4 ms·

Official report is now out: http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C%28ET-AVJ%29.pdf http://www.ecaa.gov.et/documents/20435/0

Official report is now out: http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C%28ET-AVJ%29.pdf http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+... This scenario does indeed appear to be what happened. It just looks like when they re-enabled electric trim, they didn't trim up enough, and then left it turned on. 5 seconds later, MCAS kicked in again, and then it was all over.

treis 8y ago
It sounds like they did almost everything right. There are two fateful moments: >At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working At this point they were in stable flight and the trim wasn't that extreme. It's not clear whether "manually" here means manual electric trim or trying to physically turn the trim wheel. Up until this point they had correctly diagnosed the issue and taken the proper steps. >At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units. >At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording. They re-activated electric trim control but only slightly adjusted it. MCAS kicks in to send them nose down. There's no further pilot correction recorded. Unclear here if there is an airplane issue preventing them from adjusting trim or a pilot error.
- mhandley 8y ago
  When they did that final electric trim up, the right (more reliable) ASI indicates 365 knots. VMO is 340, so they were already in real trouble. It's not at all clear that even electric trim could overcome the air loads at that point to trim up, though it does look from the graph like it responded slightly.
  - treis 8y ago
    At 05:40:30 you can see that the trim did change in response to pilot inputs at roughly the same speed. It should have been able to respond when they re-enabled electric trim unless there was some other failure. It will be interesting to see the full report with more detail about what the pilots did and why.
treis 8y ago
The other noteworthy thing is that it does look like the angle of attack sensor failed catastrophically. It was reading 10ish degrees before immediately jumping to 75. Boeing really screwed the pooch here. A 75 degree AoA is obviously impossible and should be disregarded. Let alone a situation where it goes from 10 to 75 in seconds.

treis 8y ago

It sounds like they did almost everything right. There are two fateful moments: >At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working At this point they were in stable flight and the trim wasn't that extreme. It's not clear whether "manually" here means manual electric trim or trying to physically turn the trim wheel. Up until this point they had correctly diagnosed the issue and taken the proper steps. >At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units. >At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording. They re-activated electric trim control but only slightly adjusted it. MCAS kicks in to send them nose down. There's no further pilot correction recorded. Unclear here if there is an airplane issue preventing them from adjusting trim or a pilot error.

mhandley 8y ago
When they did that final electric trim up, the right (more reliable) ASI indicates 365 knots. VMO is 340, so they were already in real trouble. It's not at all clear that even electric trim could overcome the air loads at that point to trim up, though it does look from the graph like it responded slightly.
- treis 8y ago
  At 05:40:30 you can see that the trim did change in response to pilot inputs at roughly the same speed. It should have been able to respond when they re-enabled electric trim unless there was some other failure. It will be interesting to see the full report with more detail about what the pilots did and why.

treis 8y ago

The other noteworthy thing is that it does look like the angle of attack sensor failed catastrophically. It was reading 10ish degrees before immediately jumping to 75. Boeing really screwed the pooch here. A 75 degree AoA is obviously impossible and should be disregarded. Let alone a situation where it goes from 10 to 75 in seconds.