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Old 14th Jan 2016, 00:32
  #87 (permalink)  
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 77
Posts: 1,458
The CRJ trim system, by design, should detect un-commanded motion and shutdown.
Thanks khorton,
The AD indicates that there are disconnect switches on each control wheel and I have seen pictures indicating a red 'pitch disconnect' switch on the left side of the center console.

When the autopilot is engaged, it has authority to command pitch trim motion, doesn't it? This type trim in a mechanical control system is usually activated by force sensing systems in the control linkage. Is that the case on the CRJ?
If so, then jams in the pitch control system can probably cause trim runaways.

Important caveat. I know next to nothing about the specific design characteristics of the CRJ. It is just that this specific situation has resulted in trim runaways in a number of different types of aircraft. Is there a common link? Design engineers are clever people and they learn from past problems and come up with novel solutions. They may well have circumvented this type problem with their HSTCU design.
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