Originally Posted by
derjodel
An undocumented system of which the pilots have no clue it even exists can interrupt airplane trim. If the pilot doesn't want to end in a coffin corner, they need to figure out on the spot that:
- this is not STS
- because it's not STS it must be either a bug or an undocumented system
- to save their lives they need to return the trim manually to a low/zero column force each time the undocumented command is triggered.
Despite facing those conditions, the Lion Air crew managed to react appropriately about 2 dozen cycles. Fighting the unknown system raised pilot's adrenaline and fear and induced panic. Thus, incapacitated by stress put on them, they no longer managed to manually correct the erroneous system input that was trying to - and succeeded to - kill them.
I want to be clear I was simply answering a previous poster's question about how MCAS worked, and not attempting to defend the system design.
Regarding your last paragraph, one theory is that for some reason the pilot who had been successfully countering MCAS for 24 cycles transferred control to the other pilot, who did not put in sufficiently large opposite trim inputs and lost it in three cycles.