{"id":"F2006B02319","name":"AD/ALF/5 - Fourth Stage Turbine Rotors Assembly P/N 2-141-170-23 and -27 - Replacement","slug":"ad-alf-5-fourth-stage-turbine-rotors-assembly-p-n-2-141-170-23-and-27-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41549,"registerId":"commonwealth-F2006B02319-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ALF/5 - Fourth Stage Turbine Rotors Assembly P/N 2-141-170-23 and -27 - Replacement","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 \\- ALF502 and LF507 Series\n\nAD/ALF/5 Fourth Stage Turbine Rotors Assembly\n\nP/N 2-141-170-23 and \\-27 \\- Replacement\n\n  \n1/86\n\nApplicability: All Avco Lycoming ALF 502 Series Turbo fan engines as listed in the requirement document.\n\nDocument: 1. Avco Lycoming SB ALF 502-72-0038, Rev. 1; or\n\n2. AD/LYC-T/22.\n\nNote: FAA AD T83-03-51 refers.\n\nCompliance: Within the next 10 engine operating hours.\n\nBackground: This Directive is issued to ensure compliance with the manufacturer's requirement document that introduces an improved fourth turbine rotor incorporating blades which were inspected for casting defects by more stringent inspection procedures.\n\nCompliance with the document supersedes those requirements of the Avco Lycoming SB ALF502-72-0027 listed in AD/LYC-T/21.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive focused on a specific mechanical defect in specific engine models. It remains precisely scoped to its original purpose: mandating replacement of identified faulty components."},"complexity_factors":["Single, specific mechanical part replacement requirement","Only 2 applicable document references","Simple compliance timeframe (10 operating hours)","No conditional logic or nested exceptions","Clear, unambiguous applicability statement","Minimal cross-referencing (only supersedes one prior bulletin reference)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance action on aircraft engines.\n\n**What it does:**\nThis directive orders the **replacement of fourth-stage turbine rotors** (specific parts numbered 2-141-170-23 and 2-141-170-27) in certain AlliedSignal (formerly Lycoming) ALF 502 series turbofan engines.\n\n**Who it affects:**\n- Owners and operators of aircraft using **Avco Lycoming ALF 502 Series turbofan engines**\n- Maintenance organisations servicing these engines\n\n**Why it matters:**\nThe existing turbine rotors need replacement because the manufacturer developed an improved version with blades that underwent **stricter quality inspections for casting defects** (flaws from the manufacturing process). This prevents potential engine failures that could endanger flight safety.\n\n**Key requirements:**\n- **When:** Must be done within the next **10 engine operating hours** — meaning very urgent compliance\n- **What to follow:** Either Avco Lycoming Service Bulletin ALF 502-72-0038 (Revision 1) or an earlier Australian directive AD/LYC-T/22\n- **Note:** This replaces requirements from an earlier service bulletin (ALF502-72-0027) that was referenced in previous directive AD/LYC-T/21\n\n**In short:** If you operate an aircraft with this specific engine, you must replace these turbine rotor parts almost immediately to ensure the engine meets current safety standards."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This AD replaces or modifies earlier requirements by directing replacement with an improved fourth stage turbine rotor and states that compliance with the referenced document supersedes listed requirements of Avco Lycoming SB ALF502-72-0027 as identified in AD/LYC-T/21 (Background; Document). The instrument therefore changes prior technical-standards and compliance obligations for the affected ALF 502 series engines."},"complexity_factors":["Short, mandatory compliance window (10 engine operating hours) increases operational urgency and logistical complexity (Compliance).","Cross-references to manufacturer service bulletin and another AD require operators to consult multiple documents to confirm technical steps (Document).","Technical nature of the action (turbojet turbine rotor replacement) requires qualified maintenance personnel and specific parts availability.","Supersession of earlier service-bulletin requirements introduces a need to reconcile prior compliance records and obligations (Background).","Applicability limited to a specific engine family reduces scope but concentrates impact on those operators and maintenance chains (Applicability)."],"plain_english_summary":"The directive requires owners/operators of affected Avco Lycoming ALF 502 turbofan engines to replace the fourth-stage turbine rotor (specified part numbers) within 10 engine operating hours, following the procedures in the manufacturer’s service bulletin or the referenced AD. It implements a safety-driven upgrade—new rotors use blades inspected under stricter casting controls—and imposes immediate parts, labour and downtime costs on operators."}},"importantCases":[],"_links":{"self":"/api/acts/ad-alf-5-fourth-stage-turbine-rotors-assembly-p-n-2-141-170-23-and-27-replacement","history":"/api/acts/ad-alf-5-fourth-stage-turbine-rotors-assembly-p-n-2-141-170-23-and-27-replacement/history","analysis":"/api/acts/ad-alf-5-fourth-stage-turbine-rotors-assembly-p-n-2-141-170-23-and-27-replacement/analysis","conflicts":"/api/acts/ad-alf-5-fourth-stage-turbine-rotors-assembly-p-n-2-141-170-23-and-27-replacement/conflicts","importantCases":"/api/acts/ad-alf-5-fourth-stage-turbine-rotors-assembly-p-n-2-141-170-23-and-27-replacement/important-cases","documents":"/api/acts/ad-alf-5-fourth-stage-turbine-rotors-assembly-p-n-2-141-170-23-and-27-replacement/documents"}}