Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Pratt & Whitney (PW) 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, and initial and repetitive visual inspections of the primary mount thrust load path. This proposed AD would require the same actions, but at reduced intervals for front pylon mount bolts made from MP159 material. This proposed AD results from analysis by the manufacturer that the MP159 material pylon bolts do not meet the full life cycle torque check interval requirement, in a bolt-out condition. We are proposing this AD to prevent front pylon mount bolt and primary mount thrust load path failure, which could result in an engine separating from the airplane.