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  • Originally posted by flashcrash View Post
    Thinking outside the box a little here - do we actually _know they didn't use the thumb switches more than a perfunctory couple of times? I get that the data shows the stab only moved a couple of clicks after they re-engaged the electric trim. But that's not quite the same thing. Given their overspeed condition, is it possible that even the motor driving the jackscrew was unable to fight the aerodynamic forces on the stab to move it nose up? In contrast, MCAS found it easy to move it nose-down?
    The data shows, separately:
    1) The inputs of the thumb switch
    3) The inputs of the automation (without distinguishing whether it was triggered by the AP, the MCAS or the speed trim)
    4) The position of the stabilizer.

    And what we can see is (colors correlate with the color of the trace in the FDR plot)
    a) Several thumb switch trim inputs after take-off, that are correlated with change in the stabilizer position (flaps were extended, so no MCAS)
    b) Several automation inputs after the AP is engaged, that are correlated with change in stabilizer position (MAS doesn't act when AP)
    c) Flaps handle moved to retracted, flaps start to retract
    d) In the middle of the flaps retraction the AP disengages (don't know if by itself or commanded)
    e) Flaps complete the retraction and, as soon as they get to the retracted position...
    f) Automation nose-down trim input, about 9 seconds, correlated with a stabilizer motion of about 2.5 units in the nose-down direction. Hello MCAS.
    g) About 3 seconds of nose-up thumb switch correlated with about 1 unit of nose-up stabilizer motion.
    h) 5 seconds after the thumb switch is released, another long automated nose-down input, correlated with another 2 units of nose-down stabilizer motion.
    i) A long nose-up thumb switch input correlated with an immediate stop of the MCAS automated input and immediately reversing of stabilizer motion, going up some 2 units.
    i) The CVR records the pilot discussing and confirming the use of the cutout switches.
    j) There is a 9-seconds nose-down input from the automation that is NOT correlated with any stabilizer motion, indication that the cutout switches had been turned off.
    k) A long (more than 2 minutes) lack of activity with the trim.
    l) 2 fraction-of-a-second nose-up thumb-switch clicks correlated with the stabilizer moving up a fraction of a unit (indication that they put the cutout switch back in the operative position)
    m) 5 seconds after the last thumb switch click, a 5 or 6 seconds automated nose-down trim input (must be MCAS) correlated with the stabilizer going about 1.5 units in the nose-down direction. That happen when they were at 7000 ft above the ground. They crashed some 20 seconds later.

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    --- 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 ---

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    • Originally posted by Evan View Post
      This is what really bothers me. Boeing saw what MCAS could do with the Lion Air crash and responded with this fatal procedure that removes a key system that is perfectly functional instead of simply using the MCAS on/off lever (the flap lever). And so another one bites the dust.

      Why didn't they write the emergency AD procedure to be: restore pitch/counter-trim/reduce thrust/extend flaps?

      I mean, why is nobody thinking this thing through?
      And what if the trim runaway was not due to MCAS? Then you lost valuable time with something that will not work.

      --- 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


      • Originally posted by Evan View Post
        You can safely extend flaps 1 at 250kts. That procedure I suggest lists 'reduce thrust' before 'extend flaps'. Even if you are 10kts fast at that point, it's better to risk flap damage (unlikely unless you are well above that speed) than to risk losing pitch trim authority.
        They were more than 10 knots beyond 250 just a few seconds after the 1st MCAS activation.

        --- 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 ---

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        • Originally posted by Gabriel View Post
          The data shows, separately:
          1) The inputs of the thumb switch
          3) The inputs of the automation (without distinguishing whether it was triggered by the AP, the MCAS or the speed trim)
          4) The position of the stabilizer.

          And what we can see is (colors correlate with the color of the trace in the FDR plot)
          a) Several thumb switch trim inputs after take-off, that are correlated with change in the stabilizer position (flaps were extended, so no MCAS)
          b) Several automation inputs after the AP is engaged, that are correlated with change in stabilizer position (MAS doesn't act when AP)
          c) Flaps handle moved to retracted, flaps start to retract
          d) In the middle of the flaps retraction the AP disengages (don't know if by itself or commanded)
          e) Flaps complete the retraction and, as soon as they get to the retracted position...
          f) Automation nose-down trim input, about 9 seconds, correlated with a stabilizer motion of about 2.5 units in the nose-down direction. Hello MCAS.
          g) About 3 seconds of nose-up thumb switch correlated with about 1 unit of nose-up stabilizer motion.
          h) 5 seconds after the thumb switch is released, another long automated nose-down input, correlated with another 2 units of nose-down stabilizer motion.
          i) A long nose-up thumb switch input correlated with an immediate stop of the MCAS automated input and immediately reversing of stabilizer motion, going up some 2 units.
          i) The CVR records the pilot discussing and confirming the use of the cutout switches.
          j) There is a 9-seconds nose-down input from the automation that is NOT correlated with any stabilizer motion, indication that the cutout switches had been turned off.
          k) A long (more than 2 minutes) lack of activity with the trim.
          l) 2 fraction-of-a-second nose-up thumb-switch clicks correlated with the stabilizer moving up a fraction of a unit (indication that they put the cutout switch back in the operative position)
          m) 5 seconds after the last thumb switch click, a 5 or 6 seconds automated nose-down trim input (must be MCAS) correlated with the stabilizer going about 1.5 units in the nose-down direction. That happen when they were at 7000 ft above the ground. They crashed some 20 seconds later.

          [ATTACH=CONFIG]23352[/ATTACH]

          This article is quite interesting and it explains one theory of why they only briefly thumbed the switches near the end.

          https://leehamnews.com/2019/04/05/bj...irst-analysis/

          The insufficient trim mystery after re-activation of Electric Trim
          After 7 PF commands Electric Trim Nose Up in two short cycles. I asked my selves (as did others) why these short trims? They are fighting to get the nose up to the extent they risk switching in the Electric Trim again. Then why not trim nose up continuously or for at least long cycles once Electric Trim is there? It took me several hours to find an explanation. Here my take:

          To understand the blip trims one must have flown fast jets at low altitude. At the speed ET302 is flying, 360kts, it’s hypersensitive to trim. The least trim action and the aircraft reacts violently. Any trimming is in short blips.

          As PF holds the nose up with a very high stick force, now for a long time, he’s sensitivity to release stick with trim is not there (this is what Pilots do when they trim nose up, otherwise the aircraft pitches up fast). He trims therefore in short blips and has difficulty to judge the trim effect he has achieved. His is not flying on feel. He can’t, he is severely out of trim, holding on to the Yoke with a strong pull force.

          Anyone who has flown a grossly out of trim aircraft at high speeds knows your feel is compromised. The sensors you have to rely on are your eyes, not your hands.

          PF has the horizon glued to read the aircraft. The result is the short nose-up trims we see. The nose goes up and the stick force needed is reduced. His judgment is; this is enough for now, it was a powerful response. Any MCAS attack I now trim against, then I correct my trim if I need to.

          But the aggressive MCAS, trimming with a speed 50% higher than the pilot and for a full nine seconds, kicks in at 8 with a force they didn’t expect. Speed is now at 375kts and MCAS was never designed to trim at these Speed/Altitude combinations. Dynamic pressures, which governs how the aircraft reacts to control surface movements, is now almost double it was when last MCAS trimmed (Dynamic pressure increases with Speed squared).

          The Pilots are thrown off their seats, hitting the cockpit roof. Look at the Pitch Attitude Disp trace and the Accel Vert trace. These are on the way to Zero G and we can see how PF loses stick pull in the process (Ctrl Column Pos L). He can barely hold on to the Yoke, let alone pull or trim against.

          His reduced pull increases the pitch down further, which increases the speed even more. At 05.45.30 the Pilots have hit the seats again (Accel Vert trace and Ctrl Columns force trace) and can start pulling in a desperate last move. But it’s too late. Despite them creating the largest Control Column movement ever, pitch down attitude is only marginally affected.
          I think the two key parts are that he claims in an overspeed state, trim adjustments are made very carefully, and the second point is that the MCAS trim is extremely aggressive and fast. By the time it kicked in, there were only seconds before it was nearly impossible to recover from even at that altitude.

          Comment


          • Originally posted by Gabriel View Post
            They were more than 10 knots beyond 250 just a few seconds after the 1st MCAS activation.
            About 25 seconds after flap retraction and 10 seconds after the first MCAS activation, there were around 280kts. Is that going to damage anything? Are they going to be at that speed if they had reduced thrust 10 seconds earlier?

            This isn't normal ops. Something has to give. Shutting down the pitch trim doesn't seem to save the day. Extending the flaps a bit over the placard speed almost cerrtainly will. But only as part of a simple, four-step memory procedure.

            Comment


            • Originally posted by Schwartz View Post
              This article is quite interesting and it explains one theory of why they only briefly thumbed the switches near the end.

              https://leehamnews.com/2019/04/05/bj...irst-analysis/



              I think the two key parts are that he claims in an overspeed state, trim adjustments are made very carefully, and the second point is that the MCAS trim is extremely aggressive and fast. By the time it kicked in, there were only seconds before it was nearly impossible to recover from even at that altitude.
              I am not buying it, at least yet. Several seconds after the MCAS ENDED its last activation they were pulling harder than ever on the yoke and were still at positive Gs. Besides, the MCAS is not super aggressive against a sluggish thumb switch action. Yes, it is faster, but they had 5 seconds of no thumb switch activity (with them still pulling up very hard) and they could have used it at any point before or after that. As soon as the MCAS started to apply nose-down trim would have been a good moment. The force on the stick were increasing, the nose was starting to drop and the Gs were reducing. What other indication you need that you need help pulling up?

              --- 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


              • Originally posted by Evan View Post
                About 25 seconds after flap retraction and 10 seconds after the first MCAS activation, there were around 280kts. Is that going to damage anything? Are they going to be at that speed if they had reduced thrust 10 seconds earlier?

                This isn't normal ops. Something has to give. Shutting down the pitch trim doesn't seem to save the day. Extending the flaps a bit over the placard speed almost cerrtainly will. But only as part of a simple, four-step memory procedure.
                I don't know. First you have to answer the other question: what if the runaway was not due to the MCAS? Then extending some flaps would be meaningless.

                And you say "if they had reduced thrust 10 seconds earlier" (that is by the time of the 1st MCAS activation). Well, why didn't they? Not because they didn't have the instruction to retract the flaps. They didn't reduce thrust even when they were overspending straight into the ground.

                --- 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


                • Originally posted by Evan View Post
                  About 25 seconds after flap retraction and 10 seconds after the first MCAS activation, there were around 280kts. Is that going to damage anything? Are they going to be at that speed if they had reduced thrust 10 seconds earlier?

                  This isn't normal ops. Something has to give. Shutting down the pitch trim doesn't seem to save the day. Extending the flaps a bit over the placard speed almost cerrtainly will. But only as part of a simple, four-step memory procedure.
                  God saved the FDR, and somebody has found it. And we are lucky aren't we. Otherwise this discussion might also have reached 685 entries. Incredible. But not yet with so many detail, only a few weeks after it happened.

                  Are you trying to go through the t/o and climb procedures of a 737 Max without really sitting in the cockpit? I'd assume that's not easy.

                  As far as I know it from a quite good Boeing simulator (Randazzo), with 280 KIAS nothing should break into pieces on board a Boeing jet, not by far. Not without flaps.

                  My question for this forum entry #686 was, what was the state of the autopilot. And I've found a good source who says 'off' as an answer.
                  ASN report Ethiopian Airlines flight ET #302

                  The captain attempted to engage the autopilot twice, but this resulted in two autopilot warnings.
                  So. MCAS is by default able to work although a/p is off. That's why somewhere I have seen a switch, or two switches (?), to switch off MCAS. So far it makes sense.
                  But. If I could say a wish. In my eyes a/p off and MCAS off should be one switch. And that should be the switches which you use to switch off a/p.

                  At least two of these switches can be reached way faster than this tiny MCAS switches somewhere on the cockpit floor. I'm sure.

                  Btw, let me warn you, *boring* *spoiler*, this ASN report is rather long and not really helpful, imho. Because it does not mention the word MCAS once.
                  That's what airlines are good for, amongst others,
                  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.
                  Aviation enthusiast, since more than 35 years with home airport EDDL.

                  Comment


                  • Originally posted by LH-B744 View Post
                    So. MCAS is by default able to work although a/p is off. That's why somewhere I have seen a switch, or two switches (?), to switch off MCAS. So far it makes sense.
                    But. If I could say a wish. In my eyes a/p off and MCAS off should be one switch. And that should be the switches which you use to switch off a/p.

                    At least two of these switches can be reached way faster than this tiny MCAS switches somewhere on the cockpit floor. I'm sure.
                    The MCAS is armed ONLY in MANUAL FLIGHT with FLAPS RETRACTED.
                    If the AP is on, the MCAS is off. If the flaps are not retracted, the MCAS is off.

                    And there are no MCAS switch. The report shows how the MCAS kept making trim inputs even after the trim was disconnected with the cutout switches. Only that they trim, turned off in this way, did not respond to the MCAS commands.

                    --- 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


                    • Originally posted by Gabriel View Post
                      The data shows, separately:
                      1) The inputs of the thumb switch
                      3) The inputs of the automation (without distinguishing whether it was triggered by the AP, the MCAS or the speed trim)
                      4) The position of the stabilizer.
                      Thanks. Very helpful. Appreciated.

                      Comment


                      • Originally posted by Gabriel View Post
                        I don't know. First you have to answer the other question: what if the runaway was not due to the MCAS? Then extending some flaps would be meaningless.
                        The trim suddenly pulls away from you upon flap retraction? That's how you know it's MCAS. Problem continues with flaps retracted? It's not MCAS, so go to the trim cuttoff switches.

                        And you say "if they had reduced thrust 10 seconds earlier" (that is by the time of the 1st MCAS activation). Well, why didn't they? Not because they didn't have the instruction to retract the flaps. They didn't reduce thrust even when they were overspending straight into the ground.
                        Because they lacked a memory procedure for this. What I'm suggesting is simple enough to be a memory procedure. It serves to quickly stabilize the situation, like a memory procedure.
                        I realize memory procedures must be kept to a minimum and only taught for critical situations where loss-of-control is imminent, but this IS such a situation.
                        The -Max needs a memory procedure for this.

                        It just astounds me that Boeing is not providing this procedure. What am I missing?

                        Comment


                        • Hey Evan...my head almost exploded...

                          This sure does sound like"Use broad knowledge and make stuff up on-the-go that violates procedures (like don't extend flaps unless you are at safe speeds to do so)"...I think someone once called it Cowboy improvisation?

                          Originally posted by Evan View Post
                          About 25 seconds after flap retraction and 10 seconds after the first MCAS activation, there were around 280kts. Is that going to damage anything? Are they going to be at that speed if they had reduced thrust 10 seconds earlier?

                          This isn't normal ops. Something has to give. Shutting down the pitch trim doesn't seem to save the day. Extending the flaps a bit over the placard speed almost cerrtainly will. But only as part of a simple, four-step memory procedure.
                          But fortunately, I see the last sentence that your procedure won't work if the pilots come up with it during the heat of the moment, it only works if it's written in ANOTHER type- and situation-specific memory checklist.

                          Nevertheless, nice cowboy improvisation from the keyboard at 0 Radalt and 0 Kts.
                          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                          Comment


                          • Originally posted by Evan View Post
                            It just astounds me that Boeing is not providing this procedure. What am I missing?
                            What your are missing is that it's not that simple.

                            Your fix might work- but does it STILL leave you with an airplane that is different from the other 737's and an airplane that one can argue has a nasty, death-trap behavior when the stars align?

                            Does it clearly indicate that you screwed the pooch and TeeVee and friends are going to clean up?

                            Are there other things woven into the 50 years of 737 Adaptation...I would not be surprised if there are a couple more fairly critical things that are affected by this MCAS stuff...the simple fix, may derail something else...which derails yet another thing...big $ and maybe we should have been kludging up the 757 instead of the 737.

                            Get out of the bubble, ride a bike. Even with that beautiful simplicity, $hit goes wrong...My damn bike is always jumping gears on me...
                            Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                            • I heard a SW pilot saying that his airline bought additional instrumentation on the 737max.
                              I found this video that mentions it (note that announcer gets the function of the AOA sensors wrong).
                              https://abcnews.go.com/International...ation-61659989

                              Sorry if this has been mentioned[ before

                              Comment


                              • Some disturbing revelations today in the New York Times:

                                - Boeing didn't provide detailed MCAS information to their own test pilots.
                                - MCAS was originally only intended to activate at high speeds, but it then became apparent that it was needed at low speeds as well, where a greater pitch rate and angle were needed. Thus the late-inning change to the higher rates.
                                - The FAA didn't require their approval for this because they determined that this didn't represent a "critical phase of flight".
                                - Approach-to-stall recovery at low altitude isn't a critical phase of flight.

                                Fascinating as ever.

                                https://www.nytimes.com/2019/04/11/b...-faa-mcas.html

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