737 Driver
What MCAS will then attempt to do is run the trim nose down for 9 continuous seconds and spin the trim wheel about 37 times. I’ve asked this before, and I’ll ask this again: Starting from a stabilized, in-trim platform, exactly how long should a qualified 737 type-certified Captain who is hand-flying the aircraft let the trim run in one direction before he/she does something about it?
A long time ago I asked a critical question, to which I did not get a satisfactory answer. Perhaps you can indulge me.
On the B737, the flight computers (and the FDR post-crash readout**) know exactly how much nose-down trim has been applied to the horizontal stabiliser, but the pilots do not.
The only way for them to determine this is to look at the sliding scale between the manual trim wheels, or count the number of rotations, or infer from the elevator feel forces.
Stabiliser trim position is not shown on any of the primary flight displays, and
AFAIK is not part of any routine instrument scan.
It seems that pilots have to infer runaway trim, rather than a big flashing display that could easily warn them of that fact. How un-ergonomic is this setup, that the most powerful flight control, is the one they have least information about?
Edit: **In much of the post-crash discussion, the question is asked why did the pilots stop trimming nose-up? Those comments were based on the FDR readouts, while the pilots had to infer the position of the horizontal stabiliser trim, relative to column forces and elevator feel, etc.
Edit: Or to put it even more bluntly: The pilots had to make a life-or-death decision about when to hit the trim cutoff switches, when they did not know the actual position of the horizontal stabiliser. Much of the post-crash "hindsight" analysis is based on the FDR readouts, which contain information that the pilots flying the aircraft did not have access to!?