|Quoting B747FE (Reply 4):|
That is correct. However, since a tank-to-tank transfer requires the refuel valve in the tank selected to receive the fuel to be open, it can be done on the ground only. (Even though an optional fueling control module is installed on the P4 in some airframes)
Any tank (main's or CWT) to any tank = Ground
Any tank (main's or CWT) to any engine = Air
It was possible in all 747's I have flown with the old analogue fuel system and the cockpit fuel control module installed to bypass the groudsensing by operation of the override and battery switch on the F/E refuelling panel during flight. Opening of the refuelling vlv's was then possible in FLT.
Actually I had to use "this trick", when dealing with a heavy internal leak, transferring fuel from main tank 1 to 2 during crz.
However, after installing the new digital fuel indicating system it was not possible any more.
[Edited 2010-01-30 01:15:18]
Operating a twin over the ocean, you're always one engine failure from a total emergency.