Originally Posted by
737 Driver
I agree it is an incomplete picture (which I did acknowledge), but there are some broad enough outlines from which we can draw some conclusions. If anything comes out that substantially alters our current understanding, then I'll be happy to make a correction.
As far as what was going on while the the trim switches were in the cutout position, are you referring to the gradual movement from 2.3 to 2.1 units? It apparently occurred over two and half minutes. I'm interested in seeing what the board's thoughts are on that as well, but I should point out that in the context of the overall trim movement, it is a very small and slow creep.
I was actually wondering more about what was discussed and actioned during that time. Two and and half minutes is long enough for the initial startle factor to dissipate, hopefully some insight can be gained into pilots actions during the preceding critical time.
The prelim report mentions only one attempt at manual trim at 05:41:46, roughly half way through the cutout period, surely there was other activity during that 150 seconds.
One possibility is that the trim creep was due to attempts at manual trim causing a bounce in the cables that each time resulted in slight movement in the wrong direction. In the mentour pilot video you can see this bounce as attempts are made.
Another possibility is that one of the brakes is not holding against the load but that would be a seperate failure/design flaw that is probably not needed to explain the traces.
Access to the raw FDR data should resolve this since if it was a slipping brake it would likely be continuous whereas manual trim efforts would be seen as (slight) steps with pauses.