COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES General Electric Turbine Engines - CT7 Series AD/CT7/4 Turbine Rotor Discs 8/90 Applicability: CT7-5A2/7A. Requirement: Action in accordance with General Electric Alert SB (CT7-TP series) A72-228 and A72-229. Compliance: Effective from 9 August 1990. Background: During a walnut shell-cleaning process at an overhaul facility, a number of stages 1 and 2 gas generator turbine rotor discs and stages 3 and 4 power turbine rotor discs may have been shotpeened inadvertently by walnut shells contaminated with steel shot. As a result, these parts may have a reduced low cycle fatigue (LCF) life. The Service Bulletins nominate the suspect parts and new life cycle limits.