Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to AlliedSignal, Inc. (formerly Garrett) Models TSCP700-4B, -4E, and -5 auxiliary power units (APU's). This proposal would require removal from service of certain high pressure turbine (HPT) disks identified by serial number, and replacement with serviceable parts. This proposal is prompted by the discovery of a material defect in certain HPT disk forgings that may result in HPT disk rupture prior to reaching the disk cyclic life limit. The actions specified by the proposed AD are intended to prevent an HPT disk rupture.