Airworthiness Directives; Pratt & Whitney JT9D-7R4 Series Turbofan Engines

This amendment adopts a new airworthiness directive (AD), applicable to Pratt & Whitney JT9D-7R4 series turbofan engines, that requires an initial and repetitive inspections of certain High Pressure Turbine (HPT) stage 1 and stage 2 disks utilizing an improved ultrasonic inspection method performed at an approved facility when the disks are exposed during a shop visit, and if a crack indicating a subsurface anomaly is found, removal from service and replacement with a serviceable part. This amendment 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 this AD are intended to prevent an HPC disk fracture, which could result in an uncontained engine failure, damage to the airplane, and an in-flight engine shutdown.