American Airlines Flight 742 "flight control system" problems
seven stroke, didn't most sim attempts at that fail? There's a thread here on that, but I don't recall that discussion other than being interested in how one simulates the surprise of that when people know about Sully's water landing flight.
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Sully landed in the Hudson with no loss of life. He did everything right. Yes he may have been able to return for a downwind landing but if it failed we would have a lot of dead people so I agree with his decision.
I have a flight sim 2000 in my computer that I have tried because of the turkey buzzards in TGU Honduras to simulate a bird strike with dual engine failure in a 757. I have tried the standing it on a wingtip return to land downwind because that is the only survivable outcome with the terrain and it is 50/50 on how it works out. If you land short you hit a 70 ft cliff and if you land long you go off the end up a hill but it still is your only chance of survival. If they had a big river I would take my chances on that but they don't.
I have a flight sim 2000 in my computer that I have tried because of the turkey buzzards in TGU Honduras to simulate a bird strike with dual engine failure in a 757. I have tried the standing it on a wingtip return to land downwind because that is the only survivable outcome with the terrain and it is 50/50 on how it works out. If you land short you hit a 70 ft cliff and if you land long you go off the end up a hill but it still is your only chance of survival. If they had a big river I would take my chances on that but they don't.
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Lonewolf. What I read about the sim attempts...
When an immediate turn was made, 4 out of 4 pilots made LGA.
When a 30 second, WTF, delay was added, none made LGA.
So...you see birds, you feel the bumps and lose power...how long a "WTF" delay do you have?
Now, I haven't flown the airbus. I could have been a captain on the AB320 for sully's airline. I took a 737 bid instead...it paid less too.
But I sure have flown out of LGA an awful lot...and yes me and my friends all looked down the Hudson and thought it would be a good place to land...and I give you my word it was before Sully landed there that we thought of it.
I also looked out on the Interstate 80 freeway and thought it might work too.
But I stand by my comments and echo the comments of Bubbers...you have to be looking out the freaking window and be ultra alert. Alertness can shift for different things at different altitudes. At low altitudes, small planes, big planes, birds and terrain...and all pilots should have that ''pre selected" emergency landing spot.
I also believe in what I said about banking to protect the engines, placing them below and above the formation of birds.
And I know if the DC9 had been hit by birds, it would have made KCLT on time just needing a nice washing if there was time.
When an immediate turn was made, 4 out of 4 pilots made LGA.
When a 30 second, WTF, delay was added, none made LGA.
So...you see birds, you feel the bumps and lose power...how long a "WTF" delay do you have?
Now, I haven't flown the airbus. I could have been a captain on the AB320 for sully's airline. I took a 737 bid instead...it paid less too.
But I sure have flown out of LGA an awful lot...and yes me and my friends all looked down the Hudson and thought it would be a good place to land...and I give you my word it was before Sully landed there that we thought of it.
I also looked out on the Interstate 80 freeway and thought it might work too.
But I stand by my comments and echo the comments of Bubbers...you have to be looking out the freaking window and be ultra alert. Alertness can shift for different things at different altitudes. At low altitudes, small planes, big planes, birds and terrain...and all pilots should have that ''pre selected" emergency landing spot.
I also believe in what I said about banking to protect the engines, placing them below and above the formation of birds.
And I know if the DC9 had been hit by birds, it would have made KCLT on time just needing a nice washing if there was time.
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If they had made the turn back at engine failure they may have made the runway downwind but if they had people would have probably died. Good for the pilots choosing the Hudson.
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Sully did a great job on the day and we can only hope that, if called upon, we could perform as well.
However he didn't do everything perfectly and flew @ 15-20kts slow for the config he was in for a good deal of the time and was unaware that he was doing so for bits of it. Thats why he ended up in alpha protection at about 200'
Maybe in a 737 (which will let you stall) he could have finessed the flare a bit or maybe he would have stalled, we will never know. The Airbus prevented us finding out as it stopped the aircraft's alpha increasing @ 3 degrees short of the stall by entering Alpha Prot. In my view thats better than risking a stall, I accept others see it differently
While we may not be able to agree on the merits of Airbus's control laws, and they are complex, hopefully we can agree that flying 15-20 kts below manoeuver speed is not ideal.
However he didn't do everything perfectly and flew @ 15-20kts slow for the config he was in for a good deal of the time and was unaware that he was doing so for bits of it. Thats why he ended up in alpha protection at about 200'
Maybe in a 737 (which will let you stall) he could have finessed the flare a bit or maybe he would have stalled, we will never know. The Airbus prevented us finding out as it stopped the aircraft's alpha increasing @ 3 degrees short of the stall by entering Alpha Prot. In my view thats better than risking a stall, I accept others see it differently
While we may not be able to agree on the merits of Airbus's control laws, and they are complex, hopefully we can agree that flying 15-20 kts below manoeuver speed is not ideal.
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Originally Posted by Ashling
The Airbus prevented us finding out as it stopped the aircraft's alpha increasing @ 3 degrees short of the stall by entering Alpha Prot.
While we may not be able to agree on the merits of Airbus's control laws, and they are complex, hopefully we can agree that flying 15-20 kts below manoeuver speed is not ideal.
Now if you think Sully maybe would have stalled a 737, that's a question you should direct to him and wait for the reply ...
In my view thats better than risking a stall, I accept others see it differently.
What is not acceptable is uninformed comment, btw made by a guy who obviously see himself as la crème de la crème :
Both Habsheim and Hudson have one more common trait besides both involving A320: both aeroplanes hit the deck in alpha prot with significant aft stick displacement. If flight controls were classical or brand B FBW with overridable limits, outcome would be much worse.
Last edited by CONF iture; 22nd Mar 2013 at 04:39.
Well, I do stand corrected: seemingly it is not enough just to read the report/manual/aeronautical textbook. One also needs to understand what is written. We have been recently given with good examples why it's so and I'd like to express my gratitude to certain posters for amusement they provided.
AA587 fin failed in overload. It was overloaded due to extreme sideslip. Sideslip was brought through aircraft-pilot coupling resulting in divergent yaw oscillation. Folks understanding the term "divergent oscillation" know that no amount of beefing up the structure or reducing rudder authority can help combat it yet proper use of the rudder will never, ever cause it. Fortunately, all of the aeroplane designers and those tasked with certifying aeroplanes do understand that. All pilots should too.
Microsoft flight simulator is very useful tool for teaching IFR procedures but that's about it. Aerodynamics isn't and wasn't meant to be simulated realistically. Therefore, arguments such as "I performed that in MSFS" are not considered to be quite relevant on the Professional Pilots Rumour Network
As for Airbus being misleading:
...nicely sums it up.
Claiming that airbus FBW should provide flight just below Alpha crit, with no margin since this could improve flare (Hudson) or improve climb (that infamous low & slow flyby with trees getting in the way) is cheerfully disregarding that it's not just Cl that rises just below the stall but Cd also. Such an argument may solicit reaction or give its originator not altogether savoury reputation on PPRuNe but its informational value is nil.
Wether captain Sullenberger woud have used same control inputs if it were 737 is matter of conjecture. Whether 737 approaching flare 15 kt too slow with full back yoke would have stalled is not.
PPRuNe would have been much poorer if it indeed were so.
AA587 fin failed in overload. It was overloaded due to extreme sideslip. Sideslip was brought through aircraft-pilot coupling resulting in divergent yaw oscillation. Folks understanding the term "divergent oscillation" know that no amount of beefing up the structure or reducing rudder authority can help combat it yet proper use of the rudder will never, ever cause it. Fortunately, all of the aeroplane designers and those tasked with certifying aeroplanes do understand that. All pilots should too.
Microsoft flight simulator is very useful tool for teaching IFR procedures but that's about it. Aerodynamics isn't and wasn't meant to be simulated realistically. Therefore, arguments such as "I performed that in MSFS" are not considered to be quite relevant on the Professional Pilots Rumour Network
As for Airbus being misleading:
Originally Posted by Airbus
the Flight Crew Operating Manual is not intended to provide basic jet aircraft piloting techniques or information that are considered as basic airmanship for trained flight crews familiar with that type of aircraft and with its general handling characteristics.
(...)
the Flight Crew Operating Manual is not intended to be used for teaching basic piloting skills
(...)
the Flight Crew Operating Manual is not intended to be used for teaching basic piloting skills
Claiming that airbus FBW should provide flight just below Alpha crit, with no margin since this could improve flare (Hudson) or improve climb (that infamous low & slow flyby with trees getting in the way) is cheerfully disregarding that it's not just Cl that rises just below the stall but Cd also. Such an argument may solicit reaction or give its originator not altogether savoury reputation on PPRuNe but its informational value is nil.
Wether captain Sullenberger woud have used same control inputs if it were 737 is matter of conjecture. Whether 737 approaching flare 15 kt too slow with full back yoke would have stalled is not.
What is not acceptable is uninformed comment
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[QUOTE=CONF iture;7754612]Not 3 deg short of the stall, 3 deg short of alpha max which is itself probably another 3 deg short of the stall. Full back stick the Airbus is supposed to deliver alpha max not to stop 3 deg short. The Airbus documentation is simply misleading.
You are right that Airbus's docs fail to mention that pilot inputs may be attenuated in Alpha Prot, as Sully's were, but to an extent it's common sense. Close to the limit control inputs are dampened. On conventional aircraft this is what you would do for yourself, E.G. a max rate turn, pull to the edge of the buffet then squeeze into it to avoid pulling into the heavy buffet. You attenuate your input close to the limit. The advantage of FBW is that you can make that input as aggressive as you want.
As the NTSB noted the aircraft max performed but as you, and they, note that is different to Alpha Max which is @ 3 degrees short of Alpha Stall so he was 4 to 5 degree's short of the stall AOA when he went in. We disagree about the significance of that, I feel the aircraft max performed and protected him, you feel it prevented him cushioning the impact better. The NTSB seem ambivalent about it other than saying the docs could be clearer on it and Sully's speed control could have been better. I don't want to revisit our lengthy debate, I respect your point of view even though I have a different take on it.
I believe the 3 degree gap between Alpha Max and Alpha stall is down to regulatory requirements for FBW and relates to ice formation on slats and flaps which cannot be simulated during flight tests.
No one, not even Sully, can say what would have occurred in a Boeing its conjecture. That applies to both of us Confiture.
The Airbus over rode the low speed warnings with GPWS warnings and given Sully's workload it is understandable that he didn't pick up on the speed, as the NTSB highlight. At the end of the day you fly the aircraft you are in.
My point is that if the speed control is correct the debate about control laws limiting inputs is irrelevant as is whether he would have stalled in a Boeing. We have the great luxury of thinking about all this at our leisure and in my view one of the things we should take away from it is the importance of speed control and scanning the speed tape as other warnings may mask the low speed ones. Sully did not have that luxury but admidst it all saved everyone's lives, I only have respect for what he achieved and hold him in the highest regard.
You are right that Airbus's docs fail to mention that pilot inputs may be attenuated in Alpha Prot, as Sully's were, but to an extent it's common sense. Close to the limit control inputs are dampened. On conventional aircraft this is what you would do for yourself, E.G. a max rate turn, pull to the edge of the buffet then squeeze into it to avoid pulling into the heavy buffet. You attenuate your input close to the limit. The advantage of FBW is that you can make that input as aggressive as you want.
As the NTSB noted the aircraft max performed but as you, and they, note that is different to Alpha Max which is @ 3 degrees short of Alpha Stall so he was 4 to 5 degree's short of the stall AOA when he went in. We disagree about the significance of that, I feel the aircraft max performed and protected him, you feel it prevented him cushioning the impact better. The NTSB seem ambivalent about it other than saying the docs could be clearer on it and Sully's speed control could have been better. I don't want to revisit our lengthy debate, I respect your point of view even though I have a different take on it.
I believe the 3 degree gap between Alpha Max and Alpha stall is down to regulatory requirements for FBW and relates to ice formation on slats and flaps which cannot be simulated during flight tests.
No one, not even Sully, can say what would have occurred in a Boeing its conjecture. That applies to both of us Confiture.
The Airbus over rode the low speed warnings with GPWS warnings and given Sully's workload it is understandable that he didn't pick up on the speed, as the NTSB highlight. At the end of the day you fly the aircraft you are in.
My point is that if the speed control is correct the debate about control laws limiting inputs is irrelevant as is whether he would have stalled in a Boeing. We have the great luxury of thinking about all this at our leisure and in my view one of the things we should take away from it is the importance of speed control and scanning the speed tape as other warnings may mask the low speed ones. Sully did not have that luxury but admidst it all saved everyone's lives, I only have respect for what he achieved and hold him in the highest regard.
Last edited by Ashling; 22nd Mar 2013 at 10:26.
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Confiture,
Forgive my ignorance, but there is something I do not understand here. On March 8th you said:
.
Now if the object is to minimise the rate of descent (flight path gradient) at impact and if the 'best' that pilots could do was a gradient of -1.5 degrees (NTSB report), then the target 'optimum' AoA would be about 12.5 degrees (or lower) wouldn't it? If that is so, why are you complaining that the control laws "prevented" achievement of alpha prot threshold or alpha max?
For memory, the alpha prot. threshold was 15.5 deg below 50 ft and alpha max was 17.5 deg - both of these from the NTSB report.
I can see that the attenuation of pilot's controls that accompanies the alpha prot mode could have limited his ability to get more than 9 deg pitch in the time he had available for flare starting from 50 ft, but the impact on the Hudson was between 13 and 14 deg AoA according to the NTSB, so I do not understand why you think inability to get to the alpha prot AoA threshold so important.
What am I missing?
Forgive my ignorance, but there is something I do not understand here. On March 8th you said:
11 degrees attitude is optimum for all cases, thrust or none
Now if the object is to minimise the rate of descent (flight path gradient) at impact and if the 'best' that pilots could do was a gradient of -1.5 degrees (NTSB report), then the target 'optimum' AoA would be about 12.5 degrees (or lower) wouldn't it? If that is so, why are you complaining that the control laws "prevented" achievement of alpha prot threshold or alpha max?
For memory, the alpha prot. threshold was 15.5 deg below 50 ft and alpha max was 17.5 deg - both of these from the NTSB report.
I can see that the attenuation of pilot's controls that accompanies the alpha prot mode could have limited his ability to get more than 9 deg pitch in the time he had available for flare starting from 50 ft, but the impact on the Hudson was between 13 and 14 deg AoA according to the NTSB, so I do not understand why you think inability to get to the alpha prot AoA threshold so important.
What am I missing?
Last edited by Owain Glyndwr; 22nd Mar 2013 at 12:11.
No one, not even Sully, can say what would have occurred in a Boeing its conjecture.
. He'd pull just into the buffet, as you described earlier in your post, and hold it there. Or are you suggesting he'd possibly pull straight thru and stall/spin in?
seven stroke, thanks for that, no further questions.
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LW50, it makes sense, either turn back and land immediately at lower altitudes or forget about that option. Also make sure you can do it. I have seen the other result with a vertical plunge into the ground with my own eyes at Burbank with a Bonanza losing an engine and trying to rudder back for a landing going straight in with 4 people. I taught cross control stalls as a flight instructor to prevent this type of accident.
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Capn Bloggs, the point is we don't know what would have happened in a Boeing. You may feel he could have pulled it into the buffet and held it, thing is you don't know just as no one can say he would have stalled had he been in a Boeing.
What you can say is that if he got that slow in a Boeing and then pulled hard back and held it he would have stalled but somehow I doubt he would have done that had it been a Boeing. Mind you I also doubt whether he, or anyone short of those who stall the aircraft regularly, could pull into buffet and hold it in those circumstances.
Speed control, monitoring and knowing that low speed warnings can be masked by other things is one of the key lessons from the Hudson imho. While its understandable that Sully's speed control was not ideal, task saturation, I'd assume no one here is saying that flying 15-20kts slow prior to the flare is the best way to ditch an aircraft. Its that speed control that led to the difficulty flaring, not the design of the aircraft.
What you can say is that if he got that slow in a Boeing and then pulled hard back and held it he would have stalled but somehow I doubt he would have done that had it been a Boeing. Mind you I also doubt whether he, or anyone short of those who stall the aircraft regularly, could pull into buffet and hold it in those circumstances.
Speed control, monitoring and knowing that low speed warnings can be masked by other things is one of the key lessons from the Hudson imho. While its understandable that Sully's speed control was not ideal, task saturation, I'd assume no one here is saying that flying 15-20kts slow prior to the flare is the best way to ditch an aircraft. Its that speed control that led to the difficulty flaring, not the design of the aircraft.
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No one looking at the smooth splashdown could say he didn't do it perfectly. Rate of descent was almost zero and attitude and bank were perfect. Sully did a great job. Hopefully we could have done likewise. I think most of us could but we fortunately don't get to be tested.
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Type of aircraft isn't important, pilot skills are so I give all the credit to Sully because he could have done it in any airplane. He started out in smaller planes and just happened to be in an Airbus.
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Surveillance Cameras Capture Flight 1549 Crash Landing into the Hudson River - Video
This shows the splashdown from surveilance video. It looks pretty normal to me.
This shows the splashdown from surveilance video. It looks pretty normal to me.
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Bubbers, that statement to me illustrates a real problem with the Hudson ditching.
Sully and his crew did a great job and were rightly praised but just because the outcome was successful does not mean we suspend our critical faculties. We still need to look at the incident and determine the lessons to be learnt. There are things to learn from all the great things they did but there are also lessons to be learnt from what could have gone better. Unfortunately some only look at the outcome and seem to pretend that all was perfect.
The importance of speed control and monitoring, to me, is the key lesson from the what could have gone better category.
Fact is he got slow, upto 19kts slow, that is well documented by the NTSB and beyond dispute. Its why he entered Alpha Prot and why the flare was problematic. It's also fact they splashed down at 12.5 FPS 750 FPM and I rather suspect the NTSB had access to the camera footage too but seem to have drawn a different conclusion to the one Bubbers does. But, hey, what do the NTSB know?
Sully and his crew did a great job and were rightly praised but just because the outcome was successful does not mean we suspend our critical faculties. We still need to look at the incident and determine the lessons to be learnt. There are things to learn from all the great things they did but there are also lessons to be learnt from what could have gone better. Unfortunately some only look at the outcome and seem to pretend that all was perfect.
The importance of speed control and monitoring, to me, is the key lesson from the what could have gone better category.
Fact is he got slow, upto 19kts slow, that is well documented by the NTSB and beyond dispute. Its why he entered Alpha Prot and why the flare was problematic. It's also fact they splashed down at 12.5 FPS 750 FPM and I rather suspect the NTSB had access to the camera footage too but seem to have drawn a different conclusion to the one Bubbers does. But, hey, what do the NTSB know?
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And I know if the DC9 had been hit by birds, it would have made KCLT on time just needing a nice washing if there was time.