COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Allison Turbine Engines - 250 Series AD/AL 250/37 Third Stage Turbine Wheel - Replacement 9/79 Applicability: All 250-C28 series engines fitted with third stage turbine wheel P/No. 6898553 or 6898773. Requirement: Remove affected Part Number Turbines from service. Note: FAA Emergency AD Dated 19 July 1979 refers. Compliance: 1. For turbines with more than 300 hours' time in service - Within 25 hours' time in service from 9 August 1979. 2. For turbines with less than 300 hours' time in service - Before reaching 325 hours' time in service.