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Thread: Boeing 737 Max

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    Quote Originally Posted by barbter View Post
    So where are we with the *fix*?
    All i've read is software software software, but do we know if they're fundamentally changing the way it functions, opposed to just tweaking algorithms?
    The update is in flight testing.

    The major changes- both AOA vanes will have to agree before MCAS will activate. MCAS will only activate once per flight- it will no longer reset after 5 seconds.

    edit to add: there is one other thing that has been kind of misrepresented- that is the AOA DISAGREE warning. All the planes returning to service will have this warning whether or not they have the optional AOA indicators.

    This was ALWAYS an intended to be standard on the MAX for the simple reason that all 737NG's have it as a standard feature.

    When Rockwell wrote the software for the MAX PFD's, they tied the warning to the AOA indicator- this was an error that Boeing didn't catch until about 6 months after the MAX deliveries began. They intended to fix it with a scheduled software update, but it's getting a higher priority after the accidents.

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    Quote Originally Posted by jancollc View Post
    The update is in flight testing.

    The major changes- both AOA vanes will have to agree before MCAS will activate. MCAS will only activate once per flight- it will no longer reset after 5 seconds.
    Thanks.
    But what if there's a bird strike on the one side knocking out the sensor?
    Will that mean MCAS won't activate at all?

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    Quote Originally Posted by barbter View Post
    Thanks.
    But what if there's a bird strike on the one side knocking out the sensor?
    Will that mean MCAS won't activate at all?
    Yes, that's what it means. One damaged sensor would put them out of agreement, and disable MCAS.

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  5. #1024
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    Quote Originally Posted by jancollc View Post
    Here's a pic of the nose of a 737 MAX. The flags are on the pitot tubes, the AOA vanes are below, one on each side.

    MCAS is an extension of STS, which also only uses one alpha vane at a time. Boeing's greater f-up was the degree of authority they gave MCAS. What wasn't a problem with Mach Trim and Speed Trim was a problem with MCAS due to it's ability to regenerate.

    Attachment 270616
    In last night's computer generated simulation of the outside of the aircraft during the flight there was only one sensor shown and that got completely wiped out by a bird strike apparently. I realise that the sensor need to be positioned on the nose of the aircraft but surely they can be made a bit less flimsy.

    Once that sensor was destroyed there was almost really no was back for the aircraft. That can't possibly be right.


    Regards Tyrone.

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    Quote Originally Posted by jancollc View Post
    Yes, that's what it means. One damaged sensor would put them out of agreement, and disable MCAS.
    Is that wise given that MCAS is supposed to have a significant function on the aircraft ? Could that be solving one problem but creating another ? Just asking.

    Regards Tyrone.

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    One thing I haven't seen mentioned is:- Does/can the larger engines and their forward position in the Max actually make the plane difficult to control in a pitch up attitude or is it just different from the previous versions?

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    Quote Originally Posted by Tyrone Shoelaces View Post
    ...Once that sensor was destroyed there was almost really no was back for the aircraft. That can't possibly be right.
    I don't know what you were watching, so I can't offer anything about it.

    A single sensor failure does not doom the aircraft, assuming the pilots know how to react.

    The electric trim switch cuts out the MCAS inputs. So if the stab trim starts to runaway, you should use the electric trim switch to return to a neutral column, then hit the cutoff within 5 seconds. At that point, the control should be transferred to the side that does not have the active stick shaker, and the flight should either return to the takeoff point or divert to their nearest alternate, using manual trim for the duration.

    The FDR traces from the crash flights show that- it wasn't until after they stopped applying counter-trim that they got into trouble.

    Quote Originally Posted by Tyrone Shoelaces View Post
    Is that wise given that MCAS is supposed to have a significant function on the aircraft ? Could that be solving one problem but creating another ? Just asking.
    MCAS's only function is to increase control column pressures at extreme angles of attack. It's not something that is ever supposed to activate unless the airplane is already way out of shape.

    As long as you are within the normal operating envelope, MCAS never goes off- sensor failures notwithstanding.

    MCAS as a concept is fine- the problem with the implementation was the reliance on the single sensor input and the ability to quickly regenerate, coupled with too much authority.

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    Quote Originally Posted by Mark Rand View Post
    One thing I haven't seen mentioned is:- Does/can the larger engines and their forward position in the Max actually make the plane difficult to control in a pitch up attitude or is it just different from the previous versions?
    What happens, is the back pressure on the control column that is needed to pitch the nose up, decreases as the AOA increases and the nacelles start generating lift.

    It doesn't put the plane into an unrecoverable condition- many FBW aircraft don't even provide for that sort of feedback at all.

    It's just an FAA requirement that the control column pressure has to increase as the AOA increases. MCAS was added to the Speed Trim System to do that, which is why it's only active during manual flight.

    Without MCAS, the MAX is perfectly safe to fly- but it would be different than the NG, which creates a certification issue.

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    Quote Originally Posted by jancollc View Post
    ...MCAS as a concept is fine- the problem with the implementation was the reliance on the single sensor input and the ability to quickly regenerate, coupled with too much authority.
    Can you please explain the difference between that statement above, and the statement that sort of sounds the same:

    "MCAS would work OK except for the fact that the implementation as installed was completely wrong."

    From 20 feet away and all.

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    Quote Originally Posted by jim rozen View Post
    Can you please explain the difference between that statement above, and the statement that sort of sounds the same:

    "MCAS would work OK except for the fact that the implementation as installed was completely wrong."

    From 20 feet away and all.
    Well, your question doesn't make a lot of sense to me. MCAS will be just fine with a more fault-tolerant implementation.

    Conceptually, MCAS is not substantially different from the alpha protections on Airbus jets. e.g. The use of air data inputs to automatically maintain pitch attitudes.

    On the MAX, it's not about stall prevention, it's about control column pressure- but the use of air data inputs to make auto trim adjustments is nothing new.

    I think we all know that the execution was not adequate, and the risk assessments were faulty.

    But I will say again- no single factor brings down a commercial jetliner. We can sit here and lay it all on Boeing, and guess what? You don't solve the problem- you make it worse because you have ignored all the other contributing factors.

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    Quote Originally Posted by Tyrone Shoelaces View Post
    In last night's computer generated simulation of the outside of the aircraft during the flight there was only one sensor shown and that got completely wiped out by a bird strike apparently. I realise that the sensor need to be positioned on the nose of the aircraft but surely they can be made a bit less flimsy.Regards Tyrone.
    Might I suggest a much more robust sensor/skewer also, it should have a heat source in it that could officially be called "de-icing" but its real job would be to cook the skewered goose or bird. Skewer should be long enough to go through entire bird, sensor could still get info if not too clogged with feathers. Bonus for bringing the ground crew two birds on same skewer.

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    Quote Originally Posted by Rob F. View Post
    Might I suggest a much more robust sensor/skewer also, it should have a heat source in it that could officially be called "de-icing" but its real job would be to cook the skewered goose or bird. Skewer should be long enough to go through entire bird, sensor could still get info if not too clogged with feathers. Bonus for bringing the ground crew two birds on same skewer.
    Rob, Just please... Fuck-Off!
    We already have Rozen and Triumph(something) championing for the spot, and they are way ahead of you.

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    Quote Originally Posted by Rob F. View Post
    Might I suggest a much more robust sensor/skewer also, it should have a heat source in it that could officially be called "de-icing" but its real job would be to cook the skewered goose or bird. Skewer should be long enough to go through entire bird, sensor could still get info if not too clogged with feathers. Bonus for bringing the ground crew two birds on same skewer.
    Yes but would you want stuffing Rob ? Do you have stuffing in the USA ? I'm already wishing I hadn't asked this question.

    Regards Tyrone.

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    Quote Originally Posted by Tyrone Shoelaces View Post
    Yes but would you want stuffing Rob ? Do you have stuffing in the USA ? I'm already wishing I hadn't asked this question.

    Regards Tyrone.
    Birds are only small.
    The pilot did well to swerve and hit it...

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    Quote Originally Posted by jancollc View Post
    On the MAX, it's not about stall prevention, it's about control column pressure- but the use of air data inputs to make auto trim adjustments is nothing new.
    No not about stall prevention. MCAS was a workaround so that boeing did not have to go get their original type cert.
    changed. They wanted their cake and ate it too - they wanted what is a brand new aircraft with brand new flight
    characteristics, under their original certification. So they cheated, or at least tried to cheat.

    The fact that experienced pilots who are aware of the issues, still crash the sim, means the system was badly broken.
    Yes more than one factor:

    Factor (1) MCAS
    Factor (2) broken single sensor that MCAS relies on. See (1) above.

    Airmanship not a factor. Pilots being from non-US country, not a factor.
    Factor: Boeing attempted to game the system.
    Factor: Badly designed control software.
    Factor: FAA had no idea this was happening.
    Factor: whistle blower was ignored.

    Yep multiple factors, all converging on MCAS.

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    Quote Originally Posted by jim rozen View Post
    No not about stall prevention. MCAS was a workaround so that boeing did not have to go get their original type cert.
    changed. They wanted their cake and ate it too - they wanted what is a brand new aircraft with brand new flight
    characteristics, under their original certification. So they cheated, or at least tried to cheat.
    Except the 737 MAX is not a new aircraft. It's a 737NG with different engines and winglets.

    The only difference wrt flight characteristics is the control column pressures in extreme AOA's. MCAS, as I have said prev, was added to make the flight characteristics in that regime match the NG.

    Boeing built the plane the customers were asking for. Southwest did not want a "brand new" plane- they wanted a more efficient 737. They wanted to minimize the difference training for their pilots, they wanted to leverage existing maintenance infra, etc.

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    Quote Originally Posted by jim rozen View Post
    Airmanship not a factor.
    Pilots being from non-US country, not a factor.
    Wrong.
    And wrong again...

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    I'd agree terry IF and ONLY IF the experienced USA pilots who were familiar with MCAS
    characteristics manged to fly it in the sim. They didn't.

    They crashed. So respectfully disagree with you.

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    Quote Originally Posted by jim rozen View Post
    I'd agree terry IF and ONLY IF the experienced USA pilots who were familiar with MCAS
    characteristics manged to fly it in the sim. They didn't.

    They crashed. So respectfully disagree with you.

    Those articles and Sulley's ramblings are what happens when the aircraft is mis-managed to the point of no return, even a buddy that's on it said so. And I still can't help but wonder where all this propaganda is coming from, class action law suits and all.

    In one crash they allowed the MCAS to apply TWENTY double speed bursts of nose down trim until they finally couldn't physically hold the nose up any more. All they had to do at some point is reach down and hit the trim cutout switches, something ANY Boeing driver is taught from day one.

    So I respectfully submit to you that airmanship, training and competency WAS a huge factor in those two crashes. The fact that they were third world airlines doesn't necessarily mean those attributes are lacking in their pilots but in many cases, unfortunately, it does.

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    Quote Originally Posted by Terry Keeley View Post
    ...So I respectfully submit to you that airmanship, training and competency WAS a huge factor in those two crashes. The fact that they were third world airlines doesn't necessarily mean those attributes are lacking in their pilots but in many cases, unfortunately, it does.
    This.

    Add maintenance.

    Lion Air, Batam Aero Technic (Lion Air Group Indonesia) and Xtra Aerospace USA:

    a) The replacement of the AOA sensor installed on the airplane had been mis-calibrated by the repair shop (Xtra Aerospace,Florida). On both the previous (DPS-CGK) and the accident flight the left AOA sensor was reading 21 degrees too high since the beginning of the takeoff. The US NTSB and Boeing conducted a test with a 33 degrees biased AOA sensor and concluded a Mis-calibrated sensor would be detected by the airplane’s SMYD computer during installation. Xtra’s calibration device’s selector was in the REL instead of ABS, the mis-calibration/bias of 21 degrees too high was not detected as the result. After Lion 610 crash FAA did an audit on Xtra at the end of 2018 and there were numerous findings. After the Final Report of JT610 is released the FAA revoked Xtra Aerospace certificate, preventing the company from doing business.

    b) Post installation test carried out by Batam Aero Technic (Lion Air Group) engineer in DPS was not done properly. Had the procedure was done correctly the airplane's SMYD (Stall Management Yaw Damper) computer would have had detected the mis-calibration and "AOA SENSR INVALID" message will appear. The engineer in Denpasar provided the investigation several photos including of the Captain’s PFD that was claimed to be taken after the AOA sensor replacement and of the SMYD during the installation test. However, the time shown on the Captain’s PFD was the time before arrival of AOA sensor spare part and the investigation confirmed that the SMYD photos were not of the accident aircraft. On both the previous (DPS-CGK) and the accident flight the left AOA sensor was reading 21 degrees to high since the beginning of the takeoff.

    c) The flight crew of the previous(DPS-CGK) flight did not mention the continuous activation of stick shaker (which is caused by the AOA sensor), and the use of Runaway stabiliser NNC. this lack of information to maintenance crew lead into the maintenance crew being mislead that the faulty AOA was not part of the problem, and the accident flight crew did not consider they could reoccur.

    d) The pilots did not respond appropriately during the final (accident flight):

    There was a lengthy delay for the UNRELIABLE AIRSPEED Non-Normal checklist. The captain nor the FO did not do it from memory immediately despite it is an industry standard that all NNCs classified as memory items should be executed without delay from memory. The FO had difficulties finding the UNRELIABLE AIRSPEED non-normal checklist on the QRH.

    The pilots did not declare emergency (MAYDAY) or urgency (PANPAN) to ATC, as the result they were not receiving priority and instead receive normal vectoring which actually added to their already heavy workload.

    The breakdown of CRM (Crew Resource Management): when the captain transferred the controls to the FO he did not communicate effectively that he needed to counteract multiple trim down (caused by MCAS). Therefore the FO could not anticipate the requirement to repeatedly trim up countering the MCAS.
    The manual flying skill of the FO have been identified during training.

    Furthermore the KNKT report stated that there have been 31 pages missing from the airplane's log book (AFML), Lion Air are to improve the duration and content of Safety Management System (SMS) training including the identification of hazard (this is the result of the previous pilot failure to report the continuous stick shaker and stab trim runaway NNC), and the Indonesian DGCA to improve the oversight towards airlines and maintenance organisation.

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