{"id":"F2006B07240","name":"AD/T53/11 - Replacement Of Compressor Rotor Discs and Impeller Assembly","slug":"ad-t53-11-replacement-of-compressor-rotor-discs-and-impeller-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49108,"registerId":"commonwealth-F2006B07240-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/T53/11 - Replacement Of Compressor Rotor Discs and Impeller Assembly","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)  AlliedSignal (Lycoming) Turbine Engines - T53 Series\n\n \n\nAD/T53/11 Replacement Of Compressor Rotor Discs and\n\nImpeller Assembly\n\nApplicability: All models T5309C, T5311A, T5311B engines. Document:  1. Lycoming SB No. 0033; or\n\n2. FAA AD 74-09-03; or\n\n \n\n3. AD/LYC-T/12. Compliance: Before 28 June 1974\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\n1/86\n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The text sets a clear, narrowly focused requirement (replace compressor rotor discs and impeller assembly) for three named engine models and a single compliance deadline. There is no indication in the provided text that the instrument’s scope has been expanded or narrowed from its original framing; it remains limited to the listed engine models and the specified replacement requirement, with procedural detail deferred to the referenced technical documents."},"complexity_factors":["Very short, single-action directive (replacement of specified parts).","Narrow applicability to three specific engine models (T5309C, T5311A, T5311B).","Fixed single compliance deadline (before 28 June 1974).","Technical details and procedures are not in the directive but delegated to three external documents, requiring consultation of those texts.","No procedural detail in text about exemptions, enforcement, or alternative compliance methods, which creates dependency on other sources for implementation.","Historical date and cross-references to earlier service bulletins/ADs may require archival retrieval to apply the directive practically."],"plain_english_summary":"What this instrument does, mechanically\n\n- Requires replacement of the compressor rotor discs and the impeller assembly on certain AlliedSignal (Lycoming) T53 series turbine engines. (Title)\n- Applies specifically to engine models T5309C, T5311A and T5311B. (Applicability)\n- Directs compliance with the technical instructions given in one of three referenced documents: Lycoming Service Bulletin No. 0033; FAA Airworthiness Directive 74-09-03; or AD/LYC-T/12. (Document)\n- Sets a hard compliance deadline: the replacements must be done before 28 June 1974. (Compliance)\n\nWho this affects and who decides\n\n- Aircraft operators and maintenance organisations responsible for aircraft fitted with the listed engine models are the parties obliged to comply, because the directive names the engine models and imposes a replacement requirement. (Applicability; Compliance)\n- The detailed work to be done (what parts, how to replace them, inspections) is determined by the referenced technical documents; the directive itself points to those documents as the instructions to follow. (Document)\n\nWhy it matters (stated purpose and testing that claim against visible effects)\n\n- The instrument’s title and mandatory replacement instruction indicate a safety-driven mechanical intervention: replacement of specific rotating engine components. (Title)\n- That stated purpose implies an operational cost for affected operators: parts, labour, and aircraft downtime to perform the replacements, because a mandatory component replacement before a fixed date requires maintenance input and removal from service. (Compliance)\n- The directive concentrates its obligation on operators of three engine models, so the economic cost is concentrated on that group while the safety effect (if successful) would be broader for airworthiness outcomes; the text itself does not quantify costs or benefits. (Applicability)\n\nMechanics of compliance and discretion\n\n- The directive makes compliance conditional on following one of the three named technical documents; therefore the regulator delegates technical method and specification to those documents rather than setting the procedure in the directive text itself. Operators must consult and follow whichever referenced document they rely on. (Document)\n- The timeline is fixed and short (a single deadline date). The directive does not in its text specify exemptions, phased compliance, or alternative means of compliance; any such flexibility would depend on other regulatory mechanisms or later instruments not contained in this text. (Compliance)\n\nPractical trade-offs and implementation notes\n\n- Implementation requires sourcing replacement rotor discs and impeller assemblies and arranging maintenance slots; this creates direct costs (parts and labour) and opportunity costs (aircraft out of service). (Compliance)\n- Because the directive points to external technical documents for the how-to, uncertainty or administrative burden can arise from needing to obtain and interpret those documents. (Document)\n- The directive’s effect on competition, prices, or ownership is indirect: it imposes a compliance cost on operators of the named engines which may influence their operating decisions (retain, repair, or replace engines/aircraft), but the directive itself does not set economic measures such as subsidies or penalties. (Applicability; Compliance)\n\nSource citations\n\n- Applicability: “All models T5309C, T5311A, T5311B engines.” (Applicability)\n- Technical instructions: “Lycoming SB No. 0033; or FAA AD 74-09-03; or AD/LYC-T/12.” (Document)\n- Deadline: “Before 28 June 1974.” (Compliance)\n\nNote on limits of this text\n\n- The directive imposes a specific mandatory action and deadline and points to external technical documents for the detailed procedure. The brief text here does not state the safety incident or technical failure that led to the requirement, nor does it provide cost estimates, exemptions, or enforcement procedures; those items would need to be sought in the referenced documents or other regulatory records. (Title; Document; Compliance)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue airworthiness directive focused on a specific mechanical defect in specific engine models. It has not expanded beyond its original purpose of mandating replacement of faulty compressor components."},"complexity_factors":["Very short document (approximately 200 words)","Only 3 defined applicability criteria (specific engine models)","Simple binary compliance requirement (replace parts by fixed date)","No nested exceptions or conditional logic","Three alternative compliance documents provided (simple 'or' structure)","No cross-references to other legislation beyond the enabling regulations (CAR 1998 Part 39)","Single operative requirement with clear deadline"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** issued by Australia's Civil Aviation Safety Authority (CASA) under the Civil Aviation Regulations 1998. It mandates a specific safety fix for certain aircraft engines.\n\n**What it does:**\n- Requires the **replacement of compressor rotor discs and impeller assemblies** on specific AlliedSignal (Lycoming) T53 series turbine engines\n- These are helicopter engines (commonly used in aircraft like the Bell UH-1 Iroquois \"Huey\")\n\n**Who it affects:**\n- Owners and operators of aircraft with **T5309C, T5311A, or T5311B model engines**\n- Maintenance organisations servicing these engines\n\n**Why it matters:**\n- Compressor rotor discs and impellers are critical rotating components. If they fail in flight, the engine can destroy itself (called an \"uncontained engine failure\"), potentially causing the aircraft to crash\n- This AD addresses a known safety defect to prevent catastrophic engine failure\n\n**What must be done:**\n- The replacement must be completed **before 28 June 1974**\n- Operators can follow any of three approved technical documents to perform the work:\n  - Lycoming Service Bulletin No. 0033, OR\n  - FAA Airworthiness Directive 74-09-03, OR\n  - Australian AD/LYC-T/12\n\n**Key point:** This is a **mandatory safety order** — compliance is legally required, not optional."}},"importantCases":[],"_links":{"self":"/api/acts/ad-t53-11-replacement-of-compressor-rotor-discs-and-impeller-assembly","history":"/api/acts/ad-t53-11-replacement-of-compressor-rotor-discs-and-impeller-assembly/history","analysis":"/api/acts/ad-t53-11-replacement-of-compressor-rotor-discs-and-impeller-assembly/analysis","conflicts":"/api/acts/ad-t53-11-replacement-of-compressor-rotor-discs-and-impeller-assembly/conflicts","importantCases":"/api/acts/ad-t53-11-replacement-of-compressor-rotor-discs-and-impeller-assembly/important-cases","documents":"/api/acts/ad-t53-11-replacement-of-compressor-rotor-discs-and-impeller-assembly/documents"}}