{"id":"F2006B02150","name":"AD/AC/9 - Vertical and Horizontal Stabiliser - Spar Reinforcement","slug":"ad-ac-9-vertical-and-horizontal-stabiliser-spar-reinforcement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41380,"registerId":"commonwealth-F2006B02150-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC/9 - Vertical and Horizontal Stabiliser - Spar Reinforcement","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-description: CASA Airworthiness Directive\nmeta-generator: Aspose.Words for .NET 22.10.0\nmeta-keywords: Issue NK,Aircraft below 5700 kg,Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes,Vertical and Horizontal Stabiliser - Spar Reinforcement,9\ntitle: Airworthiness Directive - AD/AC/9 - Vertical and Horizontal Stabiliser - Spar Reinforcement\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes\n\n \n\nAD/AC/9 Vertical and Horizontal Stabiliser - Spar NK\n\nReinforcement\n\nApplicability: Models 500, 560, 560A, 560E, 680, 680E, 720: S/Nos. 151 to 710. Document:  1.              Aero Commander SB No. 50; or\n\n2. FAA AD 59-4-1.\n\n \n\nCompliance: Forthwith.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument applies to the specific Twin Commander models and serial number range listed and mandates reinforcement according to the referenced technical documents, with compliance required 'Forthwith'. The text contains no indication that the scope has been expanded or narrowed relative to a prior instrument; it presents a single, delimited applicability and a single immediate compliance requirement."},"complexity_factors":["Reference to external technical documents (Aero Commander SB No. 50 or FAA AD 59-4-1) for the detailed method of compliance, requiring users to obtain and follow those materials.","Serial-number-limited applicability (Models 500, 560, 560A, 560E, 680, 680E, 720; S/Nos. 151 to 710) which requires checking individual aircraft records.","Immediate compliance requirement ('Forthwith') which raises urgency for operational planning and parts/maintenance scheduling.","Technical nature of the required work (structural reinforcement of stabiliser spars) necessitating qualified maintenance providers and parts, increasing practical implementation complexity.","Brevity of the directive itself: it delegates substantive instructions to external documents, creating potential uncertainty for operators until those documents are consulted."],"plain_english_summary":"CASA requires immediate structural reinforcement of the vertical and horizontal stabiliser spars on Twin Commander (Gulfstream/Rockwell/Aero Commander) Models 500, 560, 560A, 560E, 680, 680E and 720, serial numbers 151–710. Owners/operators must arrange and pay for the work and comply \"forthwith.\" The directive points to Aero Commander SB No. 50 or FAA AD 59-4-1 for the technical method, creating safety-driven costs, downtime and reliance on those external instructions."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue safety directive focused specifically on structural reinforcement of tail spars in a limited range of aircraft. It has not expanded beyond its original technical safety purpose."},"complexity_factors":["Extremely short document (approximately 150 words)","Only 2 defined applicability criteria (aircraft models and serial numbers)","Single compliance requirement with immediate effect","No nested conditions, exceptions, or cross-references to other legislation","References only 2 external technical documents (Service Bulletin and FAA AD)","No interpretation section or defined terms"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) issued by Australia's Civil Aviation Safety Authority (CASA). An AD is a mandatory safety notice that requires aircraft owners or operators to fix a specific problem.\n\n**What it does:** This directive orders immediate action to reinforce the spars (the main structural beams) in the vertical and horizontal stabilisers (the tail section) of certain Twin Commander aircraft models.\n\n**Who it affects:** Owners and operators of specific Twin Commander aeroplanes (models 500, 560, 560A, 560E, 680, 680E, and 720 with serial numbers 151 to 710). These are small aircraft typically used for private, charter, or light commercial operations.\n\n**Why it matters:** The tail section spars may be structurally inadequate. Without reinforcement, there is a risk of structural failure in flight, which could lead to loss of control and potentially fatal accidents. The directive requires compliance \"forthwith\" — meaning immediately, without delay.\n\n**What must be done:** Aircraft operators must follow either:\n- **Aero Commander Service Bulletin No. 50**, or  \n- **FAA Airworthiness Directive 59-4-1**\n\nBoth documents contain the technical instructions for the required reinforcement work."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-9-vertical-and-horizontal-stabiliser-spar-reinforcement","history":"/api/acts/ad-ac-9-vertical-and-horizontal-stabiliser-spar-reinforcement/history","analysis":"/api/acts/ad-ac-9-vertical-and-horizontal-stabiliser-spar-reinforcement/analysis","conflicts":"/api/acts/ad-ac-9-vertical-and-horizontal-stabiliser-spar-reinforcement/conflicts","importantCases":"/api/acts/ad-ac-9-vertical-and-horizontal-stabiliser-spar-reinforcement/important-cases","documents":"/api/acts/ad-ac-9-vertical-and-horizontal-stabiliser-spar-reinforcement/documents"}}