AN MD88 WAS DISPATCHED IN NON COMPLIANCE WITH THE INCORRECT VALVE DEFERRED AS LEAKING CAUSING FUEL MIGRATION IN FLT.

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ON THE NIGHT OF JUN/THU/03; ACFT X; AN MD88; ARRIVED AT THE GATE WITH AN INBOUND WRITE-UP FOR FUEL MIGRATION FROM THE L TO R MAIN TANKS. I INITIALLY CHKED THE LOG HISTORY AND FOUND 2 SIMILAR WRITE-UPS IN THE PAST 3 DAYS. AFTER THE FIRST WRITE-UP; THE TECHNICIANS FLUSHED THE CHK VALVES ON THE R TANK BOOST PUMPS TO ENSURE THEY WERE SEALING. AFTER THE WORK WAS PERFORMED; DURING REFUELING; THEY FOUND THE R TANK WAS CONTINUING TO FILL AFTER THE R FUELING VALVE WAS TURNED OFF. THEY ASSUMED THE FUELING VALVE WAS DEFECTIVE AND NOT CLOSING COMPLETELY; AND BECAUSE NO PARTS WERE AVAILABLE THEY DEFERRED THE ITEM TO MAINT. IN THE SECOND WRITE-UP THE PLTS DIDN'T DIRECTLY MENTION FUEL MIGRATION; BUT RATHER THE L TANK WAS EMPTING FASTER THAN THE R; WHICH WE NOW KNOW WAS BECAUSE THE FUEL WAS MIGRATING. AND BECAUSE OF THIS; THE WRITE-UP WAS TREATED AS A POSSIBLE L TANK LEAK; AND WAS SIGNED OFF AS NO LEAKS FOUND AFTER AN EXTENSIVE CHK. SO AFTER RESEARCHING THESE PREVIOUS ITEMS AND KNOWING THAT THE R TANK FUELING VALVE WAS ALREADY ON DEFERRED ITEM STATUS; I INCORRECTLY ASSUMED THAT FUEL WAS ENTERING THE R TANK THROUGH THE BYPASSING R FUELING VALVE WHEN THE ACFT'S FUEL MANIFOLD WAS PRESSURIZED. I ACCIDENTALLY OVERLOOKED THE FACT THAT THIS WOULD ONLY BE POSSIBLE IF THE XFEED AND DEFUELING VALVES WERE OPEN. SO I CHKED THAT THE PROPER PROCS HAD BEEN TAKEN TO PREVIOUSLY PLACE THE RIGHT FUELING VALVE ON DEFERRED ITEM STATUS CHKED FOR ANY POSSIBLE LEAKS; AND RELEASED THE ACFT FOR SVC AWAITING THE NEW FUELING VALVE TO ARRIVE IN STOCK. ON THE FIRST FLT THE NEXT MORNING; THE MIGRATION PROB WAS AGAIN PRESENT AND THE ACFT WAS FERRIED BACK TO ATLANTA FOR FURTHER TROUBLESHOOTING. AFTER ENTERING THE R FUEL TANK; THE TECHNICIAN FOUND A LOOSE FITTING ON THE FUEL MANIFOLD THAT WAS ALLOWING FUEL TO ENTER THE TANK; AND THAT IN FACT THE R FUELING VALVE WAS WORKING PROPERLY. AND AS OF JUN/TUE/03; THIS HAS APPEARED TO FIX THE PROB. I REALIZE NOW THAT I SHOULD NOT HAVE TRUSTED ANOTHER TECHNICIAN'S EVALUATION OF THE R FUELING VALVE; AND I SHOULD HAVE FOUND THAT A BYPASSING FUELING VALVE COULD NOT HAVE CAUSED THIS CONDITION IN THE FIRST PLACE.