Turbine D
All things otherwise equal, the common (least obtuse) factor would be oiling. Oil can withstand very high mechanical friction, given tolerances close enough to prevent metal/metal contact. If so, the problem distills to lack of oil, or too large tolerances, or some combination. I think the oil is not at fault, so it is most likely wear, beyond limiting Lubrication values. This is to say, Mechanical forces sufficient to diminish Oil's filmic properties. The TRENT is a proven concept, so what's new? More and More Thrust?
I think not. I believe it may have to do with un-attenuated vibration and/or insufficient oiling. Now the Authority has identified Oiling properties as the root, so what follows on is more than likely mitigable circumstances: eg. Vibration.
The RR Bearing mechanism seems to be proprietary. Will the need to know the results of investigation trump Commercial Protections? I would think so.
"We know the problem, but it's a secret, and we fixed it."
.....Won't "Fly" I think.
Edit: What are your thoughts on the "Stub Pipe? I would rule out flubbed manufacturing. First, the "Line Bore" mistake would snap any machining tool I'm familiar with. There is insufficient mass to counterbalance the "eccentric". The ledge on the bore is too smoothe to class as defect in manufacturing, I see it as wear induced. The "defect on the tip" is likewise not due to machining, the metal composition of the pipe would have left resistance marks, "chatter". It is too smoothe, suggesting a polish, and why would anyone polish an incision into the lip if the goal was inspection? The fractures are fresh, they are rough, and unsmoothed. The alignment of the smooth "Off-Bore" defects with the fracture location suggest a common axis of wear, suggesting a rotating mass in the bore (aspirator?), or a coupling that is misaligned. All the defects exhibited in the Photograph happened after the installation of the engine, and the beginning of service, IMO. IMO.
One other thing. If a borescope can be inserted into the Bearing cavity, and there are "Vanes" on the Stub Tip, no wear would be noticed. I think this is why the Authority in the AD required an assessment of "Clogging" at the Vanes?
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