American Airlines Flight 742 "flight control system" problems

[sevenstrokeroll]

hahaha

hey, clandistino...thanks for that information you posted...I looked at it and NONE of the tail mounted planes had to land off airport...they landed in decent shape.

AS to Bubbers CHOICE not to answer spandexmasher...I agree with you bubbers, answering an ignorant annoyance at some point is just counterproductive. But don't feel bad spandex...you just won a crusie on Carnival cruiselines...make sure you take appropriate precautions.

and IF bubbers said he rolled inverted and avoided a collision, I believe him. Every fighter pilot I've known said, "no matter what, keep 'him'' insight and you maintain the advantage.

let me add another question to the sully debate...what if he had used some flaps?

[CONF iture]

Originally Posted by Owain Glyndwr

You have made similar statements several times, but unless I have missed something, you have never suggested how this might be done. Do you have any positive proposals for how the logic might be altered to achieve what you desire?

I have no pretension or even desire here to modify the way the control law is programmed.
It can be a great idea to wish to protect an aircraft from stalling, but on that particular case on the Hudson, even if the speed was below Vref, it was still possible for Sully to reduce the vertical speed at touchdown and obtain the Airbus recommended attitude for ditching ... if only the elevators were to follow the pilot request.
Sully would have been better served with a direct law with full and known control on his elevators.

[Lord Spandex Masher]

Originally Posted by sevenstrokeroll

AS to Bubbers CHOICE not to answer spandexmasher...I agree with you bubbers, answering an ignorant annoyance at some point is just counterproductive.

But then he did answer, and dug himself further into the hole by being counterproductive.

But don't feel bad spandex...you just won a crusie on Carnival cruiselines...make sure you take appropriate precautions.

I don't feel bad as I can distinguish between fantasy and reality. Crusie? Is that a mini sort of a cruise? Or an all in oner, like a onesie?

and IF bubbers said he rolled inverted and avoided a collision, I believe him. Every fighter pilot I've known said, "no matter what, keep 'him'' insight and you maintain the advantage.

Was he trying to shoot him down then? Every pilot I've known said keep a good lookout and then you don't have to do stupid things to avoid dying. Even so perhaps you can explain how you can keep someone in sight through the floor?!

Yes what if he had used flaps? Do tell, the suspense is killing me.

[CONF iture]

Originally Posted by Ashling

1. I've tried to put forward documented reasons. The accuracy of the AoA. While the aircraft measured a max of 14.5 below 150ft there is a margin for error so the real figure might have been higher, as the corrected figure suggests, putting them closer to the stall. The designer has to take this into account and the margin is equivelent to 5kts at Flap2 (FCOM) which is quite a-lot. They might of had a 6 degree margin but it may have been as little as 3/3.5

Again, the margin is already in alpha max, that's why alpha max has not been set to alpha stall by Airbus.
Also if there was any need to correct the figures it would be on a the safe side as both temp and altimeter were for more air density than standard.
The two recorded AoA data were in agreement around 13.5 deg some 4 deg short of alpha max.

2. The energy in the aircraft. Any commercial airliner has a lag when responding to control inputs. That lag will be greater at slow speed. Obvious but true. As you say from 50ft in was 3-4 secs so not a great deal of time. They lacked the nose authority they would have had at the correct speed. Thats true in any aircraft.

We could talk about a lag if the elevators had been following the pilot inputs ... but they did not.

3. Phugoid damping. Airbus refer to this as do the BEA as does the analysis on the aircrafts performance and they all give it as the reason why Sully's control input was attenuated. Now I'm not going to pretend I fully understand this, I'm not a TP or an expert on aerodynamics, but I do know that this refers to longnitudinal stability and I think in this case it is referring to a tendancy to pitch nose up close to the stall with large control inputs. In any case its the reason the input was attenuated so is key to the whole thing. Perhaps an Airbus TP can elaborate if anyone reading all this still has the will to live. You've never really addressed this point Confiture.

I can't pretend either to explain what phugoid damping exactly is. The way I see it is if the airplane is placed level in deceleration, idle thrust, and up to full back stick is applied, the airplane won't be able to quickly stabilize precisely at alpha max. Some oscillation may develop before eventually alpha set to alpha max.

I'm also very comfortable saying that FBW will outperform the pilot, me, any of us. Just the way it is.

It seems to be the case for a GPWS maneuver but is it for a flare ?

In a conventialy controlled aircraft (for want of a better term) the stall warner would have been bleating away. Now what does the pilot do? What would you do, as again I feel you downplay this point. I wouldn't pull, not without considerable handling experience in that regime on that aircraft and as commercial pilots we simply don't get that. The absolute imperitive low down with no engines is DO NOT STALL. The Airbus took that concern away.

If anytime during the approach he got a STALL warning, or an aural SPEED caution at CONF 2, it would have been an attention getter for Sully lo lower the nose and re established the speed at Vref or higher and get a better control on the flare later on.
The SPEED caution is inactive below 100 ft, I don' t know about the STALL warning, but you don't stall at STALL warning. In alternate or direct law the STALL warning is set around the level of alpha prot for normal law so the same margin is here again.
Normal law brings a physical but also mental disconnection between what a pilot does with the sidestick and how the elevators actually move. No such thing in direct law. Easier to understand.

[Owain Glyndwr]

@ CONF iture

Sully would have been better served with a direct law with full and known control on his elevators.

So is your recommendation that if you are going to ditch the pilot should switch (or be switched) to direct law?
If so, at what point should this be done?

[BOAC]

First time I have looked at this thread - and I had to go back and check it was about "American Airlines Flight 742"!

[sevenstrokeroll]

clandestino

very glad you didn't have anything of great worth to say.

oh, and I posed the question about flaps, I didn't offer an answer.

I can imagine you and Spandex masher in the same cockpit...chatting away and forgetting to look outside.

yeah...so amusing.

"and still the villian pursued her"

[Ashling]

Confiture

Phugoid damping clearly applies in this case, Airbus said it did! We can agree that it causes oscillations, apparently on some types this can get divergent and possably beyond pilot control. I suspect its not that extreme on the Bus but clearly significant enough to protect against. Therefore the FBW prevents said oscillations by mitigating the pilots input or at least that's how I understand it.

Yes the margin is allowed for in Alpha Max which was 17.5 degrees. There was a split in the AoAs on the FDR, and the corrected figure was 16 odd degrees. It's in the performance study I posted a link to earlier. So taking that margin into account the gap between his actual real AoA and the stall may not have been as great as you have suggested.

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. Hard to push much and you'd be a fool to pull. Your in no mans land, no practise in that regime and no idea what your margin to the stall really is and in all probability no AoA gauge to tell you. The Bus took all that worry away, close to the stall FBW is ideal, carefree handling and all that, that's doubly true if you have no regular experience operating in that speed regime on type.

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.

Anyway it's clear we're now pushing a few people's patience so perhaps it's time to accept, once again, that we differ. Hopefully if nothing else it will have made a few people think themissue's through for themselves and that can't be a bad thing.

ATB

[misd-agin]

and IF bubbers said he rolled inverted and avoided a collision, I believe him. Every fighter pilot I've known said, "no matter what, keep 'him'' insight and you maintain the advantage.

Ask fighter pilots these questions -

1. If you roll inverted can you maintain visual ID with a guy below your belly?
2. Would you roll a non-aerobatic airplane and then pull towards the ground at night OR would you just save the time spent rolling and just pull back the same amount you would towards the ground?


Dog fighting rule 1 - "lose sight, lose fight" doesn't apply to avoiding midairs. If you can establish a trajectory away from the conflicting traffic it doesn't matter if you lose sight. The conflicting traffic is not going to pull 5-9 G's and lock you up with a 'winder or radar missile.

[Clandestino]

First time I have looked at this thread - and I had to go back and check it was about "American Airlines Flight 742"!

Simple tech problem that happened on that flight was successfully resolved. It had nothing to do with any kind of control problems. Goes to show that flying became so safe that reaction elicitors are reduced to using fictitious incident as pretext to air their "Airbus is dangerous", "Pilots these days just don't know how to fly" and "It was mistake ever putting high bypass engines below the wings, repent and return to Caravelle" theories.

BTW, ground effect reduces alphacrit on anything fixed winged.

[sevenstrokeroll]

if you roll inverted and lose sightof the traffic below your bellly....hmmmmm

upside down, is below up? no...upside down, below is still towards the ground and you should have a view of the traffic




AND STILL THE VILLIAN PURSUED HER.

[bubbers44]

Is there any reason you can't see out your windshield inverted? Once the other aircraft is passing you you have no reason to see through your floor boards. I am not saying I did anything special, I just avoided a midair doing what I knew would work, not taking a chance on him turning with me. Two seconds doesn't leave much time for thinking over the solution.

[Lord Spandex Masher]

How can you see through the floor? Simple question, simple answer.

You can see out of the window yes but the relative position of an aircraft passing above you when you're inverted is BELOW you. You can not see through the floor.

Unless you're BSing and they actually weren't that close you might have been able to see them at a longer range as the relative angle between you would be smaller. But then if they weren't that close would there be any need for such a ridiculous manuever?

Instead of rolling and pulling why not just pull? Or push?

[bubbers44]

So they had to fly manually. Good for them because they knew how to fly manually.

[Ashling]

Bubbers you said you had 2 secs to collision you still haven't answered how you role a Cessna 340 inverted in that time. You might have ended up inverted but not in 2 secs. Really don't get that bit at all.

Other thing, if you heading straight for the conflict rolling inverted will keep you pointed the same way. If you don't push the nose will drop and you lose visual, if you do push you stay in plane. You could pull up and roll, corkscrew style which would keep visual but you didn't say that you did that and you wouldn't achieve that in 2 secs either.

How long do a 340's engines run upside down ?

What harness did you have ?

[sevenstrokeroll]

wow

the cessna 300 series can roll pretty fast...I've seen one roll

as far as harnesses, if you do a roll well, you could even keep a glass of water from spilling...as RA HOOVER.

I believe bubbers saw traffic and maneuvered like hell and avoided it (the traffic) and went inverted in the process.

he didn't say he stayed inverted for a long time and I am sure the engines kept running

you can always disagree with someone over what they did...but since they are here and alive they did something right.

[Lord Spandex Masher]

So SSR to keep the water from spilling when you're inverted you have to do what?

[Lord Spandex Masher]

Originally Posted by bubbers44

flying a Cessna 340 over LGB when I noticed the lighting seemed different and I was nose to nose with a single engine aircraft. Not knowing which direction he was going to turn I rolled inverted because I had only one move. When he rolled right as he should have I paralleled his wings and rolled with him clearing by about 50 ft. No reports were filed but when he first saw me I was inverted. I wish I could hear his story because probably nobody would believe him. He did the right thing but I wasn't sure he would.

I instructed aerobatics so just pulled back enough to clear him after going inverted. I could pull away more than he could push over. Birds have to be seen to be avoided. Heads down means no bird avoidance so if you are flying into an airport like TGU you need to be heads up because they are in flocks and can easily be seen if you keep your eyes open, not down pushing buttons.

SSR, original quote for you to digest.

OK465, no bother, hopefully they might start getting the message.

[BOAC]

C'est des conneries, n'est-ce-pas?

[bubbers44]

Just so everybody understands rolling inverted R A Hoover demonstrated pouring a glass of water while doing a roll so obviously negative G's only happen when you maintain level flight while inverted. Bob would have preferred a wine glass.