{"id":"F2006B10708","name":"AD/HU 369/46 - Tail Rotor Drive Shaft Couplings - Inspection","slug":"ad-hu-369-46-tail-rotor-drive-shaft-couplings-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116680,"registerId":"commonwealth-F2006B10708-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HU 369/46 - Tail Rotor Drive Shaft Couplings - Inspection","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)  \nMcDonnell Douglas (Hughes) and Kawasaki 369 Series Helicopters\n\nAD/HU 369/46 Tail Rotor Drive Shaft Couplings \\- Inspection 2/81\n\nApplicability: All model 369 series helicopters.\n\nRequirement: Determine the serial numbers of the fore and aft tail rotor drive shaft couplings. The serial number is on the Bendix part number decal.\n\nRemove from service all couplings with the following serial numbers:-\n\n    (a) Hughes P/N 369H92564 couplings, serial numbers 0883U, 0932U, 0933U, 0935U, 094OU, 095OU, 0957U, 0961U, 0971U;\n\n    (b) Hughes P/N 369A5501 couplings, S/Nos. 10670U, and 10672U.\n\nNote: FAA AD 80-25-01 refers.\n\nCompliance: Within 25 hours time in service after 14 January 1981.\n\nBackground: Fatigue failure could occur to certain tail rotor drive shaft couplings.","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. It has not expanded beyond its original purpose of grounding specific defective components."},"complexity_factors":["Very short document (under 200 words)","Only 2 specific part numbers affected","Simple binary compliance: check serial number, remove if matched","No defined terms section","No cross-references to other legislation (only a reference to a related FAA directive for context)","Single compliance deadline with no conditional exceptions"],"plain_english_summary":"This is an **Airworthiness Directive** — essentially a mandatory safety order for aircraft. It applies to **all McDonnell Douglas (Hughes) and Kawasaki 369 series helicopters**.\n\n**What it requires:**\n- Helicopter operators must check the serial numbers on specific tail rotor drive shaft couplings (these are mechanical parts that transfer power to the tail rotor).\n- If the couplings match certain serial numbers listed in the directive, they **must be removed from service immediately**.\n\n**Why this matters:**\n- These specific couplings have a manufacturing defect that could cause **fatigue failure** — meaning they could crack and break during flight due to repeated stress.\n- A failed tail rotor drive shaft coupling could cause loss of tail rotor control, potentially leading to a crash.\n\n**When it had to be done:**\n- Within 25 hours of flight time after 14 January 1981.\n\n**Key point:** This is a **retroactive safety fix** — it doesn't apply to new helicopters, but requires immediate action on existing aircraft already in service."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive imposes a targeted safety measure limited to particular tail rotor coupling serial numbers on all model 369 series helicopters. The stated background risk (fatigue failure) lines up with the specific removal requirement. The text does not expand or broaden the population affected beyond the stated applicability and the listed serial numbers, and does not add discretionary exceptions or broader obligations; therefore the scope remains consistent with the directive’s stated purpose (Applicability; Requirement; Background)."},"complexity_factors":["Narrow, targeted scope: applies only to tail rotor drive shaft couplings on model 369 helicopters (Applicability; Requirement).","Clear identification method: serial numbers are read from a Bendix part-number decal (Requirement).","Finite, short list of specific serial numbers to remove (Requirement: list (a) and (b)).","Short compliance window (25 hours TIS after 14 Jan 1981) increases logistical urgency (Compliance).","Cross-reference to FAA AD 80-25-01 introduces an external technical reference but does not add procedural ambiguity (Note).","Implementation risk if decals are missing or illegible — requires operators to substitute procedures or remove parts to comply (Requirement)."],"plain_english_summary":"What this directive does (mechanics)\n\n- The Civil Aviation Safety Authority (CASA) requires owners/operators of McDonnell Douglas (Hughes) and Kawasaki 369-series helicopters to inspect the fore and aft tail rotor drive shaft couplings (Applicability; Requirement).\n- The inspection consists of locating the Bendix part-number decal on each coupling and recording the coupling serial number (Requirement).\n- If a coupling has any of the listed serial numbers (two part‑numbers with a short list of serials), that coupling must be removed from service (Requirement: list (a) and (b)).\n- Operators must complete this inspection and any removals within 25 hours time in service after 14 January 1981 (Compliance).\n- The directive refers to FAA AD 80-25-01 for related material (Note).\n\nOfficial stated purpose\n\n- The directive’s stated reason is to address a risk that “fatigue failure could occur to certain tail rotor drive shaft couplings” (Background). That is the safety objective the directive asserts.\n\nWho pays, who decides, and what changes\n\n- Who decides: CASA issued the airworthiness directive and sets the requirement (header and Applicability/Requirement). The directive itself prescribes the mandatory action.\n- Who pays: The text requires owners/operators to identify and remove affected couplings. That implies owners/operators bear the direct costs of inspection time and of removing and replacing parts (Requirement; Compliance). The directive does not state any funding or compensation.\n- What behaviour changes: Operators must (1) inspect specified couplings to read serials from the Bendix decal, and (2) take any coupling with a listed serial number out of service (Requirement). This may require ordering and installing replacement couplings and temporarily withdrawing aircraft from service until repairs are done (implied by removal-from-service requirement).\n\nCosts, incentives and trade‑offs (mechanisms, not conclusions)\n\n- Direct compliance cost: time to inspect each helicopter and the cost of replacing any coupling that matches the listed serial numbers (Requirement; Compliance).\n- Operational impact: the 25‑hour compliance window may force accelerated maintenance scheduling and short‑term loss of aircraft availability while the inspection/replacement occurs (Compliance).\n- Incentives for suppliers and maintenance providers: removing specific serial-numbered parts creates immediate demand for replacement couplings or repair services for affected operators (Requirement).\n- Identification dependency and implementation risk: the inspection method depends on a Bendix part-number decal being present and legible. If a decal is missing, illegible, or detached, operators may need alternative means to identify the part or choose to remove the part to ensure compliance, increasing time and cost (Requirement).\n- Administrative discretion: the directive prescribes a clear, binary action (inspect and remove specified serial numbers). The text shows little to no operational discretion for operators—either the serial number matches and the coupling must be removed, or it does not (Requirement).\n\nCompliance burden and enforcement cues\n\n- The directive sets a short, specific compliance timeframe (25 hours TIS from 14 Jan 1981) creating a high-priority compliance burden (Compliance).\n- The AD references a corresponding FAA action (Note), which operators and maintenance organisations may consult for technical background or procedures but the removal requirement is explicit in this instrument (Note; Requirement).\n\nPotential concentrated benefits and diffuse costs (mechanism view)\n\n- Concentrated benefit mechanism: manufacturers or suppliers of replacement couplings and maintenance providers will see concentrated, short‑term demand from operators that must replace removed parts (Requirement).\n- Diffuse cost mechanism: the cost of inspection and replacement is borne individually by operators of affected helicopters; no redistribution or compensation is specified in the instrument (Requirement).\n\nSummary sentence\n\n- In plain terms: this CASA airworthiness directive tells every operator of model 369 helicopters to check the serial numbers on their tail rotor drive shaft couplings (from the Bendix decal) and to remove from service any couplings that appear on the specified serial-number lists, within 25 hours of service time from 14 January 1981, with the stated purpose of preventing possible fatigue failure (Applicability; Requirement; Compliance; Background; Note)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hu-369-46-tail-rotor-drive-shaft-couplings-inspection","history":"/api/acts/ad-hu-369-46-tail-rotor-drive-shaft-couplings-inspection/history","analysis":"/api/acts/ad-hu-369-46-tail-rotor-drive-shaft-couplings-inspection/analysis","conflicts":"/api/acts/ad-hu-369-46-tail-rotor-drive-shaft-couplings-inspection/conflicts","importantCases":"/api/acts/ad-hu-369-46-tail-rotor-drive-shaft-couplings-inspection/important-cases","documents":"/api/acts/ad-hu-369-46-tail-rotor-drive-shaft-couplings-inspection/documents"}}