Airworthiness Directives; Pratt & Whitney JT9D Series Turbofan Engines

This amendment revises an existing airworthiness directive (AD), applicable to certain Pratt & Whitney (PW) JT9D series turbofan engines, that currently requires initial and repetitive fluorescent penetrant inspections (FPI) for cracks in cooling air holes of first stage high pressure turbine (HPT) disks, and replacement of cracked disks with serviceable parts. In addition, the current AD requires initial and repetitive FPI for cracks in tie bolt holes of certain other affected second stage HPT disks installed in PW JT9D series turbofan engines. This amendment calls out the second stage HPT hub assembly by part number (P/N) in addition to the hub P/N for clarification of affected parts, and references a service bulletin that does not change any of the requirements in the AD, but better explains the inspection procedures that are referenced in the current AD. This amendment also increases the repetitive inspection interval of first stage HPT disks. This amendment is prompted by the need to clarify the inspection procedures and the parts affected by this AD and by a re- evaluation of the risk analysis, based on new data from service, to establish a new repetitive inspection interval for the first stage HPT disk. The actions specified by this AD are intended to prevent turbine disk failure due to cooling air hole or tie bolt hole cracking, which could result in an uncontained engine failure and damage to the aircraft.