PPRuNe Forums - View Single Post - MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Old 24th Sep 2019, 15:28
  #2589 (permalink)  
Join Date: Jan 2008
Location: uk
Posts: 806
Originally Posted by Tomaski View Post
The underlying presumption in this particular case is that the pilots could have used the fully functioning Main Electric Trim to return the aircraft to somewhere close to an in-trim state before turning off the electrics. Yes, we know that didn't happen, and the reason why that didn't happen is an important discussion. However, we need to first recognize that the capability was actually there.
That presumption is an assumption that might not turn out to be valid. Absent reports of actual flight tests with MCAS (as it was) triggering, and knowing the the sims are now being found to be inaccurate in this area (e.g. trim wheel forces) there are only three crews who have tested this assumption, two of them crashed.

First LionAir flight seems to have managed, but not sure we know who was flying. Second LionAir flight the Captain appeared to be losing but only gradually, but it appears (although I'm not sure it's been confirmed) that he handed over to the FO who didn't seem to have the capability.

ET flight, in contrast, the Capt appeared to be losing but after one MCAS asks the FO to "trim up with him" which seems to result in much longer period of Main Electric Trim followed by call to cut-out (why? maybe MET stopped working? - they certainly weren't back in trim).

What does this mean? - I don't know. Any 737 driver ever asked colleague to help with the trim switches, ever? (and if so, why). After Lion I would have absolutely agreed with you, from an engineering point of view the capability is there. But after ET report, I don't know any more. That call for assistance in trimming up needs investigating.
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