What happened
During the climb phase, approximately 1,000 feet above ground level, the crew of a Boeing 747-240 heard a thudding noise. This was immediately followed by a loss of power in the number two engine. The flight crew successfully completed an engine shutdown procedure and returned to the departure airport, where they performed an uneventful landing. No injuries were reported.
The aircraft, powered by General Electric CF6-50E2 engines, sustained damage to several components, including the number one engine, the left main wing landing gear doors, and both the leading and trailing edge flaps of the left wing.
The investigation
Mechanical examination of the number two engine revealed that the turbine rear frame and a portion of the fan mid shaft (FMS) from the low pressure turbine module were missing.
Investigators found a fracture face on the forward end of the FMS, which exhibited circumferential cracks and multiple fatigue origins. Additionally, certain areas of the FMS showed evidence of being heat affected. The investigation determined that this FMS had been previously installed in a different CF6-50 engine that had experienced a failure of the number 3 bearing inner race. While company personnel had inspected that previous engine, records indicated they did not inspect the FMS for heat-affected material. Fatigue cracks within these heat-affected zones contained debris and Sermetel paint.