Whitney J58 turboramjet that powered the SR-71 Blackbird.

The problem is that by solving the no-static-thrust drawback, adding a turbojet negates the no-moving-parts selling point.

There are missiles that use solid fuel rockets to solve the problem, using the exhaust of the rocket to compress the air in the ramjet, which is sometimes referred as a ramrocket. However, there doesn't seem to be aircraft using this kind of engine, and missile engines have quite different constraints.

Is there an aircraft engine, working or theoretical, that works as a ramjet in cruise mode, can take off on its own power (without requiring ground installations or a detachable first stage/mothership), and doesn't have the many complicated moving parts of a turboramjet? What are its expected characteristics? If not, what are the showstoppers?

And why can't we simply inject some oxidiser (for example WFNA) to produce static thrust?

Well the Pratt & Whitney J58 engines which powered the SR-71 worked in a similar fashion, using a bypass system which allows the engine to operate as a ramjet at high speeds and a turbojet engine at lower speeds.

By the very nature of a ramjet, it relies of stagnation pressure at the intake and inlet throat to pressurize the airflow prior to combustion.  It is just not possible to achieve these kinds of stagnation pressures at speeds under Mach 2 or so.  There was an article in Air & Space magazine a while back about two enterprising Canadian teenagers who tried to fashion a homemade ramjet from iron sewer pipes to power a sled.  They couldn’t get the design to work for this reason.

As such, you would unfortunately need another type of engine to accelerate an aircraft to these fast speeds where a ramjet could work.  Turbojets work well for this application.  So do rocket boosters.  Injecting oxidizer would not be very useful here as airflow through the engine is not fast enough to ensure sustained combustion.


List of airlines and aircraft types at Copenhagen Airport (CPH) Is there a website with a list of all the airlines that fly to Copenhagen Airport (CPH), and with what aircraft types they fly to Copenhagen?

I have found a list of airlines at the website from Copenhagen Airport, but no cargo airlines are mentioned there, and also no aircraft types. I have started with that list and typing over the aircraft types from the complete fleet from Wikipedia or the website of the airline itself, and then looking at Flightradar 24 which aircraft of the fleet is actually used to fly to and from CPH, but it takes a really long time and due to summer/winter schedules I will probably miss out on some.

Or if anyone has tips for a faster (and more accurate) solution if such a list does not exist...

This can be obtained from the Eurocontrol Data, if you are a student they might allow you to acces the data:
https://ext.eurocontrol.int/

You have to request for an account there.


Is a "breakover feature" required for airliner seats? A "breakover feature" in airline seats is supposed to  assist in absorbing head impacts during a crash, when the passengers are in the brace position. However in some scenarios, most notably the forced water landing of  US Airways Flight 1549, the NTSB investigation found that the seats did not have this feature, which led to shoulder injuries in some of the passengers who were in the brace position.

My questions are:

Is it mandated by the FAA that seats in all commercial airliners
should have a breakover feature?
As a passenger, how do I know if the seats in my plane have this feature?
If the seats don't have such a feature, is it still wise to adopt the brace position in case of a crash or forced landing?

I can't speak to the regs, but my understanding of the brace was primarily to protect your head, not being as exposed to any debris, and not having very far to travel to bang against something.

As far as I understand (and I'm less sure of this), your back being in a curved position like this is better able to absorb impact/jarring than if it's vertical and you drop suddenly, or are whipped forward and backward by suddenly arresting horizontal motion.


Can pressurized aircraft be flown without pressurizing Are there any pressurized aircraft models which can also be flown without pressurizing the cabin?

For example, if there were a short ferry flight, or a flight where the aircraft never got high enough for pressurization to be necessary, is it possible to have the aircraft remain unpressurized?

Yes you simply fly with the pressurization system set to a mode that holds the outflow valve open so the air conditioning air being pumped in can't "inflate" the cabin; it all just goes overboard.  Most transport aircraft have a specific QRH procedure for "unpressurized flight", which among other things, limits the maximum altitude to 10000 ft, the altitude that most people can tolerate without any risk of becoming hypoxic.

Airlines will ferry airplanes from place to place unpressurized for maintenance.  An airliner may also be forced to descend due to a pressurization problem, and they will descend to 10000 ft and may even continue to destination at that altitude, weather permitting, as long as there aren't other problems present that dictate an immediate diversion.


Non-precision approaches for which constant descents are not approved? I noticed an interesting note -- circled in red pencil below -- on the KEEO RNAV (GPS) RWY 03 approach the other day:

Why would the FAA apparently prohibit constant-descent final approaches to this airport, given the operational benefits they provide to aircraft of many types? (While props can get away with a lot more on approach than a jet can -- diving and driving is still more workload than maintaining a constant descent.)

Probably because it's so shallow: you have 8+ NM to descend about 1100'. On a 3 degree angle, you'd typically decsend 1100' in a little over 3 miles.  I'll leave it to good folks with calculators to work out exactly what angle this would be, but it's under 1.5 degrees, so probably below whatever limit TERPS gives for depicting an angle there.

One solution would be to remain at the FAF altitude until reaching a calculated "fly-off" point, at which time you would descend at a 3 degree angle until reaching published MDA + 50', at which point you continue or go around.  But that probably takes specific FMC software & perhaps a tailored approach chart, so with only this one your option pretty much looks to be "dive" (not that far) "and drive" (quite a bit).

Though that gets you to an MDA that is 1700'+ above the TDZE...

ACTUALLY, ON FURTHER CONSIDERATION: It isn't too shallow, it's a steep path from FAF to TDZE, 3000' in 8 NM (would be 9NM at 3 degrees). And the angle to do that probably doesn't quite clear the WAGOK step-down, meaning your vertical path becomes even steeper at that point than it starts out.

So rather than publish gradient***s*** steeper than (whatever the TERPS limit is), and increasing after the step-down fix, they just say NA & let you "make it work" on your own.

I notice that there is no VDP published here, either...


What to do with excess fuel before flight? I've read that it's recommended to store a plane with full fuel tanks to prevent water contamination.  Some small general aviation planes, however, would exceed their maximum gross take off weight with full fuel and just two adult passengers of average weight.  One option, of course, is to fly with less than a full fuel tank.  This seems like it could be a problem if 50 gallons of fuel need to be dumped which cost the pilot $300.  My question is: what does a pilot do with the extra fuel that needs to be discarded before the flight?

You have a few options,

You can burn it off. Laps in the pattern are great for this. Get to the airport before you need to depart and practice some landings. This may cost you in terms of dollars but at least you are not just dumping it.

You can dump it into gas cans if you have them. Every small GA plane i have ever encountered (mostly pipers) has fuel sumps for testing your fuel during your preflight. Most of these sumps can be latched open and you can drain it into a gas can for use later. you should always test for water before doing this. If you rent you should ask the FBO what their policies are on dumping/reusing fuel. I cant find any specific legislation on it but it seems that its common practice (for the airlines at least) to only put the fuel back in the same plane (or within the same fleet) to prevent cross contamination of things that can build up in the tanks.

The sump on the pipers I fly looks like this

(source)

Dont have the plane filled up. If you rent planes like many GA pilots do and you plan to take up 4 friends for an evening sight seeing flight ask the FBO to not fill the tanks if someone is using it before you.

Dont use all the tanks. This will vary plane to plane but some planes have 2 or more fuel tanks which may be independently selectable. You may be able to (weight and balance permitting) keep some of the tanks dry if you know you regularly short hops with big loads.

For the sake of a complete answer I will mention that planes can be flown over gross weight, I don't advocate this nor would I ever attempt it but it does happen here and there, here is a discussion on it if you are curious.


When to go missed on a non-precision approach? I am training to get my instrument rating and I have come across a confusing point.   I understand that, when flying a precision approach, you go missed upon reaching the decision height for that approach if visual reference to the runway environment is insufficient to complete the landing.   I also understand that on a non precision approach you will descend to the minimum decision altitude for that approach and then fly at that altitude until you reach the missed approach point, after which you will go missed.   My question is, how do you know when you've reached the missed approach point on a non-precision approach?

These three charts in particular confuse me:

In this approach, which has an option for either an ILS (precision) or LOC/DME (non-precision) approach, the beginning of the dotted line which signifies the missed approach path does not have any DME value or intersection information.   There is an intersection after it at 7.5 DME.   Which of these two points would be the missed approach point for the LOC/DME approach?   How would you know when you reached the MAP if it is where the dotted line begins?

(Click to view)

In this approach the dotted line which signifies the missed approach path seems to begin at the runway threshold.   If this were the MAP, (with no localizer) would you have to start a timer after you cross KOLLI intersection to know you have gone 2.4nm and thus are over the runway threshold?   Is the MAP actually at the beginning of the runway as it seems?   Are there any ways of knowing you are at the MAP without a stopwatch?

(Click to view)

Finally, this IAP is similar to the first.   Unlike the first though, there is no DME intersection after or near the beginning of the dotted missed approach line.   Is the MAP for the localizer approach here just at the beginning of the runway as it seems to be in the second approach?   Again, would you have to use a stopwatch or are there any other ways?

(Click to view)

Non precision MAP fixes are identified in a number of ways:

Fixes identified by additional terrestrial Navaids eg intersections between the localizer and radial directions from other Navaid beacons like VORs, NDBs, etc..
Fixes identified by DME slant ranges.
Fixes identified by flying a linear course from an identified FAF at a specific airspeed for a specific time.
Fixes identified by area navigation systems.
Fixes identified by specific GNSS waypoints (RNAV GPS).

For the ILS or LOC/DME rwy 5 KCGZ, when flying the LOC/DME, Your MAP is on localizer at MDA at 7.5 NM DME from the Stanfield (TFD) VORTAC.  There is no other means using the equipment required to fly this approach procedure to identify the MAP.

For the LOC rwy 22 into KCDW, your MAP is on localizer at or above MDA when you cross the threshold of rwy 22.  Flying the approach at the correct category airspeed, you can also time it using the table in the lower left corner of the plate.  But the plate clearly says that the MAP is 5.4 NM from the FAF.

For the ILS or LOC 1 into KILG, the LOC rwy 1 MAP is again on localizer at MDA when the aircraft crosses the threshold of rwy 1.  This is defined by the approach timetable on the lower right of the plate.


Do stunt jets use laser distance meters to align with one another to maintain formations? My question is about Jets/planes performing acrobatic formations to stay well-aligned with the other jets/planes in formation. I could see a laser-distance meter coming in handy.

No they don't. They rely on visual cues. Basically each pilot aligns features. For example, it could be the wingtip of the plane next to him/her to a letter or feature on another plane.

(YouTube) POV; the drawn circle is merely an illustration.

And they all follow the lead's commands via radio. As when to turn, when to pull, for how long (based on the tone of the voice), etc.

As a team gains experience, they start to bring the distance closer. Not usually noticeable by the crowd.

Source: Blue Angels: A Year in the Life


Are there specific engine TBO requirements for aircraft used in flight instruction? If I own a plane, say a Piper arrow, and I want to charge 175/hr for the aircraft and 50/hr for instruction, is there any regulation on when to perform engine overhauls (TBO)?
askacfi.com and avweb.com indicate no TBO requirements.
However, 14 CFR Subchapter G - Air Carriers and Operators for Compensation or Hire: Certification and Operations may indicate I do.
What specific regulations show what is or is not required?

§91.409   Inspections. (b) Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person
(other than a crewmember) for hire, and no person may give flight
instruction for hire in an aircraft which that person provides,
unless within the preceding 100 hours of time in service the aircraft
has received an annual or 100-hour inspection…

You can rent out your airplane without complying with 100 hour inspections provided that you don’t provide both the pilot and the airplane. Insurance will be a lot more, probably 3-4 times as much. If you are renting it out you might have more than 100 hours in a year so you need to make sure you  comply with 100 hour ADs.
I do it with my Cherokee from time to time when I know people who want to learn to fly. The students can use any CFI they want and pay them separately from renting. Depending on how many people want to learn, I have an open pilot policy with only some CFIs and me as named insureds or if there are only a few students, everyone is a named insured.
Edit: The only maintenance requirement for Part 91 operators is 91.409 discussed above. TBO is not specifically mentioned in the FARs so you won’t find a rule saying that you don’t have to comply with manufacturer’s TBOs. I have a folder of 116 Legal Interpretations and NTSB opinions. A search of them finds no mentions of TBOs.
As you point out there are lots of articles that mention it. I'd trust them. This AVWebarticle by maintenance guru Mike Busch says,

Both Lycoming and TCM publish engine TBOs in the form of non-mandatory
service bulletins. Some Part 121/135 operators have Operations
Specifications that require them to comply with all manufacturer’s
service bulletins (even non-mandatory ones), while others have Op
Specs that require compliance only with mandatory service bulletins.


Do transoceanic airliners monitor marine VHF emergency frequencies? I know that modern jetliners often have a multitude of radio equipment on board, including VHF, HF, satellite, etc.

From what I've read (such as here), it's customary for jetliners to monitor 121.5 MHz for aircraft emergency traffic.

Do commercial airliners traveling transoceanic routes also monitor marine VHF channel 16 (156.8 MHz), a common frequency used by ships in distress?

If so, is this a fairly customary, routine matter (like monitoring 121.5 MHz) or is it simply up to the crew of each aircraft?

156.8 MHz

Crews don't listen to channel 16 of the marine band.

Channel 16 is used by marine with FM, while a VHF aviation receiver demodulates only AM, and the upper limit of the VHF band for aviation is 137 MHz.

Channel 16 is monitored by local marine agencies -- coast guards -- e.g. CROSS in France and USCG in the US.

Aircraft are only required to carry an equipment able to receive and transmit on emergency frequencies used by aviation.

Emergency frequencies other than channel 16 are also used in marine, including 121.5 MHz, e.g. by EPIRBs. The use of 121.5 MHz for marine EPIRBs was to allow monitoring by aircraft.

Air regulation for listening 121.5 MHz

EPIRBs monitoring by aircraft is not relevant any more as EPIRBs are now efficiently monitored by satellite (COSPAS-SARSAT). However 121.5 MHz is still monitored ("guarded") by aircraft, in particular for interception response purposes. The requirement is specified in ICAO Annex 10 (volume II) to the Chicago Convention:

  5.2.2.1.1.1 Aircraft on long over-water flights, or on flights over designated areas over which the carriage of an emergency locator
  transmitter (ELT) is required, shall

  continuously guard the VHF emergency frequency 121.5 MHz , except for those periods when aircraft are carrying out communications on
  other VHF channels or when airborne equipment limitations or cockpit
  duties do not permit simultaneous guarding of two channels.

  5.2.2.1.1.2 Aircraft shall continuously guard the VHF emergency frequency 121.5 MHz in areas or over routes where the possibility of
  interception of aircraft or other hazardous situations exist, and a
  requirement has been established by the appropriate authority.

  5.2.2.1.3 Aeronautical stations shall maintain a continuous listening watch on VHF emergency channel 121.5 MHz during the hours of
  service of the units at which it is installed.

ICAO standard and recommended practices ("SARPs") for international aviation activity are recommendations, but they are generally implemented in the national regulations by the member states.

406 MHz

121.5 MHz is being replaced by 406 MHz, as this is the frequency of the COSPAS-SARSAT organization. This organization provides a permanent monitoring worldwide through the use of polar orbit satellites augmented by geostationary satellite relays.


Why is a special certification needed to land at Paro Airport? Why is Paro Airport (currently the only international airport of Bhutan) considered one of the most dangerous airports to land in the world?

Is it because of the mountains? In my opinion, Princess Juliana International Airport is also as challenging as Paro.

Why do the pilots need a special certification to land there?
How do they achieve this certificate?

The approach to Paro is unbelievably complicated. It is flown visually through a valley with high mountains all around and no sight of the airport until the last moment. Here is a cut of a map with the approach paths:

Approach to runway 15, marked in red, is worse in this regard. The ridge is rather close to the airport, so the final turn usually ends over the runway threshold. The wings get level with 30–50 ft (10–15 m) remaining only (here's a video). The approach to runway 33, marked in blue, allows a bit more of a straight final, but not by much. In either case the aircraft must emerge from the turn with correct altitude, speed and rate of descent. So the pilot has to know landmarks in the valley and how to judge correct approach profile by them. The approaches also often involve turning around higher in the valleys which again must be done by landmarks at places where it is known to be possible. It is this knowledge pilots have to demonstrate before they can attempt the approach (as pilots in command).

There are other airports where pilots have to receive special training to be permitted to fly there, for example the Samedan Airport near St. Moritz in Switzerland, which is similar mix of high altitude, high mountains around and visual approach, though it's still a lot easier as the airport is visible from much greater distance.

There is however nothing similarly difficult on Princess Juliana Airport. It appears approaches to Princess Juliana are only flown to runway 10 and these are over flat sea and flat beach. The runway is visible from great distance and the approach is straight. The featureless water makes it slightly harder to judge height than solid ground, but that's what the approach lights (VASI/PAPI) and distance-altitude table are for (there is no ILS at TNCM, only VOR-DME). And there are many airports with approach over water, so it's nothing unusual for the pilots. If there was approach to runway 28, it would have to be off-axis to avoid the hills on the island, but it does not appear to be used at all.

The pilot, Marek Tůma, who ferried in and for first 3 months commanded the ATR-42-500 A5-RGH, wrote a 4-part report (2, 3, 4; unfortunately in Czech) about flying in Bhutan.

According to that the training involved:

Couple of hours on simulator (in Bangkok).
Then they were permitted to ferry the plane to Paro.
Flight as observers with the training captain who showed them all the relevant landmarks in reality.
Some practice circuits.

They couldn't fly with the training captain in the other seat, because they were ATR-42 pilots and the training captain flies A320-family (and possibly still has rating for the older BAe146, but not ATR-42).

He also wrote that while on early flights when temperatures are still low the performance is good, later in the day it becomes marginal and they often needed to follow the valley quite far before they managed to climb above the mountains. Careful planning and weight and balance calculation was always necessary.


Has anyone burned hydrogen in a gas turbine? I am just wondering if supplying compressed hydrogen to a gas turbine (combustor) would be a better fuel as it has three times the octane rating of kerosene. It just seems better all around.

Yes, indeed the plan to build a hydrogen-powered jet laid the groundwork for using hydrogen in the Centaur rockets and the upper stages of the Saturn 5. While hydrogen was used only experimentally in test rigs, the Soviet Union built a derivative of a regular airliner, the Tupolev 155, for testing hydrogen and natural gas in flight.

EDIT: NACA also did in-flight testing. Please see @jayhendren's answer for details.

So yes, the Tu-155 was indeed flown on several occasions with one hydrogen-powered turbofan. While the left and center engine remained NK-8s, the right engine was replaced by a NK-88 which was adapted for LNG and hydrogen. Other projects like one for a hydrogen-powered supersonic airliner sadly ended with the Soviet Union itself.

Tu-155 Cutaway view (picture source)

Hydrogen is also the prime propellant in hypersonic ramjets, but those are not turbines.

Hydrogen has a wide mixing ratio with air where it will burn. Also, being gaseous, it mixes much more quickly with air, so the combustion chamber can be small. When a converted J-57 was experimentally run on hydrogen in 1957,

  The test engineers were agreeably surprised by the ease of engine operation. They ran it at full power and throttled back so far that the air fan was revolving so slowly the individual blades could be counted. Under this latter condition, the throttle could be opened and the engine would quickly and smoothly accelerate to full power. They found that the temperature distribution was good and there were no major problems.

But Niels is correct - its low density makes hydrogen problematic. As Alexis W. Lemmon, Jr., reported in May 1945 in his report on possible jet fuels (from history.nasa.gov):

  "Although the liquid hydrogen-liquid oxygen system has by far the highest specific impulse performance of any system considered in this report, the low average density of the fuel components almost completely eliminates this system from all but very minor applications."


Are Boeing 737-800s grounded? I’m flying on a WestJet Boeing 737-800 from Honolulu to Vancouver and then on to Toronto in July, returning on the same type of aircraft in August. Are these aircraft still grounded and are they similar to the MAX 8?

The 737-800 is not grounded (and never has been). The aircraft type has an excellent safety record. Since 1997 over 5000 have been produced.

The 737 MAX 8 is its successor. The aircraft is very similar to the 737-800. One of the differences is the placement (more forward and higher) of the slightly bigger engines. This changed the stability of the aircraft under certain flight conditions, causing Boeing to introduce the Maneuvering Characteristics Augmentation System (MCAS). The MCAS played a crucial role in two recent crashes of the 737 MAX 8, leading to the grounding of the aircraft type.

The 737-800 does not have such a system and is therefore not affected.

Airlines typically use IATA aircraft codes (3 letters) or ICAO aircraft type designators (4 letters) to indicate the aircraft type used on the flights.

For the Boeing 737-800 the ICAO type designator is B738, while the IATA codes are 738 and 73H.

The Boeing 737 MAX 8 has the ICAO type designator B38M and IATA code 7M8.


Is an A&P certificate ever required to work on military aircraft? Are military aviation mechanics - including civilian contractors - ever required to obtain an A&P certificate to work on active military aircraft?

Not usually, A&P is an FAA regulation/certification, and the US Military is not required to abide by FAA regulations. Even military pilots don't (always) have pilots licenses (not FAA ones).

It is possible though that they may ask a civilian contractor to have an A&P, but this would be on a contract-by-contract basis. The US Military does operate a number of civilian-type aircraft that they may have serviced.


How long are modern variants of the F-16 expected to be in production? The F-16 seems to keep receiving updates and new aircraft appear to still be in production, e.g. the F-16I and F-16Q. It seems there are also several upgrades being developed and installed, such as radar (AESA) and radar detection warning systems.

Has any authority on the subject attempted to estimate how long the F-16 is expected to be in production? Is there any estimated limit on for how long a budget fourth generation airframe can be used as the basis of a modern combat aircraft?

I'm not looking for speculation from StackExchange users but rather a reference to a statement made by one or several external authority -- to avoid making this question opinion based. Some sensible original reasoning is only a bonus as far as I'm concerned.

I can only imagine myself that countries that keep buying F-16s do so for budget reasons -- however, there must also be some real value in buying F-16s in 2019, since these are after all large sums of money even if it is bleak in comparison to e.g. F-35s or F-22s.

An article last month in the Greenville News about the relocation of the F-16 production line provided this comment:

  The Trump administration fast-tracked a $1 billion F-16 deal with
  Bahrain, Navarro said. Deals closed or on the verge of closing since
  then guarantee the plant in Greenville will stay busy at least through
  2025 and likely much longer, he said.

The "likely much longer" will be based on future sales (and Government approval of those sales.) It's a good plane at a competitive price, but a change in the marketplace could mean it ends after this contract build.


How does the automatic battery cut off logic prevent complete battery discharge on ground in the A320? I was reading in the electrical systems of the a320 FCOM and in one of the notes it stated that the batteries have an automatic cutoff logic which prevents them from getting completely discharged when on the ground. (Parking)

But how does this logic exactly work? As the batteries are permanently connected to the hot bus in which they will continue to discharge

According to this page: http://theflyingengineer.com/projects/airbus-tech/electrical/

A Battery Automatic cut-off logic prevents the batteries from discharging completely when the aircraft is on the groung [sic] (Parking).
Automatic battery contactors open when :

The a/c is on the gorund [sic].
The BAT P/b s/w’s are at AUTO
The main power supply (EXT PWR+GEN) is cut off
Battery Voltage is low.

Nothing should automatically disconnect the batteries from the corresponding HOT BUS, so if something is left on the HOT BUS it would continue to drain the battery.


What is this tab above the DC-10's #2 engine? What is this big rectangular tab (?) thingy extending backwards just above the DC-10's #2 engine? What does it do?

(wikimedia.org, picture modified to point out the tab thingy)

(airliners.net via szextant.blogspot.com)

It mostly houses the same stuff that's on an underwing engine pylon: bleed air ducts, wiring, fuel and hydraulic hoses and tubes that connect to the engine core and accessories. The aft part of the structure where it tapers is just there out of aerodynamic necessity.


During a turn, will slip necessarily lead to altitude lost? During aircraft turns, will slip necessarily lead to altitude lost?
During aircraft turns, will skid necessarily lead to altitude gain?

Think of a slip or skid that the aircraft is flying sideways (referred to as uncoordinated).  This does increase drag, and therefore it requires either more power, or given sufficient speed, increased pitch to maintain altitude compared to flying straight through the air in coordinated flight.

A "skid" is when the aircraft nose is pointed inside a turn where the pilot feels centrifugal force outside the turn, like in a skidding car.  In a slip, the nose is pointed outside the turn whereby the pilot feels a force of falling down into the turn.  In straight flight, whether the nose is pointed left or right, uncoordinated flight is called a slip either way: a forward slip for losing altitude, and a side slip for landing.


What is the estimate for total number of flight hours in the world? Working on a type of estimate model for aviation and was wondering if there was an approximate total number of flight hours in a year across the industry as a whole?

Edit: Counting only Commercial Flights

In 2018 there were about 37.8 million commercial flights. If we multiply this number with the overall average flight duration, we get the answer. Unfortunately I could not find a result for this directly.

We can however calculate it from the data provided by the MIT Airline Data Project. The data says there were 3,954 aircraft available on average in 2018 that accumulated a combined 13,398,545 flight hours with 3.82 departures per aircraft per day on average. This means the average flight duration was

$$ d = \frac{13\,398\,545 \, \mathrm{h}}{3954 \times 365 \times 3.82} \approx 2.43 \, \mathrm{h} $$

This is just based on various US carriers, so the world average might be somewhat different, but since US carriers fly a wide variety of flights from short domestic routes to ultra-long haul international routes, I assume this number to be close to the true answer.

The resulting total number of flight hours is then

$$ 37.8 \cdot 10^{6} \times d \approx \mathbf{91.8 \cdot 10^6 \, h} $$

This does not yet include GA traffic or military flights.


Does the MD-80 seat layout affect the balance of the aircraft? The MD-80 family has a 2-3 seat layout as seen in this image:

Does the layout have any influence on the balance of the aircraft and if so what is used to balance out the weight?

Image from seatguru.com

The "D" seat is very near the aircraft centerline, and thus the roll axis. Since roll moment is the distance from the roll axis times weight, if the distance is small, the roll moment is very small. What roll moment is created can easily be canceled by a little bit of aileron trim if needed.

The water tank on MD-80s is also placed on the LH side of the cargo. Full this is about 350 lbs, further from the centerline than the "D" seats. Also the LH side has an extra service door in the aft and the front LH door is larger than the R1 door, although the RH side also has the cargo doors.


How many fuel pumps does a Katana DA20 have? How many fuel pumps does a Diamond DA20 have? And since the fuel pump sends fuel to the engine, if you turn it off after the takeoff as the check list says, how will the fuel reach the engine?

There are 2 fuel pumps on the Diamond DA20. One is electric and is controlled by the pilot and one is mechanically driven by the engine and is constantly running while the engine is running.

After take off, you switch the electric one off and the mechanical one keeps supplying the engine with fuel.


Can someone identify the Make and Model of airplane that this fuselage belonged to? This gutted fuselage remnant was photographed by my mother at Whaler's Bay on Deception Island in Antarctica in 1994.  Deception Island is directly south of the Falkland Islands in the narrow area between South America and Antarctica.  Where the wing attached to the fuselage there is grey hand-printed writing that appears to be: 3G9SAY.  Below the windows, also in grey printing are three lines of faded print.  The first line appears to be something like: ESTACION JERASSIEN.  The second line appears to be: BARDA HARE. And the third line appears to be: AGRVFACIAL PIORK.  But I stress that I'm doing a lot of guessing at these letters so interpret them loosely.  Thank you for your assistance in identifying this aircraft.

That looks like the remains of a De Havilland DHC-3 Otter
It used to wear the registration VP-FAK.

British Antarctic Survey (BAS) and the de Havilland Aircraft Heritage Centre at Salisbury Hall, London Colney have agreed on a long term loan for BAS DHC-3 Otter VP-FAK.  This historic artefact was recovered from Deception Island, Antarctica in April 2004 where it had lain for nearly 40 years since the aircraft was grounded due to structural problems.
De Havilland Canada Otter VP-FAK c/n 294 made its maiden flight in
Canada on 17 October, 1959.  It was shipped to Deception Island
arriving on 26 January 1960 before assembly and flying on 3 February.
The aircraft was flown by aircrew seconded from the RAF to BAS when it
carried the identity 294 with RAF roundels.  Flying conditions in the
Antarctic are very demanding and the aircraft was damaged a number of
times, the last time at Adelaide, making its last flight from there to
Deception Island on 7 March 1967.  Following an inspection it was
grounded due to structural problems, having flown 981.30 hours and
made 853 landings.  The aircraft was stored outside at Deception
Island in a dismantled state until recovery to Rothera ready for
shipping to Britain, where it arrived at Grimsby on 8 May 2005.

More information here


Which one has a higher success rate between Infrared homing and Radar homing missiles, for air to air combat? I know Infrared missiles don't work on long ranges, so I will keep my question limited to short ranges only, in which both missiles can work.

In such short ranges, which guidance system has more chances of success/kill in an air to air combat? Infrared homing or Radar homing?

If one can also lump in Active radar homing and Passive radar homing in his/her answer, that will be an added bonus. Thanks!

This topic is very broad, and there is copious material available on it. Therefore, this answer will be generalized.

IR targeting is very useful against jet engine aircraft, because there is a clearly defined thermal contrast in the thermal output of the engines. At close range it is low cost and low complexity compared to a passive radar targeting system. It is essentially, a point and shoot.

Passive radar targeting utilizes a more powerful, larger antenna on the deploying aircraft, and relies on the more powerful illumination which the targeting aircraft is capable of. If the illuminating transmitter is in the front of the deploying aircraft, then the aircraft's attitude must be maintained to continue to illuminate the target until strike.  This exposes the deploying aircraft to increased risk, and is avoided in close quarters.

Active radar targeting requires more on the missile electronics, but can work better in a point and shoot environment, and does not require the deploying aircraft to continue illumination of the target, allowing evasive maneuvers and pursuit of other threats.

The trade space between targeting methodologies is great and is dependent upon situational conditions. For example, at a long range, a passive radar targeting method can provide increased target strike assurance, and lowers the SWAP (size, weight and power) of the targeting package in the missile.

At close range, IR homing is often selected because it works well on close targets, has the best SWAP, allowing more weight for ordinance and motor.

All targeting systems have their disadvantages.  For example, while IR is very effective against jet engines, having the sun, or even glint can foil them, as can IR flares. Shooting against a ground target may not be as effective with an IR seeker, but it is done.  A passive radar seeker can be more effective against countermeasures, particularly when multi-static radar is employed.  In that case, several transmitters illuminate the target, from different aspects, and the passive receiver in the targeting unit can eliminate most countermeasures.

In the world of countermeasures, there are similarities. For example, IR Chaff is about as effective as RF Chaff, and does a good job at breaking target lock and inhibiting target acquisition.

Getting back to active radar, the SWAP is greatest for this targeting system, but it has the ability to act autonomously, similar to IR targeting. Antenna diameter is a limiting factor for good SN ratios. But this strategy is good for point and shoot, and works well at closer ranges.

With respect to kill rates, that is highly dependent upon the type of target and we haven't narrowed the discussion to aircraft vs ship vs vehicle, which influence the choice due to background radiation, reflections, etc.

The question is extremely broad, and coverage of the broad topic with multiple questions in this venue is limited.


Is there a commonly recognized placeholder airline name? I'm wondering if there is a common placeholder name for an airline, either implying a legally disclosed or fictional entity, which is frequently used?

For instance, I've seen the terms containing 'widgets' used very often in an economics context. John Doe is often used in legal cases.

*"Placeholder names are words that can refer to objects or people whose names are temporarily forgotten, irrelevant, or unknown in the context in which they are being discussed." -Wikipedia

I think Oceanic Airlines is well known fictive airline. It is used widely in Lost and also Alias, Castle, JAG, Category 6: Day of Destruction and in Executive Decision (the material from this movie was reused in a lot of low budget movies).


Where are the seaport conventions for VFR charts explained? VRF charts contain information about seaports. For example, 00 - 50 in the formation block for HNL seems to be for a waterway:

Another example is 23W for 1C9:

Where are these conventions explained? I can't seem to find them in the Legend or User Guide.

"00 - 50" means a landing surface at 00 feet MSL, unlighted, and 5000 feet (nominal, 4970-5069 actual) long.
At aerodromes with both land and water surfaces, it is customary to suffix the water ones with "W" (pronounced Water, not Whiskey) to avoid confusion.


Is this glider stable? In level flight all forces must be in balance,that mean center of overall pressure(lift) is in line with C.G.

Disturbance comes  in such way that shift C.P. back.

Is this glider stable?
If I use aircraft stability definition,glider is not stable ,because neutral point is in front of C.G.
(for me glider is  stable,because lift in reality act in CP,so lift make counter clock wise torque about C.G., this plane will put  nose down.better to consider pitch moments for every AoA with corresponding  position of center of pressure..)
I dont understand why proffesor draw lift at A.C., if lift act at C.P. ?

Typical Designs
You're starting out from a fairly mistaken idea of how things normally work. In particular, you're showing the horizontal stabilizer lifting upwards.
At least in most normal designs, the horizontal stabilizer does not lift upward at all. In fact, it's normally flying at a negative angle of attack, so its "lift" is actually pushing downward on the tail.
We normally start by looking at the center of lift (CP) of the wing by itself. That'll typically be somewhere around 40-45% of mean aerodynamic chord (MAC).
The CG is at least somewhat forward of that (25% of MAC is a pretty common starting point).
Then you trim the downward lift from the horizontal stabilizer to maintain level flight. The CP acts as basically the fulcrum point. We put the horizontal stabilizer at the end of a long tail to give it a lot of "leverage", so it doesn't have to generate much downward pressure to maintain level flight.
This is what gives static stability. If you stall the wing, it will lose lift. As the wing loses lift, the CG being so far forward will cause the aircraft to pitch nose down. That, in turn, will (at least normally) reduce the wing's angle of attack, so it will recover from the stall.
If the CG were arranged where you've shown it, behind the CP, you wouldn't get that automatic stall recovery--if the wing or (especially) the horizontal stabilizer stalled, the CG would be far enough back that the aircraft would tend to pitch nose up, increasing the angle of attack, stalling the airfoil even more deeply (a "deep stall", which is usually unrecoverable).
Alternative Designs
Although it's fairly unusual, you could do a design where you kept the CG somewhat behind the CP, but loaded the wing more heavily than the horizontal stabilizer. In this case, both the wing and the stabilizer would be lifting upwards, but since the wing is more heavily loaded, at higher angles of attack, the wing would stall before the stabilizer, and when that happened, the nose would drop.
To achieve the front wing being more heavily loaded than the rear, you typically end up having to shrink the front wing, and (to maintain overall lift) expand the rear wing. And that gives a canard design, such as the Rutan Vari-EZ and Long-EZ, and the Quickie Q2. Thanks to their use of canards, the Rutan designs are extremely stall resistant. The Quickie claimed to be completely stall proof (and as far as I know, that was accurate).


What is this small number on the top right of an IAP? I've looked in the instrument procedures handbook, and I cannot locate a reference for what this 5-digit number on the top right above the approach name is.

What is this number, and what does it mean?

It is the year followed by the day of the year of the last ammendment to the chart. If there have been no changes to the chart since it was first issued, this space is blank. In this case the chart was revised on the 171st day of 2019. If you look at the bottom left hand portion of the chart, the date shows the last time the procedure was revised e.g.—17AUG17. Apparently there were changes to the chart (obstacles,  name of the airport, typos in the notes, etc.) that did not affect the procedure, so the dates are different.

Refer to the Aviation Chart User’s Guide.

  The Date of Latest Revision is shown on the top margin above the
  procedure title. The Date of Latest Revision identifies the Julian
  date the chart was last revised for any reason. The first two digits
  indicate the year, the last three digits indicate the day of the year
  (001 to 365/6).

  The FAA Procedure Amendment Number, located on the left bottom margin
  below the City, State, represents the most current amendment of a
  given procedure. The Procedure Amendment Effective Date represents the
  AIRAC cycle date on which the procedure amendment was incorporated
  into the chart. Updates to the amendment number and effective date
  represent procedural/criteria revisions to the charted procedure,
  e.g., course, fix, altitude, minima, etc.


Why is "runway behind you" useless? I was recently answering this question and for some reason it made me think of this fairly famous aviation saying

  The three most useless things to a pilot are the altitude above you, runway behind you and fuel on the ground

Now, I get altitude above you - you may as well use some of it lest you meet a mountain. I also get fuel on the ground - if in any doubt fuel up before you go.

But I'm not sure I understand why "runway behind you" is useless in this context

Could someone explain?

The runway ahead of you is useful to accelerate and - if needed - to decelerate.

If you enter (or touch down) the runway in the middle, you will not be able to benefit from the part of the runway behind your entering point. It is the same as if that part would not exist. Therefore it is useless.


Why don't all commercial aircraft transmit GPS data in real time? It seems strange that trucks and taxis can be set up to transmit GPS data in real time but aircraft cannot.  Wouldn't this be a useful function and feasible to implement?

Most commercial aircraft transmit their GPS-based position twice per second. This is part of their Automatic Dependent Surveillance – Broadcast (ADS–B) broadcasts. The problem with providing world-wide receiver coverage for this system is that the frequency it uses only travels line via line of sight, so it won't travel past the horizon.

Providing coverage over large bodies of water would require a network of buoys, which would be quite expensive.

Another possibility is to put ADS-B receivers on satellites. This concept has been developed by (Aireon) on the Iridium Next satellite constellation. The system (66 satellites + 9 spares) became operational in 2019 and provides global coverage.


What are some common factors that affect GA aircraft manufacturability? Recently, we've seen Icon go through layoffs due to production delays related to "Manufacturability". I assume this is due to their wing structure in part, but I'm curious, in general, how a company goes about designing with manufacturability in mind.

This answer can only scratch the surface - a good answer would take you several days to read.

Manufacturability is the combination of several things which combine to

improve the repeatability of the finished products without much individual reworking, and
reduce the work hours required to produce a given component or system

under the local conditions (wage level, worker skills, energy prices, logistics etc.). This list of factors is incomplete but should give you an idea what is involved.

This is done by selecting the proper techniques (lots of jigs and molds for repeatability, the fewest amounts of parts and joints for reducing man hours) and by designing the system such that producing the components and combining them into the finished product can be done quickly and with the available workforce.

An example: When Fairchild joined up with Dornier, they planned to relocate the production of the Do-328 from Bavaria to Arizona. The production line in Germany was set up for the local workforce, and since they were highly skilled metal workers, the holes they drilled manually were straight within ±2°. In the USA, however, Fairchild could not find enough adequately trained workers, so the production line would had needed jigs for every single hand-drilled hole - and there were lots of them on the 328. The whole endeavor floundered because the production line was not designed for manufacturability under the new local conditions, and remedying this would had cost too much.

Another example would be the Tu-4. This was a Russian copy of the Boeing B-29, which the Russians had ample time to study after some landed in Eastern Siberia after attacks on Japan. But it was no cheap knock-off: The Tupolev design bureau redid the design, airframe, engines, systems and all, in metric dimensions, so standard Russian gage sizes, fasteners and tools could be used. It was re-designed for manufacturing, in other words.


Are these logged time assumptions correct for commercial checkride applicants? If an applicant is an ASEL private pilot without an instrument rating, are these assumptions correct?

Multi-engine dual time can be used to satisfy the 10 hours complex time requirement
Cross-country time flown as a solo student pilot can be used to satisfy some of the 50 hours total cross-country required, including the long (300 mile) cross-country flight
Cross-country time flown as multi-engine instruction cannot be used as cross-country PIC because the pilot was not rated in category and class

Your question is slightly unclear, but I'm assuming the following:

You're asking about the US/FAA Part 61 requirements
The candidate is planning to take the CSEL checkride
The candidate holds a private ASEL certificate, without an instrument rating
The candidate has received some MEL training (you didn't say how much), but isn't yet rated for MEL

In that case, the answers are:

61.129(a)(3)(ii) requires 10hrs of instruction in a complex or turbine aircraft, but it doesn't say how many engines the aircraft has to have or what the training has to include. So using time from general MEL training is fine.
The FAA has said that 'double-dipping' time from private to commercial is not allowed, therefore flight time as a solo student cannot count towards the commercial certificate (Theriault (2010) interpretation).
If the pilot was receiving instruction in an aircraft that they weren't rated for then there's no way for them to log PIC time because none of the scenarios in 61.51(e) for logging PIC time apply. As you said, logging PIC as sole manipulator of the controls also requires you to be rated in the aircraft.

(This question is related.)


Is Naproxen (medication) approved for flight? Is Naproxen an approved FAA medication? I have found 2 separate websites which comment on this type of medication that seem to be somewhat ambiguous, at least to the degree that I'm looking for.

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/pharm/dni_dnf/
https://www.leftseat.com/medcat1.htm

Is there a singular location to find out if a medication is approved or not approved? Specifically I'm looking for Naproxen.

There's no fully authoritative source for this information, other than consulting an AME directly. AOPA's medication database is considered pretty reliable (and it says Naproxen is allowed) but their generic disclaimer explains why you can't just look up a medication in a list:

  Although these medications are generally allowed by the FAA for flight
  duties, there are variables with each individual's situation that
  could render a particular medication inappropriate for flying because
  of case history or adverse side effects. Some medications are being
  used "off label". This means that a drug is prescribed for symptoms
  that do not fall within the FDA's approval guidelines for that drug.
  This is just one example of why the FAA might not approve a drug that
  is on the list.

In other words, as with all medical questions you have to consult a  professional to get the right answer for your personal situation.


What units are used for the horizontal grid lines on a sectional? On a standard 1:500,000 aviation sectional chart, the map is broken down into quadrangle "sections" with a maximum elevation figure printed in blue in the center.

Using a chart-plotter I can see that the vertical (north-south) grid lines printed on the chart are in units of nautical miles.  Each quadrangle is 30 nautical miles vertically, and roughly 20.5 nautical miles wide (west-east).

What's confusing me is that the scale printed on the horizontal portion of the quadrangle section doesn't appear to be in nautical miles, statute miles, or even kilometers.  What does the horizontal scale represent?  Is there a unit associated with the horizontal grid?

One tick mark along a horizontal grid line on a sectional chart denotes one minute of longitude. At the equator (but nowhere else), this is also equal to one nautical mile.  The further from the equator, the less the distance that is spanned by one minute of longitude.

One tick mark along a vertical grid line on a sectional chart denotes one minute of latitude, which is also equal to one nautical mile, anywhere on the earth's surface.

(The above comments assume a perfectly spherical earth.  Therefore they are not completely accurate, but they are close enough for nearly all aviation purposes.)

It is important to understand that at any given point on a sectional chart-- in fact, at ALL points on a sectional chart-- horizontal and vertical distances are portrayed at the same constant scale.  If you want to measure a given horizontal (or diagonal) distance in nautical miles, you can mark it off on a piece of paper and then hold it against the tick marks on a vertical grid line to get the distance in nautical miles.  Or you can just use a chart plotter.

For larger-area charts, it is necessary to vary the horizontal and vertical scales, to accomodate the curvature of the earth.


What is the vertical speed limit when altitude mode is engaged? This question applies to Airbus' autopilot but may not be restricted to just this manufacturer (there must be equivalent modes on ATR, Embraer, Dassault Falcons, etc.)

For the vertical plan, the autopilot offers different modes. Among those, there are V/S where it tries to keep the selected vertical speed, and Alt, where it tries to keep the selected altitude.

When in Alt mode, if the aircraft is not at the required altitude, then the autopilot commands a vertical manoeuvre to reach the desired altitude. My question is: during this manoeuvre, is the vertical speed limited and if is this limit configurable in flight by the pilots? (If not, I imagine it is limited to what can be achieved in open climb or open descent modes.)

EDIT: The question comes from the hypothetical situation where aircraft is flying towards a target altitude and the pilots want to limit the vertical speed for any reason (e.g. a better vertical separation with another traffic)

What you are describing is the managed climb mode of the Airbus, where the Flight Management Computer (FMC) determines the optimum climb speed and the autoflight system will then pitch to maintain this speed.

From the A320 FCOM (Autoflight - AP/FD Vertical Modes):

  Climb Mode (CLB)

  CLB mode guides the aircraft in a managed climb, at either a managed or a selected target speed, to an FCU selected altitude, taking into account altitude constraints at waypoints. The system also considers speed constraints if the target speed is managed. [...]

  The pilot can arm the CLB mode during the takeoff, go around, climb and cruise phases and engage it during the climb and cruise phases.

The vertical speed is therefore determined by the difference of the current and the target airspeed. All protections like stall protection based on angle of attack still apply, which may limit the actual climb rate.

The same logic also applies when descending instead of climbing, where the aircraft will maintain a given descent speed by pitching at idle thrust instead of climb thrust.

Once you get close to the selected altitude, the ALT* mode will take over, which follows a vertical speed instead of pitching for speed:

  Altitude Acquire Mode (ALT*)

  ALT* (green) mode guides the aircraft to acquire the FCU selected altitude.

  ALT* (magenta) guides the aircraft to acquire an altitude constraint provided by the Flight Management.
  Once the aircraft has reached the altitude, the altitude mode (ALT green or magenta) engages.

  Engagement Conditions

  The mode engages when the aircraft reaches the altitude capture zone defined by the aircraft vertical speed
  (among other parameters).

  [...]

  Guidance

  The ALT* mode has internal V/S guidance that is a direct function of the difference between present altitude
  and altitude target. This V/S internal guidance has priority over the target speed. Therefore if a thrust reduction
  occurs in ALT* (Engine out), the vertical speed order will not be modified and a speed variation will occur. The ALT*
  mode does not have a mode reversion that results from speed variation.

  [...]

  ALT* and ALT CSTR* modes have internal protections that decreases the vertical speed when VLS or VMAX is reached (VLS or VMAX becomes the priority target).

  [...]

  The system switches automatically to ALT (altitude hold) when the altitude deviation becomes less than 20 feet.

The vertical speed is therefore only limited by the internal guidance logic, but will be overwritten when VLS or VMAX are reached providing the usual flight envelope protections.


If flaps are used on takeoff, when should they be retracted? If a pilot uses a notch of flaps on takeoff, when do they get retracted? At that time, what changes (i.e. climb rate, speed, pitch)?

NOTE: I have purposefully not specified the type of airplane.

The short answer is, it depends. The FAA Airplane Flying Handbook merely states that this can be performed once the aircraft has established positive climb, but does not specify exactly when.

Ultimately two situations arise:

The airplane is sufficiently large/high performance that normal operating procedures specify the use of flaps for all takeoff scenarios, in which case the manufacturer or the operator (if applicable) may well specify a flap retraction schedule, which seeks to allow the aircraft to accelerate effectively during climb out, avoid overstressing the flaps by having the aircraft fly past the maximum speed for each flap setting, while at the same time maintain a comfortable margin above stall speed.
The airplane only requires flaps for certain kinds of takeoffs such as maximum performance or soft-field efforts. In that case, procedures may be somewhat looser in defining the exact moment of flap retraction. A climb checklist, should you choose to use one, will likely mention the flap configuration as an action/verification item, so that would likely be a good moment to retract them if you haven't done so already. Personally , I usually retract them passing through 200-300 feet AGL, which usually coincides to the aircraft being at least half-way between clean configuration Vx and Vy (I've been mostly flying Skyhawks, Skylanes, Arrows, and Huskies). Whichever way you do it though, you want to avoid retracting them too low and too slow, but also forgetting about them and blowing through Vfe (which even light, slow airplanes can do quite handily).

With respect to the actual changes in aircraft behavior, you'll likely notice the following things:

A slight-nose down moment as wing's characteristics change, which influences the airflow reaching your horizontal stabilizer. The converse applies when extending flaps. Mind you, this is an airplane model-specific thing and one that seemed most noticeable to me in the Cessna family of light singles.
For the same power setting and pitch attitude, the aircraft will begin to accelerate quicker for each notch of flap retraction.
Climb rate is trickier as it is dependent on your power setting, airspeed, and pitch angle; your inputs will matter. However, generally speaking, the reduction in drag would lead to a greater difference between power available (or power set) and power required, so, all things being equal, you would likely see an increase in climb rate.


What qualifies for "mass disseminated data" for an abbreviated briefing? I'm reading about the different types of pre-flight briefings you can get and in the section for Abbreviated Briefing (AIM 7-1-4c) is mentions the phrase "mass disseminated data".

  Request an Abbreviated Briefing when you need information to supplement mass disseminated data...

Is there a particular definition or list of what qualifies for "mass disseminated data"? I often use aviationweather.gov to get a good overview of what's going on before a flight. Does that qualify?

If you look a page or two earlier in the AIM in section 7-1-5(b) the FAA gives two examples:

  b. Standard Briefing. You should request a Standard Briefing any time you are planning a flight and you have not received a previous
  briefing or have not received preliminary information through mass
  dissemination media; for example, TIBS, TWEB (Alaska only), etc.

That's interesting because TIBS was just discontinued (yesterday!) and TWEB is only in Alaska  (weather.gov says it's in other states too but that appears to be out of date according to the FAA's procedures). I have no idea what they include in "etc."

Personally, until I looked into this question I always assumed that "mass disseminated media" meant your local TV station's weather reports :-)


What is the difference between iSpec2200 and S1000D specifications? I know the iSpec2200 and S1000D are the specifications which are used in the aircraft maintenance manual, I have to know how they actually work in the aviation domain and what is the difference between them.

I've only worked with S1000D, but what I understand is that they share a common origin in ATA Spec100, with some differences being:

iSpec2200

maintains a focus on "legacy", monolithic publications
scope is more limited to aircraft
specification costs money (https://publications.airlines.org/CommerceProductDetail.aspx?Product=274)

S1000D

focuses on modular data, with concepts such as data modules and the CSDB
scope is more generalized to any product (air, land, sea, etc.)
specification is free (http://public.s1000d.org/Downloads/Pages/S1000DDownloads.aspx)


How does the GE H75 eliminate the need for hot section inspections? Operators of the Pratt & Whitney Canada PT6 will be familiar with the need for hot section inspections half way to TBO. General Electric is touting the lack of hot section inspection requirements for their GE H75 engine. How did GE eliminate the need for the added inspections?

this is because the fact that GE H series engines do not have fuel nozzles and feed fuel into combustion chamber through a rotating shaft. this design is much less sensitive to the fuel quality and combustion deposits in comparison with usual fuel nozzles


What is "Defense Area" on a VFR Sectional Chart? What is "Defense Area" on a VFR Sectional Chart? The words "DEFENSE AREA" (in all caps) appear all along the US/Mexico border in blue. It's the biggest text on the chart. Interestingly enough, the same words don't seem to be along the US/Canada border.
Someone on airliners.net said this:

You're correct, there is a difference between a ADIZ and a Defense Area. A defense area is an area established on non-federal lands located within the United States, its possessions or territories, for the purpose of safeguarding classified defense information or protecting government equipment and/or material.
The establishment of a national defense area temporarily places such non-federal lands under the effective control of the Department of Defense and results only from an emergency event.
I am surprised that it is charted though, unless of course the government is getting ready for the flood of illegals coming to California to get drivers licenses and registering to vote.

That makes it sound like a ground thing, not an air thing. Then there's this, in the CFR 99.3:

Unless designated as an ADIZ, a Defense Area is any airspace of the United States in which the control of aircraft is required for reasons of national security.

And in the CFR 99.49:

All airspace of the United States is designated as Defense Area except that airspace already designated as Air Defense Identification Zone.

And in the AIM:

Defense Area means any airspace of the contiguous U.S. that is not an ADIZ in which the control of aircraft is required for reasons of national security.

So, what exactly is this Defense Area on my Sectional Chart and do I need to worry about it or think about it as I fly?
From the CFR 99.3 quote, what does this mean?

in which the control of aircraft is required for reasons of national security

FAR 99.3 defines a Defense Area as an area in which air traffic can be controlled in the interest of national security. In other words, non-ADIZ airspace in which SCATANA or a similar plan can be implemented. In other words, all domestic airspace. It used to be clear that all airspace was Defense Area until FAR 99 got rewritten a couple of times in 2001-2004 when they were trying to figure out if the DC SFRA was an ADIZ. Now, the FAR that explicitly says that all non-ADIZ airspace is Defense Area is gone (to who knows where).

Nonetheless, all airspace that isn't an ADIZ is Defense Area, from sea to shining sea.

So why is it depicted on the southern border? To clarify that the airspace is not an ADIZ.

Take a look at this piece of the San Diego TAC. Notice how out in the ocean, the ADIZ is an actual 2-dimensional region. It's depicted with solid magenta lines with dots protecting the inside of the ADIZ. But at the beach, it devolves into a 1-dimensional line. But it's still depicted as the magenta line with dots. Look right there at the beach what has to happen, how the dots have to jump over the line. Thing is, since the ADIZ is a line there, the dots are actually outside of it, they can't protect the inside of it (since there is no inside to protect) and it looks like maybe all of California is an ADIZ, when it isn't. So the words DEFENSE AREA are printed there across the border from CONTIGUOUS US ADIZ to emphasize that the dots aren't actually protecting an ADIZ area; the ADIZ is too narrow to be correctly depicted.


How does aviation deal with satellite and Moon laser ranging, and other scientific lasers in the sky? It seems there are many scientific laser ranging stations around the globe and some are mobile.

Scientists Bounce Laser Off Soviet Lunar Rover Lost On Moon Decades Ago. Source

Questions

How dangerous are those scientific laser beams for passengers and crew, and for the aircraft?
Is there a NOTAM or a temporary flight restriction associated with scientific laser activity?

Background

For satellite laser ranging:

  In satellite laser ranging (SLR) a global network of observation
  stations measures the round trip time of flight of ultrashort pulses
  of light to satellites equipped with retroreflectors. This provides
  instantaneous range measurements of millimeter level precision which
  can be accumulated to provide accurate measurement of orbits and a
  host of important scientific data.

International Laser Ranging Service - Map of stations. Source.

and for the Moon:

  Laser beams are used because they remain tightly focused for large
  distances. Nevertheless, there is enough dispersion of the beam that
  it is about 7 kilometers in diameter when it reaches the Moon and 20
  kilometers in diameter when it returns to Earth. Because of this very
  weak signal, observations are made for several hours at a time. By
  averaging the signal for this period, the distance to the Moon can be
  measured to an accuracy of about 3 centimeters.

For astrophysics purposes:

  Adaptive optics systems require a wavefront reference source in order
  to correct atmospheric distortion of light. Sufficiently bright stars
  are not available in all parts of the sky [...], one can create an
  artificial guide star by shining a laser into the atmosphere.

See also

Thanks to Federico, a very nice timelapse video of laser activity at Mauna Kea (by Sean Goebel).

Is there a NOTAM or a temporary flight restriction associated with laser ranging activity?

Apparently yes:

The lasers on the telescopes are in the range of 15-40 watts. The FAA calls a no-fly zone over the area when a laser is in use, and two people have to stand around outside in the freezing temperatures and watch for airplanes. Each of them has a kill switch to turn off the laser in case an airplane comes near. [...]
To clarify, the FAA does not have a no-fly zone, but instead issues a “Notice to Airmen” or NOTAM about the laser operations.

I also worked on an Adaptive Optics project and it was given for granted that NOTAMs would be issued by the people in charge of the experiments.
Example of NOTAM:

FDC 0/7651 ZDC .. SPECIAL NOTICE .. LASER OPERATIONS EFFECTIVE
1005010001 UTC UNTIL 1112312359 UTC. SCIENTIFIC AND RESEARCH LASER
OPERATIONS WILL BE CONDUCTED AT THE NASA GODDARD SPACE CENTER IN
GREENBELT, MARYLAND, LOCATED AT 390113N/764939W. THE SYSTEM IS
INTERMITTENT, WITH POSSIBLE OPERATIONS HAPPENING 24 HOURS A DAY, 7
DAYS A WEEK. THE LASER BEAM MAY BE INJURIOUS TO PILOTS/AIRCREWS AND
PASSENGERS EYES FOR A DISTANCE OF 98,000 FEET ABOVE GROUND LEVEL.
HOWEVER, THIS SYSTEM USES A LASER HAZARD REDUCTION SYSTEM RADAR THAT
IS SLAVED TO THE TELESCOPE MOUNT TO ENSURE THE LASER IS DEACTIVATED IN
THE EVENT AN AIRCRAFT APPROACHES. THE AREA WILL ALSO BE MONITORED BY
OBSERVERS AND THE LASER BEAM WILL BE TERMINATED IF NONPARTICIPATING
AIRCRAFT ARE DETECTED. LASER IRRADIANCE LEVELS WILL NOT EXCEED THE
MAXIMUM PERMISSIBLE EXPOSURE LEVELS WITHIN THE LASER FREE, CRITICAL
FLIGHT, AND SENSITIVE FLIGHT ZONES. OTHER VISUAL EFFECTS, E.G.,
FLASHBLINDNESS, AFTER IMAGE, GLARE, AND DISTRACTION MAY OCCUR AT
GREATER DISTANCES. THE POTOMAC TRACON /PCT/ PHONE NUMBER 540-349-7541
IS THE FAA COORDINATION FACILITY.

How dangerous is a laser beam for passengers and crew, and for the aircraft?

For the aircraft (meaning the hull) it is no danger, 40 watts of unfocused power (astronomers do not need laser beams in the sky as focused as the beams in an optics lab) do not affect the hull.
For the eyes of pilots and passengers it can instead be extremely dangerous, see Why is laser illumation of a cockpit an emergency?


Is there any reason in principle that large aircraft couldn't be converted to be controlled remotely? Suppose the pilot or pilots of a plane become incapacitated for whatever reason. At the moment, there is nothing that can be done from the outside to stop it other than to shoot it down (am I right?).

Would it in theory be possible that planes have a 'safe landing' program built in that, at a signal from the ground takes over control? It then does everything necessary to land correctly and automatically at a nearby airport.

I realise I am making a lot of assumptions here. My main question is not about the logistics  of what would have to happen on the ground, nor is it about whether a new generation of terrorists could hack into such a system for their own purposes. It is about how easily current autopilots could be adapted to have a 'land safely' option. What modifications would the manufacturers have to install within the plane itself that would make this possible?

Summary

Is it true that currently, the only way to control a runaway aircraft is to shoot it down?
In theory could an existing autopilot have a simple interface that is retrofitted such that a single signal from the ground  sets it in 'return to base' mode and produces a safe landing?

Yes for reasons of hacking prevention. There is no way to be absolutely sure any interface can't be hacked to crash the plane remotely into a suburb.
Yes autopilots can follow a track of navigation marks to an airfield and can auto-land using the ILS.

But again there is no way to ensure only signals from people who have the best intentions with the plane can activate that mode.


What is decalage and how it affects airplane performance? What is decalage in airplanes and how important is it in respect to  airplane performance?

This article from flying magazine has a nice definition (including some history)

  Decalage — a French word meaning “shift” or “offset” — is, broadly
  speaking, a difference between the incidences of any two lifting
  surfaces. It was originally applied to the two wings of a biplane: In
  the usual arrangement, the upper wing was farther forward than the
  lower and had a larger (can’t get away from that term!) angle of
  incidence — called positive decalage — so that it stalled first,
  shifting the center of lift aft and providing an automatic nose-down
  moment for recovery.

  In a monoplane, the term refers to the angles at which the wing and
  the stabilizer (or canard) are attached to the fuselage. For an
  airplane to be longitudinally stable, it must have positive
  aerodynamic decalage; roughly speaking, the forward surface must be at
  a greater angle of attack than the aft one. This principle applies to
  conventional airplanes and to canards alike.


Why do some military aircraft carry two datalink pods? I was taking a look at pictures of the SLAM-ER when I noticed an F/A-18C carrying two AWW-13 datalink pods on its left wing. Why carry a second one? Does it increase signal strength or something?

Source: https://commons.wikimedia.org/wiki/File:F-18C_with_SLAM-ER_missile_and_AWW-13_pods_in_flight.jpg

That pic is from "the Naval Air Warfare Center, Weapons Division (NAWCWD)"
So, testing and development.
Possible reasons (purely speculative):

Testing capability/performance from the 2 different wing stations.
Test/compare different software configs in each.
Ferry one to somewhere else.


What is this thing on a FDX MD11 (MD10?)? I assume something forward looking; not sure why there and how they got this to play nicely with radar

It's the infrared sensor for the Enhanced Flight Vision System (EFVS).
From FedEx Newsroom June 23, 2008:

FedEx Express is the first major commercial carrier in the airline
industry to receive a Supplemental Type Certificate from the FAA for
the advanced system, authorizing its installation in the company’s
fleet of Boeing MD-10 freighters. The company’s goal for the system is
to improve the level of flight safety by increasing visibility of
pilots during adverse weather conditions and darkness.
A unique application of Honeywell International “Head Up Display”
(HUD) technology combined with infrared “Enhanced Flight Vision
System” (EFVS) technology of Elbit Systems of America Commercial
Aviation-Kollsman Business Unit, positions the system as the leader in
the avionic visual technologies market.
The Honeywell HUD interfaces with aircraft navigational and flight
data systems in presenting a high resolution liquid crystal display of
critical flight guidance information. This is overlaid with real-time
EFVS infrared video of the outside world that is displayed in an
overhead unit in the captain’s forward field of view using
state-of-the-art HUD “combiner” technology. Elbit Systems Ltd.,
Electro-Optics-Elop manufactures the combiner glass.

The combined image appears like this:

Source: FedEx


Can the ball on a turn coordinator be to the full right/left while the wings are level? Can it ever happen in a wings level flight that the Turn and Slip indicator ball is to the full right/left? If so then when and what will be the flight path of such an aircraft? Thanks in advance.

Yes, when the rudder is highly deflected. The slip indicator gives us information on the yaw axis of the airplane and "level flight" is generally in relation to a neutral pitch and power situation (i.e. not climbing or descending). An aircraft can be yawed with rudder input alone and subsequently cause the slip ball to deflect as appropriate.


What kind of materials is being used for Fighter jets glass shields? What kind of materials is being used for Fighter jets glass shields and is that different from what they use for commercial jets?

Today, the canopy is a multi-layer structure. In case of the F-16, it consists of three layers:

The innermost layer is 0.5 inch thick polycarbonate and drape-molded into the compound curvature shape.
The center layer is 0.05 inch polyurethane to bond the inner to the outer layer.
The outer layer is a 0.125 inch layer of acrylic (PMMA).

The canopy is bolted to a metal frame for assembly. Some canopy also use explosive cord on the outer layer to fracture the material shortly before the ejection seat fires.

F-16 canopy (picture source)

For less fast aircraft, a single layer of acrylic is sufficient. Funnily, the company which produces most of those canopies doesn't even have a page in Wikipedia. They use flat PMMA sheets and drape-mold them over a mandrel. The secret of their process is the grease they put on the mandrel so the acrylic flows easily into shape.


During multiengine training, are pilots taught how to use the throttles for control? The use of a multiengine aircraft’s throttles for steering and pitch control is critically important should the aircraft’s primary flight controls fail or severely malfunction; are pilots nowadays taught this potentially-lifesaving skill during training for a multiengine rating?

No.  In a piston multi course the focus is on flying the airplane and single engine procedures.  Loss of rudder control in something like a Seminole is not a big deal unless the engine quits after that and then you have a problem, and it's not one of controlling yaw with differential thrust.

If your rudder cables broke with both engines running you would naturally use bits of differential power to center the ball as required while flying straight, and little rudder is required to turn so that's not a big deal and you would just leave it and put up with a bit of adverse yaw. This all wouldn't require much training to figure out.

Sioux City was what you would call a freak event, with multiple simultaneous failures of flight controls for all axes, that is not catered to in design in the first place (notwithstanding the mistake, on the DC-10, of running all the hydraulic lines though one choke point; most airplanes separate control runs as much as possible to cater to turbine burst events).  They were trying to control both pitch and roll, with differential thrust to turn by skidding and by using the pitching moment of increasing/decreasing thrust to climb/descend.

No type course trains for that.  There are a million one-of-a-kind events you can dream up, which can theoretically happen, for which airliners are not certified to cope with, and where a crew might have to figure things out on the go.  If you had to train for all of them, the type course would take years to complete.


What do tower controllers do when the airport is quiet? Listening Hayward Executive Tower on LiveATC in the night, I noticed ATC can be quiet for periods of more than 30 minutes, and sometimes the communication is not even with an aircraft, but with a maintenance car.

What do ATC operators when the airport is quiet?

The same things people do when working jobs like night shift guard shack operator... catch up on paperwork, read, study, listen to music, etc.


Does the stator blade angle changes? Why? I have read that when jets are on the ground their compression ratio changes. With this change the stator compressor's blade angle changes. Is this true?

The picture above shows the velocity triangles for one axial compressor stage. You can see that a big factor for the angle at which the airflow leaves the rotor, is strongly dependent on U the rotational speed of the rotor. So when the engine runs at different powersettings the air is gone come at the stators at different angels(since U is changing). Since the stators are like wings and have an optimal angle of attack, it makes sense to make them rotate so they can always keep this optimum angle, even if the oncoming flow changes its angle.
So it doesn't really have much to do with whether the plane is on the ground or not, the major factor for the stator adjustment is the changing rotational speed of the compressor rotors.


Was the March 2019 Rafale jet ejection incident investigated? This is one of the wildest stories I’ve ever heard of.  Then again, this is CNN’s disaster-a-minute-for-ratings kind of reporting.

https://www.cnn.com/travel/article/france-fighter-jet-ejection-scli-intl/index.html

A group of French co-workers organizes a ride for a 64 year old fellow worker in a Dassault Rafale jet fighter wherein the man panics during flight and pulls the ejection handle, bailing out mid flight and landing in a field near the German border.

I stare completely baffled at this as to

How these people managed to convince the French Air Force to let this man ride back seat in a jet fighter
without any kind of familiarization or ejection seat training and
Nobody noticed the guy’s level of discomfort during pre-flight taxi or even takeoff?

Was there any in-depth investigation to the incident and if so, what was determined to be the root cause(s)?

Here are a few key points translated from the media coverage on the official BEA report (PDF, in French):

The passenger was a 64 years old manager of a shipping company.
The French Air Force carries out such passenger flights occasionally.
The passenger wore a pulse watch which recorded between 136bpm and 142bpm prior to the flight, safe to say the man was under a lot of stress.
The report states that the situation produced significant peer pressure on the passenger: A significant number of colleagues from work, who had organized the event, were present.
In order to max the element of surprise, the passenger passed the required medical exam the same day. (As a consequence of this accident, there is now a 10 day mandatory delay between the exam and the actual flight.)
The physician issued the medical certificate under the condition that the flight must not exceed 3G. This information, however, did not reach the pilot due to what the report calls a "technical problem". (This type of aircraft reaches close to 4G during a normal takeoff.)
The passenger wasn't correctly equipped: The anti-G trousers as well as the chinstrap were too loose, the helmet visor folded up. The passenger lost his helmet mid air after the ejection.
The passenger ejected in a phase of the takeoff with negative G forces.

Most likely, the passenger was under an extraordinary amount of stress and tried to hold onto something in negative G, unfortunately the eject cord.

There's, however, another not so fun fact:

The pilot should have been ejected automatically along with the passenger. This mechanism failed! The pilot could have ejected himself nonetheless, but chose not to. It was due to this technical malfunction that the French Air Force didn't lose such an expensive machine.

(sources: Le Point, BFM TV)


What happens if an aircraft declares an emergency while there is another aircraft ahead cleared to land? Lets assume this situation: In a controlled airport, two aircraft are approaching for landing. #1 is about to touch the runway (let's assume it is within 1~2 miles from touch zone).

Then #2 declares a emergency.

Is there any rule that require that the first airplane starts a go around, either by its decision or by controller's?

Some assumptions:

There is enough separation from #1 to #2. If #1 was allowed to land and it successfully does, that will not significantly interfere with #2 landing.
Airfield has just one runway.
I'm limiting this to a international accepted, US and/or Brazilian rule.

My concern is that if some incident occurs with #1 on landing, like a gear collapsing, that may render the runway unsuable, causing trouble for the trailing aircraft in emergency.

Speaking in other words: Is an aircraft cleared to land even if another is approaching in a emergency situation?

No, the airport wouldn't be closed, and the #1 aircraft doesn't need to go around nor be sent around.

The risk of him shutting down the runway is very slight, and is probably of the same magnitude of risk that sending him around to hold until #2 has landed & the runway has been checked and reopened, would put him into a low-fuel emergency state.

If they are both about the same distance (actually, time) away, then the emergency aircraft has priority (assuming that he doesn't decide to hold in order to troubleshoot, burn down fuel, prepare for the landing, etc), but essentially closing the airport from the time that the emergency has been declared until the emergency aircraft lands, isn't something I've ever seen or heard of.

The runway is often closed following an emergency landing until it can be checked by an airport vehicle, to ensure that it is clear of debris, spilled fuel/oil/hydraulic fluid/etc. And if the emergency aircraft can't clear the runway under its own power, it takes time to get it towed off, possibly pinning the landing gear (to prevent unintended retraction) first. Plus there may be an evacuation after the landing. So closing the runway for some time after the emergency aircraft lands, is entirely possible.

But if the airport has planes in the pattern & the emergency aircraft is 50 miles out, it'd be better to let those who want/need to land, do so, rather than risk them running low on fuel airborne while awaiting the runway's reopening.  Same basic logic applies in the #1 / #2 scenario posed above.

If aircraft regularly had their gear collapse & shut down runways unexpectedly, that would be a different story. But that's exceedingly rare, so that isn't the contingency that all planning is based on.


Is it legal for a non-IFR rated pilot to fly a SID on a VFR flight? Just wondering in case the pilot is unfamiliar with the airport / terrain or is flying at night and wants obstacle / terrain separation.

It depends what you mean by 'flying a SID'. If it is just following the procedure without violation of VFR (i. e. you are above VFR weather minimums for a given airspace, you maintain your own separation from traffic, don't violate ATC clearances, don't enter controlled airspace without a clearance etc.) - yes, it's perfectly legal. You can fly any route you want, your choice (again, I assume that you do not violate ATC clearances).

If you mean by 'flying a SID' obtaining an ATC clearance to fly a SID - if it is an IFR clearance, than no, it is illegal. You cannot request IFR clearance if you or your aircraft is not IFR rated, except the cases when you are training for an IFR (and have a CFII next to you).


Are the PW1100G and PW1400G engine series not certified by the FAA? I was digging around the FAA type certificate data sheet (TCDS) database and I could not find the entries for the PW1100G and PW1400G engines series. I then went to the EASA TCDS database and both of them were categorised under the PW1100G-JM title. Have these two engine series not been certified by the FAA? Was it because they were for European aircraft OEMs (PW1100G for A320neo, PW1400G for Irkut MC-21)?

They are certified by the FAA. The following 1100/1400 models:

  PW1133G-JM, PW1133GA-JM, PW1130G-JM, PW1129G-JM, PW1127G-JM, PW1127GA-JM, PW1127G1-JM, PW1124G-JM, PW1124G1-JM, PW1122G-JM,PW1431G-JM, PW1431GA-JM, PW1431GH-JM, PW1428G-JM, PW1428GA-JM, PW1428GH-JM

Are certified under TCDS (type certificate data sheet) E00087EN (PDF).

Note: The certificate holder is International Aero Engines, LLC, and I was able to find it by searching https://rgl.faa.gov for "E00087EN", which I got from the neo's TCDS.


What vertical flight profile could be expected from an aircraft if the pilots were incapacitated? If there were nobody at the controls what kind of vertical profile could be expected from, for example, a modern airliner?

After reaching the cruise altitude I assume the pilot just sets a nav route and altitude on the onboard computer or at least set the trim to avoid having to constantly adjusting the altitude manually.

Emergency descent (like during a decompression event where you need to get from cruise to 10k ft ASAP to make sure the people in the back survive) shouldn't make a nice curve. It only wastes time you don't really have.

Normal operation means the pilot activates the autopilot during cruise which will fly the programmed course set by the pilot. It will stay follow that course (or put itself in a holding pattern on the final fix) until it runs out of fuel or the pilot intervenes when it is cleared for descent. This happened with Helios Airways Air flight 522; both pilots were incapacitated shortly after ascent and the plane put itself in a hold and crashed when it ran out of fuel after more than an hour.

A plane where there is nothing controlling the altitude (when control is lost due to loss of hydraulics for example) will follow a phugoid cycle. That is a series of dives and climbs as the elevators gain and lose bite on the air with speed.


Has anyone attempted to recreate the Sack AS-6 (German Saucer-wing)? I remember seeing pictures of this as a kid and wondered whether anyone has since recreated this saucer-wing aircraft and made it work?

Source (excuse the pun)

I'm not aware of anyone making a replica of the Sack AS-6 (the aircraft was destroyed when the Allies reached the area); however, there are other examples of saucer (circular wing)- like the Rowe UFO, which flies quite happily.

Rowe UFO; image from youtube grab

Then there is also the Vought V-173, whose design is quite similar.

Vought V-173 By Unknown - http://www.flickr.com/photos/sdasmarchives/4822056685/, Public Domain, Link


How can someone without a pilot's license arrange an initial test flight for a homebuilt aircraft? I think this has more to do with culture and expectations than actual rules, so maybe this might attract opinionated answers, but I still want to know what people think:

If a person were to construct their own homebuilt, like a Kitfox or RV, without first obtaining their PPL, how can they go about completing the 25 hour initial test phase required for the new aircraft?

This encompasses a subset of questions:

Is it customary to pay an experienced pilot to do it, acknowledging the risk involved with the activity?
Or is free use of an aircraft and loggable time/experience compensation enough?
Is it generally hard to find someone willing to do this for you (maybe do this with you is a better phrase since you will be part of the ground crew)?

Even licensed, experienced pilots often hire other pilots who have experience in test flying and hopefully time in the same model to perform the initial flights. Expect to pay for the service; test pilots do not do the work to build time. How hard it will be to find someone to do it depends on many factors such as the type of aircraft, the reputation of the design, your location and your willingness to allow the testing to take place at a safe field, the quality of your work, if you worked with an EAA chapter and at least one advisor, the quality of your build logs and photos, the quality of your flight test program docs, etc., etc. The EAA can further advise you on this, the membership fee is well worth it.