{"id":"F2009L01972","name":"AD/CF34/17 - High Pressure Seal","slug":"ad-cf34-17-high-pressure-seal","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":79168,"registerId":"commonwealth-F2009L01972-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"General Electric Turbine Engines - CF34 ","sectionType":"division","heading":"General Electric Turbine Engines - CF34 Series","content":"### General Electric Turbine Engines - CF34 Series\n\n| AD/CF34/17 | High Pressure Seal | 6/2009 |\n| ---------- | ------------------ | ------ |\n\n| Applicability: | General Electric Company (GE) CF34-1A, -3A, -3A1, -3A2, -3B, and -3B1 turbofan engines, with high-pressure (HP) rotor 4-step air balance piston stationary seals(4-step seals), part numbers (P/Ns) 4923T54G01, 6019T90G03, 6037T99G01, 6037T99G02, and 6037T99G03, installed.Note 1: These engines are installed on, but not limited to, Bombardier, Inc. Aeroplane models CL-600-2A12, -2B16, and -2B19.                                                                                                                                                          |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Remove the 4-step seals, P/Ns 4923T54G01, 6019T90G03, 6037T99G01, 6037T99G02, and 6037T99G03.2. Incorporate an 8-step seal, either by modifying the existing 4-step seal to an8-step seal, or by replacing it with an 8-step seal.Information on modifying the seal and part number configuration charts, can be found in GE Service Bulletin (SB) No. CF34-AL S/B 72-0238, dated 27 July 2007(CL-600-2B19), and SB No. CF34-BJ S/B 72-0217, dated 27 July 2007(CL-600-2A12 and CL-600-2B16).Note 2: FAA AD 2009-07-12 Amdt 39-15871 dated 26 March 2009 refers. |\n| Compliance:    | At the next piece part exposure after the effective date of this AD, unless the actions have already been done.DefinitionFor the purposes of this AD, piece-part exposure means when the 4-step seal is removed from the engine or when the combustion liner is removed.                                                                                                                                                                                                                                                                                            |\n|                | This Airworthiness Directive becomes effective on 4 June 2009.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |\n| Background:    | This AD results from the investigation of an airplane accident. Both engines experienced high-power flameout. Rotation of the HP rotors was not maintained during descent and the engines could not be restarted.                                                                                                                                                                                                                                                                                                                                                   |\n\n|     | The issuing of this AD is intended to prevent the inability to restart both engines after flameout due to excessive friction of the 4-step seal, which could result in subsequent forced landing of the aeroplane. |\n| --- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n17 April 2009","sortOrder":0},{"sectionNumber":"AD/CF34/17","sectionType":"part","heading":"AD/CF34/17","content":"## AD/CF34/17","sortOrder":1},{"sectionNumber":"High Pressure Seal","sectionType":"part","heading":"High Pressure Seal","content":"## High Pressure Seal","sortOrder":2},{"sectionNumber":"6/2009","sectionType":"part","heading":"6/2009","content":"## 6/2009","sortOrder":3}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"No. The AD's scope aligns with its stated purpose: it targets specified 4-step seals on listed CF34 engines and mandates modification or replacement to 8-step seals per GE service bulletins to prevent restart failure after flameout (Applicability; Requirement; Background)."},"complexity_factors":["Narrow technical applicability: specifies particular CF34 engine models and five distinct 4-step seal part numbers (Applicability).","Compliance timing: obligation is triggered at the 'next piece-part exposure', which depends on each operator's maintenance schedule and creates operational scheduling variability (Compliance; Definition).","Procedure dependency: allows either modification of existing 4-step seals or replacement with 8-step seals and refers to GE Service Bulletins for the method and part-number changes, creating reliance on OEM documentation and parts availability (Requirement).","Safety-critical outcome: the AD responds to an accident investigation and targets a single failure mechanism (excessive seal friction) that could prevent engine restart; consequence of non-compliance is high (Background; Requirement).","Operational burden falls on aircraft operators and maintenance organisations to perform the seal change and to source or carry out the modification per GE SBs, implying direct maintenance cost and parts-management responsibilities (Applicability; Requirement)."],"plain_english_summary":"Requires operators of GE CF34-1A, -3A, -3A1, -3A2, -3B and -3B1 engines fitted with listed 4‑step high‑pressure rotor seals to remove and either modify or replace them with 8‑step seals at the next piece‑part exposure. Affects aircraft operators and maintenance providers; intended to reduce excessive seal friction that could prevent engine restart after flameout, thereby lowering forced‑landing risk."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope — addressing a specific mechanical defect in specific engine models. It has not expanded beyond the original safety issue identified from the accident investigation."},"complexity_factors":["Single, specific technical requirement (replace/modify one component)","Only 5 specific part numbers affected","Clear compliance deadline ('next piece part exposure') with simple definition provided","No nested exceptions or conditional logic","Short document (approximately 300 words)","Only 1 defined term ('piece-part exposure')","Straightforward applicability table"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's aviation regulator (CASA) for specific aircraft engines.\n\n**What it does:**\nOrders airlines and aircraft operators to replace or modify a particular engine seal (the \"4-step seal\") in certain General Electric CF34 jet engines. The old seal must be swapped for a new \"8-step seal\" design.\n\n**Who it affects:**\nOperators of Bombardier regional jets (CL-600 series) powered by specific GE CF34 engine models. This includes airlines flying these aircraft in Australia.\n\n**Why it matters:**\nThis directive was triggered by a real accident where both engines on a plane flamed out (stopped working) at high power. The pilots couldn't restart the engines during descent because the old 4-step seal created too much friction, preventing the engine's high-pressure rotor from spinning properly. The fix prevents a repeat of this dangerous scenario, which could force an emergency landing."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cf34-17-high-pressure-seal","history":"/api/acts/ad-cf34-17-high-pressure-seal/history","analysis":"/api/acts/ad-cf34-17-high-pressure-seal/analysis","conflicts":"/api/acts/ad-cf34-17-high-pressure-seal/conflicts","importantCases":"/api/acts/ad-cf34-17-high-pressure-seal/important-cases","documents":"/api/acts/ad-cf34-17-high-pressure-seal/documents"}}