{"id":"F2006B09704","name":"AD/F27/137 - Rudder Horn Assembly and Control Rod","slug":"ad-f27-137-rudder-horn-assembly-and-control-rod","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115870,"registerId":"commonwealth-F2006B09704-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F27/137 - Rudder Horn Assembly and Control Rod","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)  \nFokker F27 Series Aeroplanes\n\nAD/F27/137 Rudder Horn Assembly and Control Rod 11/94\n\nApplicability: Model F27 Mk 100 through Mk 700 series, all serial numbers, if in pre-SB F27/27- 131 configuration.\n\nRequirement: Action in accordance with Fokker SB F27/27-131.\n\nNote: RLD AD 94-105 (A) refers.\n\nCompliance: Prior to 1 March 1996.\n\nBackground: A number of cracked or broken rudder horns have been reported to the manufacturer.\n\nAn investigation revealed that impact overload, caused by heavy gust conditions while parked, had caused the initial fracture.\n\nThe RLD has determined that an unsafe condition has been identified that may exist or develop in other aircraft of the same type design, and therefore requires fitment of an improved rudder horn assembly and control rod.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive’s scope aligns with its stated purpose: to require fitment of an improved rudder horn assembly and control rod on affected F27 aircraft that remain in the pre-SB F27/27-131 configuration (Applicability, Requirement). The instrument does not expand or narrow that technical scope beyond requiring compliance with the referenced service bulletin and imposing a compliance date (Requirement, Compliance)."},"complexity_factors":["Narrow applicability limited to specific F27 Mk100–Mk700 models that remain in the pre-SB F27/27-131 configuration (Applicability).","Dependence on external technical document (Fokker SB F27/27-131) for all technical steps; the AD itself contains no procedural detail (Requirement).","Hard compliance deadline (Prior to 1 March 1996) creates a fixed scheduling constraint (Compliance).","Clear causal finding (cracked/broken rudder horns from impact overload) but corrective action limited to hardware retrofit, requiring parts and maintenance resources (Background, Requirement).","Cross-reference to another directive (RLD AD 94-105 (A)) which may create linked compliance tasks or interpretations (Note)."],"plain_english_summary":"What this instrument requires\n\n- This airworthiness directive applies to Fokker F27 Mk 100 through Mk 700 aeroplanes that are still in the \"pre-SB F27/27-131\" configuration (Applicability).  If your aeroplane is in that pre-service-bulletin state, the directive requires you to carry out the action set out in Fokker Service Bulletin F27/27-131 (Requirement).\n\nWho it affects\n\n- Owners and operators of the listed F27 models that have not yet been modified in accordance with SB F27/27-131. The directive only applies to aircraft that remain in the pre-SB configuration (Applicability).\n\nWhat you must do, and by when\n\n- Fit an improved rudder horn assembly and control rod in accordance with Fokker SB F27/27-131 (Requirement).\n- Complete that work before 1 March 1996 (Compliance).\n\nWhy this was issued (source statement)\n\n- The manufacturer reported a number of cracked or broken rudder horns. The investigation identified impact overload from heavy gusts while parked as the initiating cause. The responsible authority (RLD) determined an unsafe condition may exist or develop in other aircraft of the same type design and therefore requires the improved fitment (Background). The directive also cross-references RLD AD 94-105 (A) (Note).\n\nHow it operates in practice (mechanics, responsibilities, and immediate consequences)\n\n- The directive does not include its own technical steps; it mandates compliance with the Fokker service bulletin (Requirement). That means affected operators must consult SB F27/27-131 to learn the exact modification steps and standards.\n- Responsibility to comply falls on the operator/owner of each affected aircraft: they must determine whether the aircraft is in the pre-SB configuration (Applicability) and, if so, arrange the modification (Requirement, Compliance).\n- The directive sets a fixed deadline for compliance (Prior to 1 March 1996). The timing constraint creates a scheduling requirement for maintenance planners and may require aircraft to be taken out of service to undergo the modification.\n\nImmediate implementation and compliance considerations\n\n- The directive mandates a retrofit (fitment of improved parts) rather than, for example, an operational restriction. The precise scope of work, parts required and labour time are specified in the referenced Fokker service bulletin rather than in the directive itself (Requirement).\n- The directive identifies the hazard (cracked/broken rudder horns initiated by gust impact) and prescribes a hardware change as the corrective measure (Background, Requirement).\n\nTrade-offs, costs and operational effects (source-grounded)\n\n- Who pays: the directive places the obligation to fit the improved assembly on the owners/operators of affected aircraft because they must have the SB work completed (Applicability, Requirement, Compliance). The directive does not state who bears parts or labour costs; those are not specified in the text provided.\n- Compliance burden: operators must inspect configuration status, schedule the SB work, and have the modification performed to the standard set out in the Fokker service bulletin (Applicability, Requirement). The directive’s effectiveness depends on the completeness and availability of the service bulletin’s instructions.\n- Decision-making and discretion: the directive requires action in accordance with the manufacturer’s SB; it does not create discretionary alternatives or exemptions in this text. Any further discretion (for deferral, alternative methods, or approvals) would depend on regulatory procedures not stated here.\n\nWhere to look next\n\n- For the detailed technical steps, parts list, and labour guidance follow Fokker SB F27/27-131 as referenced in the Requirement. Consult RLD AD 94-105 (A) where noted for related action or context (Note)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating a rudder assembly upgrade."},"complexity_factors":["Very short document (under 200 words)","Only 1 substantive requirement (comply with manufacturer's service bulletin)","No defined terms section — all terms are standard aviation industry terminology","Single, unambiguous compliance deadline","No nested conditions or exceptions","Clear applicability criteria (specific aircraft models and serial numbers)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\nOrders owners and operators of certain Fokker F27 aircraft to replace or upgrade the **rudder horn assembly and control rod** — parts that connect the pilot's foot pedals to the rudder (the movable part of the tail that steers the plane left and right).\n\n**Who it affects:**\nAnyone operating Fokker F27 Mk 100 through Mk 700 series aircraft that haven't already been modified according to Fokker Service Bulletin F27/27-131.\n\n**Why it matters:**\nSeveral aircraft were found with **cracked or broken rudder horns**. The cause? Wind gusts hitting parked planes hard enough to damage these parts. A broken rudder horn means the pilot can't control the aircraft's direction — a serious safety risk. The directive requires the fix to be done **before 1 March 1996** to prevent accidents.\n\n**Key terms explained:**\n- **Service Bulletin (SB):** A manufacturer's official instruction for inspecting, fixing, or upgrading aircraft parts.\n- **Pre-SB configuration:** Aircraft that haven't had the manufacturer's recommended modification yet.\n- **RLD:** The Dutch aviation authority (Rijksluchtvaartdienst), indicating this safety issue was first identified in the Netherlands."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f27-137-rudder-horn-assembly-and-control-rod","history":"/api/acts/ad-f27-137-rudder-horn-assembly-and-control-rod/history","analysis":"/api/acts/ad-f27-137-rudder-horn-assembly-and-control-rod/analysis","conflicts":"/api/acts/ad-f27-137-rudder-horn-assembly-and-control-rod/conflicts","importantCases":"/api/acts/ad-f27-137-rudder-horn-assembly-and-control-rod/important-cases","documents":"/api/acts/ad-f27-137-rudder-horn-assembly-and-control-rod/documents"}}