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 28/31 Main Rotor Transmission Clutch Assembly 5/89 DM Applicability: All model F28 series helicopters equipped with P/N 28- 13401-1, Formsprag CL 40526-1 through -7 main rotor transmission clutch assembly. Requirement: Action in accordance with Enstrom Service Directive Bulletin No 0068. Additionally, for F-28F, F280F and 280FX helicopters inspect clutch assembly for part number. If clutch P/N 28- 13401-1 fitted, replace with clutch P/N 28-13401-2 before further flight. Note: FAA AD 89-04-09 refers. Compliance: At next inspection for issue of a Maintenance Release or by 31 March 1989 whichever occurs first. Background: Failure of the 28-13401-1 clutch has resulted in severe damage to helicopters.