NTSB Identification: ANC05IA020.
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Nonscheduled 14 CFR (D.B.A. Polar Air Cargo)
Incident occurred Wednesday, December 29, 2004 in Anchorage, AK
Probable Cause Approval Date: 12/20/2005
Aircraft: Boeing 747-123, registration: N858FT
Injuries: 3 Uninjured.
NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.
The 14 CFR Part 121 international cargo flight had an under-cowl fire in the number four engine during takeoff. The crew shut down the engine, activated the fire extinguishing system, and returned to the airport. An inspection of the engine disclosed that the entire outboard engine cowl was missing, and the engine had extensive fire damage. A fuel tube to the oil cooler was observed to have separated from the coupler attaching it to the oil cooler, leaving a gap of about one-half inch. The oil cooler uses the heat-exchange principle, exchanging heat via high quantity fuel flow. The fuel tube is about one and one-quarter inches in diameter, and has a working pressure of about 200 psi. Separation of the fuel tube assembly connection occurred at the brazed sleeve joint between the ferrule and the fuel tube. An examination and X-ray mapping revealed that the brazed joint did not meet the minimum requirement for filler material adhesion required in Aerospace Material Specification (AMS) 2664F for silver brazing.
The National Transportation Safety Board determines the probable cause(s) of this incident to be: The failure of a high-pressure fuel line fitting, which resulted in an engine fire during takeoff/initial climb. Full narrative available
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