@FCeng84 I get most of what you've said, makes sense and moreover it matches my understanding of the high-AOA function in the NG, but this bit I don't get.
Originally Posted by
FCeng84
STS and MCAS are both functions implemented within the autopilot and thus use the same path to the stabilizer that the autopilot uses for autotrim when it is engaged and controlling the elevator.
If I understand the NG functional descriptions that I have acquired, Autopilot and STS take the same signal path which goes through the column switch module and then the console cutout switches, to the actuator. Now, we know MCAS
doesn't honor the fwd/aft-column-cutout switches so there must, surely, be either a different signal path or some new bypass/override signal to the column switch module (unless MAX STS doesn't honor the fwd/aft-column switches either?) ?
Unless the column switch module has changed from an actual switch in the path (which is how I understand the NG docs - I may be wrong?) to merely a signal of switch position back to the FCC which then decides in software whether that "cutout switch" is effectively in the signal path or not?
Note: the above, would be a sort of red flag to me, because software is
far more flexible than switches and relays, which is great
until it goes wrong, by accident or design - it is very easy to change code such that a check/gate/switch point is unintentionally bypassed, and then Murphy decrees it will only be for a set of circumstances/inputs that aren't in the tests.
Generally much harder to
unintentionally bypass a relay or switch.
The "flaps up" signal from FCC to stab trim actuator must have changed in some way as well, because MCAS is apparently trimming at flaps-down speed when flaps are up?
Appreciate any clarification you can give, also fully understand if it goes beyond the system understanding that you can share - in which case I will remain with my speculation until more is published.
PS: If anyone wants me to post the NG details or diagrams that I am talking about then I can, I didn't want to make this post too large. Plus I get the impression FCeng84 doesn't need them!