Before revision: from fuselage to wing tanks Centre of gravity control transfers from the tail (trim) tanks forward to the wings as fuel is expended Maintaining fuel in the wing tips (to help stop the wings bending due to lift in flight) & transferring to the main tanks after landing Controlling fuel jettison during an emergency to reduce the aircraft weight.
After revision: from fuselage to wing tanks Centre of gravity control transfers from the tail (trim) tanks forward to the wings as fuel is expended Maintaining fuel in the wing tips (to alleviate wing bending due to lift in flight) & transferring to the main tanks after landing Controlling fuel jettison during an emergency to reduce the aircraft weight.