{"id":"F2006B09079","name":"AD/DHC-3/3 - Main Undercarriage Compression Strut","slug":"ad-dhc-3-3-main-undercarriage-compression-strut","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52868,"registerId":"commonwealth-F2006B09079-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-3/3 - Main Undercarriage Compression Strut","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-3 (Otter) Series Aeroplanes\n\n \n\nAD/DHC-3/3 Main Undercarriage Compression Strut NK\n\nApplicability: All models with S/Nos 1 to 40.\n\n \n\nRequirement: Action in accordance with De H Canada TNS Otter No 23.\n\n \n\nNote: Canadian AD 54-4 refers.\n\n \n\nCompliance: Forthwith.\n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive applies to a defined set of aircraft (DHC-3 S/N 1–40) and requires implementation of measures set out in De Havilland Canada TNS Otter No. 23. The instrument does not expand applicability beyond that set or add new categories of aircraft; it mirrors and cross-references the Canadian AD framework (Canadian AD 54-4) and therefore does not change the original, document‑specified scope. (Applicability) (Requirement) (Note)"},"complexity_factors":["Narrow and specific applicability (only DHC-3 serial numbers 1–40) reduces scope complexity. (Applicability)","Directive text is short and does not include technical procedures, increasing reliance on an external technical document (De Havilland Canada TNS Otter No. 23). (Requirement)","Immediate compliance requirement (“Forthwith”) raises operational urgency and logistical complexity for affected operators. (Compliance)","Cross-reference to a foreign AD (Canadian AD 54-4) introduces a cross-jurisdictional dependency and potential need to reconcile documents. (Note)","Regulatory enforcement is straightforward (mandatory AD) but technical interpretation rests with the referenced TNS and maintenance organisations, concentrating technical discretion. (Requirement)"],"plain_english_summary":"### What this instrument does, in plain terms\n\n- It is an airworthiness directive that requires action on the main undercarriage compression strut of De Havilland (DHC-3) Otter aeroplanes. (Requirement)\n- It applies only to DHC-3 aircraft with serial numbers 1 to 40. (Applicability)\n- The directive does not set out the detailed corrective steps itself; it instructs operators to follow the procedures in De Havilland Canada Technical Newsletter Service (TNS) Otter No. 23. (Requirement)\n- The required action is to be carried out immediately — the compliance time is “forthwith”. (Compliance)\n- The instrument explicitly refers to a related Canadian airworthiness directive (Canadian AD 54-4). (Note)\n\n### Who it affects\n\n- Owners and operators of DHC-3 (Otter) aeroplanes with serial numbers 1–40. (Applicability)\n- Maintenance organisations contracted to perform the work called for in De Havilland Canada TNS Otter No. 23. (Requirement)\n\n### Why it matters (stated purpose and practical implications)\n\n- Stated purpose: the AD directs operators to implement the measures set out in De Havilland Canada TNS Otter No. 23 concerning the main undercarriage compression strut. The instrument itself does not include an explanatory rationale; the referenced Canadian AD and the TNS likely explain the safety concern. (Requirement) (Note)\n\n- Who pays: the direct financial cost of following the TNS procedures (inspections, repairs, part replacement, labour, and any aircraft downtime) will fall on the affected aircraft owners or their operators, and on maintenance providers under contract. (Applicability) (Requirement)\n\n- Who decides and enforces: the directive is issued under the Civil Aviation Regulations framework and is a mandatory airworthiness directive for affected aircraft; the regulatory authority (as identified in the header) enforces compliance. (COMMONWEALTH OF AUSTRALIA — Civil Aviation Regulations 1998; SCHEDULE OF AIRWORTHINESS DIRECTIVES)\n\n- Behaviour change required: affected operators must obtain and implement the actions in De Havilland Canada TNS Otter No. 23 without delay, which may require inspections, modifications or grounding until work is completed. (Requirement) (Compliance)\n\n### Costs, incentives, trade-offs and implementation considerations\n\n- Concentrated population: only a defined, small set of aircraft (S/N 1–40) are subject to the rule, so costs are concentrated on a limited group of owners/operators. The benefit of corrective action accrues primarily to those aircraft and their users. (Applicability)\n\n- Compliance burden and timing: the directive’s “forthwith” compliance deadline raises the immediacy of the burden. Operators may incur accelerated scheduling costs, urgent parts procurement costs, and aircraft downtime. (Compliance)\n\n- Cross‑jurisdictional reliance and implementation risk: the AD references an external manufacturer document (De Havilland Canada TNS Otter No. 23) and a Canadian AD (54-4) rather than setting out the remedial steps in full. This creates a dependency on accessing and interpreting those external documents correctly, which can add administrative and operational friction. (Requirement) (Note)\n\n- Discretion and operational choices: the text leaves the specific technical method and scope of work to the TNS. Operators and approved maintenance organisations must interpret and apply the TNS requirements; the local regulator enforces that the actions have been completed. This concentrates technical discretion with the holder of the TNS and with maintenance organisations executing it. (Requirement)\n\n- Effects on private enterprise and market aspects: the measure imposes compliance costs on individual aircraft owners/operators, which may reduce short‑term availability of affected aircraft and raise operating costs for businesses that rely on them. It does not, on its face, change ownership rights or contract freedom, but it does limit operational freedom until compliance is achieved. (Applicability) (Requirement) (Compliance)\n\n- Opportunity costs: time and money spent complying with the directive cannot be used for other maintenance, upgrades, or operations during the same period. (Compliance)\n\n- Transparency: because the AD points to external materials for technical detail, transparency of the specific required actions depends on access to and clarity of De Havilland Canada TNS Otter No. 23 and the referenced Canadian AD. (Requirement) (Note)\n\n### Practical takeaway\n\nOperators of DHC-3 Otters with serial numbers 1–40 must promptly follow the procedures in De Havilland Canada TNS Otter No. 23 for the main undercarriage compression strut. The directive is mandatory and immediate; affected operators should secure the referenced TNS and plan for the direct costs, aircraft downtime, and any coordination with maintenance organisations and the regulator. (Applicability) (Requirement) (Compliance) (Note)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical component on specific aircraft. It has not expanded beyond its original narrow purpose."},"complexity_factors":["Extremely short document — approximately 100 words","Only one substantive requirement referencing an external technical document (TNS Otter No. 23)","No defined terms section","No conditional logic or nested exceptions","Single applicability criterion (serial numbers 1-40)","Cross-reference to one Canadian AD and one manufacturer document only"],"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:**\n- Requires immediate inspection or repair of the **main undercarriage compression strut** (a critical shock-absorbing component in the landing gear) on certain De Havilland Canada DHC-3 \"Otter\" aircraft.\n- Affected planes are **serial numbers 1 through 40** — the earliest production models.\n\n**Who must act:**\n- Owners and operators of these specific DHC-3 Otter aircraft.\n\n**What they must do:**\n- Follow the technical instructions in **De Havilland Canada Technical News Sheet (TNS) Otter No. 23**.\n- **\"Forthwith\"** means immediately — no grace period.\n\n**Why it matters:**\nLanding gear failures can be catastrophic. This AD addresses a known safety issue identified by the manufacturer and the Canadian aviation authority (whose equivalent directive, **Canadian AD 54-4**, is referenced). Compliance is legally mandatory — flying without addressing this violates civil aviation safety regulations."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-3-3-main-undercarriage-compression-strut","history":"/api/acts/ad-dhc-3-3-main-undercarriage-compression-strut/history","analysis":"/api/acts/ad-dhc-3-3-main-undercarriage-compression-strut/analysis","conflicts":"/api/acts/ad-dhc-3-3-main-undercarriage-compression-strut/conflicts","importantCases":"/api/acts/ad-dhc-3-3-main-undercarriage-compression-strut/important-cases","documents":"/api/acts/ad-dhc-3-3-main-undercarriage-compression-strut/documents"}}