A fractured turbine blade led to an engine shutdown on a Qantas 747 flight from Sydney to Singapore last year, the ATSB has found.
The flight landed safely in Singapore following the May 9, 2011 incident, which occurred roughly 100 km east of Bali.
The ATSB determined that a fatigue crack originating near the blade inner root platform on the Rolls-Royce RB211-524 engine caused an increase in exhaust gas temperatures and engine vibration, forcing the flight crew to shut down the engine.
Despite detailed modelling and analysis by Rolls-Royce, the underlying cause of the turbine blade failure has not been fully identified, the ATSB said. But it is believed that wear and loss of material from the turbine blade outer interlocking shrouds had reduced the rigidity and damping effects of the shroud and “may have contributed to the high-cycle fatigue cracking and failure,” the report added.
Rolls-Royce is continuing to study the underlying mechanism of the failure and issued a service bulletin in October 2011 instructing operators to inspect IP turbine blades for missing shroud interlock material.