Originally Posted by
Ian W
That is an interesting set of statements.
So MCAS gets reset when there is a pilot 'electric' trim - so the first series of trim events we see from the pilot is to return the trim to the wanted nose up to level flight. There is a pause and MCAS trims 2.5ND. This is repeated.
The run up to the dive the electric trim is just blipped and trim not returned to level flight. From the description the effect of this on MCAS is that it resets in the current 2.5 ND and then adds another 2.5ND and so on with every blip. So by blipping the trim the PF was actually making MCAS ratchet nose down after each blip reset???
From that description the best approach with an errant MCAS is CUT OFF the stab trim, the next best approach is live with the pull force MCAS has given or trim right back to level. The absolute worst thing to do is just 'blip' the electric trim as each blip resets MCAS which then winds in another 2.5ND.
Which is what happened in the last few seconds of the flight.
I see lots of folks assuming MCAS trims 2.5ND each time - but that's not what I get from the description of MCAS, which provides:
Stabilizer incremental commands are limited to 2.5 degrees and are provided at a rate of 0.27 degrees per second. The magnitude of the stabilizer input is lower at high Mach number and greater at low Mach numbers.
So - depending on speed and AoA, MCAS will trim
up to 2.5ND - correct? Or - is there something else that confirms MCAS trimmed JT610 2.5ND repeatedly, and then continuously?