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 28/24 Main Rotor Retention Assembly - Inspection 10/82 Applicability: All model F-28A, F-28C, F-28F, 280, 280C and 280F. Document: Enstrom Service Directive Bulletin No. 0057. Note: FAA AD 82-16-09 Amdt. 39-4429 refers. Compliance: Within 100 hours time in service after 31 October 1982, and thereafter at intervals not exceeding 200 hours time in service. Background: Manufacture reports misalignment of the nylon shims has worn grooves in the inner surfaces of the blade grip.