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

This amendment supersedes an existing airworthiness directive (AD), applicable to Pratt & Whitney PW4164, PW4168, and PW4168A series turbofan engines. The current AD requires initial and repetitive torque checks for loose or broken bolts used to secure the engine to the airplane made from INCO 718 material (front pylon mount bolts). The current AD also requires the replacement of the bolts, if necessary, with new bolts, and establishes a new cyclic life limit for the front pylon mount bolt. This amendment adds requirements for initial and repetitive torque checks of front pylon mount bolts made from a new material, MP159, and initial and repetitive visual inspections of the primary mount thrust load path. This amendment is prompted by the use of front pylon mount bolts made from MP159 material and fatigue testing that shows that the forward engine mount bearing housings have insufficient fatigue life expectancy. 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.