AD 94-7786

Abstract

This amendment adopts a new airworthiness directive (AD) that is applicable to General Electric Company (GE) CT58-110 and -140 series turboshaft engines. This action supersedes priority letter AD 93-10-09 that currently requires inspection of the forward and aft cooling plate locating groove or channel (rabbet groove) of stage 1 and stage 2 turbine wheels for cracks and minimum radii, and replacement, if necessary, with serviceable turbine wheels. In addition, that AD reduces the cyclic life limit of certain stage 1 and stage 2 turbine wheels based on the cycles since new and the rabbet groove radius. This action retains the inspection requirements of the current priority letter AD, but adds an additional eddy current inspection of the stage 1 and stage 2 turbine wheels, accelerates the inspection schedule, reduces the cyclic life limit of certain stage 1 and stage 2 turbine wheels below the published limits and those imposed by the priority letter AD, and provides for the removal from service of certain stage 1 and stage 2 turbine wheels. This amendment is prompted by an extensive analytical study performed by GE as a result of an uncontained stage 2 turbine wheel failure on a GE Model CT58-140-1 turboshaft engine. The actions specified by this AD are intended to prevent an uncontained engine failure and damage to the aircraft.

Applicability · by US fleet size

• VERTOL 107 1 tails

Compliance instructions

Required actions, compliance times, parts/serial numbers and methods of compliance are in the Federal Register publication — not paraphrased here. Read AD on Federal Register ↗