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.
A stab trim runaway affecting the fly ability of the aircraft is no time to “figure out “ anything. The figuring out happens back on terra firma. Whether the source of the runaway is a short circuit in a switch or motor, MCAS or anything other source, when the aircraft experiences uncommanded flight control movements in pitch it’s a stab trim runaway for which there is a clear and simple memory drill. The instinctive thing would to pull or push to restore the desired path then trim for it with the electric trim switches, even if it means long burst of trim. Whatever it takes. If the trim continues to be uncontrollable, turn it off and manually trim with the wheel, however one has to be flying at something less than Vmo to do that which means controlling the thrust or, in other words, flying the airplane.