{"id":"F2006B02808","name":"AD/B737/104 - Rudder Power Control Unit Inspection","slug":"ad-b737-104-rudder-power-control-unit-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42150,"registerId":"commonwealth-F2006B02808-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/104 - Rudder Power Control Unit Inspection","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/B737/104 Rudder Power Control Unit Inspection 6/97\n\nApplicability: Main rudder power control units (PCU) that are to be fitted to Model 737 airplanes and which are identified in Boeing Service Letter 737-SL-27-112-B, dated February 6, 1997.\n\nRequirement: To identify, inspect and repair suspect main rudder PCUs prior to fitment to Model 737 aircraft in accordance with the requirements of Boeing Service Letter 737-SL-27- 112-B dated February 6, 1997.\n\nNote: FAA AD 97-05-10 refers.\n\nCompliance: After 90 days of the effective date of this Directive, the requirement is to be completed prior to fitment of a replacement main rudder PCU to an aircraft.\n\nThis Airworthiness Directive becomes effective on 22 May 1997.\n\nBackground: The FAA has received a report of cracking of the internal summing lever of the main rudder PCU on a model 737 airplane. Investigation showed that a Hi-Lock bolt had been installed in the lever assembly by a repair station instead of the correct specification bolt (Boeing Part No. 66-22749-1). The larger bolt radius of the Hi Lock bolt in the shoulder to shank transition area was such as to create an interference fit with the bearing that caused the inner race of the bearing to crack. Such cracking, if not detected and corrected could lead to seizure of the bearing and possible uncommanded rudder movement. This Directive requires that all replacement main rudder PCUs are inspected before fitment to ascertain if they are suspect and if so to ensure that they have been subject to the corrective action detailed in US FAA AD\n\n97-05-10.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope. It was issued specifically to address the identified safety risk of cracked bearings in rudder PCUs due to incorrect bolt installation, and it targets exactly those parts and that specific defect without expansion into broader maintenance requirements."},"complexity_factors":["Single, specific technical requirement (inspect and repair specific PCUs)","Only one defined applicability criterion (PCUs identified in Boeing Service Letter 737-SL-27-112-B)","Clear compliance deadline (90 days from effective date, then prior to fitment)","No nested exceptions or conditional logic","Short document (approximately 250 words)","Single cross-reference to FAA AD 97-05-10 for technical details","Straightforward cause-and-effect background explanation"],"plain_english_summary":"This rule requires anyone fitting replacement main rudder power control units (PCUs) to Boeing 737s in Australia to inspect units identified in Boeing’s Feb 1997 service letter for a known manufacturing/assembly defect and repair any “suspect” units per Boeing before installation. It responds to findings that incorrect Hi‑Lock bolts can crack an internal bearing, risking uncommanded rudder movement and loss of control. Compliance begins within 90 days of 22 May 1997."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The Directive is narrowly targeted at a specific safety defect (incorrect Hi-Lock bolt causing bearing cracking in the main rudder PCU) and requires inspection and corrective action for replacement PCUs identified in the Boeing Service Letter. It does not broaden the subject matter beyond that original safety concern; it remains a focused, corrective measure rather than a broader regulatory expansion."},"complexity_factors":["Very short directive (single-issue AD)","Limited number of operative provisions (Applicability, Requirement, Compliance, Background)","One external OEM document referenced (Boeing Service Letter 737-SL-27-112-B)","One external regulator document referenced (FAA AD 97-05-10)","Simple timing condition (after 90 days, action required prior to fitment)"],"plain_english_summary":"**What this Directive does (mechanically)**\n\n- Applies to: main rudder Power Control Units (PCUs) that are intended for fitment to Boeing Model 737 aeroplanes and that are specifically identified in Boeing Service Letter 737-SL-27-112-B (6 Feb 1997). [Applicability]\n- Action required: identify any replacement main rudder PCU that falls within the applicability, inspect it, and if it is “suspect”, carry out the corrective work specified in Boeing Service Letter 737-SL-27-112-B (which follows the corrective action in FAA AD 97-05-10). [Requirement]\n- Timing: after 90 days from the Directive’s effective date, you must complete the inspection and any corrective action before fitting a replacement main rudder PCU to an aircraft. [Compliance]\n- Why: investigation found an incorrect bolt (a Hi-Lock bolt) installed in the summing-lever assembly by a repair station. The incorrect bolt’s dimensions can press on a bearing, cracking its inner race; if undetected, that cracking can lead to bearing seizure and possible uncommanded rudder movement. The Directive aims to prevent that failure mode. [Background]\n\n**Who is affected**\n\n- Aircraft operators who acquire replacement main rudder PCUs for Boeing 737s.\n- Maintenance organisations and repair stations that overhaul or supply these PCUs (they must identify and inspect units and perform required repairs before fitment).\n- Parts suppliers and brokers who trade in replacement PCUs: supplied units must meet the inspection/repair requirement prior to fitment.\n\n**Who pays and who decides**\n\n- The economic cost (inspection time, possible repair or rework, delays sourcing replacement units) will fall primarily on the organisation that supplies and/or fits the replacement PCU — typically the operator or their contracted maintenance/repair station. [Requirement; Compliance]\n- The maintenance/repair provider decides whether a unit is suspect and must perform the corrective action in accordance with Boeing’s Service Letter (and the referenced FAA AD). CASA enforces compliance by virtue of this being an Airworthiness Directive. [Requirement; Compliance]\n\n**Practical effects on behaviour and markets**\n\n- Maintenance providers must check incoming or stock replacement PCUs against Boeing Service Letter 737-SL-27-112-B and inspect units before fitment. Suspect units must be repaired per the specified procedure.\n- Repair stations are incentivised to use the correct specification fasteners and to document repairs to avoid a unit becoming “suspect”.\n- Operators may face slightly higher lead times or costs when sourcing replacement PCUs if fewer units are serviceable without remedial work, and may prefer suppliers who can certify compliance.\n\n**Compliance burden, risks, and trade-offs**\n\n- Compliance burden: inspection and possible repair or rework before fitment. This requires following OEM-prescribed procedures (Boeing Service Letter) and may impose downtime and labour/parts cost. [Requirement; Compliance]\n- Implementation risk: the directive relies on external documents (Boeing Service Letter and FAA AD). If those documents are unclear or supply-chain traceability is weak, identifying suspect units could be operationally difficult. [Requirement; Background]\n- Safety benefit: reduces risk of bearing cracking, seizure, and potential uncommanded rudder movement by preventing incorrect bolt installation and ensuring corrective action is taken. [Background]\n\n**Reference to source mechanisms**\n\n- The Directive operates by mandating pre-fitment inspection/repair of parts identified in Boeing Service Letter 737-SL-27-112-B and by referencing FAA AD 97-05-10 for the corrective action. It is an enforceable CASA Airworthiness Directive and must be complied with before fitting replacement PCUs after the 90-day window. [Applicability; Requirement; Compliance; Background]"}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-104-rudder-power-control-unit-inspection","history":"/api/acts/ad-b737-104-rudder-power-control-unit-inspection/history","analysis":"/api/acts/ad-b737-104-rudder-power-control-unit-inspection/analysis","conflicts":"/api/acts/ad-b737-104-rudder-power-control-unit-inspection/conflicts","importantCases":"/api/acts/ad-b737-104-rudder-power-control-unit-inspection/important-cases","documents":"/api/acts/ad-b737-104-rudder-power-control-unit-inspection/documents"}}