Originally Posted by
bill fly
As has been very well explained, the reason for MCAS was to cause ANU stick force to increase or at least not to decrease when AoA approaches stall angle. That was a certification requirement.
However, by repeating the trim input at remaining high AoA, something more than just desired stick force increase is achieved.
What is needed is a one time increment in stick force to bring the Max into line with the other 737 models - if that was the aim.
This can be achieved by adding feel spring force to the control run, cut in point determined by AoA.
If there were then a fault in the AoA signal, the increment would be applied - once - which would be trimmable and controllable.
The whole sorry idea of playing with the stab trim to achieve what is really a desired primary control feel correction is unnecessary and as we see, unsatisfactory and potentially dangerous.
A feel spring solution should satisfy the certification authorities and the desire by the manufacturer to keep the Max in the 737 family, rating wise.
But your proposed solution wouldn’t be free to produce. The Boeing solution used existing hardware and a bit of new software.
Its not difficult to see why Boeing went the way it did. To me the question is what level of scrutiny did the plan receive.