{"id":"F2006B08978","name":"AD/DHA-3/21 - Corrosion of Wing and Centre Section Spar Booms - Inspection","slug":"ad-dha-3-21-corrosion-of-wing-and-centre-section-spar-booms-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52588,"registerId":"commonwealth-F2006B08978-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHA-3/21 - Corrosion of Wing and Centre Section Spar Booms - Inspection","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nDHA-3 (Drover) Series Aeroplanes\n\nAD/DHA-3/21 Corrosion of Wing and Centre Section\n\nSpar Booms \\- Inspection\n\n  \n9/71\n\nApplicability: All models.\n\nRequirement: 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:\n\nNote: Intercrystalline corrosion may be recognised by the presence of blisters on the surface of the material or flaking parallel to the grain flow.\n\n    1.2 For the purpose of the inspection, temporarily remove the following items from the aeroplane:\n\n    (a) Seats and cabin equipment affecting access to centre section spar web cut- outs.\n\n    (b) Wing fillets.\n\n    (c) Tank doors.\n\n    (d) Wing leading edge between fuselage and engine nacelles.\n\n    (e) Protective coating from the accessible areas of the centre section upper and lower spare booms.\n\nNote: Restore protective coating when the inspection is completed.\n\n    1.3 Inspect the following areas using a mirror where necessary:\n\n    (a) All visible surfaces of the centre section upper and lower booms including the interior surfaces.\n\n    (b) Vertical and horizontal surfaces of the upper and lower spar booms in the tank bays.\n\n    (c) All sections of the wing spar booms visible through existing inspection holes and lighting holes in the auxiliary spars.\n\n    (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.\n\n    2. If corrosion is present take the following action:\n\n    2.1 Centre Section Upper Boom and Outer Wing Upper Booms:\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n    (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.\n\n    (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.\n\n    2.2 Centre Section Lower Booms and Outer Wing Lower Booms :\n\n    (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.\n\n    (b) Where corrosion has occurred at holes or rivets replace the affected booms before further flight.\n\nNote: 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.\n\nCompliance: At intervals not exceeding 12 months.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"Based solely on the provided text, the AD does not indicate a change to its original scope: it applies to 'All models' (Applicability), mandates inspections at intervals not exceeding 12 months (Compliance), and prescribes inspection access, remedial actions, and materials. No expansion or narrowing of applicability or interval is evident in the instrument as supplied."},"complexity_factors":["Technical specificity: inspects for intercrystalline corrosion and recognises signs like blisters or grain‑parallel flaking (Requirement 1.1 and Note).","Access and labour burden: requires temporary removal of seats, fillets, tank doors, leading edge and stripping protective coating to reach inspection areas (Requirement 1.2 (a)–(e)).","Repair prescription and material specs: blending to 0.010 inch below corrosion, use of dioxidine, zinc‑chromate priming and clear water‑resistant lacquer (2.1(a) and Note).","Regulatory discretion: replacement or repair must follow a repair scheme approved by the Secretary or manufacturer; removal limits also require approval (2.1(a), 2.1(b), 2.2(a)).","Safety‑critical flight restriction: lower boom corrosion at holes/rivets requires replacement before further flight (2.2(b)).","Recurring compliance: inspections mandated at intervals not exceeding 12 months (Compliance).","Broad applicability: applies to 'All models', widening operator coverage and potential aggregate cost (Applicability)."],"plain_english_summary":"Requires annual inspection of the wing and centre‑section spar booms on DHA‑3 (Drover) aeroplanes for intercrystalline corrosion, including temporary removal of fittings and protective coating to access inspection areas. If corrosion is found the directive prescribes blending, treating, repairing under an approved scheme, or replacing booms, and restoring protective finishes.\n\nAffects aircraft owners/operators and maintenance organisations, who bear the costs and downtime of inspections, removals, repairs and parts; the regulator must approve repair schemes and limits."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope — addressing a specific structural corrosion issue in a single vintage aircraft type (DHA-3 Drover). It has not expanded beyond its original safety purpose of preventing wing spar failure through mandatory inspection and repair protocols."},"complexity_factors":["Single specific aircraft type (DHA-3 Drover) with limited applicability","Clear procedural structure with numbered steps (1.1, 1.2, 1.3, 2.1, 2.2)","Technical aviation terminology requires domain knowledge but is explicitly defined (e.g., 'intercrystalline corrosion' explained in Note)","Two distinct repair pathways based on location of corrosion (holes/rivets vs other areas) and beam position (upper vs lower)","Specific part numbers cited (P/N FS3-5109A and FS3-5113A) for aileron pulley brackets","Precise material specifications for repair (dioxidine, zinc-chromate, water-resistant lacquer)","No cross-references to other legislation or complex conditional logic","Single compliance deadline (12-month intervals) with no exceptions or alternative methods stated"],"plain_english_summary":"This Airworthiness Directive requires owners/operators of DHA‑3 Drover aeroplanes to perform annual inspections for hidden intergranular corrosion in the wing-to-fuselage spars. It mandates removal of interior panels and inspection (using mirrors as needed), with repair (grind/treat or replace upper beams) or mandatory replacement of lower beams if corrosion is found.  \n\nBecause the Drover is a vintage aircraft, these checks prevent progressive structural deterioration that could lead to catastrophic wing failure."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dha-3-21-corrosion-of-wing-and-centre-section-spar-booms-inspection","history":"/api/acts/ad-dha-3-21-corrosion-of-wing-and-centre-section-spar-booms-inspection/history","analysis":"/api/acts/ad-dha-3-21-corrosion-of-wing-and-centre-section-spar-booms-inspection/analysis","conflicts":"/api/acts/ad-dha-3-21-corrosion-of-wing-and-centre-section-spar-booms-inspection/conflicts","importantCases":"/api/acts/ad-dha-3-21-corrosion-of-wing-and-centre-section-spar-booms-inspection/important-cases","documents":"/api/acts/ad-dha-3-21-corrosion-of-wing-and-centre-section-spar-booms-inspection/documents"}}