{"id":"F2006B09041","name":"AD/DHC-2/23 Amdt 1 - Stabilising Fins","slug":"ad-dhc-2-23-amdt-1-stabilising-fins","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52750,"registerId":"commonwealth-F2006B09041-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-2/23 Amdt 1 - Stabilising Fins","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-2 (Beaver) Series Aeroplanes\n\nAD/DHC2/23\n\nAmdt 1\n\n  \nStabilising Fins 8/91\n\nApplicability: Model DHC-2 Mk I and Mk II Beaver aircraft equipped with EDO Model 679-4930 floats; or floats or amphibious floats listed in Type approval Number A-22, at Issue 20, but not equipped with fins as specified in the Requirement Document.\n\nRequirement: Action IAW the Technical Requirements of Transport Canada AD CF-83-09 R2. Compliance: Unless already accomplished; prior to further flight after 8 August 1991.\n\nBackground: Flight tests indicate that a DHC-2 Beaver Mk I or Mk II equipped as a floatplane or an amphibious floatplane, may exhibit hazardous adverse directional stability when not equipped with fins as specified.\n\nThis amendment is raised in response to Revision 2 of the Requirement Document, which has been issued to combine AD CF-76-15 (25 Aug 76) and AD CF-83-09 R1 (2 Mar 89), and to include wipline ventral fin and stabilising fins.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The amendment changes scope by combining two prior airworthiness directives (AD CF-76-15 and AD CF-83-09 R1) and by explicitly including additional fin types—the wipline ventral fin and stabilising fins—within the mandatory requirements. The directive makes compliance with Transport Canada AD CF-83-09 R2 mandatory for the specified DHC-2 float-equipped aircraft that are \"not equipped with fins as specified,\" thereby expanding the technical requirement set operators must follow (\"This amendment...\" paragraph; Requirement; Applicability)."},"complexity_factors":["Limited and specific applicability (only DHC-2 Mk I and Mk II with particular float models or floats listed in Type Approval A-22) increases clarity but requires operators to check model and type-approval details (Applicability).","Mandates compliance with an external technical document (Transport Canada AD CF-83-09 R2) rather than reproducing technical instructions, which requires obtaining and interpreting that document (Requirement).","Immediate compliance deadline tied to flight status (must comply prior to further flight after 8 August 1991) creates operational urgency and potential grounding costs (Compliance).","The amendment consolidates and supersedes earlier directives and adds additional fin types (wipline ventral fin and stabilising fins), which requires checking historical ADs and the revised Requirement Document for differences (\"This amendment...\" paragraph).","Practical implementation depends on spare-parts supply and access to qualified installers, factors not specified in the directive but essential for timely compliance (Requirement; Compliance)."],"plain_english_summary":"This CASA airworthiness directive mandates that certain DHC‑2 (Beaver) float and amphibious floatplanes using specified EDO/Type‑A22 floats be fitted with stabilising (and wipline ventral) fins where not already installed, following Transport Canada AD CF‑83‑09 R2. It makes the retrofit mandatory before further flight, affecting owners/operators (who bear cost and downtime) and maintenance providers, to address hazardous adverse directional stability."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard amendment to an existing Airworthiness Directive. The scope remains tightly focused on the specific safety issue (directional stability of DHC-2 floatplanes) and has not expanded beyond the original purpose of mandating stabilising fin installation."},"complexity_factors":["Very short document (under 300 words)","Only 4 defined applicability criteria (specific aircraft model, float types, type approval number, and exclusion for already-equipped aircraft)","Single compliance action with clear external reference (Transport Canada AD CF-83-09 R2)","No nested conditional logic or exceptions beyond the 'unless already accomplished' clause","No internal cross-references to other sections of Australian legislation","Straightforward deadline (fixed date, not calculated or conditional)"],"plain_english_summary":"**What this is:** An Airworthiness Directive (AD) — essentially a mandatory safety order for aircraft.\n\n**What it does:** Requires owners and operators of specific De Havilland Canada DHC-2 \"Beaver\" aircraft (Mk I and Mk II models) to install **stabilising fins** on their floats if they haven't already.\n\n**Who it affects:**\n- Owners and operators of DHC-2 Beaver floatplanes or amphibious floatplanes\n- Specifically those using EDO Model 679-4930 floats, or floats/amphibious floats approved under Type Approval Number A-22 (Issue 20)\n- Only applies if the aircraft **doesn't already have** the required fins installed\n\n**Why it matters:** Flight testing revealed these aircraft can become dangerously unstable in the air — specifically, they can develop hazardous \"adverse directional stability\" (meaning the plane becomes difficult or impossible to control directionally) when flying without these fins. This creates a serious crash risk.\n\n**What must be done:**\n- Install fins according to **Transport Canada AD CF-83-09 R2** (the Canadian aviation safety authority's technical requirements)\n- **Deadline:** Before the aircraft flies again after 8 August 1991\n\n**Why this amendment exists:** Transport Canada updated their safety requirements (combining two older directives and adding new fin options including \"wipline ventral fins\"). Australia is adopting those updated Canadian standards to keep our aircraft safe."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-2-23-amdt-1-stabilising-fins","history":"/api/acts/ad-dhc-2-23-amdt-1-stabilising-fins/history","analysis":"/api/acts/ad-dhc-2-23-amdt-1-stabilising-fins/analysis","conflicts":"/api/acts/ad-dhc-2-23-amdt-1-stabilising-fins/conflicts","importantCases":"/api/acts/ad-dhc-2-23-amdt-1-stabilising-fins/important-cases","documents":"/api/acts/ad-dhc-2-23-amdt-1-stabilising-fins/documents"}}