Originally Posted by
Lost in Saigon
It has been said time and time again: MCAS is not for stall protection.
MCAS is only there to provide the correct elevator feel at high angles of attack to meet the FAA certification requirements. You can still stall the aircraft, the only difference is how the elevator feels. With MCAS the elevator feels like every other aircraft you have flown. Without MCAS the elevator feels light at high angles of attack.
In my opinion, the original MCAS design was really not that big a deal. Boeing and FAA probably decided one Angle of Attack sensor was enough because it still flies just fine without MCAS. It just feels different. If the Angle of Attack sensor fails and MCAS operates incorrectly, you just trim it away with the thumb switches. (Lowering the flaps for landing also deactivates MCAS) If you get tired of playing with the trim switches to keep the nose up, then just turn off the Electric Stab switches and trim manually. No big deal right?
WRONG.... It seems that there are pilots who will have difficulty with this simple concept of FLY THE AIRCRAFT so now Boeing has refined MCAS to make it less likely to confuse these pilots. Now it takes 2 Angle of Attack sensors to agree before MCAS activates, AND it will not apply nose down trim repeatedly. That should make it safe for all pilots. YES?
But, for some reason, people are still not satisfied. It seems these people have a real hate-on for Boeing and the FAA. I think this is all an over reaction to a simple design underestimation that has an easy solution.
I read several hundred posts ago MCAS uses a circuit that trims faster than the thumb switches, which is a key part of the problem. Just using the thumb switches is what the first victims did, and we have all been told that was obviously wrong and poor airmanship.
This was not a case of unaware pilots not noticing that the plane was trimming down, or not knowing the basics of how to fly an airplane. The most convincing arguments that I read here for pilot error is that they were too slow to recognize the problem and use the procedure that Boeing specifies (although even that gets fuzzy as Boeing used to specify a more detailed procedure that is now not taught because runaway trim was rare to non-existant before the MAX.)
The variety of "simple concepts" presented as solutions here that would have also crashed the MAX is concerning. My understanding of the current "party line (see Dominic Gates in the Seattle Times) is that the first pilots erred by not turning the electric trim off, and the second pilots erred by turning the electric trim off
too soon. My unqualified understanding is that the ideal procedure is to use the electric trim to undo the MCAS input (while not letting go of the switch for a moment) and then (presumably without letting go of the trim button) turning off electric trim to disable MCAS. (I do not believe that is the standard response to a trim runaway which is an argument against the concept that the pilots erred by not applying the trim runaway procedure.)
We cannot forget that two planes from two different respectable airlines with legally qualified pilots crashed in short order, which is not something that happens very often. There is so far no reason to believe that those pilots were any more or less skilled than the thousands of their brethren so if this was just the sad fact that pilots don't know how to fly anymore, we should expect to see major airplane crashes every six months or so. We do not, which is why the plane was grounded despite Boeing's and the FAA's objections.