COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Cessna 180, 182 and Wren 460 Series Aeroplanes AD/CESSNA 180/21 Amdt 1 Main Spar and Lower Skin 11/67 Applicability: All models in agricultural category. Requirement: Carry out a visual inspection for cracking of the wings in the following areas: 1. The corners of the skin cutouts through which the lift strut fork passes. 2. All visible elements of the main spar lower flange front and rear faces in the region of the lift strut attachment. Particular attention should be paid to the areas around the spar to skin rivets. The affected areas must be thoroughly cleaned before inspection. Compliance: Before 4000 hours component time in service and thereafter at intervals not exceeding 100 hours time in service.