Australian investigators have traced the cause of last November's Qantas Airways Boeing 747-400 contained engine failure to the engine's high pressure compressor (HPC) blade, which had broken off at the root.
The aircraft, registration VH-OJD, had departed Singapore for Sydney on 5 November 2010 when its number one Rolls-Royce RB211-524G engine failed while it was climbing through 2,000 ft above sea level. The aircraft returned to Singapore after the flight crew dumped fuel.
Inspections of the engine showed that the powerplant's HPC stage one blade had "liberated at the blade root", said the Australian Transport Safety Bureau (ATSB) in its final report into the incident.
"The liberated blade resulted in severe damage to all stages of the HPC," it added.
The blade root failure and subsequent damage to the HPC were "consistent with previous HPC stage one root failures", said the ATSB. Including the November 2010 incident, Qantas had experienced nine such blade root failures, it added.
Engine manufacturer Rolls-Royce had previously issued three service bulletins for the engine to address blade issues prior to the incident, said the bureau.
The latest of the three service bulletins, issued in February 2009, had introduced a modified blade "with a revised geometry" which "could provide protection against root failures". "The revised geometry was designed to be more tolerant to stresses induced by blade tip rub," said the ATSB.
However, this modified blade had not been incorporated into the engine that failed in the Qantas incident. Currently, about 18% of Qantas' RB211-524G engines have been modified to the latest standard, said the ATSB.
In response to the incident, Qantas is continuing to modify its engines to the latest standard at engine shop visits, it added.
"However, should the rate of failures increase significantly, a review of current modification policy will be undertaken," said the ATSB.
The engine involved in the incident was subsequently replaced and the aircraft was returned to service.
A RB211-524G engine was also involved in an engine failure on another Qantas 747 on 30 August 2010 shortly after take-off from San Francisco. In that failure, which was uncontained, ejected material punctured a hole in the engine and damaged the aircraft's leading edge flaps. The ATSB is still investigating that incident.
Source: Air Transport Intelligence news