COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHC-6 (Twin Otter) Series Aeroplanes AD/DHC-6/37 Side Seat Rail Attachment Rivets - Inspection and Modification Applicability: All models with S/Nos. 136 to 350, 353, 356, 360 to 366 and 368. Document: De Havilland of Canada SB No. 6/302. 12/73 Compliance: 1. For aeroplanes with side facing seats: Within 200 hours time in service after 1 January 1974 or before 1 April 1974 whichever occurs first. 2. For aeroplanes with forward or aft facing seats: Within 1200 hours time in service after 1 January 1974 or before 1 January 1975 whichever occurs first.