I stand by the theory that this is not MAX specific and that Boeing have been caught out on a technicality only(albeit a very embarassing one).
Its difficult to theorize without any data but I am guessing STS doesnt actually exist on the MAX but has been replaced by the "enhanced" MCAS,which actually performs the same or very similar function(s).The accident report will have to use the new name MCAS and since no pilots actually have any FCOM data on that system but only on its presumably very similar predecessor, STS,its a difficult but mandatory admission for Boeing to make before the investigation continues.
However,we know that the previous commander recognized the unwanted insidious trim and actually noted it in the tech log as STS input simply because he had never heard of MCAS.The NG AMM clearly describes how STS will trim to the stops under certain conditions if the pilot doesnt intervene.
The fact that it hasnt happened on the NG doesnt mean it cant; rather,it just means the specific sequence hasnt lined up yet,or if it has it was controlled by the crew.Suppose 610 hadnt crashed (for example if the AoA failure had been right side on 610,then there wouldnt have been any trim down as FCC A would have been controlling...1st flight of day) and Lionair maintenance got it right on the 5th attempt and finally fixed the fault.Would there be an AD?..............
Its those holes in the swiss cheese again that have to line up for an accident to occur.
Point being,that whether we choose to call it STS or MCAS,unwanted insidious trim contributed to this accident. Insidious because its not actually a runaway.Insidious because it can be overriden ..Insidious because the AP stab trim motor is quieter and slower.Insidious because the noise of the continuous stick shaker was highly distracting.
I see that the press are out in fulll force proclaiming Boeing causes air disaster...well,they may well be in for a bit of trouble, but this accident was avoidable and the crew wouldnt need to know the difference(s) between STS/MCAS to do so.The previous flight proves that.