Atr ATR72 incident near St. Croix, January 12, 2010

The NTSB's narrative final · quoted from the NTSB record

During takeoff the No. 1 (left) engine fire warning illuminated in the cockpit. The pilot declared an emergency, shut down the No. 1 engine and discharged one fire bottle. The fire warning continued and the pilot discharged the second bottle; but the fire warning did not extinguish. The pilot performed an air turnback and landed the airplane uneventfully approximately 11 minutes later. Engine testing at the manufacturer’s facility revealed a large fuel leak emanating from the No. 2 fuel nozzle manifold adapter-to-transfer tube O-ring connection. Examination revealed two manufacturing defects in the No. 2 fuel nozzle manifold adapter. The first defect, poor surface finish, caused damage to the transfer tube O-ring during the installation process, initiating an internal fuel leak. The second defect, blockage of the internal safety tell-tale drain due to an improper machining and subsequent cleaning procedure, prevented the leaking fuel from flowing into the tell-tale drain and being detected by maintenance personnel. Examination of the transfer tubes revealed an undersized O-ring retention zone, which allowed the O-ring to fit loosely such that it was not capable of withstanding continuous maximum fuel pressure load. Eventually the O-ring failed to seal properly, fuel leaked and was ignited by the hot combustor case. The undersized O-ring retention zone was created during the cleaning and overhaul process of the transfer tube.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.