To CONF iture:
You are correct, with all boost pumps running in both main tanks there would be no crossfeed if a crossfeed valve were to be in the open position. However, if only the APU is running (with boost pumps off on the overhead panel) there would be a crossfeed. But that would be a temporary condition.
An undetected open position can be ruled out. First of all, an open crossfeed valve in disagree with the pushbutton would generate a valve light in the pushbutton and EICAS advisory and status messages would be displayed (after 10 seconds). No way it would go unnoticed by the crew.
I am not aware of any automatic crossfeed valve selection. To my knowledge crossfeed valve operation is a manual selection only.
With regards to when the APU flap (assuming you mean the APU door) started to move. That may be a tougher nut to crack. I can think of a few possible scenarios:
- APU started by the crew: Not mentioned by the AAIB in their report S1/2008. Could very well have been the case even if not mentioned by the AAIB.
- APU autostart: For that to happen, power would have to have been removed from left and right transfer buses in flight. That did not happen because the ram air turbine (RAT) would have automatically extended during an APU autostart. There is photographic evidence the RAT did not extend in flight. It extended after impact on the ground.
- APU door open due to other causal factors: Answer to this will have to wait for the final report. This is where several holes in the swiss cheese would have had to line up before a failure of this nature could occur.
As discussed before, i can think of a possible (but very unlikely) scenario where the APU fuel shut off valve control relay could have been affected. The same scenario would have affected the spar valve control relays. Temporary loss of power to the 28v dc hot battery bus, making both the spar valve- and APU fuel s/o vlv control relays susceptible to EMI reverse logic. If (i stress if) EMI was present it could have caused the spar valve control relays to close and the APU fuel s/o vlv relay to open, possibly latched in that position when power was restored until the EMI source disappeared, returning the system to a normal logic condition. The effects would be:
* Closing (or partially closing) of the spar valves restricts fuel flow to the engines.
* Opening the APU fuel s/o vlv control relay, instructing the APU fuel shutoff valve to open, may have triggered a signal to ELMS to open the APU door?
Ready to be flamed . . . .but . . . "when you have eliminated the impossible, whatever remains, however improbable, must be the truth", Sherlock Holmes used to say.
Green-dot