Narrative:

Prior to flight asked FBO to top all tanks, completed preflight before fuel truck finished filling left main and auxiliary tanks, therefore didn't check those. Taxi and cleared for takeoff. On liftoff advised by tower and observed left auxiliary gas cap came loose. Gas escaped (18.8 gallons). Cleared for go around, landed and returned to FBO for refueling. FBO acknowledged error. No charge for fuel. Departed without incident. Airport police took notes for report.

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Original NASA ASRS Text

Title: RETURN LAND SITUATION AFTER AN ALERT TWR CTLR WARNS DEP TFC OF FUEL SIPHONING FROM L TANK ON TKOF.

Narrative: PRIOR TO FLT ASKED FBO TO TOP ALL TANKS, COMPLETED PREFLT BEFORE FUEL TRUCK FINISHED FILLING L MAIN AND AUX TANKS, THEREFORE DIDN'T CHK THOSE. TAXI AND CLRED FOR TKOF. ON LIFTOFF ADVISED BY TWR AND OBSERVED L AUX GAS CAP CAME LOOSE. GAS ESCAPED (18.8 GALLONS). CLRED FOR GAR, LANDED AND RETURNED TO FBO FOR REFUELING. FBO ACKNOWLEDGED ERROR. NO CHARGE FOR FUEL. DEPARTED WITHOUT INCIDENT. ARPT POLICE TOOK NOTES FOR RPT.

Data retrieved from NASA's ASRS site as of July 2007 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.