{"id":"F2005L02396","name":"AD/B737/113 Amdt 1 - Rudder Power Control Unit Replacement","slug":"ad-b737-113-amdt-1-rudder-power-control-unit-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":36845,"registerId":"commonwealth-F2005L02396-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Boeing 737 Series Aeroplanes","sectionType":"division","heading":"Boeing 737 Series Aeroplanes","content":"### Boeing 737 Series Aeroplanes\n\n| AD/B737/113 Amdt 1 | Rudder Power Control Unit Replacement | 10/2005 |\n| ------------------ | ------------------------------------- | ------- |\n\n| Applicability: | Model 737 series aeroplanes, having a main rudder power control unit (PCU) and vernier control rod bolts that are identified in Boeing Alert Service Bulletin (ASB) 737-27A1202 Revision 2, dated August 7, 1997.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |\n| -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Perform the test requirements of Part I of the Accomplishment Instructions of Boeing ASB 737-27A1202.2. Replace the rudder PCU in accordance with Part II of the Accomplishment Instructions of Boeing ASB 737-27A1202.3. Replace the dual servo valve and a bolt in the PCU in accordance with Part III of the Accomplishment Instructions of Boeing ASB 737-27A1202.4. Replace the vernier control rod and two dual load path bolts in accordance with Part IV of the Accomplishment Instructions of Boeing ASB 737-27A1202.5. Replace two nutplates on the control rod in accordance with Part V of the Accomplishment Instructions of Boeing ASB 737-27A1202.Accomplishment of the requirements of AD/B737/201 (FAA AD 2002-20-07) constitutes terminating action for the requirements of this Directive.Note 1: Some aircraft may already meet some of the requirements of Boeing ASB 737-27A1202 through compliance with previous CASA ADs (B737/79 and B737/99), however, these aircraft may still require on-going inspections and/or component replacement dependent on the scope of previous actions completed. This directive supersedes AD/B737/79 & AD/B737/99. Pending the cancellation of ADs B737/79 & 99, compliance with this directive can be considered as achieving compliance with ADs/B737/79 & 99.Note 2: FAA ADs 97-14-04, 96-23-51 and 94-01-07 all refer to inspection, test and replacement actions on Boeing 737 rudder systems and are all referenced in Boeing ASB 737-27A1202. |\n\n| Compliance: | 1. To be completed every “A” check and every time a PCU is replaced.2. Within 24 months after 26 February 1998.3. Within 24 months after 26 February 1998.4. Within 24 months after 26 February 1998.5. Within 24 months after 26 February 1998.The compliance times remain unchanged by this issue.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |\n| ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|             | This Amendment becomes effective on 29 September 2005.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |\n| Background: | This AD makes compliance with a Boeing ASB mandatory. The Boeing ASB gives instructions to ensure that the secondary servo slide in the dual servo valve of the rudder PCU operates correctly. The ASB also requires the replacement of the vernier control rod and two dual loadpath bolts in the rudder PCU assembly. The eventual aim of the ASB is to have all rudder PCUs replaced with a modified item which is not prone to jamming.Previous Boeing Service Bulletins and FAA ADs had addressed some of the problems identified with the rudder control system, but this latest bulletin incorporates a comprehensive test, inspection and component replacement procedure which overcomes the possible effects of a jam in the secondary slide of the rudder PCU assembly.Amendment 2 is issued in response to FAA AD 2002-20-07, which requires incorporation of a new rudder control system; which when incorporated, supersedes the requirements of AD 97-14-04, the Requirement document of this Directive. |\n\n![](image.001.png)  \nDavid Punshon  \nDelegate of the Civil Aviation Safety Authority\n\n19 August 2005","sortOrder":0},{"sectionNumber":"AD/B737/113 Amdt 1","sectionType":"part","heading":"AD/B737/113 Amdt 1","content":"## AD/B737/113 Amdt 1","sortOrder":1},{"sectionNumber":"Rudder Power Control Unit Replacement","sectionType":"part","heading":"Rudder Power Control Unit Replacement","content":"## Rudder Power Control Unit Replacement","sortOrder":2},{"sectionNumber":"10/2005","sectionType":"part","heading":"10/2005","content":"## 10/2005","sortOrder":3}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This amendment remains focused on its original purpose: addressing rudder PCU safety in Boeing 737 aircraft. While it consolidates and supersedes previous directives (B737/79 and B737/99), this represents streamlining rather than scope creep. The amendment incorporates updated FAA requirements but maintains the same core safety objective — preventing rudder jamming through component replacement and testing."},"complexity_factors":["Multiple cross-references to external Boeing documents (Alert Service Bulletin 737-27A1202) and FAA Airworthiness Directives (97-14-04, 96-23-51, 94-01-07, 2002-20-07)","Five distinct compliance requirements with different timing rules (some tied to 'A' checks, some to calendar dates)","Conditional logic regarding terminating action — compliance with AD/B737/201 (FAA AD 2002-20-07) can end the obligations under this directive","Complex applicability criteria requiring identification of specific part numbers and configurations","Note 1 contains layered conditional logic about partial compliance from previous directives and ongoing inspection requirements","Technical aviation terminology throughout (PCU, servo valve, vernier control rod, dual load path bolts, nutplates) requiring specialized knowledge"],"plain_english_summary":"This mandatory CASA Airworthiness Directive requires operators of Boeing 737s with certain rudder PCUs to test and replace affected units and internal components to eliminate a jamming risk in the dual servo valve. It targets aircraft fitted with parts listed in Boeing Alert Service Bulletin 737-27A1202 Rev 2.\n\nIt matters because a jammed rudder PCU can cause unexpected or stuck rudder movement and potential loss of control; the AD supersedes two earlier directives."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":true,"description":"This amendment broadens and formalises the earlier approach. Earlier work and ADs addressed parts of the rudder PCU problem through inspections and selective actions; this amendment makes Boeing ASB 737-27A1202 Revision 2 mandatory and requires a sequenced set of tests and component replacements (Parts I–V), rather than leaving compliance to piecemeal service bulletins or prior ADs. It also adds an explicit terminating-action route (comply with FAA AD 2002-20-07 / AD/B737/201) and formally supersedes earlier CASA ADs (B737/79 and B737/99). Concretely, the scope has shifted from a set of prior, partial inspection/replacement mandates to a comprehensive mandatory test-and-replace regime covering multiple specific PCU components and establishing recurring inspection timing (every A-check) and fixed replacement deadlines (24 months after 26 Feb 1998)."},"complexity_factors":["Cross-reference to an external Boeing document (ASB 737-27A1202 Revision 2) that contains the detailed step-by-step work — requires reading a second document to know exact technical actions.","Five discrete mandatory actions (Parts I–V) with different technical scopes (test, PCU replacement, dual servo valve and bolt replacement, vernier rod and dual-load-path bolts replacement, nutplate replacement).","Multiple cross-references to other airworthiness directives (CASA ADs B737/79, B737/99 and FAA ADs including 97-14-04, 96-23-51, 94-01-07, and FAA AD 2002-20-07/AD/B737/201) which affect compliance requirements and terminating actions.","Multiple compliance triggers and timelines: recurring requirement (every A-check and when PCU replaced) plus a set of 24-month static deadlines for Parts II–V.","Conditional terminating action: completing AD/B737/201 removes obligations under this AD — creates an either/or compliance path.","Notes that some aircraft may already comply partially through earlier ADs, requiring record comparisons and potentially differing follow-up actions (nested conditionality).","Technical specificity: the measure targets particular components (secondary servo slide, dual servo valve, vernier control rod, dual-load-path bolts, nutplates), requiring specialised maintenance and parts logistics.","Supersession of earlier ADs (this directive supersedes AD/B737/79 & AD/B737/99) which requires fleet-wide reconciliation of prior compliance histories."],"plain_english_summary":"**What this instrument does (mechanically):**\n\n- Makes the instructions in Boeing Alert Service Bulletin (ASB) 737-27A1202 Revision 2 mandatory for a specified subset of Boeing 737 series aeroplanes — specifically those that have a main rudder power control unit (PCU) and vernier control rod bolts identified in that ASB (Applicability).\n- Requires operators to carry out the test in Part I of the ASB and, depending on the outcome, to perform the component replacement actions set out in Parts II–V of the ASB:\n  - replace the rudder PCU (Part II);\n  - replace the dual servo valve and a bolt in the PCU (Part III);\n  - replace the vernier control rod and two dual-load-path bolts (Part IV);\n  - replace two nutplates on the control rod (Part V) (Requirement 1).\n- Makes compliance with a later FAA airworthiness directive (FAA AD 2002-20-07, referenced here as AD/B737/201) a terminating action: if an operator has done what that FAA AD requires, the actions in this directive are completed (Requirement Note).\n- Sets the timing for compliance: the test action must be done at every “A” check and whenever a PCU is replaced; the replacement parts/actions in Parts II–V were required within 24 months after 26 February 1998 for affected aeroplanes (Compliance 1–5).\n\n**Why CASA requires this (official rationale):**\n\n- Boeing’s ASB is intended to ensure the secondary servo slide in the dual servo valve of the rudder PCU operates correctly and to remove suspected causes of jamming in the rudder PCU assembly (Background).\n- The ASB seeks to replace older PCUs with a modified PCU less prone to jamming; earlier Boeing service bulletins and FAA ADs addressed parts of the problem, while this ASB provides a comprehensive test, inspection and replacement procedure (Background).\n\n**Who this affects and who pays:**\n\n- Aircraft operators that fly Boeing 737 series aeroplanes with a main rudder PCU and vernier-control-rod bolts identified in Boeing ASB 737-27A1202 Revision 2. Those operators must arrange the tests and any mandated replacements (Applicability; Requirement).\n- The operator bears the direct costs: parts, labour, and aircraft downtime to perform tests and fit replacements. The requirement to do the test during every “A” check can reduce incremental downtime but imposes a recurring inspection/maintenance task (Compliance 1).\n\n**Who enforces the rule and what changes in behaviour:**\n\n- The Civil Aviation Safety Authority (CASA), through its delegate, enforces the directive (signature/authority lines). Operators must maintain records proving compliance and either perform the ASB steps or show they have achieved the terminating action by complying with AD/B737/201.\n\n**Practical trade-offs, implementation risks and effects on operators (tested against costs and incentives):**\n\n- Costs and disruption: replacing PCUs, valves, bolts, nutplates and vernier rods is parts- and labour-intensive. If a PCU is replaced only when defective, the rule raises the chance of proactive replacement if the ASB indicates a vulnerability.\n- Timing and scheduling: mandating the test at each “A” check integrates inspection into routine maintenance, which can limit additional downtime but creates a recurring compliance cost.\n- Supply and lead-time risk: the measure depends on availability of replacement PCUs and parts; delays in supply would extend downtime or force temporary operational changes.\n- Duplication/record reconciliation: some aircraft may already have complied with earlier CASA ADs (B737/79 and B737/99) or other FAA ADs; operators must confirm the scope of prior work against the ASB to determine remaining actions (Note 1).\n- Regulatory interactions: the directive cross-references earlier CASA ADs and FAA ADs; accomplishing FAA AD 2002-20-07 can terminate the need to follow this directive’s steps, so operators may choose the path (comply with this ASB or adopt the FAA-mandated system change) that best fits fleet economics (Requirement Note; Background).\n\n**Concrete operational effect:**\n\n- Operators must test the rudder PCU per the ASB at every A-check and whenever the PCU is replaced, and they must replace specified components within the set compliance windows unless they have already achieved the terminating action via AD/B737/201 (Requirement; Compliance).\n\n**Source citations (where to look in the text):**\n- Applicability: identifies which 737s are covered.\n- Requirement (Parts I–V of Boeing ASB 737-27A1202 Revision 2): lists the tests and replacements required.\n- Compliance: sets when the actions must be done (every A check; within 24 months after 26 Feb 1998 for Parts II–V).\n- Background: explains the safety concern (secondary servo slide jamming) and the link to FAA ADs.\n\n(End of summary.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-113-amdt-1-rudder-power-control-unit-replacement","history":"/api/acts/ad-b737-113-amdt-1-rudder-power-control-unit-replacement/history","analysis":"/api/acts/ad-b737-113-amdt-1-rudder-power-control-unit-replacement/analysis","conflicts":"/api/acts/ad-b737-113-amdt-1-rudder-power-control-unit-replacement/conflicts","importantCases":"/api/acts/ad-b737-113-amdt-1-rudder-power-control-unit-replacement/important-cases","documents":"/api/acts/ad-b737-113-amdt-1-rudder-power-control-unit-replacement/documents"}}