Bearfoil
You propose a "false bearing" developing between IPT and LPT NR. You also suggest two possible causes for this contact. Fire is one, and Shaft failure another.
In a design of an engine, fire and shaft failure are important items that must be addressed due to severe resulting consequences. In the Trent 900, I think fire was the culprit, not shaft failure.
I would offer that in the two previous failures, the disc was retained because there was not overspeed. In one case, (Miami) the Disc had separated from the Drive Arm in a "Circumferential Fracture".
I Agree.
For the reputed cause of QF32 uncontained failure, RR has offered "Oil Fire". Oil Fire in the Roller Bearing case was due to uncontrolled combustion specifically (Your tenet).
Not exactly. The fire did not occur inside the roller bearing box, it occurred in the cavity which is part of the frame next to the IPT disc.
From the EASA AD's:
An uncontained engine failure has recently occurred on a Rolls-Royce RB211
Trent 900 involving release of high energy debris and resulting in damage to
the aeroplane. Analysis of the available elements from the incident
investigation shows that an oil fire in the High Pressure / Intermediate Pressure
(HP/IP) structure cavity may have initiated a sequence of events leading to
rupture of the drive arm of the IP Turbine (IPT) disc and subsequent overspeed and burst of that same disc.
The IPT rotor did overspeed on the Trent 900 and there was evidence of molten metal splatter on the recovered portion of the fractured disc.
Again, from a EASA AD introducing a electronic software modification:
Engine Fuel & Control – Intermediate Pressure Turbine Overspeed
Protection System Software – Introduction
The LPT shaft was protected during all of this event by the presence of the IPC/IPT shaft. Everything went outward, some rearward but not as much as if the IPT rotor blades had born the brunt clashing with the Stage 1 LPT nozzle vane airfoils.
Do you have an opinion on the generation and advance of the "Oil Fire"? How do you read the AD's prior to November 4? Do you consider the Splines as exonerated?
I think everything in the Trent engine was operating normally. Remember, the engine had been inspected for spline wear and must have passed the requirements for continued operation as no corrective action was required. Obviously spline wear at an early stage of engine life is of concern and requires a more permanent corrective other than shortened periodic inspection. I do wonder if there is unusual vibration or harmonics being passed through the system when splines are wearing so rapidly. This vibration, if present, could affect anything in the torque field.