{"id":"F2006B09135","name":"AD/DHC-6/46 Amdt 4 - Flap Operating Rod Assemblies and Control Rods","slug":"ad-dhc-6-46-amdt-4-flap-operating-rod-assemblies-and-control-rods","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115688,"registerId":"commonwealth-F2006B09135-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/46 Amdt 4 - Flap Operating Rod Assemblies and Control Rods","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-6/46\n\nAmdt 4\n\n  \nFlap Operating Rod Assemblies and Control Rods 2/92\n\nApplicability: Model DHC-6 series.\n\nRequirement: Action in accordance with the technical requirements of Transport Canada AD CF- 79-22 R1.\n\nNote: De Havilland SB 6/388 Revision C and SB 6/502 refers.\n\nCompliance: As specified in the Requirement Document with a revised effective date of 3 February 1992 for Australian registered aircraft. The compliance of the previous issue of this Directive was “as per Requirement Document”.\n\nBackground: Instances of stress-corrosion cracking have occurred on original equipment 2024-T3 alloy flap control rods. Amendment 4 introduces SB 6/502 and the appropriate inspection interval for 6061-T6 control rods pursuant to Transport Canada’s Aging Aircraft program. The effective date required by Transport Canada is extended by four months.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive remains tightly focused on its original purpose: ensuring the airworthiness of flap control rods on DHC-6 aircraft. Amendment 4 expands the scope slightly to include 6061-T6 alloy rods in addition to the original 2024-T3 rods, but this is a logical extension of the same safety issue (stress-corrosion cracking) rather than mission creep. The directive has not grown beyond aircraft maintenance safety into unrelated regulatory areas."},"complexity_factors":["Short, single-purpose directive (approximately 200 words)","Only 1 defined applicability term ('Model DHC-6 series')","Minimal conditional logic — compliance is mandatory with clear deadline","Heavy reliance on external documents (Transport Canada AD, De Havilland Service Bulletins) for technical detail, keeping the legislative text brief","Simple amendment structure — Amendment 4 adds one new inspection requirement and extends one deadline"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance actions on certain aircraft.\n\n**What it does:**\n- Requires owners and operators of **De Havilland DHC-6 Twin Otter aircraft** to inspect and maintain the **flap operating rod assemblies and control rods** (the mechanical parts that control the wing flaps used during takeoff and landing).\n\n**Why it matters:**\n- **Safety risk:** The original equipment control rods were made from **2024-T3 aluminium alloy**, which has developed **stress-corrosion cracking** — a dangerous condition where metal weakens and can fail suddenly.\n- **New requirements:** This update (Amendment 4) adds inspection requirements for replacement rods made from **6061-T6 alloy** (a different metal mix), which were previously thought to be safe but now also need monitoring as part of Canada's Aging Aircraft program.\n- **Timeline:** Australian-registered aircraft must comply by **3 February 1992** — four months later than Canada's deadline.\n\n**Who must follow this:**\n- Anyone operating or maintaining **DHC-6 Twin Otter series aircraft** registered in Australia.\n\n**What they must do:**\n- Follow the technical instructions in **Transport Canada AD CF-79-22 R1** (Canada's equivalent safety order).\n- Consult **De Havilland Service Bulletins 6/388 Rev C and 6/502** for detailed inspection and replacement procedures."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"Amendment 4 expands the Directive’s scope by introducing De Havilland SB 6/502 and by adding an explicit inspection interval for 6061‑T6 control rods (Background; Note). It also specifies a revised effective date for Australian-registered aircraft of 3 February 1992 and extends Transport Canada’s effective date by four months (Compliance; Background). Previously the Directive’s compliance statement was simply ‘‘as per Requirement Document’’; the amendment replaces that with a specified effective date for Australia (Compliance)."},"complexity_factors":["Cross-jurisdictional reliance on an external Airworthiness Directive (Transport Canada AD CF-79-22 R1) rather than containing full technical instructions internally (Requirement).","References to multiple manufacturer service bulletins (De Havilland SB 6/388 Revision C and SB 6/502) that operators must obtain and follow (Note).","Material-specific inspection rules (distinguishing 2024‑T3 alloy and 6061‑T6 control rods) that create separate inspection needs (Background).","A change in effective date for Australian-registered aircraft and an extension of Transport Canada’s date by four months, adding a timing wrinkle to compliance planning (Compliance; Background).","Previous compliance wording was terse (‘as per Requirement Document’), so the amendment’s specification of a revised effective date requires operators to reconcile prior wording with new timing (Compliance)."],"plain_english_summary":"This amendment requires owners/operators of DHC‑6 (Twin Otter) aircraft to comply with Transport Canada AD CF‑79‑22 R1, adds De Havilland SB 6/502 and inspection intervals for 6061‑T6 flap control rods, and sets a revised Australian effective date. It responds to observed stress‑corrosion cracking on flap control rods, shifts timing for Australian registrants, and places inspection and repair costs and implementation responsibility on aircraft owners/operators."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-46-amdt-4-flap-operating-rod-assemblies-and-control-rods","history":"/api/acts/ad-dhc-6-46-amdt-4-flap-operating-rod-assemblies-and-control-rods/history","analysis":"/api/acts/ad-dhc-6-46-amdt-4-flap-operating-rod-assemblies-and-control-rods/analysis","conflicts":"/api/acts/ad-dhc-6-46-amdt-4-flap-operating-rod-assemblies-and-control-rods/conflicts","importantCases":"/api/acts/ad-dhc-6-46-amdt-4-flap-operating-rod-assemblies-and-control-rods/important-cases","documents":"/api/acts/ad-dhc-6-46-amdt-4-flap-operating-rod-assemblies-and-control-rods/documents"}}