Originally Posted by
SLFstu
(From an ex hardware/software tech writer) - a comment about software rather than aeronautics. If the timeline story (CVR derived) in comparison to the FDR traces is accurate, here is something weird from the preliminary report's data nobody has commented on.
The third MCAS activation lasting 9 or so seconds starting at 05:40:41 did not alter stab pitch trim because the FO had just cut power to the stabilizer jackscrew motor. The report glibly notes that fact. But why did MCAS even try to activate, as if sitting there fat, dumb and stupid? Exactly what type of coding allows the FCC to attempt to command AND trim when both STAB TRIM switches are already set to CUTOUT? Seems the designed use case never anticipated this sequence.
So it appears that this bolted on chunk of MAX-only software was not monitoring real-time trim motor electrics. Hell no, you cannot do that - a loom change might be required and that would disturb the production line and possibly delay certification! Or better yet, a few lines of more rigorous code were required.
Way up in the thread at least 2 incredulous posters suggested, sarcastically I think, that an intern might have programmed MCAS_1? Makes you wonder.
I agree, but this anomaly is only part of the story. There is also the question of why there are so few electric trim corrections considering the circumstances? MCAS has massive authority despite massive AoA disagreement. Surely, the obvious solution is for MCAS to be automatically disabled but not electric trim? Why would the engineers even contemplated MCAS continuing to operate with significant AoA disagree? What is the effect of a constant input on the pickle switch? Does it give continuous control authority or intermittent authority?
It is fairly obvious that the automated system should have disabled MCAS authority as soon as there was significant disagreement with the two AoA sensors. Blaming the pilots is not sufficient, the more fundamental defect is plainly a Boeing issue and seemingly inexcusable. I feel that the pilots needed to act within the first 15 or 20 seconds of stick shaker but failed to recognize the issue quickly enough. The question is how many crews would have acted quickly enough and why should they have to react at all? It is all so unnecessary.
It is suggested that Boeing provided the MCAS system to overcome approval considerations. However, it does not make sense to leave it to the pilots to disable MCAS when it could be handled automatically. Neither does it make any sense to disable electric trim completely in order to disable MCAS.
...Just touching the surface of the negligent design and certification issues...