Salute!
After all the certification comments so far, I just had to read the stuff myself. You know me, heh heh.
And now I can see plenty of reason for discussion.
The relevant paragraphs I see deserving of the most disussion and interpretation and such are 25.671, in particular 25.672 Stability augmentation and automatic and power-operated systems. Of particular interest is (a) warning indications, and then (b) and (c) which outline system reaction to failures. This phrase is one that stands out to me; My bold...
(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without
requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.
My understanding is Boeing assumed the crew would interpret repeated down trim that religiously followed opposite trim by the crew, after waiting 5 seconds, to be "runaway trim". Sure enuf, disabling the trim system can be argued to satisfy Part 25 requirements. But with STS, I can see misunderstanding what is failing especially with no warning indication or even knowledge of the new system! GASP!
Gotta go now, poof!!