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Nope, they left out the angle of attack indicator which their pilots are not trained to use. They had no clue that they were leaving the disagree indicator with

Nope, they left out the angle of attack indicator which their pilots are not trained to use. They had no clue that they were leaving the disagree indicator with it and that this indicator was crucial for an MCAS that they didn’t know existed, and why doesn’t the MCAS handle the disagree correctly while the autopilot can?

inferiorhuman 7y ago
why doesn’t the MCAS handle the disagree correctly while the autopilot can? The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. The Ethiopian pilots (for some reason) kept trying to engage autopilot. Unfortunately for them MCAS is only needed when autopilot is disabled.
- cmurf 7y ago
  It is correct to say the autopilot disconnects, and will not reconnect, when there's AoA disagreement. This is mentioned in the emergency Airworthiness Directive as one of the indicators for MCAS upset. It's not unusual to engage autopilot during climbout, I only see one explicit instance in the preliminary report for autopilot engagement, and two warnings, and two disconnects.
- nraynaud 7y ago
  That’s ignoring cat III landings. When landing in dual autopilot there is no disengage possible.
- FabHK 7y ago
  AFAIK, the autopilot disengages when there's an AoA disagree (=handling it correctly), while MCAS doesn't disengage, instead diving the plane into the ground (=not handling it correctly).
- Someone1234 7y ago
  > The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. The Ethiopian pilots (for some reason) kept trying to engage autopilot. Unfortunately for them MCAS is only needed when autopilot is disabled. Factual errors in this post include: - MCAS wasn't designed because "autopilot systems cannot cope with AoA disagree." MCAS couldn't handle AoA disagree, that's the whole crux of the problem. - MCAS wasn't enabled at all when autopilot was. Only manual flying. - MCAS was designed to simulate the non-Max 737's thrust curve to maintain a similar type rating FOR PILOTS. It had nothing to do with autopilot at all. - The Ethiopian Airline pilots never tried to enable autopilot, and didn't "keep trying to engage autopilot" that's pure fiction. MCAS used trim to counter-act an overeager upwards angle during key parts of the flight like take-off. It used electronic trim to accomplish this and a single AoA sensor to determine when. The Ethiopian Airline pilots, per the initial crash report, correctly disabled the electronic trim system (both disabling the yoke trim switch and MCAS). However were unable to manually re-trim the aircraft using the trim wheels due to the aerodynamic forces placed on the aircraft (via hard trim counteracted by hard elevator). This forced the Ethiopian Airline pilots into a difficult choice; and they ultimately decided to re-enable electronic trim and use the yoke trim switch (which is more powerful) to fix the trim. Unfortunately MCAS trimmed the aircraft further, they lost control, and the aircraft crashed. At no point did autopilot play any role in the crash.
  - inferiorhuman 7y ago
    MCAS wasn't designed because "autopilot systems cannot cope with AoA disagree." Reread what I wrote. MCAS wasn't enabled at all when autopilot was. Only manual flying. Quite literally what I wrote. The Ethiopian Airline pilots never tried to enable autopilot, and didn't "keep trying to engage autopilot" that's pure fiction. I'm not sure what you're going on about. You can see plain as day that the captain engaged the autopilot — there are five AP warnings on the graphs in the preliminary report. You can also see the position of the AP master switch (which, yes, they engaged autopilot with the stick shaker going off). You can even read through the transcripts where they're fiddling with the autopilot throughout the whole flight.
    - Someone1234 7y ago
      Your own post contradicts itself on that point: > The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. And: > Unfortunately for them MCAS is only needed when autopilot is disabled. Pick one. Either MCAS "came into play" to "cope with AoA disagree" because "the autopilot systems cannot" or "MCAS is only needed when autopilot is disabled."
      - inferiorhuman 7y ago
        Pick one. Either MCAS "came into play" to "cope with AoA disagree" because "the autopilot systems cannot" or "MCAS is only needed when autopilot is disabled." The statements aren't mutually exclusive. Not even a little bit. Autopilot eventually disengaged because there was an AoA disagree. MCAS was active because the autopilot was disabled. That's how MCAS works. That's the only situation in which MCAS could be engaged. And that doesn't mean that MCAS was designed to mitigate the problems related to an AoA disagreement.
        cjbprime 7y ago
        FWIW, I recall reading that Airbus uses three AoA sensors because autopilot becomes disabled when AoA is inoperable, and Boeing gets away with two because it does not disable autopilot on AoA disagree.

inferiorhuman 7y ago

why doesn’t the MCAS handle the disagree correctly while the autopilot can? The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. The Ethiopian pilots (for some reason) kept trying to engage autopilot. Unfortunately for them MCAS is only needed when autopilot is disabled.

cmurf 7y ago
It is correct to say the autopilot disconnects, and will not reconnect, when there's AoA disagreement. This is mentioned in the emergency Airworthiness Directive as one of the indicators for MCAS upset. It's not unusual to engage autopilot during climbout, I only see one explicit instance in the preliminary report for autopilot engagement, and two warnings, and two disconnects.
nraynaud 7y ago
That’s ignoring cat III landings. When landing in dual autopilot there is no disengage possible.
FabHK 7y ago
AFAIK, the autopilot disengages when there's an AoA disagree (=handling it correctly), while MCAS doesn't disengage, instead diving the plane into the ground (=not handling it correctly).
Someone1234 7y ago
> The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. The Ethiopian pilots (for some reason) kept trying to engage autopilot. Unfortunately for them MCAS is only needed when autopilot is disabled. Factual errors in this post include: - MCAS wasn't designed because "autopilot systems cannot cope with AoA disagree." MCAS couldn't handle AoA disagree, that's the whole crux of the problem. - MCAS wasn't enabled at all when autopilot was. Only manual flying. - MCAS was designed to simulate the non-Max 737's thrust curve to maintain a similar type rating FOR PILOTS. It had nothing to do with autopilot at all. - The Ethiopian Airline pilots never tried to enable autopilot, and didn't "keep trying to engage autopilot" that's pure fiction. MCAS used trim to counter-act an overeager upwards angle during key parts of the flight like take-off. It used electronic trim to accomplish this and a single AoA sensor to determine when. The Ethiopian Airline pilots, per the initial crash report, correctly disabled the electronic trim system (both disabling the yoke trim switch and MCAS). However were unable to manually re-trim the aircraft using the trim wheels due to the aerodynamic forces placed on the aircraft (via hard trim counteracted by hard elevator). This forced the Ethiopian Airline pilots into a difficult choice; and they ultimately decided to re-enable electronic trim and use the yoke trim switch (which is more powerful) to fix the trim. Unfortunately MCAS trimmed the aircraft further, they lost control, and the aircraft crashed. At no point did autopilot play any role in the crash.
- inferiorhuman 7y ago
  MCAS wasn't designed because "autopilot systems cannot cope with AoA disagree." Reread what I wrote. MCAS wasn't enabled at all when autopilot was. Only manual flying. Quite literally what I wrote. The Ethiopian Airline pilots never tried to enable autopilot, and didn't "keep trying to engage autopilot" that's pure fiction. I'm not sure what you're going on about. You can see plain as day that the captain engaged the autopilot — there are five AP warnings on the graphs in the preliminary report. You can also see the position of the AP master switch (which, yes, they engaged autopilot with the stick shaker going off). You can even read through the transcripts where they're fiddling with the autopilot throughout the whole flight.
  - Someone1234 7y ago
    Your own post contradicts itself on that point: > The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. And: > Unfortunately for them MCAS is only needed when autopilot is disabled. Pick one. Either MCAS "came into play" to "cope with AoA disagree" because "the autopilot systems cannot" or "MCAS is only needed when autopilot is disabled."
    - inferiorhuman 7y ago
      Pick one. Either MCAS "came into play" to "cope with AoA disagree" because "the autopilot systems cannot" or "MCAS is only needed when autopilot is disabled." The statements aren't mutually exclusive. Not even a little bit. Autopilot eventually disengaged because there was an AoA disagree. MCAS was active because the autopilot was disabled. That's how MCAS works. That's the only situation in which MCAS could be engaged. And that doesn't mean that MCAS was designed to mitigate the problems related to an AoA disagreement.
      - cjbprime 7y ago
        FWIW, I recall reading that Airbus uses three AoA sensors because autopilot becomes disabled when AoA is inoperable, and Boeing gets away with two because it does not disable autopilot on AoA disagree.