3 ms·

somehow the pilots were able to bring the nose back up... it was only (apparently) after multiple nose downs that they eventually failed to recover the plane. W

by gmoot 8y ago

somehow the pilots were able to bring the nose back up... it was only (apparently) after multiple nose downs that they eventually failed to recover the plane. What was going on there? The MCAS activated several times, each time ratcheting the stabilizer down by 2.5 degrees. Every time the pilots tried to correct for it, it would engage again. That is what caused the characteristic up/down flight pattern. There are a lot of details in this story: https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/ https://www.seattletimes.com/business/boeing-aerospace/faile...

js2 8y ago
I've read that but it still leaves me confused. Say trim is at 0°. MCAS sets it to nose down pitch of 2.5°. Pilot pulls back yoke. Why doesn't pilot then also look over at the stab indicator, see that it's at 2.5° nose down and reset it with the electric trim switch back to 0°? If the pilot had done that, when MCAS runs again, doesn't it set the stab back to 2.5° nose down? So the pilot and MCAS should be fighting over 2.5° of trim. What it seems like happened is MCAS ran the stabilizer to 2.5°, but the pilot didn't reset it back to 0, but just back enough he could counter with the elevator. So MCAS keeps cranking the stab each time a bit further nose down and the pilot keeps only partially countering MCAS, instead of running the stab fully back to 0. The pilot was clearly aware stab trim had something to do with the situation because there were stab adjustments from the pilot. What I can't make sense of is the pilot only partially countering MCAS. I realize the Lion pilots didn't know about MCAS and so their mental model must have been flawed. I'm even more confused about the Ethiopian Air pilots who should have known about MCAS. edit: also this - https://news.ycombinator.com/item?id=19442160 https://news.ycombinator.com/item?id=19442160

by gmoot 8y ago

js2 8y ago

I've read that but it still leaves me confused. Say trim is at 0°. MCAS sets it to nose down pitch of 2.5°. Pilot pulls back yoke. Why doesn't pilot then also look over at the stab indicator, see that it's at 2.5° nose down and reset it with the electric trim switch back to 0°? If the pilot had done that, when MCAS runs again, doesn't it set the stab back to 2.5° nose down? So the pilot and MCAS should be fighting over 2.5° of trim. What it seems like happened is MCAS ran the stabilizer to 2.5°, but the pilot didn't reset it back to 0, but just back enough he could counter with the elevator. So MCAS keeps cranking the stab each time a bit further nose down and the pilot keeps only partially countering MCAS, instead of running the stab fully back to 0. The pilot was clearly aware stab trim had something to do with the situation because there were stab adjustments from the pilot. What I can't make sense of is the pilot only partially countering MCAS. I realize the Lion pilots didn't know about MCAS and so their mental model must have been flawed. I'm even more confused about the Ethiopian Air pilots who should have known about MCAS. edit: also this - https://news.ycombinator.com/item?id=19442160 https://news.ycombinator.com/item?id=19442160