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While cruising at flight level 220 between Kimmi and Ablok, approximately 220 NM north-west of Cairns, the crew of the Dash 8 heard a muffled sound that was followed by an increase of the left engine inter turbine temperature. The crew reduced the engine power and returned the aircraft to Cairns.

The engine examination revealed that the reported problem was the result of a failure of the number 5 bearing. The bearing cage contained two cracks and was open. Some roller pockets in the bearing cage were enlarged and distorted, which allowed the rollers to rotate in the plane of the cage. Some other rollers were immobilised and contained large flats. Six of the 12 rollers had a smaller diameter than the rest. Their surface was abraded and smeared, consistent with heavy contact loads.

Because of several similar failures, the engine manufacturer had issued service bulletin number 21472R2, on 25 February 1999, introducing an improved number 5 bearing. The service bulletin advised that engines of serial numbers subsequent to the failed engine were already fitted with the new bearing. It further recommended that number 5 bearings on all other Pratt & Whitney PW100 engine models should be replaced when the engines were disassembled and access was available. The improved bearing had not been installed on this engine.

General details
Date: 25 June 1999 Investigation status: Completed 
Time: 1230 hours EST  
Location   (show map):407 km NW Cairns, Aero. Investigation type: Occurrence Investigation 
State: Queensland Occurrence type: Abnormal engine indications 
Release date: 15 November 2000 Occurrence class: Technical 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft details
Aircraft manufacturer: de Havilland Canada 
Aircraft model: DHC-8 
Aircraft registration: VH-SDA 
Serial number: 482 
Type of operation: Air Transport Low Capacity 
Damage to aircraft: Minor 
Departure point:Cairns, QLD
Departure time:1130 hours EST
Destination:Horn Island, QLD
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Last update 13 May 2014