Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to AlliedSignal Inc. (formerly Garrett Auxiliary Power Division) GTCP85 Series auxiliary power units (APUs), that currently requires removing the existing turbine wheel shroud and installing one constructed of Hastelloy ``S'' material, or installing a containment augmentation ring. This action would delete the option of installing a turbine shroud constructed of Hastelloy ``S'' material. This proposal is prompted by a report of insufficient APU containment capability with the Hastelloy ``S'' shroud alone installed. The actions specified by the proposed AD are intended to prevent turbine shroud fragments from exiting the APU and puncturing the APU compartment, which could result in reduced fire extinguishing capability in the APU compartment.