{"id":"F2006B10361","name":"AD/HILLER 12/36 Amdt 1 - Main Drive Torsion Coupling P/N 21047-15 - Inspection of Lower Plate","slug":"ad-hiller-12-36-amdt-1-main-drive-torsion-coupling-p-n-21047-15-inspection-of-lower-plate","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115977,"registerId":"commonwealth-F2006B10361-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HILLER 12/36 Amdt 1 - Main Drive Torsion Coupling P/N 21047-15 - Inspection of Lower Plate","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)  \nHiller UH-12 Series Helicopters\n\nAD/HILLER 12/36\n\nAmdt 1\n\n  \nMain Drive Torsion Coupling\n\nP/N 21047-15 \\- Inspection of Lower Plate\n\n  \n10/82\n\nApplicability: All Hiller UH-12E series, UH-12L series, OH-23G, OH-23F helicopters, fitted with a torsion coupling P/N 21047-15.\n\nRequirement: Conduct a fluorescent penetrant inspection of the lower half of the coupling, around the entire perimeter of the base where the eight cut out windows are located between the wear sleeve and the lower flange to which the rubber is bonded.\n\nFAA AD 82-16-07 refers.\n\nCompliance: Within 10 hours’ time in service after 4 August 1982, and thereafter at periods not exceeding 50 hours’ time in service.\n\nBackground: Due to a possible manufacturing defect, all P/N 21047-15 couplings are to be inspected for cracks in the area of the lower plate windows. There have been two cracked couplings reported on local helicopters.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This document is labelled as Amendment 1 (Amdt 1) to AD/HILLER 12/36, indicating it is an amended version of a prior directive. The text provided sets a mandatory inspection procedure, a tight initial deadline and a 50‑hour recurring interval for helicopters fitted with coupling P/N 21047-15 (Requirement, Compliance, Applicability). The document itself does not include the prior version, so the exact nature of the change from the original instrument cannot be determined from this text alone."},"complexity_factors":["Technical specificity: requires fluorescent penetrant inspection of a defined physical area of the coupling (Requirement).","Tight compliance timing: initial inspection within 10 hours after 4 August 1982 and recurring every 50 hours (Compliance).","Narrow applicability: applies only to helicopters of specified makes/series fitted with P/N 21047-15 (Applicability).","Operational impact: recurring inspections introduce repeated maintenance events and downtime.","Reference to external instrument: cross-reference to FAA AD 82-16-07 increases traceability requirements (Requirement).","Detection reliability: effectiveness depends on inspection technique and access to the specified window area (Requirement)."],"plain_english_summary":"# What this instrument does\n\nThis airworthiness directive (AD) requires operators to inspect a specific helicopter part: the main drive torsion coupling, part number 21047-15, fitted to certain Hiller UH-12 and OH-23 models. The inspection must look for cracks around the perimeter of the lower half of the coupling where eight cut-out windows are located (the area between the wear sleeve and the lower flange where rubber is bonded). (Requirement)\n\n- Who it applies to: All Hiller UH-12E and UH-12L series, and OH-23G and OH-23F helicopters that have coupling P/N 21047-15 installed. (Applicability)\n- What must be done: A fluorescent penetrant inspection of the lower half of the coupling around the full perimeter of the base where the eight windows are located. (Requirement)\n- When it must be done: Carry out the first inspection within 10 hours time-in-service after 4 August 1982, and then repeat at intervals not exceeding 50 hours time-in-service. (Compliance)\n- Why it is required (as stated): The AD says there may be a manufacturing defect and that two cracked couplings have been reported locally; the inspection is intended to detect cracks in the lower plate windows. (Background)\n- Reference: The AD refers to an FAA airworthiness directive (FAA AD 82-16-07). (Requirement)\n\nWho pays and who decides\n\n- Who pays: Operators/owners of affected helicopters bear the direct costs of inspections, any maintenance downtime, and any repairs or replacement if cracks are found. (Applicability, Compliance, Requirement)\n- Who decides: The Civil Aviation Safety Authority (CASA) issued the AD and sets the mandatory inspection requirement; operators are required to comply with the specified inspection method and timetable. (Header, Requirement, Compliance)\n\nPractical mechanics and incentives\n\n- Compliance mechanics: Inspections must use fluorescent penetrant technique and must focus on the specified area of the lower plate windows. The AD sets a short initial deadline (10 hours) and a recurrent interval (50 hours) that will require regular access to the coupling and repeated maintenance activity. (Requirement, Compliance)\n- Incentives: Detecting cracks early reduces the risk of in-service coupling failure; this creates an incentive for timely inspections or for replacement of the coupling with a different part if available. Operators may choose to replace the coupling to avoid recurring inspection costs or to reduce inspection frequency if a serviceable alternative exists. (Background, Requirement)\n\nCosts, trade-offs and implementation issues\n\n- Direct costs: Technician labour, materials for fluorescent penetrant inspection, inspection equipment, and possible replacement parts if cracks are found. (Requirement, Compliance)\n- Downtime and opportunity cost: The initial 10-hour deadline and 50-hour recurring interval create recurring out-of-service time that may disrupt operations. (Compliance)\n- Detection risk and implementation risk: The effectiveness of fluorescent penetrant inspection depends on technique and access to the window area; inadequate inspections could miss cracks, and overly conservative interpretation could lead to unnecessary replacements. (Requirement)\n- Compliance burden: The AD prescribes a specific inspection method and fixed intervals; this reduces operator discretion about how or when to inspect within those limits. (Requirement, Compliance)\n\nMarket and operational effects\n\n- Effects on private service providers: Independent maintenance providers will perform inspections and any repairs, creating demand for inspection services and replacement parts. (Requirement)\n- Private choice: Operators can choose to comply by performing the inspections as required, or they may choose to replace the coupling if they judge that replacement is preferable to ongoing inspections. The AD itself mandates inspection; it does not, in this text, grant alternative compliance methods. (Requirement)\n\nDistribution of benefits and costs\n\n- Concentrated benefits: Operators who find and fix cracked couplings avoid a specific mechanical failure risk. (Background)\n- Diffuse costs: All operators with the affected part incur inspection costs and downtime according to the compliance schedule. (Applicability, Compliance)\n\nOther points\n\n- The AD explicitly refers to an FAA AD (FAA AD 82-16-07), which is cited but the text does not describe any alternative compliance or alignment mechanisms beyond that reference. (Requirement)\n\nOverall, the directive mechanically imposes a mandatory, recurring inspection regime on operators of specified Hiller helicopters fitted with coupling P/N 21047-15, with costs borne by those operators and the stated purpose of detecting a possible manufacturing defect that has produced two local crack reports. (Requirement, Background, Compliance)\n"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard, narrow Airworthiness Directive focused on a specific safety-critical inspection. It has not expanded beyond its original purpose of addressing a known defect in a specific aircraft part."},"complexity_factors":["Single, clearly defined applicability clause (specific helicopter models and part number)","One straightforward inspection requirement with precise location description","Simple compliance timeline (initial + recurring intervals)","No defined terms section or interpretation provisions","No cross-references to other legislation (only reference to related FAA AD for background)","No conditional logic, exceptions, or exemptions","Total length: approximately 150 words"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order for aircraft owners and operators. It applies to specific **Hiller helicopters** (UH-12E, UH-12L, OH-23G, and OH-23F models) that use a particular part called a **torsion coupling** (part number 21047-15).\n\n**What it requires:**\n- Owners must inspect a specific component — the lower half of this coupling — using a special crack-detection method called **fluorescent penetrant inspection** (a process where dye is applied to reveal tiny cracks not visible to the naked eye).\n- The inspection must focus on the area around eight cut-out windows on the base of the coupling.\n\n**When it must be done:**\n- First inspection: within 10 hours of flying time after 4 August 1982\n- Repeat inspections: every 50 hours of flying time thereafter\n\n**Why it exists:**\nA manufacturing defect may cause cracks in this part. Two cracked couplings were found on helicopters in Australia, creating a safety risk. This AD ensures the problem is caught before it causes failure.\n\n**Who issued it:**\nThe Civil Aviation Safety Authority (CASA), following a similar US Federal Aviation Administration directive (FAA AD 82-16-07)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hiller-12-36-amdt-1-main-drive-torsion-coupling-p-n-21047-15-inspection-of-lower-plate","history":"/api/acts/ad-hiller-12-36-amdt-1-main-drive-torsion-coupling-p-n-21047-15-inspection-of-lower-plate/history","analysis":"/api/acts/ad-hiller-12-36-amdt-1-main-drive-torsion-coupling-p-n-21047-15-inspection-of-lower-plate/analysis","conflicts":"/api/acts/ad-hiller-12-36-amdt-1-main-drive-torsion-coupling-p-n-21047-15-inspection-of-lower-plate/conflicts","importantCases":"/api/acts/ad-hiller-12-36-amdt-1-main-drive-torsion-coupling-p-n-21047-15-inspection-of-lower-plate/important-cases","documents":"/api/acts/ad-hiller-12-36-amdt-1-main-drive-torsion-coupling-p-n-21047-15-inspection-of-lower-plate/documents"}}