Originally Posted by
DaveReidUK
I don't know what I'd call them, but if there was a channel for them on the FDR I would expect there also to be a separate channel for raw pickle switch position, and the logical one to show on the trace readout would be the latter (as appears to be the case).
Well, there is a large number, certainly in excess 100, of true/false datapoints recorded by the FDR, the manual trim up/trim down to be one of them where each (trim up, trim down) have its own true/false state.
If all those datapoints should run one or two wires each directly to the FDR then the connection on the FDR would need to be humongously large. And there would be introduced a not insignificant additional risk for wire shorts due to the added number and lenghts of wire which in its own is a safety risk for the aircraft.
So I am thinking you are jumping to conclusions and is not really considering the different methods of collecting all these data. Letting the FCC and other electronic boxes send data to the FDR via a buss greatly reduces the complexity of collecting all those data. And the buss is there anyway, how else to cellect data about engine conditions, flight parameters like acceleration etc?
So I am in line with the others here questioning exactly how the thumb switch signal is collected. I would hazard a guess it is NOT collected by running one or two discrete wires from the thumb switches all the way to the FDR.