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Old 18th Nov 2018, 17:03
  #1386 (permalink)  
Join Date: Jan 2008
Location: uk
Posts: 806
Originally Posted by gearlever View Post
Did MCAS replace STS on the max or is it another feature besides STS?
In terms of operationally, looking for changes/differences docs I haven't seen anything that suggests STS has been removed or changed, and since MCAS wasn't documented at all...

The actual hardware or software implementation is a different matter - STS (previously implemented by the FCC) might have been replaced by something new that does STS and MCAS but the STS bit behaves the same as old STS. However, given that the intent was to change as little as possible, I think it is more likely that MCAS is an additional feature besides, either additional hardware or just software.

There does seem to have been some hardware change though - further up the thread there is an image showing that the two Trim CutOut switches have changed, both labelling and functionality. Where before there was one switch to cutout the control column trim switch and one to cutout the automatic (labelled as "autopilot" but actually the autopilot and the manual-flight STS signals used the same circuit), now there are two switches (primary and backup) which cut both. This means there have been changes, suspect related to MCAS and possibly significant in this event, to the physical architecture. What those changes are we don't yet know, from public info.
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