{"id":"F2006B07246","name":"AD/T53/17 - Centrifugal Compressor Impellers","slug":"ad-t53-17-centrifugal-compressor-impellers","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":49129,"registerId":"commonwealth-F2006B07246-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/T53/17 - Centrifugal Compressor Impellers","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nAlliedSignal (Lycoming) Turbine Engines \\- T53 Series\n\nAD/T53/17 Centrifugal Compressor Impeller 3/86\n\nApplicability: All model T5317A, T5313B and T 53-L-13B series engines with centrifugal Compressor Impeller P/N 1-100-078-07 and 08 installed.\n\nRequirement: Inspect impeller in accordance with Lycoming Service Bulletin No 0052.\n\nCompliance: 1. On T5313B and T53-L-13B series engines within 200 engine operating cycles on impellers that have accumulated 4600 cycles and thereafter at intervals not exceeding 500 cycles.\n\n2. On T5317A engines within 200 engine operating cycles on impellers that have accumulated 3500 cycles and thereafter at intervals not exceeding 500 cycles.\n\nBackground: This Directive is issued to reflect the manufacturers special inspection requirements, advised in LYC SB NO 0052, which are necessary to enable these impellers to achieve the maximum life limits advised in Service Bulletins No 0020 and 0034.","sortOrder":0}],"analysis":{"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 specific engine models. It has not expanded beyond its original safety purpose."},"complexity_factors":["Very short document (under 300 words)","Only 3 defined applicability criteria (engine models and part numbers)","Simple conditional structure: two compliance paths based on engine model","No cross-references to other legislation or regulations beyond the parent Civil Aviation Regulations 1998","Single requirement with clear timing triggers (operating cycles)","No nested exceptions or complex definitions"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires specific inspections of certain helicopter engines to prevent mechanical failure.\n\n**What it does:**\n- Orders owners and operators to inspect the **centrifugal compressor impeller** (a spinning part that compresses air in the engine) on specific AlliedSignal (Lycoming) T53 series turbine engines.\n- The inspection must follow the manufacturer's Service Bulletin No. 0052.\n\n**Who it affects:**\n- Anyone operating aircraft with these specific engine models: **T5317A, T5313B, and T53-L-13B**.\n- Specifically targets engines with impeller part numbers **1-100-078-07 and 1-100-078-08**.\n\n**When inspections are due:**\n- **T5313B and T53-L-13B engines:** Within 200 operating cycles once the impeller hits 4,600 total cycles, then every 500 cycles after that.\n- **T5317A engines:** Within 200 operating cycles once the impeller hits 3,500 total cycles, then every 500 cycles after that.\n\n**Why it matters:**\nThese impellers have defined maximum life limits, but they need special inspections to actually reach those limits safely. Without these checks, the impeller could fail in flight — potentially causing engine failure and endangering lives. This AD makes the inspections legally mandatory rather than just a manufacturer recommendation."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive does not expand or narrow the set of parts or engines beyond those identified; it implements the manufacturer’s special inspection requirements by mandating inspections per Lycoming Service Bulletin No 0052 for the specified impellers and engine models. The Background states the AD was issued to reflect the manufacturer’s inspection requirements necessary to enable the impellers to reach the maximum life limits given in Service Bulletins No 0020 and 0034, so the scope aligns with that stated original intent (Requirement; Background)."},"complexity_factors":["Narrow applicability: specific engine models (T5317A, T5313B, T53-L-13B) and specific impeller part numbers (1-100-078-07, 1-100-078-08) (Applicability).","Reference to an external technical document (Lycoming Service Bulletin No 0052) for the detailed inspection procedure (Requirement).","Different threshold cycles before the first mandated inspection depending on engine model (4,600 cycles for T5313B/T53-L-13B; 3,500 cycles for T5317A) and a common repeat interval (500 cycles) (Compliance, items 1–2).","Timing window requirement to perform the initial inspection within 200 engine operating cycles after reaching the threshold (Compliance).","Operational and administrative tracking of engine operating cycles required to demonstrate compliance (Compliance)."],"plain_english_summary":"What this instrument does (mechanics):\n\n- Requires inspections of specific centrifugal compressor impellers (part numbers 1-100-078-07 and 1-100-078-08) installed in AlliedSignal (Lycoming) T53 series turbine engines. The inspections must be carried out in accordance with Lycoming Service Bulletin No 0052 (Requirement).\n\nWho it affects:\n\n- Aircraft owners and operators that use engines of model T5317A, T5313B or T53-L-13B fitted with the listed impeller part numbers (Applicability).\n- Maintenance organisations and engineers who perform engine inspections and repairs, because they must follow the referenced service bulletin (Requirement).\n\nWhat it requires and when (timing):\n\n- For T5313B and T53-L-13B engines: inspect any impeller that has already accumulated 4,600 engine operating cycles within the next 200 engine operating cycles, and then repeat inspections at intervals not exceeding 500 cycles thereafter (Compliance, item 1).\n- For T5317A engines: inspect any impeller that has already accumulated 3,500 engine operating cycles within the next 200 engine operating cycles, and then repeat inspections at intervals not exceeding 500 cycles thereafter (Compliance, item 2).\n\nWhy it was issued (stated purpose):\n\n- The directive implements the manufacturer’s special inspection requirements, as set out in Lycoming Service Bulletin No 0052, which the AD says are necessary to enable these impellers to reach the maximum life limits given in Service Bulletins No 0020 and No 0034 (Background). That is the official purpose claim; the directive achieves that mechanically by mandating the referenced inspections (Requirement; Background).\n\nWho pays, who decides, and what behaviour changes:\n\n- Who pays: operators or their maintenance contractors pay for the inspections, any resulting maintenance, and the operational downtime required to perform them. The AD does not subsidise or specify funding—operators bear the direct cost (Requirement; Compliance).\n- Who decides: the Civil Aviation Safety Authority issues the airworthiness directive, but the technical content of the inspection is delegated to the manufacturer’s Service Bulletin No 0052, which maintenance personnel must follow (Applicability; Requirement).\n- Behaviour changes required: operators must (a) identify affected engines and impellers, (b) track accumulated engine operating cycles for those impellers, (c) schedule and carry out the inspection within the specified 200-cycle window when the threshold is reached, and (d) repeat inspections every 500 cycles thereafter (Applicability; Compliance; Requirement).\n\nCompliance burden, incentives and trade-offs:\n\n- Compliance burden: tracking cycle counts, scheduling inspections within a 200-cycle window after a threshold is reached, and repeating inspections every 500 cycles creates ongoing administrative and maintenance resource requirements for operators and maintenance providers (Compliance; Requirement).\n- Incentives: by mandating inspections that align with the manufacturer’s bulletin, the AD reduces the technical discretion of operators about inspection frequency but provides a clear path to meeting the manufacturer-advised life limits (Requirement; Background). Operators gain the ability to keep impellers in service up to the stated life limits only if they meet the inspection regime; failing to inspect risks non-compliance with the AD.\n- Trade-offs and opportunity costs: operators must allocate maintenance time and resources to these inspections rather than other maintenance or operational tasks; there will be direct inspection costs and possible removal/repair costs if inspections find defects. The AD does not specify remediation actions beyond requiring the inspection per the service bulletin (Requirement; Background).\n\nImplementation and operational risk:\n\n- The AD depends on the content and availability of Lycoming Service Bulletin No 0052 for the technical inspection procedure; variations in interpretation or capability among maintenance providers could affect consistency of implementation (Requirement; Background).\n- The AD sets a strict timing regime (200-cycle window, then 500-cycle repeating intervals) which creates scheduling risk if operators are unable to access maintenance resources in time (Compliance).\n\nConcentrated benefits and diffuse costs (mechanism, not judgement):\n\n- The potential safety or durability benefit from catching impeller issues accrues to individual engine owners/operators and their passengers; the costs (inspection and downtime) are borne by those same operators and their maintenance contractors. The AD does not create an ongoing subsidy or offset to those costs (Applicability; Requirement; Compliance; Background)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-t53-17-centrifugal-compressor-impellers","history":"/api/acts/ad-t53-17-centrifugal-compressor-impellers/history","analysis":"/api/acts/ad-t53-17-centrifugal-compressor-impellers/analysis","conflicts":"/api/acts/ad-t53-17-centrifugal-compressor-impellers/conflicts","importantCases":"/api/acts/ad-t53-17-centrifugal-compressor-impellers/important-cases","documents":"/api/acts/ad-t53-17-centrifugal-compressor-impellers/documents"}}