Air France A330 - Missing over Atantic

Discussion in 'Flight Following' started by SCCutler, Jun 1, 2009.

  1. onwards

    onwards Pattern Altitude

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    This.

    I'm trying to think of in that cockpit, and this happening under all that stress. The stall horn goes off. You make input changes. it starts again. You have 300 people on the plane, no faith in the instruments, no way to see anything outside, and are starting to panic. So you roll back the controls, and the horn goes off. But the controls don't make sense, so you try going to something more normal. The stall horn starts again.

    Oh... my... god.

    Turning off the stall horn when it's potentially unreliable.... that's horrible design. Instead have it make a different kind of sound, to alert the pilot to the fact that it has been turned off. I am surprised this has not been highlighted more significantly - this issue is all on Airbus, who designed and built the plane with this "killer feature" (literally).
     
  2. matthammer

    matthammer Pre-takeoff checklist

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    Agreed. It's easy to blame the dead pilots. But, seriously, put yourself in their position. All the confusing and even contradictory indications they were receiving from their systems would likely confuse the heck out of the best of us. I also haven't heard anything to the effect that the pilots had a history of incompetence, so I have no reason to believe that they were anything short of the professionals they should have been. Pilot error? Sure. They made the control inputs that brought the plane down. But they made those control inputs on the basis of a bunch of crap information that their "state-of-the-art" airbus was giving them. Sometimes it's the contributing factors that push things over the edge.
     
  3. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    To play Devil's Advocate, how would you deal with the stall system when the plane is on the ground? The whole idea behind that particular design was to prevent nuisance warnings when the plane was on the ground.

    As well as I can remember, the stall system is based on the Angle of Attack vane, and that can be all over the place on the ground.
     
  4. matthammer

    matthammer Pre-takeoff checklist

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    Weight on wheels?
     
  5. SkyHog

    SkyHog Touchdown! Greaser!

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    Nuisance warnings on the gound are much better than dead people in the sea.

    Not being a smartass, just sayin', I hoe that the fear of nuisance isn't used to continue the use of a potentially scary failure model.
     
  6. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    Yeah, that. It is called an Air/Ground switch on some airplanes.

    True that, but nuisance warnings on takeoff roll are not much better than nothing at all.

    In Airbus's defense, no one ever thought that a crew would get that far into a stall. It hasn't ever happened before. You can bet there is probably a redesign in the works.
     
  7. Everskyward

    Everskyward Administrator Management Council Member

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    Does the Airbus have a shaker or is the stall warning something else?
     
  8. Inverted

    Inverted Cleared for Takeoff

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    Thats because Airbus expected more out of the pilots who would fly their aircraft. Shouldn't have to redesign an aircraft because pilots forget how to fly. Pilots need to remember the basics. Its tough to remember that stuff when flying an aircraft that should fly for you. But in the end all pilots should be able to recognize a stall and recover from it or prevent it, in any airplane.
     
  9. ebacon

    ebacon Line Up and Wait

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    Greg,

    Here are some other crashes that occurred due to super stall/deep stall condition. IMO it is a situation that designers should be aware of.

    http://en.wikipedia.org/wiki/Stall_(flight)#Deep_stall
     
  10. Auburn_CFI

    Auburn_CFI Pre-takeoff checklist

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    I agree and disagree. This was an incredibly complex situation when you factor in the control laws designed by Airbus. That being said, there should have been and there will be training in the future to address this exact issue due to its complex nature. Airbus design is not synonymous with any other type of airliner. The old saying that it's just another airplane doesn't fit into this scenario. That is one thing that Boeing has done very well in my opinion, but this isn't a Boeing v. Airbus debate, and for the record I think they both build terrific airplanes. It just isn't as simple as say the Colgan crash which was very simply pilot error. Just my $.02.
     
  11. sba55

    sba55 En-Route

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    I think my question remains, though. Would a regular stall warning ever happen when you push the nose down? If the stall warning did come on here when pitch was decreased, it's if anything an indication that things aren't working correctly or that they are not working in the way I expect or understand.

    In either case, I would ignore the stall warning and get the nose down. I admit it would be incredibly confusing, but if I had somebody else to talk to about what was going on, I wonder what would get me to conclude that the stall warning was right and that the fundamental principles of physics were wrong....

    I don't think I understand the system well enough to truly understand what was going on here.
     
  12. COFlyBoy

    COFlyBoy Line Up and Wait

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    They would have been reluctant to just push down because they could overspeed the aircraft. As high as they were,the difference between the stall speed and mach 1 is very small. Non-supersonic planes don't like going transonic. I'm sure the pilots were concerned about that.

    Still, I think they should have set a known attitude and known power and let it ride. My crusty old primary flight instructor (who had 10's of thousand's of hours in big jets) drilled me with "Proper pitch and power produces predictable performance".

    I wonder what is in the "Unreliable IAS" checklist.
     
  13. COFlyBoy

    COFlyBoy Line Up and Wait

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    The A330 doesn't have a t-tail, so I don't think that is at issue. The elevator and trim were commanded full up, which should drive the plane into a stall. I'll bet it would've recovered pretty quick once the AoA was lowered to something reasonable.

    [EDIT] OK I read a little more. The wing would not have been eclipsing the stabilizer, but it could be that they drove the AoA so high the the stabilizer had stalled and could not get the nose back down. 40 degrees AoA is almost falling not flying.
     
    Last edited: Jul 30, 2011
  14. sba55

    sba55 En-Route

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    I understand the overspeed issue, but wouldn't there be another alarm for that? Why wouldn't they have at least tried it?
     
  15. gismo

    gismo Touchdown! Greaser!

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    I'd inhibit the low speed disable unless the gear was down or maybe unless there was weight on the wheels.
     
  16. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    Ok, but if I have my facts straight, the airplane was at 10 degrees nose up, (a reasonable pitch attitude in a climb) but the angle of attack was at 40 degrees, which isn't reasonable. But they have no way of easily knowing what their angle of attack was. So here they are, with what they thought was erroneous airspeed indications. They are at 10 degrees nose up at basically wide open throttle, which SHOULD have given them pretty good climb rate. But they weren't climbing because they were in fact in a stall.

    All of that to say that a given pitch with a given power setting will not ALWAYS produce the result you would expect.
     
  17. gismo

    gismo Touchdown! Greaser!

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    My neighbor who's been flying the A330 for quite a while said that as a result of the AF accident their recurrent sim training includes a high altitude reversion to direct law with loss of airspeed indication. IIRC it's something like TOGA power and +7° pitch up. He said that's supposed to put the plane's IAS safely between min and max speed.
     
  18. Doggtyred

    Doggtyred En-Route

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    Squat switch on the gear works great.
     
  19. Jim Logajan

    Jim Logajan En-Route

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    So the facts are:

    1. Three experienced pilots on board.
    2. Airspeed indications become unreliable due to pitot icing.
    3. As a result of the erroneous airspeed and confusing automated warning systems, the pilots induce a stall at high altitude.
    4. Throughout the stall and descent the flight crew did not recognize the condition of the aircraft and did not take correct measures necessary to return the aircraft to level flight.
    5. As a result all aboard the Northwest Airlines Flight 6231 Boeing 737 are killed.

    Thirty-five years later only point 5 needs editing. (I copied point 4 verbatim from the NTSB report, linked below.)

    http://www.airdisaster.com/reports/ntsb/AAR75-13.pdf
     
  20. Dave Siciliano

    Dave Siciliano Final Approach

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    Jim: I'm really torn over this. I'm certainly not disagreeing in any manner: things like this have happened before. Three ATP rated pilots with good levels of experience, the attitude indicator worked from what I can tell, and they had back up analog instruments. Yes, there were a lot of things that distracted them, but it sure is confounding. Just shaking my head.

    Best,

    Dave
     
  21. denverpilot

    denverpilot Taxi to Parking

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    I have a small nit-pick... how are you determining that the attitude indicator was working? I've been suspicious of that the whole time...
     
  22. Henning

    Henning Ejection Handle Pulled

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    There was one thing distracting them really, every other indication was situationaly correct for being in a fully developed stall. There was really only the stall horn causing confusion, and for that the designer who decided that the system should cancel the stall warning on a single point of data with no indication that in fact a stall does not exist, should be sent to the Guillotine, and I'm serious. That was a design fail of Epic proportions and all those responsible for that system should die.

    None the less, the captain was a total failure as well as were the seat warmers under his command. The plane wanted to fly out, all they had to do was let the nose down and leave the power in. Once they had made it into the FL 2xx's that the Mmo/Vs spread opens up enough to be able to safely recover by hand on a straight up- Pitch/Power settings and that is what the captain should have ordered, but he didn't.
     
  23. Henning

    Henning Ejection Handle Pulled

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    Absolutely nothing indicates it wasn't working.
     
  24. TangoWhiskey

    TangoWhiskey Touchdown! Greaser!

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    This recommendation is a sad comment on the state of affairs in airline training. Have we trained a generation of ab initio button pushers?

     
  25. Everskyward

    Everskyward Administrator Management Council Member

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    Has that been determined? If the airplane was that deep into the stall would this have worked as a recovery technique? I think that some deep stall situations in transport category jets can become unrecoverable. I don't know if this was the case here.
     
  26. Henning

    Henning Ejection Handle Pulled

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    As soon as he let off the stick and dropped the nose, the stall horn came back on showing it was responding to pitch change, then they pulled the power levers back. Everything about that showed that the plane was still accurately responding to control inputs.
     
  27. gismo

    gismo Touchdown! Greaser!

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    It's my understanding that the A330 transfers fuel to the rear in cruise to make the plane more efficient and that CG shift might indeed preclude a recovery from a deep stall using the elevator to pitch down. That said, the combination of nose down elevator and trim (assuming the "fixed" portion of the stabilizer moves to adjust trim) ought to be extremely powerful and would likely be sufficient to drop the nose.

    There's one recovery method that's supposed to work on the most stubborn swept wing designs but it requires a lot of altitude to complete successfully. Basically you let the plane roll over to approximately 90° bank and rudder the nose down. At 10,000MSL there probably wasn't enough room left for that but at 20-25k it ought to work.
     
  28. ebacon

    ebacon Line Up and Wait

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    This airplane also has a feature that pumps fuel into the tail to move CG aft during cruise. Apparently that makes cruise flight more fuel efficient.

    The downside, it would seem to me, is that being heavy in the back would make it more difficult to correct the excessive AOA situation. Using down elevator might reduce the AOA enough to reactivate the stall horn but its not clear to me that there was enough elevator influence to break the stall.

    I dunno. I'm just a 180 hr. PPL trying to understand this tragedy.
     
  29. SkyHog

    SkyHog Touchdown! Greaser!

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    Why do some airliners lack the ability to recover from a deep stall? Is it because of a lack of elevator authority?
     
  30. Everskyward

    Everskyward Administrator Management Council Member

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    http://goliath.ecnext.com/coms2/gi_0199-11989369/Deep-stall-aerodynamics-you-didn.html

     
  31. bob_albertson

    bob_albertson Pre-takeoff checklist

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    That would be of little use since a stall detection and warning systems are all based on an alpha detection system. A squat switch would not be good enough to inhibit stall detection on the ground since something like a bounced landing will not inhibit the stick pusher since the weight would be off the gear at that time. You don't want a stick pusher pushing you're nose down when you bounce a landing :).

    You can think of this system as being similar to a gear retraction inhibit system on most light twins. You can not have just one input to account for all the variable. You'll want to inhibit the stall detection system by a combination of inputs from a few various systems. Squat switch would only be one part of the equation :wink2:.

    There is a reason why systems like these are not overly simple systems :)
     
  32. bob_albertson

    bob_albertson Pre-takeoff checklist

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    I think the easiest way to explain it without getting into the aerodynamics behind it is to just say that swept wing stall characteristics do not yield to easily reattaching the airflow over the wing. The reason is that on swept wing aircraft the center of lift moves forward as the wing stalls and causes an upward pitch for the plane.

    Bob
     
  33. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Will the Airbus even let you roll over to 90º bank? :dunno:
     
  34. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    In Normal Law, no. But they weren't in Normal Law, so yes they could have done that.
     
  35. Lance F

    Lance F Pattern Altitude

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    The stall horn came back on at 60kts, still a looong way from recovery. The THS, trimable horizontal stabilizer, had gone to full pitch up. The elevator may not have been able to overcome this, and the only way to have corrected this was to use the trim hand wheel, something that just isn't normally done in an AB.

    I have read a lot about the technical situation these poor souls faced. In our armchairs this upset is recoverable. However I do not think it's that simple. Might some pilots been able to recover? Probably. Could most? I doubt it.

    There is lot of blame to be thrown around. To put it all on the pilots is a political copout.
     
  36. gismo

    gismo Touchdown! Greaser!

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    If holding aft stick caused the trim to go full nose up, why wouldn't holding forward stick cause it to go full nose down?

    With the proper training I expect most AB pilots could have easily avoided this trap.
    But that's the French way.
     
  37. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    Has anyone ever fully explained why that happened? I had forgotten that detail and I can't quite figured out how that could happen.
     
  38. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    Been a long time, but I am pretty sure the system doesn't work that way. Why would it trim into a stall?
     
  39. Everskyward

    Everskyward Administrator Management Council Member

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    I think that with the proper training most pilots could and should have avoided getting very far into a stalled situation. They should have at least recognized that they were stalling. However I'm not convinced that many pilots could have recovered once the airplane was falling and not flying. Maybe it was possible, maybe not.

    I don't think it has anything necessarily to do with Airbus either. None of these types of airplanes are certified to be recoverable from all situations.
     
    Last edited: Aug 4, 2011
  40. Greg Bockelman

    Greg Bockelman Administrator Management Council Member

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    I am still not quite sure how they got into the stall in the first place.