7 ms·

So MCAS put them in a hard to recover position which required electric trim to recover, and as soon as they turned on the electric trim MCAS turned on again and

So MCAS put them in a hard to recover position which required electric trim to recover, and as soon as they turned on the electric trim MCAS turned on again and forced them into a crash? Then this is much worse than initially suggested, it means a pilot can be aware of MCAS and still be put in a extremely dangerous position due to the extreme control authority of the module.

dsfyu404ed 8y ago
Per the article a combination of things put them in that situation. Not just MCAS. Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else? Complex systems that have millions of man hours spent making them safer don't usually have back to back failures because of one faulty subsystem. We've incrementally refined commercial air travel to the point where single source accidents are basically nonexistent. I'm not saying that MCAS isn't mostly to blame but the fact that the maximum inputs from the pilot is still lesser than the control authority from the trim raises some serious questions MCAS or not. Had "extend flaps" been at the bottom of the checklist that would have disabled MCAS and likely prevented this crash.
- quenstionsasked 8y ago
  MCAS issues nose-down, speed increases and nose pitches down. Nose never pitches back up. Plane crashes. Sure, maybe some complex combination of maneuvers could have helped them out of this but there's really everything pointing the blame at this one system. Pilots did what the boeing manual suggested (even included at the end of this report).
  - deleted 8y ago
    [deleted]
- fgonzag 8y ago
  It's true there were aggravating factors, like the inability to manually rectify trim, which (would seem to me) would be a aerodynamic or design issue. The point still stands, the root cause was MCAS, without it this would never have happened. MCAS would not have pitched them into a dive, and even if they were pitched into a dive by some non MCAS system, they would have been able to turn on electric trim and recover. MCAS both caused the situation, and made fixing it impossible, so it was the root cause of the crash.
  - Rooster61 8y ago
    > The point still stands, the root cause was MCAS Agreed. One could argue that the AoA reading mismatch was the root cause, but the plane alerted the pilots to the discrepancy just as it was meant to (through stick shake and panel readouts). They were aware of the issue, took measures to mitigate them, and MCAS still drove the plane into the ground.
  - dsfyu404ed 8y ago
    Likewise had Boeing designed a control surfaces system such that the pilot always has more control authority than the trim this also would not have happened. I didn't say that MCAS wasn't the lions share root cause here. It's just not as simple as the "hurr durr, MCAS bad" that a lot of people keep trying to portray the more nuanced statements of various regulatory agencies as being equivalent to. MCAS might be bad but on an aircraft with a different trim system it wouldn't be "hurr durr" levels of bad.
    - deleted 8y ago
      [deleted]
    - rootusrootus 8y ago
      Are there any airliners from any manufacturer where the pilot always has enough authority to override full trim?
      - VBprogrammer 8y ago
        I doubt this is possible. If it was it would be a certification requirement because it would make any trim runaway incident trivial.
      - upofadown 8y ago
        Airbus just gives you a joystick with no force feedback at all. So yes ... but an entirely different philosophy. You tell the aircraft what you want it to do and it figures out how to do it. I suppose these recent events could be used as an argument against the idea of doing essentially fly by wire but then putting in a whole lot of extra stuff to make it seem that you are not doing fly by wire.
- crooked-v 8y ago
  MCAS forced the trim to a point where (because of aerodynamics) it was impossible to manually change the trim even after disabling MCAS, and was designed in such a way that it was impossible to engage the electrical trim controls (which could have saved the plane in this case) without also reenabling MCAS.
  - dsfyu404ed 8y ago
    Flaps out supposedly would have kept MCAS off but the pilots weren't expected to know that.
    - ams6110 8y ago
      Post Lion Air, they should have known that.
      - simion314 8y ago
        Why exactly? if Boeing did not updated the manuals and checklists how would pilots know that? from internet forums? Should a pilots ignore the checklists and try steps he read on the internet ? I could not find if Boeing updated their manuals/checklists after the first crash.
        cjbprime 8y ago
        Yes, Boeing issued this service bulletin after Lion Air: http://www.avioesemusicas.com/wp-content/uploads/2018/10/TBC-19-Uncommanded-Nose-Down-Stab-Trim-Due-to-AOA.pdf http://www.avioesemusicas.com/wp-content/uploads/2018/10/TBC... And the FAA made it an emergency airworthiness directive in response. The steps on it were broadly followed by the Ethiopian flight.
        cladari 8y ago
        Am I missing it because I don't see flaps mentioned anywhere in that link.
- dao- 8y ago
  > Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else? Because the other factors don't single this flight out, and the plane wouldn't have crashed without MCAS misbehaving, or more fundamentally, without the flawed plane design that required such a system in the first place.
- rob74 8y ago
  Sadly, it looks like those millions of man hours of incremental safety refinement also created a false sense of security. That (and management overriding engineering concerns) are the only explanations I have for how MCAS was implemented: because it had to be able to correct the pitch-up tendency of the 737 MAX and stay "invisible", so additional training could be avoided, Boeing apparently chose to use only one AOA sensor as "single source of truth" - because using both would have increased the chance of the system having to deactivate itself, which would probably have made the FAA mandate the additional training that Boeing wanted to avoid. This is just my personal theory however...

dsfyu404ed 8y ago

Per the article a combination of things put them in that situation. Not just MCAS. Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else? Complex systems that have millions of man hours spent making them safer don't usually have back to back failures because of one faulty subsystem. We've incrementally refined commercial air travel to the point where single source accidents are basically nonexistent. I'm not saying that MCAS isn't mostly to blame but the fact that the maximum inputs from the pilot is still lesser than the control authority from the trim raises some serious questions MCAS or not. Had "extend flaps" been at the bottom of the checklist that would have disabled MCAS and likely prevented this crash.

quenstionsasked 8y ago
MCAS issues nose-down, speed increases and nose pitches down. Nose never pitches back up. Plane crashes. Sure, maybe some complex combination of maneuvers could have helped them out of this but there's really everything pointing the blame at this one system. Pilots did what the boeing manual suggested (even included at the end of this report).
- deleted 8y ago
  [deleted]
fgonzag 8y ago
It's true there were aggravating factors, like the inability to manually rectify trim, which (would seem to me) would be a aerodynamic or design issue. The point still stands, the root cause was MCAS, without it this would never have happened. MCAS would not have pitched them into a dive, and even if they were pitched into a dive by some non MCAS system, they would have been able to turn on electric trim and recover. MCAS both caused the situation, and made fixing it impossible, so it was the root cause of the crash.
- Rooster61 8y ago
  > The point still stands, the root cause was MCAS Agreed. One could argue that the AoA reading mismatch was the root cause, but the plane alerted the pilots to the discrepancy just as it was meant to (through stick shake and panel readouts). They were aware of the issue, took measures to mitigate them, and MCAS still drove the plane into the ground.
- dsfyu404ed 8y ago
  Likewise had Boeing designed a control surfaces system such that the pilot always has more control authority than the trim this also would not have happened. I didn't say that MCAS wasn't the lions share root cause here. It's just not as simple as the "hurr durr, MCAS bad" that a lot of people keep trying to portray the more nuanced statements of various regulatory agencies as being equivalent to. MCAS might be bad but on an aircraft with a different trim system it wouldn't be "hurr durr" levels of bad.
  - deleted 8y ago
    [deleted]
  - rootusrootus 8y ago
    Are there any airliners from any manufacturer where the pilot always has enough authority to override full trim?
    - VBprogrammer 8y ago
      I doubt this is possible. If it was it would be a certification requirement because it would make any trim runaway incident trivial.
    - upofadown 8y ago
      Airbus just gives you a joystick with no force feedback at all. So yes ... but an entirely different philosophy. You tell the aircraft what you want it to do and it figures out how to do it. I suppose these recent events could be used as an argument against the idea of doing essentially fly by wire but then putting in a whole lot of extra stuff to make it seem that you are not doing fly by wire.
crooked-v 8y ago
MCAS forced the trim to a point where (because of aerodynamics) it was impossible to manually change the trim even after disabling MCAS, and was designed in such a way that it was impossible to engage the electrical trim controls (which could have saved the plane in this case) without also reenabling MCAS.
- dsfyu404ed 8y ago
  Flaps out supposedly would have kept MCAS off but the pilots weren't expected to know that.
  - ams6110 8y ago
    Post Lion Air, they should have known that.
    - simion314 8y ago
      Why exactly? if Boeing did not updated the manuals and checklists how would pilots know that? from internet forums? Should a pilots ignore the checklists and try steps he read on the internet ? I could not find if Boeing updated their manuals/checklists after the first crash.
      - cjbprime 8y ago
        Yes, Boeing issued this service bulletin after Lion Air: http://www.avioesemusicas.com/wp-content/uploads/2018/10/TBC-19-Uncommanded-Nose-Down-Stab-Trim-Due-to-AOA.pdf http://www.avioesemusicas.com/wp-content/uploads/2018/10/TBC... And the FAA made it an emergency airworthiness directive in response. The steps on it were broadly followed by the Ethiopian flight.
        cladari 8y ago
        Am I missing it because I don't see flaps mentioned anywhere in that link.
dao- 8y ago
> Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else? Because the other factors don't single this flight out, and the plane wouldn't have crashed without MCAS misbehaving, or more fundamentally, without the flawed plane design that required such a system in the first place.
rob74 8y ago
Sadly, it looks like those millions of man hours of incremental safety refinement also created a false sense of security. That (and management overriding engineering concerns) are the only explanations I have for how MCAS was implemented: because it had to be able to correct the pitch-up tendency of the 737 MAX and stay "invisible", so additional training could be avoided, Boeing apparently chose to use only one AOA sensor as "single source of truth" - because using both would have increased the chance of the system having to deactivate itself, which would probably have made the FAA mandate the additional training that Boeing wanted to avoid. This is just my personal theory however...