Engine manufacturer Rolls-Royce initiated the removal of 53 Trent 900 engines from service following last November's uncontained engine failure on a Qantas Airways Airbus A380.
The Australian Transport Safety Bureau (ATSB), which released an update into the 4 November 2010 incident on 18 May, said the engines were removed due to concerns over the wall thickness of the engines' oil feed pipes.
Investigations into the uncontained engine failure have so far showed that it was caused by a manufacturing defect in an oil feed pipe, which caused a section of the pipe to thin and subsequently crack. The crack led to a oil leak and internal oil fire that weakened the engine's intermediate pressure (IP) turbine disk, which separated from the turbine shaft and punctured the engine case and wing structure.
At the time of the incident, there were three oil feed pipe modification standards for the IP turbine case of Trent 900 engines, said the ATSB. The IP turbine case has been identified as module 51. In previous media reports, these modification standards were referred to as "mod A", "mod B" and "mod C".
The first modification standard, known as FW48020, was applied to 42 engines manufactured between October 2005 and May 2008. The second, referred to as FW59326, was on 67 engines produced between July 2007 and March 2009. Finally, the latest modification standard, FW64481, was applied to 97 engines manufactured between March 2009 and January 2011.
The uncontained engine failure, which prompted inspections of Trent 900 engines, subsequently led to the removal of 53 engines from service, said the ATSB,
All 42 FW48020 standard engines were removed because Rolls-Royce was "unable to establish whether these oil feed tubes had been manufactured to specification", it added. This was due to "a lack of measurement records" for the pipes.
Another 10 engines with the newer FW59326 standard were also removed from service, said the ATSB. Seven of these 10 engines had oil feed pipe wall thicknesses of less than 0.5mm, the minimum stipulated by Rolls-Royce. The remaining three engines were removed after an evaluation of their manufacturing measurement records. Overall, measurement records for a number of FW59326 engines were also unavailable, said the ATSB, which did not specify the number.
Such records were available for engines with the latest FW64481 modification standard, but one such engine was removed from service as its oil feed pipe wall thickness did not meet the minimum limit as well.
All remaining Trent 900 engines met or exceeded this requirement, said the ATSB.
The investigation into the incident is still ongoing, with the ATSB expecting to complete gathering of information into the case by end-July. It aims to complete analysis of this information by May 2012.