{"id":"F2006B02448","name":"AD/ARRIEL/18 Amdt 1 - 2nd Stage Nozzle Guide Vanes","slug":"ad-arriel-18-amdt-1-2nd-stage-nozzle-guide-vanes","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41704,"registerId":"commonwealth-F2006B02448-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ARRIEL/18 Amdt 1 - 2nd Stage Nozzle Guide Vanes","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Safety Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \n\nAIRWORTHINESS DIRECTIVE\n\n![](image.001.png)\n\n![](image.001.png)  \nOn the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/ARRIEL/18 and issues the following AD under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\nTurbomeca Turbine Engines \\- Arriel Series\n\nAD/ARRIEL/18\n\nAmdt 1\n\n  \n\n2nd Stage Nozzle Guide Vanes 11/2004 DM\n\nApplicability: TURBOMECA ARRIEL 1B, 1D and 1D1 model engines incorporating MOD TU 202, except those engines having 2nd stage nozzle guide vanes which are detailed in TURBOMECA Service Bulletin (SB) No. 292 72 0231 Revision 5.\n\nRequirement: Action in accordance with paragraph 2.B, operating instructions, of TURBOMECA SB No. 292 72 0231 Revision 5, dated 22 July 2004.\n\nNote: DGAC AD F-2004-088R1 (EASA reference No 2004-8068) refers.\n\nCompliance: Unless previously accomplished in accordance with earlier revisions of TURBOMECA SB 292 72 0231, during the next deep maintenance, or at the next occasion the engine is sent to a repair centre or at the latest before 31 December 2006, whichever occurs first.\n\nThis Amendment becomes effective on 30 September 2004.\n\nBackground: This Directive is issued to detect and prevent a possible perforation of the 2nd stage nozzle guide vanes (NGV) and the formation of an aerodynamic wake upstream of the 2nd stage NGV. Such a wake may lead to the rupture of a 2nd stage turbine blade followed by an uncommanded engine shutdown.\n\nThis amendment clarifies the applicability of the engines affected. The requirements detailed now only apply to those engines fitted to single engine helicopters.\n\nThe original issue of this Directive becomes effective on 30 September 2004.\n\n![](image.002.png)  \n\nJames Coyne\n\nDelegate of the Civil Aviation Safety Authority 14 September 2004\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 22 September 2004.\n\n  \n\nPage 1 of 1","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The amendment narrows and clarifies applicability: the requirement now applies only to Arriel 1B/1D/1D1 engines (with MOD TU 202) when fitted to single‑engine helicopters and excludes engines already fitted with the 2nd‑stage NGVs per Turbomeca SB 292 72 0231 Revision 5. The technical requirement and compliance timing remain otherwise unchanged."},"complexity_factors":["Depends on an external manufacturer Service Bulletin (Turbomeca SB No. 292 72 0231 Revision 5) and specifically paragraph 2.B, creating a documentary dependency for compliance.","Exclusion for engines already fitted in accordance with SB Revision 5 requires operators to verify modification status of each engine.","Applicability is model‑ and modification‑specific (Arriel 1B/1D/1D1 with MOD TU 202) and further limited to engines fitted to single‑engine helicopters, requiring operator-level identification of engine/airframe pairings.","Multiple compliance triggers (next deep maintenance, next repair‑centre visit, or a fixed calendar date) give scheduling flexibility but impose tracking and record‑keeping burdens.","The AD revokes and replaces a prior AD, so operators must reconcile regulatory history and past compliance actions.","Technical root cause (NGV perforation → aerodynamic wake → turbine blade rupture) means inspections/repairs require specialist maintenance capability and may incur parts/labour costs.","Cross-reference to DGAC/EASA AD adds an international regulatory coordination element for operators and maintenance organisations."],"plain_english_summary":"Requires operators of Turbomeca Arriel 1B, 1D and 1D1 engines (with MOD TU 202) to follow paragraph 2.B of Turbomeca Service Bulletin 292 72 0231 Revision 5—unless the engine already has the specified 2nd‑stage nozzle guide vanes. Compliance is at the next deep maintenance, the next occasion the engine goes to a repair centre, or by 31 December 2006. The AD aims to detect/prevent perforation of 2nd‑stage nozzle guide vanes that could cause an aerodynamic wake, turbine blade rupture and an uncommanded engine shutdown; the amendment limits application to engines on single‑engine helicopters."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"This amendment narrows the scope compared to the original AD. The background explicitly states: 'This amendment clarifies the applicability of the engines affected. The requirements detailed now only apply to those engines fitted to single engine helicopters.' The original AD presumably applied to all affected engines regardless of aircraft configuration; this version restricts mandatory compliance to single-engine helicopter installations only, likely recognising that multi-engine helicopters have operational redundancy that mitigates the safety risk."},"complexity_factors":["Single, clearly defined applicability section with specific engine models and modification numbers","One primary requirement referencing an external technical document (Turbomeca Service Bulletin)","Simple compliance deadline structure with three alternative triggers (maintenance, repair, or fixed date)","Limited cross-referencing: one note referencing French DGAC and EASA equivalents, one regulatory citation (CASR 1998 subregulation 39.1(1))","No nested exceptions or conditional logic beyond the applicability carve-out for engines already compliant with earlier bulletin revisions","Background section provides clear safety rationale in plain language"],"plain_english_summary":"This Airworthiness Directive requires operators of single‑engine helicopters fitted with specified Turbomeca Arriel 1B/1D/1D1 engines to follow a manufacturer service bulletin to inspect and remedy the 2nd‑stage nozzle guide vanes. It addresses vane perforation that can cause turbulent flow, turbine blade failure and sudden engine shutdown.\n\nEngines already corrected per earlier bulletin are exempt. Compliance is required by the next deep maintenance/repair‑centre visit or by 31 December 2006."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-arriel-18-amdt-1-2nd-stage-nozzle-guide-vanes","history":"/api/acts/ad-arriel-18-amdt-1-2nd-stage-nozzle-guide-vanes/history","analysis":"/api/acts/ad-arriel-18-amdt-1-2nd-stage-nozzle-guide-vanes/analysis","conflicts":"/api/acts/ad-arriel-18-amdt-1-2nd-stage-nozzle-guide-vanes/conflicts","importantCases":"/api/acts/ad-arriel-18-amdt-1-2nd-stage-nozzle-guide-vanes/important-cases","documents":"/api/acts/ad-arriel-18-amdt-1-2nd-stage-nozzle-guide-vanes/documents"}}