Originally Posted by
safetypee
bsieker #3326, The important aspect is that there is no change in the pitch trim position.
Yes there is. The creep in the lines is too consistent for it to be random sampling errors (which are also there and clearly visible as jitter.)
Thus the indications toward the end off the flight probably identifies reactivation of the elect trim, even two pulses recorded due to selecting the two switches back to an active state; either without further pilot elect trim input by choice, or due to a certification inhibit (? discussed elsewhere), or with manual elect trim, it was not strong enough to overpowered the tail forces (from the crew’s perception the latter situations were of an elect trim fail)
True, these low-resolution traces need to be read very carefully, but I think a slight nose-up trim change is clear from the trace around the time the two manual trim switch inputs are recorded. Yes, we don't know the sampling frequency for pitch trim position, but as can be seen from the areas in the graph where it changes rapidly, it cannot be less than once per seconds, so that very very slow decrease from 5:30:45 to 5:43:10, and the following very slight increase between 5:43:10 and 5:43:20 are real. Both these movements are also mentioned in the textual part of the report.
The mention of failure of both electric and manual trim was much earlier, during the time where we assume that the cutout switches were in the cutout position. That to me is the most scary part that even for these moderate control column loads that can be held for several minutes, manual trim would not work at all. I had always assumed that in all but
extreme out-of-trim situations, mechanical trim would be available.
Bernd