{"id":"F2006B06708","name":"AD/S-76/26 Amdt 1 - Vertical Stabiliser Pylon Leading Edge Skin","slug":"ad-s-76-26-amdt-1-vertical-stabiliser-pylon-leading-edge-skin","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":114521,"registerId":"commonwealth-F2006B06708-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/S-76/26 Amdt 1 - Vertical Stabiliser Pylon Leading Edge Skin","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)  \nSikorsky S-76 Series Helicopters\n\nAD/S-76/26\n\nAmdt 1\n\n  \nVertical Stabiliser Pylon Leading Edge Skin 11/85\n\nApplicability: All models.\n\nRequirement: 1. Sikorsky Alert Service Bulletin No. 76-55-9; or\n\n    2. Sikorsky Alert Service Bulletin No. 76-55-11 (Terminating Action); or\n    3. Sikorsky Customer Service Notice No 76-141B (Terminating Action). Compliance: For para. E(1) of ASB 76-55-9: Within the next 25 hours time in service after 25\n\nMarch 1983 and thereafter at intervals not exceeding 25 hours time in service.\n\nFor para. E(2) of ASB 76-55-9: Within the next 100 hours time in service after 25 March 1983 and thereafter at intervals not exceeding 100 hours time in service.\n\nBackground: Cracks have been found in service in the pylon upper leading edge skin near the tail rotor gear box. This Directive has been amended to provide terminating action for modified helicopters. However, note that CSN 76-141 no longer constitutes terminating action for the requirements of AD/S-76/29. The reason is that forward spar cracks have been found in modified helicopters, although at this stage there have been no reports of L.E. skin cracks. It is expected that an improved modification will be developed by the manufacturer.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"The amendment adds terminating-action options for modified helicopters and prescribes recurring inspection intervals (25 or 100 hours depending on procedure). It also clarifies that CSN 76-141 no longer terminates obligations under AD/S-76/29 because forward spar cracks were discovered; the manufacturer is expected to supply an improved modification."},"complexity_factors":["Multiple compliance paths set out (Sikorsky ASB 76-55-9; ASB 76-55-11 terminating; CSN 76-141B terminating) increases decision points for operators.","Different mandated inspection intervals tied to specific procedures (25 hours vs 100 hours) create operational scheduling requirements.","Interplay with a related directive (AD/S-76/29) where CSN 76-141 no longer constitutes terminating action adds cross-referencing complexity.","Technical uncertainty noted (forward spar cracks found in modified helicopters; manufacturer expected to develop improved modification) creates possible rework and regulatory updates.","Applicability to all S‑76 models simplifies scope but increases the universe of affected operators."],"plain_english_summary":"This Airworthiness Directive requires operators of all Sikorsky S‑76 helicopters to inspect and/or modify the vertical stabiliser pylon upper leading edge skin using specified Sikorsky service bulletins or a customer service notice (Requirement). It mandates repeating inspections—every 25 or every 100 flight hours depending on the procedure (Compliance)—because cracks were found near the tail rotor gearbox; the amendment adds terminating modification options but removes one customer‑notice’s terminating effect for a related AD after forward‑spar cracks were discovered (Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a narrow, technical airworthiness directive focused on a specific structural defect in a specific helicopter model. The amendment slightly adjusted the compliance options (removing one terminating action due to new safety data) but did not expand beyond the original safety purpose of addressing pylon skin cracks."},"complexity_factors":["Short, single-purpose document (1 page)","Only 3 defined compliance paths (two service bulletins and one customer notice)","Simple conditional structure: inspect repeatedly OR do terminating action","Cross-references to manufacturer documents (ASB 76-55-9, ASB 76-55-11, CSN 76-141B) but these are external, not internal legislative references","One amendment layer with straightforward background explanation","No nested exceptions or complex defined terms"],"plain_english_summary":"This CASA Airworthiness Directive mandates inspections and/or a manufacturer-approved permanent repair for Sikorsky S‑76 helicopters to address cracking in the vertical stabiliser pylon leading‑edge skin near the tail rotor gearbox. Operators must carry out repetitive inspections (25/100‑hour intervals) or incorporate a terminating service‑bulletin fix.\n\nThe AD was amended because the original repair didn’t fully prevent cracks; one repair option was removed pending a better fix. Compliance is mandatory to prevent tail‑structure failure and potential loss of control."}},"importantCases":[],"_links":{"self":"/api/acts/ad-s-76-26-amdt-1-vertical-stabiliser-pylon-leading-edge-skin","history":"/api/acts/ad-s-76-26-amdt-1-vertical-stabiliser-pylon-leading-edge-skin/history","analysis":"/api/acts/ad-s-76-26-amdt-1-vertical-stabiliser-pylon-leading-edge-skin/analysis","conflicts":"/api/acts/ad-s-76-26-amdt-1-vertical-stabiliser-pylon-leading-edge-skin/conflicts","importantCases":"/api/acts/ad-s-76-26-amdt-1-vertical-stabiliser-pylon-leading-edge-skin/important-cases","documents":"/api/acts/ad-s-76-26-amdt-1-vertical-stabiliser-pylon-leading-edge-skin/documents"}}