{"id":"F2006B09103","name":"AD/DHC-6/16 Amdt 5 - Wing Front Spar Attachment Fittings","slug":"ad-dhc-6-16-amdt-5-wing-front-spar-attachment-fittings","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115656,"registerId":"commonwealth-F2006B09103-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/16 Amdt 5 - Wing Front Spar Attachment Fittings","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)  \nDHC-6 (Twin Otter) Series Aeroplanes\n\nAD/DHC-6/16\n\nAmdt 5\n\n  \nWing Front Spar Attachment Fittings 3/87\n\nApplicability: All models with serial numbers 1 to 210 inclusive.\n\nRequirement: Action in accordance with de Havilland of Canada Service Bulletin No 6/174 Revision D, Part A or Part B as applicable.\n\nCompliance: For Part A of SB 6/174: At intervals not exceeding 500 hours time in service or 3 months, whichever occurs first.\n\nFor Part B of SB 6/174: Within 100 hours time in service after 31 July 1974, unless already accomplished.\n\nNote: The repetitive inspections of Part A may be discontinued upon installation of unused de Havilland fittings P/N C6WM 1133-1 and -2.\n\nBackground: Stress corrosion cracks have been found in service. The Service Bulletin requires inspection of the fittings and re- torquing of the wing attach bolts. This revision implements Revision D to the SB. Canadian AD’s CF-69-4, CF-69-5 and CF-76-08 refer.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"This amendment (Amdt 5) implements Revision D of de Havilland Service Bulletin No 6/174 and updates the AD to require actions in accordance with that revision (Requirement; Background). The AD sets the specific compliance intervals and preserves an option to discontinue repetitive inspections upon installation of particular replacement fittings (Note). The AD text does not provide a clause‑by‑clause comparison to prior versions, so the visible scope change is the formal adoption of Revision D of the Service Bulletin as the required technical standard."},"complexity_factors":["Applicability limited to a defined serial number range (1–210), which narrows affected population but requires serial verification.","Mandates compliance by reference to an external technical document (de Havilland Service Bulletin No 6/174 Revision D) divided into Part A and Part B, requiring operators to determine which part applies.","Two different compliance regimes (repetitive intervals for Part A; short initial compliance window for Part B) increase operational scheduling complexity.","Provides an option to discontinue recurring inspections only upon installation of specific part numbers (P/N C6WM 1133-1 and -2), creating a decision trade-off (recurring cost vs one‑off replacement) and potential supply dependency.","Technical procedures (inspection details, re‑torquing specifications) are delegated to the Service Bulletin, so compliance requires accurate interpretation and execution of that external document.","References foreign ADs (Canadian ADs), adding cross‑jurisdictional context though no further detail is supplied in the text."],"plain_english_summary":"What this instrument does, mechanically\n\n- The Civil Aviation Safety Authority (CASA) requires owners/operators of de Havilland DHC-6 (Twin Otter) aeroplanes with serial numbers 1–210 to carry out maintenance work specified in de Havilland of Canada Service Bulletin No 6/174 Revision D (either Part A or Part B as relevant). (Applicability; Requirement)\n\n- For aircraft covered by Part A of the Service Bulletin, CASA requires repeated inspections at intervals of no more than 500 hours time-in-service or every 3 months, whichever comes first. (Compliance)\n\n- For aircraft covered by Part B of the Service Bulletin, CASA requires that the action be completed within 100 hours time-in-service after 31 July 1974, unless it has already been done. (Compliance)\n\n- Operators may stop the repetitive Part A inspections if they install unused de Havilland fittings P/N C6WM 1133-1 or -2. (Note)\n\nOfficial rationale and the safety issue the rule addresses\n\n- The AD states that stress corrosion cracks have been found in service in the front spar attachment fittings, and the Service Bulletin prescribes inspection of the fittings and re‑torquing of the wing attach bolts. The amendment implements Revision D of that Service Bulletin. (Background; Requirement)\n\nWho pays, who decides, and what behaviour changes\n\n- Who pays: The aircraft owner/operator pays for the inspections, bolt re‑torquing, and any replacement fittings or labour required to comply. (Requirement; Compliance; Note)\n\n- Who decides: CASA has mandated compliance by reference to the de Havilland Service Bulletin; operators must follow the SB parts specified by the AD. (Requirement)\n\n- Behaviour changes required: Operators must conduct regular, documented inspections at the prescribed intervals (Part A) or complete the initial action within a short compliance window (Part B). Alternatively, operators can choose to install the specified unused fittings (P/N C6WM 1133-1 and -2) to stop the recurring inspection requirement. (Compliance; Note)\n\nCosts, incentives and trade-offs\n\n- Ongoing inspection cost vs one‑off replacement: The AD creates a clear trade-off. Continuing the Part A inspection regime imposes recurring maintenance time and labour costs and aircraft downtime. Installing the specified unused fittings creates a one‑off cost (parts and installation) but removes the recurring inspection requirement. (Compliance; Note)\n\n- Unspecified magnitude of costs: The AD does not quantify labour, parts or downtime costs, so the financial impact on operators depends on local rates, availability of fittings, and how often the inspections are due. (Compliance; Note)\n\nImplementation risk and compliance burden\n\n- Implementation risk: The AD references a structural safety concern—stress corrosion cracks in the fittings—so non‑compliance carries safety risk as described in the Background. The AD itself does not quantify the safety probability or consequences. (Background)\n\n- Compliance burden: Operators must schedule and perform inspections at fixed intervals, retain evidence of compliance, and potentially source specific replacement fittings (P/N C6WM 1133-1 and -2) if they choose to end the inspections. The AD relies on the Service Bulletin text for the technical steps, so operators or maintenance organisations must interpret and follow that SB. (Requirement; Compliance; Note)\n\nEffects on private enterprise, competition and choice\n\n- Independent maintenance providers can perform the mandated inspections and bolt re‑torquing under the SB instructions; the AD does not restrict who may carry out the work, so market providers can compete to supply the service and fittings, subject to normal regulatory approvals for maintenance work. (Requirement)\n\n- Operators retain a choice between ongoing inspections (recurring cost) and replacing fittings (one‑off cost) to remove the inspection requirement, allowing differing commercial responses depending on fleet usage, cost of downtime, and parts availability. (Compliance; Note)\n\nOther procedural notes and cross‑references\n\n- This AD is an amendment implementing Revision D of Service Bulletin 6/174. It also refers to related Canadian airworthiness directives CF‑69‑4, CF‑69‑5 and CF‑76‑08. The AD text does not detail what changed between earlier ADs and this amendment beyond stating it implements Revision D. (Background)"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is Amendment 5 to an existing Airworthiness Directive. The scope remains tightly focused on wing front spar attachment fittings for early serial number DHC-6 aircraft. The amendment simply updates the referenced Service Bulletin to Revision D — it does not expand applicability, add new aircraft types, or broaden the safety issue beyond the original stress corrosion cracking concern."},"complexity_factors":["Short, single-purpose instrument focused on one specific aircraft type and component","Only 2 defined compliance pathways (Part A and Part B of referenced Service Bulletin)","Simple conditional logic: repetitive inspections OR one-time action based on prior completion","Single exemption condition (installation of specific new parts discontinues Part A)","Heavy reliance on external document (Service Bulletin 6/174 Rev D) — actual technical requirements not reproduced in the AD itself","No nested exceptions or cross-references to other legislation beyond noting related Canadian ADs"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\nThis directive requires owners and operators of certain de Havilland DHC-6 \"Twin Otter\" aeroplanes (serial numbers 1 through 210) to inspect and maintain the **wing front spar attachment fittings** — critical structural components that connect the wings to the fuselage.\n\n**Who must comply:**\n- Anyone operating DHC-6 Twin Otter aircraft with serial numbers 1–210\n- Maintenance organisations servicing these aircraft\n\n**What must be done:**\nOperators must follow **de Havilland Service Bulletin 6/174 Revision D**, which comes in two parts:\n- **Part A:** Repeated inspections every **500 flight hours or 3 months** (whichever comes first) — checking for stress corrosion cracks and re-torquing (tightening to specified tension) the wing attachment bolts\n- **Part B:** A one-time inspection within **100 flight hours after 31 July 1974** (unless already done)\n\n**The good news:**\nIf you install brand new de Havilland fittings (part numbers C6WM 1133-1 and -2), you can stop doing the repetitive Part A inspections.\n\n**Why it matters:**\nStress corrosion cracks were discovered in these fittings during actual service. These cracks could lead to **structural failure of the wing attachment** — potentially catastrophic. This directive (Amendment 5) updates the requirements to match the manufacturer's latest safety guidance (Revision D of the Service Bulletin)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-16-amdt-5-wing-front-spar-attachment-fittings","history":"/api/acts/ad-dhc-6-16-amdt-5-wing-front-spar-attachment-fittings/history","analysis":"/api/acts/ad-dhc-6-16-amdt-5-wing-front-spar-attachment-fittings/analysis","conflicts":"/api/acts/ad-dhc-6-16-amdt-5-wing-front-spar-attachment-fittings/conflicts","importantCases":"/api/acts/ad-dhc-6-16-amdt-5-wing-front-spar-attachment-fittings/important-cases","documents":"/api/acts/ad-dhc-6-16-amdt-5-wing-front-spar-attachment-fittings/documents"}}