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-3/21 Corrosion of Wing and Centre Section Spar Booms - Inspection 9/71 Applicability: All models. Requirement: 1.1 Inspect all accessible areas of the centre section spar upper and lower booms and wing spar booms for the presence of intercrystalline corrosion as follows: Note: Intercrystalline corrosion may be recognised by the presence of blisters on the surface of the material or flaking parallel to the grain flow. 1.2 For the purpose of the inspection, temporarily remove the following items from the aeroplane: (a) Seats and cabin equipment affecting access to centre section spar web cut- outs. (b) Wing fillets. (c) Tank doors. (d) Wing leading edge between fuselage and engine nacelles. (e) Protective coating from the accessible areas of the centre section upper and lower spare booms. Note: Restore protective coating when the inspection is completed. 1.3 Inspect the following areas using a mirror where necessary: (a) All visible surfaces of the centre section upper and lower booms including the interior surfaces. (b) Vertical and horizontal surfaces of the upper and lower spar booms in the tank bays. (c) All sections of the wing spar booms visible through existing inspection holes and lighting holes in the auxiliary spars. (d) If corrosion is found on the exposed portions of the upper or lower spar booms and the aileron pulley bracks (P/N FS3-5109A and FS3-5113A) are to be removed and the mating surfaces of the brackets and spars are to be inspected for corrosion. 2. If corrosion is present take the following action: 2.1 Centre Section Upper Boom and Outer Wing Upper Booms: COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES (a) Blend out corrosion occurring at any location other than around holes or rivets to a minimum depth of .010 inch below the observed depth of the corrosion. The amount of material removed shall not exceed limits approved by the Secretary or the manufacturer of the aeroplane. Treat the reworked areas with dioxidine, prime with zinc-chromate and seal with clear water- resistant lacquer. (b) When intercrystalline corrosion has occurred at holes or rivets replace the affected booms with new booms or repair in accordance with a repair scheme approved by the Secretary. 2.2 Centre Section Lower Booms and Outer Wing Lower Booms : (a) Where corrosion has occurred in areas other than at holes or rivets replace the affected booms with new booms or repair in accordance with a repair scheme approved by the Secretary. (b) Where corrosion has occurred at holes or rivets replace the affected booms before further flight. Note: Replacement booms should be anodised, sealed and zinc- chromate primed prior to installation. Prime all rivets with zince-chromate immediately prior to driving. After installation seal all accessible areas with clear water- resistant lacquer. Compliance: At intervals not exceeding 12 months.