QAVION
Don't know the why's & wherefores but on all our -400Fs, APU GEN #1 ON, #2 AVAIL. Same with EXT PWR (1 ON, 2 AVAIL).
As a note for external power; the -400F needs both ext busses plugged in to the GPU; #1 for lowerdeck cargo handling, #2 for maindeck cargo & maindeck doors.
Now that I've mentioned that, I remember I couldn't open the side-cargo door the other day in ZRH. After a lot of running around, found both #1 & #2 ext pwr "ON". #2 reset to "AVAIL"; as if by magic, the door opens...
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rgds Rat