I know they turned off the trim. They turned it off when the airplane was too far nose down.
They had successfully brought it back to normal trim with the electric trim switches, which had overridden MCAS. Then, the trim gets turned off.
The 3rd crew that survived had no idea MCAS existed. All they knew was misbehaving trim => turn it off. They also had repeatedly used the electric trim switches to return trim to normal. Then they turned it off.
This procedure was documented in an Emergency Airworthiness Directive sent to all MAX pilots, including the EA crew.
The only skill required was to use the electric trim switches to restore normal trim, which all three crews did, and then turn it off.
The point is, it is not necessary to know why the trim is misbehaving, it was only necessary to know how to turn it off. Emergency procedures are like this - they're not debugging procedures, they're about regaining control. Save the debugging for the mechanics on the ground.
P.S. the LA crew restored normal trim 25 times, and never did turn it off.
They had successfully brought it back to normal trim with the electric trim switches, which had overridden MCAS. Then, the trim gets turned off.
The 3rd crew that survived had no idea MCAS existed. All they knew was misbehaving trim => turn it off. They also had repeatedly used the electric trim switches to return trim to normal. Then they turned it off.
This procedure was documented in an Emergency Airworthiness Directive sent to all MAX pilots, including the EA crew.
The only skill required was to use the electric trim switches to restore normal trim, which all three crews did, and then turn it off.
The point is, it is not necessary to know why the trim is misbehaving, it was only necessary to know how to turn it off. Emergency procedures are like this - they're not debugging procedures, they're about regaining control. Save the debugging for the mechanics on the ground.
P.S. the LA crew restored normal trim 25 times, and never did turn it off.