Quoting 3db, post #439:
"An electromagnetic pulse may have caused the logic states to reverse, at least until everything re-set itself – however, I would have expected that to be recorded in the FDR somewhere or some other anomaly would make the AAIB think “what caused that reading” on the FDR?"
Fuel control switch position is a DFDR parameter. If spar valve position is a DFDR parameter i don't know. If it is, then it would be interesting to know which position is recorded. Is it the moment the valve is in transit from the open to the closed position or only when fully closed?
If only recorded when the valve reaches the fully closed position but not when in transit, then there may be no record of the valves moving to a partially closed position if reverse logic lasted shorter than it takes the valves to fully close. At the moment that the system re-sets it takes an equivalent amount of time for the valves to reach the fully open position again. For example, if a valve moves from fully open to fully closed in say, 15 seconds but the reversed logic lasted for only 12 seconds (valve almost closed) it would have meant the valve was in transit for a total of 24 seconds in which fuel flow to the engines would have been restricted.
Would such an unscheduled (perhaps only partial) closing of the valves generate an EICAS status message? When reviewing the system logic regarding the spar valve fault indications and projecting this on the condition of reversed logic to the control relay, i don't think so (see AMM: Functional Description of Engine Fuel Spar Valve - Fault Indications).
Next question to answer is, and i stress again it is only theory, if EMI would have corrupted the spar valve control system, how much transmitting power (radiated field emission) would be required to make a 28 Vdc relay move from run to cutoff position? I estimate that to be very large.
Regards,
Green-dot