What was found
RIGHT FUEL TANK DUMPING FUEL INTO CTR TANK IN FLIGHT. TURNED ON CTR TANK RT BOOST PUMP & TURNED OFF RT TANK FUEL PUMPS. LANDED WITH 5400 LBS LT TANK, 4000 LBS RT TANK & 2000 LBS IN CTR TANK. FLIGHT BEGAN WITH 16000 LBS FUEL ON BOARD & CTR TANK ALMOST EMPTY. CARGO FLIGHTS ARE OF 30 MINS DURATION & CTR FUEL TANK ALMOST NEVER USED AT ALL. ACFT TURNED AROUND & LANDED BACK AT AIRPORT. TOTAL FLIGHT TIME 0.6 HRS, BLOCK 8. REPLACED CTR TANK ON WAY FUEL CHECK VLV. FLAPPER RETURN SPRING WAS BROKEN, TOP & BOTTOM FLAPPERS REMAINED OPEN ALLOWING FUEL MIGRATION BACK INTO CTR TANK FROM RT WING TANK. FUEL MIGRATION ISSUES NOW RESOLVED.