{"id":"F2006B08816","name":"AD/DC4/11 - Vertical Stabiliser Attachment Fittings, AN Type Bolts - Replacement","slug":"ad-dc4-11-vertical-stabiliser-attachment-fittings-an-type-bolts-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52228,"registerId":"commonwealth-F2006B08816-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DC4/11 - Vertical Stabiliser Attachment Fittings, AN Type Bolts - Replacement","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)  Douglas DC4 Series Aeroplanes\n\n \n\nAD/DC4/11 Vertical Stabiliser Attachment Fittings, NK\n\nAN Type Bolts - Replacement\n\nDocument: 1. Douglas SB (DC4) No. 11 dated 4 November, 1946; or\n\n \n\n2. FAA AD 47-2-2; or\n\n \n\n3. ANO 105.1.16.2.5.10, Issue 2.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-purpose airworthiness directive focused solely on a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original safety purpose."},"complexity_factors":["Extremely short document (approximately 200 words)","Only one substantive requirement: replace specific bolts","No defined terms section","No conditional logic or nested exceptions","Simple cross-references to three external technical documents rather than internal legislative cross-references","Single aircraft type applicability (Douglas DC-4 Series)","No penalty provisions, review mechanisms, or administrative procedures included"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** for **Douglas DC-4 aircraft** — a specific safety order issued by Australia's Civil Aviation Safety Authority (CASA).\n\n**What it does:**\n- Requires the **replacement of certain bolts** (called \"AN Type bolts\") that attach the **vertical stabiliser** (the tail fin that keeps the plane flying straight) to the rest of the aircraft.\n- These bolts are located at the **attachment fittings** — the metal brackets that connect the stabiliser to the fuselage.\n\n**Why it matters:**\n- If these bolts fail in flight, the vertical stabiliser could detach or become loose, causing **loss of control** and potentially a crash.\n- This AD mandates a specific maintenance action to prevent that catastrophic failure.\n\n**Who it affects:**\n- **Owners and operators** of Douglas DC-4 series aeroplanes (a four-engine propeller aircraft from the 1940s, still used in some cargo and specialty operations).\n- **Licensed aircraft maintenance engineers** who work on these planes.\n\n**Compliance:**\n- The directive references three technical documents that provide the detailed instructions:\n  1. A 1946 Douglas Service Bulletin\n  2. An older FAA (US) Airworthiness Directive from 1947\n  3. An Australian National Order from the 1940s-50s era\n\nThis is a **mandatory safety fix** — operators must comply or the aircraft cannot legally fly."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"Based on the text supplied, the AD requires replacement of AN‑type bolts on vertical stabiliser attachment fittings and implements that requirement by directing operators to follow one of three listed technical documents (Douglas SB No. 11; FAA AD 47‑2‑2; ANO 105.1.16.2.5.10 Issue 2). There is no indication in the provided text that the scope of who or what is covered has been expanded or narrowed from an earlier intent; it remains focused on bolt replacement for DC‑4 vertical stabiliser attachments as set out in the directive and its referenced documents."},"complexity_factors":["The AD text is short and technical but relies entirely on cross‑referenced external documents for the detailed procedure (Document: 1–3).","Referenced documents include historical material (Douglas SB dated 1946 and FAA AD 1947) which may be difficult to obtain or interpret for modern maintenance organisations (Document: 1–3).","The AD excerpt provided does not show explicit compliance timing, part numbers, or acceptance criteria in itself, creating potential ambiguity about scope and proof of compliance (absence of detail in AD text).","Multiple alternative reference documents are permitted, so operators must choose which source to follow and ensure equivalence in outcomes (Document: 1–3).","Regulatory placement under Civil Aviation Regulations Part 39 requires formal enforcement and record‑keeping by operators, adding administrative compliance tasks (header: Civil Aviation Regulations 1998, PART 39 - 105)."],"plain_english_summary":"What this instrument does, in plain English\n\n- This is an airworthiness directive applying to Douglas DC‑4 series aeroplanes titled “AD/DC4/11 — Vertical Stabiliser Attachment Fittings, NK — AN Type Bolts - Replacement.” It requires replacement work on the AN‑type bolts used in the vertical stabiliser attachment fittings (the text identifies the subject and corrective action: bolt replacement) (see AD/DC4/11 title and Document list).\n\nHow the requirement is implemented\n\n- The directive does not itself set out step‑by‑step instructions in the text provided. Instead it directs operators to follow one of three source documents for the technical procedure: Douglas Service Bulletin (DC4) No. 11 dated 4 November 1946; or FAA AD 47‑2‑2; or ANO 105.1.16.2.5.10 Issue 2. Compliance therefore consists of carrying out the replacement described in one of those referenced documents (see Document: 1–3).\n\nWho it affects and who decides\n\n- Aircraft owners and operators of Douglas DC‑4 series aeroplanes are the parties required to act: they must arrange for the bolt replacement and associated inspections/repairs as specified in the referenced document they use. Maintenance providers who perform the work are also affected because they must follow the procedures in the referenced documents.\n\n- The Civil Aviation Safety Authority (CASA), under the Civil Aviation Regulations Part 39 framework, issues and enforces this directive (AD/DC4/11 appears in the Schedule of Airworthiness Directives under Part 39 – 105) and therefore decides that the replacement is mandatory for continued airworthiness (see header: Civil Aviation Regulations 1998, PART 39 - 105).\n\nWhy it matters (official rationale and practical trade‑offs)\n\n- The official purpose (implicit in an AD of this form) is to address a safety concern in the vertical stabiliser attachment by replacing specified bolts; the directive achieves this by mandating a defined maintenance action via reference to technical documents (see AD title and Document list).\n\n- Costs and incentives: owners/operators pay for parts, labour, and aircraft downtime to perform the replacement. Maintenance organisations gain work from the required task. The AD channels the technical solution by mandating one of the listed documents, which reduces discretionary variation in how the issue is fixed but requires affected parties to obtain and follow those external documents (Document: 1–3).\n\n- Compliance burden and implementation risk: the directive relies on cross‑referenced service/airworthiness documents rather than specifying procedures in the AD text. That means operators must obtain and correctly apply the referenced document they choose. If the AD text lacks explicit schedules, part numbers or acceptance criteria in the provided excerpt, that can create ambiguity about timing and exact scope, increasing administrative effort to interpret and demonstrate compliance (see Document: 1–3).\n\n- Bureaucratic discretion: the AD establishes a mandatory corrective action enforced through the airworthiness directive process. The text supplied does not show discretionary exemptions or alternatives beyond the three listed documents; operators’ latitude is therefore limited to which of the listed documents they adopt (see Document: 1–3).\n\n- Effects on private choice and markets: the AD compels a safety‑related maintenance action. That imposes direct costs on aircraft owners/operators and creates demand for parts and maintenance services. The directive centralises the technical remedy by reference, which reduces variability between providers but does not itself prescribe the supplier of parts or labour.\n\n- Trade‑offs and opportunity cost: resources spent on complying (parts, labour, downtime) cannot be used elsewhere; that is the principal economic cost to owners/operators. The AD’s approach—referencing existing service/airworthiness documents—lowers drafting complexity of the AD itself but increases reliance on historical documents that operators must source and follow (Document: 1–3).\n\nKey source pointers\n\n- This AD is listed under the Commonwealth of Australia Civil Aviation Regulations 1998, Part 39 (Schedule of Airworthiness Directives) and is identified as AD/DC4/11, titled as above.\n- The technical action is to replace AN‑type bolts in the vertical stabiliser attachment fittings, with procedures and detail to be taken from one of the three referenced documents: Douglas SB (DC4) No.11 (4 Nov 1946); FAA AD 47‑2‑2; or ANO 105.1.16.2.5.10 Issue 2 (see Document: 1–3)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dc4-11-vertical-stabiliser-attachment-fittings-an-type-bolts-replacement","history":"/api/acts/ad-dc4-11-vertical-stabiliser-attachment-fittings-an-type-bolts-replacement/history","analysis":"/api/acts/ad-dc4-11-vertical-stabiliser-attachment-fittings-an-type-bolts-replacement/analysis","conflicts":"/api/acts/ad-dc4-11-vertical-stabiliser-attachment-fittings-an-type-bolts-replacement/conflicts","importantCases":"/api/acts/ad-dc4-11-vertical-stabiliser-attachment-fittings-an-type-bolts-replacement/important-cases","documents":"/api/acts/ad-dc4-11-vertical-stabiliser-attachment-fittings-an-type-bolts-replacement/documents"}}