Originally Posted by
Loose rivets
I hadn't read that AV item before. Frankly, I'm going to have to go back to it several times to absorb it in its entirety.
By this, I mean the not-quite-so-easy-to-understand second cut-out switch circuitry. Is this contained overview statement correct? Grief, no wonder it wasn't understood in a iPad ramble. Even after a lifetime's love of electronics, stepping on that aircraft and truly understanding the systems would be a serious challenge.
The quotes are one question, split, and in reverse order.
Again, one of the main bee-in-my-bonet's issues. Just what is the truth about that second (underfloor) column switch? I know, it's the third time I've shouted that question.
I am not a pilot, but I have eletrical and automation background.
Based on the wirings that are available on the net the systems are as stated.
MCAS is not stopped by column switches!
MCAS cannot be disabled without cutting off manual electrical trim, which means only wheel cranking can be used if CUT OFF switches are used.
CUT OFF switches are connected in series, and renamed PRI and B/U, either one will CUTOFF all electrical controls (manual thumb on control column, autopilot, STS, MCAS), while on NG one switch will cut off automatic trim, while the other whole cut off the electrics.
Such change has been made to make the system more reliable, in case one of the CUTOFF contacts will fail (?????), note that i could not find any official comment on that by Boeing...so take that as a rumor.
anyway, connecting those switches in series might imply that previous (NG and before) design was unsafe...
my take is that the designers did not want the pilots to be able fo disable MCAS and could not remove one switch from the cockpit wihout incurring in SIM training, or having to explain why has been removed i.e. becuase of MCAS. Experts in certification please call me wrong
cheers