{"id":"F2006B06715","name":"AD/S-76/34 - Electrical Power - Essential Bus Modification","slug":"ad-s-76-34-electrical-power-essential-bus-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":114531,"registerId":"commonwealth-F2006B06715-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/S-76/34 - Electrical Power - Essential Bus Modification","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Sikorsky S-76 Series Helicopters\n\n \n\nAD/S-76/34 Electrical Power - Essential Bus Modification 10/84\n\nApplicability: All model S-76A Helicopters fitted with Allison 250-C30/250-C30S series engines. Requirement:              Modify essential bus installation in accordance with Customer Service Notice CSN\n\n76-149 dated 2 July 1984.\n\n \n\nNote: FAA Emergency Telegraphic Airworthiness Directive AD No. T84-16-51 refers.\n\n \n\nCompliance: Within 100 hours time in service from 21 August 1984 but no later than 15 September 1984.\n\n \n\nBackground: Uncontained engine turbine wheel failures have been experienced. This Directive requires modification of the essential bus installation such that turbine wheel failures will not result in the loss of essential electrical services.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive with a single purpose: mandating a specific electrical system modification to address a known catastrophic failure mode. It has not expanded beyond its original safety intent."},"complexity_factors":["Single, specific aircraft model and engine combination (S-76A with Allison 250-C30/250-C30S)","One clear compliance action (modify per Customer Service Notice CSN 76-149)","Simple time-based compliance window (100 hours or fixed date, whichever comes first)","No defined terms section, no cross-references to other legislation beyond a note about the corresponding FAA directive","Background explanation provided in plain language","Total length is approximately 150 words"],"plain_english_summary":"Owners/operators of Sikorsky S‑76A helicopters fitted with Allison 250‑C30 engines must modify the essential electrical bus. This CASA airworthiness directive responds to uncontained turbine wheel failures that could sever power to critical flight instruments, ensuring pilots retain essential systems to land safely. It applied urgently to Australian operators with a short compliance window."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"Scope remains limited to the specific fleet identified (S‑76A with Allison 250‑C30/250‑C30S engines) and to modifying the essential electrical bus per CSN 76‑149 (Applicability; Requirement). The AD prescribes a remedial hardware/configuration change within a fixed compliance window (Compliance) and is framed to prevent loss of essential services caused by uncontained turbine wheel failures (Background). No expansion of applicability or purpose is indicated in the text."},"complexity_factors":["Narrow technical applicability: applies only to S‑76A helicopters with Allison 250‑C30/250‑C30S engines (Applicability).","Mandated remedial action references an external document for the technical method—Customer Service Notice CSN 76‑149 dated 2 July 1984—so implementers must consult that CSN for details (Requirement).","Short, fixed compliance window (within 100 hours from 21 August 1984 or by 15 September 1984) creates operational scheduling pressure and potential grounding costs (Compliance).","Safety trigger stated as uncontained turbine wheel failures; the directive changes equipment configuration to alter failure consequences rather than engine design (Background).","Regulatory enforcement rests with the issuing authority (Civil Aviation Safety Authority) via the AD framework, so liability, recordkeeping and proof of compliance fall to operators (whole instrument)."],"plain_english_summary":"Requires all Sikorsky S‑76A helicopters fitted with Allison 250‑C30/250‑C30S engines to modify the essential electrical bus according to Customer Service Notice CSN 76‑149 (2 July 1984). Owners/operators must carry out the work within 100 flight hours from 21 August 1984 or by 15 September 1984. The mechanical change is intended to prevent an uncontained engine turbine wheel failure from causing loss of essential electrical services."}},"importantCases":[],"_links":{"self":"/api/acts/ad-s-76-34-electrical-power-essential-bus-modification","history":"/api/acts/ad-s-76-34-electrical-power-essential-bus-modification/history","analysis":"/api/acts/ad-s-76-34-electrical-power-essential-bus-modification/analysis","conflicts":"/api/acts/ad-s-76-34-electrical-power-essential-bus-modification/conflicts","importantCases":"/api/acts/ad-s-76-34-electrical-power-essential-bus-modification/important-cases","documents":"/api/acts/ad-s-76-34-electrical-power-essential-bus-modification/documents"}}