3 ms·
> They should have been able to get back to a neutral stabilizer position, disabled electronic control, and manually trim from there. Yes. But that's not what
by phire 8y ago
> They should have been able to get back to a neutral stabilizer position, disabled electronic control, and manually trim from there.
Yes. But that's not what the checklist in Boeing's MCAS bulletin said.
It said, disable the electric trim motor then trim manually.
In hindsight, prehaps it should have said "return stabilizer to neutral then disable electric trim motor".
I wonder if Boeing did that deliberately, because a bulletin with a modified checklist would have undercut Boeing's implied narrative that a procedure already existed and it was the Lion Air pilots fault for not using the existing runaway stab trim checklist. Or did Boeing simply not test the procedure in a simulator?
- treis 8y agoI'm definitely interested in seeing the details. IIRC, the jack screw was found fully extended. I wonder if that's recoverable with only 1,000ft of height even using electric trim.
- phire 8y agoYou might be onto something. I went and took a look at the the Lion air data: https://spectrum.ieee.org/image/MzE4Mjg2OQ.jpeg https://spectrum.ieee.org/image/MzE4Mjg2OQ.jpeg They were successfully doing trim up commands for at least 21 cycles to counter the MCAS trim down commands. Then after the last few activations, they try pressing trim up again, but the button presses are shorter and the stabiliser barely moves up. Did MCAS push the stabiliser down past a point the aerodynamic forces were so strong that even the electric trim motor was having problems trimming up? That could explain why the last 4 trim up commands were so short, if the pilots heard a large electric motor stuck noise they might have stopped holding the button.