Fatigue cracking in a turbine blade has been identified as the cause of an engine malfunction that required crew flying a Qantas Boeing 747-400 to shut down one of its engines in-flight.
The incident took place on 9 May 2011 onboard the aircraft, with registration VH-OJH, powered by Rolls-Royce RB211-524 engines, while it was operating a flight between Sydney and Singapore.
As the aircraft transited over Bali and climbed from 36,000ft (11,000m) to 38,000ft, the crew noticed an abnormal increase in vibration and exhaust gas temperature levels in the number four engine. They reacted by reducing the engine's thrust, but the vibration remained at near-maximum levels. The crew shut down the engine and continued to Singapore without further incident.
The investigation by the Australian Transport Safety Bureau (ATSB) found that the engine malfunction was because of the separation of a single intermediate-pressure (IP) turbine blade, which was a result of high cycle fatigue cracking. It also noted that wear to the interlocking shrouds of the IP turbine blades may have led to the development of the fatigue crack.
Shortly after the incident, Rolls-Royce issued a service bulletin calling for borescope inspections on the RB211-524 engines to confirm that the interlocks were in acceptable condition, with inspections to be completed by 30 June. It subsequently reissued the bulletin on 11 July to include crack acceptance and reinspection criteria.
The ATSB says Qantas conducted the inspections across its fleet of RB211-powered 747s but identified no other instances of excessive wear.