What happened
On 17 December 2009, a Boeing 747-200F cargo aircraft, registration 9V-JEB, departed Singapore Changi Airport bound for Hong Kong. Approximately five minutes into the flight, while climbing through 7,000 feet, the crew heard a loud bang and noticed the smell of burning oil in the cockpit. The No. 4 engine experienced a rapid drop in oil pressure, oil quantity, and rotor speeds.
Following the event, the crew shut down the affected engine and initiated an emergency return to Changi Airport. The aircraft landed safely without any injuries to the six people on board. Post-flight inspections confirmed that the No. 4 engine had suffered an uncontained failure, with significant internal components missing and debris causing damage to the aircraft's pylon, wing, and vertical stabilizer.
The investigation
Investigators from the TSIB conducted a detailed teardown of the General Electric CF6-50E2 engine in Turkey. The examination focused on the damage to the low pressure turbine (LPT) and high pressure compressor (HPC) sections. The investigation established that the stage 3 LPT rotor and several subsequent blade sections, along with the exhaust nozzle and center body, had been ejected from the engine.
Technical analysis revealed that the S3 LPT disk forward spacer arm had undergone a circumferential fracture. Metallurgical testing of the HPC blades also identified high cycle fatigue as a factor in the failure of certain compressor components. Furthermore, the investigation looked into the communication channels between the operator and the engine manufacturer, as well as the operator's internal maintenance monitoring processes.
Findings
- The uncontained failure was caused by a circumferential fracture of the S3 LPT disk forward spacer arm.
- This failure was driven by vibration resulting from high pressure rotor imbalance.
- The operator's internal documentation regarding the evaluation of engine health monitoring recommendations was inconsistent and lacked clear records of the decision-making process.
- There was a breakdown in safety communication, as the operator had failed to update the engine manufacturer regarding changes in personnel responsible for receiving safety information.
- The engine manufacturer's system lacked a mechanism to confirm that critical safety alerts were successfully received by operators.