Originally Posted by
Goldenrivett
safetypee
I don't see why. The preliminary report says
"At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,4002 ft, two momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in the ANU direction from 2.1 units to 2.3 units."
The crew could still wind the stab trim ANU using the manual electric trim 32 seconds before impact. The question has to be why didn't they use the manual electric trim to remove the elevator load completely then isolate the system using the two pedestal switches.
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.
Edit: Reuters has an excellent article, citing some very knowledgeable sources:
https://www.reuters.com/article/us-e...-idUSKCN1RA0DP
The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said.
It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke.