COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES AlliedSignal (Lycoming) Turbine Engines - ALF502 and LF507 Series AD/ALF/12 Introduction of Improved Third Stage Turbine Rotor Assembly 13/93 Applicability: All ALF502 L and R series engines with third stage rotor assemblies listed in the Requirement Documents. Requirement: Install improved or reworked third stage turbine rotor assemblies in accordance with Textron-Lycoming Service Bulletins ALF502L 72-270 or ALF502R 72-270 as applicable. Note: FAA AD 93-14-13 also refers. Compliance: Effective 1 January 1994. As detailed in the Requirement Documents. Background: This Directive is issued to address reports of cracking in the third stage turbine disc blade retention slots and requires either fitment of an improved disc or rework of existing discs to provide a revised blade retention slot profile.