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747 operators must watch for signs of wear and fatigue

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A rare engine malfunction on a Boeing 747-400 reminds operators to be alert to signs of wear and fatigue.

A Qantas Boeing 747-400 on a flight between Sydney and Singapore on 9 May 2011 experienced a malfunction in one of its engines that led the crew to shut it down. The aircraft continued safely to Singapore.

Operators of Rolls Royce RB211-524 engines have been alerted to the potential for wear and degradation of the IP turbine blade interlocking shrouds...

Indications from the engine included an increase in exhaust gas temperature and vibrations, which continued after the crew reduced the engine’s thrust. The ATSB found that the problem resulted from the failure and separation of a single intermediate-pressure (IP) turbine blade.

The blade had fractured following the initiation and growth of a fatigue crack from an origin area near the blade inner root platform. The manufacturer undertook detailed modelling and analysis. While it has not fully identified the root cause of the fracture, wear and loss of material from the turbine blade interlocking shrouds may have reduced the rigidity and damping effects of the shroud, contributing to the high-cycle cracking and failure.

The engine manufacturer issued a non-modification service bulletin in October 2011. The Bulletin required operators to perform a once-around-the-fleet inspection of IP turbine blades for missing shroud interlock material by June 2012. The aircraft operator advised that they had completed inspections across their fleet with no instances of excessive wear detected.

Operators of Rolls Royce RB211-524 engines have been alerted to the potential for wear and degradation of the IP turbine blade interlocking shrouds, with the possibility that this mechanism, if not detected and addressed, could lead to turbine blade cracking and loss. Service experience has shown that the probability of a failure of an IP turbine blade failure is very low and while it may cause malfunctions necessitating shutdown, the risks to flight are minor.

Read the investigation report AO-2011-062.

 
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Last update 04 January 2013