{"id":"F2006B02308","name":"AD/ALF/12 - Introduction of Improved Third Stage Turbine Rotor Assembly","slug":"ad-alf-12-introduction-of-improved-third-stage-turbine-rotor-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41538,"registerId":"commonwealth-F2006B02308-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ALF/12 - Introduction of Improved Third Stage Turbine Rotor Assembly","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/12 Introduction of Improved Third Stage\n\nTurbine Rotor Assembly\n\n  \n13/93\n\nApplicability: All ALF502 L and R series engines with third stage rotor assemblies listed in the Requirement Documents.\n\nRequirement: Install improved or reworked third stage turbine rotor assemblies in accordance with Textron-Lycoming Service Bulletins ALF502L 72-270 or ALF502R 72-270 as applicable.\n\nNote: FAA AD 93-14-13 also refers.\n\nCompliance: Effective 1 January 1994. As detailed in the Requirement Documents.\n\nBackground: This Directive is issued to address reports of cracking in the third stage turbine disc blade retention slots and requires either fitment of an improved disc or rework of existing discs to provide a revised blade retention slot profile.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive applies to the engines and rotor assemblies specified in the Applicability paragraph and requires installation or rework as described in the Requirement paragraph. The instrument's stated purpose is to address reported cracking in third stage turbine disc blade retention slots (Background). The text does not expand or narrow that stated scope beyond those specified engines and the remedial actions in the Requirement Documents, so the scope as presented remains consistent with the directive's stated intent (Applicability, Requirement, Background)."},"complexity_factors":["Technical specificity: compliance must follow Textron‑Lycoming Service Bulletins ALF502L 72-270 or ALF502R 72-270 (Requirement).","Narrow applicability: applies only to ALF502 L and R series engines with third stage rotor assemblies listed in the Requirement Documents (Applicability).","Mandatory remedial action: requires either fitting an improved disc or reworking existing discs to a revised profile (Requirement, Background).","Fixed compliance date: effective 1 January 1994, creating a time-bound obligation (Compliance).","Cross-reference to another regulator's AD (FAA AD 93-14-13), which may require coordination for internationally operated aircraft (Note)."],"plain_english_summary":"The directive mandates that operators/owners of AlliedSignal (Lycoming) ALF502 L and R engines fitted with certain third‑stage rotor assemblies must install an “improved” or reworked third‑stage turbine rotor per Textron‑Lycoming service bulletins, to address reported cracking in blade retention slots.  \n\nIssued and enforced by CASA (effective 1 Jan 1994) the rule prescribes the engineering method via the manufacturer’s bulletins and places compliance scheduling and costs on the affected engine operators."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, original airworthiness directive with a narrow, well-defined scope addressing a specific safety-critical defect in a specific engine series. There is no evidence of scope creep; the directive precisely targets the identified cracking issue in third stage turbine discs."},"complexity_factors":["Single, specific technical requirement with clear alternative compliance paths (replacement OR rework)","Only 2 defined applicability criteria (engine series and specific rotor assemblies)","Cross-references to external technical documents (Service Bulletins) rather than internal legislative provisions","No nested exceptions or conditional logic — straightforward mandate with single compliance deadline","Short document (approximately 150 words of substantive text)","Single background rationale with no competing policy objectives"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). Think of it as a \"recall notice\" for aircraft engines, but with legal force.\n\n**What it does:** It requires owners and operators of specific AlliedSignal (Lycoming) ALF502 and LF507 series turbine engines to replace or modify the **third stage turbine rotor assembly** — a critical rotating component in the engine's hot section.\n\n**Who it affects:** Anyone operating aircraft with ALF502 L or R series engines that have certain third stage rotor assemblies (specific part numbers are listed in the referenced service bulletins).\n\n**Why it matters:** The engine manufacturer found **cracking in the blade retention slots** of the turbine disc — the grooves that hold the turbine blades in place. If these cracks progress, blades could detach at high speed, causing catastrophic engine failure and potentially bringing down an aircraft. The fix involves either:\n- Installing a new, improved disc design, OR\n- Reworking (machining/modifying) existing discs to a safer profile\n\n**What must be done:** Compliance is mandatory by **1 January 1994**, following the technical instructions in Textron-Lycoming Service Bulletins ALF502L 72-270 or ALF502R 72-270 (depending on engine variant). The FAA issued an equivalent directive (AD 93-14-13), showing this was a coordinated international safety response."}},"importantCases":[],"_links":{"self":"/api/acts/ad-alf-12-introduction-of-improved-third-stage-turbine-rotor-assembly","history":"/api/acts/ad-alf-12-introduction-of-improved-third-stage-turbine-rotor-assembly/history","analysis":"/api/acts/ad-alf-12-introduction-of-improved-third-stage-turbine-rotor-assembly/analysis","conflicts":"/api/acts/ad-alf-12-introduction-of-improved-third-stage-turbine-rotor-assembly/conflicts","importantCases":"/api/acts/ad-alf-12-introduction-of-improved-third-stage-turbine-rotor-assembly/important-cases","documents":"/api/acts/ad-alf-12-introduction-of-improved-third-stage-turbine-rotor-assembly/documents"}}