Aviation safety investigations & reports

In-flight engine malfunction – Boeing 747-438, VH-OJH, 100 km south-east of Bali International Airport, Indonesia, 9 May 2011

Investigation number:
AO-2011-062
Status: Completed
Investigation completed

Summary

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What happened

On 9 May 2011, a Qantas Airways Limited Boeing 747-400 aircraft, registered VH-OJH, was enroute from Sydney, NSW to Singapore, when during climb from 36,000 ft to 38,000 ft, the crew noted abnormal indications from the No.4 engine. The indications included an increase in both the exhaust gas temperature and vibration levels. The flight crew reduced the engine’s thrust, however the vibration continued near maximum levels and the engine was subsequently shut down.

The aircraft continued to Singapore for a safe landing and disembarkation of the passengers and crew.

What the ATSB found

The increase in the exhaust gas temperature and vibration from the No.4 engine was a direct result of the failure and separation of a single intermediate-pressure turbine blade. The turbine blade had fractured following the initiation and growth of a fatigue crack from an origin area near the blade inner root platform. Detailed modelling and analysis was undertaken by the engine manufacturer following the occurrence, and while the root cause for the IP turbine blade failure was not fully identified at the time of this report, it was considered that the 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 manufacturer has advised that they are continuing work to understand the underlying mechanism of the failure and will advise the ATSB if any further information is obtained.

What has been done as a result

The engine manufacturer issued non-modification service bulletin (NMSB) 72-G739 in October 2011, which instructed operators to perform a once-around-the-fleet inspection of IP turbine blades for missing shroud interlock material. Accomplishment of this task was recommended by June 2012, taking advantage of any earlier planned maintenance opportunities. The operator indicated that they had completed inspections across the fleet with no instances of excessive wear identified.

Safety message

Operators and maintainers of Rolls-Royce RB211-524 engines are alerted to the potential for wear and degradation of the intermediate-pressure 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, however, that the probability of an intermediate-pressure turbine blade failure (from any mechanism) is extremely low, with only three reported occurrences across the RB211-524 engine operating history. While blade separation will likely cause malfunctions necessitating an in-flight engine shut down, the associated risks to the safety of continued flight are minor, in the context that such failures are very likely to be contained (i.e. no liberated debris) and procedures for managing engine failures in transport-category aircraft are detailed and effective.

Download Final Report
[Download  PDF: 1.66MB]
 
 
Alternate: [Download  DOC: 1.43MB]
 
General details
Date: 09 May 2011   Investigation status: Completed  
Time: 2336 UTC    
Location   (show map): 100 km south-east of Bali International Airport, Indonesia   Investigation type: Occurrence Investigation  
State: International   Occurrence type: Engine failure or malfunction  
Release date: 19 December 2012   Occurrence class: Technical  
Report status: Final   Occurrence category: Incident  
  Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 747  
Aircraft registration VH-OJH  
Serial number 24806  
Operator Qantas  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Sydney, NSW  
Destination Singapore  
Last update 14 November 2018