{"id":"F2006B10362","name":"AD/HILLER 12/37 - Soloy Conversion: Power Turbine Governor Control System - Modification","slug":"ad-hiller-12-37-soloy-conversion-power-turbine-governor-control-system-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115979,"registerId":"commonwealth-F2006B10362-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HILLER 12/37 - Soloy Conversion: Power Turbine Governor Control System - 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)  Hiller UH-12 Series Helicopters\n\n \n\n# AD/HILLER 12/37 Soloy Conversion: Power Turbine\n\nGovernor Control System - Modification Applicability: All Soloy turbine conversion UH12D/E and E (4 Place) helicopters. Requirement:               Soloy Conversions S.B. 06-560.\n\nCompliance: Prior to the issue of the next Maintenance Release after 30 June 1985.\n\n# 6/85\n\n \n\nBackground: The design, applicable prior to the issue of the Requirement Document, could result in loss of collective pitch control. This modification includes a spring bungee unit that will allow the collective lever to operate independently, if the governor cable seizes.\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","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive sets a targeted mandatory modification for a defined set of aircraft converted by Soloy. The text presents a single technical change (install the spring bungee unit per Soloy S.B. 06-560) with a specified compliance window; there is no indication in the document that the scope was broadened or narrowed relative to the instrument's stated purpose."},"complexity_factors":["Narrow applicability: applies only to Soloy turbine conversion UH12D/E and E (4 Place) helicopters (Applicability).","Single, specific technical requirement: mandates installation of the modification described in Soloy Conversions S.B. 06-560 (Requirement).","Fixed compliance timing tied to routine maintenance: must be completed prior to the next Maintenance Release after 30 June 1985 (Compliance).","Dependence on an external technical document (service bulletin) for installation details, creating a need to obtain and follow that bulletin (Requirement).","Safety-critical mechanical nature requiring qualified maintenance actions, with implementation quality affecting outcome (Background; Requirement)."],"plain_english_summary":"This directive mandates fitting the spring-bungee modification in Soloy Conversions S.B. 06-560 to the Power Turbine Governor Control on Soloy‑converted Hiller UH‑12D/E (4‑place) helicopters, to be done before the next Maintenance Release after 30 June 1985. It prevents loss of collective pitch control if the governor cable seizes; owners/operators pay parts and labour and must schedule the work during routine maintenance."},"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 narrow class of aircraft. It has not expanded beyond its original purpose of mandating a single modification to prevent collective pitch control failure."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 3 defined applicability criteria (specific helicopter models)","Single technical requirement referencing an external service bulletin (S.B. 06-560)","Simple compliance deadline structure (date-based with Maintenance Release trigger)","No nested exceptions, conditional logic, or cross-references to other legislation","Straightforward cause-and-effect safety rationale"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA).\n\n**What it does:**\nIt requires owners and operators of specific Hiller helicopters (UH-12D/E models that have been converted to turbine power by a company called Soloy) to modify their **power turbine governor control system**.\n\n**The safety problem:**\nThe original design had a dangerous flaw. If the governor cable seized up (got stuck), the pilot could lose control of the **collective pitch** — that's the lever that controls how much lift the helicopter generates. Losing this control mid-flight is potentially catastrophic.\n\n**The fix:**\nInstall a **spring bungee unit** (a flexible mechanical backup) that allows the collective lever to keep working even if the governor cable jams.\n\n**Who must comply:**\nAnyone operating a Soloy turbine-converted Hiller UH-12D, UH-12E, or UH-12E (4 Place) helicopter.\n\n**When:**\nBefore the helicopter's next **Maintenance Release** (a formal certificate saying the aircraft is safe to fly) issued after 30 June 1985.\n\n**Why it matters:**\nThis directive prevents a known mechanical failure mode that could cause pilots to lose altitude control, potentially leading to crashes."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hiller-12-37-soloy-conversion-power-turbine-governor-control-system-modification","history":"/api/acts/ad-hiller-12-37-soloy-conversion-power-turbine-governor-control-system-modification/history","analysis":"/api/acts/ad-hiller-12-37-soloy-conversion-power-turbine-governor-control-system-modification/analysis","conflicts":"/api/acts/ad-hiller-12-37-soloy-conversion-power-turbine-governor-control-system-modification/conflicts","importantCases":"/api/acts/ad-hiller-12-37-soloy-conversion-power-turbine-governor-control-system-modification/important-cases","documents":"/api/acts/ad-hiller-12-37-soloy-conversion-power-turbine-governor-control-system-modification/documents"}}