For the reasons described above and pending conclusion of the incident investigation, this AD requires repetitive inspections of the Low Pressure Turbine (LPT) stage 1 blades and case drain, HP/IP structure air buffer cavity and oil service tubes in order to detect any abnormal oil leakage, and if any discrepancy is found, to prohibit further engine operation.
Someone is going to have to help me out here.
We have a seal structure that for lack of a better term has a weepage and drain tubes to handle normal flow provided that there is a proper pressure supplied in the air buffer cavity.
So for lack of a better analogy then possibly there is some disturbance in the air buffer pressue cavity supply that can happen at higher thrust settings allowing the seal to become ineffective due to the higher gas velocities at or near the air supply point for the air buffer cavity.
Just a wild guess, if so could be an easy fix to the design.
VFD