UNEXPLAINED AND UNCONTROLLABLE FUEL XFER INFLT ON AN AIRBUS A320 RESULTS IN AN OVERWT OUT OF FUEL BAL LNDG.

Narrative

AFTER DEPARTING IAD WITH A NORMAL FUEL LOAD DISTRIBUTION AND CLBING THROUGH FL270; WE RECEIVED AN AUTO FUEL XFER FAULT ECAM. UPON SELECTING THE FUEL PAGE; WE NOTICED THE L TANK AT 10.5 GALS AND DECREASING WITH FUEL OF APPROX 9.5 GALS IN THE CTR TANK. WE READ THE FUEL LEAK CHKLIST AND ASKED THE FLT ATTENDANT TO CHK FOR ANY LEAK FROM THE L-HAND WING OR ENG. HER RESPONSE WAS NEGATIVE. WE THEN NOTICED THE CTR TANK FUEL INCREASING WHILE THE L TANK CONTINUED TO DECREASE. I ELECTED TO RETURN TO IAD AND WE CONTACTED MAINT. EVEN AFTER OPENING THE XFEED VALVE AND TURNING OFF THE L TANK BOOST PUMPS; THE L TANK CONTINUED TO XFER FUEL TO THE CTR TANK AT A FASTER RATE THAN ENG BURN. AT APPROX 13.0 GALS IN THE CTR TANK; THE R TANK BEGAN TO INCREASE. I ASKED FOR EMER VEHICLES TO MEET US AFTER LNDG. AFTER CONSULTING WITH MAINT; WE ELECTED TO MAKE AN OVERWT AND OVER FUEL BAL LNDG. WE LANDED AT APPROX 151000 LBS AND A FUEL IMBALANCE OF OVER 8000 LBS (L 4100 LBS; CTR 13000 LBS; R 12800 LBS). I ELECTED TO USE NO THRUST REVERSERS DUE TO UNKNOWN FUEL SIT AND IMBALANCE. AT LNDG; RUDDER TRIM WAS 3.2 L. AFTER AN UNEVENTFUL LNDG; EMER VEHICLES FOUND NO EXTERNAL LEAKS AND WE TAXIED IN. MAINT ADVISED US THEY SUSPECTED A STUCK OPEN VALVE. ACCORDING TO THE BOOK; THIS IS NOT SUPPOSED TO HAPPEN.