Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Pratt & Whitney JT9D series turbofan engines. This proposal would 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 proposal is prompted by loss of integrity in the oil system, which allows oil to migrate into high temperature metal cavities in the turbine exhaust case and cause oil fires. The actions specified by the proposed AD are intended to prevent oil fires in and around the No. 4 bearing area, which could result in excessive 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.