Narrative:

During routine scheduled air carrier flight to ZZZ; it was discovered after 4 hours of flight; that there may be a fuel leak in the right fuel system. Departure was uneventful except for being held to a lower cruise altitude initially for traffic. Looking at fuel usage after the first hour; it was noted that the left fuel tank was out of balance by 500 pounds lower than the right tank and the total burn was 400 pounds over flight plan burn. For the next 2 hours everything was normal with each hourly check of the fuel and other system. While conducting hour #4 fuel check it was noticed that there was now a problem with the fuel system; specifically the right side; 1000 pounds less than the left side. While there was enough fuel to continue to the destination with no delay; 1500 pounds of fuel was unaccounted for. The captain contacted the dispatcher via company radio and it was decided to divert into ZZZ2; since we were 20 mi and closing at that time. An emergency was declared with center and the captain ran the QRH fuel leak procedure and we diverted uneventfully to ZZZ2 complying with all company and aircraft procedures. The fire crew was standing by on the ground and did a thorough check of the aircraft on the runway and escorted us to the gate when it was determined safe to do so. It was discovered that there was a fuel leak coming from the right engine nacelle. A maintenance logbook entry was made at the gate; passenger deplaned and switched to a new aircraft for the trip to ZZZ.

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Original NASA ASRS Text

Title: FLT CREW OF A320 EXPERIENCE FUEL LEAK ENROUTE. DIVERT TO NEARER SUITABLE ARPT FOR INSPECTION.

Narrative: DURING ROUTINE SCHEDULED ACR FLT TO ZZZ; IT WAS DISCOVERED AFTER 4 HRS OF FLT; THAT THERE MAY BE A FUEL LEAK IN THE R FUEL SYS. DEP WAS UNEVENTFUL EXCEPT FOR BEING HELD TO A LOWER CRUISE ALT INITIALLY FOR TFC. LOOKING AT FUEL USAGE AFTER THE FIRST HR; IT WAS NOTED THAT THE L FUEL TANK WAS OUT OF BAL BY 500 LBS LOWER THAN THE R TANK AND THE TOTAL BURN WAS 400 LBS OVER FLT PLAN BURN. FOR THE NEXT 2 HRS EVERYTHING WAS NORMAL WITH EACH HRLY CHK OF THE FUEL AND OTHER SYS. WHILE CONDUCTING HR #4 FUEL CHK IT WAS NOTICED THAT THERE WAS NOW A PROB WITH THE FUEL SYS; SPECIFICALLY THE R SIDE; 1000 LBS LESS THAN THE L SIDE. WHILE THERE WAS ENOUGH FUEL TO CONTINUE TO THE DEST WITH NO DELAY; 1500 LBS OF FUEL WAS UNACCOUNTED FOR. THE CAPT CONTACTED THE DISPATCHER VIA COMPANY RADIO AND IT WAS DECIDED TO DIVERT INTO ZZZ2; SINCE WE WERE 20 MI AND CLOSING AT THAT TIME. AN EMER WAS DECLARED WITH CTR AND THE CAPT RAN THE QRH FUEL LEAK PROC AND WE DIVERTED UNEVENTFULLY TO ZZZ2 COMPLYING WITH ALL COMPANY AND ACFT PROCS. THE FIRE CREW WAS STANDING BY ON THE GND AND DID A THOROUGH CHK OF THE ACFT ON THE RWY AND ESCORTED US TO THE GATE WHEN IT WAS DETERMINED SAFE TO DO SO. IT WAS DISCOVERED THAT THERE WAS A FUEL LEAK COMING FROM THE R ENG NACELLE. A MAINT LOGBOOK ENTRY WAS MADE AT THE GATE; PAX DEPLANED AND SWITCHED TO A NEW ACFT FOR THE TRIP TO ZZZ.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.