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-6/11 Engine Mount Ring - Modification 3/66 Applicability: All model PC-6/B-H2 with S/Nos. 564, 569, 572, 574, 575, 580, 581, 582 and 583. Document: Pilatus SB No. 56. Compliance: At next engine change after 15 April 1966.