{"id":"F2006B06711","name":"AD/S-76/29 Amdt 4 - Vertical Pylon Forward Spar","slug":"ad-s-76-29-amdt-4-vertical-pylon-forward-spar","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":114524,"registerId":"commonwealth-F2006B06711-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/S-76/29 Amdt 4 - Vertical Pylon Forward Spar","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-76/29\n\nAmdt 4\n\n  \nVertical Pylon Forward Spar 3/94\n\nApplicability: All Sikorsky S-76A helicopters without Sikorsky Modification Kit 76070-20086 (steel straps which reinforce the aluminium cap angles of the vertical pylon forward spar; referred to in Sikorsky Alert Service Bulletin No. 76-55-12).\n\nRequirement: 1. Inspect for cracks in the cap angles, web, and web doubler of the vertical pylon forward spar, and in repairs and reinforcements near the tail rotor shaft cut-out in the vertical pylon forward spar, or near the fuselage shear deck, as follows:\n\n    (a) Remove the tail rotor drive shaft fairings near the vertical pylon, exposing the shear deck and vertical pylon forward spar;\n\n    (b) Using a clean cloth and a suitable solvent, clean all accessible areas of the spar around the cut-out for the tail rotor drive shaft;\n\n    (c) Using a light, visually inspect the forward side of the spar for cracks near where the shear deck attaches to the spar web, and web doubler;\n\n    (d) Using a light and mirror, and looking through the tail rotor drive shaft cut-out, visually inspect the aft side of the spar for cracks.\n\n2. Retire from service the cap angles of the vertical pylon forward spar.\n\nNote: FAA ADs 91-08-03 and 91-24-13 refer.\n\nCompliance: 1. Inspect every 50 hours or less.\n\n2. Retire before 1420 hours component time in service. This amendment is effective from 3 March 1994.\n\nBackground: The vertical pylon forward spar has a long history of cracking. This directive allows operation for a limited period, with frequent inspections, but eventually the cap angles must be replaced or reinforced before the inspections become unreliable in the face of widespread multiple site fatigue damage. For convenience, the requirements of AD/S76/56 are now included in this directive. The main change introduced in Amendment 4 is the exemption of helicopters fitted with Mod Kit 76070-20086, since Sikorsky’s analysis suggests that the steel spar straps, and the doubler which joins the web and shear deck, should impart a long fatigue life.\n\nThe earlier mod kits in Sikorsky Customer Service Notice No. 76-141 have proved unsuccessful, so are not exempt.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"The legislation maintains its original narrow scope — regulating a specific structural fatigue issue on one helicopter model. Amendment 4 slightly narrows the scope by exempting modified helicopters, but this is a refinement rather than scope creep. The incorporation of requirements from AD/S76/56 is explicitly noted as a convenience consolidation, not an expansion of regulatory reach."},"complexity_factors":["Single, specific applicability criterion (one helicopter model, one modification kit exemption)","Two straightforward compliance requirements (inspection interval and retirement threshold)","Four-step inspection procedure with clear sequential actions","Minimal cross-referencing (only two FAA ADs mentioned in a note, not incorporated by reference)","No nested exceptions or conditional logic — the exemption for modified helicopters is absolute","Background section provides clear rationale without creating additional legal obligations"],"plain_english_summary":"This safety directive requires Sikorsky S-76A operators to perform frequent visual checks (every 50 flight hours or less) of the vertical pylon forward spar’s aluminium cap angles and to retire those aluminium parts before they reach 1,420 flight hours, to prevent fatigue-crack development that could lead to tail-structure failure. Helicopters fitted with Sikorsky Modification Kit 76070-20086 (steel strap reinforcement) are now exempt under Amendment 4 because the reinforcement markedly reduces cracking risk."},"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":3,"scope_assessment":{"changed":true,"description":"Amendment 4 narrows the scope by exempting S‑76A helicopters fitted with Sikorsky Mod Kit 76070‑20086; previously the directive applied to all S‑76A. The Background to the amendment explicitly states this exemption as the main change, and notes earlier mod kits remain non‑exempt."},"complexity_factors":["Safety‑critical inspection and retirement requirements (visual inspection, retirement at 1,420 hours) increase operational urgency and maintenance planning (Requirement; Compliance).","Frequent recurring inspection interval (every 50 hours) creates ongoing labour and downtime costs for operators (Compliance).","Physical access steps: removal of tail‑rotor drive shaft fairings, cleaning, use of mirror and light — adds complexity to inspection tasks and tooling needs (Requirement 1(a)–(d)).","Narrow applicability and a single explicit exemption (Sikorsky Mod Kit 76070‑20086) require operators to verify modification status of each aircraft (Applicability; Background).","Cross‑references to prior ADs and incorporation of earlier directive requirements mean operators must track multiple related directives for full compliance (Note; Background).","Technical judgement limited: inspections are visual (not non‑destructive testing), making detection dependent on access and inspector skill, which affects reliability and compliance risk (Requirement 1(c),(d))."],"plain_english_summary":"Operators of Sikorsky S‑76A helicopters without Sikorsky Mod Kit 76070‑20086 must inspect the vertical pylon forward spar around the tail‑rotor drive cut‑out every 50 flight hours and retire the spar cap angles before 1,420 component hours. The Civil Aviation Safety Authority enforces these maintenance and replacement requirements; operators pay for inspections, any access work and the mandated retirement or reinforcement. Helicopters fitted with the specified steel‑strap mod kit are exempt by this amendment."}},"importantCases":[],"_links":{"self":"/api/acts/ad-s-76-29-amdt-4-vertical-pylon-forward-spar","history":"/api/acts/ad-s-76-29-amdt-4-vertical-pylon-forward-spar/history","analysis":"/api/acts/ad-s-76-29-amdt-4-vertical-pylon-forward-spar/analysis","conflicts":"/api/acts/ad-s-76-29-amdt-4-vertical-pylon-forward-spar/conflicts","importantCases":"/api/acts/ad-s-76-29-amdt-4-vertical-pylon-forward-spar/important-cases","documents":"/api/acts/ad-s-76-29-amdt-4-vertical-pylon-forward-spar/documents"}}