COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F27 Series Aeroplanes AD/F27/81 Engine Mount Tubes - Inspection 12/73 Applicability: All model F27 on which engine mount P/N 27.1-8101-000-403 with S/Nos. 590 to 725 have been installed. Requirement: 1. Inspect referenced engine mount tubes in accordance with Fokker F27 SB F27/71- 25 for cracks using the radiographic technique as detailed; or 2. Inspect the engine mount tubes detailed in Fokker F27 SB F27/71-25, for cracks using an alternative non destructive technique approved by the Secretary. Compliance: Within 500 hours time in service after 31 December 1973 and there-after at intervals not exceeding 1 year.