{"id":"F2006B09309","name":"AD/EC 120/3 Amdt 4 - Reinforced Coupling Tube Assembly","slug":"ad-ec-120-3-amdt-4-reinforced-coupling-tube-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":53413,"registerId":"commonwealth-F2006B09309-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/EC 120/3 Amdt 4 - Reinforced Coupling Tube Assembly","content":"![](image.001.png)\n\n![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/EC 120/3 Amdt 3 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 EC 120 Series Helicopters\n\nAD/EC 120/3\n\nAmdt 4\n\n  \nReinforced Coupling Tube Assembly 9/2004\n\nApplicability: All Eurocopter EC 120B helicopters fitted with engine-to-main gearbox (MGB) coupling tube Part Number (P/N) C631A1101101 and/or fitted with the engine mount comprising the parts detailed in paragraph 1.A. of Eurocopter EC 120 Alert Service Bulletin (ASB) No. 04A005.\n\nRequirement: 1. EC120B helicopters not incorporating an engine mount block modified in accordance with Eurocopter EC120 ASB No. 71.003 AND prior to serial number 1170 AND not incorporating Eurocopter EC120 Service Bulletin (SB) No.\n\n71.005:\n\n    Perform a visual inspection of the engine to MGB coupling tube in accordance with Paragraph 2.B of Eurocopter EC120 ASB No. 05A003; and\n\n    b. Remove from service, MGB coupling tube P/N C631A1101101 assemblies found to be cracked; and\n\n    c. Remove from service, MGB coupling tube P/N C631A1101101 assemblies.\n\n    2. EC120B helicopters prior to serial number 1170 and not incorporating an engine mount modified in accordance with Eurocopter EC120 SB No. 71.003:\n\n    Remove from service, engine mount components detailed in Paragraph 1.A of Eurocopter EC120 ASB No. 04A005.\n\n    3. EC120B helicopters serial number 1170 and higher and EC120B helicopters incorporating an engine mount modified in accordance with Eurocopter EC120 SB No. 71.003, but not modified in accordance with Eurocopter EC120 SB No. 71.005:\n\n    Perform a visual inspection of the engine to MGB coupling tube in accordance with Paragraph 2.B of Eurocopter ASB 05A003; and\n\n    b. Remove from service, MGB coupling tube P/N C631A1101101 assemblies found to be cracked; and\n\n    c. Remove from service, MGB coupling tube P/N C631A1101101 assemblies.\n\n    4. EC120B helicopters all serial numbers which have modified in accordance with Eurocopter EC120 SB No. 71.005:\n\n    Remove from service, MGB coupling tube P/N C631A1101101 assemblies.\n\n    5. For MGB coupling tube P/N C631A1101101 assemblies held as spares:\n\n    Perform a dye penetrant inspection of the MGB coupling tube in accordance with paragraph 2.B of Eurocopter SB 71.005.\n\nThe inspection detailed in Requirement 1 (a) and Requirement 3 (a) of this directive may be carried out and certified by the pilot provided the pilot has completed an approved training program.\n\nNote : DGAC Airworthiness Directive F-2003-325 R1 refers.\n\nCompliance: Requirement 1.\n\n    Unless previously accomplished, prior to further flight; and thereafter at intervals not to exceed 5 flight hours from last inspection or following the last flight of the day, whichever occurs first.\n\n    b. Before further flight.\n\n    c. Prior to exceeding 1,000 hours time in service (TIS) for the MGB coupling tube.\n\nRequirement 2.\n\na. Remains unchanged as detailed in Amendment 3 of this Directive, prior to 30 June 2004.\n\nRequirement 3.\n\n    Unless previously accomplished, within 25 flight hours from the effective date of this directive and thereafter at intervals not to exceed 25 flight hours.\n\n    b. Before further flight.\n\n    c. Prior to exceeding 20,000 hours TIS for the MGB coupling tube. Requirement 4.\n\na. Prior to exceeding 20,000 hours TIS for the MGB coupling tube.\n\nRequirement 5:\n\na. Before fitment to a helicopter modified in accordance with Eurocopter EC120 SB No. 71.005 and where the coupling tube was previously fitted to a helicopter not modified in accordance with Eurocopter EC120 SB No. 71.005.\n\nThis Amendment becomes effective on 2 September 2004.\n\nBackground: This Directive was originally issued to address a report of cracks being found in a reinforced engine to MGB coupling tube assembly. The investigation of that report has determined a certain engine mount configuration may induce excessive loading on the coupling tube. In response, the manufacturer has released an improved engine mount, revised the reinforced coupling tube inspection procedures and revised the life limits for the reinforced coupling tube assembly. This Amendment introduces terminating action of the inspections for helicopters modified by Eurocopter EC120B SB 71.005.\n\nAmendment 3 of this Airworthiness Directive became effective on 25 December 2003 Amendment 2 of this Airworthiness Directive became effective on 16 May 2002.\n\nAmendment 1 of this Airworthiness Directive became effective on 15 November 2000.\n\nThe original issue of this Airworthiness Directive became effective on 3 May 2000.\n\n![Signature of Bernard Malcolm Hole, Delegate of the Civil Aviation Safety Authority.](image.002.png)  \n\nBernard Malcolm Hole\n\nDelegate of the Civil Aviation Safety Authority 23 July 2004\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on Gazette Date.","sortOrder":0}],"analysis":{"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"},"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":true,"description":"The original directive (effective May 2000) addressed cracks in coupling tubes. Over four amendments, the scope expanded significantly: from simple inspection requirements to a complex matrix of serial-number-dependent actions, introduction of life limits (1,000 and 20,000 hours), spare parts inspection requirements, and terminating actions via manufacturer service bulletins. The directive now regulates not just the coupling tube but also engine mount configurations and modification status tracking."},"complexity_factors":["Five distinct requirement categories (Requirements 1-5) applying to overlapping but different subsets of aircraft based on serial numbers and modification status","Multiple cross-references to external manufacturer documents (Eurocopter ASB 04A005, 05A003, SB 71.003, 71.005) that are not reproduced in the text","Nested conditional logic: applicability depends on serial number (<1170 vs ≥1170) AND modification status (SB 71.003, SB 71.005) AND engine mount configuration","Four different compliance timelines with different triggers (prior to further flight, within 25 flight hours, at intervals not exceeding 5 or 25 flight hours, time-in-service limits of 1,000 vs 20,000 hours)","Exception for pilot-performed inspections contingent on completion of \"approved training program\" (undefined in the document)","Amendment structure references previous versions (Amdt 1, 2, 3) and their effective dates, creating temporal complexity","Specific part numbers (P/N C631A1101101) and French regulatory cross-reference (DGAC Airworthiness Directive F-2003-325 R1)"],"plain_english_summary":"This CASA safety order addresses cracking in the coupling tube of certain Eurocopter EC 120B helicopters — a failure that can sever power to the rotors. It requires inspections, removal of cracked tubes, and replacement/upgrade of parts on affected helicopters, with some routine checks allowable for trained pilots. Owners, operators and maintenance engineers of specified EC 120B serials are directly affected. The directive is crucial for flight safety and offers a terminating modification (Service Bulletin 71.005) to end repetitive inspections."},"flash_summary":{"complexity_score":7,"scope_assessment":{"changed":true,"description":"This amendment alters scope compared with the original AD by introducing a clear terminating action for helicopters modified in accordance with Eurocopter SB No. 71.005 (the AD states this explicitly in the Background and Requirement 4). It also revises inspection procedures and life limits for the reinforced coupling tube assembly and extends explicit requirements to spare parts (Requirement 5). Compared with the original intent (to require inspections on discovery of coupling‑tube cracking), the amendment adds: (a) differentiated compliance regimes based on serial number and embodiment of two different SBs, (b) a path to terminate recurring inspections via a manufacturer modification, and (c) mandatory inspection/decommissioning actions for spares — cumulatively broadening the set of actions and administrative steps operators must take."},"complexity_factors":["Multiple conditional branches: five separate Requirement blocks (1–5) with mutually different tests and actions.","Cross‑references to at least four external manufacturer documents (Eurocopter ASB No. 05A003, ASB No. 04A005, SB No. 71.003, SB No. 71.005) for procedural details.","Different treatment by helicopter serial number (prior to SN 1170 vs SN 1170 and higher) and by embodiment of two separate service bulletins (71.003 and 71.005).","Multiple and non‑uniform compliance timings: \"before further flight,\" repeating inspections at intervals not to exceed 5 flight hours or 25 flight hours, and life limits at 1,000 TIS or 20,000 TIS.","Mixed inspection methods and delegations: visual inspection, dye‑penetrant inspection for spares, and allowance for pilot‑certified inspections conditional on approved training.","Terminology that requires technical knowledge (part numbers, engine mount component lists in ASB, coupling tube life limits) and record‑keeping to track differing clocks for different aircraft.","Revocation and replacement of a prior AD (administrative cross‑linking and history), which requires operators to reconcile prior compliance with the new requirements."],"plain_english_summary":"**What this instrument does (mechanically)\n\n- Revokes the previous version of the same airworthiness directive and replaces it with updated mandatory instructions for Eurocopter EC120B helicopters.\n- Requires inspections, removal from service, or replacement of a reinforced engine-to-main gearbox (MGB) coupling tube assembly (P/N C631A1101101) and, in some helicopters, removal of certain engine‑mount components. (See Requirement 1–5.)\n- Sets different actions depending on helicopter serial number and whether specific manufacturer modifications (Eurocopter SB No. 71.003 and SB No. 71.005) have been incorporated. (Requirements 1–4.)\n- Allows certain visual inspections to be carried out and certified by the pilot if the pilot has completed an approved training program. (Requirement 1(a) and 3(a).)\n- Requires dye‑penetrant inspection of spare coupling tubes before fitting in particular circumstances. (Requirement 5.)\n- Establishes specific compliance windows: immediate (before further flight), repeating intervals (every 5 or 25 flight hours), and life limits (1,000 or 20,000 hours time-in-service (TIS) depending on the configuration). (Compliance section.)\n\nWhy CASA says it matters (stated purpose)\n\n- The manufacturer and CASA state the directive addresses reports of cracks found in the reinforced coupling tube assembly. The investigation identified that a particular engine‑mount configuration may place excessive loads on the coupling tube, increasing cracking risk. The AD therefore mandates inspections, removal of cracked or affected parts, and, as a long‑term fix, installation of an improved engine mount (terminating action). (Background; Requirement 2; Requirement 4.)\n\nWho this affects\n\n- Owners and operators of Eurocopter EC120B helicopters that either have coupling tube P/N C631A1101101 fitted or have an engine mount comprising the parts listed in Eurocopter EC120 ASB No. 04A005. (Applicability.)\n- Maintenance organisations and pilots performing pre‑flight/periodic inspections (pilots may inspect if trained). (Requirement 1(a) and 3(a).)\n- Parts suppliers and pools holding spare coupling tubes, because some spares must be dye‑penetrant inspected before fitting. (Requirement 5.)\n\nHow it changes behaviour and who bears the costs\n\n- Operators must institute additional inspection routines (daily or every few flight hours depending on configuration) and remove from service any coupling tubes found cracked. (Requirement 1(a)–(c); Requirement 3(a)–(c); Compliance.)\n- For helicopters of earlier serial numbers or those without the improved engine mount, operators may be required to remove and replace engine mount components. (Requirement 2; Compliance.)\n- Where helicopters have been modified per SB No. 71.005, the directive provides a terminating action: coupling tubes are to be removed from service (Requirement 4) and the inspections required for unmodified aircraft cease once the terminating modification is installed (Background; Requirement 4).\n- Direct costs fall on helicopter owners/operators: inspection labour (or pilot training and time), replacement of coupling tubes and engine‑mount parts, and downtime while parts are fitted. Suppliers holding spare coupling tubes may incur inspection costs or value loss if parts must be removed from service. Indirect costs include aircraft out‑of‑service time and administrative compliance burden.\n\nImplementation, compliance and operational details to note\n\n- The AD cross‑references multiple manufacturer documents (Eurocopter ASB No. 05A003, ASB No. 04A005, SB No. 71.003, SB No. 71.005) for the procedural details of inspections and part identification; compliance requires following those documents. (Requirement text and Background.)\n- The directive sets several different compliance timing rules (for example: \"before further flight,\" repeating inspections at intervals not to exceed 5 flight hours or 25 flight hours, and life limits at 1,000 or 20,000 hours TIS). Operators must track these different clocks depending on aircraft serial number and modification status. (Compliance.)\n- The AD allows pilots to perform and certify certain visual inspections if they complete an approved training program; this shifts some inspection labour from maintenance organisations to operators/pilots where permitted. (Requirement 1(a) and 3(a).)\n\nRisks, trade‑offs and practical considerations (analytical lens)\n\n- Compliance depends on the operator correctly identifying the helicopter configuration (serial number and which SBs have been embodied) and applying the right inspection schedule and life limits. Misidentification risks non‑compliance or missed cracks. (Applicability; Requirements 1–4.)\n- The directive relies on manufacturer service bulletins for the inspection and removal procedures. That centralises technical judgment with the manufacturer’s documents and places a compliance cost on operators to obtain and follow them. (Requirements cross‑referencing ASBs/SBs.)\n- Terminating action (installation of SB 71.005) reduces recurring inspection cost for helicopters modified to that standard, but imposes a one‑off modification cost. Operators will weigh upfront modification cost against ongoing inspection and replacement costs. (Background; Requirement 4.)\n- Allowing trained pilots to certify visual inspections reduces maintenance‑shop labour costs and may speed turnaround, but it transfers responsibility to operators to ensure training and to maintain records; it may also increase variability in inspection quality. (Requirement 1(a) and 3(a).)\n- Spare parts held in inventory must be inspected before use in some situations, which may impose additional inventory management and inspection costs for parts suppliers and operators. (Requirement 5.)\n\nPrimary behavioural effect in one sentence\n\n- Operators must identify affected EC120B helicopters, follow the matching inspection/removal schedule (or install the specified terminating modification), and either discard or replace cracked or identified coupling tubes and certain engine‑mount components in line with the stated compliance windows. (Requirements 1–5; Compliance.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-ec-120-3-amdt-4-reinforced-coupling-tube-assembly","history":"/api/acts/ad-ec-120-3-amdt-4-reinforced-coupling-tube-assembly/history","analysis":"/api/acts/ad-ec-120-3-amdt-4-reinforced-coupling-tube-assembly/analysis","conflicts":"/api/acts/ad-ec-120-3-amdt-4-reinforced-coupling-tube-assembly/conflicts","importantCases":"/api/acts/ad-ec-120-3-amdt-4-reinforced-coupling-tube-assembly/important-cases","documents":"/api/acts/ad-ec-120-3-amdt-4-reinforced-coupling-tube-assembly/documents"}}