{"id":"F2009L00507","name":"AD/ARRIEL/31 - Reduction Gear Box Intermediate Pinion","slug":"ad-arriel-31-reduction-gear-box-intermediate-pinion","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":77152,"registerId":"commonwealth-F2009L00507-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Turbomeca Turbine Engines - Arriel Serie","sectionType":"division","heading":"Turbomeca Turbine Engines - Arriel Series","content":"### Turbomeca Turbine Engines - Arriel Series\n\n| AD/ARRIEL/31 | Reduction Gear Box Intermediate Pinion | 3/2009 |\n| ------------ | -------------------------------------- | ------ |\n\n| Applicability: | Arriel 1B, 1D and 1D1 turboshaft engines, all serial numbers.Note 1: These engines are known to be installed on, but not limited to, EurocopterAS 350 B, AS 350 BA, AS 350 B1 and AS 350 B2 helicopters.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |\n| -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | Replace the Reduction Gear Box Intermediate Pinions (P/N 0 292 70 779 0) with Pinions incorporating Turboméca modification TU 232 in accordance with Turboméca Mandatory Service Bulletin 292 72 0276 Version B dated6 November 2008 or later approved revision.Note 2: EASA AD 2009-0002 dated 7 January 2009 refers.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |\n| Compliance:    | No later than 28 February 2011, unless previously accomplished.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |\n|                | This Airworthiness Directive becomes effective on 12 March 2009.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |\n| Background:    | Several events of rupture of the Arriel 1 Reduction Gear Box Intermediate Pinion have been reported in service. The ruptures have been determined to be originated at the pinion teeth root due to increased vibratory stresses. This increase in vibratory stresses is mainly caused by increased teeth wear over engine life time.The rupture of the Reduction Gear Box Intermediate Pinion may result in an overspeed of the Power Turbine and, subsequently, an uncommanded engine in-flight shutdown. This could lead to an emergency autorotation landing on a single-engine helicopter.To reduce the level of vibratory stresses and improve tooth resistance, Turboméca modification TU 232 incorporates the addition of a damping ring below the teeth and a shot peening of the teeth roots. These modifications reduce the risk of incipient fatigue cracks. |\n\n|     | This AD requires the replacement of all Reduction Gear Box Intermediate Pinions with Pinions incorporating Turboméca modification TU 232. |\n| --- | ----------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n27 January 2009","sortOrder":0},{"sectionNumber":"AD/ARRIEL/31","sectionType":"part","heading":"AD/ARRIEL/31","content":"## AD/ARRIEL/31","sortOrder":1},{"sectionNumber":"Reduction Gear Box Intermediate Pinion","sectionType":"part","heading":"Reduction Gear Box Intermediate Pinion","content":"## Reduction Gear Box Intermediate Pinion","sortOrder":2},{"sectionNumber":"3/2009","sectionType":"part","heading":"3/2009","content":"## 3/2009","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":3,"scope_assessment":{"changed":false,"description":"The directive's scope is confined to Arriel 1B, 1D and 1D1 engines (all serial numbers) and mandates replacement of the specified pinion with the TU 232-modified part per Turboméca service instructions. It does not broaden applicability beyond those engines or impose additional operational restrictions."},"complexity_factors":["Narrow technical scope: targets a single serviceable part (Reduction Gear Box Intermediate Pinion P/N 0 292 70 779 0) on specified Arriel 1B/1D/1D1 engines (Applicability).","Mandatory actions tied to manufacturer documentation: replacement must follow Turboméca Mandatory Service Bulletin 292 72 0276 or a later approved revision (Requirement).","Fixed compliance deadline (28 February 2011) creates scheduling and parts-availability pressure for operators (Compliance).","Safety-critical consequence if not complied with: pinion rupture can cause power-turbine overspeed and uncommanded engine shutdown (Background).","Technical remedy requires specific physical changes (damping ring addition and shot peening) likely needing workshop facilities, labour and downtime (Background / Requirement).","Cross-reference to foreign regulator material (EASA AD 2009-0002) adds an administrative trace for approvals and revisions (Requirement / Note 2).","Record and certification tasks for maintenance provenance and effective dates (effective date 12 March 2009) add minor administrative burden (Compliance / header)."],"plain_english_summary":"This Airworthiness Directive requires owners/operators to replace a specific Reduction Gear Box Intermediate Pinion (P/N 0 292 70 779 0) on Turboméca Arriel 1B, 1D and 1D1 turboshaft engines with a pinion modified by Turboméca TU 232, in line with Turboméca Mandatory Service Bulletin 292 72 0276 (or later approved revision). The change responds to reported pinion ruptures caused by increased vibratory stresses and wear; the modified pinion adds a damping ring and shot peening to reduce fatigue risk. Compliance was required by 28 February 2011."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical failure mode in specific engine models. It has not expanded beyond its original purpose of mandating a particular hardware replacement."},"complexity_factors":["Single, specific technical requirement with clear part number and modification reference","No defined terms section or interpretation provisions","Minimal conditional logic — one blanket requirement with single compliance deadline","No cross-references to other legislation (only references to manufacturer service bulletin and EASA AD for context)","Short, self-contained document (approximately 300 words of substantive content)","Single applicability criterion based on engine model and serial number"],"plain_english_summary":"This mandatory CASA Airworthiness Directive requires owners/operators of Arriel 1B, 1D and 1D1 turboshaft engines (used in AS 350 helicopters) to replace a cracking Reduction Gear Box Intermediate Pinion with an improved, damped and shot‑peened version by 28 February 2011. It affects operators, owners and maintenance organisations and addresses a critical failure mode that can cause in‑flight engine overspeed/shutdown and emergency landings."}},"importantCases":[],"_links":{"self":"/api/acts/ad-arriel-31-reduction-gear-box-intermediate-pinion","history":"/api/acts/ad-arriel-31-reduction-gear-box-intermediate-pinion/history","analysis":"/api/acts/ad-arriel-31-reduction-gear-box-intermediate-pinion/analysis","conflicts":"/api/acts/ad-arriel-31-reduction-gear-box-intermediate-pinion/conflicts","importantCases":"/api/acts/ad-arriel-31-reduction-gear-box-intermediate-pinion/important-cases","documents":"/api/acts/ad-arriel-31-reduction-gear-box-intermediate-pinion/documents"}}