Date: 201506
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Aircraft component: APU Fuel System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Confusion
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Flight Deck / Cabin / Aircraft Event Passenger Misconduct
Detector: Person Ground Personnel; Person Flight Crew; Person Flight Attendant
When detected: Aircraft In Service At Gate
Result: Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Upon arrival after completing the parking checklist and after opening the L1 door; the two forward flight attendants; the first officer; and I smelled a faint fuel smell which we all assumed and agreed was coming from outside the aircraft given that there was an aircraft right next to us fueling. Our APU was running and the winds were gusting from the northwest which was directly towards our tail at the gate.My first officer and I also discussed the likely possibility of a fuel spill somewhere near us on the ramp. In my experience on this aircraft is it is not uncommon to get a faint; exhaust like fume smell in the air conditioning system and thick condensation during hot; muggy summer nights such as this one was. I assume the smell was stronger in the cabin than in the cockpit since both the FO (First Officer) and I had our air vents closed. The flight attendants requested that I make a PA stating that everything was ok and there was no cause for alarm and we are aware of the condensation and smell; which I did. The two forward flight attendants also informed me that 'they opened the doors in back' which I thought meant that the two rear flight attendants had opened the rear aircraft doors for ventilation. Our number three and one FA's (Flight Attendant) meant to inform me that passengers were exiting through the over wing exits. This was a simple misunderstanding that was caused by task saturation in the cockpit; monitoring the APU indications; and determining the cause of the smell.I was later informed that passengers took it upon themselves to open all four over wing exits and exit onto the wing. I was told that it was estimated that 15-20 people were on each wing at one point. Our number two flight attendant vocally told passengers to stop exiting through the over wing exits. She had no chance to prevent passengers from initiating the uncommanded evacuation given the crowded aisle and interior that is typical of everyone standing when the seat belt sign is turned off. Our number four flight attendant made a PA instructing passengers to stop and to not evacuate or exit though the over wing exits. I did not hear this PA.The FO and I opened our air vents and the fuel odor got stronger and the condensation thickened. I then shut off the Ram Air; APU AIR switch; and both packs; which caused the fuel smell to lessen considerably in intensity and the condensation stopped completely. A man who works the ramp came up to the cockpit and told us we had fuel leaking out of the APU. I then told him to connect external power and I began to shut down the APU. I also told the first officer to go outside and inspect the APU fuel leak with the ops personnel. We informed ground of the fuel leak and we requested ARFF (Aircraft Rescue and Firefighting) to come inspect the area as a precaution; which they did.I was told by the gate agent that only one person had jumped off the left wing. I was told by operations and my flight attendants that a few passengers came back into the airplane through the over wing doors; and the rest exited the wings on baggage belt loaders. There were no injuries that I know of. This was confirmed by all four flight attendants and operations personnel. Upon inspection of the APU; fuel was in fact leaking out of the non-ram door area and the fuel spill was about fifteen feet in diameter. I was instructed by maintenance to pull 5 circuit breakers; which I did; secured the airplane with the securing check; and made the appropriate entries in the maintenance logbook.




Synopsis: After parking at arrival gate aircraft experienced an APU fuel leak. Fumes spread throughout the cabin before passengers de-planed. Over wing exits were deployed and some passengers temporarily exited onto the wings. APU was shut down and fumes dissipated.