American Airlines Flight 742 "flight control system" problems
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Originally Posted by Ashling
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.
Sully started the APU to make sure to keep optimum electrical and hydraulic power, and certainly not to maintain what is called normal law BTW, to allow him to 'pull full back with impunity and leave the aircraft to figure it out'.
Would you challenge Sully face to face on that one ?
As the NTSB said the aircraft max performed
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.
OTOH there was an opportunity to improve the touchdown, but the System is not programmed for it.
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Originally Posted by Owain Glyndwr
That is your number. I have yet to see any published numerical data from AI to support stall at 20.5 deg AoA with CONF 2 (or 3).
Gordon Corps - FLIGHT INTERNATIONAL - AUG 86
Not so. Ground effect is there irrespective of elevator deflection
You are ducking the issue here also. The point of my remarks was that pitch rate is important. You continually ignore this effect.
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Conf iture
Explain to me please how a remark made by Gordon during a demonstration of the FBW concept on an A300 a year before the A320 ever flew becomes a definitive statement of A320 performance?
BTW, the pitch was actually constant over the last 3 seconds according to the detailed plots in the NTSB Performance Group Report, and you still refuse to address the possibility that it was the pitch rate in the previous 8 seconds that triggered the command restriction, neither do you recognise that there are other flare techniques that have been shown to give better results even using the current laws.
"Around 20 deg"
Gordon Corps - FLIGHT INTERNATIONAL - AUG 86
Gordon Corps - FLIGHT INTERNATIONAL - AUG 86
BTW, the pitch was actually constant over the last 3 seconds according to the detailed plots in the NTSB Performance Group Report, and you still refuse to address the possibility that it was the pitch rate in the previous 8 seconds that triggered the command restriction, neither do you recognise that there are other flare techniques that have been shown to give better results even using the current laws.
Last edited by Owain Glyndwr; 10th Apr 2013 at 16:35.
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Couple of quotes from the NTSB
The NTSB concludes that, despite being unable to complete the Engine Dual Failure checklist, the captain started the APU, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane remained in normal law and maintained the flight envelope protections, one of which protects against a stall.
Despite not reaching this portion of the Engine Dual Failure checklist, the captain stated during postaccident interviews that he thought that he had obtained green dot speed immediately after the bird strike, maintained that speed until the airplane was configured for landing, and, after deploying the flaps, maintained a speed “safely above VLS,” which is the lowest selectable airspeed providing an appropriate margin to the stall speed. However, FDR data indicated that the airplane was below green dot speed and at VLS or slightly less for most of the descent, and about 15 to 19 knots below VLS during the last 200 feet.
The flight envelope protections allowed the captain to pull full aft on the sidestick without the risk of stalling the airplane.
The NTSB concludes that, despite being unable to complete the Engine Dual Failure checklist, the captain started the APU, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane remained in normal law and maintained the flight envelope protections, one of which protects against a stall.
Despite not reaching this portion of the Engine Dual Failure checklist, the captain stated during postaccident interviews that he thought that he had obtained green dot speed immediately after the bird strike, maintained that speed until the airplane was configured for landing, and, after deploying the flaps, maintained a speed “safely above VLS,” which is the lowest selectable airspeed providing an appropriate margin to the stall speed. However, FDR data indicated that the airplane was below green dot speed and at VLS or slightly less for most of the descent, and about 15 to 19 knots below VLS during the last 200 feet.
The flight envelope protections allowed the captain to pull full aft on the sidestick without the risk of stalling the airplane.
Last edited by Ashling; 10th Apr 2013 at 23:33.
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More from the BEA this time
In alternate law, considering the airspeed management and flap configuration, it is likely that stall alarms would have been triggered several times during the descent, and the risk of actually stalling would have been high
A stall alarm during the flare would have had severe consequences, the only way to avoid stall being to reduce the pitch angle
In fact, the phugoid oscillation damping function only prevented the pilot from increasing the AoA, because the energy management during the descent did not make it possable to reduce the vertical speed at impact.
In reality phugoid oscillations induce pitch variations that can have more severe consequences than a high vertical speed when entering water
In alternate law, considering the airspeed management and flap configuration, it is likely that stall alarms would have been triggered several times during the descent, and the risk of actually stalling would have been high
A stall alarm during the flare would have had severe consequences, the only way to avoid stall being to reduce the pitch angle
In fact, the phugoid oscillation damping function only prevented the pilot from increasing the AoA, because the energy management during the descent did not make it possable to reduce the vertical speed at impact.
In reality phugoid oscillations induce pitch variations that can have more severe consequences than a high vertical speed when entering water
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Confiture
There was no risk of stalling in normal law and they were in normal law because Sully started the APU. I credit him for knowing that.
If your in alternate law or a 737 at VLS -19, or equivelant, there is a very high risk of a stall. Fact. If you think there isn't a risk of a stall in that speed regime you are a dangerous fool.
You reckon you could fly a 737 that slow with stall warners and shake shakers going off and flare it under that pressure ....... well do you
I will continue to be tense and uptight about stalls thankyou very much, at the heights Sully was at there would be no coming back from one, you would be well advised to take heed and not suggest incorrect stall recovery procedures as you clearly have.
Oh and I wouldn't challenge Sully about a thing, as the NTSB and BEA have made clear, he did a great job, I fully concur. I would however challenge the mantra that pretends it was all perfect. That denies us the opportunity to learn what could have been improved and to train to that end. I would hope that we could agree on at least that.
There was no risk of stalling in normal law and they were in normal law because Sully started the APU. I credit him for knowing that.
If your in alternate law or a 737 at VLS -19, or equivelant, there is a very high risk of a stall. Fact. If you think there isn't a risk of a stall in that speed regime you are a dangerous fool.
You reckon you could fly a 737 that slow with stall warners and shake shakers going off and flare it under that pressure ....... well do you
I will continue to be tense and uptight about stalls thankyou very much, at the heights Sully was at there would be no coming back from one, you would be well advised to take heed and not suggest incorrect stall recovery procedures as you clearly have.
Oh and I wouldn't challenge Sully about a thing, as the NTSB and BEA have made clear, he did a great job, I fully concur. I would however challenge the mantra that pretends it was all perfect. That denies us the opportunity to learn what could have been improved and to train to that end. I would hope that we could agree on at least that.
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@Ashling:
I don't think CONF iture really cares about the minutae of the Hudson ditching. As he hinted at earlier, what this is really about for him is his theory that if the flight control logic gave Capt. Asseline just a couple of extra degrees of pitch at Habsheim, the trees would have been cleared and all would have been well.
For him this is akin to religious conviction, and no amount of evidence to the contrary will sway him from his quest.
I don't think CONF iture really cares about the minutae of the Hudson ditching. As he hinted at earlier, what this is really about for him is his theory that if the flight control logic gave Capt. Asseline just a couple of extra degrees of pitch at Habsheim, the trees would have been cleared and all would have been well.
For him this is akin to religious conviction, and no amount of evidence to the contrary will sway him from his quest.
Originally Posted by Dozy
For him this is akin to religious conviction, and no amount of evidence to the contrary will sway him from his quest.
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Originally Posted by Owain Glyndwr
Explain to me please how a remark made by Gordon during a demonstration of the FBW concept on an A300 a year before the A320 ever flew becomes a definitive statement of A320 performance?
But as you do think to know better than Gordon ... I'm listening.
BTW, the pitch was actually constant over the last 3 seconds according to the detailed plots in the NTSB Performance Group Report, and you still refuse to address the possibility that it was the pitch rate in the previous 8 seconds that triggered the command restriction
neither do you recognise that there are other flare techniques that have been shown to give better results even using the current laws.
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Originally Posted by Ashling
There was no risk of stalling in normal law and they were in normal law because Sully started the APU. I credit him for knowing that.
You start an APU to secure a main source for electrical power.
You reckon you could fly a 737 that slow with stall warners and shake shakers going off and flare it under that pressure ....... well do you
One single stick shaker activation on the Hudson would have unambiguously warned Sully that his attention on the speed was not ideal. Instead of it the system acted on the elevators independently of the stick position, masking the reality. Transparency has much better taste.
I will continue to be tense and uptight about stalls thankyou very much, at the heights Sully was at there would be no coming back from one, you would be well advised to take heed and not suggest incorrect stall recovery procedures as you clearly have.
You would be well advised to quote ...
Opting for one of the airports around would have been an invitation for stalling, but not the Hudson, that's where that crew did so well.
But you're all over stall ... and there was none.
Any idea how unprotected aircrafts managed to glide without stalling ?
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Any reason it would have changed ... ?
neither do you recognise that there are other flare techniques that have been shown to give better results even using the current laws.
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Originally Posted by Owain Glyndwr
Yes - it's called flight testing.
So you accept that the current laws are capable to being used to better effect?
Originally Posted by Ashling
You said you would recover from a stall warning at 150 the same way you would at 3000, by releasing the backpressure.
That is incorrect
That is incorrect
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Good ... I'm still listening ...
Quote:
So you accept that the current laws are capable to being used to better effect?
Did I ever say the contrary ?
So you accept that the current laws are capable to being used to better effect?
Did I ever say the contrary ?
Last edited by Owain Glyndwr; 11th Apr 2013 at 14:26.
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Originally Posted by Owain Glyndwr
And I'm still waiting for you to supply evidence to justify your value of 20.5 degrees for alphastall.
You can always try Ashling ... "As you rightly state, Alpha Max is not Alpha stall. I think the gap is 3 degrees or so"
Maybe he has the Official post flight test document to state that alpha stall is around 20 deg ... ?
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You don't accept the word fron an Airbus guy ... but have nothing to advance.
What I don't accept is the calm acceptance that nothing changed after he made that remark to a journalist. At that point in time, before flight test, he would have been obliged to rely on information from wind tunnel tests corrected for Reynolds Number effects using empirical corrections based on experience with other aircraft designs tested in the same wind tunnel. That work was done in the UK so I have some knowledge of it. Small differences between these predictions and flight test results are not uncommon.
Like you I am limited by the absence of any published definitive post-flight data for the aircraft, so like you I cannot offer a definitive value. What I can say is based on memory and that tells me that the stall AoA ('g' break) varies slightly with flap angle but generally lies around 19 degrees.
Last edited by Owain Glyndwr; 12th Apr 2013 at 08:37.
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Confiture
You are of course correct, the aim of the initial part of a stall recovery is to reduce the AoA to remove the warning or break the stall.
However you talked about releasing the back pressure to achieve this which is incorrect, you move the stick forward, reducing power or moving the stab trim if needed to gain control authority.
It's an important difference as just releasing the back pressure may not work if the aircraft has auto trimmed or you have manually trimmed.
Both Boeing and Airbus recomend moving the stick forward at the first symptom of the stall, warning, shaker, buffet etc.
At 150', with no engines, well, as Alex Ferguson says, it's squeaky bum time.
You are of course correct, the aim of the initial part of a stall recovery is to reduce the AoA to remove the warning or break the stall.
However you talked about releasing the back pressure to achieve this which is incorrect, you move the stick forward, reducing power or moving the stab trim if needed to gain control authority.
It's an important difference as just releasing the back pressure may not work if the aircraft has auto trimmed or you have manually trimmed.
Both Boeing and Airbus recomend moving the stick forward at the first symptom of the stall, warning, shaker, buffet etc.
At 150', with no engines, well, as Alex Ferguson says, it's squeaky bum time.
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Originally Posted by Ashling
you move the stick forward, reducing power or moving the stab trim if needed to gain control authority.
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Originally Posted by Owain Glyndwr
Small differences between these predictions and flight test results are not uncommon.
But whatever the figure you consider as to be reliable, the key point of that discussion is still the following one :
Originally Posted by NTSB
there was some additional angle of attack margin available to flare the airplane and reduce the descent rate at touchdown