{"id":"F2006B02825","name":"AD/B737/123 - Rudder Control System Component Changes","slug":"ad-b737-123-rudder-control-system-component-changes","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42167,"registerId":"commonwealth-F2006B02825-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/123 - Rudder Control System Component Changes","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/B737/123 Rudder Control System Component Changes 2/99\n\nApplicability: All Boeing model 737-100, \\-200, \\-300, \\-400, \\-500 series aeroplanes.\n\nRequirements: Install new rudder pressure reducer (RPR) and yaw damper coupler (YDC) in accordance with the instructions in Boeing Alert Service Bulletin 737-27A1206 dated 19 November 1998.\n\nNote: FAA AD 97-14-03 Amdt 39-10060 refers.\n\nCompliance: On completion of AD/B737/116 but no later than 26 March 2002.\n\nThis Airworthiness Directive becomes effective on 25 February 1999.\n\nBackground: To lessen the effects of large rudder deflections, Boeing has provided instructions to incorporate a hydraulic rudder pressure reducer in the “A” hydraulic system supply line in the main rudder power control unit. Also, to improve significantly the reliability of the YDC, a new unit has been designed using technology that was not available at the time of the original design. These changes have been brought about following an investigation into the reliability and effectiveness of the B737 yaw control system by the FAA and NTSB. AD/B737/116 was issued in March 1998 to install the wiring changes necessary for the introduction of the hardware associated with this Directive.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard Airworthiness Directive with a narrow, specific safety purpose. The scope remains exactly as intended: mandating specific hardware modifications to address identified safety risks in the 737 rudder system. There is no evidence of scope creep or expansion beyond the original safety intent."},"complexity_factors":["Very short document (approximately 200 words)","Only 2 defined technical terms (RPR and YDC, both explained in context)","Single clear compliance requirement with one deadline","No cross-references to other legislation sections (only mentions related FAA document and previous AD as background)","No conditional logic or exceptions — applies to all listed aircraft models uniformly","Straightforward applicability statement listing specific aircraft models"],"plain_english_summary":"This safety order requires Australian operators of Boeing 737-100/200/300/400/500 series to install two rudder-control upgrades—a rudder pressure reducer and a yaw damper coupler—to fix yaw-control reliability issues identified by US investigators. It’s intended to prevent sudden, potentially catastrophic rudder movements and follows an earlier directive that installed necessary wiring; work was required by 26 March 2002 per Boeing’s November 1998 instructions."},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"Scope remains focused on the same listed Boeing 737 series and prescribes installation of specific rudder/yaw components. The Directive supplements earlier AD/B737/116 (which required wiring changes) by adding hardware installation instructions and a compliance deadline, rather than expanding the fleet or adding new categories of obligation beyond those models."},"complexity_factors":["Technical hardware change to hydraulic and flight‑control systems (RPR and YDC) requiring certified maintenance procedures and specialised parts.","Dependence on an external technical document (Boeing Alert Service Bulletin 737‑27A1206) for the actual installation instructions.","Cross‑references to prior domestic AD (AD/B737/116) and to FAA AD 97‑14‑03, requiring coordination with earlier compliance steps.","Applicability across multiple 737 submodels (100, 200, 300, 400, 500) obliges fleet‑wide scheduling and parts logistics for operators.","Fixed compliance window (on completion of AD/B737/116 but no later than 26 March 2002) creates time pressure and operational planning constraints.","Safety‑critical nature increases regulatory scrutiny and may require certificate/record updates and oversight by CASA.","Potential downtime and costs fall to aircraft operators (parts, labour, grounding), creating budgetary and commercial impacts.","Limited regulatory discretion in the AD text—the requirement is mandatory, but practical scheduling and sourcing leave operators operational choices."],"plain_english_summary":"Mandates installation of a hydraulic rudder pressure reducer (RPR) and a redesigned yaw damper coupler (YDC) on Boeing 737‑100/200/300/400/500 aircraft per Boeing Alert Service Bulletin 737‑27A1206. The changes aim to reduce large rudder deflections and to improve yaw damper reliability after FAA/NTSB investigation. Aircraft operators bear the cost, scheduling and downtime; the Civil Aviation Safety Authority enforces compliance by a set deadline tied to prior AD/B737/116."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-123-rudder-control-system-component-changes","history":"/api/acts/ad-b737-123-rudder-control-system-component-changes/history","analysis":"/api/acts/ad-b737-123-rudder-control-system-component-changes/analysis","conflicts":"/api/acts/ad-b737-123-rudder-control-system-component-changes/conflicts","importantCases":"/api/acts/ad-b737-123-rudder-control-system-component-changes/important-cases","documents":"/api/acts/ad-b737-123-rudder-control-system-component-changes/documents"}}