Australian safety regulators have issued a final report on the engine failure and emergency landing on Nov. 4, 2010, including more details about the incident and a review of manufacturing failings at engine-maker .
The incident saw flight QF32 return to Singapore’sshortly after takeoff due to an uncontained failure in one of its engines. The cause has already been traced to an oil fire in the engine, resulting from a cracked oil feed pipe in the high pressure/intermediate pressure (HP/IP) hub assembly. The wall width of some oil feed pipes –including the one that cracked on the Qantas aircraft – was found to be thinner than design specifications due to a misaligned bore.
The Australian Transport Safety Bureau (ATSB) says in its final report that the crack in the oil pipe resulted from fatigue, and “developed over some time.” The crack became wide enough to allow oil to be released into the buffer space between the bearing chamber and the hot air surrounding the IP turbine disc. The oil was released as an atomized spray, and the air within the buffer space was hot enough for the oil to ignite.
The resulting fire eventually affected the IP turbine disc drive arm, resulting in the separation of the disc from the drive shaft. “Following the separation of the disc, the engine behaved in a manner different to that anticipated by the manufacturer during engine design and testing,” the ATSB says. The disc accelerated to a speed “in excess of its structural capacity” and burst into three main segments, which punctured the engine case.
Regarding Rolls-Royce, the ATSB found that the misalignment of the counter bores in the feed pipes “was the result of movement within the HP/IP bearing support assembly during manufacture and that a number of opportunities existed during the design and manufacture processes where the misaligned oil feed stub pipe counter bores could have been identified and managed.” According to the final report, “those opportunities were missed for a number of reasons, but generally because of ambiguities within the manufacturer’s procedures and the non-adherence by a number of the manufacturing staff to those procedures.”
The factors that led to the mistakes occurred over a number of years, and “highlighted the importance of manufacturers providing clear procedures and of personnel complying with those procedures,” the ATSB says. The safety agency says it has worked with the aircraft and engine manufacturers “to ensure that any identified safety issues were addressed and actions taken to prevent a similar occurrence.”
Responding to the final report, Rolls-Royce says it “supports the conclusions” of the ATSB. “This was a serious and rare event which we very much regret,” says Colin Smith, the manufacturer’s director for engineering and technology. “At Rolls-Royce we continually strive to meet the high standards of safety, quality and reliability that our customers and their passengers are entitled to expect. On this occasion we clearly fell short.”
Smith says Rolls-Royce has “already applied the lessons learned throughout our engineering, manufacturing and quality assurance procedures to prevent this type of event from happening again.” The company says it has also carried out its own investigations to understand and address what went wrong.
Specifically, the engine-maker says it has modified engine software to prevent a turbine disc from bursting due to over-speeding. It has also introduced better quality assurance processes with supporting training, improved manufacturing and design procedures, and revised the analysis of “the likely effects on an engine in the event of a component failure.”