firstfloor (with apologies to wingsfolded)
You have essentially encapsulated the AD itself. There is concern that spline wear can lead to aft migration of the Aft Shaft, so indeed the Splines DO attenuate Axial movement, through the abutment face referenced in the AD. If one reads the Current AD, and prior AD's incorporated by Reference to them, one knows that the wear limit for the Spline is approximately 2mm, as measured on the "crest" of the Spline.
The Splines are helical, and allow for some inter rotation as the Thrust goes from Drive to Driven. Notice that the only (ball) bearing supporting the Aft IP Shaft is the #2 Thrust (Ball) bearing, and that this Shaft is directly supported through the Spline interface.
Nothing has been released as to exactly where the "Oil Fire" took place. Some assume at the Roller Bearings just forward of the IP Disc, others (myself) believe the fire occurred in the cavity containing IPC and HPC ball bearings. The telltale on the LPT Shaft suggests placement directly inside the joint where the Fore and Aft IP Shafts connect. The Aft IP Shaft end does not extend through the width of the Thrust bearing, meaning that all the energy between the two Shafts, is borne through a narrow section of the Splined Joint.
Keep in mind also that the Splines DO attenuate thrust (resist it), though not completely, they terminate at a ring that effaces the inner race of #2 Ball Bearing. Also take note that only a short section of Splines needs to fail to allow aft travel, they do not need to fail utterly.
I can appreciate your concern, but this is not nonsense.
Last edited by bearfoil; 24th Dec 2010 at 14:20.