{"id":"F2006B09305","name":"AD/EC 120/1 - Tail Gearbox - Load Measurements","slug":"ad-ec-120-1-tail-gearbox-load-measurements","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":53402,"registerId":"commonwealth-F2006B09305-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/EC 120/1 - Tail Gearbox - Load Measurements","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)  \nEurocopter EC 120 Series Helicopters\n\nAD/EC 120/1 Tail Gearbox \\- Load Measurements 6/99\n\nDM\n\nApplicability: All EC120B helicopters equipped with tail gearbox part number:\n\nC652A010 1051 or C652A010 1052 with the following serial numbers: M101 - M124 (incl) and M126.\n\nRequirements: 1. Remove the tail rotor hub and the tail gearbox and measure the operating load of the pitch change control rod in accordance with instructions in para 2B(1) of EUROCOPTER EC120 Service Bulletin No. 01.001.\n\n    2. Reinstall the tail gearbox and tail rotor hub in accordance with manufacturer’s instructions (work cards 65.21.00, 4-2 and 64.21.00, 4-2 resp).\n\n    3. Replace the tail gearbox with a compliant gearbox (ie. a gearbox with non applicable serial number or one which has acceptable operating loads in accordance with 1. Above).\n\nNote: DGAC AD 1999-151-001(A) dated 07 April 1999 refers.\n\nCompliance: 1. Within 50 flying hours of the effective date of this Directive but no later than 30 September 1999.\n\n    2. If loads measured at requirement 1 above are equal to or less than 1.2 daN.\n\n    3. Prior to next flight if loads measured are greater than 1.2 daN, This Airworthiness Directive becomes effective on 12 May 1999.\n\nBackground: In service experience has detected a case of significant binding of the tail rotor pitch change control rod which could lead to loss of control of the aircraft. This Directive introduces tests on certain Tail Gearboxes to identify defective assemblies.","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"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive’s scope aligns with the stated safety concern—targeting specific gearbox serial numbers and prescribing measurement, reinstall or replace actions with clear compliance deadlines—so it does not expand beyond its original safety-remediation intent."},"complexity_factors":["Narrow applicability: limited to EC120B with specified gearbox part and serial numbers (reduces legal scope but requires serial verification).","Technical procedure reliance: measurement must follow EUROCOPTER Service Bulletin para 2B(1) and manufacturer work cards (operator must have technical capability or use approved maintenance provider).","Defined numerical threshold (1.2 daN): a clear pass/fail criterion simplifies decision-making but makes precise measurement critical.","Operational disruption: removal/reinstallation of hub and gearbox creates downtime and labour costs.","Parts replacement risk: non-compliant gearboxes must be replaced, exposing operators to parts lead times and expense.","Tight compliance timeline: 50 flight hours or immediate grounding if over limit increases scheduling pressure.","Safety-critical enforcement: consequences of non-compliance concern airworthiness and regulatory enforcement.","Recordkeeping and certification obligations for maintenance actions and measurements."],"plain_english_summary":"This Airworthiness Directive requires operators of Eurocopter EC120B helicopters with specific tail gearbox serial numbers to remove the tail rotor hub and gearbox, measure the pitch-change control rod operating load using the manufacturer’s service instructions, then reinstall or replace the gearbox if loads exceed 1.2 daN. Compliance is required within 50 flight hours or before next flight where the limit is exceeded.\n\nWho pays and decides: helicopter owners/operators must bear inspection, downtime and any replacement costs; measurements follow Eurocopter work cards and the Service Bulletin, creating a technical compliance and parts-availability burden."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a targeted airworthiness directive addressing a specific safety defect in specific helicopter serial numbers. It has not expanded beyond its original purpose of identifying defective tail gearboxes."},"complexity_factors":["Short, single-purpose directive with only 3 requirements","Limited applicability: specific helicopter model, two part numbers, and specific serial number ranges","Single cross-reference to Eurocopter Service Bulletin No. 01.001 and French DGAC AD 1999-151-001(A)","Simple conditional compliance structure (two thresholds: ≤1.2 daN vs >1.2 daN)","No defined terms section; uses standard aviation terminology","Clear, sequential numbering (1, 2, 3) with straightforward mechanical instructions"],"plain_english_summary":"This CASA safety order requires owners/operators of Eurocopter EC120B helicopters with specified tail gearbox serials to inspect and test the tail gearbox pitch‑change control rod for binding. If measured operating load exceeds the limit, the gearbox must be replaced and the helicopter grounded until fixed.  \n\nThe check must be done within 50 flight hours or by 30 Sept 1999. This prevents loss of tail‑rotor control and follows a DGAC safety action."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ec-120-1-tail-gearbox-load-measurements","history":"/api/acts/ad-ec-120-1-tail-gearbox-load-measurements/history","analysis":"/api/acts/ad-ec-120-1-tail-gearbox-load-measurements/analysis","conflicts":"/api/acts/ad-ec-120-1-tail-gearbox-load-measurements/conflicts","importantCases":"/api/acts/ad-ec-120-1-tail-gearbox-load-measurements/important-cases","documents":"/api/acts/ad-ec-120-1-tail-gearbox-load-measurements/documents"}}