American Airlines Flight 742 "flight control system" problems
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Ashling - exactly. Critical analysis would review all the things done correctly and less incorrectly.
Reviewing the FDR and CVR is interesting.
Due to low airspeed(AOA limit) there was no flare. Same as BA 038.
Reviewing the FDR and CVR is interesting.
Due to low airspeed(AOA limit) there was no flare. Same as BA 038.
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misd again...
I didn't say the engines on the DC9 would get damaged.
First off, if you are going to hit the engines on a DC9 (and they have been), you have to get by the fuselage, they aren't just sticking out in front of the wing.
Now, you mention damage...and that presumes the bird can do the damage...but the inlet on the jt8d is much smaller than the inlet/fan on the CFM 56, right?
maybe the birds would hit the bullet or the lip and not get by.
and of course the engines are not FADEC , just good old fashioned fuel controllers.
so...its my view...and of course unless you come up with the big bucks, the birds and a DC9, we won't really know.
but do look at a flock of birds...its almost like a anice delta wing...if they hit the 9 on the nose, would they get to the engines? of course they would on the airbus or 737...but
anyway...yes sully did fine...any landing you can swim away from is just fine.
could it have been better? I think so. But any landing you can swim away from is just fine.
And I hope all the pilots out there think about how they could do better, what they might do better etc...and not just accept that sully did it perfectly.
I didn't say the engines on the DC9 would get damaged.
First off, if you are going to hit the engines on a DC9 (and they have been), you have to get by the fuselage, they aren't just sticking out in front of the wing.
Now, you mention damage...and that presumes the bird can do the damage...but the inlet on the jt8d is much smaller than the inlet/fan on the CFM 56, right?
maybe the birds would hit the bullet or the lip and not get by.
and of course the engines are not FADEC , just good old fashioned fuel controllers.
so...its my view...and of course unless you come up with the big bucks, the birds and a DC9, we won't really know.
but do look at a flock of birds...its almost like a anice delta wing...if they hit the 9 on the nose, would they get to the engines? of course they would on the airbus or 737...but
anyway...yes sully did fine...any landing you can swim away from is just fine.
could it have been better? I think so. But any landing you can swim away from is just fine.
And I hope all the pilots out there think about how they could do better, what they might do better etc...and not just accept that sully did it perfectly.
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Originally Posted by Owain Glyndwr
What am I missing?
The airplane reached 9 deg of AoA when the alpha-protection threshold value was still at 8 deg.
Obviously the alpha-protection threshold value is dependent of the altitude and configuration. AFAIK those values are nowhere in the Airbus documentation reserved to the pilot. They only appear in the different incident/accident reports.
Now, how do you call an "attenuation of pilot's controls that accompanies the alpha prot mode which could limit the ability to get more than 9 deg pitch in the time available for flare starting from 50 ft" if not a restriction ?
Let Sully pull another 2 deg of pitch to obtain the recommended attitude for ditching and benefit from it by decreasing his vertical speed at touchdown.
Adequate margin was in the aerodynamics as alpha max was still 4 deg away.
No immediate risk for stalling.
Originally Posted by Clandestino
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.
Also the benefit from the CI rise over the Cd rise is exactly what is needed for the short term and that's what Airbus figured out by implementing alpha max ... as long they allow to get it.
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sevenstrokeroll - the birds went right into the compressor section. Bullseye, and bullseye on any engine.
FADEC vs. cable controls doesn't matter if the core inlet is blocked and/or damaged so severely that it's continously compressor stalling.
What's the size difference between a JT8D vs. a CFM56? Compressor inlet difference is probably minimal.
FADEC vs. cable controls doesn't matter if the core inlet is blocked and/or damaged so severely that it's continously compressor stalling.
What's the size difference between a JT8D vs. a CFM56? Compressor inlet difference is probably minimal.
JT8D (on DC-9) - fan diameter 39.9 inches; area 1250 in^2
JT8D-200 series (MD-80 et seq.) was larger. 49.9 inches diameter
CFM56-5B - fan diameter 68 inches; area 3631 in^2
I also expect 7sr's point was that the engines are protected by wing and fuselage airflow (and the wing itself to some extent, in a climb attitude):
http://www.fiddlersgreen.net/aircraf...-DC-9-NASA.jpg
http://cdn-www.airliners.net/aviatio.../2/1171294.jpg
(although - ahem - that second picture is probably not how one would wish to achieve a climb attitude.)
JT8D-200 series (MD-80 et seq.) was larger. 49.9 inches diameter
CFM56-5B - fan diameter 68 inches; area 3631 in^2
I also expect 7sr's point was that the engines are protected by wing and fuselage airflow (and the wing itself to some extent, in a climb attitude):
http://www.fiddlersgreen.net/aircraf...-DC-9-NASA.jpg
http://cdn-www.airliners.net/aviatio.../2/1171294.jpg
(although - ahem - that second picture is probably not how one would wish to achieve a climb attitude.)
Last edited by pattern_is_full; 24th Mar 2013 at 21:13.
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The engines couldn't develop power because of the damage to the compressor blades and VSV's. That's downstream of the core inlet and fan diameter does not apply.
Last edited by misd-agin; 25th Mar 2013 at 01:24.
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Confiture:
The airplane reached 9 deg of AoA when the alpha-protection threshold value was still at 8 deg.
Obviously the alpha-protection threshold value is dependent of the altitude and configuration. AFAIK those values are nowhere in the Airbus documentation reserved to the pilot. They only appear in the different incident/accident reports.
The airplane reached 9 deg of AoA when the alpha-protection threshold value was still at 8 deg.
Obviously the alpha-protection threshold value is dependent of the altitude and configuration. AFAIK those values are nowhere in the Airbus documentation reserved to the pilot. They only appear in the different incident/accident reports.
The principle of alpha-protection is well documented though, and it is difficult (for a non-pilot) to see what practical use could be made of a knowledge of the actual numbers since as we all know, AoA is not displayed to the pilot.
Now, how do you call an "attenuation of pilot's controls that accompanies the alpha prot mode which could limit the ability to get more than 9 deg pitch in the time available for flare starting from 50 ft" if not a restriction ?
Let Sully pull another 2 deg of pitch to obtain the recommended attitude for ditching and benefit from it by decreasing his vertical speed at touchdown.
But I note that other pilots, presumably using different flare techniques, managed to achieve the desired low descent rates, which leads me to believe that the control attenuation was a limit on Sully's flare but may not be generally applicable.
Margin is already included, that's why alpha max is not set at alpha stall.
Last edited by Owain Glyndwr; 26th Mar 2013 at 05:01.
Originally Posted by sevenstrokeroll
First off, if you are going to hit the engines on a DC9 (and they have been), you have to get by the fuselage, they aren't just sticking out in front of the wing.
Originally Posted by CONFiture
The airplane reached 9 deg of AoA when the alpha-protection threshold value was still at 8 deg.
Originally Posted by NTSB
According to FDR data, the airplane touched down on the Hudson River at an airspeed of 125 KCAS with a pitch angle of 9.5° and a right roll angle of 0.4°. Calculations indicated that the airplane ditched with a descent rate of 12.5 fps, a flightpath angle of -3.4°, an AOA between 13° and 14°, and a side slip angle of 2.2°.
Originally Posted by CONFiture
Now, how do you call an "attenuation of pilot's controls that accompanies the alpha prot mode which could limit the ability to get more than 9 deg pitch in the time available for flare starting from 50 ft" if not a restriction ?
Originally Posted by CONFiture
Adequate margin was in the aerodynamics as alpha max was still 4 deg away.
Originally Posted by CONfiture
Also the benefit from the CI rise over the Cd rise is exactly what is needed for the short term
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Owain
If you look in the FCTM under Operational Philosophy, Protections, High Angle of Attack Protections, there is a graph that makes it pretty clear that V alpha max is short of V Stall 1g
Alpha Prot also increases by 1degree in the last 50ft provided the Config remains the same. That's not in the books as far as I know.
There is also a graph below that one that makes the point that FBW aircraft significantly outperform non FBW aircraft when it comes to pulling up suddenly from low speed in the approach Config at Vapp converting to max AoA.
Type in Airbus 320 phugoid damping into google and a couple of interesting articles come up.
If you look in the FCTM under Operational Philosophy, Protections, High Angle of Attack Protections, there is a graph that makes it pretty clear that V alpha max is short of V Stall 1g
Alpha Prot also increases by 1degree in the last 50ft provided the Config remains the same. That's not in the books as far as I know.
There is also a graph below that one that makes the point that FBW aircraft significantly outperform non FBW aircraft when it comes to pulling up suddenly from low speed in the approach Config at Vapp converting to max AoA.
Type in Airbus 320 phugoid damping into google and a couple of interesting articles come up.
Last edited by Ashling; 25th Mar 2013 at 13:04.
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clandestino...and tell us of the PW engine on the king air?
and tell us if a bird hit the fuselage and was ripped apart prior to entering the intake?
sorry clandestino...you must account for more than basic suck, squeeze bang blow
and tell us if a bird hit the fuselage and was ripped apart prior to entering the intake?
sorry clandestino...you must account for more than basic suck, squeeze bang blow
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Ashling,
Thank you for that google tip; the Airbus submission to the NTSB was particularly interesting, as I hadn't realised that when in alpha-protect the aircraft develops a phugoid. In normal law there isn't a phugoid. So then we have:
Now that means that the features that limited Sully's flare are necessary for stability and that removing them might have adverse consequences on the approach to flare. [edited 26/03]
Also, that last sentence is, IMHO, the key - height of flare initiation is the important parameter.
BTW, the picture I have seen illustrating the various 'alphas' is a schematic with the differences dictated by presentational requirements as much as actual values. I would be surprised if there was much between alphamax and alpha stall - the commercial pressures are too high to allow much leeway when competitors are basing their products on alpha-stall
Thank you for that google tip; the Airbus submission to the NTSB was particularly interesting, as I hadn't realised that when in alpha-protect the aircraft develops a phugoid. In normal law there isn't a phugoid. So then we have:
There are feedbacks within the AoA protection law aiming at damping the phugoid mode (low frequency mode). Without these feedbacks, an aircraft upset from its stabilized flight point up to constant high AoA would enter a phugoid (which is, by definition, a constant AoA oscillation) without possibility to stabilize the trajectory. As a consequence, commanded AoA is modulated: for instance, if aircraft speed is decreasing and/or pitch attitude is increasing, pilot's commanded AoA is lowered in order to avoid such a situation to degrade.
Trying to run simulation without such damping features on the very last seconds of the flight, without considering what could have been the effect such features brought upstream during the flight on the overall Aircraft trajectory and management by the crew would be pure speculation, as not supported by technical facts.
On the last 10 sec in the air of Flight 1549 , DFDR data show that pitch attitude is increasing and CAS decreasing. Then, the phugoid damping terms are non null and are acting in the sense to decrease the finally commanded AoA vs. the stick command, in order to prevent the Aircraft from increasing the phugoid features.
......
..... with a loss of engine thrust, as in Flight 1549, the aircraft energy management significantly increases the pilot workload. Under these circumstances, aircraft is still able to reach the optimum water impact configuration, but this is a demanding task which requires time and significant pilot focus. Typically, the flare initiation height will be critical to the achievement of the optimum water entry conditions.
Trying to run simulation without such damping features on the very last seconds of the flight, without considering what could have been the effect such features brought upstream during the flight on the overall Aircraft trajectory and management by the crew would be pure speculation, as not supported by technical facts.
On the last 10 sec in the air of Flight 1549 , DFDR data show that pitch attitude is increasing and CAS decreasing. Then, the phugoid damping terms are non null and are acting in the sense to decrease the finally commanded AoA vs. the stick command, in order to prevent the Aircraft from increasing the phugoid features.
......
..... with a loss of engine thrust, as in Flight 1549, the aircraft energy management significantly increases the pilot workload. Under these circumstances, aircraft is still able to reach the optimum water impact configuration, but this is a demanding task which requires time and significant pilot focus. Typically, the flare initiation height will be critical to the achievement of the optimum water entry conditions.
Also, that last sentence is, IMHO, the key - height of flare initiation is the important parameter.
BTW, the picture I have seen illustrating the various 'alphas' is a schematic with the differences dictated by presentational requirements as much as actual values. I would be surprised if there was much between alphamax and alpha stall - the commercial pressures are too high to allow much leeway when competitors are basing their products on alpha-stall
Last edited by Owain Glyndwr; 26th Mar 2013 at 05:03.
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I think most of us would have held best glide speed for flap configuration and flared to stop 750 fpm descent below 50 ft. I still see a normal touchdown rate well below 750 fpm in the video but I know what 750 fpm profile is and it would have a mighty big splashdown. His looked normal. Look at the video. The NTSB was probably looking at his final descent before flare. Yes, he would have done better with a 737 but he was flying an Airbus and was restricted to Airbus rules. That is why I never flew the Airbus. If it aint a Boeing, I ain't going.
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Bubbers, do the google search I suggested above, look at analysis by the chairman of the board that comes listed as 1 or 2. All the FDR graphs are at the end. Either every sensor was out or they hit at 750fpm. Sorry just the way it is, looks can be deceptive.
Not so sure about the Seattle Tractor mind you, rudder hard overs, fuel filters clogging snuffing out both engines, cargo doors flying off taking pax along for the ride, batteries burning, rad alts that force the engines to idle, spoilers that don't stow when you firewall the engines which ain't great for GPWS pull ups as you tend to hit the hill etc etc
I've flown both, and enjoyed flying both and am gratefull I've had the chance to do so. They're aircraft, they both have good and bad points, both can kill you if you get sloppy and haven't done your homework or are just plain unlucky.
Maybe he would have done better in a 737, maybe he would have done worse. We will never know. We can, however, surmise that had his speed control been the same its pretty likely he would have triggered a stall warning. As I recall there's no AOA gauge in the 737 so no way to know the margin therefore you have to honour the warning by pushing or at the very least holding the attitude. That might be tricky at 150' and 1200 - 1500 fpm rod. At least in the Bus (in normal law because he started the APU) he could pull with confidence that the aircraft would not stall. Just a thought.
Not so sure about the Seattle Tractor mind you, rudder hard overs, fuel filters clogging snuffing out both engines, cargo doors flying off taking pax along for the ride, batteries burning, rad alts that force the engines to idle, spoilers that don't stow when you firewall the engines which ain't great for GPWS pull ups as you tend to hit the hill etc etc
I've flown both, and enjoyed flying both and am gratefull I've had the chance to do so. They're aircraft, they both have good and bad points, both can kill you if you get sloppy and haven't done your homework or are just plain unlucky.
Maybe he would have done better in a 737, maybe he would have done worse. We will never know. We can, however, surmise that had his speed control been the same its pretty likely he would have triggered a stall warning. As I recall there's no AOA gauge in the 737 so no way to know the margin therefore you have to honour the warning by pushing or at the very least holding the attitude. That might be tricky at 150' and 1200 - 1500 fpm rod. At least in the Bus (in normal law because he started the APU) he could pull with confidence that the aircraft would not stall. Just a thought.
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interesting thread as it diverged
boys and girls...its been an interesting thread.
flares, laws, engine inlets, birds, good job, could have done better etc.
I dare say this conversation should have been part of the investigation, but as jimmy stewart said in the film, "The man who shot liberty valence", PRINT THE LEGEND.
IF you are good and lucky, I'll take a DC9 or 737 (prefer DC9). If you are average, maybe an airbus might be better...
but all in all, better to be lucky than good!
flares, laws, engine inlets, birds, good job, could have done better etc.
I dare say this conversation should have been part of the investigation, but as jimmy stewart said in the film, "The man who shot liberty valence", PRINT THE LEGEND.
IF you are good and lucky, I'll take a DC9 or 737 (prefer DC9). If you are average, maybe an airbus might be better...
but all in all, better to be lucky than good!
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ahhh...there's the rub
a plane that prevents stupid things...great
but...that also prevents heroic things...that's bad.
I AM REMINDED of the general aviation plane called the MOONEY...some of you will know where I am going with this.
The Mooney has a full time ''wing leveler''. And a little tiny button on the yoke that turns it off so you can make a turn.
IN essence, you never have to demonstrate straight and level flying, as the wing leveler is doing it for you .
So, how about the airbus having a little button on the yoke that you press to over ride all protective LAWS?
Need to bank 80 degrees? Press the button MAX!
Need to stall? PRESS THE BUTTON MAX!
And all the other times the plane is watching and protecting you from being stupid.
but...that also prevents heroic things...that's bad.
I AM REMINDED of the general aviation plane called the MOONEY...some of you will know where I am going with this.
The Mooney has a full time ''wing leveler''. And a little tiny button on the yoke that turns it off so you can make a turn.
IN essence, you never have to demonstrate straight and level flying, as the wing leveler is doing it for you .
So, how about the airbus having a little button on the yoke that you press to over ride all protective LAWS?
Need to bank 80 degrees? Press the button MAX!
Need to stall? PRESS THE BUTTON MAX!
And all the other times the plane is watching and protecting you from being stupid.