{"id":"F2006B02309","name":"AD/ALF/13 - Third Stage Compressor Disc Inspection","slug":"ad-alf-13-third-stage-compressor-disc-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41539,"registerId":"commonwealth-F2006B02309-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ALF/13 - Third Stage Compressor Disc Inspection","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/13 Third Stage Compressor Disc Inspection 13/93\n\nApplicability: All Textron-Lycoming ALF 502 L and R series engines incorporating 3rd stage compressor discs as detailed the Requirement documents.\n\nRequirement: Inspect affected 3rd stage compressor discs in accordance with Textron-Lycoming Service Bulletins ALF 502L 72-259 or ALF 502R 72-259 as applicable.\n\nNote: FAA AD 93-10-07 also refers.\n\nCompliance: Effective 1 January 1994. As detailed in the Requirement Documents.\n\nBackground: A number of 3rd stage compressor discs have been identified where the Sermetel W protective coating may be defective due to improper surface preparation. This can lead to lack of adhesion and subsequent flaking of the coating. Degraded coating can result in corrosion of the disc and potential disc failure.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, one-off safety directive addressing a specific manufacturing defect in specific engine models. It has not expanded beyond its original purpose of mandating inspection of defective compressor disc coatings."},"complexity_factors":["Single, specific mechanical component targeted (3rd stage compressor disc)","Only two applicable service bulletins referenced","No nested exceptions or conditional compliance pathways","Straightforward applicability test (engine model + component presence)","Single compliance date with no phased implementation","Minimal defined terms (only standard aviation terminology like 'L' and 'R' for left/right engine variants)"],"plain_english_summary":"This is an **Airworthiness Directive** — 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:**\nOrders owners and operators of certain **AlliedSignal (Lycoming) ALF 502 and LF507 series turbine engines** to inspect the **third-stage compressor discs** for a dangerous manufacturing defect.\n\n**The problem:**\nSome compressor discs have a protective coating called \"Sermetel W\" that may have been applied incorrectly. If the surface wasn't prepared properly, the coating can flake off, allowing the metal disc underneath to corrode. A corroded disc can crack and break apart during flight — potentially causing catastrophic engine failure.\n\n**Who must act:**\nAnyone operating aircraft with **Textron-Lycoming ALF 502 L or R series engines** that have the affected third-stage compressor discs.\n\n**What they must do:**\nFollow the inspection procedures in specific **Textron-Lycoming Service Bulletins** (ALF 502L 72-259 or ALF 502R 72-259, depending on engine model). These documents detail exactly how to check the discs and what to do if problems are found.\n\n**When:**\nThe directive became mandatory on **1 January 1994**.\n\n**Why it matters:**\nCompressor discs spin at extremely high speeds. If one fails due to corrosion, it can destroy the engine and potentially damage the aircraft. This directive prevents that by catching defective coatings before they cause accidents."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope aligns with its stated purpose: it targets third‑stage compressor discs on Textron‑Lycoming ALF 502 L and R engines and requires inspection per the referenced service bulletins to detect degraded protective coating and corrosion that could lead to disc failure. The AD does not expand beyond that technical focus and delegates inspection procedures to the manufacturer service documents. (Applicability; Requirement; Background)"},"complexity_factors":["Narrow technical scope limited to specific engine models and a specific component (third‑stage compressor disc). (Applicability)","Compliance depends on external manufacturer service bulletins rather than being self‑contained in the AD text, adding a step to obtain and interpret those documents. (Requirement)","Requires technically skilled maintenance inspections and potential follow‑up repairs, which are specialised but routine for certified maintenance organisations. (Requirement)","Cross‑reference to an FAA airworthiness directive introduces inter‑jurisdictional alignment but not additional procedural complexity within the AD itself. (Note)","The AD does not set inspection thresholds or procedures in the text, leaving operational detail to the service bulletins and maintenance organisations. (Requirement)"],"plain_english_summary":"This directive requires owners/operators and maintenance organisations of Textron‑Lycoming ALF 502 L and R series engines to inspect specified third‑stage compressor discs (effective 1 Jan 1994). Inspections must follow the manufacturer’s service bulletins cited by the AD because Sermetel W coating applied to some discs may flake, allowing corrosion and risking disc failure. Compliance shifts inspection and repair costs and procedural detail to operators and the Textron‑Lycoming service instructions."}},"importantCases":[],"_links":{"self":"/api/acts/ad-alf-13-third-stage-compressor-disc-inspection","history":"/api/acts/ad-alf-13-third-stage-compressor-disc-inspection/history","analysis":"/api/acts/ad-alf-13-third-stage-compressor-disc-inspection/analysis","conflicts":"/api/acts/ad-alf-13-third-stage-compressor-disc-inspection/conflicts","importantCases":"/api/acts/ad-alf-13-third-stage-compressor-disc-inspection/important-cases","documents":"/api/acts/ad-alf-13-third-stage-compressor-disc-inspection/documents"}}