Originally Posted by
gums
Salute!
@Gilles
I am willing to bet that most of us think of "runaway trim" as a fairly constant uncommanded trim that we didn't expect. The MCAS trim implementation is maybe ten seconds of nose down unless you use the manual trim switch or wheel, then it "rests" for 5 seconds and tries to kill you again!!! So sympton is like "intermittent trim" or basically FUBAR trim, especially if not briefed on the MCAS implementation and realizing that the stick shaker and stall alarm was telling me to push over, but Hal was overdoing it.
The previous Lion Air crew turned off the trim and until we hear their testimpny, they may not have realized that their own plane had MCAS failure. And looking at their FDR plots, it was classic MCAS. just like flight 610 the next day.
@CONSO The flap retraction altitude/procedure for the 737MAX is not in my memory bank Seems that normal retraction requires a trim change in most planes ( Airbus, Viper, Raptor, maybe 777 excepted), but not flying that type I am not sure. In any case, it's a configuration change and that is not a great time to have uncommanded trim you are not expecting or trained for.
For the "shut up and wait" folks!! This is a "rumor" forum, but if I were flying this type I would sure as hell be reviewing everything I could get my hands on about the systems' operation ofter gear up and establishing a stabilized climb, and talking with other pilots flying the beast.
Gums opines....
Possibly off topic, but, why would brand new aircraft sensors and indicators fail within months? The software, MCAS, is reliant on good data, if the data was always good then there wouldn't be a problem with the software. The question is, why is the data so bad? Why is MCAS reliant on AOA sensors that fail within months of introduction? Yes, I agree that MCAS shouldn't have been slipped in by the backdoor, but we probably still wouldn't know much about it if it was actually functioning the way it was supposed to! Are all these billions of dollars spent on automation software being pumped into unreliable hardware?
At least Southwest took it's own initiative by adding an extra AOA indicator into 737 MAX for crew to cross-check erroneous data, but, shouldn't that be a Boeing responsibility and hence fitted to the worldwide fleet? I doubt Ethiopian purchased or insisted on these upgrades.
I'm not jumping the gun, and certainly not claiming this was the problem with this flight, just picking up on others comments on MCAS.