Originally Posted by
GordonR_Cape
I think your assertion contains several logical inconsistencies:
1. The momentary trim inputs may be an artifact of the FDR data sampling algorithm, or the crew stopped trying when the trim wheels didn't turn after a few seconds. We don't really know for sure, and IMO you can't build an argument on such evidence.
2. The recorded increase in the stabiliser ANU position may also be a data artifact, or backlash in the cables and pulleys, or the trim motor locking mechanism. There are a number of suggestions from other sources (including EASA), that what you describe is physically impossible at high airspeeds and aerodynamic loads.
3. Re-enabling the trim switches after runaway trim, is not documented in any procedure, so cannot count towards the certification process. They could re-write the procedures, but currently it seems to fail certification under those extreme conditions.
1. Not so. Every time they used the yoke trim switches from 5:38 (takeoff) through 5:41, the trim responded as it should have. IMO, the Pilot Flying did not use enough trim to restore an in-trim condition, even though he had the ability if he had tried.
2. The move between 2.1 and 2.3 when the trim was disabled certainly may be any of those. I doubt it would have had a significant effect at normal airspeeds, but was exacerbated near VMO.
3. Again, I disagree with you. They re-enabled the trim, but did NOT attempt to use the yoke trim switches after doing so! In similar dire straits I may have re-enabled the trim, but NOT until after I had the yoke trim switches held in the ANU position. If the trim did not IMMEDIATELY begin to go toward ANU, I would have cut out the trim again.