I have been following this thread with interest, and have to agree with OE that turbomachinery faults can and do propagate through many levels.
QF32 brought to light the T900 issues with regard to spline wear. Helical spline coupling between compressor and turbine appears to me to be simple and ingenious - the torque generated by the turbine naturally closes the spline coupling. It is a solution conducive to modularity.
AD EASA AD 2010-0008 and its revision reveal problems with regard to IP shaft spline wear. To quote the AD, 'The shaft to coupling spline interface provides the means of controlling the turbine axial setting and wear through of the splines would permit the IP turbine to move rearwards. Rearward movement of the IP turbine would enable contact with static turbine components and would result in loss of engine performance with potential for in-flight shut down, oil migration and oil fire below the LP turbine discs prior to sufficient indication resulting in loss of LP turbine disc integrity.'
It seems an unlikely proposition that the AD and the QF32 incident are unrelated, but that is merely my own personal opinion. No matter what our engineering discipline might be, coincidences like this are rare.
From the data reproduced in ATSB preliminary report AO-2010-089, it appears that at time 02:00:22 oil temperature and pressure values begin to diverge from the recorded values for the other engines.
N3 vibrations increased to an extremely high and non-typical value, while N1 and N2 shaft speeds slowed. N3 shaft speed increased - possibly as the EEC increased fuel demand to compensate? Is this perhaps an indication of a bearing in some severe distress?
Here in this forum we can only speculate, however we must note that the AD makes no mention of the impact upon engine bearings in the event of shaft displacement due to spline wear - it only identifies the consequences of IP shaft rearward movement that would 'enable contact with static turbine components and would result in loss of engine performance with potential for in-flight shut down, oil migration and oil fire below the LP turbine discs prior to sufficient indication resulting in loss of LP turbine disc integrity'.
Returning to the ATSB published data, we observe unusual vibrations from the aircraft body lateral accelerometer at the time of 'thrust drop' and which is coincident with N1 and N2 shaft speeds dropping to zero.
Personally, I suspect that this coincides with the time at which bearing overheat (causing increased oil temperature) and mechanical interference with static LP turbine components may have caused the IP drive arm fracture.
Furthermore, and from the data published, I suspect that that the oil fire commenced at this point because this is when EGT commenced its rise. P30 collapse resulted in a fuel shut off - but I suspect the IPT disc was already in the 'departure lounge'. If I am correct, then the oil fire had little to to do with the IPT drive arm fracture. An engine surge possibly contributed more energy to the break-up of the distressed IPT disc than the resulting oil fire that was of short duration. I seem to recall that was already suggested in this forum but I may be incorrect?
I am therefore hypothesising that the stub oil pipe failure may therefore have resulted from HP/IP bearing faliure and a consequential and excessive HP vibration. Of course, the spline wear problem may have contributed to stub pipe fatigue. There seems to be some merit in returning to the IP spline AD issue and in particular to its cause.
Of course this is all speculative hypothesis based upon information and thinking published in the public domain. Please feel free to shout me down - I'm a new guy here and won't be offended. We can only learn.