Date: 201211
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Fuel Storage System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Situational Awareness; Human-Machine Interface
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; General Declared Emergency; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: In cruise flight approximately 45 minutes from takeoff the 'FUEL PAGE' on the lower ECAM displayed a fuel imbalance. The right wing tank was flashing. Because there were no ECAM Actions; the Captain referred to the QRH for the fuel imbalance problem. We determined the right wing had the correct amount of fuel and that the left wing was the problem. We contacted the flight attendants via the inter-phone and asked them to take a look out the window at the left wing and report back if they saw anything; possibly vapor; streaming off the wing. The Captain attempted to contact Dispatch [via the] phone but was unable. He then contacted Dispatch via ACARS. The flight attendants called back and confirmed they and a deadheading pilot saw fuel coming off the left wing. The Captain then went to the fuel leak section of the QRH and determined via the 'FUEL PAGE' and we agreed we needed to get on the ground because we were losing fuel fast. We determined the nearest airport and the Captain advised ATC we were going to divert and declared an emergency. I continued to fly the aircraft; ATC cleared us as requested. The Captain sent Dispatch an ACARS message with our plan and advised the flight attendants. I continued to fly the aircraft direct to the airport while the Captain was getting local ATIS; checking landing weight; runway performance data and working the radar because of the weather in the area. The Captain then completed the QRH procedure. We discussed shutting down the left engine if we could determine if the fuel was coming from the engine nacelle or engine. I said we were just south of the airport and would be on the ground in minutes; thus we decided to get the aircraft on the ground as quickly as possible. We landed uneventfully and taxied clear of the runway. The Captain had me shut down the left engine and switch off all of the left tank pumps. We then taxied to a holding pen where we shut the right engine down while CFR and a Mechanic inspected the aircraft. The leak had slowed to a drip and we were towed to the gate and deplaned.We later learned the seal that connected the oil to fuel heat exchanger to the fuel system had failed.




Synopsis: An A319 flight crew diverted to the nearest suitable airport upon discovering a leak in the left engine fuel system.