Date: 201506
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
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: Distraction; Troubleshooting; Confusion; Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Flight Crew
When detected: Aircraft In Service At Gate
Result: General Evacuated
Contributing factors: Human Factors; Aircraft
Primary problem: Human Factors

Narrative: Upon arrival into Airport ZZZ; 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 the MD-80 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 in ZZZ. I assume the smell was stronger in the cabin than in the cockpit since both the FO 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 FAs; 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. The FA 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 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 ZZZ 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: A fuel odor; later identified as an APU fuel issue; was detected as passengers began to deplane at the gate. A partial; uncommanded; evacuation was initiated by several passengers via the over wing exits. No injuries were reported.