Originally Posted by
FWRWATPLX2
The Boeing Quick Reference Handbook (QRH), Chapter 9, page 9.1 "Runaway Stabilizer". That is/was all the Pilots needed to know to deal with the Abnormal situation. Disconnect the Autopilot. It may require both Pilots to hold the Control Column/Yoke. The Stab Trim Cutout Switches should both be immediately moved to CUTOUT (Off) and leave them in CUTOUT, but the Pilot(s) in the accident aircraft switched them back to NORMAL (On).
With the STAB TRIM to CUTOFF, don't experiment by turning it back to NORMAL.
And therein lies the whole problem. If you had read the complete accident report, it was found that the procedure using the cutoff switches was found to be ineffective because of the aerodynamic loads put on the stab in the out of trim condition, which meant that a manual re-trimming of the aircraft was physically impossible. The only way to re-trim was to to relax the pressure on the controls and then madly try manually re-trimming. This would be a daunting proposition with the nose pointing at the ground.
In the original design of this system, before MCAS, this may have been feasible with early intervention, but with the additional and repeated input of MCAS it would quickly become impractical. This is why the Stab Trim switches were put back to Normal, to try and recover some trim control, not knowing of course that the MCAS was still adding nose down trim.
So the crux of the problem was that the pilots were applying an outdated response to a problem that they didn't, and couldn't understand.