Originally Posted by
fotoguzzi
(Not a pilot) This random internet grab from 2009 (authenticity unknown to me) does say to use electric trim and does not say to apply it again if runaway continues.
As these are terse instructions, if one might soon be grabbing a rotating wheel, and not long after that, hand cranking it, [would he] not want to do the best possible work with the electric trim before cutout?
Hello Foto,
Thanks for posting the checklist page.
It is good to follow a non normal or emergency checklist to see what the writer had in mind, before taking to the air sometimes.
In this case the items in point 2. about operating main electric trim are provisional to the autopilot having been on before. Here the writer covers
the case where the autopilot could have been causing the runaway.
Having disengaged the AP there is now the choice of the runaway having stopped, which allows manual flight with normal trim inputs OR if it doesn't stop, no longer is electric trim desired - but stab trim cutout switches off.
Now in these accidents the AP was not engaged, so point 2. did not apply - and as the stab movement continues, pass point 3. and you are left with point 4. - no trim, cutoff switches off.
This is where the "recommended checklist" does not properly cover the case of rogue MCAS operation, despite claims to the contrary. A dedicated checklist is required. A checklist which, if studied on the ground would provide insight into dealing with this complex failure.
And to answer the point further up about, how do the pilots recognise rogue MCAS operation? - at the first accident, they couldn't, since nobody knew of the system - at the second accident after the publicity they may well have realised what was wrong but the runaway checklist is insufficient alone to deal with it (reasons above) and that checklist is what they had.