COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Eurocopter AS 355 (Twin Ecureuil) Series Helicopters AD/AS 355/33 Amdt 1 Tail Rotor Front Drive Shaft 5/89 Applicability: All model AS 355 fitted with forward drive shaft P/N 355A34-1037-00. Requirement: Action in accordance with Aerospatiale Service Bulletin No 05-20 Revision 2. Compliance: 1. Within 50 hours TIS after 7 December 1988 or by 31 December 1988, whichever occurs first. Thereafter, reinspect at intervals not exceeding 100 hours time in service. 2. Before removal and after installation of the following components: - forward drive shaft elements, - oil cooler, - fan, - oil cooler or fan support. 3. If abnormal vibration is noted in the fan assembly, 4. If a crack is found on one of the oil cooler or fan supports. Background: The manufacturer has advised of a forward drive shaft failure caused by excessive unbalance of a main gearbox oil cooler fan assembly. A further revision of the requirement document requires the compliance requirements to be expanded.