Originally Posted by
Machinbird
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FCeng84, could this statement be also interpreted as fixing a non-linearity in control response at high AOA? Is that the type of improvement in handling characteristics being created?
To address your question I think it is important to be very clear with regard to your phrase "non-linearity in control response". The FAR in question speaks to the progression of column pull force required to command increased AOA. Well behaved stability characteristics would involve the need for the pilot to apply ever increasing column pull to command ever increasing AOA. Not having that desired characteristic could be a result of either the pitching moment vs. AOA (Cm-alpha) characteristic of the overall airplane or the pitching moment vs. column (Cm-column or similarly Cm-elevator) generated via deflection of the column. The net effect that the FARs speak to is how these two sources of pitching moment (AOA vs column) balance one against the other.
The issue that MCAS addresses is non-linearity of Cm-alpha stability derivative. The pitching moment generated by the elevator (and thus the column) is much more linear. As I have mentioned in previous posts, it is not a matter of the pilot having insufficient ability to generate pitching moment via the column. The issue is that as AOA increases into a range higher than normal operation (near and beyond the AOA for stick shaker activation), the amount of nose down pitching moment generated by additional increase in AOA is not sufficient to require the FAR mandated increase in column pull to balance.