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-6/37 Flat End Rib - Inspection 6/76 Applicability: All models prior to S/No. 744. Document: Pilatus SB No. 124. Compliance: Within 10 hours time in service after 19 May 1976 and thereafter at intervals not exceeding 100 hours time in service until modified.