Date: 201203
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B747-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Aircraft component: Fuel Storage System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Attendant
When detected: Taxi
Result: Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Environment - Non Weather Related
Primary problem: Aircraft

Narrative: Taxiing out for takeoff on the parallel taxiway near the approach end of Runway XXL; the Flight Attendant at door 4R called the flight station and informed us that he was seeing some kind of liquid coming off the right wing. I sent a First Officer downstairs to investigate. He reported that he could see what appeared to be fuel venting from the right outboard wing area; but with winds blowing out of the south between 20-28 knots it was hard to determine exactly where the fuel was coming from. We notified Tower that we would have to return to the gate for maintenance. A company aircraft was on the north side of the parallel runway at the approach end waiting for takeoff. He had an excellent view of our right wing area as we turned on to Runway XXR and we asked him to let us know what he saw. He confirmed we had fuel venting from the outboard section of our right wing. As we cleared the runway on to Taxiway C; engine #4 was shut down as a precaution. We notified Maintenance; Customer Service; and Dispatch of our situation and Tower notified the fire department of our fuel venting. A mobile fire department vehicle was dispatched to look at our right wing as we taxied to return to the terminal on Taxiway C. The fire department personnel confirmed fuel venting and dispatched several fire trucks to follow us in. We shut down all engines and requested a tug to tow us in as a precaution. Maintenance instructed us to tow to the maintenance area. We arrived at the maintenance parking area and Maintenance and the fire department came on board as did an Airport Officer to assist us as necessary. The fuel venting slowly subsided and Maintenance drained some fuel and the venting eventually stopped completely. We were at the Maintenance parking for just over an hour and our passengers were provided beverages and food under the supervision of our Lead Flight Attendant. I kept them apprised of our situation and they were able to use the bathrooms and make cell phone calls. About an hour later; the fire department gave their permission for us to tow to the International Terminal. This was a better alternative than trying to remove passengers and their luggage and bus them to the terminal. We departed the Maintenance area under tow. Customer Service met us as did Maintenance and we were informed the flight was now canceled for maintenance and would be rescheduled to depart the next morning. We contacted the crew desk; confirmed we would be the flight crew on that flight the next day and proceeded to the layover hotel. All ground support agencies were extremely professional and helpful. A job well done goes to the Flight Attendant for diligently noticing the fuel venting and notifying the pilots of what he observed.




Synopsis: A B747-400 Flight Attendant noticed fuel venting from the outboard section of right wing during taxi out. After confirming the situation; the Captain eventually taxied to the gate where the flight was canceled.