Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Pratt & Whitney JT9D-7R4 series turbofan engines. This proposal would require initial and repetitive inspections of certain High Pressure Turbine (HPT) stage 1 and stage 2 disks utilizing an improved ultrasonic method when the disks are exposed during a shop visit, and if a subsurface anomaly is found, removal from service and replacement with a serviceable part. This proposal is prompted by the results of a stage 1 HPT disk fracture investigation which has identified a population of HPT stage 1 and 2 disks that may have subsurface anomalies formed during the forging process. The actions specified by the proposed AD are intended to prevent HPT disk fracture, which could result in an uncontained engine failure, damage to the aircraft, and an in-flight engine shutdown.