Originally Posted by
737 Driver
I will agree that any human pilot at some stage in his training will be easily overwhelmed by even the most basic aircraft emergency scenarios. That is why we train so extensively for them. I had previously posted that in the Ethiopian accident, the Captain did fly the aircraft after a certain fashion, and that he had defaulted to his training. The problem was that he defaulted to the wrong training. Just about all of the ET302 Captain's initial actions can be understood in the context of a normal takeoff profile. Unfortunately, a normal takeoff profile left him in a highly unstable position from which dealing with the ultimate stab trim problem became a bridge too far.
The ET pilot possibly followed the Boeing UAS flow chart I posted earlier that covered AoA failure as a 'false' positive ending with "pilot with correct display becomes pilot flying" which apparently did not happen.
He was able to engage autopilot for 30 seconds (again a questionable move). Until the AP disconnected as flaps were retracted the situation was not extreme, I will leave it to others how 'normal' the profile was.
At 05:40:00 the first MCAS input occurs followed by insufficient re-trim, surprise, lack of training experience with magnitude of MCAS input? This led to rapid speed increase
At 05:40:20 the second MCAS input occurs, interrupted by pilot trim at 04:40:27.
The crew carried out the runaway stab procedure at 05:40:35. From the trace it appears that the pilot may have been trimming at this point and was interrupted by the cutout switches.
Had they waited until AC was in trim we likely would not be discussing this..
Looking at the sequence above: At 05:40:00 the AC was not in extreme state By 05:40:35 they were left with likely inoperable manual trim and approaching, but not yet at VMO.
Things went from "interesting to extreme" in 35 seconds during which the crew followed the runaway trim procedure, albeit without first fully trimming the AC.
From other posts they may not have seen the update procedure with the 'note' about first trimming.
That is
35 seconds with only 2 MCAS inputs to get to an extreme state.
One thing that the prelim report does not cover is what
was going on during the two and a half minutes until the final sequence. Surely they were not just sitting there with a couple of ATC exchanges.
Here is one scenario:
Trim cutout, both switches as per procedure
Attempts to use manual trim are not successful due to loading (speed still < VMO)
Pilot remembers 737NG had 2 cutout modes, auto and all, depending on slide ware version he "trained" with the change in MAX may not have been mentioned, even if it was it was not stressed.
They try first one then the other switch, no electric trim.
Further attempts to use manual trim?
Next relevant snip from the report:
At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try.
At 05:41:54, the First-Officer replied that it is not working.
Final puzzle is why only brief trim inputs after they re-enabled trim.