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Old 5th Apr 2019, 10:57
  #3282 (permalink)  
Join Date: Nov 2007
Location: dublin
Posts: 176
Originally Posted by spornrad View Post
In the prelim. report is a clear statement by the FO that the manual trim attempt did not work as advertised in the AD.
There is also a subtle hint that probably shows why the pilots in a last desperate attempt did reengage the trim motors, and how the pilots were desperately trying to follow the AD and manually resetting the trim, which was most likely aerodynamically blocked:
After the cutout, there is a very slow, long, subtle nose-down movement of the fin according to the report. What do you do when the crank is blocked, instinctively? You're rattling it! And then in this phase it moves only a few hairs nose-down, but not a bit Nose-Up.
Then, in desperation, they probably switched on the electric motors again, only to find out now, with two very short trim-up switch attempts, that in the meantime, electric trim quit working too (speed has meanwhile increased further). A nightmare.

This last attempt to implement the AD has now reset MCAS. And then comes design-wise (but is not in the FCOM or the AD, was never mentioned in training), while they still think about what to do next, after 5 s the final death blow of MCAS ...

The plane systems (MCAS and Trim) and the AD procedure just did not give them a fair chance IMHO.

An excellent overview over these 60 year old speed issues with the 737 trim system can be found in many old manuals and here:
excellent article with diagrams- all thanks to Peter Lemme. Itís a pity that level of schematic is not easily available to lone pilots.
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