Originally Posted by
Maninthebar
Good questions, but as I said much much earlier, I think we can turn this one on its head and ask "what enabled the supernumerary Captain on the prior flight to recognise, at least in part, that CUTOUT was the solution?". I believe that, even then, electric trim was re-engaged albeit briefly.
So, even with 3 heads in the cockpit, one of whom was free from immediate control issues, it did not appear to that crew the Trim Runaway NNC was the obvious choice.
The jump seat pilot was in a better position to see the trim wheels spinning, watching the videos of runaway trim it is blindingly obvious from jumpseat view, likely much less so for pilots where it would be in peripheral vision, and has been pointed out hearing it over the stick shaker is questionable.
As to why it was not handled exactly per Trim Runaway NNC once recognised (re-enabling trim) one factor is that it did not match the at the time checklist perfectly since the 'runaway' was not continuous.