American Eagle AT72 at Saint Croix on Jan 11th 2010, engine fire on takeoff
Last Update: August 9, 2013 / 21:12:39 GMT/Zulu time
The sealing failure between the fuel nozzle adapter assembly and fuel transfer tubes that allowed fuel to leak into the nacelle fire zone where it was subsequently ignited by the hot combustor case. Contributing to the failure was a combination of manufacturing defects of the fuel nozzle adapter assembly by the manufacturer and incorrectly overhauled fuel transfer tubes by the engine manufacturer. Contributing to the incident was a second defect of the fuel nozzle adapter assembly by the manufacturer which prevented maintenance personnel from detecting the internal fuel leak.
The NTSB reported that initial examination of the engine showed a large fire had occurred, the hydraulic system and engine oil systems were intact, only evidence of where the fire originated was a small wetted area on a fuel nozzle and a coked fuel nozzle heat shield. Further analysis identified following sequence of events:
"The primary O-ring was initially damaged when it was inserted into the fuel nozzle manifold adapter which had the rough internal bore. The damaged primary O-ring started leaking sometime after assembly. The blockage of the cross-drilled hole in the fuel nozzle manifold adapter prevented fuel from passing to the telltale drain where a mechanic would detect the primary O-ring leak. The secondary O-ring now acting as the primary O-ring prevented the fuel from leaking out of the manifold assembly and onto the hot combustor case. The secondary O-ring was unable to withstand the increased fuel pressure in the manifold because the tolerances of the transfer tubes were beyond limits causing a loose fit between the O-ring and the transfer tube. This loose fit caused the secondary O-ring to become extruded and eventually fail causing the external leak and undercowl fire."
This article is published under license from Avherald.com. © of text by Avherald.com.
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