Announcement

Collapse
No announcement yet.

Airbus planes can't stall. Or can they?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Airbus planes can't stall. Or can they?

    It seems that they can, but I really don't understand how the flight control logic let this happen.

    One minute later gusts with winds up to 14 knots from 340 degrees were recorded at the aerodrome, at about the same time the aircraft just intercepted the localizer runway 03 at 2140 feet MSL with automation, autopilot and autothrust, engaged, however, the indicated airspeed began to decay and the attitude began to gradually increase. When the indicated airspeed decreased through 114 knots (Vapp 126 knots) an automated "SPEED" warning was triggered. A target speed of 131 KIAS was selected into the speed window of the flight control unit. Autothrust began to accelerate the engines slowly, however, speed was already decreasing at 7 knots per second, the autopilot automatically disconnected, the Alpha Protection function activated. Alpha Floor activated when the speed reached 83 KIAS, the aircraft reached a minimum speed of 74 KIAS before the aircraft began to accelerate again, the maximum angle of attack was 33.4 degrees together with right roll and loss of altitude. The aircraft reached 43.6 degrees right roll, 3924 feet rate of descent, the EGPWS sounded "Glideslope", "PULL UP" and "SINKRATE" in sequence. As the aircraft lost altitude and gradually increased speed, the crew, now manually controlling the aircraft now with flight augmentation computers 1 and 2 inoperative, gradually regained control of the aircraft, arrested the descent at 884 feet MSL and began to climb the aircraft again.
    Aviation Herald - News, Incidents and Accidents in Aviation


    74 KIAS? 33deg of AoA? 43.6deg of roll?
    H.A.L.L was not supposed to allow this.
    And I don't understand how they managed to keep the sink rate below 4000fpm in that condition.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

  • #2
    Originally posted by Gabriel View Post
    H.A.L.L was not supposed to allow this.
    With all the bazillion lines of code in my PC and nearly 30 years of development, you'd think it wouldn't crash either...

    (And of course, a plane CAN be stalled at ALMOST any attitude and airspeed.)
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

    Comment


    • #3
      Originally posted by 3WE View Post
      (And of course, a plane CAN be stalled at ALMOST any attitude and airspeed.)
      Of course that the corollary of that principle is that a plane can be prevented from stalling at almost any attitude and airspeed. And that's what the Airbus' computers are supposed to do.

      --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
      --- Defend what you say with arguments, not by imposing your credentials ---

      Comment


      • #4
        Originally posted by Gabriel View Post
        It seems that they can, but I really don't understand how the flight control logic let this happen.


        Aviation Herald - News, Incidents and Accidents in Aviation


        74 KIAS? 33deg of AoA? 43.6deg of roll?
        H.A.L.L was not supposed to allow this.
        And I don't understand how they managed to keep the sink rate below 4000fpm in that condition.
        Well, for one thing, a dual FAC failure = alternate law. Not clear on the chain of events here or when or why the two FAC's went offline…

        According to the QAR the alpha protection activated at 93 KIAS and controlled the elevators fully down for a period of 7 seconds, causing both flight augmentation computers to drop offline
        …causing Alpha Prot to be lost.

        Also, alpha protect limits the pitch the pilot can command. I don't think it can protect against high AoA caused by vertical windshear. Roll angles up to 67° in normal law are allowed if the pilot maintains sidestick input.

        Comment


        • #5
          FAO: Gabriel

          So....

          Stall training is finally adjusted in a manner that makes you happy...

          ...and we have what might be a stall-related crash in Russia, the Gabriel post on a 737 near-stall story at another forum and the Gabrield Airbus actual stall story here...

          ...I dunno- maybe it was better before, even though Pinnacle, Colgan and Air France were eye-rollers...
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

          Comment


          • #6
            Originally posted by Evan View Post
            Well, for one thing, a dual FAC failure = alternate law. Not clear on the chain of events here or when or why the two FAC's went offline…

            …causing Alpha Prot to be lost.
            Hmm, ok, That would explain a couple of things.
            However alpha floor still worked after that?

            Also, alpha protect limits the pitch the pilot can command. I don't think it can protect against high AoA caused by vertical windshear.
            Apparently the vertical windshear was in the downward direction, thus reducing the AoA not increasing it.

            And in any event, the stall caused by an upward windshear should be transient because:
            - natural stability of the airplane would lower the nose and seek the original AoA (unless the crew resist the natural nose-down with pull-up inputs), and
            - the envelope protection would further add nose-down inputs to recover from an excessive AoA (unless the plane reverts to some non-normal law that inhibits this protection).

            Roll angles up to 67° in normal law are allowed if the pilot maintains sidestick input.
            Yes, but the plane will apply increasing amount of "roll level" inputs past 33 (?) degrees of bank, thus creating an artificial roll stability. That, of course, unless the pilots maintain sidestick input (only with sustained full sidestick input can the plane reach 67°, if anything below full is maintained then the plane will stabilize at somewhere between 33 and 67). But:
            - I don't see why the pilots would hold sustained sidestick inputs.
            - All of the above is valid if there is enough roll authority, something doubtful at 74 KIAS and 33° of AoA.

            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
            --- Defend what you say with arguments, not by imposing your credentials ---

            Comment


            • #7
              Originally posted by 3WE View Post
              So....

              Stall training is finally adjusted in a manner that makes you happy...

              ...and we have what might be a stall-related crash in Russia (IF THERE WAS ONE THING THAT THESE PILOTS DID RIGHT WAS PREVENT THE STALL BY LOWERING THE NOSE; A BIT TOO MUCH PERHAPS), the Gabriel post on a 737 near-stall story at another forum (BUT THAT WAS DUE TO A JAMMED CONTROL; THE PILOTS WERE ACTUALLY APPLYING A COMBINED 200LB OF PUSH-DOWN FORCE; BUT THEY DIDN'T FOLLOW MY PROCEDURE BECAUSE THEY DIDN'T USE NOSE-DOWN TRIM WHEN PUSH DOWN PROVED INEFFECTIVE) and the Gabriel Airbus actual stall story here... (WHICH WAS RECOVERED WHEN THE PLANE DID WHAT THE PILOTS SHOULD HAVE DONE BUT DIDN'T: LOWER THE NOSE. AIMING FOR TOGA AND 10° NOSE UP WOULD HAVE BEEN A DEATH SENTENCE HERE)

              ...I dunno- maybe it was better before NOT!!!
              .

              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
              --- Defend what you say with arguments, not by imposing your credentials ---

              Comment


              • #8
                Originally posted by Gabriel View Post
                ...
                Just pointing out the ironing
                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                Comment


                • #9
                  Originally posted by 3WE View Post
                  Just pointing out the ironing
                  I know, but don't tell me that you didn't expect or even had the intention to trigger my rant.

                  --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                  --- Defend what you say with arguments, not by imposing your credentials ---

                  Comment


                  • #10
                    Originally posted by Gabriel View Post
                    Of course that the corollary of that principle is that a plane can be prevented from stalling at almost any attitude and airspeed. And that's what the Airbus' computers are supposed to do.
                    Even the one on AF447?

                    Comment


                    • #11
                      Originally posted by Gabriel View Post
                      Hmm, ok, That would explain a couple of things.
                      However alpha floor still worked after that?
                      I think we need a clearer idea of the sequence of events. Alpha floor may have kicked in before the FAC's were lost. The most disturbing question here for me is WHY did 7 secs of downward elevator take two FAC's offline?

                      Yes, but the plane will apply increasing amount of "roll level" inputs past 33 (?) degrees of bank, thus creating an artificial roll stability.
                      Beyond 33° the protections will roll to 33° if the sidestick is released, assuming there is still roll authority, assuming you are still have the protections… why would the PF roll full deflection in the first place? Maybe he was having a bad dream.

                      Comment


                      • #12
                        Originally posted by EconomyClass View Post
                        Even the one on AF447?
                        And that's what the Airbus computers are supposed to do in normal law.
                        Fixed.

                        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                        --- Defend what you say with arguments, not by imposing your credentials ---

                        Comment


                        • #13
                          Originally posted by Evan View Post
                          I think we need a clearer idea of the sequence of events. Alpha floor may have kicked in before the FAC's were lost. The most disturbing question here for me is WHY did 7 secs of downward elevator take two FAC's offline?
                          Just guessing. Maybe that's an intentional feature, so control of the plane is returned to the pilots in case of this response being triggered by a faulty input.

                          Or why wouldn't the AoA be reduced after 7 seconds of full-nose-down input? Maybe the AoA is sending a faulty "high AoA" input and the AoA is not so high?

                          Those thoughts would cross my mind when designign the system.

                          --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                          --- Defend what you say with arguments, not by imposing your credentials ---

                          Comment


                          • #14
                            Originally posted by Gabriel View Post
                            Just guessing. Maybe that's an intentional feature, so control of the plane is returned to the pilots in case of this response being triggered by a faulty input.
                            hmmm… but then it would be intentionally designed to leave the pilots in alternate law as well in this scenario. You can't have normal law if you lose both of the FAC's.

                            Comment


                            • #15
                              Originally posted by Evan View Post
                              hmmm… but then it would be intentionally designed to leave the pilots in alternate law as well in this scenario. You can't have normal law if you lose both of the FAC's.
                              I guess you can't have normal law with an unreliable AoA indication.

                              In other words, more or less the same that happens with the unreliable airspeed, only that in this case the affected units are the ADRs.

                              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                              --- Defend what you say with arguments, not by imposing your credentials ---

                              Comment

                              Working...
                              X