{"id":"F2006B04798","name":"AD/BO 105/1 - Tandem Hydraulic Units - Water in Servo Valve","slug":"ad-bo-105-1-tandem-hydraulic-units-water-in-servo-valve","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44586,"registerId":"commonwealth-F2006B04798-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BO 105/1 - Tandem Hydraulic Units - Water in Servo Valve","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)  Eurocopter BO 105 Series Helicopters\n\n \n\nAD/BO 105/1 Tandem Hydraulic Units - Water in Servo Valve 4/86\n\nApplicability: All Model BO 105 series up to and including S/No. 750 fitted with one of the following Tandem hydraulic units, Part Numbers, 105-45021, 105-45023, 105-45028,\n\n105-83001, 105-83011, D133-3073, DSK1-30142.\n\n \n\nRequirement: MBB Alert Bulletin No. 26.\n\n \n\nCompliance: Within 25 hours time in service after 30 April 1986 or for spares, unless already accomplished, before installation in an aircraft.\n\n \n\nBackground: Entry of water into the servo valve and subsequent freezing of this water, when temperatures drop below freezing, may cause blocking of the controls in one direction.\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 limits its scope to BO 105 series helicopters up to and including S/No. 750 fitted with the listed tandem hydraulic unit part numbers and requires the specific manufacturer bulletin actions. The text does not expand or narrow that applicability beyond naming those serial numbers and parts, so the scope is consistent with the stated technical remedy and stated risk (Applicability; Requirement)."},"complexity_factors":["Narrow applicability: specified helicopter model range and explicit list of tandem hydraulic unit part numbers (Applicability).","Single corrective action path: directive directs compliance with a single manufacturer’s MBB Alert Bulletin rather than multiple alternative procedures (Requirement).","Short, fixed compliance window: 25 hours TIS after a specified date for in-service aircraft and a before-installation rule for spares (Compliance).","Technical execution required: actions involve inspection/treatment of hydraulic servo valves and require qualified maintenance (Requirement).","Operational impact concentrated: cost and downtime fall on owners/operators of the affected helicopters rather than a broad industry group (Applicability; Compliance)."],"plain_english_summary":"This directive requires owners/operators of BO 105 helicopters (up to serial no. 750) fitted with specified tandem hydraulic units to carry out the manufacturer’s MBB Alert Bulletin actions on those units before further flight and to avoid installing untreated spares. \n\nIt addresses a risk that water in the servo valve can freeze and block control movement; work must be done within 25 flight hours after 30 April 1986 for in-service aircraft, with costs and downtime borne by the owners/operators."},"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 in specific aircraft. It has not expanded beyond its original purpose of mandating inspection/repair of water ingress in servo valves for the identified helicopter models."},"complexity_factors":["Very short document (under 200 words)","Only 7 defined part numbers in applicability section","Single compliance requirement with clear deadline","No cross-references to other legislation beyond one manufacturer bulletin","No conditional logic or nested exceptions","Straightforward cause-and-effect explanation in background section"],"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 compulsory recall notice, but for aircraft parts rather than cars.\n\n**What it does:** It requires owners and operators of specific **Eurocopter BO 105 helicopters** to inspect and fix a dangerous problem with their **tandem hydraulic units** (the systems that help control the helicopter's flight surfaces). The problem? Water can get into a component called the **servo valve**, freeze in cold weather, and **block the flight controls in one direction** — which could cause a crash.\n\n**Who it affects:** Anyone operating BO 105 helicopters with serial numbers up to 750 that have specific hydraulic part numbers listed (including 105-45021, 105-45023, and others).\n\n**What must be done:** Operators must follow the instructions in **MBB Alert Bulletin No. 26** (the manufacturer's safety notice) within **25 flight hours after 30 April 1986**. If you have a spare hydraulic unit sitting on a shelf, you must fix it **before installing it** in any aircraft.\n\n**Why it matters:** Frozen water in flight controls can kill people. This AD exists to prevent accidents by forcing operators to address a known design flaw before it causes a crash."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bo-105-1-tandem-hydraulic-units-water-in-servo-valve","history":"/api/acts/ad-bo-105-1-tandem-hydraulic-units-water-in-servo-valve/history","analysis":"/api/acts/ad-bo-105-1-tandem-hydraulic-units-water-in-servo-valve/analysis","conflicts":"/api/acts/ad-bo-105-1-tandem-hydraulic-units-water-in-servo-valve/conflicts","importantCases":"/api/acts/ad-bo-105-1-tandem-hydraulic-units-water-in-servo-valve/important-cases","documents":"/api/acts/ad-bo-105-1-tandem-hydraulic-units-water-in-servo-valve/documents"}}