{"id":"F2006B08688","name":"AD/CT7/4 - Turbine Rotor Discs","slug":"ad-ct7-4-turbine-rotor-discs","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":51845,"registerId":"commonwealth-F2006B08688-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CT7/4 - Turbine Rotor Discs","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)  General Electric Turbine Engines - CT7 Series\n\n \n\nAD/CT7/4 Turbine Rotor Discs 8/90\n\nApplicability: CT7-5A2/7A.\n\n \n\nRequirement: Action in accordance with General Electric Alert SB (CT7-TP series) A72-228 and A72-229.\n\n \n\nCompliance: Effective from 9 August 1990.\n\n \n\nBackground:  During a walnut shell-cleaning process at an overhaul facility, a number of stages 1 and 2 gas generator turbine rotor discs and stages 3 and 4 power turbine rotor discs may have been shotpeened inadvertently by walnut shells contaminated with steel shot. As a result, these parts may have a reduced low cycle fatigue (LCF) life. The Service Bulletins nominate the suspect parts and new life cycle limits.\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","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope is confined to the CT7-5A2 and CT7-7A engines and to the rotor discs nominated in the General Electric Alert Service Bulletins. The instrument requires following those SBs and sets an effective compliance date (9 August 1990). There is no text in the instrument indicating an expansion or narrowing of scope beyond those stated applicability and SB-nominated parts."},"complexity_factors":["Narrow applicability limited to CT7-5A2 and CT7-7A engines (explicit in 'Applicability: CT7-5A2/7A').","Reliance on external technical documents (General Electric Alert SBs A72-228 and A72-229) for the required actions (explicit in 'Requirement').","Need to identify which specific rotor discs were subject to contaminated walnut-shell shot-peening and apply revised low cycle fatigue life limits (stated in 'Background').","Administrative tasks: implementing SB procedures, updating life records, scheduling inspections/repairs (implied by Service Bulletins nominating parts and new life cycle limits)."],"plain_english_summary":"This directive requires operators and maintenance organisations for GE CT7-5A2/7A engines to implement GE Alert Service Bulletins A72-228 and A72-229 (effective 9 Aug 1990) because walnut‑shell cleaning contaminated with steel shot may have reduced low‑cycle fatigue life of certain rotor discs. Affected parts must be inspected, re‑lifed, repaired or replaced and records updated; direct compliance costs fall to the operators/maintainers."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive addressing a specific manufacturing/maintenance defect discovered in 1990. It has not expanded beyond its original purpose of addressing contaminated turbine rotor discs from a specific cleaning incident."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 2 defined applicability criteria (engine models CT7-5A2 and CT7-7A)","Single requirement referencing external documents (the Service Bulletins) rather than setting out detailed technical steps","No nested conditional logic or exceptions","No cross-references to other legislation or regulations beyond the parent Civil Aviation Regulations 1998","Straightforward compliance date with no phased or conditional implementation"],"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) for aircraft engines.\n\n**What it does:** It requires owners or operators of specific General Electric CT7 turbine engines (models CT7-5A2 and CT7-7A) to follow two specific General Electric Service Bulletins (A72-228 and A72-229). These bulletins identify certain turbine rotor discs that may have been accidentally damaged during cleaning and sets new, stricter limits on how long those parts can be used before they must be replaced.\n\n**Why it matters:** During engine overhauls, some turbine discs were cleaned using walnut shells that were contaminated with steel shot (a blasting material). This accidental \"shotpeening\" (a surface-hardening process that was not supposed to happen) may have damaged the metal and reduced its fatigue life — meaning the parts could crack or fail earlier than expected. Since turbine rotor discs spin at extreme speeds and temperatures, a failure could cause catastrophic engine damage and potentially endanger the aircraft and passengers.\n\n**Who must comply:** Anyone operating or maintaining aircraft with these specific CT7 engine models must follow the Service Bulletins' instructions and respect the new, reduced life limits for the affected parts. The directive took effect on 9 August 1990."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ct7-4-turbine-rotor-discs","history":"/api/acts/ad-ct7-4-turbine-rotor-discs/history","analysis":"/api/acts/ad-ct7-4-turbine-rotor-discs/analysis","conflicts":"/api/acts/ad-ct7-4-turbine-rotor-discs/conflicts","importantCases":"/api/acts/ad-ct7-4-turbine-rotor-discs/important-cases","documents":"/api/acts/ad-ct7-4-turbine-rotor-discs/documents"}}