Originally Posted by
Dora-9
What are "manual electric trim inputs"? The implication, though I didn't find it, is that the trim cut-out switches were re-instated.
I believe that refers to the trim switches on the control column (that activate the electric trim servos)... as opposed to the trim wheel.
I think what you're looking for is in the summary in the top right:
On 10 March 2019, left air data system faults on a Boeing 737-MAX 8 soon after departing Addis Ababa were followed by autopilot disconnection, left stick shaker activation and two successive periods of automatic nose down stabiliser causing EGPWS ‘DON’T SINK’ alerts. Recovery was achieved using manual stabiliser trim but prior to a third automatic pitch down, the trim system was switched off as per the runaway stabiliser drill but briefly reinstated to help recover from it. Recovery from a fourth automatic pitch down was not achieved and a high speed dive led to terrain impact six minutes after takeoff.
The text itself doesn't say as much, but I agree that it seems to imply that at some point, the stab trim was turned back on in an effort to apply ANU trim... which unfortunately, let the MCAS kick in 5 seconds later and trim AND to 1.0
For approximately the next 2˝ minutes, the stabiliser position moved in the AND direction from 2.3 to 2.1 units whilst “aft force was being applied to both control columns which remained aft of (the) neutral position”. The crew confirmed to each other that after disconnecting the stabiliser trim, they could no longer control it (although there was no mention on the CVR of whether this was attempted using the control column switches or the pitch trim wheel). During this time, the right side (correct) indicated airspeed increased from approximately 305 KIAS through Vmo (340 KIAS) and the right side overspeed aural warning was activated and remained active thereafter. The left side displayed airspeed remained up to 25 knots less than that on the right side. During this time, the Captain asked the First Officer to request radar vectors to return to the airport and the flight was given a right turn onto 260°. Towards the end of this 2˝ minute period, both pilots were recorded as calling out “left alpha vane” and the Captain announced that “pitch is not enough” shortly before “two momentary manual electric trim inputs in the ANU direction were recorded”. These inputs resulted in pitch trim (stabiliser) position moving in the ANU direction from 2.1 units to 2.3 units.
Approximately five seconds after this final manual electric pitch trim input, a fourth period of AND automatic pitch trim command occurred and the pitch trim (stabiliser) position moved in the AND direction from 2.3 to 1.0 units over approximately 5 seconds. Despite the pilots’ added and simultaneous aft control column input throughout the remainder of the flight, the aircraft nose down pitch attitude continued to increase, eventually reaching 40° nose down with the recorded pitch trim (stabiliser) position varying between 1.1 and 0.8 units.