Narrative:

After rotation on runway a; I noticed the right wing main tank fuel cap had come off and the fuel started vaporizing rapidly out of the tank. We were just about to respond to ATC when they notified us of the event from their perspective. We knew we needed to get the airplane on the ground as soon as possible as the fuel gauges showed we had lost over 200 pounds out of the tank in less than 30 seconds. The tower asked us which runway we wanted; we requested and were granted runway B considering that if we attempted a full pattern back to a; there was a high likelihood of exhausting our right fuel tank and causing a possible engine flameout. This required a steep right 270 degree turn and an immediate left 90 degree turn back to align the aircraft with the runway. We landed normally; and taxied back to FBO to refuel.

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Original NASA ASRS Text

Title: A BE90 MAIN WING TANK FUEL CAP CAME OFF AFTER TAKEOFF. THE FLT CREW MADE AN IMMEDIATE RETURN TO LAND AT THEIR DEP ARPT.

Narrative: AFTER ROTATION ON RWY A; I NOTICED THE R WING MAIN TANK FUEL CAP HAD COME OFF AND THE FUEL STARTED VAPORIZING RAPIDLY OUT OF THE TANK. WE WERE JUST ABOUT TO RESPOND TO ATC WHEN THEY NOTIFIED US OF THE EVENT FROM THEIR PERSPECTIVE. WE KNEW WE NEEDED TO GET THE AIRPLANE ON THE GND ASAP AS THE FUEL GAUGES SHOWED WE HAD LOST OVER 200 LBS OUT OF THE TANK IN LESS THAN 30 SECONDS. THE TWR ASKED US WHICH RWY WE WANTED; WE REQUESTED AND WERE GRANTED RWY B CONSIDERING THAT IF WE ATTEMPTED A FULL PATTERN BACK TO A; THERE WAS A HIGH LIKELIHOOD OF EXHAUSTING OUR R FUEL TANK AND CAUSING A POSSIBLE ENG FLAMEOUT. THIS REQUIRED A STEEP R 270 DEG TURN AND AN IMMEDIATE L 90 DEG TURN BACK TO ALIGN THE ACFT WITH THE RWY. WE LANDED NORMALLY; AND TAXIED BACK TO FBO TO REFUEL.

Data retrieved from NASA's ASRS site as of May 2009 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.