Date: 202104
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Airspace: Class B ZZZ; Class E ZZZ1
ATC / advisory: Tower ZZZ
Aircraft component: Fuel Storage System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Communication Breakdown; Time Pressure
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Fuel Issue; Inflight Event / Encounter Fuel Issue
Detector: Person Air Traffic Control; Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Aircraft

Narrative: Preflight and pushback were uneventful. We started the left engine and taxied out on one [engine] with an ATC designated takeoff time of XA:44L. We started the second engine during taxi; all uneventful. While holding #1 for takeoff; Tower informed us that a [other] airline crew had noticed what they thought might be a fuel leak. We immediately thought of returning to the gate; but then Tower came back and told us to disregard the previous concern and that it was a different aircraft with the possible leak. We were then cleared for takeoff. Just before switching us to Departure; Tower said that there appeared to be some vapor coming from around our left engine. We scanned the instruments to see if there were any parameters that would be cause for concern; but everything looked normal. It was also humid air; and sometimes contrails can be seen in those conditions coming from the flaps during takeoff. Once above 10;000 feet; the Captain called Flight Attendant 1 and asked him to look at the left wing/engine to see if he could see any leaks or causes for concern. Once his visual inspection was complete; he called back and said that he did see what appeared to be vapor coming from under the left engine. We then had him come up to the cockpit; and the Captain sent me back to confirm the Flight Attendant's concerns. I did see what appeared to be vapor coming from under the left engine; although it was difficult to tell exactly where the vapor was coming from. I went back up to the cockpit; told the Captain what I had seen; and we immediately began considering divert options. During this entire time; we were still climbing out and monitoring our fuel; including the fuel burn; engine fuel flow; and balance between wing tanks. During climb out; all of the indications seemed to be normal; but once we leveled off; the fuel burn began to diverge slightly from the planned fuel at each waypoint; and the imbalance between wing tanks began to grow; but it was all still within limits. Engine fuel flow was normal with no difference between the two engines. While continuing to monitor our fuel; ATC said that they had received a call from ZZZ Operations telling them that a runway inspection after our departure had revealed that we had leaked fuel on takeoff. At that point; we made the decision to divert. The weather was clear everywhere; and we had multiple good divert options. The Captain coordinated with Dispatch and we made the decision to divert to ZZZ2. The Captain spoke to the flight attendants and the passengers while I coordinated with ATC for the diversion. While enroute to ZZZ2; the fuel imbalance really became apparent. Just as were handed off to ZZZ2 Approach; we got the ECAM for FUEL IMBALANCE - FUEL LEAK PROCEDURES APPLY. We focused on the approach and landing; and planned to shut down the left engine once clear of the runway. We coordinated with ZZZ2 approach to have ARFF (Aircraft Rescue and Firefighting) meet us in the echo pad to confirm we weren't leaking fuel; and then follow us to our gate. We executed that plan without incident; parked the aircraft at the gate and deplaned the passengers.  Obviously we would have preferred to not take this airplane into the air. Maybe not a causal factor; but I would like to know if our ground crew noticed anything during or after engine start. We started the left engine first while still pushing back; and then made a right turn out that would have given them a good look at the problem engine. [The other] airline obviously noticed something; although once the Tower said that it was a different aircraft; we no longer considered a return to the gate. Once we had taken off; I felt that we handled the issue appropriately. Although I can't be sure if there were indications during engine start; I would hope that our ground crews are alert to any possible abnormalities that could arise during/after engine starting; including leaks.


Second narrative: After pushback; Ground informed us we had a wheels up time to ZZZ of XA:44. We started the left engine and decided to single engine taxi until we got closer to departure time. I made about 130 degree right turn from the ramp to the taxiway. When we got over to the other side of the terminal; we started the right engine; about 6 minutes prior to our wheels up time. As we were running the final checklist items the Tower called and said [another] airline had reported a plane with what looked like a fuel leak. as we were talking about it; the Tower called us back and said disregard it was a different aircraft. The Tower then cleared us for takeoff. After we were airborne the Tower told us it look like there was vapor coming off the left engine. All the engine parameters we normal so we continued our climb. After we got above 10;000 feet I called Flight Attendant 1 and asked him to go look at the left engine to see if there was any fluid he could see. He called back and said he saw something so I sent the First Officer back to see if he could tell what it was and where it was coming from. He said it was hard to tell but it did look like vapor coming from under the engine. The fuel was not out of balance more than normal and we checked the fuel against the flight plan and it was not significantly off so we continued the climb. We were looking at our options in case we had to divert when Center called and said ZZZ had inspected the runway after we took off and found fuel on the runway. At that point we tried to call Company OPS to get a phone patch to Dispatch but no answer. I got on the crew phone app on the iPad and got in touch with our Dispatcher and we decided to go to ZZZ2. As we went further towards ZZZ2 the fuel imbalance started to appear. It was very slow but it was noticeable. As we approached ZZZ2 at 12;000 just before talking to Approach; we got an ECAM [Electronic Centralized Aircraft Monitor] fuel imbalance; fuel leak procedure apply. We already knew we had a fuel leak. Landed in ZZZ2 without incident. Had the ARFF make sure the fuel leak had stopped after we shutdown the engine on the echo pad away from the gate. Taxied to the gate and deplaned the passengers.  I think when ATC called us back and said disregard then cleared us for takeoff; it took away any thought about returning to the gate.  I was very surprised our ground personnel did not notice the leak after we started the engine.


Synopsis: Flight Crew reported miscommunication lead to a departure with a fuel leak that required a diversion and a precautionary emergency landing.