Trim only sets AoA

[Vessbot]

BluSdUp, thanks for engaging despite the reluctance. Your characterization of the severity of the thrust pitch couple matches what else I’ve read about it. However, I still see a disconnect between that, and your suggestion of the consequences of pulling the thrust back in the MAX crashes.

I don’t doubt at all the severity of their high speed problem. But here again what you posit as the solution (“HAD to reduce power”) seems to ignore what you said about the couple, and to be based in the everyday mentality of flying constant altitudes, where thrust is related to speed and the automatic trimming that’s done by the autopilot (or, less often, the manual trimming done by the pilot) falls to the background to the point of being ignored and even forgotten about.

But this trimming, along with the fundamental AOA-speed relationship that it feeds into, is not a side effect that can be neglected but rather is central to the plane’s flight. In order to slow down (level or otherwise), the AOA MUST be increased, which necessitates back elevator and/or back trim. Since they were out of both, this was not possible. To the extent that it was possible (like them tapping into a last-ditch previously unknown reserve of strength) they could have made that same elevator change, meaning the same AOA change, meaning the same speed reduction; with or without a thrust reduction. BUT if they did it without the thrust reduction, it would result in a climb. So they would get the same speed reduction, with the benefit of gaining altitude in this low altitude control emergency, AND WITH LESS RESISTANCE to their aft pull, due to the lack of pitch down couple.

So, to summarize with some example numbers:

4 deg. AOA = 400 knots
5 deg. AOA = 350 knots

And this is true regardless of thrust, and whether they’re in a climb, descent, or level.

Losing that 50 knots would require that same 1 deg. AOA increase, which must be commanded by the elevator regardless of vertical path. Losing that speed by climbing rather than by thrust reduction is A. more possible (lack of pitch down couple) and B. more beneficial (gaining altitude).

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I guess the best way to simulate this in one's head (or, simulator) is to start stabilized level, at high speed, and in trim. This represents the X pounds of forward stick force due to the runaway-then-cut-out stab, and the -X pounds of aft stick force from your hands. Since X-X is zero, we can represent this by being in trim and you're not allowed to touch the yoke or trim control (since they were already pulling as hard as they can). Now we're in the semi-stabilized condition of the first crash before the final plunge.

So, then, what happens when thrust is reduced?

Now let's modify this by representing that extra superhuman oomph that might have saved them, by pulling on the yoke with the force of one pinky finger hooked around it. Would you be better off simultaneously reducing thrust in an attempt to maintain level flight (and having the thrust pitch couple now counteracting your pinky), or rather leaving the thrust alone and pulling up into a climb, thus buying yourself altitude, time, and options?

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To put all this in another way: Since pulling into a climb reduces speed just as easy as (actually, easier than) reducing thrust, what would be the purpose of reducing thrust in the MAX crash scenario?