Turbine D
I was referring to old engineer's comments on the bearing case. Re: T/O LAX. It is the availibility of rated thrust that allows a 380 (Gross) to take off at all from LAX?
The area between HP/IP "support structure" seems to mean to most people the diaphragm supporting the roller bearings. It isn't important either way. The roller bearings I believe are victims, not progenitors. Anyway, the bearing box is affixed one assumes with the very bolts the AD demanded be borescoped, though a borescope could not conceivably measure torque. It could present damage to the rolling surfaces and raceways, assumedly this result would give RR the go-ahead to remove the engine, or prevent further use, (grounding).
Now, if the stub pipe entered service looking as it did in the pic, I'm quite surprised. One sees random scoring on the bore's wall, a channel cut into the bore, (the supposed Q/A blunder) and fractured rim with an ugly circular wear deficit on the coupling's face. This is caused by vibration, and I'm taking wagers. The couple may have failed, though it may have stayed attached, and been uncoupled at disassemble.
The OIL FIRE is almost certainly the result of A and B, as you say.
A........High powered vibration of several expressions.
B....... Severe fatigue due Oiling issues and Raceway, ball wear caused by the combination, oil starvation and vibration. Ball bearings are a "seam", and can vibrate at their own rate, driven by vibs on either side of the support. They are not rigid, and are subject to remarkable load that can reverse several times a second. Now if the bearings wear enough, the axial travel expands, and the IPT can contact the Stator inner, and the Vanes Platform, Outer. This is not my text, but a straightforward paraphrase of the AD.
C........loss of Oil line integrity, and fire. There is no evidence of a fire in the LPT cave, and most interpretations of the fire have it in the annulus between the HPT and IPT. This could of course blow the bearings to bits (rollers), but something simpler and more mechanical is likely to have happened. No need for Occam on this one. Follow the AD, the Wear, the concern, the Burst, the Grounding, and the struggle to refit, repair, and replace. Oil Fire is merely the penultimate failure, not the cause.
Look for insidious Fan Vibration, Fan shaft IPC damage, and weakening of the area around the HPT bearing and the IPT bearing. there is a 20,000 RPM net interface between these bearings. Oil fire is patent on test, though not widely known. The fire is of course a primary suspect, but needn't be at all the procuring cause of failure, just as overspeed is unlikely, given the proximate architecture of the IPT/Stator and the almost certain instantaneous loss of IPT Blades due to Axial Drift aftward. The LPT shaft and Turbines are remarkably free of damage, or even discoloration. Had the IPT blades been lost instant, the Massive Pressure in the LPT barrel would have (and seems to have) blown everything out the bolted together LP case and the IP case separation and missing pieces of case.The HPT was intact, and prevented access to any portion of the Gas path forward of its dynamic seal. Hence the exit of everything out the visible holes in the case.
Again, this is not my conclusion, and certainly not unsupported by the history prior to, the damage during, and the spin around the repair/refit/replace. It is what the Authority predicted, and probably with Rolls critical input. But no, we want it to be a duff piece of tube, flying in the face of enormous effort (unsuccessful) to prevent this very thing from occurring. Spline wear-vibration, oil issues. Bearing wear-vibration, oil issues, Fire-vibration-oil feeds.
The EEC, EMU. Next................
Last edited by bearfoil; 4th Jan 2011 at 00:01.