Originally Posted by
A and C
May be I’m getting confused but it was my understanding that the BBJ Aircraft all used cabin pressure to move the fuel into the centre tank.
that would mean that the wing tanks need to withstand the same pressure the cabin needs to withstand.
this is unlikely as it would incur additional weight.
the other direction is the one needed in flight and therefore more interesting.
if the center tank can only be filled on the ground that's perfectly allright.
and getting the fuel from the center tank that is at cabin pressure into the wings is trivial you just open a valve. (making sure the tank can get air from the cabin so it doesn't collapse)