{"id":"F2006B02485","name":"AD/AS 355/31 - Tail Rotor Gearbox Casing","slug":"ad-as-355-31-tail-rotor-gearbox-casing","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"repealed","isInForce":false,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41741,"registerId":"commonwealth-F2006B02485-current","compilationNumber":null,"startDate":"2026-04-01","status":"Repealed","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AS 355/31 - Tail Rotor Gearbox Casing","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 AS 355 (Twin Ecureuil) Series Helicopters\n\nAD/AS 355/31 Tail Rotor Gearbox Casing 1/88\n\nApplicability: All model AS 355 Series helicopters.\n\nRequirement: 1. Inspect the tail rotor gearbox casing in accordance with Para 1C(2) of SB No 05.18.\n\n2. Inspect and modify the tail rotor gearbox in accordance with Para 1C(3) of SB No 05.18.\n\nCompliance: For Para 1: Within 50 hours time in service after 18 November 1987 and thereafter at intervals not exceeding 50 hours time in service, until modification AMS 350A07- 8535 (polishing blend radii) is incorporated. After modification, inspect at intervals not exceeding 400 hours time in service.\n\nFor Para 2: Prior to exceeding 1100 hours total time in service or within 100 hours time in service after 18 November 1987, whichever is the later.\n\nBackground: The manufacturer has received reports of cracking in the blade horn support yoke radius just inboard of where the tail rotor control bellcrank pivot bolt is located.","sortOrder":0}],"analysis":{"kimi_summary":{"_metrics":{"model":"kimi-k2.5","source":"moonshot-batch","completionTokens":1645},"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a targeted airworthiness directive addressing a specific mechanical defect (cracking in the tail rotor gearbox casing). It has not expanded beyond its original safety purpose."},"complexity_factors":["References external technical document (Service Bulletin No 05.18) without reproducing its content","Multiple conditional compliance deadlines ('whichever is the later', 'until modification is incorporated')","Technical aviation terminology requiring specialized knowledge (bellcrank pivot bolt, blade horn support yoke)","Specific modification part number references (AMS 350A07-8535)"],"plain_english_summary":"This directive requires owners/operators of Eurocopter AS 355 helicopters to perform repeated inspections of the tail rotor gearbox casing for cracks and to carry out a permanent modification per the manufacturer’s Service Bulletin No. 05.18. Inspections are every 50 flight hours until the AMS 350A07-8535 modification is done, then every 400 hours. The modification must be completed by 1,100 total hours or within 100 hours after Nov 18, 1987, whichever is later.\n\nIt addresses cracks in the blade-horn support yoke radius that could cause loss of tail-rotor control."}},"importantCases":[],"_links":{"self":"/api/acts/ad-as-355-31-tail-rotor-gearbox-casing","history":"/api/acts/ad-as-355-31-tail-rotor-gearbox-casing/history","analysis":"/api/acts/ad-as-355-31-tail-rotor-gearbox-casing/analysis","conflicts":"/api/acts/ad-as-355-31-tail-rotor-gearbox-casing/conflicts","importantCases":"/api/acts/ad-as-355-31-tail-rotor-gearbox-casing/important-cases","documents":"/api/acts/ad-as-355-31-tail-rotor-gearbox-casing/documents"}}