Originally Posted by
FCeng84
Denti - thanks for your reply. I feel as if your words have finally drilled something into my thoughts that I had not been allowing in before. I think I was just too stuck on the classic notion of a stick pusher in the form of a new, external "muscle" of some sort. What I think you are suggesting is that because the pilot is already pulling the column when the AOA range of concern is reached, why not increase required pull force by stiffening the variable column feel gradually as a function of AOA? The 737 column feel system (both NG and MAX) already has functionality to provide a relatively sharp increase in column stiffness when passing through an AOA threshold somewhere beyond stick shaker AOA. It may be possible to modify this to provide a more gradual increase in stiffness that would address the issue for which MCAS was fitted.
I'll give this some more thought, but I feel you (and others making similar suggestions - my apologies for not recognizing those earlier) may be on to something here. I'll check with some people I know who are more expert on the associated requirements to see if this might be another approach that would satisfy the associated cert regulations.
Thanks, again - the value of the public square that PPRUNE is needs to be acknowledged and maintained.
FCeng84
Denti - Considering this further there are two probable show stopper issues that get in the way of using variable column / elevator feel as a means of providing the certification compliance that is achieved with MCAS:
1. The variable feel arrangement on 737MAX does not allow for continuous adjustment of the feel system pressure as a function of AOA. There are provisions to provide a step increase in pressure when an AOA threshold is exceeded as one of the layers of awareness to the crew that they are getting to high AOA, but it would require considerable additional equipment to turn that into a continuously variable feel pressure level defined as a function of AOA.
2. There is not enough column / elevator feel system adjustment range to provide the compensation that would be needed. This is particularly true at high Mach / speed where the nominal setting for the feel system is rather high to begin with. There is not enough range left in the system from there to max pressure to sufficiently offset the Cm-alpha characteristic that must be addressed to meet the FARs.