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  • 737 rudder hardover

    Three incidents I believe were attributed to this phenomena (and a further 4-5 suspected), and in the end it was the PCU from the Pittsburgh accident which investigators finally managed to get to jam through extensive testing.

    It appears to me (a layman, mind you) that the tests they did to the PCU perhaps didn't correctly represent the actual conditions of the accidents. They basically froze the PCU and then injected it with super-hot hydraulic fluid, and while it's great that hardware modifications were made to prevent that event from occuring again, the feeling I get is that perhaps they were barking up the wrong tree.

    I know for a fact that Parker Hannifin (the manufacturer of the PCU) as well as "people within the industry" (quoted from a documentary I saw) claim they didn't get it right. It's understandable that the PH would take this stance, but still...

    Thoughts?

  • #2
    Originally posted by Nirwanda View Post
    Thoughts?
    Yes.

    We may not know exactly what happened.

    The thing was super carefully designed to work correctly almost 100% of the time...

    They proved that reversals COULD occur...they did not necessarily replicate exactly what happened in the crashes...

    Works for me.
    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
      Yes.

      We may not know exactly what happened.

      The thing was super carefully designed to work correctly almost 100% of the time...

      They proved that reversals COULD occur...they did not necessarily replicate exactly what happened in the crashes...

      Works for me.
      It is pretty much established. Remember there was a case where the plane DID NOT crash. In that case they had the intact system and the intact pilots to get all the information needed.

      --- 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
        [QUOTE=Gabriel;658582]It is pretty much established. Remember there was a case where the plane DID NOT crash. In that case they had the intact system and the intact pilots to get all the information needed.[/QUOTE

        The problem stopped happening as well...

        Comment


        • #5
          Originally posted by Gabriel View Post
          It is pretty much established. Remember there was a case where the plane DID NOT crash. In that case they had the intact system and the intact pilots to get all the information needed.
          Indeed, the overall theory seems to be strongly supported by the alignment of many factors and a couple other incidents beyond the two crashes.

          However, I perceived that the original post was focused on the hydraulic actuator and specifically that the super extra cold actuator with super extra hot oil did not represent normal conditions, and thus questioned if such an extreme test was valid...

          I think the answer is that the hot-cold hydraulic test does NOT say, "The actuator might reverse in normal conditions". Instead it says, "The actuator CAN reverse, and maybe...in some small set of extremely unusual conditions including, but maybe not limited to super cold-super hot, it might reverse...maybe...

          ...and even with all that wishy washyness, it is consistent with the overall theory, even though by itself, is not exact proof of what happened.
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

          Comment


          • #6
            Originally posted by 3WE View Post
            Indeed, the overall theory seems to be strongly supported by the alignment of many factors and a couple other incidents beyond the two crashes.

            However, I perceived that the original post was focused on the hydraulic actuator and specifically that the super extra cold actuator with super extra hot oil did not represent normal conditions, and thus questioned if such an extreme test was valid...

            I think the answer is that the hot-cold hydraulic test does NOT say, "The actuator might reverse in normal conditions". Instead it says, "The actuator CAN reverse, and maybe...in some small set of extremely unusual conditions including, but maybe not limited to super cold-super hot, it might reverse...maybe...

            ...and even with all that wishy washyness, it is consistent with the overall theory, even though by itself, is not exact proof of what happened.
            As you said. the test only proves that a rudder reversal hard-over CAN happen, not that it happened.
            At the same time, the accidents and incidents investigated proof that a rudder reversal hard-over was the only thing that could explain, for example, the plane yawing to the left with the pilot applying full pressure on the right rudder pedal (to the point of stepping so hard on it that he overcame his won weight raising himself from the seat).
            Now connect the dots...

            It is pretty much established that the PCU caused a rudder reversal hard-over. Even if what caused that PCU behavior is not 100% clear.

            --- 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 Gabriel View Post
              It is pretty much established that the PCU caused a rudder reversal hard-over- AND THAT THERE WAS A FAILURE MODE WHERE THE THING WOULD OPERATE 'IN REVERSE'.
              Fixed.

              Apologies for being pedantic with the emphasis, but I think that's sort of what the initial post was hinting at- someone felt that the hot + cold test wasn't 100% valid...The fact that the thing could operate in reverse was a critical discovery.
              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

              Comment


              • #8
                Originally posted by Nirwanda View Post
                and while it's great that hardware modifications were made to prevent that event from occuring again, the feeling I get is that perhaps they were barking up the wrong tree.
                Well, I think adding redundancy where it was needed in first place was barking up the right tree, even if the accidents weren't caused by this weakness. They proved that a vulnerability existed and closed that vulnerability. I still would like to know why Boeing didn't make it redundant to begin with, and why they spent almost ten years in denial aftert he first incident while still not making it redundant.

                Comment


                • #9
                  Originally posted by Evan View Post
                  Well, I think adding redundancy where it was needed in first place was barking up the right tree, even if the accidents weren't caused by this weakness. They proved that a vulnerability existed and closed that vulnerability. I still would like to know why Boeing didn't make it redundant to begin with, and why they spent almost ten years in denial aftert he first incident while still not making it redundant.
                  Because the vulnerability was discovered only after a plane survived the incident. The previous cases had been closed without identifying what went wrong, there were suspicions that a wrong pilot reaction to an upset generated by wake turbulence could be the cause.

                  --- 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
                    Because the vulnerability was discovered only after a plane survived the incident. The previous cases had been closed without identifying what went wrong, there were suspicions that a wrong pilot reaction to an upset generated by wake turbulence could be the cause.
                    No, I mean the design using a single rudder actuator with a single servo. That obviously lacked redundancy. That doesn't mean that is was obviously prone to reversal. But my feeling is that Boeing chose not to revise the design after the initial investigation because doing so would appear to be an admission of design weakness and thus open them up to liability. So the 737 fleet remained in operation with this weakness until 2002.

                    Anyway, you know how I feel. The 737 should have been retired by now and Beoing should have a 21st-century single-aisle airframe in production.

                    Comment


                    • #11
                      Originally posted by Nirwanda View Post
                      Three incidents I believe were attributed to this phenomena (and a further 4-5 suspected), and in the end it was the PCU from the Pittsburgh accident which investigators finally managed to get to jam through extensive testing.

                      It appears to me (a layman, mind you) that the tests they did to the PCU perhaps didn't correctly represent the actual conditions of the accidents. They basically froze the PCU and then injected it with super-hot hydraulic fluid, and while it's great that hardware modifications were made to prevent that event from occuring again, the feeling I get is that perhaps they were barking up the wrong tree.

                      I know for a fact that Parker Hannifin (the manufacturer of the PCU) as well as "people within the industry" (quoted from a documentary I saw) claim they didn't get it right. It's understandable that the PH would take this stance, but still...

                      Thoughts?
                      Yes, indeed. In a 747 I know (at least) three different axes, in order of appearance, elevator, aileron, rudder, and in my eyes, the throttle quadrant is the fourth axis.

                      Thus, I immediately had this one in mind:
                      16 years ago, a long haul airbus has lost her rudder inflight.

                      You can say that I probably watch to many TV broadcasts with Greg Feith in it. But everytime I see this man, I again learn something! Yes, documentaries.

                      If we ask Flight Captain Chesley Sullenberger III, surely we both seem to be laymen, me probably even more than you. That's why I stumbled across the word PCU. I'd call that a rudder servo.

                      If that's the thing we are talking about, then I mentioned the wrong flight #.. Back then in November 2001, 265 people died not due to a frozen rudder servo. The complete tailfin broke into pieces "due to unnecessary rudder inputs", as Greg Feith would've written it.

                      Where do pilots learn to excessively use the pedals?! Since I know how to use a Baron 58 propeller simulator, I always use aileron to manually ensure LNAV (sorry, Boeing language, but we are on topic).
                      The cockpit changes (a little bit) but the procedure does not change if you sit in a 747.

                      In case of a doubt we should ask
                      a) a B748 test pilot
                      or
                      b) a B747 flight instructor
                      or
                      c) the LH B747 fleet chief.

                      But I don't think that I have learned something wrong.
                      The German long haul is alive, 65 years and still kicking.
                      The Gold Member in the 747 club, 50 years since the first LH 747.
                      And constantly advanced, 744 and 748 /w upper and lower EICAS.
                      This is Lohausen International airport speaking, echo delta delta lima.

                      Comment


                      • #12
                        Originally posted by LH-B744 View Post
                        Thus, I immediately had this one in mind:
                        16 years ago, a long haul airbus has lost her rudder inflight.
                        That accident bothers me. If you can break the rudder by manual input, to me that's a design flaw. I don't care who's piloting the airplane.

                        Comment


                        • #13
                          Originally posted by Nirwanda View Post
                          That accident bothers me. If you can break the rudder by manual input, to me that's a design flaw. I don't care who's piloting the airplane.
                          If you are talking about the AA A300 in 2001, it lost the whole fin, not just the rudder.
                          And you can brake almost any plane with manual input. Especially something like a 737.

                          --- 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 Evan View Post
                            No, I mean the design using a single rudder actuator with a single servo. That obviously lacked redundancy. That doesn't mean that is was obviously prone to reversal. But my feeling is that Boeing chose not to revise the design after the initial investigation because doing so would appear to be an admission of design weakness and thus open them up to liability. So the 737 fleet remained in operation with this weakness until 2002.

                            Anyway, you know how I feel. The 737 should have been retired by now and Beoing should have a 21st-century single-aisle airframe in production.
                            Wow. A (not yet) online friend who also thinks that a PCU is a servo? And I swear, I didn't read your #10 entry here, before I wrote my #11. But that's not the reason... Am I allowed to quote you twice?
                            The 737 should have been retired by now and Beoing should have a 21st-century single-aisle airframe in production.
                            Wow. You know which airline is mentioned in the B737 en wiki as the 737 launch customer? I wasn't aware of that. First flight of a Boeing 737: and that's again a remarkable day, February 10th 1968. The airline? Well, that must've been the day when the LH B737 fleet chief began his work... But "we" are not able to celebrate these golden jubilee in February. Spohr today does not own one single B737. Founding member of the 737 club, but we left the club in .... ? Which in my eyes is a shame!

                            If you ask me and/or if you've read my forum entry in the Delta 747 topic, then you can see the successor for the DL 747. Imho the DL-A359. And for the LH 737?
                            LH-A320 and LH-A321.

                            LH-A320 can't be a bad a/c. Spohr flies it. But is an Airbus able to be the legal successor of a Boeing 737, which since half a century is everywhere on the planet?

                            You ask me? - No.

                            Greetings and a Happy New Year!
                            The German long haul is alive, 65 years and still kicking.
                            The Gold Member in the 747 club, 50 years since the first LH 747.
                            And constantly advanced, 744 and 748 /w upper and lower EICAS.
                            This is Lohausen International airport speaking, echo delta delta lima.

                            Comment


                            • #15
                              Originally posted by Gabriel View Post
                              If you are talking about the AA A300 in 2001, it lost the whole fin, not just the rudder.
                              And you can brake almost any plane with manual input. Especially something like a 737.
                              Yes I meant that accident, and yes it was the whole fin which makes it even worse.

                              How else can you structurally break a fully functioning modern aircraft by input (aside from overspeed).
                              i'm genuinly curious

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