Jump to Content

Factual information

Summary

On 22 October 2004, at approximately 0510 Australian Eastern Standard Time, an Australian registered (VH-EBU), Boeing Company 747-338 aircraft, was being operated on a scheduled passenger service from Honolulu, in the United States of America, to Sydney, Australia.  Near the instrument flight rules reporting point ISTEM, located approximately 700 nautical miles north-east of Sydney, the flight crew had been cleared by air traffic control to climb from flight level (FL) 340 to FL360.  When the crew set climb thrust on the engines, they reported that they felt a vibration in the aircraft and the number-3 engine airborne vibration monitor lights illuminated, indicating that the number-3 engine had an abnormal vibration level.  The crew shut down the number-3 engine and continued to Sydney.

A subsequent engineering examination of the number-3 engine indicated that a low pressure turbine (LPT) second stage blade had failed.  The engine, a Rolls-Royce RB211-524D4 turbofan, serial number 12682, was removed from the aircraft and the recovered LPT blade fragments were sent to the Australian Transport Safety Bureau (ATSB) for detailed examination.  At the time of the failure, the engine had a recorded time in service of 71,200 hours and 11,221 cycles since new and 14,787 hours and 2,513 cycles since repair. The ATSB examination revealed that the LPT blade had failed as a result of high cycle fatigue cracking (HCF), originating at an anomalous inclusion in the blade material. Details of the failed LPT blade examination are contained in the Technical Analysis report (Appendix A).

Previous LPT blade failures

The engine manufacturer reported that there had been three previous LPT blade failures in this engine type.  Two of the events were attributed to engine fuel mal-distribution and subsequent blade excitation, leading to HCF and failure.  There was no detail provided on the third event. The failure of this blade type was a rare event, given that the engine type has accumulated in excess of 25 million flight hours in service.

LPT blade life monitoring

The LPT blades in the Rolls-Royce RB-211 series engines do not have a defined blade retirement life and are maintained on condition; being monitored throughout their service life by inspection and engine trend analysis.  Once the engine LPT performance parameters change to pre-determined levels, the engine is removed for overhaul or repair.  During engine overhaul, the LPT blades are subject to inspections to determine if they meet the dimensional requirements for continued service.  LPT blades may be exchanged between various engines during this process.

The engine manufacturer's Time Limits Manual for RB211-524 series engines specified that LPT blades are 'Group B' parts and states that it is 'considered necessary to life mark or maintain life records of Group B parts'. While it was evident that engine serial number 12682 had been overhauled in accordance with the manufacturer's requirements, the individual LPT blades' service lives were not recorded and so the age and life history of the failed blade could not be determined.

 
Share this page Comment