{"id":"F2006B08706","name":"AD/DART/20 - High Pressure Turbine Nozzle Guide Vanes","slug":"ad-dart-20-high-pressure-turbine-nozzle-guide-vanes","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":51893,"registerId":"commonwealth-F2006B08706-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DART/20 - High Pressure Turbine Nozzle Guide Vanes","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 - 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Rolls Royce Turbine Engines - Dart Series\n\n \n\nAD/DART/20 High Pressure Turbine Nozzle Guide Vanes 11/87\n\nApplicability: All Dart RDa-6 series engines.\n\n \n\nRequirement: 1. Action in accordance with Rolls Royce SB Da 72-451 Rev 5; or\n\n \n\n2. AD/RRT/33.\n\n \n\nCompliance:  As detailed in the Requirement Document. Background: Reissue of AD/RRT/33.\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":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD is described as a reissue of AD/RRT/33 (Background). The text provided does not state any expansion or narrowing of applicability; it continues to apply to \"All Dart RDa-6 series engines\" and requires action per the referenced Service Bulletin or AD (Applicability; Requirement). Therefore there is no indication in this document that the scope has changed from the previous AD."},"complexity_factors":["Short, narrowly targeted directive with a single engine family as applicability (low variety of affected equipment) (Applicability)","Relies on external technical documents (Rolls Royce SB Da 72-451 Rev 5 and AD/RRT/33) for procedural detail, creating dependency on those documents (Requirement; Compliance)","Provides an alternative compliance route, which reduces rigidity but adds decision-making for operators (Requirement)","Lacks technical detail within the AD itself, so interpretation and execution rely on reading and applying the referenced Service Bulletin or AD (Requirement; Compliance)","Clear regulatory origin and legal status reduce legal ambiguity about enforcement (Header)"],"plain_english_summary":"What this instrument changes mechanically\n\n- It requires owners/operators of Rolls Royce Dart RDa-6 series engines to carry out specific maintenance or modification actions specified in a separate technical document. The directive gives two compliance routes: follow Rolls Royce Service Bulletin Da 72-451 Rev 5, or follow the actions set out in AD/RRT/33. (Requirement; Applicability)\n\nWho it affects\n\n- All operators and owners of Dart RDa-6 series engines. They must arrange for the work specified in the referenced documents and meet the timing and procedural requirements contained in those documents. (Applicability; Requirement; Compliance)\n\nWho decides and how compliance is determined\n\n- The Civil Aviation Safety Authority (under the Schedule of Airworthiness Directives) issues the directive and sets the legal requirement that the actions in the referenced documents be followed. Compliance is judged by following the procedures and timescales \"as detailed in the Requirement Document.\" The directive also provides an alternative compliance path by referring to AD/RRT/33. (Header; Requirement; Compliance)\n\nOfficial rationale and what the reissue means\n\n- The document states it is a reissue of AD/RRT/33. That is the stated background for this directive. (Background)\n\nPractical effects on behaviour, incentives and costs\n\n- Who pays: owners/operators pay for whatever inspections, repairs, replacements or modifications the referenced Service Bulletin or AD requires. (Requirement; Compliance)\n- Incentives: operators must choose between two compliance routes (the Rolls Royce Service Bulletin or AD/RRT/33) and will select the route that best fits their operational, technical and cost constraints. (Requirement)\n- Compliance burden and administrative steps: operators must obtain and follow the detailed Requirement Document (the Service Bulletin or AD), schedule the work, and document compliance to the regulator. The AD itself does not list the specific tasks — it refers operators to the Requirement Document for the exact procedures and timing. (Requirement; Compliance)\n- Discretion: the directive limits discretion by mandating compliance with a specified Service Bulletin or an alternative AD, but it leaves the substantive method and timing to those referenced documents. The presence of an alternative (AD/RRT/33) provides some choice about how to meet the obligation. (Requirement)\n\nTrade-offs, opportunity costs and implementation notes\n\n- Trade-offs: operators will face downtime and repair costs in order to meet the directive. Those costs are balanced against the regulatory requirement to perform the specified work. (Requirement; Compliance)\n- Opportunity costs: resources used to satisfy this AD (parts, labour, aircraft out-of-service time) cannot be used elsewhere until the work is complete. (Requirement; Compliance)\n- Implementation risk and access to information: because the AD refers to external documents for technical detail (Rolls Royce SB Da 72-451 Rev 5 or AD/RRT/33), operators must obtain and follow those documents precisely to be compliant. The AD itself contains no technical procedures; the correctness of compliance depends on the content of those referenced documents. (Requirement; Compliance)\n\nWhat changes compared with the previous directive\n\n- The document states it is a reissue of AD/RRT/33; the AD text itself does not state any substantive expansion or narrowing of applicability. It simply restates the requirement and references the service bulletin or AD as the method of compliance. (Background; Requirement)\n\nSource citations\n\n- Issuer and legal basis: Commonwealth of Australia, Civil Aviation Regulations 1998, Part 39 — Schedule of Airworthiness Directives. (Header)\n- Applicability: \"All Dart RDa-6 series engines.\" (Applicability)\n- Requirement: \"Action in accordance with Rolls Royce SB Da 72-451 Rev 5; or AD/RRT/33.\" (Requirement)\n- Compliance: \"As detailed in the Requirement Document.\" (Compliance)\n- Background: \"Reissue of AD/RRT/33.\" (Background)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard, narrow airworthiness directive focused on a specific mechanical component in a specific engine series. It has not expanded beyond its original safety purpose."},"complexity_factors":["Extremely short document (under 200 words)","Only 1 defined applicability (specific engine series)","Simple binary compliance path (two alternative options)","No nested exceptions or conditional logic","No cross-references to other legislation beyond a single related AD and manufacturer service bulletin","Single operational requirement with clear alternative compliance routes"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft engines.\n\n**What it does:**\nThis directive requires owners and operators of **Rolls-Royce Dart RDa-6 series turbine engines** to inspect or replace the **High Pressure Turbine Nozzle Guide Vanes** — critical components that direct hot gases onto the turbine blades. These parts operate under extreme heat and stress; if they fail, the engine can lose power or fail completely.\n\n**Who must comply:**\nAnyone operating, maintaining, or owning aircraft powered by Dart RDa-6 series engines (commonly used in regional turboprop aircraft like the Fokker F27 and some HS 748 models).\n\n**What must be done:**\nOperators must follow one of two paths:\n- **Option 1:** Carry out the specific inspection and maintenance procedures detailed in **Rolls-Royce Service Bulletin Da 72-451 Revision 5** (technical instructions from the engine manufacturer); OR\n- **Option 2:** Comply with **AD/RRT/33** (an earlier, related safety directive).\n\n**When to do it:**\nAccording to the timelines set out in whichever document the operator chooses to follow.\n\n**Why it matters:**\nThis directive was **reissued** to replace an older directive (AD/RRT/33), likely to incorporate updated technical knowledge or revised procedures. It ensures these aging but still-operational engines remain safe. Non-compliance means the aircraft cannot legally fly in Australia."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dart-20-high-pressure-turbine-nozzle-guide-vanes","history":"/api/acts/ad-dart-20-high-pressure-turbine-nozzle-guide-vanes/history","analysis":"/api/acts/ad-dart-20-high-pressure-turbine-nozzle-guide-vanes/analysis","conflicts":"/api/acts/ad-dart-20-high-pressure-turbine-nozzle-guide-vanes/conflicts","importantCases":"/api/acts/ad-dart-20-high-pressure-turbine-nozzle-guide-vanes/important-cases","documents":"/api/acts/ad-dart-20-high-pressure-turbine-nozzle-guide-vanes/documents"}}