Airworthiness Directives; Pratt & Whitney JT9D Series Turbofan Engines

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Pratt & Whitney JT9D series turbofan engines. This AD will require installation of an improved No. 4 bearing internal oil pressure tube, initial and repetitive inspections of the No. 4 bearing oil pressure tube for turbine exhaust case (TEC) strut clearance and alignment, and, if necessary, replacement with serviceable parts. This amendment is prompted by loss of integrity in the oil system that allows oil to migrate into high temperature metal cavities in the turbine exhaust case and cause oil fires. The actions specified by this AD are intended to prevent oil fires in and around the No. 4 bearing area that could cause excessive thermal growth of the sixth stage low pressure turbine (LPT) disk, liberation of the sixth stage LPT disk, uncontained engine failure, and damage to the airplane.