ATA 28

Fuel Dumping From Tip Tanks
Scenario
During a long cross-country flight, you land with 2,250 pounds of fuel and request a full load of fuel including tip tanks. You leave electrical power on the buses during the refueling, in order to enter flight plans and shorten the time on the ground. As the fuel truck pulls away, you confirm a full fuel load on board, and get ready to restart engines and continue flight operations. During the start procedures, soon after the fuel boost pumps are selected to “ALT”, fuel begins to pour out of the wing fuel vents.
Correction
During the previous leg, tip tank fuel automatic transfer occurred at the normal point (approximately 6,600 pounds remaining). The control circuit opened the transfer valves and fuel was transferred from the tips to the wing tanks. This control circuit electrically latches in and remains in that configuration until power is removed from the auto transfer relay. If the transfer system remains active (valves open) and the fuel booster pumps are turned on, tip tank fuel will be forced into the wing and fuselage fuel storage areas, overflow into the fuel vent plumbing and exit through the wing fuel vents. Momentarily removing #1 distribution bus power or simply opening the AUTO TRANSFER circuit breaker will unlatch the holding circuit and prevent the situation. Service Bulletin 1124-28-098 modifies the control circuit. The electrical latch will be defeated when the aircraft has landed, allowing the auto transfer relay to de-energize. This service bulletin is effective for all serial numbers prior to 391.
Yes, this can occur during regular maintenance. If the transfer valves are open, all tanks are full, and the fuel boost pumps are activated, fuel will be forced from the vent system.