{"id":"F2006B08830","name":"AD/DC4/24 - Propeller De-Icing System - Modification","slug":"ad-dc4-24-propeller-de-icing-system-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52273,"registerId":"commonwealth-F2006B08830-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DC4/24 - Propeller De-Icing System - Modification","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/DC4/24 Propeller De-Icing System - Modification NK\n\nDocument: 1. Douglas SB (DC4) No. 91, dated 3 August 1948 and revised 16 September 1948; or\n\n \n\n2. ANO 105.1.16.2.5.23, 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\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope: mandating a specific safety modification for a particular aircraft type (Douglas DC-4). There is no evidence of scope creep or expansion beyond the original safety purpose."},"complexity_factors":["Very short document (approximately 150 words)","Only 2 technical references to external documents","No defined terms section","No conditional logic or nested exceptions","Single straightforward requirement: modify system per specified standard","No cross-referencing to other legislation beyond the enabling Civil Aviation Regulations 1998"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order — issued by Australia's Civil Aviation Safety Authority (CASA) for **Douglas DC-4 series aircraft**.\n\n**What it does:**\n- Requires owners and operators of DC-4 planes to **modify the propeller de-icing system** (the equipment that prevents ice from building up on the propellers during flight).\n- The modification must follow one of two technical documents:\n  1. **Douglas Service Bulletin No. 91** (dated August/September 1948), or\n  2. **ANO 105.1.16.2.5.23, Issue 2** (an older Air Navigation Order).\n\n**Who it affects:**\n- Anyone who owns, operates, or maintains a Douglas DC-4 aircraft in Australia.\n\n**Why it matters:**\n- Propeller ice buildup can cause **vibration, loss of thrust, or even engine failure**. This directive ensures older DC-4 aircraft meet updated safety standards for cold-weather operations. Compliance is **legally mandatory** — you cannot legally fly the aircraft without making this modification."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"The supplied AD text does not indicate any change in scope from an earlier instrument; it prescribes a modification for Douglas DC4 series aeroplanes and points to two reference documents for the technical requirements (Douglas SB No. 91; ANO 105.1.16.2.5.23 Issue 2). There is no material in the excerpt showing an expansion or narrowing of scope compared with a prior stated intent."},"complexity_factors":["Technical nature of the required work (propeller de‑icing system modification) requiring specialist maintenance skills and parts.","Dependency on external technical documents for substantive detail (Douglas SB No. 91 and ANO 105.1.16.2.5.23 Issue 2) rather than containing full technical instructions in the AD itself.","Age and provenance of one referenced document (Douglas SB dated 1948, revised 1948) which may increase difficulty locating current drawings, parts or interpretation.","Narrow applicability (applies specifically to Douglas DC4 series aeroplanes) which concentrates obligations on a small operator population with specialised maintenance chains.","Regulatory compliance mechanics (need to obtain documents, perform modification, and record compliance) impose administrative and operational burdens.","Potential ambiguity in the AD text (for example the label “Modification NK” appears without explanatory text in the supplied extract).","Supply‑chain risk for obsolete parts or specialised components, implied by the vintage of the aircraft and referenced documents.","Limited information in the AD itself about timing, allowed alternatives, or exemptions, requiring operators to consult the referenced documents or the regulator for detail."],"plain_english_summary":"This Airworthiness Directive requires Douglas DC‑4 series aeroplanes to have their propeller de‑icing system modified in accordance with one of two specified historical technical documents. It affects owners/operators and the maintenance organisations that must perform and certify the work; costs and downtime fall to the operator. Issued under the Part 39 AD framework by CASA, the directive mandates compliance with the referenced service instructions for continued airworthiness and legal operation."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dc4-24-propeller-de-icing-system-modification","history":"/api/acts/ad-dc4-24-propeller-de-icing-system-modification/history","analysis":"/api/acts/ad-dc4-24-propeller-de-icing-system-modification/analysis","conflicts":"/api/acts/ad-dc4-24-propeller-de-icing-system-modification/conflicts","importantCases":"/api/acts/ad-dc4-24-propeller-de-icing-system-modification/important-cases","documents":"/api/acts/ad-dc4-24-propeller-de-icing-system-modification/documents"}}