{"id":"F2006B02525","name":"AD/AS 355/75 Amdt 1 - MGB Free-Wheel","slug":"ad-as-355-75-amdt-1-mgb-free-wheel","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41781,"registerId":"commonwealth-F2006B02525-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AS 355/75 Amdt 1 - MGB Free-Wheel","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Safety Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \n\nAIRWORTHINESS DIRECTIVE\n\n![](image.001.png)  \n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/AS 355/75 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\n![](image.001.png)  \n\nEurocopter AS 355 (Twin Ecureuil) Series Helicopters\n\nAD/AS 355/75\n\nAmdt 1\n\n  \n\nMGB Free-Wheel 4/2004 TX\n\nApplicability: AS 355 E, F, F1, F2 and N model helicopters fitted with a combiner gearbox pre- MOD 077212 that has less than 10 flying hours since new, or since overhaul or since repair.\n\nRequirement: Replace the free wheel rollers in the combiner gearbox as detailed in Eurocopter Alert Telex No. 63.00.21 R2\n\nNote: DGAC Telex AD UF-2004-021 refers.\n\nCompliance: Prior to further flight\n\nThis Amendment becomes effective on 26 February 2004.\n\nBackground: This amendment is in response to the manufacturer now identifying that the problem of slippage is not caused by insufficient cleaning of preservation fluid, but due to a change in the process that is applied to the free wheel rollers. The change from the “Bonderite” to “Parcolubrite” process has not provided the free wheel adherence in the first few hours of operations. Subsequently the applicability and the requirements now detailed are to address the cause of the problem.\n\nThis directive was issued to address a report of an engine overspeed event involving an AS355 helicopter during the single engine phase of an acceptance flight. The engine overspeed resulted from free-wheel clutch slippage was originally believed to be due to insufficient cleaning of preservation fluid from the main gearbox.\n\nThe original issue of this Directive became effective 21 January 2004.\n\n![](image.002.png)  \n\nJames Coyne\n\nDelegate of the Civil Aviation Safety Authority 23 February 2004\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 26 February 2004.\n\n  \nPage 1 of 1","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"The amendment revokes the original AD and narrows/targets the corrective measure: it shifts from addressing cleaning of preservation fluid to mandating replacement of free‑wheel rollers for combiner gearboxes manufactured before MOD 077212 with less than 10 flying hours. This modifies both the stated root cause and the required remedial action (Background; Applicability; Requirement)."},"complexity_factors":["Narrow technical applicability — applies only to AS355 E/F/F1/F2/N with combiner gearbox pre‑MOD 077212 and <10 flying hours (Applicability).","Immediate mandatory compliance — action required 'Prior to further flight', creating urgent grounding/repairs (Compliance).","Dependence on external service instruction — corrective action must follow Eurocopter Alert Telex No. 63.00.21 R2 (Requirement).","Legal replacement of prior directive — this AD revokes AD/AS 355/75 and issues an amendment, requiring operators to follow the new directive (first paragraph).","Shift in root‑cause understanding — remedy changed because manufacturer found a change in roller treatment process (Bonderite → Parcolubrite) caused early slippage, not preservation fluid residue (Background).","Verification burden — operators must determine MOD 077212 status and hours since new/overhaul/repair to establish applicability (Applicability).","Operational/logistical implication — mandatory replacement of rollers implies parts, maintenance time and potential downtime for affected aircraft (Requirement)."],"plain_english_summary":"This AD requires replacement of the free-wheel rollers in the combiner gearbox on Eurocopter AS 355 E/F/F1/F2/N helicopters fitted with combiner gearboxes pre‑MOD 077212 that have under 10 flying hours (Requirement; Applicability). It affects owners/operators of those helicopters and is issued to prevent free‑wheel clutch slippage linked to a manufacturing process change in roller treatment (Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"The original directive was issued in January 2004 based on a misunderstanding of the root cause (presumed cleaning fluid residue). This amendment significantly narrows the applicability to only those gearboxes with the specific manufacturing process change and fewer than 10 hours, while also correcting the technical basis for the requirement. The scope shifted from a broader cleaning-related issue to a specific manufacturing process defect."},"complexity_factors":["Single-page document with straightforward structure (Applicability, Requirement, Compliance, Background)","Limited conditional logic: only two main criteria (specific models AND specific gearbox modification status AND hour threshold)","No nested exceptions or complex cross-referencing to other legislation—only references to manufacturer telexes","Technical aviation terminology requires domain knowledge but the regulatory structure itself is simple","Clear, unambiguous compliance deadline ('prior to further flight')"],"plain_english_summary":"This safety order grounds certain Eurocopter AS 355 (Twin Ecureuil) helicopters with a specific pre-modification combiner gearbox that has less than 10 flying hours, requiring immediate replacement of the free‑wheel rollers per the manufacturer’s instructions before further flight. It responds to a manufacturing-change–related clutch slip that caused an engine overspeed during test flight and prevents similar catastrophic failures."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-as-355-75-amdt-1-mgb-free-wheel","history":"/api/acts/ad-as-355-75-amdt-1-mgb-free-wheel/history","analysis":"/api/acts/ad-as-355-75-amdt-1-mgb-free-wheel/analysis","conflicts":"/api/acts/ad-as-355-75-amdt-1-mgb-free-wheel/conflicts","importantCases":"/api/acts/ad-as-355-75-amdt-1-mgb-free-wheel/important-cases","documents":"/api/acts/ad-as-355-75-amdt-1-mgb-free-wheel/documents"}}