Narrative:

First officer did walk around when we got to aircraft. No problems. Near departure time smelled fuel. Upon investigation we found out there had been a fuel spill and even with the aircraft not being fueled; there was fuel spilling out of the naca fuel vent under the right wing. I had the aircraft de-boarded and turned off the air conditioning packs. The problem was written up in the logbook and maintenance eventually fixed the problem. It was explained to me there was a faulty valve that didn't close and that he got it to close and the leak stopped. The fuel leaking prior was residual and there was just fuel under the wing and on the ramp. The fire department sprayed the wing and the spill on the ground; after they mopped up what they could. We boarded got a new release and left. The fuel was 8.51 in left tank 15.7 or so in the center and 8.71 in the right. After takeoff climbing through 10;000 ft I got a call from the flight attendant at the rear of the aircraft telling me that we had a spray off the right wing about 5 inches in diameter near the wing and winglet area. It was night and the white wing nav light lit it up. Upon further discussion; I determined this was not a vortex from humid air as the other wing was not the same. The suspected fuel did not dissipate only became a smaller diameter when we sped up. No checklist in the QRH applied to a suspected wing fuel leak; only an engine fuel leak. We elected to return for landing and declared an emergency. Unfortunately I used the term 'I am declaring an emergency' rather than ICAO 'mayday mayday mayday.' there was some confusion about the nature of our emergency and the request for arff to follow the aircraft and assess the leak. We landed and returned to a hardstand area; arff followed to hardstand saw no fuel leaking. The fuel was 8.51 in left 12.0 or so in the center and 8.71 in the right. I was concerned about faulty valves in wrong positions; why did the right tank not decrease if it was over full or some fueling issue? Also our nearest alternate was an airport 300+ NM away. There was some confusion about the nature of the emergency due to language; and some confusion to where to park. Some hold points were not on the airport diagram. I believe the ATC was giving us the terminal gate name not the number for the ramp. The flight attendants did a great job; the passengers noticed the spray as well and were happy to be back.

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Original NASA ASRS Text

Title: B737-800 flight crew is informed of a fuel leak from the right wing vent during passenger boarding. Maintenance is called and a faulty fueling valve is discovered and closed. After departure fuel is reported venting from the right wing tip by a Flight Attendant and the crew elects to return to the departure airport.

Narrative: First Officer did walk around when we got to aircraft. No problems. Near departure time smelled fuel. Upon investigation we found out there had been a fuel spill and even with the aircraft not being fueled; there was fuel spilling out of the NACA fuel vent under the right wing. I had the aircraft de-boarded and turned off the air conditioning packs. The problem was written up in the logbook and Maintenance eventually fixed the problem. It was explained to me there was a faulty valve that didn't close and that he got it to close and the leak stopped. The fuel leaking prior was residual and there was just fuel under the wing and on the ramp. The fire department sprayed the wing and the spill on the ground; after they mopped up what they could. We boarded got a new release and left. The fuel was 8.51 in left tank 15.7 or so in the center and 8.71 in the right. After takeoff climbing through 10;000 FT I got a call from the Flight Attendant at the rear of the aircraft telling me that we had a spray off the right wing about 5 inches in diameter near the wing and winglet area. It was night and the white wing Nav light lit it up. Upon further discussion; I determined this was not a vortex from humid air as the other wing was not the same. The suspected fuel did not dissipate only became a smaller diameter when we sped up. No checklist in the QRH applied to a suspected wing fuel leak; only an engine fuel leak. We elected to return for landing and declared an emergency. Unfortunately I used the term 'I am declaring an emergency' rather than ICAO 'Mayday Mayday Mayday.' There was some confusion about the nature of our emergency and the request for ARFF to follow the aircraft and assess the leak. We landed and returned to a hardstand area; ARFF followed to hardstand saw no fuel leaking. The fuel was 8.51 in left 12.0 or so in the center and 8.71 in the right. I was concerned about faulty valves in wrong positions; why did the right tank not decrease if it was over full or some fueling issue? Also our nearest alternate was an airport 300+ NM away. There was some confusion about the nature of the emergency due to language; and some confusion to where to park. Some hold points were not on the airport diagram. I believe the ATC was giving us the terminal gate name not the number for the ramp. The flight attendants did a great job; the passengers noticed the spray as well and were happy to be back.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.