Originally Posted by
WillFlyForCheese
I've been thinking about this - and don't believe it can be an accurate statement of the purposeful design of the system. Here's why . . .
MCAS will, when data input dictates, trim AND. It will do so for 9 seconds or so - and then take a 5 second break. When it's taking its break - it's not fulfilling the purpose of 25.173 - right?
If the purpose of the system is to compensate for stick feel - it wouldn't take a break - because the lift generated by the cowlings doesn't take a break.
If tdracer is still around on this topic - I'd like to know how the designed 5-second stand down plays into the purposeful design of the system. It just doesn't make sense to me.
There are two followup aspects to your question, depending on the version of MCAS 1.0 and MCAS 2.0:
- MCAS 1.0 was designed to satisfy the criteria that you describe, though not smoothly, due to the 5 second pause.
- MCAS 2.0 may remove the option of repeated trim during the same high AOA "event", depending on the definition of event. This would not satisfy the 25.173 criteria, if it allowed the pilots to do a second pull into the high AOA region, after interrupting MCAS by blipping the stabiliser trim switches.
Long ago I posted this assertion: It is logically impossible to design a system that satisfies both limited MCAS activation and 25.173 criteria simultaneously. One of the two limits has to be broken in some scenarios, for example pilots repeatedly entering the high AOA condition. I have not seen any evidence to contradict my assertion.