Originally Posted by
FCeng84
LEOCh,
Very good questions and excellent example diagram. Most of the focus in this and other threads related to how MCAS behaves with an AOA sensor that is failed to a very high value (or with a large positive bias) describes MCAS activating for its full increment in one shot. MCAS actually schedules its airplane nose down stabilizer motion over a range of AOA starting at the activation value and extending as AOA goes higher. If you transition through this AOA range quickly (faster than the stab can run to keep up with the schedule) the whole MCAS increment goes in as one continuous trim event. If AOA increases slowly, however, MCAS will put in a little stabilizer at a time to keep up with the MCAS stab vs. AOA schedule. The MCAS trim will go in at the same 0.27 deg/sec rate but the trim will start and stop as needed depending on AOA time history.
FCeng84
Thanks, that makes a good deal of sense. I think if MCAS is updated with improved robustness of AoA sensing, and some sort of total stab authority limitation, it should be comparable to STS in risk. Besides the oddities of the system trimming against you to provide stable aircraft behaviour, STS is not controversial from a safety viewpoint. I guess the politics of sensor/algorithm/software fixes to aerodynamics will be very toxic for the near future though.