{"id":"F2006B09308","name":"AD/EC 120/2 Amdt 2 - Engine to Main Gearbox (MGB) Coupling Tube Assembly","slug":"ad-ec-120-2-amdt-2-engine-to-main-gearbox-mgb-coupling-tube-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":53411,"registerId":"commonwealth-F2006B09308-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/EC 120/2 Amdt 2 - Engine to Main Gearbox (MGB) Coupling Tube Assembly","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation 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\n![](image.001.png)  \nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/EC-120/2 Amdt 1 and issues the following AD under subregulation 39.1 (1) of CAR 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\nEurocopter EC 120 Series Helicopters\n\nAD/EC-120/2\n\nAmdt 2\n\n  \n\nEngine to Main Gearbox (MGB) Coupling Tube Assembly\n\n  \n5/2002\n\nApplicability: All Eurocopter EC 120B helicopters equipped with engine to MGB coupling tube assembly P/N C631A1002101.\n\nRequirement: Remove engine to MGB coupling tube assembly, P/N. C631A1002101 and associated engine support assembly components from service, in accordance with Eurocopter Service Bulletin EC 120.\n\nNote: DGAC AD 2000-058-003(A) R1 refers.\n\nCompliance: Effective 16 May 2002; engine to MGB coupling tube assembly, P/N. C631A1002101 and associated engine support assembly components may not be installed in an aircraft from when this amendment becomes effective.\n\nThis Amendment becomes effective on 16 May 2002.\n\nBackground: This Directive was issued to address reports of cracks occurring in the engine to MGB coupling tube assembly that could result in failure of the tube occasioning an autorotation landing. This amendment reflects the DGAC declaring coupling tube P/N C631A1002101 and associated engine support fittings to be non-airworthy.\n\nAmendment 1 of this Airworthiness Directive became effective on 23 March 2000.\n\nThe original issue of this Airworthiness Directive became effective on 17 September 1999.\n\n![Signature of Eugene Paul Holzapfel, Delegate of the Civil Aviation Safety Authority.](image.002.png)  \n\nEugene Paul Holzapfel\n\nDelegate of the Civil Aviation Safety Authority 7 April 2002\n\n![](image.001.png)\n\nThe above AD is notified in the Commonwealth of Australia Gazette on 24 April 2002.\n\n  \n\nPage 1 of 1","sortOrder":0}],"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":2,"scope_assessment":{"changed":true,"description":"This amendment expanded the corrective action compared with the earlier AD versions by revoking Amendment 1 and requiring complete removal from service and a prohibition on reinstalling the specified coupling tube assembly and associated engine support components (Requirement & Compliance). The Background states the change reflects the DGAC declaring those parts non-airworthy — a move from earlier corrective measures (which in many similar AD histories start as inspections or restricted-use actions) to an outright grounding of the listed P/Ns. Concretely, the scope changed from prior measures to a total ban on installing the specified P/N and a mandatory removal obligation, concentrating compliance costs on operators and suppliers of that part."},"complexity_factors":["Single aircraft model (Eurocopter EC 120B) affected","Single part number listed (P/N C631A1002101) and associated engine support components","Short, discrete actions required (remove parts; do not reinstall)","One clear compliance date (16 May 2002)","Relies on one external technical document (Eurocopter Service Bulletin EC 120)","Minimal cross-references (revokes previous amendment; refers to DGAC AD)","No nested conditions or multiple exception layers"],"plain_english_summary":"**What this instrument does (mechanics)**\n\n- Applies to: all Eurocopter EC 120B helicopters that have the engine-to-main-gearbox (MGB) coupling tube assembly with part number (P/N) C631A1002101 (Applicability).\n- Requires: removal from service of that coupling tube assembly (P/N C631A1002101) and the associated engine support assembly components (Requirement).\n- How to comply: removal must be done in accordance with the procedures in the referenced Eurocopter Service Bulletin EC 120 (Requirement).\n- Timing and prohibition: effective 16 May 2002; from that date the specified coupling tube and associated parts may not be installed in any aircraft (Compliance).\n- Administrative action: the AD revokes the prior Amendment 1 and is issued under the Civil Aviation Regulations authority noted on the AD.\n\n**Why the regulator gave this instruction (stated reason)**\n\n- The AD cites reports of cracks in the coupling tube assembly that could lead to tube failure and an autorotation landing (Background).\n- It reflects the French airworthiness authority (DGAC) declaring the coupling tube P/N C631A1002101 and associated engine support fittings non-airworthy (Background).\n\n**Who this affects and what they must do**\n\n- Affected parties: owners/operators of Eurocopter EC 120B helicopters, aircraft maintenance organisations, maintenance engineers, and spare-parts suppliers holding or intending to install P/N C631A1002101 or the listed engine support components (Applicability & Requirement).\n- Required actions: locate any installed parts with the listed P/N, remove those parts from service following the Eurocopter service bulletin, update maintenance records, and do not install those P/N parts on any aircraft after the effective date (Requirement & Compliance).\n\n**Practical consequences, costs and implementation issues**\n\n- Who pays: aircraft owners/operators bear the direct cost of removal, possible replacement components, labour, and aircraft downtime.\n- Supply risk: compliance depends on availability of approved replacement parts or retrofit kits; if replacements are scarce, operators could face longer downtime or grounding while awaiting parts.\n- Operational impact: helicopters with the affected parts cannot continue using them after the effective date; if a proper replacement is not available, aircraft may be grounded until corrected.\n- Administrative burden: operators must identify affected serials, track removals in maintenance records, and coordinate with maintenance organisations to follow the Eurocopter service bulletin.\n- Regulatory mechanism: the AD relies on the manufacturer's service bulletin for technical instructions and references the DGAC action; CASA enforces compliance under the Civil Aviation Regulations.\n\n**Trade-offs and incentives**\n\n- Safety vs cost: the directive removes a part deemed to have a risk of structural cracking to mitigate a safety hazard; that increases immediate maintenance costs and potential aircraft downtime for operators.\n- Concentration of costs: cost burden is concentrated on EC 120B operators and their maintenance providers; benefit (reduced risk of in-flight component failure) accrues to operators, passengers and the public generally.\n- Effects on aftermarket/suppliers: a ban on installing the specified P/N reduces demand for that part and shifts demand to replacement designs or approved alternatives; suppliers holding the condemned P/N incur devaluation or disposal costs.\n\n**Implementation risk and discretion**\n\n- CASA has delegated authority to issue the AD; compliance requires following an external Eurocopter service bulletin, which places technical reliance on the manufacturer’s instructions (Requirement).\n- The AD does not detail replacement part numbers or retrofit procedures in the text itself; operators must obtain and follow the service bulletin for the exact technical steps (Requirement).\n\n(References in parentheses refer to the labelled sections of the AD: Applicability, Requirement, Compliance, Background.)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is Amendment 2 of an existing Airworthiness Directive. The scope remains tightly focused on the original safety issue (cracked coupling tubes in EC 120 helicopters). The amendment simply updates the regulatory action to reflect that the French aviation authority (DGAC) has now formally declared the part non-airworthy, reinforcing the ban. No expansion beyond the original safety purpose."},"complexity_factors":["Single, clearly defined applicability (one helicopter model, one specific part number)","Straightforward requirement: remove and do not reinstall the specified part","No conditional logic, exceptions, or nested provisions","Minimal cross-referencing (only one referenced service bulletin and one French aviation authority directive)","Short document (1 page) with clear structure (Applicability, Requirement, Compliance, Background)","No defined terms section — all technical terms are either self-explanatory or standard aviation terminology"],"plain_english_summary":"This AD bans a specific engine-to-main-gearbox coupling tube assembly (P/N C631A1002101) from use in Eurocopter EC 120B helicopters and requires its immediate removal along with related engine supports. It took effect 16 May 2002.\n\nIt affects EC 120B owners, operators and maintenance providers because cracks in the part can cause complete failure, loss of engine power and a forced autorotation—an extremely hazardous event."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ec-120-2-amdt-2-engine-to-main-gearbox-mgb-coupling-tube-assembly","history":"/api/acts/ad-ec-120-2-amdt-2-engine-to-main-gearbox-mgb-coupling-tube-assembly/history","analysis":"/api/acts/ad-ec-120-2-amdt-2-engine-to-main-gearbox-mgb-coupling-tube-assembly/analysis","conflicts":"/api/acts/ad-ec-120-2-amdt-2-engine-to-main-gearbox-mgb-coupling-tube-assembly/conflicts","importantCases":"/api/acts/ad-ec-120-2-amdt-2-engine-to-main-gearbox-mgb-coupling-tube-assembly/important-cases","documents":"/api/acts/ad-ec-120-2-amdt-2-engine-to-main-gearbox-mgb-coupling-tube-assembly/documents"}}