{"id":"F2006B09149","name":"AD/DHC-6/61 Amdt 1 - Wing Main Spar Lower Cap Angles","slug":"ad-dhc-6-61-amdt-1-wing-main-spar-lower-cap-angles","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115715,"registerId":"commonwealth-F2006B09149-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/61 Amdt 1 - Wing Main Spar Lower Cap Angles","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  DHC-6 (Twin Otter) Series Aeroplanes\n\n \n\n# AD/DHC-6/61\n\nAmdt 1\n\nApplicability: All models.\n\n# Wing Main Spar Lower Cap Angles 7/91\n\n \n\nRequirement: Action in accordance with the Technical Requirements of Transport Canada AD CF- 87-02, R1.\n\n \n\nNote: De Havilland SB 6/492 Revision A refers.\n\n \n\nCompliance: As specified in the Requirement Document with a revised effective date of 11 July 1991 for Australian registered aircraft.\n\n \n\nBackground: Exfoliation corrosion in the main spar cap lower angles has been reported on older aircraft. Amendment 1 is raised to reflect a revision of the related Country of origin AD which was issued to remove flight hour limitations from the compliance time requirements.\n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a targeted safety directive addressing a specific structural corrosion issue in one aircraft type. The amendment merely updates compliance timing methodology without expanding the scope beyond the original safety purpose."},"complexity_factors":["Very short document (under 300 words)","Only 1 substantive requirement (comply with Canadian AD)","No defined terms section — relies entirely on external document (Transport Canada AD CF-87-02 R1)","Single amendment with straightforward change (removing flight hour limits)","No nested conditions or exceptions within the text itself"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order for aircraft owners and operators. It applies to all **de Havilland DHC-6 Twin Otter aircraft** registered in Australia.\n\n**What it does:**\n- Requires owners/operators to inspect and address **corrosion in the wing's main structural support** (specifically the \"lower cap angles\" of the main spar — think of this as critical metal brackets that hold the wing together).\n- The inspection must follow technical instructions from **Transport Canada** (the Canadian aviation safety authority), specifically their directive CF-87-02, Revision 1.\n\n**Why it matters:**\n- **Exfoliation corrosion** (a type of metal decay that flakes like layers of an onion) was found in older aircraft. Left unchecked, this could weaken the wing structure and potentially lead to catastrophic failure.\n- This amendment removes previous **flight hour limitations** on when the work must be done — meaning compliance deadlines are now based on calendar time or other criteria rather than how many hours the plane has flown.\n\n**Who must act:**\n- Anyone operating a DHC-6 Twin Otter in Australia must ensure this inspection/maintenance is completed by **11 July 1991** (for Australian-registered aircraft)."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Amendment 1 changes the compliance timing established by the original country-of-origin AD by removing flight-hour limitations from the compliance-time requirements (Background). For Australian-registered aircraft the compliance is tied to a revised effective date of 11 July 1991 (Compliance), which alters when and potentially how many aircraft must comply compared with the earlier wording."},"complexity_factors":["Relies on external documents (Transport Canada AD CF-87-02, R1 and De Havilland SB 6/492 Rev A) for technical detail","Directive changes compliance timing (removal of flight-hour limitations) without restating procedures","Applies to all models of the DHC-6 series (broad applicability)","Technical subject matter (spar corrosion) requires specialist maintenance interpretation","Effective date revision introduces a specific administrative compliance deadline"],"plain_english_summary":"This directive requires all De Havilland DHC‑6 (Twin Otter) aircraft registered in Australia to comply with Transport Canada AD CF‑87‑02 Revision 1 (and the referenced De Havilland service bulletin) with a revised effective date of 11 July 1991. It was issued because of reported exfoliation corrosion in main spar cap lower angles; operators must pay for inspections and corrective work. The amendment removes flight‑hour limits from compliance timing."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-61-amdt-1-wing-main-spar-lower-cap-angles","history":"/api/acts/ad-dhc-6-61-amdt-1-wing-main-spar-lower-cap-angles/history","analysis":"/api/acts/ad-dhc-6-61-amdt-1-wing-main-spar-lower-cap-angles/analysis","conflicts":"/api/acts/ad-dhc-6-61-amdt-1-wing-main-spar-lower-cap-angles/conflicts","importantCases":"/api/acts/ad-dhc-6-61-amdt-1-wing-main-spar-lower-cap-angles/important-cases","documents":"/api/acts/ad-dhc-6-61-amdt-1-wing-main-spar-lower-cap-angles/documents"}}