At assorted points in this thread we've wondered whether the Memory/QRF section for an IAS Disagree included an alert about the StabTrim issue, or whether it's in a separate Memory/QRF section. What I've seen so far suggests that the Runaway StabTrim in Manual Flight issue is NOT mentioned in the IAS Disagree section - but I've not really seen the QRF for this exact model of 737. Anyone?
A good question.
Imagining what the crew might have been be faced with on takeoff, it looks like at some point they probably had the symptoms of UAS: differing airspeed indications including warnings of the same. The AML entries for the previous flight(s) would have been a factor in the diagnosis, as was the limited time available to reach an initial conclusion and do something about it. Would you expect the aircraft to be exactly in trim? Not really as you don’t know for sure what your airspeed actually is. Are there indications of anything else that might be wrong that needs to be addressed *right now*, considering the workload already present? Well, there are some clues but it would take a lot of dot-joining and spare capacity.
To me, the killer is that, in general, the trigger for isolating the stabiliser in most aircraft is a warning that the stabiliser is out-of-control and/or the pilot detecting continuous stabiliser motion. It is likely that *neither* of these triggers was present because a) the system was working as designed (no warning) and b) the stabiliser motion was likely intermittent and reversible and with UAS you’d be expecting varying trim loads until you reached a steady state.
This is total speculation but looking at it from a HF perspective, I suspect that the primary task of controlling the airframe was challenging enough that they didn’t get very far along the road of analysing the problem before it overcame them...