{"id":"F2006B06717","name":"AD/S-76/36 - Fuselage - Engine Compartment Centre Firewall - Inspection of No. 1 Tail Drive Shaft for Adequate Clearance","slug":"ad-s-76-36-fuselage-engine-compartment-centre-firewall-inspection-of-no-1-tail-drive-shaft-for-adequ","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":114535,"registerId":"commonwealth-F2006B06717-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/S-76/36 - Fuselage - Engine Compartment Centre Firewall - Inspection of No. 1 Tail Drive Shaft for Adequate Clearance","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-76/36 Fuselage - Engine Compartment Centre\n\nFirewall - Inspection of No. 1 Tail Drive Shaft for Adequate Clearance\n\nApplicability: All model S-76A Helicopters.\n\n \n\nRequirement: Sikorsky Alert S.B. 76-53-24. Sikorsky CBT-TP-84-098.\n\n \n\nCompliance: Unless already accomplished, before further flight after 12 February 1985.\n\n \n\nBackground:  A report indicates No. 1 section tail rotor drive shaft became severed due to interference with doubler P/N 76070-20057-101.\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\n \n\n \n\n \n\n\n3/85\n\nTX\n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in a specific helicopter model. It has not expanded beyond its original purpose of preventing tail drive shaft failure due to interference with the doubler plate."},"complexity_factors":["Extremely short document (approximately 150 words)","Only 4 operative sections: Applicability, Requirement, Compliance, and Background","No defined terms section — all terms are either common aviation terminology or reference external technical documents","No conditional logic or nested exceptions","Single cross-reference to external technical standards (Sikorsky Service Bulletin and CBT document)","Clear, unambiguous compliance deadline with simple 'unless already accomplished' exception"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order — issued by Australia's Civil Aviation Safety Authority (CASA) for a specific type of helicopter.\n\n**What it does:**\n- Requires owners and operators of **Sikorsky S-76A helicopters** to inspect the No. 1 tail drive shaft (a critical component that transfers power to the tail rotor) to ensure it has adequate clearance from a nearby structural part called \"doubler P/N 76070-20057-101\" (a reinforcement plate in the engine compartment).\n\n**Why it matters:**\n- A tail drive shaft that rubs against this doubler can become **severed (cut completely through)**. If that happens in flight, the tail rotor loses power, the helicopter can spin uncontrollably, and the result is typically a crash with fatalities.\n- This AD was issued after a report confirmed this exact failure mode had occurred.\n\n**Who must comply:**\n- Anyone operating an S-76A helicopter in Australia.\n\n**What they must do:**\n- Follow the inspection procedures in **Sikorsky Alert Service Bulletin 76-53-24** and **CBT-TP-84-098** (technical documents from the manufacturer specifying exactly how to check the clearance).\n\n**When:**\n- Before the helicopter flies again after **12 February 1985** (unless already done).\n\n**Bottom line:** This is a life-critical safety fix. No S-76A could legally fly in Australia after mid-February 1985 without this inspection being completed first."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive’s scope remains an immediate inspection requirement for the No. 1 tail drive shaft on all S-76A helicopters to verify clearance from the identified doubler (Applicability; Requirement; Background). The AD implements that inspection obligation with a firm compliance deadline (Compliance) and does not expand or narrow the stated inspection requirement relative to the operational problem described in the background."},"complexity_factors":["Narrow applicability: applies only to all Sikorsky S-76A helicopters (Applicability).","Single, concrete required action: inspection of the No. 1 tail drive shaft for clearance (Requirement).","Immediate compliance date: must be done before further flight after 12 February 1985, creating an operational deadline (Compliance).","Dependence on external documents: inspection and remediation rely on Sikorsky Alert Service Bulletin 76-53-24 and CBT-TP-84-098 (Requirement), requiring operators to obtain and follow those materials.","Potential for additional corrective work: if clearance is inadequate, repairs or part changes may be needed, adding time and cost (Background; Requirement).","Regulatory enforcement: the AD leaves limited discretion to operators beyond the exception for work already completed (Compliance)."],"plain_english_summary":"What this directive does mechanically:\n\n- It requires operators of all Sikorsky S-76A helicopters to inspect the No. 1 tail rotor drive shaft for adequate clearance relative to the engine compartment centre firewall and the doubler identified (P/N 76070-20057-101) (Applicability; Background).  The inspection must be done in accordance with the Sikorsky materials the directive references (Sikorsky Alert Service Bulletin 76-53-24 and Sikorsky CBT-TP-84-098) (Requirement).\n- The inspection is mandatory before any further flight after 12 February 1985, unless the inspection has already been completed (Compliance).\n\nWhy the directive was issued (the stated rationale):\n\n- The directive cites a report that the No. 1 section of the tail rotor drive shaft became severed because it contacted the doubler (Background). The AD therefore directs an immediate inspection to confirm adequate clearance (Requirement; Compliance).\n\nWho pays, who decides, and what changes in behaviour:\n\n- Who pays: helicopter operators (owners/aircraft operators) bear the direct costs of carrying out the inspection and any corrective work required (Compliance; Requirement). Costs include labour, any replacement parts and the opportunity cost of aircraft downtime while the inspection or repairs are carried out (Compliance).\n- Who decides: the Civil Aviation Safety Authority (through this Airworthiness Directive) mandates the action and points operators to Sikorsky’s service bulletin and technical publication for the inspection procedure (Applicability; Requirement). Operators must follow the AD’s timeline: inspection before further flight after the specified date (Compliance).\n- Behaviour change: operators must stop flying affected aircraft until the inspection is performed (unless it has already been done). If the inspection shows inadequate clearance, operators must follow the manufacturer’s corrective instructions as referenced (Requirement).\n\nImplementation, incentives and trade-offs:\n\n- Compliance burden and timing: the AD requires immediate compliance before further flight (Compliance). That creates an operational impact: aircraft may be grounded until inspection and any repairs are completed, producing lost flying time and possible revenue loss for operators (Compliance).\n- Information and action delegated to manufacturer documents: the AD does not set out inspection steps in full but refers to Sikorsky Alert S.B. 76-53-24 and CBT-TP-84-098 (Requirement). Operators therefore must obtain and follow those Sikorsky materials to complete the mandated work, which imposes a small administrative burden to source and apply the referenced documents (Requirement).\n- Enforcement and discretion: the AD leaves little discretion for operators about whether to carry out the inspection once the AD is applicable; the only conditional statement is “unless already accomplished” (Compliance). Enforcement of the AD is a regulatory function of the issuing authority (Applicability; Compliance).\n\nEffects on private enterprise, competition and other market attributes:\n\n- Impact on maintenance providers: independent maintenance organisations can perform the inspection and any corrective work, subject to normal regulatory approvals; the AD does not specify exclusive providers (Requirement).\n- Competition and ownership: the directive does not alter ownership or market structure; it imposes a safety obligation on operators (Applicability; Requirement).\n- Prices and productivity: operators face potential short-term productivity losses and repair costs, which could be reflected in operational costs or service availability if aircraft are out of service (Compliance).\n\nRisks and unintended consequences to watch for (as implied by the text):\n\n- If clearance issues are widespread, there could be a spike in maintenance demand and parts requirements; the AD itself does not quantify frequency or corrective actions (Background; Requirement).\n- Because the AD points to manufacturer materials for procedure and remedial actions, differing interpretations or variability in execution could arise across maintenance providers (Requirement)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-s-76-36-fuselage-engine-compartment-centre-firewall-inspection-of-no-1-tail-drive-shaft-for-adequ","history":"/api/acts/ad-s-76-36-fuselage-engine-compartment-centre-firewall-inspection-of-no-1-tail-drive-shaft-for-adequ/history","analysis":"/api/acts/ad-s-76-36-fuselage-engine-compartment-centre-firewall-inspection-of-no-1-tail-drive-shaft-for-adequ/analysis","conflicts":"/api/acts/ad-s-76-36-fuselage-engine-compartment-centre-firewall-inspection-of-no-1-tail-drive-shaft-for-adequ/conflicts","importantCases":"/api/acts/ad-s-76-36-fuselage-engine-compartment-centre-firewall-inspection-of-no-1-tail-drive-shaft-for-adequ/important-cases","documents":"/api/acts/ad-s-76-36-fuselage-engine-compartment-centre-firewall-inspection-of-no-1-tail-drive-shaft-for-adequ/documents"}}