Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Pratt & Whitney PW4000 series turbofan engines. This proposal would reduce life limits of certain 4th stage low pressure turbine (LPT) disks. It would also allow the original life limits of the disks to be restored if reoperation is performed to incorporate the original slotted cooling hole configuration. This proposal is prompted by reports that a change of a cooling hole geometry, which was introduced in the design of certain 4th stage LPT disks, inadvertently caused a reduction on the cooling air flow to the disk and an increased level of stress. The actions specified by the proposed AD are intended to prevent an uncontained disk failure and damage to the aircraft.