Originally Posted by
DaveReidUK
As far as I recall, the references were to Boeing inhibiting electric trim movement of the THS in the direction that would put the aircraft further out-of-trim, at some points in the flight envelope. If it's a "fact" that electric trim can't move the stab back towards a trimmed state, either, then can we have some non-anecdotal evidence of that, please ?
The electric stab trim* is prevented from running nose down further than about 2.9 units down. It can however run nose up from 0 units.
*= pilot selected electric trim. MCAS apparently has trim authority all the way to zero units.
Ironically, when I did my first 737-400 transition course 30 years ago I was told the electric trim was limited to 2.9 units nose down to prevent a runaway from causing an unrecoverable loss of control. That was at Boeing, btw.