Originally Posted by
John Marsh
I'm puzzled by:
At this stage, they were still using the manual electric trim system, i.e. not trying to turn the trim wheels by hand. I assume the trim wheels are firmly linked and can therefore be used by both pilots together, in theory. But how could using the trim switches on both sides simultaneously make any difference, on the MAX or any previous 737?
Whatever his reasoning, it seems the Captain thought this would help; presumably with an electric trim problem he thought existed.
I'm hoping that a detailed analysis of the CVR recording will add clarity, in this area and generally.
Not saying this WAS the logic, but one possibility.
Trim switches usually have multiple contacts, to try to prevent single failures causing runaways. There may be logic (even just basic wiring type) that requires both sets of sensors to be in agreement before a trim switch is taken as a valid command.
Suppose your trim switch seems to be working - but whenever you let go the trim moves "on it's own". One possible thought that could flash through your head is an intermittent fault on the copilot side (usually pilot side has priority, but as soon as the pilot lets go, the copilot switch can work)
You MIGHT think that if the copilot puts a command in as well, it may either reinforce your command OR cause his switch to vote itself out if there is any residual fault. In someways its a bot like pressing harder on a switch in the hope that works - and sometimes it does under specific mechanical circumstances.
Total random theory, i admit.