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So I don't see how the Ethiopian air gets into a situation where they can't manually trim. The Ethiopian flight was flying dramatically faster than a typical

So I don't see how the Ethiopian air gets into a situation where they can't manually trim. The Ethiopian flight was flying dramatically faster than a typical flight at that altitude would. If they followed the IAS disagree checklist that would explain the increased air speed as the general idea is to give the airplane enough thrust avoid a stall until you figure out which side has the correct air speed. Higher airspeed = more difficult to manually trim. They should have been able to get back to a neutral stabilizer position, disabled electronic control, and manually trim from there. They were barely 1,000 ft above the ground (if that). You could easily lose 1,000 ft fiddling with the elevator to unload the stabilizer to manually trim it into a safe position. The Lion Air crew had far more altitude to work with (they were at 6,000-7,000 ft at their highest IIRC). FWIW I think whoever's downvoting some of these comments is really hindering the discourse here. I think what you've posted is factually wrong, but not worthy of a downvote because it mostly seems to be wrong due to missing pieces from the puzzle (and not out of malice).

treis 8y ago
>Higher airspeed = more difficult to manually trim. The point, which I think you missed, is that you don't need to manually trim. Look at the image I linked to. It's MCAS down 2.5 degrees. Pilots up 2.5 degrees. MCAS down 2.5 degrees. Pilots up 2.5 degrees. It's a repeated cycle of the pilots getting trim to where they want it and the MCAS kicking in to nose them down. I suppose if you wait until the MCAS has trimmed all the way you might find yourself in an unrecoverable situation. But I'm not sure how that would happen and doesn't reflect what we saw in the Indoneisa Air crash.
- inferiorhuman 8y ago
  The point, which I think you missed, is that you don't need to manually trim. Look at the image I linked to. It's MCAS down 2.5 degrees. Pilots up 2.5 degrees. MCAS down 2.5 degrees. Pilots up 2.5 degrees. It's a repeated cycle of the pilots getting trim to where they want it and the MCAS kicking in to nose them down Yeah that's what the Lion Air crew did, and it worked until it didn't (lost control in a turn?). But counter the trim with the push buttons and then hit the cutout is not in any Boeing QRH (yet?). As a non-pilot this seems like a reasonable option, but there may be something glaringly obvious as to why it's a bad idea. Even if this is the ultimate solution it's quite different to how you'd react in an NG and will come with extra training. Basically a bad situation all around. If I've parsed everything appropriately the Ethiopian crew did try to turn the stab trim motors back on presumably to regain control over the stabilizer and we saw how that worked out. There's just not a lot of room for diagnostic work at that altitude.
  - treis 8y ago
    >Yeah that's what the Lion Air crew did, and it worked until it didn't (lost control in a turn?) IIRC the pilot handed control over to the copilot so that he could investigate the issue. The copilot stopped counteracting the trim. Part of the reason that the MCAS got passed regulators is that it was not given enough authority to override the pilots. It can send you on a wild ride, but it can't crash the plane unless the pilot doesn't counter act the trim when the MCAS is paused.
    - inferiorhuman 8y ago
      IIRC the pilot handed control over to the copilot so that he could investigate the issue. The copilot stopped counteracting the trim. From what I saw on that graph someone was trimming up as the plane nosedived. Take a look starting at the 23:30:53 mark. Someone was hitting the trim up button and MCAS was continuing to input trim down until the crash. The big problem with the preliminary report is the X axis, IMO. It's different on the graphs between the two flights, and there's not enough precision... but to me it looks like either hardware failure or the FO was simply not inputting enough trim up. They fought that plane all the way into the ground. Part of the reason that the MCAS got passed regulators is that it was not given enough authority to override the pilots. From what I've read MCAS as described to the FAA (relatively low limit on the down trim) was different than MCAS as implemented (about 4x larger movements allowed). Additionally it's not clear if the repeated down trim was by design or by bug. I think that even MCAS in its current state is probably something most pilots could recover from as long as they know what to expect. The way MCAS works now (both in terms of the amount of authority as well as the misdirection from "unrelated" warnings) combined with zero documentation is a recipe for additional crashes.

treis 8y ago

>Higher airspeed = more difficult to manually trim. The point, which I think you missed, is that you don't need to manually trim. Look at the image I linked to. It's MCAS down 2.5 degrees. Pilots up 2.5 degrees. MCAS down 2.5 degrees. Pilots up 2.5 degrees. It's a repeated cycle of the pilots getting trim to where they want it and the MCAS kicking in to nose them down. I suppose if you wait until the MCAS has trimmed all the way you might find yourself in an unrecoverable situation. But I'm not sure how that would happen and doesn't reflect what we saw in the Indoneisa Air crash.

inferiorhuman 8y ago
The point, which I think you missed, is that you don't need to manually trim. Look at the image I linked to. It's MCAS down 2.5 degrees. Pilots up 2.5 degrees. MCAS down 2.5 degrees. Pilots up 2.5 degrees. It's a repeated cycle of the pilots getting trim to where they want it and the MCAS kicking in to nose them down Yeah that's what the Lion Air crew did, and it worked until it didn't (lost control in a turn?). But counter the trim with the push buttons and then hit the cutout is not in any Boeing QRH (yet?). As a non-pilot this seems like a reasonable option, but there may be something glaringly obvious as to why it's a bad idea. Even if this is the ultimate solution it's quite different to how you'd react in an NG and will come with extra training. Basically a bad situation all around. If I've parsed everything appropriately the Ethiopian crew did try to turn the stab trim motors back on presumably to regain control over the stabilizer and we saw how that worked out. There's just not a lot of room for diagnostic work at that altitude.
- treis 8y ago
  >Yeah that's what the Lion Air crew did, and it worked until it didn't (lost control in a turn?) IIRC the pilot handed control over to the copilot so that he could investigate the issue. The copilot stopped counteracting the trim. Part of the reason that the MCAS got passed regulators is that it was not given enough authority to override the pilots. It can send you on a wild ride, but it can't crash the plane unless the pilot doesn't counter act the trim when the MCAS is paused.
  - inferiorhuman 8y ago
    IIRC the pilot handed control over to the copilot so that he could investigate the issue. The copilot stopped counteracting the trim. From what I saw on that graph someone was trimming up as the plane nosedived. Take a look starting at the 23:30:53 mark. Someone was hitting the trim up button and MCAS was continuing to input trim down until the crash. The big problem with the preliminary report is the X axis, IMO. It's different on the graphs between the two flights, and there's not enough precision... but to me it looks like either hardware failure or the FO was simply not inputting enough trim up. They fought that plane all the way into the ground. Part of the reason that the MCAS got passed regulators is that it was not given enough authority to override the pilots. From what I've read MCAS as described to the FAA (relatively low limit on the down trim) was different than MCAS as implemented (about 4x larger movements allowed). Additionally it's not clear if the repeated down trim was by design or by bug. I think that even MCAS in its current state is probably something most pilots could recover from as long as they know what to expect. The way MCAS works now (both in terms of the amount of authority as well as the misdirection from "unrelated" warnings) combined with zero documentation is a recipe for additional crashes.