COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Enstrom F-28 Series Helicopters AD/ENST 28/10 Tail Cone Attachment Bolts - Inspection and Replacement 1/76 Applicability: All model F-28A with S/Nos. 03 to 347, and Model 280 with S/Nos. 1001 to 1030. Document: Enstrom Service Note No. 0029. Compliance: 1. Inspect within 50 hours time in service after 15 January 1976 and thereafter at intervals not exceeding 50 hours time in service until replaced. 2. Replace within 300 hours time in service after 15 January 1976.