COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES DHA-3 (Drover) Series Aeroplanes AD/DHA-3/28 Centre Section Main Spar Upper Boom Attach Fitting - Inspection 3/74 Applicability: All models. Requirement: Visually inspect the visible spaces of the centre section main spar upper boom LH and RH wing attach fitting for cracks, particularly for those which may originate at the bushing holes of the front and rear lugs. Compliance: Before 1 May 1974, and thereafter at intervals not exceeding 1 year.