{"id":"F2006B10356","name":"AD/HILLER 12/29 Amdt 4 - Main Drive Torsion Coupling - Inspection and Replacement","slug":"ad-hiller-12-29-amdt-4-main-drive-torsion-coupling-inspection-and-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115967,"registerId":"commonwealth-F2006B10356-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HILLER 12/29 Amdt 4 - Main Drive Torsion Coupling - Inspection and Replacement","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 12/29\n\nAmdt 4\n\n  \n\nMain Drive Torsion Coupling \\- Inspection and Replacement\n\n  \n11/84\n\nApplicability: All Hiller models fitted with Torsion couplings Part Number 21046-5, 21047-9, 21047-11.\n\nRequirement: 1. (a) Inspect the torsion coupling in accordance with Hiller Service Manual Section 21-2-42, para. “C”. In addition, inspect the mating surfaces between the upper and lower halves of the torsion coupling for indications of relative movement between the surfaces.\n\n    (b) Inspect the six upper coupling mounting studs for cracking and wear, and the upper coupling flange holes for elongation.\n\n    (c) Ensure that a zero clearance fit exists between the upper mounting studs and flange holes. It should be necessary to use the flange jack screw holes to separate the upper and lower sections.\n\n    (d) Remove from service any coupling with indications of movement between surfaces, damaged studs, or clearance between studs and holes.\n\n2. Remove from service all P/N 21047-9 or 21047-11 couplings with serial numbers 497 through 766.\n\nNote: The dimensional criteria given in Hiller SB UH-12-21-1 is no longer valid.\n\nCompliance: 1. For para. 1 of the requirement document \\- before installation of a coupling, and thereafter at periods not exceeding 300 hours’ time in service.\n\n2. For para. 2 of the requirement document \\- within 100 hours’ time in service after 31 July 1982.\n\nBackground: This Directive is raised in issue to amend the applicability to include specific Part Numbered Torsion couplings only.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"This is Amendment 4, and the background explicitly states it was issued to 'amend the applicability to include specific Part Numbered Torsion couplings only.' This represents a narrowing of scope from earlier versions — the directive has been refined from broader application to a precisely defined set of part numbers (21046-5, 21047-9, 21047-11). Additionally, it explicitly invalidates a previous technical standard (Hiller SB UH-12-21-1), indicating the regulatory approach has shifted from relying on manufacturer service bulletins to mandating specific CASA-directed actions."},"complexity_factors":["Short, single-purpose document (approximately 250 words)","Only 3 defined part numbers and 1 serial number range to track","Simple two-part compliance structure with clear time intervals (300 hours / 100 hours)","No nested exceptions or conditional logic — requirements are absolute","Single cross-reference to Hiller Service Manual Section 21-2-42 (external technical document)","Plain language inspection criteria ('cracking and wear', 'elongation', 'zero clearance fit')","Background section explains the amendment rationale in one sentence"],"plain_english_summary":"This Airworthiness Directive affects Hiller UH-12 helicopters fitted with torsion couplings P/N 21046-5, 21047-9, or 21047-11, requiring pre-installation and 300‑hour inspections for movement, cracks, stud wear, elongated holes or looseness, and immediate removal from service if defects are found. It also mandates permanent removal of P/N 21047‑9/21047‑11 couplings S/N 497–766 within 100 flight hours after 31 July 1982.\n\nThe amendment narrows applicability to specific part numbers and cancels a prior Hiller dimensional standard."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"Background states the directive 'amend[s] the applicability to include specific Part Numbered Torsion couplings only.' The AD therefore narrows/clarifies scope to helicopters fitted with P/N 21046-5, 21047-9, 21047-11 and additionally mandates removal of P/N 21047-9 or 21047-11 units with serial numbers 497–766. It also withdraws the dimensional criteria in Hiller SB UH-12-21-1, shifting compliance reliance to the AD and the referenced service manual."},"complexity_factors":["Technical inspection standard references Hiller Service Manual Section 21-2-42, para. 'C' (Requirement 1(a)) — requires access to and interpretation of manufacturer's procedures.","Multiple inspection items: mating-surface relative movement, six upper coupling mounting studs for cracking/wear, and flange hole elongation (Requirements 1(a)–(c)).","Operational tolerance: requires a 'zero clearance fit' and use of flange jack screw holes to separate halves — practical rigging and tooling implications (Requirement 1(c)).","Mandatory removals: immediate removal criteria for any coupling showing movement/damage, and wholesale removal of P/N 21047-9 or 21047-11 with serial numbers 497–766 (Requirement 1(d) & 2).","Compliance timing constraints: inspections before installation and at intervals not exceeding 300 hours; removal of specified serial numbers within 100 hours after 31 July 1982 — creates scheduling pressure (Compliance).","Contradiction with prior guidance: note that dimensional criteria in Hiller SB UH-12-21-1 is expressly no longer valid — requires reliance on this AD and the service manual instead (Note)."],"plain_english_summary":"This airworthiness directive requires owners/operators of Hiller UH‑12 helicopters fitted with torsion couplings P/N 21046‑5, 21047‑9 or 21047‑11 to inspect the main drive torsion coupling and associated studs for movement, cracking, wear or clearance and to remove specified couplings. It sets inspection timing (before installation and every 300 hours) and a short-term removal deadline for certain serial-numbered couplings; operators bear the cost and must follow Hiller service manual procedures."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hiller-12-29-amdt-4-main-drive-torsion-coupling-inspection-and-replacement","history":"/api/acts/ad-hiller-12-29-amdt-4-main-drive-torsion-coupling-inspection-and-replacement/history","analysis":"/api/acts/ad-hiller-12-29-amdt-4-main-drive-torsion-coupling-inspection-and-replacement/analysis","conflicts":"/api/acts/ad-hiller-12-29-amdt-4-main-drive-torsion-coupling-inspection-and-replacement/conflicts","importantCases":"/api/acts/ad-hiller-12-29-amdt-4-main-drive-torsion-coupling-inspection-and-replacement/important-cases","documents":"/api/acts/ad-hiller-12-29-amdt-4-main-drive-torsion-coupling-inspection-and-replacement/documents"}}