How exactly are checklists shared between the pilots? Plane startups are shared between the crew

But how exactly? Does the captain do the startup and then ask the copilot if everything is correct? How exactly does it work? Is it aircraft specific or airline specific?

Typically, both pilots will set up "their" stuff as prescribed in the airline SOP's, and then the checklist will be called for.

At my airline, the captain has certain switches that he sets and certain systems that he checks -- generally things on his side of the overhead panel along with his flight instruments -- and the FO does likewise.  The FO performs the initial setup of the FMC, with both pilots checking what has been loaded (since some of the data comes in over a datalink).  Then, the captain briefs certain items, the clearance and routing are discussed, and then the captain calls for the checklist.  In flight, the flying pilot will call for the checklist (although if he's late in calling for it, the monitoring pilot my suggest, "are you ready for the Descent Checklist").

At my airline, the FO (or, in flight, the monitoring pilot) reads each item on the checklist, both pilots verify the switch or condition, and the captain responds.  Everything in the checklist is standardized, so the responses are predictable.  For instance, if the Before Takeoff checklist challenge is "Anti-ice" then the response might be "Off" or "Engine On, Wing Off" (since you don't operate on the ground with Wing anti-ice turned on in the 737).  But both pilots should be looking at the switch position to confirm that what is actually set (a) makes sense, given the conditions, and (b) matches what the Captain states.

Other operations will have some variation in this.  In another organization, the challenge "Altimeters" was answered "30.03, Pilot" followed by "30.03 Copilot" and then "30.03 Navigator".  Where I am now, we'd simply have both pilot check that the altimeters all match the ATIS setting, and the captain responds "30.03, set".  Either method works in a 2-pilot aircraft; with a Navigator and a Flight Engineer and a Loadmaster, crews in my old aircraft did things a little differently, in ways that made good sense in that operation.

So yes, the precise details of how all this is done are very aircraft- and airline-specific.


Why doesn't GE replace all 4 engines for on their flying test bed instead of just 1? GE (General Electric) flies Boeing 747s equipped with new engines that are being tested. Why can't they equip the test airplane with all 4 of the new engines? Wouldn't the thrust be imbalanced by replacing only 1 engine? As you can see, it may have 1 big engine and 3 smaller ones:

Other times, smaller engines are being tested. Would the smaller engine provide enough thrust for a large, heavy airplane like the 747?

They only change one, because that one is a new engine that is being tested.

If you are testing a new engine you change 1 at first so if it fails you have 3 others.  If you change all 4 and there is a systematic defect in the design, now you have 0 good engines instead of 3.

You will also see that the test engine isn't always one suitable for a 747.  This is because they may be testing a new design or a new alternative fuel and it is safer to test an unknown with 3 good engines (e.g. a 747) rather than with just 1 good engine (any two-engine airplane).  This increases the safety margin if the test engine fails.

Running a different engine with a different thrust rating requires some thought about asymmetric thrust.  Doing this on a 4-engine airplane simplifies this greatly over a 2-engine airplane.  Ways to accommodate different thrust from the odd engine:

De-rate the new engine so it only produces thrust equivalent to the normal engine
Run the new engine at reduced thrust
If the new engine is inboard, reduce the outboard engine thrust to balance the total yawing moment from that wing with the other side.
Don't worry about it and trim the airplane to compensate.

The other advantage to doing this on a 747 is that a 4th engine is technically not really needed as a 747 can takeoff, fly and land with only 3 operating engines.


Is there a penalty for changing the approach procedure after accepting one? For example: If you request a visual approach and get approved, but you meant to request an ILS approach, are you not allowed to change it?

Is there some type of penalty for changing approaches after you've already received one?

For example in the video, "PilotsEYE.tv - A380 Landing KSFO San Francisco", the copilot misread a visual approach as ILS, and was given the ILS, but despite the captain's disapproval, they didn't make another call requesting the change.

There is no penalty per se, but visual approaches in particular have lower separation requirements, so having to switch you back to a non-visual approach may require ATC to make corrections (e.g. delay vectors, speed control or, in extreme cases, a missed approach), which may feel like a penalty.


What are the conditions under which one would normally switch on the Engine and the Wing Anti Ice? As per the title. But I would also like to know if both (Engine and Wing) are turned on at the same time or if different conditions dictate the use of each one. I am specifically interested in the case for the B737NG.

In general the cowls get operated way more than the wings, because the operating requirements are more stringent, because ice can form on cowl inlets more readily than the wings in conditions near freezing (temperature drop from inlet flow) and the consequences can be worse when the ice is shed.
Can't speak for the 737, but on the CRJs at least, the cowls have to be on in conditions where the wings don't, such as flying in visible moisture above 230 kts (above which the wings only have to be on if you get an actual detection of ice on the airframe).  So when you depart in real icing or "technical icing" (visible moisture below a certain temperature) conditions, both wings and cowls will be on, but during the enroute climb you don't need the wings on without an ICE caution message, whereas you still have to put the cowls on pretty much any time you are in cloud.
In the CRJ program the duty cycle of the cowl AI system was several times higher than the wing AI system because of this, and I'm sure most airliners are similar.


Why does the spool speed increase with altitude for a turbofan engine (single spool & double spool)? So, I want to see the effect of altitude on the compressor characteristic of a single spool & double spool turbofan engine at constant flight speed and TIT (turbine inlet temp).

I am aware that as the altitude increases, density decreases, mass flow decreases which ultimately reduces thrust.

As well as, with an increase in altitude the fuel consumption decreases, due to a decrease in inlet temperature which leads to a lesser amount of compressor work to be done* (From e.g. seventh edition Gas Turbine Theory by H.I.H. Sarvananamuttoo, G.F.C. Rogers, H. Cohen, P.V. Straznicky and A.C. Nix).

But as the compressor work is directly proportional to the spool speed, I would expect the spool speed to be lower as well. (Correct me if I am wrong). But in the plot shown, the shaft speed parameter (N/$\sqrt(T_{02})$) seems to increase from 0.73 to 0.89 for single spool and 0.86 to 0.91 for double spool with increase in altitude. Why does the spool speed increase with altitude?

As you note - as altitude increases, air density decreases.

The work done by the compressor stages therefore also decreases at any given rotational speed. If we assume constant power applied to the compressor stages (not entirely correctly) then the speed will increase until the work done matches the power input.

The overall work done by the engine will still decrease, due to decreased combustion, but the spool speed is going to increase a certain amount.


Can I fly with an airband receiver in the United States? I'm flying with American Airlines on a cross-country flight soon and was thinking about bringing along my airband receiver/scanner since it'd be fun to listen to ATC.

It looks like I'd be unable to use it during the flight since any type of radio isn't allowed. I don't see any TSA restrictions on them. Am I safe in assuming that I can bring it along and listen to it in the airport terminal without any trouble with security?

This is probably more a travel question than an aviation one, but I did some Googling of various aviation and travel sites and the consensus seems to be this:

You can carry the scanner with you, but if you're unlucky and encounter the wrong TSA agent on the wrong day then you may be asked a lot of questions at security (the TSA's "Can I Bring..." tool seems to consider scanners to be generic electronic items)
Using the scanner while sitting in the airport is fine, but if you attract attention to yourself then you may be questioned by the police or airport security
You may not use a two-way radio on board the aircraft, because they're specifically required to be off at all times (this is in every airline's safety instructions that I've seen); that shouldn't apply to a radio that only receives but the cabin crew might ask you to turn it off anyway if they're not sure about it
Even if you did operate the scanner in the air, the reception is terrible and you'll probably hear only the aircraft's crew, not ATC

Note that this information is for the USA only, many other countries are very strict about possession and use of scanners or two-way radios and in the UK (for example) just listening to ATC is actually illegal.


How long did it take to set up a portable runway? How long did it take to set up those metal runways? Were the metal sheets spiked into the ground? How big were they? Also, how are commercial runways built?

Google is your friend. Try it. "perforated metal airstrip"

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

"A runway two hundred feet wide and 5000 feet (1500 m) long could be created within two days by a small team of engineers."


Why does "airplane mode" turn off Bluetooth and WLAN if I can just turn them on again? On my (Android) phone, enabling airplane mode automatically disables all wireless antennas except for GPS and NFC (I assume the latter is either passive or way too low power for anyone to care about).  In particular, it disables mobile data (4G/LTE, or whatever it has roamed onto), WLAN (WiFi), and Bluetooth.

However, I can turn WLAN and Bluetooth back on again without disabling airplane mode.  Asking the airline, as suggested in this answer, is useless.  During the safety briefing of every flight I remember in the recent past, they would say something along the lines of "You can use electronic devices as long as they're in airplane mode," or very rarely, "You need to switch your electronic devices completely off until we hit 10k feet, and then use them in airplane mode."  But they don't tell you anything more specific in the safety briefing or on the information card (e.g. "WLAN is fine, but keep Bluetooth off" or similar).  At the same time, most airlines clearly want you to turn on WLAN so that they can sell you internet access.

The obvious interpretation is that you can do whatever you want as long as your device is in airplane mode ("They said to put everything in airplane mode, and I did, so I complied with their instructions.").  But that actually doesn't make sense.  I own multiple devices which only have Bluetooth and/or WLAN antennas (e.g. the Nintendo Switch, most smart watches, and probably a truckload of other non-phone devices).  In most cases, you can turn both antennas back on after enabling airplane mode.  At that point, airplane mode is just a pretty little icon that appears in your device's status bar.  It doesn't actually do anything (but is presumably still required).

What is the point of disabling Bluetooth and WLAN if you're not prohibited from turning them on again?  What is the point of even having airplane mode on devices that don't support mobile data in the first place?

"Airplane mode" is a convenience feature provided by the phone manufacturer. You can choose to turn it off anytime in violation of the rules, so there is no difference there.

What it does may not match the regulation in any particular geography as rules vary. Regardless of any particular device the airline sets rules to ensure that no device:

1) Interferes with navigation signals required by the aircraft, particularly at landing

2) Confuses cellphone towers on the ground which expect radio signals in roughly a planar orientation near the ground

The airline gets its rules from the FAA/EASA... and indirectly from the FCC... What was considered "airplane mode" by the FAA changed in 2013. Testing determined that wifi and bluetooth did not cause sufficient interference with ground based nav signals, so that prohibition was relaxed. An old phone's "airplane mode" may be too restrictive.

There was no change to the rule on cellphone voice communication, which remained prohibited. Once the aircraft is sufficiently high no ground based cell tower can receive any signal, so this prohibition mid-flight is effectively meaningless.


How are altitudes handled with airports near or above transition altitude? Transition altitude refers to the altitude above which all altimeters are set to a standard pressure setting (typically 29.92 inHg) instead of to the local surface pressure, and altitudes are given in flight levels (the standard-pressure altitude, divided by 100; for instance, with one’s altimeter set to standard pressure and reading 52,900 feet, one would say “flight level 529” rather than “52,900 feet”) rather than in feet above mean sea level (MSL).  The height of the transition altitude depends on where you’re flying; for instance, transition altitude is at 18 kft in the United States, 10 kft in Australia, and as low as 6 kft or even lower in parts of Europe.

Low transition altitudes raise the possibility of an airport’s height above sea level being close to, or even above, the transition altitude; this wouldn’t be an issue in the United States (where only the very highest one or two mountain peaks reach above the 18-kft transition altitude, and this altitude is well into the Death Zone anyways unless one is exceptionally well-acclimated to very high altitudes) or Australia (where even the highest peaks are less than 8 kft above MSL, well below the 10-kft transition altitude), but could easily become a problem in regions with both high terrain and low transition altitudes (such as Europe, which has many high mountains - and, more to the point, many airports high up in mountainous areas - combined with transition altitudes that go at least as far down as 6 kft), as maintaining terrain clearance requires knowing what one’s altitude actually is, rather than knowing what altitude the pressure at the static ports would correspond to if the local altimeter setting was 29.92 inHg.

How do airports located at elevations near to, or above, transition altitude handle this?  Does the airspace around these airports use a local transition altitude higher than elsewhere?  Do approaches and landings at, and takeoffs from, these airports rely solely on radar, rather than barometric, altimeters?  Something else?

I don't have an authoritative source for what the various regulatory agencies in the various regions use for publishing their transition altitudes, but your assumption is pretty close: airspace is planned so that no airport is "that close" to the transition level.

Some TAs are defined across large swaths, such as the US, Canadian, Australian TAs.  Some TAs are more broken up, even within political boundaries.  I believe Brazil (or at least one of the South American countries) has different TAs for different "terminal areas".

There has been on-again/off-again discussions in the European region of establishing a common TA, but (as of this date) that has not happened.  You will see fairly low TAs in low, flat areas like The Netherlands, but higher TAs in the mountainous regions.

Again, all of these TAs are "planned out" so that there is no danger of being too low while assigned to a flight level, and so that you are back on QNH well before you are on approach to an airport.


What is the shed bus in the Phenom 100? I recently came across a part of the electrical system of aircraft named SHED BUS. I am specifically asking for the Embraer Phenom 100.

Source (Page 122), Added red square

What is the SHED BUS for and what is it doing?

The shed bus powers non-essential aircraft systems. In the case of the phenom 100 this is things like the air conditioning, passenger power sockets and entertainment systems, the toilet and some lighting.

The shed bus is the first thing to lose power (be shed) should the aircraft not be generating enough electricity through, for example, a generator dropping offline.


In lost comms situations, when and where do the pilots of big commercial jets expect to get green light from tower? In the event of lost comms, GA pilots are generally expected to circle over the airport looking for light gun signals from the tower. What about big commercials jets? Are they also expected to circle over the airport until they see green light from the tower?

One of my flight instructors once told me, in real lost comms situations, don't circle over the airport and just take a traffic pattern and land, because the tower is already aware of your situation and they will clear traffic for you accordingly, if you were squawking 7600. I was not sure at the time he was right on this, but maybe that's the case for big commercial jets.

So what does the tower expect from the pilots of Boeing or Airbus in lost communications? Do they expect you to circle over them looking for light signals or just go ahead land expecting to get the signals on the pattern?

In the US, for VFR, the answer to both of your questions (when and where) is when you are established on downwind. You may not be able to see the light signal if you circle above. I don't think it matters what size the aircraft is. In IFR operations, you may not even be able to see the tower, and as 757toga points out there are different rules.

This actually happened to me years ago at a tower controlled airport in California (although I was in a small aircraft). Radio stopped working. Not sure if it was transmitting so I continued to transmit my intentions just in case the transmitter was functional. I squawked 7600. I observed the traffic pattern and entered downwind at a 45. Sure enough, a few seconds later, solid green light from inside of the tower was seen. I rocked my wings to acknowledge the light signal, then controller put down the light gun. It was faint, but visible in the daylight, but if you weren't looking right at it, you wouldn't see it. (Most glass at towers is pretty thick and at an angle so I suspect it absorbs, diffuses, and/or refracts some of the light guns intensity). I never talked to the tower about it, but its possible they were shooting the light at me before I entered the downwind, but its possible I couldn't see it until I was at traffic pattern altitude and established on the downwind leg. Also, keep in mind that it is a light gun with a narrow beam, they have to hold it up and aim through a scope like a rifle at the cockpit, so you need to acknowledge you received the signal so they can put it down. Some small airports only have one controller, so s/he can't really look out for other traffic while holding the light gun up at you.

Had uneventful landing, and got light signal on the ground to taxi to parking. It worked just like it was supposed to.

See AIM section "4−3−13 Traffic Control Light Signals" for additional information.


Why are no HAPS (High Altitude Platform Station) solar planes of a biplane design? HAPS are fragile due to weight constaints, e.g. NASA’s Helios. Biplanes are more robust.

Although biplanes have high drag, HAPS only need to move slowly because at their operating height the wind speed is less than 50 mph, and to maintain station they only need to overcome that.

A biplane is more robust than a monoplane per unit weight. This is because the monoplane supporting beam has to live inside the max vertical depth of the wing. With a biplane the beam can be as deep as the vertical distance between the upper and lower wing. The biplane has a worse lift to drag ratio than equiv monoplane. But drag increases dramatically with air speed. As the HAPS is only slow flying maybe the drag is acceptable. At high altitude the Reynolds number decreases, this raises stall speed. Stall speed goes down with lower wing loading (plane weight / wing area). Biplane wing loading is lower so will have a lower stall speed. Of course it's all trade offs. These are arguments for the biplane.


What are good strategies for the "impossible turn"? For reference, I fly a Cessna 172.

I've read about a couple of different strategies for the impossible turn (attempting to turn back to the airport after engine failure at low altitude).

The first strategy is the one I've heard most commonly on aviation websites and videos: that is, essentially, maintain a best glide and try to make the turn as quickly as possible without stalling.  Unfortunately, a slow turn also means you'll have to turn a little more than 180 degrees to get back to the runway.

The second strategy I've heard is not generally mentioned in the typical safety videos (at least that I've seen). A former flight instructor had mentioned that you could complete the impossible turn by pushing the nose down and using the additional airspeed and downward angle to execute an extremely sharp turn that would keep you closer to the runway; when you come out of the turn, you won't have to worry as much about lining back up with the runway.

Strategy 2 is clearly more risky, at least for someone who has not practiced the maneuver, so that could explain why I don't see it mentioned in most safety videos. I was wondering if anyone here had an opinion on either maneuver (or other options) for executing the impossible turn and, if possible, links to literature explaining it.

Thanks in advance.

The already linked question has a link to this study. Its authors seem to have done the calculations and concluded that turn with 45° bank flown on the edge of stall lets you do it with smallest loss of altitude. Which is the point here. Don't forget you still need to glide back to the runway.

As rbp mentions below, flying the turn at edge of stall is extremely dangerous, so in practice you should plan turning around only from altitude from which the turn can be made with limit above stall (and don't forget in 45° bank the stall speed is ~20% higher and quickly increases with more bank) you are confident you can manage to maintain. This increases the altitude above which you should only attempt it but the optimal bank angle remain 45°.

If you used higher bank angle, you'd have to fly faster so you'd still have enough vertical lift to balance your weight. That would mean you'd need more lateral lift (even for the same turn rate the lateral acceleration is proportional to speed) to complete the turn and this lift would come with it's additional induced drag. Drag equals energy loss and the only energy you have at that point is potential energy due to altitude. So such turn would spit you out lower, which is the last thing you need. And note, that this is exactly your second option.

Also note, that due to reasons mentioned by rbp below your margin between stall warning and severe stall is even lower in higher bank, so that's another reason against that option.


How exactly do ICAO's VOR-based minimum separation standards work? This question is aimed at Air Traffic Controllers who are familiar with ICAO Separation minima.  DOC 4444 states the following:

  Lateral separation between two aircraft exists when: VOR: both
  aircraft are established on radials diverging by at least 15
  degrees and at least one aircraft is at a distance of 28 km (15 NM) or
  more from the facility (see Figure 5-4)

Note that i have highlighted the word "diverging". The only example given here is when two aircraft are flying away from the VOR (diverging).

Q#1. In this scenario the VOR is located at the airport. Two aircraft are departing that airport, when the leading aircraft is 15nm or more from the VOR on radial 020, the following aircraft is laterally separated when he flies on radial 035. Is this correct?

Q#2 What if both aircraft are less than 15 nm? How many degrees of separation must there be in that case?

Q#3 What about when one aircraft is flying away from the VOR and the other one is flying towards the VOR? AC1 is flying away from the VOR on R015 and is 20nm from it at FL060 . AC2 is flying towards the VOR on R030 and is at 25NM descending through FL060. Are these two aircraft separated?

Q#4 Same scenario as mentioned above, but AC1 is 10NM from the VOR and AC2 is 20NM from the VOR (same radials and levels as mentioned above).  Are they separated?

Q#5 What if both aircraft are flying towards the VOR? AC1 is flying to the VOR on radial 010 maintaining FL200, 30NM from the VOR. AC2 is flying to the VOR and is at FL210 35NM from it on radial 025. Does this mean that since you have at least 15 degrees on the radials, that AC2 could continue its descent through FL200?

Also are there any sites,videos, other manuals or resources that have a better explanation on ICAO separation minima (other than DOC 4444)?

Exactly. As long as the aircraft are diverging (i.e. flying away from the VOR), one of the aircraft is at least 15nm away from the VOR and both are at least 15 degrees (radials) apart, the separation is achieved.
You cannot use VOR separation with less than 15nm distance. The other option that can be used is "geographical separation", ref ICAO Doc 4444 5.4.1.2.1.1.
As they are still more than 15 nm away from the VOR, I would say yes. There would need to be however a certain restriction in place for the inbound aircraft to cross 15 DME (or preferably much before to have some margin) at FL50/5000ft or below, to ensure separation.
Yes. As far as one aircraft is 15nm or more away from the VOR, the separation is ensured. The photo in your question nicely depicts this, as it shows that only one (the furthest) aircraft has to be 15nm or more away from the VOR.
Yes, but you would have to ensure that they are vertically separated before the last inbound aircraft reaches 15nm from the VOR.


What disadvantages does flying a drone close under a ceiling have? If I want a drone (quadcopter) to be flying always under a surface and close to this surface (i.e: under a table 5cm away from the surface), which are the disadvantages this would have in the lift generation of the drone?

How much would be the lift lost due to this flying conditions (in percentage or with calculations if possible)?

For a quadcopter, flying close underneath a flat surface will increase the amount of lift produced, but this will make it harder to control (unless the quadcopter is equipped with appropriate control software).
According to comments by Alex and Peter Kämpf, if you fly a quadcopter close underneath a flat surface, the quadcopter will tend to get "sucked up" and collide with the surface. You will have to reduce power dramatically in order to go back down.
You could probably make a quadcopter under a ceiling easier to control by equipping it with a proximity sensor (or perhaps an accelerometer) and software which automatically reduces power when the aircraft gets close to a ceiling. It could take a lot of tuning, but with the right control algorithm, it would probably be easy to maintain a constant distance under the ceiling.
So, why does a quadcopter behave this way? I don't know if any research has been done on this, but I can make an educated guess.
For aircraft flying above a flat surface, the ground effect increases the amount of lift produced. When the wings are near the ground, a high-pressure region is created between the wings and the ground, thereby increasing the amount of lift.
So for aircraft flying below a flat surface, presumably something similar happens. The propellers create a low-pressure region between themselves and the upper surface. That once again increases the amount of lift produced.
(In the extreme case, with an object which is in contact with the upper surface, it's possible for the object to create a low-pressure region above itself, and thereby keep itself up, using no power at all. That's what a suction cup is.)
For posterity, here are the comments by Alex and Peter Kämpf that I referenced above:

I can say that when I fly my smaller sized quads indoors that its more of a suction cup response. The few that I have all have generally the same effect. If I fly to close to the ceiling I end up sucked up to it where then I have to dramatically drop throttle before they are released. It takes a surprisingly little amount of power to maintain the suction effect. Keep in mind they all have duct motors with a flat surface on top (no camera or antenna sticking in the way) so that may provide more suction action as well. – Alex 2019-01-16 15:50:56Z
There is an important difference: While 'regular' ground effect is dynamically stable, this inverted ground effect is the opposite. Coming close to the ceiling means that the quadcopter will be sucked up until it collides with the ceiling. – Peter Kämpf 2019-01-16 16:26:17Z


Are four-engined airplanes calibrated to put out the same thrust for both their inner and outer engines? Is there a slight difference baked into the aircraft's throttle control systems or are they always pumping out the exact same thrust as each other?

If the fuel control is hydromechanical (old engines) or electronically trimmed hydromechanical (not so old engines designed in the 70s and 80s), you set each thrust lever to achieve a target value on the fan RPM (N1) indicators or Engine Pressure Ratio indicator (EPR) indicators (for a pure jet).  Each engine will be set to its takeoff thrust setting, which should be the same for each since they are all the same model, but the thrust levers may or may not quite line up due to mechanical and other tolerances (there are limits).

On some modern airplanes with Full Authority Digital Engine Control, you move the levers to a detent setting, usually one for climb and one for take off, that is created by a roller running in a track inside the quadrant for each lever, that drops into a dip in the track; you can feel it click into place.

For takeoff you push them up through the climb detent to the takeoff thrust detent, so it's "click click". That position tells the FADEC computers to set takeoff power and the levers will all be perfectly lined up, the position being a function of the detents in the quadrant.  Of course, if it's got an autothrottle system, the computers take care of moving the levers as well.

In any case, the thrust settings for each engine should be the same, unless the airplane had engines with different thrust ratings inboard and outboard for some reason, and which would be an unpopular feature with most airlines.  I'm not aware of one.


How can this aircraft be stable/maneuverable? The new wave of electric VTOL aircraft concepts (Joby Aviation, Zee, Lilium, Airbus A$^3$, etc...) has produced some audacious unconventional designs.
Now my question, is how Lilium's concept can be stable and/or maneuverable, given the following configuration:

What strikes me is a lack of a surface that creates a force to counteract the momentum generated by the distance between the wing's lift and the gravitational force.
And although control around the yaw axis seems possible with differential thrust, I wonder how the aircraft is controlled around the pitch axis.
From the forward part of the fuselage some canard-like surfaces with integrated propellers are deployed to provide hovering capabilities, however it seems these are supposed to be retracted during forward flight.

Some might suggest the pictures are pure artwork, but Lilium and its investors appear to believe in the concept:

10m€ funding from London-based venture capital firm

What strikes me is a lack of a surface that creates a force to
  counteract the moment generated by the distance between the wing's
  lift and the gravity force.

You are not alone. Believe it or not, Lilium contacted me for advice, and I asked them basically the same thing. They never responded.

I agree with you, this thing will never fly and investors will get burned.

My advice to them would be to sweep the wings forward. This allows to keep the fuselage basically unchanged - you don't want the main spar to go where the pilot sits. But given the small wings this needs substantial sweep.

Update to this answer, February 2020:

Now they have beefed up their canard and skipped retractability, but all they can show is hovering flight for a few minutes at most. Sill no aerodynamic flight. The 300 km range and hour long flight time still are impossible with near-term technology. My verdict stands: Investors will get burned.


What is the use of Stub Wings on Helicopters? Some Helicopters like Russian Mi-24, UH-60 etx have Stub Wings. What is the role of such wings?

Russian Mi-24

UH-60

In addition to serving as support for weapons, we must have in mind that they're both quite fast for a helicopter - 335 km/h (208 mph) for Mi and 294 km/h (183 mph) for UH. At such speeds, even small wings yield considerable aerodynamic effects, just like in planes. From Wikipedia article we can learn that Mi's wings can provide up to 25% of total lift at speed and important stability to counter tendency to Dutch Roll.

Curiously, both mentioned platforms exist in wingless configuration. For UH-60 it's quite common, while Mi-24 had it's wings removed for breaking records. This hints that Mi-24 is much more dependent on it's wings than UH-60.


Can autopilot track ILS without any internal heading reference? I am asking about the internal design of the autopilot of a CRJ200 (no autoland).
I was flying an ILS approach when the AHRS heading started to drift rapidly by 30 degrees. The autopilot somehow was not able track the ILS and started to to fly an "S" turns. After this incident I had a discussion with TRE. He insisted that the ILS has nothing to do with heading. I think that it's impossible or very difficult to design an ILS tracking autopilot without internal heading reference.
How can an autopilot know that a plane is turning and how much without some internal heading reference? Can anybody provide any info on this topic and how the autopilot is implemented?

I'll give an answer with the caveat that I haven't used the system in over 10 years. So maybe do some additional research.
The Collins Proline Flight Director used on the 200 (it's not the Autopilot per se, it's the Flight Director telling the AP what to do), and most similar ones I would expect, needs heading, bank angle and turn rate data to anticipate and judge correction heading offsets, intercept angles, etc, to track navigation solutions whether on "white needles" (FMS navigation) or "green needles" (direct radio signal navigation like VOR or LOC).
If you think about it, it has to; the Flight Director is substituting for your brain, and it needs the same data, about where the airplane is headed and how much it's turning, that you would need to hand fly an approach on raw data.
If you're hand flying and drifting to the left of the loc, you mentally estimate the heading change needed to re-intercept the loc, fly the new heading and wait.  Without compass information you would have a pretty tough time doing it with any efficiency.  If your heading indication did the same thing while you were hand flying, you would probably end up doing something similar if you kept trying to fly the LOC by ignoring the heading indication.
So if the AHRS gyrocompass unit the Flight Director is slaved to starts to slew on its own, it'll get confused and go into a kind of software loop with the resulting S turns.  I would assume that selecting XFER to select the opposite FD/AHRS system fixed the problem.


Is the emergency fluorescent floor lighting strip along the aisle an item on the MEL? Was travelling on a Airbus A320 (night flight) and during the safety briefing noticed that the  fluorescent floor lighting strip referred to in the evacuation instructions was totally absent.  Both sides of the aisle.

I could see the marks on the floor carpet where it must have been earlier tacked on. Was removed and went unreplaced for whatever reason.

Is it OK for an aircraft to fly without this item? Seemed pretty essential to me for a safe evacuation in the dark.

Edit: I did try & take a photo but unfortunately didn't come out so well.

Those lights don't have to be mounted to the floor. They can also be seat mounted.

http://www.bruceind.com/index.php?option=com_k2&view=item&id=90:escape-path-lighting-systems&Itemid=189

http://www.astronics.com/_images/aircraft-safety/EPM%20033010.pdf

This is the AC that provides guidance on the requirements of the system. http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC25.812-1A.pdf

The regulation is 14CFR 25.812


What is the viability of stacking passengers in an airplane cabin? I've came across on youtube a new design for stacking passengers in an airplane cabin, that looks at first sight interesting.

What would be the advantages and drawbacks of such a design? Why this is not common in today's airplanes?

I see several challenges with this design, both technological and not:

Making that design safe enough will be difficult, the structure you add in the cabin would need to be strong enough to maintain rigidity in a crash. That much rigidity would add weight, and would add loads to the structure
The pod walls will make it hard to get by people in the single narrow aisle. In an open design you can squeeze by people in the aisle, in a walled design you'd have no place to go
This design would greatly limit carry-on storage to only what could fit under the seat in front of you
Parents with small children and families traveling together would have a hard time with this design as there's no more than 2 seats together, and limited space for sky cots
Access to a sick passenger would be restricted
Passengers with limited mobility would have a hard time getting into and out of these pods
Comfort is the biggest problem I see with this design. Anyone in one of those pods is spam in a can with limited visibility and movement. Personally I think it looks awful and I would go out of my way to avoid flying with an airline using it


What is the normal descent rate for airliners? A few days ago I was on a flight from SFO to AUS (Airbus 320) and I was shocked by the steep angle of descent into AUS. I have been on over a hundred commercial flights but I've never experienced such a steep descent. I checked the flight on flightaware.com and noticed that the descent rate was 3,000 to 4,000 fpm. On other days the descent rate is closer to 2,500 fpm.

Flightaware data: My flight vs another flight.

Two questions about this:

What is considered a "normal" descent rate for the A320?
What could be the reason for the exceptionally steep descent compared to a normal flight?

There are a few possibilities, there's no way to know which is correct without more information:

There could have been an emergency on board. If someone is showing signs of a serious illness pilots will get the plane on the ground in a hurry to get the person medical attention as soon as they can. Or there could have been an issue with the airplane or a passenger, like someone very drunk and unruly in first class, say
As @falstro said it could have been a slam-dunk approach, where a controller directs airplanes to do steeper descents to solve sequencing issues. Pilots know if they say "unable" that they probably won't get another approach for awhile, so they'll accept a steep descent to get on the ground sooner
It could have been a request of the pilots for a non-emergency reason, like them trying to make up scheduling time, or to stay within fuel limits


Where can I find the regulations on the minimum stall speed for a GA aircraft? I am designing a new GA aircraft that will enter service in 2028. I am looking for the FARS specifying the required minimum stall speed but different sources seem to say different things. On Cornell's Law school website, the Vstall is specified in 23.49. I found the same info on another site.

However, when I check eCFR, 23.49 doesn't exist. In fact, the regulations seem to end at 23.262. Were these other regulations amended or deleted? Which source should I use?

On August 30, 2017, a completely new body of regulations for small aircraft has been put in place which does not distinguish between normal or utility airplanes but low speed (below 250 KTAS) and high speed designs (> 250 KTAS). It also distinguishes between four levels depending on the number of seats (0-1, 2-6, 7-9 and 10-19 passengers). The spirit of the new regulation is to no longer prescribe design-specific rules but more abstract goals in order to limit risk, leaving the details to the aircraft builder.

Also, the number of rules has been drastically cut, and their numbering starts where the old numbering ended. Therefore, 23.49 has become 23.2110 and no longer gives a specific stall speed. All it does is to direct the applicant to determine a stall speed and details what conditions must be covered.

I expect that you have not formally started the certification process of your design, because that date determines which regulations apply. You are now free to select the stall speed of your design as long as you can demonstrate that the aircraft can be operated safely without exceptional pilot skill or strength.

But you can always count on Eurocrats when a body of regulations which has grown like cancer is to be preserved and extended. In their version (CS-23), the maximum stall speed of 113 km/h or 61 knots is still alive and well. However, Amendment 5 has now copied the new body of regulations as well and replaces the old certification standard in the name of global harmonization.

The old regulations reflect the experience which has been collected over decades. Many rules can be traced back to a specific accident and it helps to read through them and to consider why this specific rule has been implemented. Your new design might employ a clever way to avoid that particular condition at all, and then the new liberty of the new regulations will be helpful. But it would be foolish to throw all that experience overboard - a lower stall speed makes any airplane easier to fly. When things happen less quickly and less kinetic energy is involved, more accidents can be avoided and the damage in those that still occur will be lower.


Do safety-critical avionics systems run Linux? I have heard diverse things about this. Some people claim that running Linux on safety-critical avionics systems is a very bad idea. On the other hand some people (who are rather unfamiliar with avionics) said this is not true.

So I would like to know, do aircraft nowadays run on a Linux distribution?
Is it a good idea to incorporate Linux in aircraft? If not, why?

None of the avionics systems I've worked on have used Linux or any consumer-type operating system. There are a few main issues.

First is the practical. Most safety-critical avionics involve a control loop and thus have a real-time requirement. That means it's not just important to run a process and get an answer, you need to get the answer within a tightly-controlled time constraint.  Every critical software process on an aircraft is scheduled to ensure that you have a stable control loop.  To do that, you need a real-time OS and Linux isn't one.

Second is the need for certification.  Software used on an aircraft has to be developed to meet the appropriate development assurance level (DAL) for the associated hazard level.  Safety critical systems are required to meet DAL level "A". Any OS you use has to meet the same DAL as the function running on it.  These requirements are defined in RTCA DO-178C. Linux wasn't developed to this standard. There are only a few OS/software development platforms that are capable of being certified. Green Hills, Wind River, and LynxOS are the few systems I'm familiar with that meet the requirements.

There is also one other constraint in that certification requires very stringent version control.  Avionics will exist in the field for many years and any changes to it have to be certified as well.  Generally, there's no valid reason to update the OS on an old unit, and in many cases you couldn't without upgrading hardware (which is a bigger expense no one wants). So in updating an old unit I have to build the 'new' software to run on the whatever version of OS currently exists in the product. That could be a 15 or 20 years old (or older) platform. A rapidly evolving OS such as Linux would have a negative impact on long term product support.


How does the Eurocopter Blue Edge and Blue Pulse rotor blade design work? In response to my question about quieter helicopters,  KeithS mentioned the Eurocopter Blue Edge helicopter blade design.

According to an article I found on them, there appears to be two components at the very least: a boomerang style rotor tip (Blue Edge) and piezoelectric active flaps (Blue Pulse) on the trailing edges.

How do these (as well as other changes) affect the noise level (i.e., what is the aeronautic principle behind their design)? Also, the sound reduction itself seems relatively modest (3-4 decibels), but is the quality or tone of the sound perceptually different such that it seems much quieter?

EC155 helicopter. Compared with a conventional blade, the Blue Edge has a tip with both forward and rearward sweep.
This gives the blade more time to interact with the vortex 'shed' by the rotor, reducing the characteristic impulsive (slap-slap) blade-vortex interaction noise generated by a helicopter.
The active trailing edge flap harmonises the frequency thus making it quieter.


For how long can an Embraer E195 airplane glide at malfunction? E195 specs:

Maximum Takeoff Weight 52,290 kg
Max Cruise Speed M 0.82
Cruise altitude: 35000 feet

Assume the weather condition is perfect (no clouds or gust winds). Also assume this airplane is fully loaded and just reached cruising altitude at its max speed. There and then, both jet motors immediately stops due to malfunction. No fire or anything, they just stop.

Given this scenario; will this aircraft be able to "glide" downwards for an emergency landing, or will it just drop dead and head for the earth? If it won't glide, how long will it take until it reaches the ground for impact?

(Reason for asking: me, being horribly scared of flying, just took a trip with this exact plane model, and I could not get the above thoughts out of my mind)

It's a rather 'clean' plane. Its maximum L/D is, probably, at least 14. (The table shows cruise L/Ds. The L/Dmax is probably much higher in all cases...) Properly handled, and from 35000ft, it might glide for more than 140 kms...

From https://en.wikipedia.org/wiki/Lift-to-drag_ratio :


What kind of g-forces do birds experience and how does it compare to humans? So bit of an odd one, but I was just looking at a sea-gull flying and wondering what kind of G-forces it could see in day to day flight?

There are probably very fast birds of prey that when pulling out of dives must experience fairly high G Force, but can they (in general) handle more or less than a human flying an aircraft?

Birds regularly experience up 10-14 G according to this website. After looking at how birds and insects fly, scientists came up with the conclusion as to how birds cope with this is because:

  Animals will always have some advantages over machines, such as the ability to use their nervous systems to sense subtleties about the environment around them and alter their flight accordingly.

further up near the top, it mentions comparisons between birds and high performance military aircraft, such as this:

  A Blackbird jet flying nearly 2,000 mph covers 32 of its own body lengths per second. But a common pigeon covers 75 of its body lengths a second.
  The roll rate of the aerobatic A-4 Skyhawk plane is about 720 degrees per second. The roll rate of a barn swallow is more than 5,000 degrees per second.
  Some military aircraft can withstand gravitational forces of 8-10 G (Earth's gravity is equal to 1 G). Many birds routinely experience G-forces greater than 10 G and up to 14 G.

According to another website the reason humans can't cope with high g's as well is because:

  Every bit of our muscular-skeletal system is naturally crafted to deal with Earth’s gravity. Were you to travel to a planet that had a more significant gravity, a more massive planet with 5 G’s for example, you would either be unable to lift yourself off the ground, our the new weight-force would be so much that the air would be forced out of your lungs and your eyes would explode (something gruesome for sure).


Can a plane with 2 sets of shorter wings fly? I am proposing a plane that has 2 short wings of the same size on either side of the fuselage (two in the front and two in the back). Rather than using the horizontal stabilizer to destroy lift, the wings in the back help create lift and adjust the pitch of the plane.

One problem that I thought of is the wingtip vortex created by the front wing hitting the back wings. I'm guessing this can be resolved by placing the back wings higher than the front wings (from a front view of the fuselage).

Could this work?

What you are proposing is called a "tandem wing", and it's been done before. A brief search should produce more than enough research papers about the advantages and disadvantages of this particular design.

The near-complete absence of multiple-wing designs in modern aviation should be a hint that the design has issues. Unless you particularly need the advantages of the design more than the drawbacks, there's no particular reason to use it.


Is it normal practice to use 25 degrees of flaps when taking off at max weight in a PA-28-181? I recently started renting a plane (PA-28-181) from a new flight school and had to get checked out before I had the "OK" to rent.

I had brought 2 family members with me during my checkout because...

They wanted to experience a small plane for the first time
My intentions with the plane were to have the option to fly with a full load of passengers (which I couldn't do in the planes I was used to flying) so I wanted to experience what flying at max gross weight was like.

During the checkout, while in the runup area going through my checklist, the instructor encouraged me to go back through my checklist. Eventually after hearing this suggestion multiple times and not understanding what he was hinting to, he came out and said "You need to set your flaps to 2 notches because we're at max weight".

I hadn't heard this before and I'm not seeing a ton of discussions about this type of thing online. His point was, the flaps would increase lift since we're heavy - that makes sense to me... But they also increase drag.

Note: this was not a short-field takeoff. 5,503ft paved runway, although it was hot (90+ degrees fahrenheit).

So, this leaves me with 3 questions:

Is this correct? When you're on the "heavy" end of the spectrum, should you be deploying flaps?
If so, what would be the proper flap setting at max gross weight?
Since, in this case, the point wasn't to clear an obstacle, would you simply climb out at Vy instead of Vx?

The PA-28-181 POH I have read says to set first stage of flap (10 degrees) for a normal takeoff, and 2 stages (25 degrees) for a short or soft field takeoff. I've flown PA-28s quite a bit and I've never heard any suggestion of using 25 degrees for a normal takeoff. At maximum weight on a hot day at sea level 5,503ft should be plenty at 10 degrees, even if you are at 4000 ft pressure altitude it should still be sufficient, so I see no reason to set 25 degrees.

Setting 25 degrees for takeoff increases lift at the cost of drag, and risk as you are closer to performance limits. An engine failure on takeoff with 25 degrees of flap will give you less time to get the nose down, and stall characteristics are harsher with more flap.

If the runway was shorter I would see 25 degrees as good advice. There are plenty of light aircraft pilots who don't do performance calculations before they fly, drilling 25 degrees of flap when heavy into them may just save their bacon on a hot day on a short airfield.


Are helicopters impacted by fog more than airplanes? With the crash of Kobe Bryant's helicopter, it seems a lot of focus has been placed on the helicopter flying low in fog (under "special VFR"). However, I've seen several suggestions that the helicopter should not have been flying at all

Weather reports indicated that a low cloud cover was present on the day of the crash, further complicating flying. Bryant's pilot was operating the craft under a special clearance for poor weather conditions and reportedly had experience in such situations.

The pilot was IFR rated, but if the investigation proves pilot error it raises the question if helicopters should be more limited in fog. Wired makes it sound even more dire

Flying without sight of the ground or other landmarks can quickly become dangerous, Whitcomb says, because helicopters are not inherently stable. Just staying level and on course demands working four controls at once, using your hands and feet, and keeping track of how each input affects all the others. If you lose sight of where you are and you don’t use your instruments properly, you may not realize you’re turning, or dropping, or even upside down. “You’ll get disoriented within seconds,” Whitcomb says.
Navigating by instrument can also be mentally taxing, says Scott Shappell, who chairs the Department of Human Factors and Behavioral Neurobiology at Embry-Riddle Aeronautical University. He compares visual flight conditions to driving down a familiar highway. Flying by dashboard is more like driving through Rome for the first time—while working a stick shift. “It’s definitely more work,” Shappell says. “The risk goes up.”

Are helicopters really that much more impacted than airplanes by fog?

No.  If anything, given a helicopter can fly a much slower cruise speed than an airplane typically does, they do not require the visibility minimums which fixed wing aircraft do.  VFR weather minimums for a helicopter in uncontrolled airspace are 1/2 mile versus 1 mile for airplanes.  Be that as it may, a helicopter is still vulnerable to Loss of Control Inflight (LOCI) due to pilot error just like any other aircraft.


Do intermeshing rotor helicopters have a swasplate? If no, then how do cyclic and collective controls work? Looking at the Kaman K-Max and H-43 Huskie, it looks like they rely entirely on rotor flaps. How are they controlled?

What's missing from the picture is the hydraulic actuators that move the swash plate. The K-max and all other Kaman helicopters have cyclic and collective control via servo-tabs behind the trailing edge of the blades. These can be deflected manually. The servo tabs are visible on this picture:

Further info from this site, which also shows a cutaway drawing revealing the thin control rods inside the rotor hub fairing:

  The servo flap is a small airfoil located at about 75 percent span of the rotor blade, situated on the trailing edge of each rotor blade. These flaps are controlled by the pilot through push-pull control rods and their function is similar to that of an elevator on fixed wing airplanes. Moving the trailing edge of the flap upward moves the leading edge of the main rotor blade up. This increases the rotor pitch or the lift in very much the same manner as the elevator, on a fixed wing aircraft, changes the angle of attack on the wing. Thus the helicopter pilot can cause the angle of attack of the flap to increase or decrease in pitch, causing the helicopter to alternately dive or climb.


Why do airfoils in an airplane's wings have different shape and size along its span? Why wings of an airplane consist of different shape and size of airfoil. What will happen if the thickness of wing are same throughout the wing?

If the airfoil profile does not change along the span, then we can expect the entire wing to enter a stall condition at the same time. This means the stall break will be sudden and sharp.

If instead we transition between several different airfoil profiles along the span of the wing, we can get different portions of the wing to stall at different airspeeds/angles of attack/load factors, rendering the stall more gradual and furnishing the pilot with warning that the stalling process has begun.

Furthermore, if we profile the wing so the wing root begins to stall first while the wing tip is still flying, then we can reduce the tendency of an incipient stall to roll the plane and also maintain aileron authority and hence roll controllability longer into the stall than if the wingtip and the aileron stalled first.


Vertical and horizontal separation between cruising and climbing aircraft I was recently a passenger on a commercial aircraft at cruise altitude when I noticed another aircraft just reaching its cruising altitude while crossing our flightpath from below, at what looked like a very close distance.

I looked up the two flights (LH491, AC172 on Nov 10, 2018) on Flightradar 24, linearly interpolated the following values in Excel to roughly 2-3 seconds resolution, and calculated the great circle distance between the coordinates:

AC 172 was heading 106° at the very end of its climb to FL 350. LH 491 was heading 51°, cruising at FL 350.

The smallest horizontal separation by my calculation was about 3.67 nm (at 1300 ft vertically). When we reached 1000 ft vertical separation, that distance was about 4.7 nm.

To my understanding, aircraft at these altitudes should always have a separation of least 1000 ft or 5 nm.

Not being an aviation professional myself, could someone please help me understand what was happening here?

I'm sure there must be a duplicate question, but I couldn't find one that involves both the vertical and horizontal components.

I think you may have answered your own question note the use of the word OR

  To my understanding, aircraft at these altitudes should always have a
  separation of least 1000 ft or 5 nm.

If you take a look at your data the aircraft are always separated by 1000 feet OR 5nm. The singular exception to this is when you have the separation quoted at 4.81 miles and 982ft. This can to an extent be explained away by the inaccuracies in systems like FlightRadar24


Why didn’t the Captain of Cathay Pacific flight 780 shut down engine 1 and land with a more reasonable speed? In the approach phase, engine 1 of Cathay Pacific flight 780 got stuck at about 70% N1 and it forced the crew to do an overspeed landing (230knots).

Why didn't they shut it off by turning the fuel pumps off? Is there a backup mechanism if the fuel valve fails like in this scenario?

You can find the full incident report here and this topic is touched upon briefly, but in short they had little to no time to entertain any other options but a full speed landing.

  It was not until the aircraft [was] on the final descent for landing that
  the Commander realised they could not reduce the thrust on the number
  1 engine. The speed was not controllable and from that point, there
  was no time for the crew to consider other strategy nor procedure to
  cope with such emergency situation.

and more in the conclusion section...

  t. At that stage, there was no time for the flight crew to consider other
  strategy nor procedure to cope with such emergency situation. The
  flight crew concentrated on flying the aircraft for a safe landing.

First off, the engine was throwing errors throughout the flight and they were talking to the maintenance team at other points. Ultimately, the proper steps were taken and everything was done by the book. They were prepared for an engine-out landing. When you have a runaway engine malfunction (or throttle stuck at full) shutting down prior to landing may not be the right decision if the running engine provides no immediate safety risk. If you shut down a problematic engine in flight you run the serious risk of not being able to get it started again.

Considering that most airports have a bit (or a lot) of extra runway, EMAS systems and often land at the end of the runway, coming in overspeed and burning through your tires and brakes may be safer than cutting the engine and potentially falling short of the runway.


What skills do aviators have uniquely that could cross over to another industry? I have developed sensitivities to several chemicals used in aerospace. I have to make a shift away from our industry, so I would like to know what are qualities in aviators that would be unique and set us apart from other candidates in a good way. One that immediately comes to mind is our respect for inherent risk. What other tacit knowledge or soft skills apply?

I'm just asking but, have you thought about teaching PPL/ATPL? It's obviously not the same income as a pilot (usually), but you still keep in 'our industry' which I'm sure you really like the most.

Sorry about those sensitivities...


What is the definition of "best L/D"? What does "best L/D" mean? Is it meaningless without context? Do you need to know "best for what?"

Or, is it synonymous with max L/D?

Best $L/D$ is short hand for the airspeed where you have the best ratio of Lift to Drag, and is the same as $\textrm{max}\ L/D$.

If you graph Airspeed -vs- the $L/D$ ratio, it will look something like this:

The peak point of the graph would be the "best" $L/D$ and represents the airspeed where the airplane is the most aerodynamically efficient.  For unpowered flight, it is the airspeed which will result in the best glide ratio.


How can I calculate the force on the nose gear at landing? How can I calculate the force applied on nose gear during landing as nose gear touches the runway little after the landing gear?
I understand force calculations in this question but I think it applies on main gear. How is the force on the nose gear calculated?

Calculating the loads on the nose and main landing gear isn't really different. The answer you linked is a highly simplified approach you should be able to use for the nose landing gear too, but I will provide a "less simplified" approach to calculate the vertical forces. The braking force is already greatly described there.

A simplified approach

First you need to know the impact speed and the spring and damping characteristic of your landing gear.

At touch down there are three possible cases:

Main landing gear touches the ground first. Then the airplane rotates down with an angular speed $\omega_L$. The impact speed of you nose landing gear is therefore $$V_{Impact} = \omega_L \cdot d $$ $d$: distance between the
main and the nose landing gear.
Nose landing gear touches the ground first. (For now empty, if I get time I'll write about it later)
Both landing gears touch the ground at the same time. For a glide angle $\gamma$ the impact speed will be: $$V_{Impact} = V\cdot \sin(\gamma)$$ $V$: airplane speed

The stiffness ($k$) and damping characteristic ($c$) of the landing gear depend mainly on the suspension and the tires used. Tires inflated with a wrong pressure can be really dangerous as they can increase the load on the landing gear.

Putting this data together into a mass spring damper model like in the image

gives you an equation for the nose landing gear movement: $$m\cdot \ddot{x}+c\cdot \dot{x}+k\cdot x = -m\cdot g$$
For the reduced mass $m$ in the model use the mass carried by the nose landing gear.
$$m = LM \cdot \frac{d-d_{CG}}{d}$$
$d_{CG}$: distance from the nose landing gear to the center of gravity

$LM$: aircraft landing mass

$g$: gravity constant

The initial condition for the differential equation is: $$\dot{x}(t=0) = -V_{Impact}$$
The impact occurs at $t=0$.

To calculate the force on the nose landing gear you just have tofind the maximum acceleration and add the static and dynamic loads: $$F_{max}=-m\cdot g -m\cdot \ddot{x}_{max}$$

Real world problems

While the calculations above works for really stiff wings, in reality the loads on the landing gear will be (probably) higher. This is due to the inertial forces of the oscillating aircraft structure.

If you don't understand where this forces come from try moving your arms up and down while standing: you will feel small forces on your feet. Now repeat the experiment with two 60t heavy wings as in the A380 and you'll see that the forces are not neglectable. And were do the oscillations come from? The same as with a guitar string: after a small excitation (plucking the strings/ landing impact) the structure (guitar string/ aircraft wings) begins to oscillate.

What other things doesn't this model take into account? Coupling between nose and main landing gear, rotation inertia, nonlinear tire characteristics,...


What do the dashed extended green lines on this PFD mean? The most important source of information for the pilot is the PFD

Those are radials off of the HME navaid, which is tuned in both Nav receivers. The two radials displayed correspond to the courses set in the two course select windows.

Putting a navaid's identifier into the FMC "FIX" page can also generate similar bearing lines, although there would be a green circle around the navaid in that case.

An ILS (also the departure runway in the flightplan) extended centerline shows as white, not green, and appears when that ILS (or any other) approach is active in the route, rather than when the frequency is tuned.


How does terrain alert system work? How does the voice in landing phase figure out the altitude from the runway? Is it reading the altitude from altimeter or totally separate system?

How accurate is the reading?

Where is the reference point for altitude measurement? is it from landing gears?

For altitude callouts during the landing phase (2500, 1000, 500, 400, ... 100, 50, 20, 10), the computer simply reads the data from the radar altimeter.

The radar altimeter uses radio waves to measure the vertical distance between the airplane and any ground / obstacle below. The radio altimeter is mounted on the underside of the fuselage. They are usually accurate up to feet. This is different than the standard altimeter in the cockpit, which measure air pressure.

The radio altimeter has no idea where the runway is; if there is uneven terrain leading to the airport, or if the pilots' descend profile does not match the glideslope, the readings (and thus the callouts) will not reflect the height above runway elevation.

Note that the airlines can customize the altitude callouts. Different manufacturers also uses slightly different callout patterns.

The second type of audio alerts are messages from a Terrain Awareness and Warning System (TAWS). These systems uses radio altimeter, and may combine information from other sources, such as GPS and a global terrain database, to issue alert messages to the pilots if terrain impact is imminent.

Since the radio altimeter is only capable of detecting ground directly below, it is unable to provide timely warnings in certain situations, e.g. approaching a steep hill. By integrating with GPS data and a terrain database, the computers can predict the flight path of the aircraft and issue warnings if a risk of collision exists.


Are there any privately owned large commercial airports? Do any large, commercial airports exist that aren’t owned and run by the city government they exist in/near?

To provide context, I’m talking major airports that handle commercial airline volume. Do any (hub or regional) airports exist that are fully owned and operated by private companies vs government authorities? Or is this a total fallacy? I could understand companies big enough to have their own corporate fleet/airstrip, but I’m talking a full-scale airport with airlines the public can use.

Building an airport is a very expensive endeavor and usually involves government subsidies or is completely done by the local government. In recent decades, most government owned airports in Europe have however been transformed into companies that both own and operate the airport, usually with the government as initial owner of this company. Since this privatization, some governments have sold their shares of the company resulting in completely privately owned airports.

Going through the 20 busiest airports in Europe from Wikipedia's list, the following airports are completely or by majority privately owned:

London Heathrow Airport owned by Heathrow Airport Holdings
London Gatwick Airport with a majority ownership by GIP
Rome Leonardo da Vinci-Fiumicino owned by Aeroporti di Roma (3.8% government owned)
Zürich Airport owned by Flughafen Zürich AG (38.38% government owned)
Copenhagen Airport owned by Københavns Lufthavne (39.2% government owned)
Lisbon Airport owned by Vinci SA, although operated by the government

The following airports are run by a private company, but they are majority government owned:

Paris Charles de Gaulle Airport and Orly Airport owned by Groupe ADP (50.6% state owned)
Amsterdam Airport Schiphol owned by Royal Schiphol Group (92% government owned)
Frankfurt Airport owned by Fraport (51.47% government owned)
Madrid-Barajas, Barcelona-El Prat and Palma de Majorca owned by Aena S.A. (51% owned by ENAIRE, which is a public corporate entity)
Munich Airport owned by Flughafen München GmbH (100% government owned)
Oslo Gardermoen owned by Avinor (100% state owned)
Manchester Airport owned by Manchester Airport Holdings (64.5% government owned)

The following airports are directly owned by the local governments:

Istanbul Atatürk Airport
Dublin Airport

I am not sure who exactly owns Sheremetyevo and Domodedovo in Moscow.


Is there a minimum distance between a runway and a public road? Does the FAA require a minimum distance the between the TDZ of a runway and a public road?

The reason I ask is because an aircraft landing at a small GA airport (Garnett Municipal, K68) came across the roadway I was driving on low enough that if I'd been 200 yards up the road he'd have hit my truck. Or at least he'd have had to go around.

From the satellite pic you can see that the end of the runway is about 30 feet from the road. The TDZ is about 150 feet. A 3° approach would put you just short of 8' AGL at the road, which is just about exactly how high he was. My truck has a clearance of 10', so it's quite possible to strike vehicles on the road if one is too focused on the runway.

Although it's not a highway (that's about 1000' from the runway), it's the only paved road going east/west for several miles so it gets a bit of traffic

Is it common to put a runway so close to a road?

Yes, there is a minimum area that must be free of obstructions and closed to vehicles, but only for airports that have air carrier operations (see 14 CFR 139.309) or that receive FAA grants. AC 150/5300-13A - Airport Design has all the technical details; the actual distances are calculated from formulas, so there's no single answer. If you're really curious, you can read all the gory details in Chapter 3 and this FAA FAQ has a (very) simplified explanation:

  What is the size of the RSA [Runway Safety Area]?

  The RSA is a rectangular box surrounding
  the runway and is based on the runway design code. The dimensions
  range from 120 feet to 500 feet in width and 240 feet to 1000 feet in
  length beyond the departure end of the runway. (see FAA Advisory
  Circular 150/5300-13, Airport Design) Generally, on airports that
  serve air carrier aircraft, the RSA extends 250 feet either side of
  the runway centerline and 1000 feet beyond each end of the runway.

You didn't mention which airport you're asking about, but presumably it's either privately owned and/or doesn't receive FAA grant money.


What is the true formula for parasite drag? I found this site with formulas to calculate for the parasite drag. But I wondered if these formulas are to calculate parasite drag or the parasite drag coefficient? So do you have to multiply the calculated value with the square of the velocity, as in the formula for the general drag force?

I also wonder if there is a difference between the wetted area of an airfoil and the normal planform area?

The philosophy employed on the Stanford site is to convert the product of drag coefficient and corresponding surface area to a "drag area", which is technically the area of a body with a drag coefficient of 1. See page 1-8 in Sighard Hoerner's book "Fluid Dynamic Drag" for the definition and tons of helpful real-world data on drag.

To convert this into a drag force, it still needs to be multiplied with the dynamic pressure, which is the product of the square of the velocity, the air density and the factor 0.5. No further inclusion of the surface area is needed, as this is already factored into the drag area values of each drag component.

Using the drag coefficient lets you compare the relative dragginess of drag components (friction drag, pressure drag, ...). If you want to compare the dragginess of aircraft components (wing, fuselage, tail surfaces, ...), using their drag area adds a factor for their size, making it easier to compare the relative influence of the drag of different aircraft components on total drag.

To answer your second question: Planform area is the wing area you see in the top view of an aircraft, and the wetted area is the actual area which is exposed to airflow. If you start with the planform area, you need first to subtract the part of the wing which is inside the fuselage. Next, you double the result to account for both sides, top and bottom, and then you divide this sum by the cosine of the dihedral angle and the cosine of the incidence angle to arrive at your wetted area.


How are conflicts between pilot flying and pilot not-flying over aircraft control resolved? A question about the "my aircraft" protocol led to several answers that explain how the pilot flying (PF) can delegate control to the pilot not flying (PNF).

It also seems that a pilot (e.g. returning from a break) can assert "I have control" without the other pilot first offering control.

From what I've read, unlike with ATC communications, the exact phrases used vary from airline to airline and are not the subject of rules or guidance by authorities such as the FAA. It also seems that in some airlines, some pilots are more casual about the use of standard phrases.

The only fixed idea seems to be that as long as both pilots have uttered some complementary phrase, both should now be aware that a transfer of control has occurred, and to whom.

This led me to wonder: under what circumstances can the PF refuse the PNF's request, how would they phrase this and does the other pilot or pilots always defer to the senior pilot?

The whole idea behind the policies and procedures for transferring control of the aircraft between the pilots is so that everybody is always on the same page.  Somebody always needs to be flying the aircraft.

If I want to hand control over to the other pilot, and he doesn't want it/can't take it, he would simply explain why not.  I have never seen standard operating procedures (SOP's) that explain how to refuse, as simply saying no or unable should let the other pilot know that there is a problem and should be the beginning of a conversation about it.  On the other hand, the SOP's do cover the scenario where the other pilot doesn't respond.

This is why there is always a challenge/response as part of handing off control.  If the other pilot were incapacitated and I didn't realize it, I would say "You have the flight controls" (or whatever phrase that the SOP's require) and wait for his response.  If they didn't respond, I wouldn't just blindly stop flying the airplane and assume that they are.  Instead, I could say it again or look over at them to see what was going on and figure out what the problem was while continuing to fly the airplane.

Now, to request control from the other pilot (rather than requesting them to take control), I would simply skip the first part and say "I have the flight controls" and they should respond with "You have the flight controls."  Again, it's a challenge/response situation so that everybody is on the same page.

In either case, the captain is the final authority and can always override a request.  Airline policies are all very clear that if there is a disagreement, the captain has the "tie breaking" vote.


What does automatic pitch trim is available mean, when bank angle is below 33°? I was reading about the bank angle protection mode in an A320. I have a few doubts about it.

I know that if the bank angle exceeds 33 degrees then automatic pitch trim is not available and hence of the side stick is released the aircraft would come back to a bank angle of 33 degrees and stabilise. But I don't understand what happens if the bank angle is BELOW 33 degrees. I read that the automatic pitch trim is available. What does that mean?

In the context of the A320 as you are describing, pitch trim does not mean trimming with the horizontal stabilizer. Instead, it means that up to 33 deg bank angle, no aft stick pressure is needed to maintain horizontal flight, or more precisely, the load factor (for example, at 33 deg bank, the load factor is approximately 1.15g).

Up to 33 deg bank, the Normal Mode automatically commands the necessary load factor with the longitudinal side stick neutral. Since Normal Mode also ensures a neutral spiral stability up to 33 deg bank outside of High Speed Protection, you can maintain a coordinated level turn with side stick completely neutral.

Beyond 33 deg, longitudinal stick neutral no longer commands the necessary load factor for horizontal flight. Therefore, you would need to have aft pressure. Furthermore, there is positive spiral stability, which means non-zero lateral pressure is also required to maintain the bank angle.

For more information, you could consult: source 1 and source 2.


How do CH-47 pilots lower the tail during a pinnacle landing? (thedrive.com)

Given the recent rescue of a climber on Mt. Hood by a Chinook, how are the pilots able to lower the tail in this situation? Is this just the natural angle during a hover, or are there some adjustments the pilots can make to the fore and aft collective individually?

A careful balance of nose-up cyclic and decreased collective to stick the aft of the ship firmly in place. Not so much a landing, as flying with the aft gear and ramp planted.


What are the recent developments in the satellite-based tracking of aircraft? I find it pretty unsettling that in 2016 it is still not possible to track transoceanic flights using flightradar24 or flightaware, because of lack of coverage.

When the unfortunate MH370 accident occurred, I stumbled upon news of the British company Inmarsat launching, or discussing the launch of, a series of satellites to help track transoceanic flights anywhere in the World, that could also be useful to determine vertical separation.

Quite a few months have passed and I seem to have lost track of this. So I am here to ask those who know more about it:

what are the recent developments in the satellite-based tracking of aircraft?

The German Space Agency (DLR) worked with ESA to track flights from space using ADS-B, the same technology behind flightaware etc.
Some info about it is here

A commercial entity, called Aireon, is planning a global constellation to monitor aircraft that will piggy-back upon the next generation of Iridium satellites. But, unfortunately, the recent setbacks to SpaceX launch capabilities have delayed Aireon's schedule. The first launch of the Iridium-NEXT satellites occurred on Jan 14th 2017 and the entire constellation - providing near global ADS-B coverage - is planned to be complete by mid-2018.

Aside from ADS-B, there is also research going on to track aircraft through their exhaust emissions (something I'm working on right now). Nothing is published about that yet, though.


Do fighters or bombers ever ditch their weapons? I was just reading about the reasons why commercial aircraft will sometimes need to dump (or otherwise consume) their extra fuel. Things like decreasing landing weight, speed, reducing fire risk, etc.

It seems like the same would apply to fighter and bomber aircraft with their weapons as well.

Do these aircraft ever ditch their weapons (presumably in a disarmed state) if forced to land in an emergency? If not, why?

Introduction

I have experience flying the A7-E Corsair off the USS Nimitz in the mid-1980's. There were typical scenarios that would require us to either jettison fuel, ordinance, or other stores. Below you will find a description of some of these scenarios.

 Take off

I was in a brief with my Skipper for a night hop, and he asked me perhaps the best question any one ever asked me in a brief. I didn't have an answer, but started practicing that flight until I left the Navy. He asked, "Salt, what do you do after your take-off checklist while under tension, and right before you salute for the catapult shot?" He went on to describe what he thinks and does.

Reach out look at and touch the salvo jettison button. Physically touch it.
Grab the lower ejection handle.
Salute and come back inside to look at the airspeed indicator. If you don't have 175 knots by the end of the cat stroke eject. No questions.

Every catapult shot I took from that day on I practiced his advice. There were 2 buttons available to jettison stores attached to the pylons under the wing. One was the select jettison, which allowed you to pick a location under the wing, and then jettison that store. The salvo jettison was a big red button close to the middle of the instrument panel, and did not discriminate. Both buttons were next to one another. All stores were ejected from the pylons. If you had a catapult shot that didn't give you enough airspeed off the bow this was an option to buy some immediate lift.

I came off Cat 2 one day and made my clearing turn. As I was cleaning up the aircraft and heading to the squadron's rendezvous point I saw something in the ocean. You know what it looks like when you take a big stone and throw it in a pond? It disappears but leaves a foot print of turbulence and bubbles on the surface of the water. Well, I looked down over the water as I was heading out and saw that kind of footprint. It was as big as an aircraft and persistent, just kind of staying there without dissipating. It looked like an aircraft had ditched, but an A6 had gone off just prior to me and used the salvo jettison getting rid of all his stores.

 Tanker Duty

At times the buddy store would malfunction, and stop transferring with 500 pounds of fuel sloshing around in one of the tanks on the aircraft. You couldn't take a trap with a partially full fuel tank. The slug of fuel would shoot forward, and the tank might be ripped off the pylon. Fuel tanks were not too expensive, but the buddy store had all sorts of hardware and electronics it. Squadrons didn't like to lose these. I had a buddy store on pylon 3 and a drop tank on pylon 4.

On my last rendezvous the buddy store failed to finish transferring all the fuel in my drop tank on pylon 4 and so I said goodbye to the aircraft on my wing and called maintenance to discuss the problem. The maintenance officer got on the radio and we went over the NATOPS procedures for jettisoning the fuel tank. We found a stretch of ocean that was clear of any traffic, and after going over it once he emphasized to me, "Look at the station you selected and read it off to me." After telling him it was number 4, he finished with, "Now make sure you use select jettison and not the salvo button." I pushed the select jettison button and looked in my mirror to see the fuel tank drop away from the wing, and quickly looking in my left mirror caught the buddy store falling away as well. I swear I pushed the select jettison button, and had that image in my head. I had of course hit the salvo jettison button out routine practice of reaching for the salvo jet button every cat shot.

 Air Combat

The performance characteristics of the A7-E put it at a disadvantage against fighters designed specifically for air-to-air combat. The training we received for dealing foreign fighters suggested that, once engaged ingressing to the target, we would make a defensive turn, and if the enemy got behind our wing, jettison our bombs and other stores, e.g. fuel tanks fully committing to the fight. The fuel consumption while at military power at sea level for the subsonic A7-E was around 6,000 pounds per hour, which is quite good. On the other hand, a fighter in burner, by the time it gets to behind the A7's wing line will be fuel starved. To stay in the fight with burner will require a kill within 30 seconds.

 Landing & Dumping Fuel

We brought back weapons all the time to the ship. A good example is the AGM-62 Walleye, a 1,000 pound bomb with a television camera on the nose and in-flight avionics for "guiding" its flight. This was done either by the delivery aircraft, or a second aircraft in a stand-off position. We seldom dropped this weapon in practice, and would bring it back to the ship. We would launch with AIM-9's, when the fighters weren't hogging them all, and bring those back too.

The following acknowledges that there are Rules of Engagement, and within these rules and I will say this. As an attack pilot my mission was to put bombs on target, and if I didn't get the bombs there someone had to go back the next day and finish my job. The enemy would be waiting for that next strike. If for some reason I couldn't get to my target I would find a target of opportunity. Attack pilots don't bring their bombs home with them. Drop them somewhere.

As for fuel, tactical high performance aircraft from the time they take off are emergency fuel in a sense. By the time you got to the landing sequence you were almost always short on fuel. Emergency fuel is at 1,200 pounds and calling the ball at 2,500 pounds was pretty typical. That gave you 30 minutes in the pattern. A divert to another field where there was a climb en-route would eat at that reserve a bit more aggressively.

Every once in a while you might come back heavy with fuel. The maximum field landing weight was 5,000 pounds, and above this weight the procedure was to dump fuel. There were altitude restrictions on how low you could be to do this. The 5,000 pound limit was because the brakes would overheat. This would eventually cause the fusible plugs to blow releasing the pressure in the tires sometime later. This was to be avoided.

 Taking the Captain to NAS North Island

While at NAS China Lake I was working with the A7E software development team on aircraft software enhancements. I would go out and test the software in the operational environment. The detachment there had an A7E Trainer, which was a two seat version of the single seater. I would at times ferry personnel where required. I got a call to take a Captain to NAS North Island and this was a quick hop. I ended up landing over weight. After dropping off my cargo I headed out to the hold short and got a call from tower informing me that my breaks were smoking. I decided to get airborne so I could get home, and if the tires blew in flight, take the gear at my home base. Left the wheels in the air stream climbing out staying below the 220 knot restriction for lowering the gear. The flight was incident free.


What is this twin engine propeller aircraft flying for Garuda airlines in Indonesia in 1983? Twin propeller small civil aircraft flown by Garuda Airlines Indonesia in 1983.

aZxGQ.jpg

Looks to be a Shorts Skyvan.  Sometime called the ‘Flying Shoebox’.

https://en.m.wikipedia.org/wiki/Short_SC.7_Skyvan


What are the differences between C208 versions? I am aware of a few versions of C208:

C208 Caravan
C208 Grand Caravan
C208 Grand Caravan Amphibian

Amphibian has pantoons with retractable landing gears, but what is the difference between C208 Caravan and C208 Grand Caravan? Is it just the cargo compartment in the belly? Are there other versions of C208? What are the differences between them?

The civilian variants can be summed up in this table I made based on Wikipedia:

What to take out of this, is the different fuselage lengths, and that the amphibian comes in two fuselage lengths.

The belly-mounted cargo-hold is optional.

There are also military variants, even one that shoots missiles (an incentive to check out the Wikipedia page).


Do icing limits exist for parked aircraft? Are there any aircraft that have a limit on the amount of ice or snow that can be on the aircraft when stationary and on the ground?

I'm not aware of any limits every being published on transport airplanes.  On large aircraft, it's not too big a deal structurally because the bending loads imposed by a snow cover are not significant, since bending load applied by a couple of feet of snow (which weighs about 40lb/sqft) on such a large structure, designed to support 100+ lbs/sqft, is relatively mild.
On little airplanes, this can be a problem however.  Let 2 feet of snow, or 40 lbs/sqft, accumulate on a light aircraft or ultralight with large wings, designed to support maybe 5-15 lbs/sqft of negative load, and you will likely find the wing outboard of the strut is permanently bent down or has collapsed when you want to go flying.  Nature's just done a static load test on your wings and got carried away.
On a metal airplane, you at least take comfort in the fact that if the wing is not permanently bent down after you remove the snow, you're good to go.
On an airplane with wood spars, this is more of a gamble, because wood structures that are overloaded beyond the compression limit of the side in compression (the spar below the strut attachment bolt in the case of snow load) without overloading beyond the tension limit of the side in tension (above the strut attachment bolt, where it just breaks), can suffer from a dormant compression failure in the wood itself.
Compression failures are where the cellular structure of the wood fibres partially collapses.  This can leave the wood apparently undamaged (unless you can inspect the area to detect the tell-tale fine line across the grain), but weaken the wood in tension.  So when you go flying, and the wood below the spar attachment is loaded in tension again and has lost some fraction of its ultimate tensile strength, and you hit a bump that applies some extra G, whoops!
Anyway, if you own a light aircraft with wood spars you need to be aware of this and be extra vigilant about preventing large snow loads on the wings.  I'm not really keen on wood spars on light planes for this reason.  It's a reason you never buy a used Classic with wood spars that's had a wing tip repair (from the tip hitting the ground during a groundloop).  A friend bought an Aeronca Champ once and found his right wing had a wood compression failure above the spar bolt, caused by a wing tip strike, when he took it apart to recover it, after flying it about a year.  He was lucky; any significant negative G in that condition would have been fatal.
You could work out a limit for yourself if you know the wing loading and structural G limit for your own airplane. So if your wing loading at gross is 10 lb/sqft, and it's good for negative 2 Gs in flight, you can estimate that the wing can tolerate 20 lbs/sqft of snow accumulation, or about 1 foot thick and wouldn't want too much more than that to accumulate.


Descend via STAR, after getting crossing restriction previously The ATC issues "Cross BHAWK at FL240" initially. After few minutes, the ATC instructs "Descend Via FYTTE5 arrival". Should we comply with the crossing restriction at BHAWK, or the restriction can be omitted?
The JO 7110.65Y says

Clearance to “descent via” authorizes pilots:

To descend at pilot discretion to meet published restrictions on a STAR.

and

“Climb via SID except after Baret, maintain flight level one niner
zero.”
NOTE1. Considering the principle that the last ATC clearance issued
has precedence over the previous, the phraseology “maintain
(altitude)” alone cancels previously issued altitude restrictions,
including SID/STAR altitude restrictions unless they are restated or
modified, and authorizes an unrestricted climb or descent. Speed
restrictions remain in effect unless the controller explicitly cancels
the speed restrictions.

However, the example given in "descend via" does not say anything about "previous assigned crossing altitude." And the note given in "climb via" example only explains the phraseology "maintain" would cancel previously issued altitude.
Is there any FAA document stating the altitude restrictions assigned previously can be omitted or still valid, after getting "descend via" clearance?

The restriction to cross "BHAWK at FL240" is overridden by the controllers latest clearance to "Descend Via FYTTE5 arrival", unless they  include the instruction  descend via "EXCEPT MAINTAIN FL240".
FAA Climb Via/Descend Via Speed Clearances Frequently Asked Questions, page 6, questions 8.
If unsure, you should query ATC though.


Is the A320 family allowed to take off with the flaps retracted? Is it legal for the A320 family (A318, A319, A320 and A321) to take off without flaps?

An answer to this question states that the A300 can take off without flaps. On the other hand, the 737 family of aircraft is not approved for a no-flap takeoff. (Under the right circumstances, you might survive one, but the margins for losing an engine would be unacceptable, so no data is published for such an operation.)

For the A320 family it is not allowed. Above shows the takeoff configurations. Anything else and the takeoff warning will be triggered. I also checked the abnormal and special operations, nothing says a 0/0 takeoff is possible.

Each plane is certified for certain configurations. What applies to the A300 or 767 does not apply to all planes.

I took it one step further and checked the MEL (ignoring the fact that if the flaps are inoperative, the crew will be in for a treat when it comes to landing). At least one slats/flaps computer is required, and for the flaps/slats to be tested before the flight. The same MEL allows a takeoff if the landing gear can't be retracted.

(Click to enlarge.)

Is it impossible? Of course not. A 737-300 once crash landed on grass, was fixed, and took-off from that same grass field. Nothing is impossible. But for the day-to-day operations, the answer is no.


Could an F-35 really be 3% rare-earth? The Financial Times' China targets rare earth export curbs to hobble US defence industry states:

Fighter jets such as the F-35, a Lockheed Martin aircraft, rely heavily on rare earths for critical components such as electrical power systems and magnets. A Congressional Research Service report said that each F-35 required 417kg of rare-earth materials.

Rare Earth elements are commonplace rather than rare in high tech devices and systems these days, but usually in small quantities. The exception are rare-earth permanent magnets used in electric motors and generators.
But 417 kg sounds like a lot; it's 3.1% of a reported 13,290 kg dry weight of an F-35A.
Could this be true? Or are they counting for just for example the whole motor rather than the rare earth within it?

The ~416 kg is confirmed by multiple sources. The most useful I found[1] uses a comparison:

Product
REE

Mobile phone
0.0005 kg

Air conditioner
0.12 kg

Toyota Prius
15 kg

Lockheed-Martin F-35
416 kg

Navy surface ships
1818 kg

Navy submarines
3636 kg

Based on @MichaelSeifert's input, I've found confirmation for the REE in a Toyota Prius – its curb weight is 1380 kg (toyota.ca):

Each electric Prius motor requires 1 kilogram (2.2 lb) of neodymium, and each battery uses 10 to 15 kg (22-33 lb) of lanthanum. That number will nearly double under Toyota's plans to boost the car's fuel economy. (reuters.com; emphasis mine)

If a Toyota Prius is 1.1–2.3% rare earth by mass, then 3% for the F-35 shouldn't be surprising.
Worth noting:

Despite their name, rare-earth elements are relatively plentiful in Earth's crust, with cerium being the 25th most abundant element at 68 parts per million, more abundant than copper. [emphasis mine]

1: Ganguli, Rajive, and Douglas R. Cook. "Rare earths: A review of the landscape." MRS Energy & Sustainability 5 (2018). (PDF)


What is this vintage small airplane with low wings and twin propeller engines? Could anyone help me to identify this vintage aircraft, that can be seen in the background of this photograph, please?

It's a LET L-200 Morava, a Czech plane...
http://www.aviastar.org/air/czech/let_l-200.php