Originally Posted by
silverstrata
And why did Boeing incorportate a stall assistance system that trims, instead of using a stick pusher? This seems to go against the normal rules for flying.
My guess: Because that's what was easiest. To add a stick pusher requires adding hardware. You have to add an actuator and linkage to the control system. Adds weight and cost and parts count, and I have to think that the certification process required for a new, previously non-existent system whcih is attached to and moves the primary control system is not trivial.
On the other hand to do it via stabilizer trim is a lot simpler, you've already got all the hardware you need installed, the jack screw and it's actuator. About all it takes is adding some code to the software for the control computer.* So, there you go, no new parts, no additional weight, and no regulator looking over your shoulder saying "Whoa, you just added a mechanical system that applies control inputs to the primary control system. Lets take a look at all the specs for such systems"
* I'm kinda speculating on that, details are still a little fuzzy on what exactly the MCAS 'is" but so far it doesn't seem that there are any physical parts to it that aren't already there and used by other systems.