Originally Posted by
FCeng84
FCeng84 provides clarity ...
Thank goodness. But there still appears to be confusion.
Originally Posted by
gums
One thing all 737 pilots need to understand is this
Originally Posted by
FCeng84
One of the key elements to the baseline MCAS logic is that it will only put in a single increment of stabilizer motion as long as no pilot trim command is given.
Originally Posted by
gums
And then tell them that if the trigger event/value is still present that the process repeats.
FCeng84 and other sources I've read over the course of this and the Lion Air thread seem to say this is not true. In the existing MCAS, there is only a single 10s (or less) nose-down trim provided, even if the trigger event/value is still present,
unless the pilot makes a pitch trim input. This resets the MCAS state, resulting in a 5 second delay, followed by more nose-down trim if the condition is still met. If no pitch trim inputs are made, MCAS will not trim further down (but may restore trim). I can understand the logic to reset the MCAS state, because it can no longer make a trim/AOA association once the pilot changes the trim.
Is there a reference for what
gums says?
Originally Posted by
gums
Those Lion troops did a good job but for treating the problem as an MCAS quirk or STS working backwards as previous crew asserted, or a "runaway trim" that was not continuous. And besides, if they had heard about MCAS, then it was suposed to work making steep turns or slowing way down at cruise altitude or whatever and not be a stall prevention gizmo, and not activating just after flap retraction on takeoff.
Hoping new computer folks at Boeing do a better fault tree analysis this time.
Gums sends...
I can understand cirticism of an MCAS that should be more fault-tolerant and pilot-tolerant, and apparently that is what Boeing is designing and documenting. This has been said before, but it appears the engineers didn't consider that the pilot may make pitch trim changes that do not put the h stab into a proper position, and that the resulting state reset then could have bad consequences if the pilot hadn't already turned stab trim off.
I was happy to see data early and often from Lion 610. Having an open, informed discussion of what happened is the best way to improve safety. I hope to see this soon for ET302.