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  • The WSJ has published a claim that the 737MAX has new stall protection features that may make it impossible for pilots to overcome an erroneous pitch down command.

    Originally posted by CNN
    Citing "safety experts involved in the investigation, as well as midlevel FAA officials and airline pilots," the Journal reported Monday that the automated stall-prevention system on Boeing 737 MAX 8 and MAX 9 models -- intended to help cockpit crews avoid mistakenly raising a plane's nose dangerously high -- "under unusual conditions can push it down unexpectedly and so strongly that flight crews can't pull it back up."
    STS has been a feature since the debut of the NG's. It can be overriden (with considerable effort) by the pilots. So what are they talking about here?
    The very idea goes against Boeing's "pilot-has-ultimate-authority" philosophy. If it does turn out that Boeing developed an "airplane-has-ultimate-authority" stall protection system without air data redundancy, the entire 737MAX fleet will have to be immediately grounded and the system redesigned and recertified. That outcome could be curtains for Boeing.
    However, I find it impossible to believe the FAA would certify such a system in the first place, let alone that Boeing would be so foolish as to design one.
    So I'm highly inclined to file this report under "poor fact checking".

    On the other hand, Boeing DID design an autopilot for the NG that would occassionally--due to an undetected weakness in the logic--continue to operate without redundancy when one RA was faulty and this led to the fatal crash of Turkish 1951. That system was quietly replaced in 2003 with a reliable alternative and the press never got wind of it.

    Comment


    • Originally posted by Evan View Post
      If it does turn out that Boeing developed an "airplane-has-ultimate-authority" stall protection system without air data redundancy, the entire 737MAX fleet will have to be immediately grounded and the system redesigned and recertified. That outcome could be curtains for Boeing.
      Oh...Evan, it would take a lot more than that to cause "curtains" for Boeing, trust me.

      Comment


      • Originally posted by ATLcrew View Post
        Oh...Evan, it would take a lot more than that to cause "curtains" for Boeing, trust me.
        However, I AM sure it would generate much parlour talk.
        Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

        Comment


        • Originally posted by ATLcrew View Post
          Oh...Evan, it would take a lot more than that to cause "curtains" for Boeing, trust me.
          So, a significant delay of over 4,500 deliveries (and the potential cancellations of those orders) and the thusly expanded time to profitability and loss of public confidence on that airframe wouldn't cause a fatal shareholder panic in the age of shareholder panic. That's reassuring.

          Comment


          • Originally posted by Evan View Post
            So, a significant delay of over 4,500 deliveries (and the potential cancellations of those orders) and the thusly expanded time to profitability and loss of public confidence on that airframe wouldn't cause a fatal shareholder panic in the age of shareholder panic. That's reassuring.
            Remind me how long the Nightmareliner sat on the ground over a battery.

            Comment


            • Originally posted by ATLcrew View Post
              Remind me how long the Nightmareliner sat on the ground over a battery.
              About four months, at which point they had around 900 orders to delay. As opposed to 4,500. Perhaps Boeing could simply modify the 737 system to integrate AoA redundancy (and disengage if redundancy is lost) and get it re-certified in a similar timeframe. Or perhaps they could use their political muscle to keep the fleet flying in the meantime and only issue a recommendation for the upgrade, as they did with that treacherous autothrust unit. I think, if this turns out that the crew really had no reasonable chance of restoring flight control, the FAA would ground it until it could be re-certified as safe. That would do some real injury to a brand that absolutely depends on public trust.

              Comment


              • Every cockpit needs one of these to disable HAL.

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                • Originally posted by Evan View Post
                  The WSJ has published a claim that the 737MAX has new stall protection features that may make it impossible for pilots to overcome an erroneous pitch down command.
                  I don't believe that. The pilot can always overpower the trim wheel.

                  --- 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
                    I don't believe that. The pilot can always overpower the trim wheel.
                    I think the WSJ is just misinformed. I hope it is.

                    However, now the NY times is reporting on this...

                    Originally posted by NY Times
                    “We’ve just been informed that there’s an entire new system on the Max,” said Capt. Dennis Tajer, spokesman for the Allied Pilots Association, the union for pilots at American Airlines, and a 737 pilot.

                    He said he was referring to what is known on the new version of the plane as the M.C.A.S., or maneuver characteristics augmentation system. The previous system, and the one in the standard manual, goes by a different shorthand, E.F.S., for elevator feel shift.
                    Originally posted by NY Times
                    The pilots’ union for American Airlines, which also flies the Max 8, said Tuesday that the emergency system in question had not been included by Boeing in the standard operating manual. In addition, the flight checklist — which contains information for manually overriding the emergency system — was incorrect, the union said.
                    If this is a stall-protection system that introduces automated flight control inputs based on a single source of AoA data... this is looking very very bad for Boeing....

                    Comment


                    • From PPRUNE.ORG

                      From the extremely brief description of the MCAS, we can possibly conclude:

                      JT 610 retracted flaps to the clean configuration (MCAS becomes active)

                      Low mach number, therefore maximum rate of horizontal stabilizer of 0.27 degrees per second, and a forward deflection to the limit with a spurious AoA input.


                      And LOTS of talk of none of this being in the 'manual'

                      This is looking like a whole lotta lawsuit for Boeing

                      Comment


                      • There has been a lot of talk about this. Some have suggested Boeing needed the new system on the MAX to make it behave the same way as the NG, despite the heavier engines and altered center of gravity. This was needed for certification. But now they are saying Boeing did not clearly describe the changed behavior from the new system - possibly to keep commonality with the NG and avoid any additional training that would have been required? It is speculation, but that's one reason forums exist.

                        Comment


                        • if this turns out to be true, forget about lawsuits. people should be charged criminally. fat chance of that happening though.

                          Comment


                          • Originally posted by Black Ram View Post
                            There has been a lot of talk about this. Some have suggested Boeing needed the new system on the MAX to make it behave the same way as the NG, despite the heavier engines and altered center of gravity. This was needed for certification.
                            This comes down to Boeing's decision to postpone the Y1 project, a clean-sheet replacement to the 737-757. The 737 was designed for turbojets and regional airports without jetways or large airstairs. Its achilles heel is its limited undercarriage: it sits too low to the ground to accommodate the kind of high-bypass turbofans that the modern age requires. Nevertheless, Boeing chose to crutch the 737 into the 21st-century by mounting the larger engines forward of the wing. This allowed them to squeeze in bigger fans, but at the cost of moving the center of thrust forward, where it would have a more pronounced pitch-coupling effect.

                            The NG's therefore required the STS system to be certified. That worked out. There have been no upset incidents that I know of involving that system.

                            But the MAX required even bigger fans, and, once again, Boeing responded by pushing the engines out further ahead of the wing. The MCAS system is apparently the STS replacement needed to certify the MAX. The concerns regarding the 737's pitch coupling potential only increased and perhaps something more extreme was required to give it the same flying characteristics.

                            All this because the airframe, designed in the mid-1960's, wasn't suitable for modern turbofans.

                            The other issue, which I think we will be hearing a lot more about, is how Boeing marketed the 737MAX on the merits of cockpit commonality with customers' existing 737NG fleets. This represented a large cost-saving advantage over the A320 to operators not already flying that type. Boeing was telling potential customers that the 737MAX would require only 16 hours of type-specific transitional training. Clearly, this training did not address the new pitch augmentation system.

                            If all this proves true, then I think the fix will lie in adding at least one layer of redundancy to the MCAS system and more type-specific training, both on reacting to a malfunction and in flying the 737MAX more cautiously with the system inoperative. Because, without a properly-functioning MCAS, the 737MAX is apparently considered too unsafe to certify...

                            Note: MCAS is even not listed in the 737MAX MMEL found online. There is a listing for "speed trim function", which indicates that two units are present and dispatch requires one to be confirmed operational, provided the faulty one is disconnected.

                            Comment


                            • Originally posted by Evan View Post
                              This comes down to Boeing's decision to postpone the Y1 project, a clean-sheet replacement to the 737-757. The 737 was designed for turbojets and regional airports without jetways or large airstairs. Its achilles heel is its limited undercarriage: it sits too low to the ground to accommodate the kind of high-bypass turbofans that the modern age requires. Nevertheless, Boeing chose to crutch the 737 into the 21st-century by mounting the larger engines forward of the wing. This allowed them to squeeze in bigger fans, but at the cost of moving the center of thrust forward, where it would have a more pronounced pitch-coupling effect.

                              The NG's therefore required the STS system to be certified. That worked out. There have been no upset incidents that I know of involving that system.

                              But the MAX required even bigger fans, and, once again, Boeing responded by pushing the engines out further ahead of the wing. The MCAS system is apparently the STS replacement needed to certify the MAX. The concerns regarding the 737's pitch coupling potential only increased and perhaps something more extreme was required to give it the same flying characteristics.
                              Can you please provide more explanation of what phenomena you have in mind in reference to the parts I highlighted in bold font?

                              --- 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
                                Can you please provide more explanation of what phenomena you have in mind in reference to the parts I highlighted in bold font?
                                The STS system was needed to certify the 737NG, due to more pronounced pitch characteristics in certain situations, such as with high thrust, light gross weight and aft CoG. As I understand it, this was attributed to the relocation of the engine mounts to a position more forward of the wing, and perhaps the increased thrust of the new engines. The new power/geometry would have more pronounced pitch-up effects in these situations. As I understand it, the MAX required Boeing to further compensate for this issue with a replacement for the STS that, as I understand it, has more pronounced behaviors.

                                So now tell us about the physics...

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