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> 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. U

> 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 8y 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 8y 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 8y 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 8y 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.
    - Someone1234 8y ago
      > And that doesn't mean that MCAS was designed to mitigate the problems related to an AoA disagreement. You literally said it was designed to do just that: > The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. I still have no idea what you were trying to say there.
      - inferiorhuman 8y ago
        You literally said it was designed to do just that No, I didn't.
      - 8y ago
WillPostForFood 8y ago
Autopilot comes up several times in the report, but maybe I'm misunderstanding. Can you clarify? At 05:38:46 and about 200 ft radio altitude, the Master Caution parameter changed state. The First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded Left AOA Heat parameter changed state. At 05:38:58 and about 400 ft radio altitude, the flight director pitch mode changed to VNAV SPEED and Captain called out “Command” (standard call out for autopilot engagement) and an autopilot warning is recorded. At 05:39:00, Captain called out “Command”. At 05:39:01 and about 630 ft radio altitude, a second autopilot warning is recorded At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33 seconds later), the flaps were retracted and the pitch trim position decreased to 4.6 units. Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged. At 05:39:55, Autopilot disengaged, At 05:39:57, the Captain advised again the First-Officer to request to maintain runway heading and that they are having flight control problems. At 05:40:00 shortly after the autopilot disengaged, the FDR recorded an automatic aircraft nose down (AND) activated for 9.0 seconds and pitch trim moved from 4.60 to 2.1 units. The climb was arrested and the aircraft descended slightly.
- Someone1234 8y ago
  Before MCAS started malfunctioning. Autopilot was enabled for a short period after take-off, then disabled at 05:39:55 due to turbulence and never re-enabled. If you look at the graph in Appendix 1/page 26 -- FDR Data you'll see that the first MCAS command occurred at 05:39:30. Once autopilot was disabled it remained disabled until impact. The information you're quoting above is just included for informational reasons, it likely won't play a part in what caused this accident.
  - inferiorhuman 8y ago
    And if you look further through the transcripts you'll see that they kept playing with the flight director for reasons unknown.
chopin 8y ago
> MCAS used trim to counter-act an overeager upwards angle during key parts of the flight like take-off. Great post, but minor correction: At take-off flaps are set which disables MCAS.
salawat 8y ago
>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 Correct. - 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. Incorrect. Ish. MCAS has squat to do with thrust curves, it has to do wit control force curves. Namely bringing the amount of control column force at high AoA needed to achieve further increases in AoA in line with the expectations of a trained 737 pilot. The rest of that point is accurate though. >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. Incorrect-ish. Yes, take-off would be one of the more likely places to run into an MCAS activation, but generally speaking, even that rotation doesn't come anywhere near the AoA MCAS was meant to deal with, and to boot, flaps being engaged disables the MCAS system. >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. Trim switch is higher priority, but not more powerful per se. the trim switch was clearly overwhelmed in terms of MCAS's ability to command trim changes in 2.5 degree increments five seconds after the release of the yoke trim switch as long as it detected the high AoA. Not sure whether those trim switches are continuous direct drive (I.e. jackscrew turned as long as the switch is held down) or discrete (updates the jackscrew motors to move to next position over time, only to be overridden by MCAS five seconds later). Other than that, that looks like a fairly good summary.

inferiorhuman 8y 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 8y 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 8y 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 8y 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.
  - Someone1234 8y ago
    > And that doesn't mean that MCAS was designed to mitigate the problems related to an AoA disagreement. You literally said it was designed to do just that: > The autopilot systems cannot cope with AoA disagree, that's why MCAS came into play. I still have no idea what you were trying to say there.
    - inferiorhuman 8y ago
      You literally said it was designed to do just that No, I didn't.
    - 8y ago

WillPostForFood 8y ago

Autopilot comes up several times in the report, but maybe I'm misunderstanding. Can you clarify? At 05:38:46 and about 200 ft radio altitude, the Master Caution parameter changed state. The First Officer called out Master Caution Anti-Ice on CVR. Four seconds later, the recorded Left AOA Heat parameter changed state. At 05:38:58 and about 400 ft radio altitude, the flight director pitch mode changed to VNAV SPEED and Captain called out “Command” (standard call out for autopilot engagement) and an autopilot warning is recorded. At 05:39:00, Captain called out “Command”. At 05:39:01 and about 630 ft radio altitude, a second autopilot warning is recorded At 05:39:22 and about 1,000 feet the left autopilot (AP) was engaged (it disengaged about 33 seconds later), the flaps were retracted and the pitch trim position decreased to 4.6 units. Six seconds after the autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes. These oscillations continued also after the autopilot was disengaged. At 05:39:55, Autopilot disengaged, At 05:39:57, the Captain advised again the First-Officer to request to maintain runway heading and that they are having flight control problems. At 05:40:00 shortly after the autopilot disengaged, the FDR recorded an automatic aircraft nose down (AND) activated for 9.0 seconds and pitch trim moved from 4.60 to 2.1 units. The climb was arrested and the aircraft descended slightly.

Someone1234 8y ago
Before MCAS started malfunctioning. Autopilot was enabled for a short period after take-off, then disabled at 05:39:55 due to turbulence and never re-enabled. If you look at the graph in Appendix 1/page 26 -- FDR Data you'll see that the first MCAS command occurred at 05:39:30. Once autopilot was disabled it remained disabled until impact. The information you're quoting above is just included for informational reasons, it likely won't play a part in what caused this accident.
- inferiorhuman 8y ago
  And if you look further through the transcripts you'll see that they kept playing with the flight director for reasons unknown.

chopin 8y ago

> MCAS used trim to counter-act an overeager upwards angle during key parts of the flight like take-off. Great post, but minor correction: At take-off flaps are set which disables MCAS.

salawat 8y ago

>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 Correct. - 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. Incorrect. Ish. MCAS has squat to do with thrust curves, it has to do wit control force curves. Namely bringing the amount of control column force at high AoA needed to achieve further increases in AoA in line with the expectations of a trained 737 pilot. The rest of that point is accurate though. >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. Incorrect-ish. Yes, take-off would be one of the more likely places to run into an MCAS activation, but generally speaking, even that rotation doesn't come anywhere near the AoA MCAS was meant to deal with, and to boot, flaps being engaged disables the MCAS system. >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. Trim switch is higher priority, but not more powerful per se. the trim switch was clearly overwhelmed in terms of MCAS's ability to command trim changes in 2.5 degree increments five seconds after the release of the yoke trim switch as long as it detected the high AoA. Not sure whether those trim switches are continuous direct drive (I.e. jackscrew turned as long as the switch is held down) or discrete (updates the jackscrew motors to move to next position over time, only to be overridden by MCAS five seconds later). Other than that, that looks like a fairly good summary.