{"id":"F2006B09499","name":"AD/EMB-120/1 - Generator Control Unit (GCU)","slug":"ad-emb-120-1-generator-control-unit-gcu","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54040,"registerId":"commonwealth-F2006B09499-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/EMB-120/1 - Generator Control Unit (GCU)","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)  Embraer EMB-120 (Brasilia) Series Aeroplanes\n\n \n\nAD/EMB-120/1 Generator Control Unit (GCU) 2/91\n\nApplicability: Embraer 120 aircraft S/No’s 120004; and 120006 through to 120090 inclusive. Requirement:               Action in accordance with the technical requirements of Brazilian AD 90-09-03.\n\nNote: Embraer SB 120-024-0021 Revision 3 also refers.\n\n \n\nCompliance: Within 1000 hours time in service after 30 September 1990.\n\n \n\nBackground: Advice has been received that GCU failures may result in momentary overvoltages of sufficient amplitude to cause failure of critical aircraft systems and components.\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 \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The text shows a direct, targeted airworthiness directive aimed at specific serial-numbered Embraer 120 aeroplanes to mitigate GCU-related overvoltage risk by mandating action consistent with Brazilian AD 90-09-03 and referring to an Embraer service bulletin (Applicability; Requirement; Note; Background). There is no indication within the instrument that the directive’s scope was broadened or narrowed from its original stated purpose of addressing GCU failures."},"complexity_factors":["Serial-number-specific applicability narrows scope to a defined subset of aircraft (Applicability).","Cross-reference to a foreign airworthiness directive (Brazilian AD 90-09-03) for the technical remedy creates dependence on external technical material (Requirement).","Reference to a manufacturer service bulletin (Embraer SB 120-024-0021 Rev 3) adds another external document operators must consult (Note).","Compliance metric is measured in flight hours with a past effective date (1,000 hours after 30 September 1990), requiring operators to calculate elapsed time-in-service for compliance scheduling (Compliance).","Technical subject matter (electrical Generator Control Unit and overvoltage effects) is specialised and requires qualified maintenance personnel and possibly parts or modification kits, creating operational and logistical considerations (Background; Requirement)."],"plain_english_summary":"What this instrument does mechanically\n\n- It requires specified Embraer EMB-120 aircraft to have a technical action performed to address failures of the Generator Control Unit (GCU). The instruction for what to do is the technical content of Brazilian AD 90-09-03 (the Australian directive says “Action in accordance with the technical requirements of Brazilian AD 90-09-03”) (Requirement). The directive also refers operators to Embraer Service Bulletin 120-024-0021 Revision 3 for related guidance (Note).\n- It applies only to Embraer 120 aircraft with serial numbers 120004 and 120006 through 120090 inclusive (Applicability).\n- Operators must complete the required action within 1,000 hours time in service measured after 30 September 1990 (Compliance).\n\nWhy the rule exists (official rationale)\n\n- The directive records that failures of the GCU can cause momentary overvoltages that are large enough to damage or cause failure of critical aircraft systems and components (Background). The Australian instrument directs compliance with the Brazilian AD’s technical fixes to mitigate that risk (Requirement).\n\nWho is affected and who pays\n\n- Owners/operators of the listed Embraer 120 aircraft must have the required technical action performed (Applicability; Requirement). Practically, that means those operators bear the direct costs of inspections, repairs, modifications or replacements needed to meet the AD’s technical requirements (Requirement).\n\nHow it changes behaviour and decisions\n\n- Operators must schedule maintenance work to meet the 1,000-hour compliance window measured from the stated date, which can affect aircraft availability and maintenance planning (Compliance).\n- The Australian directive delegates the technical specification of the remedy to a foreign airworthiness directive (Brazilian AD 90-09-03) and references the manufacturer’s service bulletin; therefore, the specific technical decisions (what exactly to inspect, replace or modify) are determined by those external documents rather than being spelled out in the Australian text (Requirement; Note).\n\nImplementation, compliance burden and practical risks\n\n- Compliance burden is concentrated on the subset of operators who own the affected serial-numbered aircraft (Applicability). The burden includes costs for parts, labour, and possible aircraft downtime while the technical action is performed (Requirement; Compliance).\n- Because the directive refers to Brazilian AD 90-09-03 and an Embraer service bulletin for technical detail, operators and maintenance organisations must obtain and follow those external documents; this creates reliance on external technical material and on availability of parts and authorised maintenance procedures (Requirement; Note).\n- The 1,000-hour deadline measured from 30 September 1990 is a time-in-service metric; operators must track flight hours against that date to determine compliance timing (Compliance). If parts or approved repair procedures are in limited supply, that may create scheduling or grounding risk while owners source the remedy.\n\nTrade-offs and incentives\n\n- The directive imposes a one-off compliance cost on the affected operators to reduce the risk of electrical overvoltage events from the GCU (Background; Requirement).\n- Concentrated, identifiable operators receive the direct cost, while the safety benefit accrues to passengers, crew, and the flying public — the directive does not allocate monetary compensation or subsidies (Applicability; Requirement).\n- By referencing a foreign AD and the manufacturer’s service bulletin, the instrument channels technical work to established manufacturer/issuing-authority remedies, reducing the need for the Australian regulator to specify technical methods directly but increasing dependence on external documents (Requirement; Note).\n\nKey source citations\n\n- Issuing framework: Commonwealth of Australia — Civil Aviation Safety Authority, Schedule of Airworthiness Directives (header).\n- Applicability: Embraer 120 aircraft S/No’s 120004; and 120006 through to 120090 inclusive (Applicability).\n- Requirement: Action in accordance with the technical requirements of Brazilian AD 90-09-03 (Requirement).\n- Note: Embraer SB 120-024-0021 Revision 3 also refers (Note).\n- Compliance: Within 1000 hours time in service after 30 September 1990 (Compliance).\n- Background: GCU failures may result in momentary overvoltages capable of causing failure of critical aircraft systems and components (Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific technical defect in specific aircraft. It has not expanded beyond its original purpose of mandating GCU inspection/repair."},"complexity_factors":["Single, specific technical requirement (comply with Brazilian AD 90-09-03)","Limited applicability (specific aircraft serial numbers only)","No defined terms section","No nested exceptions or conditional logic","Straightforward compliance deadline (1000 hours time in service)","Short document (approximately 150 words of substantive content)","Single cross-reference (to Embraer Service Bulletin)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\nIt requires owners and operators of certain **Embraer EMB-120 \"Brasilia\" aircraft** (specifically serial numbers 120004 and 120006 through 120090) to inspect or fix a problem with the **Generator Control Unit (GCU)** — the device that manages electrical power from the aircraft's generators.\n\n**Why it matters:**\nThe GCU can fail in a way that causes **dangerous power spikes** (momentary overvoltages). These spikes are strong enough to knock out critical aircraft systems — think navigation, communication, or flight controls. That's obviously bad news when you're airborne.\n\n**What must be done:**\nOperators must follow the technical instructions in **Brazilian AD 90-09-03** (Brazil issued this first, and Australia is adopting it). There's also a reference to **Embraer Service Bulletin 120-024-0021 Rev 3** — manufacturer's guidance on how to fix it.\n\n**Deadline:**\nThe work must be completed within **1,000 flight hours** after 30 September 1990.\n\n**Who it affects:**\nAnyone operating the specific Embraer 120 aircraft listed — mostly regional airlines and charter operators flying these Brazilian-made turboprops."}},"importantCases":[],"_links":{"self":"/api/acts/ad-emb-120-1-generator-control-unit-gcu","history":"/api/acts/ad-emb-120-1-generator-control-unit-gcu/history","analysis":"/api/acts/ad-emb-120-1-generator-control-unit-gcu/analysis","conflicts":"/api/acts/ad-emb-120-1-generator-control-unit-gcu/conflicts","importantCases":"/api/acts/ad-emb-120-1-generator-control-unit-gcu/important-cases","documents":"/api/acts/ad-emb-120-1-generator-control-unit-gcu/documents"}}