Stalling a big plane, Question for Eric MC?
Discussion
I've just been reading about the Air France crash, Airbus A330 vanished off Radar in turbulence.
One of the theories is that it stalled at 35,000 feet after slowing down too much for turbulence.
Can anyone explain why? I'm curious.
It also still doesn't explain why the plane vanished off radar with no mayday call either. It either blew up or broke up in mid air surely.....
Condolences to all those families out there who suffered loss.
One of the theories is that it stalled at 35,000 feet after slowing down too much for turbulence.
Comment on article said:
A stall at 35,000ft – the altitude at which Flight 447 was cruising – is hard to recover from in still air. In the heart of a furious tropical storm at night, it could be near impossible. High-altitude stalls claimed several aircraft in the early days of jet aircraft.
Conventional thinking would say that stalling at high altitude would be better as there would be more time to regain control, gather speed and get the nose back up but this is seemingly not the case.Can anyone explain why? I'm curious.
It also still doesn't explain why the plane vanished off radar with no mayday call either. It either blew up or broke up in mid air surely.....
Condolences to all those families out there who suffered loss.
Any aircraft can be put into a situation where it cannot maintain lift over its wings i.e. a stall. Once a plane stalls, what happens next can be variable, depending on the natural characteristics of the aircraft, what the plane was doing prior to the stall, and the speed at which the crew recognise the situation and take corrective action.
Modern airliners should really never be put into a position (except when landing) where a stall situation arises. Obviously, in difficult flying conditions or in the dark, when reliance is placed totally on the instruments in the cockpit, stalls sometimes occur.
There have been many occasions when airliners have stalled or, for various reasons, departed controlled flight.
If the departure is sudden and dramatic (like a complete roll onto its back - as has happenbed with aircraft as large as a 747) the crew can be taken so much by surprise that it isn't obvious to them what has gone wrong and what the plane is actually doing. Therefore, if they don't know what the plane is doing, whether they apply the corrective action or not is often a matter of luck. If they do the right thing, they might get away with a major scare and possibly a slightly bent aeropplane. If they get it wrong, a crash and possibly an in-flight breakup will probably occur.
And, as I mentioned earlier, this aircraft DID NOT dispappear off radar. It wasn't being tracked by any radar at the time of the accident. It had already moved out of range of the Brazilian ATC radar sites.
Modern airliners should really never be put into a position (except when landing) where a stall situation arises. Obviously, in difficult flying conditions or in the dark, when reliance is placed totally on the instruments in the cockpit, stalls sometimes occur.
There have been many occasions when airliners have stalled or, for various reasons, departed controlled flight.
If the departure is sudden and dramatic (like a complete roll onto its back - as has happenbed with aircraft as large as a 747) the crew can be taken so much by surprise that it isn't obvious to them what has gone wrong and what the plane is actually doing. Therefore, if they don't know what the plane is doing, whether they apply the corrective action or not is often a matter of luck. If they do the right thing, they might get away with a major scare and possibly a slightly bent aeropplane. If they get it wrong, a crash and possibly an in-flight breakup will probably occur.
And, as I mentioned earlier, this aircraft DID NOT dispappear off radar. It wasn't being tracked by any radar at the time of the accident. It had already moved out of range of the Brazilian ATC radar sites.
Edited by Eric Mc on Friday 5th June 11:08
Eric Mc said:
Any aircraft can be put into a situation where it cannot maintain lift over its wings i.e. a stall. Once a plane stalls, what happens next can be variable, depending on the natural characteristics of the aircraft, what the plane was doing prior to the stall, and the speed at which the crew recognise the situation and take corrective action.
Modern airliners should really never be put into a position (except when landing) where a stall situation arises. Obviously, in difficult flying conditions or in the dark, when reliance is placed totally on the instruments in the cockpit, stalls sometimes occur.
There have been many occasions when airliners have stalled or, for various reasons, departed controlled flight.
If the departure is sudden and dramatic (like a complete roll onto its back - as has happenbed with aircraft as large as a 747) the crew can be taken so much by surprise that it isn't obvious to them what has gone wrong and what the plane is actually doing. Therefore, if they don't know what the plane is doing, whether they apply the corrective action or not is often a matter of luck. If they do the right thing, they might get away with a major scare and possibly a slightly bent aeropplane. If they get it wrong, a crash and possibly an in-flight breakup will probably occur.
And, as I mentioned earlier, this aircraft DID NOT dispappear off radar. It wasn't being tracked by any radar at the time of the accident. It had already moved out of range of the Brazilian ATC radar sites.
Sure, but the question is why a high altitude stall appears to be regarded as especially threatening. All I can think of is that perhaps controls are less effective in thinner air so it's harder to avoid or recover from the stall.Modern airliners should really never be put into a position (except when landing) where a stall situation arises. Obviously, in difficult flying conditions or in the dark, when reliance is placed totally on the instruments in the cockpit, stalls sometimes occur.
There have been many occasions when airliners have stalled or, for various reasons, departed controlled flight.
If the departure is sudden and dramatic (like a complete roll onto its back - as has happenbed with aircraft as large as a 747) the crew can be taken so much by surprise that it isn't obvious to them what has gone wrong and what the plane is actually doing. Therefore, if they don't know what the plane is doing, whether they apply the corrective action or not is often a matter of luck. If they do the right thing, they might get away with a major scare and possibly a slightly bent aeropplane. If they get it wrong, a crash and possibly an in-flight breakup will probably occur.
And, as I mentioned earlier, this aircraft DID NOT dispappear off radar. It wasn't being tracked by any radar at the time of the accident. It had already moved out of range of the Brazilian ATC radar sites.
Edited by Eric Mc on Friday 5th June 11:08
I'm sure that's a factor. At high altitudes, the difference in the maximum airspeed allowable and the minimum speed top prevent stalling gets very narrow - so getting into a stall is easier. That is why there are all sorts of stall warning systems built into these aircraft to prevent the aircraft getting into a sitaution where a stall might develop.
When flying in the dark, with no visible horizon, sometimes a situation can be developing without the crew realising it. They should, of course, be making use of their instruments to monitor the situation but even the best crews can make mistakes or allow themselves to become distracted by some other issue.
When flying in the dark, with no visible horizon, sometimes a situation can be developing without the crew realising it. They should, of course, be making use of their instruments to monitor the situation but even the best crews can make mistakes or allow themselves to become distracted by some other issue.
mybrainhurts said:
Doesn't the autopilot take care of everything these days...?
In theory - but the autopilot can be fed duff information by the computers - or it can pop out of "auto" mode if it can't cope with a developing situation. So it doesn't solve all problems and can sometimes create new ones.Nope. It can only control the aircraft up to a point, when it goes beyond this, it throws a wobbler and usually trips out.
However, modern aircraft have numerous systems to counter stalling, from stick shakers to wake up dopey crew, stick pushers to reduce the angle of attack and in the case of Airbus a system call alpha floor protection. Which gives you a warning if you are performing a manouever that is likely to lead to a stall.
You then have Alpha protection which is where the automatics try and actively prevent a stall. They can whack in the Auto throttle, bring in flaps or slats aswell as reduce the angle of attack.
High altitude stalling isn't any more dangerous really, but it is more likely to happen because of things like compressability. When flying at high altitude, the stall speed stays the same in relation to Indicated Airspeed, but as you climb your IAS reduces whilst your TAS (True Airspeed) stays the same.
You eventually get to a position called coffin corner, where you have a very small speed margin between the high speed buffet and the stall speed. This is why there is little margin for error and things can go wrong.
I know nothing about the Air France Crash or its causes, so this is just for information.
However, modern aircraft have numerous systems to counter stalling, from stick shakers to wake up dopey crew, stick pushers to reduce the angle of attack and in the case of Airbus a system call alpha floor protection. Which gives you a warning if you are performing a manouever that is likely to lead to a stall.
You then have Alpha protection which is where the automatics try and actively prevent a stall. They can whack in the Auto throttle, bring in flaps or slats aswell as reduce the angle of attack.
High altitude stalling isn't any more dangerous really, but it is more likely to happen because of things like compressability. When flying at high altitude, the stall speed stays the same in relation to Indicated Airspeed, but as you climb your IAS reduces whilst your TAS (True Airspeed) stays the same.
You eventually get to a position called coffin corner, where you have a very small speed margin between the high speed buffet and the stall speed. This is why there is little margin for error and things can go wrong.
I know nothing about the Air France Crash or its causes, so this is just for information.
Edited by IforB on Friday 5th June 13:32
mybrainhurts said:
Doesn't the autopilot take care of everything these days...?
No.It only takes care of everything in certain modes. There are serveral 'partial over ride modes' eg control wheel steering / speed intervene which allow manual/auto flight interface (a clumsy way of putting a simple thing).
Comment on article said:
A stall at 35,000ft – the altitude at which Flight 447 was cruising – is hard to recover from in still air. In the heart of a furious tropical storm at night, it could be near impossible. High-altitude stalls claimed several aircraft in the early days of jet aircraft.
I'd be surprised if the stall characteristics of a modern airliner were to make it unrecoverable, there are just so many systems designed to stop a stall in the first place. It may be difficult to recover once in a deep stall or once the aircraft has departed from controlled flight, but I find it difficult to believe the aircraft could have got into that situation at all.I'd suggest it was likely to be as a result of a catastrophic failure due to the weather or something similar. The lack of a Mayday call would suggest it was a massive problem and occupied the whole attention of the crew.
Eric Mc said:
And, as I mentioned earlier, this aircraft DID NOT dispappear off radar. It wasn't being tracked by any radar at the time of the accident. It had already moved out of range of the Brazilian ATC radar sites.
Thank goodness the news stations have experts to prevent this kind of information being misinterpreted in the rush to splurge unformation onto rolling news. Or not.
mikee boy said:
I'd be surprised if the stall characteristics of a modern airliner were to make it unrecoverable, there are just so many systems designed to stop a stall in the first place. It may be difficult to recover once in a deep stall or once the aircraft has departed from controlled flight, but I find it difficult to believe the aircraft could have got into that situation at all.
Some planes (including some quite large ones) can't reliably be recovered from a stall. I don't know if this is the case for any modern jumbos, but it might be. Given all the effort put into avoiding that sort of situation in the first place, having a stall be non-recoverable might not be seen as a big deal. It's rather like the situation we had a few years ago where several jumbos lost their tail fins due to large rudder corrections from the pilot. I'd like to have thought that planes were designed so that it is difficult/impossible to break them or lose control irrecoverably, but I think the reality is a bit less pleasant.No 747's have been lost due to over enthusiastic rudder inputs.
An A300 went down due to the rudder coming off after the F/O followed the training and advice given by the manufacturer.
You might be thinking off the 737 rudder reversal issues that seem to have caused the Colorado Springs and Pittsburgh crashes and a temporary loss of control of an Eastwinds 737 on approach to Richmond.
Certain aircraft configurations do cause problems with stall recovery. T-tail aircraft for example, they can enter a "superstall" where the downflow from the wings interrupts the airflow over the tail.
An A300 went down due to the rudder coming off after the F/O followed the training and advice given by the manufacturer.
You might be thinking off the 737 rudder reversal issues that seem to have caused the Colorado Springs and Pittsburgh crashes and a temporary loss of control of an Eastwinds 737 on approach to Richmond.
Certain aircraft configurations do cause problems with stall recovery. T-tail aircraft for example, they can enter a "superstall" where the downflow from the wings interrupts the airflow over the tail.
Edited by IforB on Friday 5th June 15:10
IforB said:
No 747's have been lost due to over enthusiastic rudder inputs.
An A300 went down due to the rudder coming off after the F/O followed the training and advice given by the manufacturer.
You might be thinking off the 737 rudder reversal issues that seem to have caused the Colorado Springs and Pittsburgh crashes and a temporary loss of control of an Eastwinds 737 on approach to Richmond.
I do remember the 737 issues, but I thought they were believed to be the result of a control system failure (jammed hydraulic valve I think). What I was thinking of was the aircraft losses that resulted from the fin separating from the fuselage after several large rudder inputs from the pilot when encountering wake turbulence. I don't remember which model it was, but it was one of the first to use a bonded fin, would that be in the A300 series? I seem to remember there was a design flaw in the control system that lead to the rudder control switching to high gain in flight instead of the other way round, so it was easy for the unsuspecting pilot to provide very large control inputs. An A300 went down due to the rudder coming off after the F/O followed the training and advice given by the manufacturer.
You might be thinking off the 737 rudder reversal issues that seem to have caused the Colorado Springs and Pittsburgh crashes and a temporary loss of control of an Eastwinds 737 on approach to Richmond.
I think it was an A300, but there was not a fault with the plane. The pilots had not been trained / briefed (I think) that the pedal sensitivity changed in flight, and also I believe the training to use the rudder to recover from wake turbulance was unusual.
If you think about the size of the rudders and the force of the air at 200 + mph swinging it from side to side so reversing the force very quickly is not a good idea. The documentary that I saw included the fact that Boeing were quick to put out a safety notice essentially saying please do not try this on our airplanes.
If you think about the size of the rudders and the force of the air at 200 + mph swinging it from side to side so reversing the force very quickly is not a good idea. The documentary that I saw included the fact that Boeing were quick to put out a safety notice essentially saying please do not try this on our airplanes.
The crash in Queens was due to the tail coming off an A300, however the actions of the crew were exactly as Airbus themselves had prescribed.
A 747 had its tail come off in Japan thanks to poor repair work after a tail strike.
The 737 rudder issue is slightly contentious as all of the parties (especially Boeing oddly enough........) coming up with a different reason for the accidents. However the NTSB decided that it was due to a design flaw. Not something that Boeing would have liked.
A 747 had its tail come off in Japan thanks to poor repair work after a tail strike.
The 737 rudder issue is slightly contentious as all of the parties (especially Boeing oddly enough........) coming up with a different reason for the accidents. However the NTSB decided that it was due to a design flaw. Not something that Boeing would have liked.
Edited by IforB on Friday 5th June 23:30
Re the autopilot keeping the aircraft out of trouble, it would appear from the ACARS messages from the AF flight that the AP disconnected. There also seems to be evidence of the Air Data systems failing, possibly due to icing or hail damage. If this was the case then the crew would have found themselves in a situation where they had no accurate airspeed or attitude information, in the dark, in the middle of a CB.
As Eric said earlier, the difference between stall speed and never exceed speed at that altitude and weight could have been in the order of 20kts. Hand flying in those that sort of situation where the aircraft is already on a knife edge would be hard enough in benign conditions, but without having reference to airspeed info and with the aircraft in Alternate Law mode they would have been hard pressed not to stall or overspeed.
As Eric said earlier, the difference between stall speed and never exceed speed at that altitude and weight could have been in the order of 20kts. Hand flying in those that sort of situation where the aircraft is already on a knife edge would be hard enough in benign conditions, but without having reference to airspeed info and with the aircraft in Alternate Law mode they would have been hard pressed not to stall or overspeed.
IforB said:
The crash in Queens was due to the tail coming off an A300, however the actions of the crew were exactly as Airbus themselves had prescribed.
A 747 had its tail come off in Japan thanks to poor repair work after a tail strike.
The 737 rudder issue is slightly contentious as all of the parties (especially Boeing oddly enough........) coming up with a different reason for the accidents. However the NTSB decided that it was due to a design flaw. Not something that Boeing would have liked.
A 747 had its tail come off in Japan thanks to poor repair work after a tail strike.
The 737 rudder issue is slightly contentious as all of the parties (especially Boeing oddly enough........) coming up with a different reason for the accidents. However the NTSB decided that it was due to a design flaw. Not something that Boeing would have liked.
Edited by IforB on Friday 5th June 23:30
The 747 had the rear bulkhead blow out, taking the tail with it. I don't think it was a Stall, simply because when the China Airlines 747 stalled over the Pacific the crew managed to get a Mayday out and recover it. Surely the AirFrance crew would be able to aswell?
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