The manufacturer’s classification, relating to the criticality of failure, of the HP/IP bearing support assembly was inappropriate for the effects of a fire within the buffer space and hence, the requirement for an appropriate level of process control was not communicated to the manufacturing staff.
In February 2012, Rolls-Royce advised the ATSB of the initiation of a major quality investigation into Trent 900 failure modes effects and criticality analysis (FMECA) inaccuracies. That investigation was commenced after it was identified that the potential for an IP turbine disc failure was not reflected in the Trent 900 FMECA certification documentation as a hazardous event. Safety action by Rolls-Royce included:
...the Trent 900 FMECAs have been reviewed and updated in light of the QF32 event. The Oil System and Transmissions FMECAs have now been updated.
The manufacturer advised that as a result of the review of the FMECA, it had reclassified the HP/IP bearing support from ‘unclassified’ to ‘reliability sensitive’. This change in classification would require the appropriate level of process control.
The ATSB is satisfied that the action taken by Rolls-Royce adequately addresses this safety issue and therefore makes no recommendation.
