Event Description
During the climb-out phase of flight, the flight crew observed a 15% decrease in the right engine's exhaust pressure ratio (EPR). Shortly thereafter, a loud bang was heard, followed by the failure of the number 2 engine. The crew executed an engine shutdown and flew the aircraft back to the departure airport without further incident.
Examination Findings
Initial examination of the failed engine revealed that the right engine top cowling had separated from the aircraft. Additionally, the lower section of the combustion case was found to be split. The engine was subsequently removed for a more detailed teardown inspection.
Investigation Results
During the engine teardown, investigators discovered that the lock ring for the number 5 fuel nozzle nut had been mis-assembled. This mis-assembly resulted in a reduction of the torque applied to the fuel nozzle nut, which in turn inadequately compressed the seal for the number 5 fuel nozzle. Consequently, the fuel nozzle leaked, allowing fuel to escape. The leaking fuel caused a localized overtemperature of the outer combustion chamber case at the 6 o'clock position, leading to the structural failure observed.