What happened
The aircraft was performing its first flight of the day following recent maintenance on the engine fuel system. While the aircraft was climbing through 7,500 feet, the fire warning system activated. In response to the alert, the flight crew extinguished the fire, secured the affected engine, and performed an emergency return to the departure airport.
The investigation
Post-flight examination of the engine identified a fuel leak originating at the #7 and #8 fuel manifold nozzle transfer tubes. Investigators discovered that the fuel manifold transfer tube locking plates for both the #7 and #8 nozzle assemblies had been improperly installed. Additionally, the 'O' rings associated with these assemblies were found to be cut and scratched.
Further inspection of the engine's overboard (fuel/oil) drain line revealed it was approximately 99% blocked by a carbon-like substance. The investigation also noted that the engine's fuel manifold and turbine support case drain lines were positioned directly opposite one another within the drain manifold. The fitting for the turbine support case drain line utilized an oversized and offset crush gasket. Evidence of fire was found in the nacelle interior, which exhibited a flame-discolored area located directly beneath this specific fitting.