In an interim factual report released the other day, the Australian Transport Safety Board essentially confirmed the sequence of events that led to the uncontained failure of one of Rolls-Royce Trent 900s on a Qantas Airbus A380 operating as QF32 on Nov. 4.
One of the many interesting aspects of the report is that the investigation team believes it has a better understanding of the failure mechanism involving the now infamous oil feed pipe on the engine.
According to the report
, which is available on the ATSB website, the team has determined that the oil pipe fatigue cracking shown in a photo in the December preliminary report is "not the area of interest" anymore. The new area of interest is located slightly to one side of the original.
The engine's intermediate pressure turbine disc failed as a result of an overspeed condition. According to the report, the disc failure was initiated by a manufacturing defect in an oil feed pipe that is machined to receive a coarse filter, according to the report. That section of the pipe sustained a fatigue crack during operations that led to an internal oil fire that weakened the IP turbine disk. "In turn, a circumferential fracture was induced around the disc, allowing it to separate from IP turbine shaft."
Below is figure 9 from the December preliminary report. This week's interim factual report takes the same photo, but moves the fatigue cracking label from the 11-1 o'clock configuration shown below to more of a 1-4 o'clock attitude.