What happened
During the initial climb-out phase of flight, the flight crew observed a significant anomaly in the right engine's performance. Specifically, they noted a 15% decrease in the Engine Pressure Ratio (EPR) for that engine. This drop in pressure was immediately followed by a loud bang and the complete failure of the number two engine.
Following the mechanical failure, the crew successfully shut down the affected engine. They then proceeded to fly the aircraft back to the departure airport without further incident. The flight landed safely, allowing for an immediate ground inspection of the aircraft.
The investigation
An initial examination of the aircraft on the ground revealed substantial damage to the right engine. The top cowling had separated from the engine assembly, and the lower section of the combustion case was found to be split open.
To determine the root cause, the engine was removed from the aircraft and subjected to a detailed teardown. This inspection uncovered a critical maintenance error: the number five fuel nozzle nut lock ring had been misassembled during previous servicing.
This misassembly prevented the correct torque from being applied to the fuel nozzle nut. As a result, the seal on the number five fuel nozzle was not adequately compressed. The compromised seal allowed fuel to leak into areas where it should not have been present. This leakage led to a local overtemperature condition in the outer combustion chamber case at the six o'clock position, ultimately causing the structural failure of the cowling and combustion case.