Summary
The Federal Aviation Administration (FAA) proposes to adopt a new airworthiness directive (AD) that is applicable to certain serial number (SN) Pratt and Whitney (PW) models PW4164, PW4168, and PW4168A turbofan engines. This proposal would require operators to initially and repetitively borescope-inspect 14th and 15th stage rubstrips located on the 13th and 14th stage stator set for wear. This proposal is prompted by reports of high pressure compressor (HPC) surges during the takeoff phase of flight that have been attributed to increased stage 14 and stage 15 HPC blade tip clearances caused by excessive wear on the HPC inner rear case rear hook. The actions specified by the proposed AD are intended to prevent engine power loss during takeoff due to HPC surge.