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Lion Air 737-Max missing, presumed down in the sea near CGK (Jakarta)

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  • 3WE
    replied
    Originally posted by Gabriel View Post
    It was already disclosed AND demonstrated as possibly contributing to a crash when Ethiopian crashed.
    Fixed.

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  • Gabriel
    replied
    Originally posted by Black Ram View Post
    MCAS is not necessarily classic trim runaway, because: 1) happens by design, not because of trim malfunction;
    That makes no sense to me. The single AoA failure is not designed into the system anymore than a short in the trim switch that would activate it.
    2) happens incrementally
    While true, other trim malfunctions can happen intermittently too (like a loose wire). I don't think this is a big factor. 5 seconds of commanded continuous trim in manual flight creating a condition where the pilot needs to fight against it should raise all the flags. ESPECIALLY if it is repeated.

    in the Ethiopian crash that unless they knew what exactly was going on very early on and acted accordingly, the manual trim would have been unusable unless they could apply the special yo-yo procedure because of their high speed. I also recall the switches were used by the Ethiopian crew, if memory serves my right, and it was not enough.
    The service bulletin and AD issued after the Lion Air crash told the pilots to re-trim the plane with the thumb switch before disconnecting the trim and to manually trim with the wheel after disconnecting the trim to remove the stick forces. The Ethiopian crew did neither. Instead, they disconnected the electric trim when the plane was already way out of trim and kept fighting the increasing stick forces as they accelerated with take-off thrust set beyond overspeed speed. Only when they started losing the battle against the stick forces they attempted to use the manual wheel. At that point, being so out of trim, flying so fast, and applying so much force on the elevator, the trim was wheel was impossibly hard to move by hand due to high friction in the jack screw.At that point they still had a few options. They could have pulled together and pitch to a marked climb attitude and retard the throttles to slow down (that would have reduced the stick forces and also made the trim wheel easier to to turn). They opted to reconnect the electric trim, one assumes that they did that to be able to trim using the thumb switch. While reconnecting the electric trim is against the procedures (which calls to keep it off for the rest of the flight), given the desperate circumstances that was actually not a bad idea. They could have reconnected the electric trim, re-trim the plane and disconnect it again and if in the meantime the MCAS kicked it again, a click in the trim would have killed it for 5 seconds. However, they reconnected the electric trim, did two super-short clicks on the trim thumb switch that barely move the stabilizer just a negligible tiny bit, and left it there. Sure enough, 5 seconds after the 2nd click the MCAS activated again. They could have killed it with the thumb switch, but they didn't. In a few seconds the trim absolutely overwhelmed the pilots' force and the plane entered a negative-Gs dive.

    But there is no way to know the airplane when such crucial information about it was not disclosed.
    Boeing NEVER disclosed the potential failure modes for trim runaway. This was no exception. The trim runway procedure was there and would have saved these flights.
    I perceive Boeing's disclosing or not of the MCAS is just a tiny detail. If the MCAS design, testing and certification had been sound, nobody would be talking about it let alone complaining about the non-disclosure. Conversely, I don't think that disclosing the MCAS would have prevented this accident. It was already disclosed when Ethiopian crashed.

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  • Evan
    replied
    Originally posted by 3WE View Post
    Evan is great at nit-picking, and arm-chair QBing. If airplane manufacturers did EVERYTHING he wanted (this goes way beyond 737-MCAXS)...we probably wouldn't have airplanes.
    Perhaps not. Oh, except for every aircraft that already has triple modular redundancy on angle-of-attack sensors, which would actually be fine by me.

    Why does Evan 'nitpick' on this issue? It could have something to do with the less-than-perfect reliability of Boeing's angle-of-attack sensors (there is a retrofit AD in the works for sensors with inadequate heaters), or the general vulnerability of angle-of-attack sensors to damage from such things as birds and jetbridges.

    I didn't (and still don't) 'nitpick' on the issue on aircraft that do not use this data to interfere with pilot commands, nor do I 'nitpick' where there are no air-data-dependent systems needed to certify the aircraft. For example, I do not 'nitpick' about the lack of a third angle-of-attack vane on the NG because fault arbitration is entirely done by the pilots via cross-checking the instruments. On aircraft where fault-arbitration is done by systems, I become more concerned, such as on the B777, which also lacks a third angle-of-attack sensor, but the B777 doesn't use that data to interfere with pilot commands (it creates warnings and force-feedback but does not actually make control-surface commands). But when angle-of-attack data is used to make automated control-surface commands, yeah, I have to notpick. So did the FAA back in the 80's when it first certified such systems.

    The alternative, as I've already pointed out, might be to use IR data as a virtual third data source and to compare and vote against the two physical sensors. It is not true triple modular redundancy, it is a triple virtual redundancy, but if it can be proven safe in certification (meaning a thorough process of testing in every conceivable scenario), then that could suffice. Physical AoA sensors, not being mounted on the actual wing, are already inherently imperfect. The local deviation in AoA, combined with other factors, can produce inaccuracies of 0.5deg or more. But with systems using a threshold safely below critical angle, this is tolerable. Perhaps a triple virtual redundancy can fall within that tolerance. Perhaps this IS what Boeing is doing with the revised MCAS logic. But now we are talking about even deeper systemic complexity. If a disagree exists between the gyros as well as the vanes (a conceivable 'swiss cheese' scenario), then what?

    What I don't want to see here is for Boeing to get away with 'solving' a complex problem by just adding more complexity to get around starting over and doing it right... followed by more 'unforeseen' disaster scenarios. The B737-Max should never have been built (or needed). And Evan really doesn't like to be a Monday-morning QB.

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  • ATLcrew
    replied
    Originally posted by 3WE View Post
    That being said, my opinion is that his hyperbole was very appropriate. Evan is great at nit-picking, and arm-chair QBing. If airplane manufacturers did EVERYTHING he wanted (this goes way beyond 737-MCAXS)...we probably wouldn't have airplanes. Bobby never said that a third vane would reduce the seating capacity to 5...But the pontification and spewing of free advice to a group of folks who do very amazing things (which require that tough decisions).
    Evan is what they call Contrary Jenkins. Whatever the industry is doing he wants the opposite. He's determined his narrative years (maybe decades?) ago, and it goes something like this: airlines bad, manufacturers really bad, pilots awful, government not so good except when it's great. Pretty much every one of his posts boils down to some combination of the above. He, of course, is entitled to push whatever narrative he wants, it's just not very interesting.

    Leave a comment:


  • ATLcrew
    replied
    Originally posted by Black Ram View Post
    The fact the crashes did not occur in the US, Canada or Europe means nothing on its own and it is a very biased way to look at this. What is the concentration of MAX airframes and hours flown at the time of the crashes?
    Southwest's Max fleet had over 90,000 hours at the time of the grounding. Just answering your question.

    Leave a comment:


  • 3WE
    replied
    Originally posted by Black Ram View Post
    Doesn't seem like that much.
    I am an outsider and not an engineer, but having stayed in Holiday Inn Express and spending 20 years on various ass-hat aviation fora:

    1. Yes it doesn't SEEM like that much.

    2. But (just venturing an outside guess), it's a LOT. There's this terrible thing called Murphy's law (and so many many stories of unintended consequences.)

    -A new hole in the plane, stress cracks.
    -New wires.
    -Modified systems to analyze the stuff
    -Computer systems that go berserk because pitot tubes ice over
    -More vanes = more malfunctions and wait until we crash a plane because the pilots are distracted by a bad AOA vane warning at the perfectly wrong time.

    I hate what I've heard about the MCAS system, but I am understanding why the fix is a pretty big deal.

    Important note: Boeing Bobby used a little bit of hyperbole when he said Evan wanted a plane that could carry 5 folks. That being said, my opinion is that his hyperbole was very appropriate. Evan is great at nit-picking, and arm-chair QBing. If airplane manufacturers did EVERYTHING he wanted (this goes way beyond 737-MCAXS)...we probably wouldn't have airplanes. Bobby never said that a third vane would reduce the seating capacity to 5...But the pontification and spewing of free advice to a group of folks who do very amazing things (which require that tough decisions).

    The number 1 tough decision is that going 50 MPH (or much faster) and 50 ft up in the air (or much higher) can be very deadly. The easy answer is "don't".

    Leave a comment:


  • Black Ram
    replied
    Originally posted by BoeingBobby View Post
    Read my original post. A: 2 switches. B: You did not see either of the two accidents happen in the US or Canadian, European country. C: Did Boeing f**k up? Yes, but you still have to know your aircraft and how to fly by hand. Evan wants every aircraft flying passengers to have so many redundant systems that they can only carry 5 pax with their bags.
    2 switches: We have talked about this. MCAS is not necessarily classic trim runaway, because: 1) happens by design, not because of trim malfunction; 2) happens incrementally; 3) is accompanied by false stall warnings and IAS disagree. Add to all this the fact the MCAS crashes happened very soon after take-off, and the possibility in the Ethiopian crash that unless they knew what exactly was going on very early on and acted accordingly, the manual trim would have been unusable unless they could apply the special yo-yo procedure because of their high speed. I also recall the switches were used by the Ethiopian crew, if memory serves my right, and it was not enough.

    Yes, you have to know your airplane. Yes, low-cost airlines in Asia are sometimes notorious for poor training and maintenance. But there is no way to know the airplane when such crucial information about it was not disclosed.

    The fact the crashes did not occur in the US, Canada or Europe means nothing on its own and it is a very biased way to look at this. What is the concentration of MAX airframes and hours flown at the time of the crashes? The only two 100% confirmed rudder hardover crashes on the 737 happened in the US - what does that mean (if anything)?

    I don't think Evan wants too much redundancy. I think he is asking for a 3rd AoA vane. Doesn't seem like that much.

    Leave a comment:


  • vaztr
    replied
    Not sure if I read about 'cracking' issues with the NG in this thread or not...

    QANTAS have grounded 3 737NGs after finding cracks in the 'pickle forks' on the planes after 22600 cycles - recommended inspection timing is 30000 cycles

    VAZ

    Leave a comment:


  • Evan
    replied
    Originally posted by Gabriel View Post
    D: For Evan's ideal solutio n, you need to add hardware and hence wight. But, as a side note, for the solution that Boeing is certifying now, no additional piece of hardware being added. Just software which doesn't weight at all.
    Hmmm. What does an AoA vane weigh? What does wire weigh? Do you really think this is a weight issue?

    Leave a comment:


  • 3WE
    replied
    Originally posted by Gabriel View Post
    Blah blah blah needed blah blah blah
    Needed in legal fine print font or NEEDED in bold font (or some gray area in between).

    Opinion noted, but, my interpretation is that we don't really know.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by 3WE View Post
    Are we convinced that DCAS is a much-needed, unrecoverable-stall prevention system? I read the comments and frankly, they side step the issue of if this is truly NEEDED. I don't want to dismiss those comments, BUT, I don't think they answer the issue of a potentially unrecoverable stall.

    I question if the trim is really fast enough to address this horrible pitch-up-at-the-worst-time behavior...if it is REALLY going to get you into an UNRECOVERABLE stall.

    I can see it HELPING, but not really MAKING THE DIFFERENCE.

    Also, I'm struggling with logic as to why this would really be needed? If the AOA gets to high, you get a stall warning...And (as always) you are supposed to remedy it BEFORE you stall.

    Why doesn't this "simply" tie in to the stall warning system.

    Why the friggen duct-tape-workaround to tie in on ONE AOA vane and then send a "trim down" signal...

    I tend to go back to it being "to make the plane FEEL LIKE the NG" instead of FEELING a little sluggish on nose down and requiring a little more shove, or holding the trim button a few extra seconds...

    We can't have it FEELING different.
    I am pretty sure that the plane would have been recoverable from a stall even without the MCAS. Remember stall procedures call for retarding thrust and using nose-down trim as needed.
    The question seems rather whether the plane would meet FAR requirements regarding controlability and control force feedback and out-of-trim condition. In other words, a) the plane may be recoverable and controllable but not within the parameters established by the FAA (that would have made the MCAS a NEED for certification) or, b) it may be controllable and within the parameters established by the FAA but behave differently than the NG to the point of requiring type-specific flight training (that would make the MCAS a need for keeping the same type rating than the NG). That is the real question for me.

    These are the FARs referenced by the investigators:

    https://www.law.cornell.edu/cfr/text/14/25.255
    https://www.law.cornell.edu/cfr/text/14/25.143

    Leave a comment:


  • 3WE
    replied
    Originally posted by Paraphrased Bobby
    Trim cutout switches
    Originally posted by Gabriel View Post
    A:
    B:
    C:
    D:
    Are we convinced that DCAS is a much-needed, unrecoverable-stall prevention system? I read the comments and frankly, they side step the issue of if this is truly NEEDED. I don't want to dismiss those comments, BUT, I don't think they answer the issue of a potentially unrecoverable stall.

    I question if the trim is really fast enough to address this horrible pitch-up-at-the-worst-time behavior...if it is REALLY going to get you into an UNRECOVERABLE stall.

    I can see it HELPING, but not really MAKING THE DIFFERENCE.

    Also, I'm struggling with logic as to why this would really be needed? If the AOA gets to high, you get a stall warning...And (as always) you are supposed to remedy it BEFORE you stall.

    Why doesn't this "simply" tie in to the stall warning system.

    Why the friggen duct-tape-workaround to tie in on ONE AOA vane and then send a "trim down" signal...

    I tend to go back to it being "to make the plane FEEL LIKE the NG" instead of FEELING a little sluggish on nose down and requiring a little more shove, or holding the trim button a few extra seconds...

    We can't have it FEELING different.

    Leave a comment:


  • 3WE
    replied
    Originally posted by BoeingBobby View Post
    If the passengers were not paying, would it have been okay?
    No, but maybe a little less insulting...sort of sucks to pay good money to get killed.

    Leave a comment:


  • Gabriel
    replied
    Originally posted by BoeingBobby View Post
    Read my original post. A: 2 switches. B: You did not see either of the two accidents happen in the US or Canadian, European country. C: Did Boeing f**k up? Yes, but you still have to know your aircraft and how to fly by hand. D: Evan wants every aircraft flying passengers to have so many redundant systems that they can only carry 5 pax with their bags.
    A: Agree.
    B: I tend to agree. However, I don't know of any MCAS runaway happening in one of those countries. This is in part good: These countries also tend to have much better maintenance, which was a critical factor in Lin Air (however it doesn't seem to have been an issue in Ethiopian where the AoA sensor was working ok until they rotated the plane for take-off and then it suddenly failed, presumably because of an impact). The only other case of MCAS runaway was the Lion Air flight previous to the accident flight where, with the help of a 3rd pilot that was jumpseatting, they eventually used the 2 switches that you mentioned in point A and started using the manual wheel for trim. And they still performed horribly (but survived). I would love to know of other instances of this case of MCAS incidents elsewhere.
    C: Agree and agree.
    D: For Evan's ideal solution, you need to add hardware and hence wight. But, as a side note, for the solution that Boeing is certifying now, no additional piece of hardware being added. Just software which doesn't weight at all.

    Leave a comment:


  • BoeingBobby
    replied
    Originally posted by Black Ram View Post
    The flaw in whose logic? I've been waiting to read real arguments from the likes of BoeingBobby, but instead I see mostly jabs and attacks at anyone who points out the seriousness of the MCAS mess and how it relates to the two MAX crashes. And in my book, this is flawed logic - saying ambiguous stuff about the author of a post instead of constructing an argument that debates what is being said in the post.
    Read my original post. A: 2 switches. B: You did not see either of the two accidents happen in the US or Canadian, European country. C: Did Boeing f**k up? Yes, but you still have to know your aircraft and how to fly by hand. Evan wants every aircraft flying passengers to have so many redundant systems that they can only carry 5 pax with their bags.

    Leave a comment:

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