American Airlines Flight 742 "flight control system" problems
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I have been busy enjoying the Florida Keys the last couple of days so haven't been on the computer so since I was the only one that went through that near miss, I know what happened, no one else does. I don't care if you believe my story or not but I survived doing what I did. Maybe turning right and diving might have worked, maybe not. I am here doing what I did and may still be here doing what you would do. Who knows? Isn't it about time to shut this discussion down and get back to something more productive? Out again.
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You do understand if you roll right 60 degrees and push down you don't turn that much but if the other guy makes the same choice to dive now you have your wing 60 degrees up and much more likely to make contact with the other aircrafts wing rather than being parallel to his wing by watching him approach you. Once he is under your belly he is no longer a threat so you don't need floor windows as one suggests over and over. Please make this the final OUT.
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Bubbers
You really need to read what you write! Bank 60 degrees right and "push" to dive? Sounds like an outside turn.
In all of this "I survived did the right thing etc", you have not even considered the other pilot! He was probably thinking WTF is he doing when he saw your manoeuvre, as he was probably expecting the "correct" rules of the air response. Yes you are still here but you were lucky.
You really need to read what you write! Bank 60 degrees right and "push" to dive? Sounds like an outside turn.
In all of this "I survived did the right thing etc", you have not even considered the other pilot! He was probably thinking WTF is he doing when he saw your manoeuvre, as he was probably expecting the "correct" rules of the air response. Yes you are still here but you were lucky.
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Since bubbers has 'signed out' on this story, I am sure it is best to leave it now for his 'memories'?
(1400 hours C310L and R, right way up most of the time, apart from the odd harmless 'sporting' with Jags and Phantoms in the Scottish LFA in days of old
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(1400 hours C310L and R, right way up most of the time, apart from the odd harmless 'sporting' with Jags and Phantoms in the Scottish LFA in days of old
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Originally Posted by Owain Glyndw
So is your recommendation that if you are going to ditch the pilot should switch (or be switched) to direct law?
As said earlier, normal law brings a disconnection between the inputs and the effective flight control movements. The pilot has actually no idea how the control surfaces are displaced. To correctly evaluate and anticipate the possible aircraft response is more of a nebulous process.
Flight control movements are transparent to the pilot.
Sully was looking for some finesse in the final act but the computers had decided otherwise.
That being said, I certainly would not mind a straightforward direct law when manually flying in final. It was a pleasure on the Boeing, don't think it would be different on the Bus ... but it would not fit too well I guess with the overall protection concept by Airbus.
Originally Posted by Ashling
When I said what would you do if you got a stall warning I was referring to a Boeing not an Airbus in normal law. If your in a Boeing (or a Bus in alternate/direct law) what are you going to do when the stall warning goes off at 150' because your too slow.
Putting the issue of the stall warning aside, in your Boeing even if you had room to pull and you did it at 50' you'd have 4 secs to impact. Given the relatively heavy weight, and slow speed I can't see 2 degrees making much difference, it would take a finite time to achieve those 2 degrees and a finite time for the aircraft to respond to that attitude change, it's a very different thing flaring at the correct speed to trying to do so 19kts slow, the aircraft won't respond the same way or anything close to it.
The pitch angle behavior of the airplane in the last 100 ft of flight is of interest, since changes in pitch have a strong influence on the flare and touchdown conditions. As noted above, in the last 50 ft, the angle of attack was about 3.5° below αmax and even 1.5° below αprot; consequently, there was some additional angle of attack margin available to flare the airplane and reduce the descent rate at touchdown.
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CONF iture
Thank you for clarifying your position. Previously I had not realised that you were stating your personal preferences.
Two small comments and then I shall shut up.
This 'disconnection' is true for any aircraft operating under a C* law or a variant thereof. For that matter it is true of any aircraft fitted with a yaw, pitch or roll damper. F16, B777, B787 and the various Airbus designs are in the first category, Concorde in the second.
From memory that is an extract from the NTSB final report on the Hudson accident, finally adopted in May 2010, a year before the Roswell G650 accident. I wonder if the NTSB would use the same wording today?
Thank you for clarifying your position. Previously I had not realised that you were stating your personal preferences.
Two small comments and then I shall shut up.
As said earlier, normal law brings a disconnection between the inputs and the effective flight control movements.
in the last 50 ft, the angle of attack was about 3.5° below αmax and even 1.5° below αprot; consequently, there was some additional angle of attack margin available to flare the airplane and reduce the descent rate at touchdown.
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Confiture
With respect your reaction to the stick shaker/stallwarning/buffet, in this case, would be very different at 3000 from 150.
At 3000 you would apply the aircrafts stall recovery procedure. I believe Boeing state that you treat the approach to the stall as an actual stall so you smoothly apply nose down elevator (trimming if needed) to remove the warning. With no engines you'd need to keep the nose down longer and further to accelerate but you'd have enough room to put yourself in a much healthier situation. If your in an Airbus, as Sully was, its enough altitude to get out of Alpha Prot and improve your energy state significantly.
That is very different to just releasing the back pressure,
At 150 engines out your in huge trouble as you can't nose down so releasing the back pressure is about all you can do. I doubt it would be enough to remove the warning, or if it did the warning might soon return as the nose may still be high enough to keep your speed were it is or still decreasing just at a slower rate (remember you are @ Flap 15 so leading edges are fully deployed so lots of drag) so your alpha might not reduce enough to exit the warning which you might re-enter prior to your flare. You may also increase your rate of descent. Its also rather dependant on were you've trimmed to as well. If you've trimmed into your speed decrease releasing the back pressure will do little but if you've not trimmed you might find that your nose pitchs further forward than you intended which may be undesirable at 150' and of course cause you to pull straight back into the warning. Of course all this under huge pressure with no training in how to do it or in handling the aircraft, on a regular basis, in that regime. Good luck. I'll take the Bus for this one thankyou.
Its also important to appreciate that the aircraft has v little excess energy at F speed -19. A flare in that state is a very different thing to one at Vapp +5. In effect you are 24 kts slower than normal. This wouldn't be a flare in the normal sense or anywhere remotely close to it. It might reduce the rate of descent a touch but as you only have 3.5 degrees to play with (taking into account the error in AoA allowed for by the gap between max and stall)
the downside if you stuff it up and stall is catastrophic and you have absolutely no practise in doing this. If your rate of descent is survivable its not worth it.
With respect your reaction to the stick shaker/stallwarning/buffet, in this case, would be very different at 3000 from 150.
At 3000 you would apply the aircrafts stall recovery procedure. I believe Boeing state that you treat the approach to the stall as an actual stall so you smoothly apply nose down elevator (trimming if needed) to remove the warning. With no engines you'd need to keep the nose down longer and further to accelerate but you'd have enough room to put yourself in a much healthier situation. If your in an Airbus, as Sully was, its enough altitude to get out of Alpha Prot and improve your energy state significantly.
That is very different to just releasing the back pressure,
At 150 engines out your in huge trouble as you can't nose down so releasing the back pressure is about all you can do. I doubt it would be enough to remove the warning, or if it did the warning might soon return as the nose may still be high enough to keep your speed were it is or still decreasing just at a slower rate (remember you are @ Flap 15 so leading edges are fully deployed so lots of drag) so your alpha might not reduce enough to exit the warning which you might re-enter prior to your flare. You may also increase your rate of descent. Its also rather dependant on were you've trimmed to as well. If you've trimmed into your speed decrease releasing the back pressure will do little but if you've not trimmed you might find that your nose pitchs further forward than you intended which may be undesirable at 150' and of course cause you to pull straight back into the warning. Of course all this under huge pressure with no training in how to do it or in handling the aircraft, on a regular basis, in that regime. Good luck. I'll take the Bus for this one thankyou.
Its also important to appreciate that the aircraft has v little excess energy at F speed -19. A flare in that state is a very different thing to one at Vapp +5. In effect you are 24 kts slower than normal. This wouldn't be a flare in the normal sense or anywhere remotely close to it. It might reduce the rate of descent a touch but as you only have 3.5 degrees to play with (taking into account the error in AoA allowed for by the gap between max and stall)
the downside if you stuff it up and stall is catastrophic and you have absolutely no practise in doing this. If your rate of descent is survivable its not worth it.
Last edited by Ashling; 8th Apr 2013 at 17:09.
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Originally Posted by Owain Glyndwr
Thank you for clarifying your position. Previously I had not realised that you were stating your personal preferences.
This 'disconnection' is true for any aircraft operating under a C* law or a variant thereof. For that matter it is true of any aircraft fitted with a yaw, pitch or roll damper. F16, B777, B787 and the various Airbus designs are in the first category, Concorde in the second.
Also, if at full stick deflection the ailerons can move full travel but the next second because one oleo momentarily compressed the ailerons are only allowed half deflection it is somehow confusing to the pilot. That' s what we learned from the report in Hamburg and don't look for such info in the FCOM ...
From memory that is an extract from the NTSB final report on the Hudson accident, finally adopted in May 2010, a year before the Roswell G650 accident. I wonder if the NTSB would use the same wording today?
The G650 was in flight testing to validate theory, the 320 was under 20 years of operation, I expect them to know what's behind alpha management by now ...
When the manufacturer largely publicizes its ability to operate safely at alpha max it is questionable how when requested the aircraft keeps 4 deg short of that setting.
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CONF iture
You are missing the point. You say that the aircraft had 3.5 deg (now escalated to 4 deg see below) margin to stall, but this is based on free air values. The Roswell accident showed that in ground effect alphastall can be reduced by as much as 3.65 deg below the free air value, which would remove all your presumed margin.
Again you miss the point. You did not dissent earlier in this discussion when I pointed out that the system does allow one to get to alpha max as shown by Habsheim. The system does however take note of the rate at which alpha max is being approached and if it looks likely that alpha max will be exceeded when proximity to the limit and rate of change are taken together then it acts to prevent any overshoot towards stall. That is what happened here.
The G650 was in flight testing to validate theory, the 320 was under 20 years of operation, I expect them to know what's behind alpha management by now ...
When the manufacturer largely publicizes its ability to operate safely at alpha max it is questionable how when requested the aircraft keeps 4 deg short of that setting.
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Thanks OK and Owain
Much more succinct and eloquents than anything I've written on it of late.
I did'nt appreciate that Alpha could increase that much in ground effect. You learn something new etc
Still a bit concerned that all Conf would do with a stall warning at 3000 is to release the back pressure.
Much more succinct and eloquents than anything I've written on it of late.
I did'nt appreciate that Alpha could increase that much in ground effect. You learn something new etc
Still a bit concerned that all Conf would do with a stall warning at 3000 is to release the back pressure.
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Originally Posted by Owain Glyndwr
You are missing the point. You say that the aircraft had 3.5 deg (now escalated to 4 deg see below) margin to stall
G650 and G4 have different wings with different characteristics as Gulfstream learned.
What about the A320 wing now ... .
Ground effect would help to an improved touchdown if only the elevators were to follow the full backstick by Sully for the last 2 seconds.
Again you miss the point. You did not dissent earlier in this discussion when I pointed out that the system does allow one to get to alpha max as shown by Habsheim.
Alpha max there ... ?
Where are your data ?
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Originally Posted by Ashling
Still a bit concerned that all Conf would do with a stall warning at 3000 is to release the back pressure.
Critical scenarios for a stall situation have more chances to develop in one try to get over an obstacle or to abusively try to extend a glide or over bank to align, none was applicable to the Hudson as Sully took very early on that sensible decision to go there for that unobstructed and 'unlimited runway'.
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Originally Posted by OK465
With a stabilized no thrust descent rate of somewhere around -1500 FPM at green dot or VFE, -700 FPM with speed decaying is already well into 'the flare'. Even with the additional AOA margin indicated on the gage, I would tend to hold what I had under these conditions at 50', or at least be extremely gentle.
In the meantime Sully fully pulled for the last 2 seconds not because he was ignorant at flying as Clandestino put it but because he thought it was the appropriate thing to do in this late stage, and the NTSB did not disapprove did they ?
If Sully would have thought he would have stalled by doing so, I do presume he would not have proceeded that way and would have also opted for an extremely gentle way instead but only him could confirm.
What I do find interesting is how simulating the Hudson in full direct law has not been tested ... ?
Would it produce the catastrophic scenarios Airbus or Ashling are prone to sell or could it simply give nicer touchdowns ... ?
You're not one of them, but what about that sudden absolute need to be stall protected ?
Did all the unprotected aircrafts that had to glide ended stalled ?
Is the 787 the dreamliner and the 320 the lifesaver ...
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add another 3 deg for alpha stall.
What about the A320 wing now ...
You are ducking the issue. Even if the A320 number is less than 3.65 deg the margin to stall will be reduced in ground effect.
For me your presumed margin to stall is too high on two counts.
Ground effect would help to an improved touchdown if only the elevators were to follow the full backstick by Sully for the last 2 seconds.
Have we talk about Habsheim yet ?
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I think there's every reason to be concerned. If you get a stall warning you treat it as such and move the column centraly forward until the warning ceases. Best not to confuse the how we should respond to a stall warning, there have been quite enough fatalities recently. I of course accept that if you have something to avoid, particularly without engines, you may have to trade energy but that is a different matter as is GPWS and you simply stated 3000' v 150'. I certainly hope thats not representative of your attitude to stall warnings in commercial aircraft but it would explain your thoughts on what is sensable in that speed regime.
BTW I remembered that the 737 adjusts the feel on the column to force you to pull harder as the speed enters the approach to stall regime so by releasing back pressure you may get a nasty shock depending were you've trimmed to of course.
Sully knew he wouldn't stall as he knew he was in direct law which he achieved by starting the APU out of sequence so he could pull full back with impunity and leave the aircraft to figure it out. As the NTSB said the aircraft max performed
I have no difficulty whatsoever in saying that a Boeing flown at the correct speeds would have been as successfull as the 320 and neither would Airbus. Might have been better. What I have trouble with is saying that in the speed regime that the aircraft was actually flown in.
The difficulty I have with your case is not that its impossable, theoreticaly, to squeeze a degree or 2 more out of it but that practicaly it doesn't stack up. You want us to believe that a pilot under immense pressure and a huge workload in an unfamiliar environment who has already allowed his speed to decrease dangerously low is going to be able to tickle the buffet with a stick shaker and stall warner/GPWS going off bearing in mind he has had no training in doing this ! Bear in mind too that the reason the stick shaker is there is because it has a low buffet to stall margin in some configs and this will mask feel of said buffet on the stick and of course he will have no idea what his actual margin is and as Owain says as he enters ground effect his alpha will increase.
Maybe an experienced pilot after a few goes in the sim might achieve something by trial and error (I know sim fidelity in the stall is good but not wholly perfect) but for me its not real world, but I agree it would be interesting to see the outcomes.
In that speed regime I'm still in a Bus
A footnote: I was wrong to refer to Owain saying alpha will increase in ground effect, it is alpha stall that reduces which is what he said earlier. My mistake, see posts below.
BTW I remembered that the 737 adjusts the feel on the column to force you to pull harder as the speed enters the approach to stall regime so by releasing back pressure you may get a nasty shock depending were you've trimmed to of course.
Sully knew he wouldn't stall as he knew he was in direct law which he achieved by starting the APU out of sequence so he could pull full back with impunity and leave the aircraft to figure it out. As the NTSB said the aircraft max performed
I have no difficulty whatsoever in saying that a Boeing flown at the correct speeds would have been as successfull as the 320 and neither would Airbus. Might have been better. What I have trouble with is saying that in the speed regime that the aircraft was actually flown in.
The difficulty I have with your case is not that its impossable, theoreticaly, to squeeze a degree or 2 more out of it but that practicaly it doesn't stack up. You want us to believe that a pilot under immense pressure and a huge workload in an unfamiliar environment who has already allowed his speed to decrease dangerously low is going to be able to tickle the buffet with a stick shaker and stall warner/GPWS going off bearing in mind he has had no training in doing this ! Bear in mind too that the reason the stick shaker is there is because it has a low buffet to stall margin in some configs and this will mask feel of said buffet on the stick and of course he will have no idea what his actual margin is and as Owain says as he enters ground effect his alpha will increase.
Maybe an experienced pilot after a few goes in the sim might achieve something by trial and error (I know sim fidelity in the stall is good but not wholly perfect) but for me its not real world, but I agree it would be interesting to see the outcomes.
In that speed regime I'm still in a Bus
A footnote: I was wrong to refer to Owain saying alpha will increase in ground effect, it is alpha stall that reduces which is what he said earlier. My mistake, see posts below.
Last edited by Ashling; 9th Apr 2013 at 18:54.
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Ashling
That is not at all what I am saying 
As he enters ground effect the lift at a given alpha will increase and the drag at a given CL will decrease. This is not the same as saying that alpha will increase.
With regard to the effect of ground on stall, the maximum lift coefficient is hardly affected, but the AoA at which it is achieved is reduced, as is the stall AoA. This effect was mentioned by IIRC one of the Boeing lecturers at the recent RAeS conference on flight testing of stalls, but the relevant graph was not dimensioned.
and as Owain says as he enters ground effect his alpha will increase.
As he enters ground effect the lift at a given alpha will increase and the drag at a given CL will decrease. This is not the same as saying that alpha will increase.
With regard to the effect of ground on stall, the maximum lift coefficient is hardly affected, but the AoA at which it is achieved is reduced, as is the stall AoA. This effect was mentioned by IIRC one of the Boeing lecturers at the recent RAeS conference on flight testing of stalls, but the relevant graph was not dimensioned.
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Thankyou Owain
I apologise for misrepresenting what you said earlier. Duly re-educated
Am I correct in saying that it is the value of Alpha Stall that decreases rather than the AoA increasing?
As I said earlier I was blissfully unaware this happened
I apologise for misrepresenting what you said earlier. Duly re-educated
Am I correct in saying that it is the value of Alpha Stall that decreases rather than the AoA increasing?
As I said earlier I was blissfully unaware this happened
Last edited by Ashling; 9th Apr 2013 at 18:37.
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Ashling
Yes, that is correct.
Plenty of early NACA evidence that on straight wings the loss is 2 to 3 degrees, but jolly difficult to find anything for modern swept wings (proprietary information I expect). Wouldn't be surprised to find that loss is bigger on swept wings with the tips closer to the ground, but the G650 values I think took everyone by surprise. I think a value around 3 deg would not be an unreasonable assumption.
Am I correct in saying that it is the value of Alpha Stall that decreases rather than the AoA increasing?
Plenty of early NACA evidence that on straight wings the loss is 2 to 3 degrees, but jolly difficult to find anything for modern swept wings (proprietary information I expect). Wouldn't be surprised to find that loss is bigger on swept wings with the tips closer to the ground, but the G650 values I think took everyone by surprise. I think a value around 3 deg would not be an unreasonable assumption.