Airworthiness Directives; AlliedSignal Inc. TSCP700-4B and -5 Auxiliary Power Units

This amendment supersedes an existing airworthiness directive (AD), applicable to AlliedSignal Inc. (formerly AiResearch and Garrett) TSCP700-4B and -5 Series Auxiliary Power Units (APUs), that currently requires restretching the first stage low pressure compressor (LPC) tie rods, or replacing affected disks at or before 8,000 cycles since new (CSN). This amendment requires removing from service affected disks, replacing them with serviceable parts, and establishing a life limit of 8,000 CSN for affected disks. This amendment is prompted by a report of a first stage LPC disk rim separation due to low cycle fatigue on an APU that had its tie rods restretched in accordance with the current AD. The actions specified by this AD are intended to prevent first stage LPC disk rim separation due to low cycle fatigue, which could result in an uncontained APU failure and damage to the aircraft.