{"id":"F2006B02985","name":"AD/B737/84 - Main Rudder Power Control Unit (PCU)","slug":"ad-b737-84-main-rudder-power-control-unit-pcu","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42344,"registerId":"commonwealth-F2006B02985-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/84 - Main Rudder Power Control Unit (PCU)","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)  \nBoeing 737 Series Aeroplanes\n\nAD/B737/84 Main Rudder Power Control Unit (PCU) 5/95\n\nApplicability: All Boeing 737 series aircraft fitted with Part Number/Serial Number PCU’s as Listed in the Requirement Document which have been modified and/or tested by Aerocontrols Inc. in Auburn, Washington.\n\nRequirement: Action in accordance with the technical requirements of FAA Telegraphic AD T95-06-53.\n\nNote: CAO 105 AD/B737/79 makes reference to Boeing SB 737-27-1185 and FAA AD 94-01-07 which are called up as Ref B and E, respectively, in the Requirement document.\n\nCompliance: As specified in the Requirement Document.\n\nBackground: The FAA has advised that two reports of in-service malfunctions of certain rudder PCU’s has been reported. The PCU’s were removed from the aircraft and subsequently failed their functional tests. Subsequent investigation confirmed that during modification of the PCU the proper tooling may not have been used to torque the spring retainer.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a targeted safety directive addressing a specific manufacturing defect in a specific component from a specific supplier. It has not expanded beyond its original purpose of addressing the Aerocontrols Inc. PCU modification issue."},"complexity_factors":["Short, single-purpose directive (approximately 200 words)","Only 1 defined applicability criterion (specific PCU part/serial numbers from Aerocontrols Inc.)","Incorporates external technical requirements by reference (FAA Telegraphic AD T95-06-53) rather than spelling them out","Contains one cross-reference to related Australian directive (CAO 105 AD/B737/79) and two US documents (Boeing SB 737-27-1185, FAA AD 94-01-07)","No nested exceptions or conditional logic — straightforward applicability and compliance structure","Technical background is concise and factual (2 paragraphs)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft.\n\n**What it does:**\nOrders owners and operators of certain Boeing 737 aircraft to inspect or fix a specific part called the **Main Rudder Power Control Unit (PCU)**. The PCU is a hydraulic component that helps control the aircraft's rudder (the vertical flap on the tail that steers the plane left and right).\n\n**Who it affects:**\nAll Boeing 737 series aircraft that have a PCU modified or tested by a specific company — **Aerocontrols Inc.** in Auburn, Washington — with particular part and serial numbers listed in a separate technical document.\n\n**Why it matters:**\nThe US Federal Aviation Administration (FAA) reported two cases where these PCUs malfunctioned during actual flight operations. When removed and tested, they failed. The suspected cause: improper tools may have been used during a previous modification to tighten a \"spring retainer\" (a component that holds a spring in place). If the PCU fails in flight, the pilots could lose control of the rudder, potentially causing a serious accident.\n\n**What must be done:**\nAircraft operators must follow the technical instructions in **FAA Telegraphic AD T95-06-53** — a US safety order that this Australian directive adopts by reference. The exact deadline and actions required are set out in that document."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"Scope remains focused on correcting potential improper modification of specific rudder PCUs modified/tested by Aerocontrols Inc.; the directive mandates following the FAA telegraphic AD and does not expand to other components or aircraft beyond the listed PCUs."},"complexity_factors":["Narrow applicability — only Boeing 737 aircraft with listed PCU part/serial numbers modified/tested by Aerocontrols (Applicability).","Reliance on an external FAA Telegraphic AD for technical steps (Requirement) increases operational dependency on another authority's document.","Compliance detail is delegated to the Requirement Document ('As specified in the Requirement Document'), so timing and exact actions are externally specified.","Safety-critical hardware (main rudder PCU) requires specialised testing and tooling, raising implementation and technical competence demands (Background).","Administrative burden to identify affected PCUs by part/serial number and record compliance.","Enforcement by CASA creates legal obligations on operators to complete and document inspections/repairs (Regulatory context)."],"plain_english_summary":"This airworthiness directive requires operators of Boeing 737 aircraft fitted with specific main rudder Power Control Units (PCUs) modified or tested by Aerocontrols Inc. to carry out the actions set out in FAA Telegraphic AD T95-06-53. CASA enforces compliance; operators must inspect, test or modify the listed PCUs as required.\n\nIt responds to two in-service malfunctions and failed functional tests traced to possible incorrect tooling when torquing a spring retainer. Operators pay for inspections/repairs and must follow external FAA technical instructions."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-84-main-rudder-power-control-unit-pcu","history":"/api/acts/ad-b737-84-main-rudder-power-control-unit-pcu/history","analysis":"/api/acts/ad-b737-84-main-rudder-power-control-unit-pcu/analysis","conflicts":"/api/acts/ad-b737-84-main-rudder-power-control-unit-pcu/conflicts","importantCases":"/api/acts/ad-b737-84-main-rudder-power-control-unit-pcu/important-cases","documents":"/api/acts/ad-b737-84-main-rudder-power-control-unit-pcu/documents"}}