Originally Posted by
FCeng84
MCAS is able to do its job with 2.5 degrees of stabilizer up to Mach 0.4 and less than 1/3rd of that at cruise. That MCAS can insert more stabilizer motion that this design limit is beyond its design requirements. There is not a control power deficiency as there is plenty of elevator to counter the design levels of stabilizer that MCAS needs.
This suggests a future MCAS software update will limit stabilizer motion to benign values sufficient to achieve design requirements, therefore excluding a scenario where MCAS could become the cause of inadvertent full stabilizer down trim. So far, so good.
However, I can't help wondering about this: if a system like MCAS is required to demonstrate flight handling characteristics in conformity with certification requirements throughout the flight envelope, without which the aircraft could not have been certified, how are those being met in the absence of MCAS after an in-flight event (following a reversion to manual trim due to e.g. erroneous activation or stabilizer trim malfunction)? Excuse the crude analogy, but this seems to compare with a normally aerodynamically sound and certified aircraft inadvertently losing a part of its structure, therefore not necessarily rendering it unflyable, but certainly outside its certified state into an emergency situation.
I'm surprised the aircraft was allowed to reach certification with this known possibility (to extend the analogy, accepting the likeliness of losing some part of the airframe in flight). Furthermore without mandating simulator training for dealing with the more unfavorable handling characteristics in approach to stall scenarios without MCAS (not even speaking of telling the flight crews about the system in the first place or training them for MCAS having under certain conditions authority to trim the stabilizer full nose down on a single sensor input - unthinkable!).