Originally Posted by
gums
Salute!
Outstanding, these last few posts. Warms the cold, crusted heart of this old engineer and government paid triggerman.
Of note, and I hinted at this over on the main thread...... FC did it, the swine! PEI has also hinted at it as have others. It’s the other things behind the curtain. And the revelation that MCAS remembers where it started is good and bad news. The bad is we are just finding out.
Imagine an an intermittent connection/bad connector from the AoA probe. MCAS activates at 35,000 feet and 0.7 M. Or so. Whoops! Uncommanded nose down trim, a/p disconnect, unreliable ias, feel difference light, alt disagree, stick shaker, Oh baby oh baby. I trim up and tricky Mach effects take hold. Oh man, oh man....... The progression is left to the experienced pilot reader here.
“lemme” has postulated the bad connection possibilities, and if I was on the Board I would be looking at all possibilities of bad connectors and wire bundles, as well as if certain shifts/crews performed either maintenance or the original assembly of the various components.... In short, it may not have been a bent probe as Saili claimed to have had one day.
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I did O.K. In my aero classes and in maintaining control of several fast movers at AoA’s you can not imagine. So youse folks with current education and design experience can explain why we can’t reconfigure the engine nacelles on the Max to help with the reduced pitch moment problem. Hell, slots, vortex generators, a few degrees here and there, something!
Gums wonders....
Gums - the sequence above in your "Imagine ..." paragraph seems to have MCAS acting before A/P disconnect. MCAS can come active following A/P disconnect if indicated AOA is high enough, but not while A/P is engaged. As for your last thoughts on aerodynamic fixes vs. MCAS, the message that always comes down with a request to the Flight Controls team is that control law change (if a viable, safe option) is the least impact means of addressing the issue of the day.