COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pilatus Porter PC-6 Series Aeroplanes AD/PC-6/23 Rudder Bottom Nose Rib - Inspection and Modification Applicability: All models prior to S/No. 685. Document: Pilatus SB No. 80. 7/68 Compliance: Inspect within 100 hours time in service after 11 July 1968 and thereafter at intervals not exceeding 100 hours time in service until modified. Modify before 1 January 1969.