Airworthiness Directives; AlliedSignal Inc. (Formerly Textron Lycoming and Avco Lycoming) Model T5313B and T5317 Series Turboshaft Engines

This amendment supersedes an existing airworthiness directive (AD), applicable to AlliedSignal Inc. (formerly Textron Lycoming and Avco Lycoming) Model T5313B and T5317 series turboshaft engines, that currently requires initial and repetitive dye penetrant inspections of the centrifugal compressor impeller for cracks, and if necessary, removal from service. This amendment requires the use of a new, more conservative minor cycle counting factors table, introduces a method for prorating past centrifugal compressor impeller usage based on the new cycle counting factors, provides an enhanced centrifugal compressor impeller inspection procedure, and eliminates flyback criteria based on crack size. For those centrifugal compressor impellers that exceed their published life limit, this amendment implements a schedule for safe removal of time-expired parts. This amendment is prompted by a report of an uncontained centrifugal compressor impeller failure and subsequent rotorcraft accident. The actions specified by this AD are intended to prevent centrifugal compressor impeller failure, which can result in an uncontained engine failure, inflight engine shutdown, or damage to the rotorcraft.