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Old 10th Apr 2019, 06:40
  #3798 (permalink)  
CP Bern von Hoesslin
Join Date: Nov 2017
Location: Frankfurt
Posts: 2
The most important tech question on the Lion are and Ethiopian crash investigations!

Ref.: 737-7/8/9 Training Manual 22-11-00, Dated 19.Sep.2016 Pages 165, 166 and 167


A simple version here.

Will the PRI Toggle when moved to CUT OUT, IS IT 100% GUARANTEE to remove -all- electrical signals to the Stab Trim Motor?

Why do I ask? "The FCC supplies MCAS signal to enter high speed mode on the stab trim motor and bypass the aft column cutout switches for trim down commands.". As we know also in error.

THUS if the B/U is in CUT OUT, then MCAS still has authority but what about PRI in CUT OUT?"

The trim commands from the FCC is processed in the "autopilot section of the motor". That means besides the FCC A in these cases, there is another controlling Software either part of the MCAS programing (thus active when a Fault like is being considered part a chain of errors in these two accidents) or a separate sub routine / program influencing the Stabilizer Motor into moving the Stabilizer that has never been mentioned before.

I'm thinking like a chicken with its head cut off, the nerves can still allow it to run around.

So the PRI in CUT OUT, does it still allow impulses from the "auto pilot section of the motor" however created, to move the stabilizer via 28VDC thru the motor un-commanded when the operating crew thinks they've isolated that electric trimming (CUT OUT), thus do not expect further electric trimming (non-pilot induced)?

To keep it simple - PRI and B/U toggles in CUT OUT there is no possible way the stabilizer movement (NU or ND) can be activated unless done manually by the crew using the Trim WHEELS OR a failure of the stabilizer mechanics i.e. excessive speeds beyond VMO, thus possibly breaking or stressing / stretching the components moving the stabilizer itself i.e. for example into the full AND position which is then fatal as non-recoverable?

Any Source I can contact, kindly PM? I do not have access to Boeing Customer Service any more.

Thanks in advance for all PPRUNER's efforts here.

CP Bernd von Hoesslin


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