C.M
We have a note in the SOPs: "During refueling, FUEL PUMPS must remain OFF".
I can only think of one issue why: during re-fueling with the CTR TK pumps ON, on the aircraft with CTR TK XFR System the CTR TKs are pushing fuel from the CTR TK into the WNG TKs while fueling. I guess the worry is the WNG TKs could be overfilled by this. They should not, the CTR TK PUMPs should switch OFF at high WNG TK level, and refuel valves should close when a high fuel level is detected...