Airworthiness Directives; Pratt & Whitney PW4164, PW4168, and PW4168A Series Turbofan Engines

This amendment revises an existing airworthiness directive (AD), that is applicable to Pratt & Whitney PW4164, PW4168, and PW4168A series turbofan engines. That AD currently requires initial and repetitive torque checks for loose or broken front pylon mount bolts made from INCO 718 material and MP159 material. That AD also requires initial and repetitive visual inspections of the primary mount thrust load path. This amendment requires extension of the cycles accumulated before performing the initial inspection, reduces the frequency of repetitive inspections for MP159 material bolts, and adds a terminating action to the primary mount thrust load path inspections by introducing a new increased durability forward engine mount bearing housing. This amendment is prompted by component testing to assess the low cycle fatigue (LCF) life of the MP159 material bolts and the development of a new design forward engine mount bearing housing that meets the 8,000 flight cycle design intent for inspection. The actions specified by this AD are intended to prevent front pylon mount bolt and primary mount thrust load path failure, which could result in an engine separating from the airplane.