Airworthiness Directives; Pratt and Whitney PW4000 Series Turbofan Engines

This amendment supersedes two airworthiness directives (AD's), AD 99-17-16 and AD 2001-15-12. Those AD's both apply to Pratt and Whitney (PW) model PW4000 series turbofan engines. AD 99-17-16 generally requires that operators limit the number of PW4000 engines with potentially reduced stability margin to no more than one engine on each airplane, and requires initial and repetitive on-wing and test cell engine stability tests. It also establishes reporting requirements for stability testing data. AD 2001-15-12 also limits the number of PW4000 engines with potentially reduced stability on each airplane by applying rules based on airplane and engine configuration. In addition, AD 2001-15-12 also requires that engines that exceed high pressure compressor (HPC) cyclic limits based on cycles-since-overhaul (CSO) are removed from service, limits the number of engines with the HPC cutback stator (CBS) configuration to one on each airplane, and establishes a minimum rebuild standard for engines that are returned to service. These AD's were prompted by reports of surges during takeoff on airplanes equipped with PW4000 series turbofan engines. This amendment continues the limitation on the number of PW4000 engines with potentially reduced stability on each airplane to no more than one, and introduces a new cool engine fuel spike test to allow engines to be returned to service after having exceeded cyclic limits or undergone work in the shop. This AD also continues the limitation on the number of engines with HPC CBS configuration to one on each airplane, places a cyclic limit on how long a CBS engine may remain in service, and establishes a minimum rebuild standard for engines that are returned to service. This amendment is prompted by further analyses of compressor surges in PW4000 engines, and continuing reports of surges in the PW4000 fleet. The actions specified by this AD are intended to prevent engine power losses due to HPC surge.