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 250/4 Sixth Stage Compressor Blades - Modification 6/68 Applicability: All model 250-C18 fitted with compressor assemblies prior to S/N CAC 20873 and Model 250-C18A fitted with compressor assemblies prior to S/N CAC 20188. Document: Allison CEB No. 250 CEB-48. Compliance: Before further flight after 19 June 1968.