{"id":"F2006B02907","name":"AD/B737/21 - Generator Control Unit (GCU) Filter Modules","slug":"ad-b737-21-generator-control-unit-gcu-filter-modules","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42249,"registerId":"commonwealth-F2006B02907-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/21 - Generator Control Unit (GCU) Filter Modules","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)  Boeing 737 Series Aeroplanes\n\n \n\nAD/B737/21 Generator Control Unit (GCU) Filter Modules 7/89\n\nApplicability: All model 737 series aircraft.\n\n \n\nRequirement: Replace OR modify the GCU filter modules in accordance with Westinghouse SB 87- 101 OR 87-102.\n\n \n\nNote: FAA AD 89-07-13 refers.\n\n \n\nCompliance: Prior to 13 December 1990.\n\n \n\nBackground: Advice has been received that GCU filter failures have occurred which have resulted in smoke in the cockpit. This condition if not corrected could lead to additional GCU failures producing smoke in the cockpit and partial loss of electrical power.\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":2,"scope_assessment":{"changed":false,"description":"The directive’s scope targets all model 737 series aircraft and mandates replacement or modification of GCU filter modules per Westinghouse SB 87-101 or 87-102, to be completed before 13 December 1990. The text does not indicate any change from that original scope or an expansion/narrowing of affected aircraft or actions."},"complexity_factors":["Single clear technical action: replace or modify GCU filter modules per one of two specified Westinghouse service bulletins (Requirement).","Fleet-wide applicability: applies to all model 737 series aircraft (Applicability).","Fixed compliance deadline creates scheduling pressure (Compliance: prior to 13 December 1990).","Dependence on manufacturer's service bulletin procedures (Requirement: reference to SB 87-101 or 87-102).","Operational logistics: need for parts, labour and aircraft downtime (implied by Requirement and Compliance)."],"plain_english_summary":"All Boeing 737 series aeroplanes must, by 13 December 1990, have their Generator Control Unit filter modules replaced or modified per Westinghouse SB 87‑101 or SB 87‑102. The directive targets owners/operators and maintenance organisations, who bear the cost and must record compliance. It aims to eliminate a failure mode that has caused cockpit smoke and could lead to further GCU failures and partial electrical power loss."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive addressing a specific mechanical defect. It has not expanded beyond its original purpose of mandating GCU filter replacement/modification to prevent cockpit smoke incidents."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 1 defined term implicitly referenced (GCU — explained in title)","No cross-references to other legislation or complex conditional logic","Single, unambiguous compliance requirement (replace OR modify)","Simple binary applicability (all model 737 series aircraft)","Fixed, absolute deadline with no exceptions or phased compliance"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). Think of it like a recall notice for aircraft, but legally binding.\n\n**What it does:** It requires owners and operators of all Boeing 737 aircraft to **replace or modify** specific electrical components called **Generator Control Unit (GCU) Filter Modules**. These parts are made by Westinghouse, and the work must follow specific service bulletins (technical repair instructions) numbered 87-101 or 87-102.\n\n**Why it matters:** The GCU filters were failing and causing **smoke in the cockpit** — a serious flight safety hazard. If left unfixed, the problem could cause more electrical failures, more smoke, and **partial loss of electrical power** to the aircraft. This directive was issued to prevent potential emergencies.\n\n**Who must comply:** Anyone operating a Boeing 737 in Australia (all models in the series).\n\n**Deadline:** The work had to be completed **before 13 December 1990**.\n\n**Key point:** This references a US Federal Aviation Administration (FAA) directive (89-07-13), showing Australia was adopting a safety measure already mandated in the United States."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-21-generator-control-unit-gcu-filter-modules","history":"/api/acts/ad-b737-21-generator-control-unit-gcu-filter-modules/history","analysis":"/api/acts/ad-b737-21-generator-control-unit-gcu-filter-modules/analysis","conflicts":"/api/acts/ad-b737-21-generator-control-unit-gcu-filter-modules/conflicts","importantCases":"/api/acts/ad-b737-21-generator-control-unit-gcu-filter-modules/important-cases","documents":"/api/acts/ad-b737-21-generator-control-unit-gcu-filter-modules/documents"}}