{"id":"F2006B03589","name":"AD/BEA 121/24 - Fuselage Angle, Diaphragm and Flange at Tailplane Spar Attachments","slug":"ad-bea-121-24-fuselage-angle-diaphragm-and-flange-at-tailplane-spar-attachments","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":43178,"registerId":"commonwealth-F2006B03589-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BEA 121/24 - Fuselage Angle, Diaphragm and Flange at Tailplane Spar Attachments","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\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)  Beagle B121 (Pup) Series Aeroplanes\n\n \n\nAD/BEA 121/24 Fuselage Angle, Diaphragm and Flange\n\nat Tailplane Spar Attachments\n\n\n7/84\n\n \n\nApplicability: All B121 series 1, 2 and 3 aeroplanes which have exceeded 2450 hours time in service.\n\n \n\nRequirement: Action in accordance with British Aerospace (Scottish Division) SB No. B121/86.\n\n \n\nCompliance: Within 50 hours time in service after 8 June 1984 and thereafter a intervals not exceeding 50 hours time in service.\n\n \n\nBackground:  The manufacturer reports that cases of rear fuselage cracks in the area of the tailplane attachment have been discovered in service.\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\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific airworthiness concern on a specific aircraft type. It has not expanded beyond its original purpose of mandating repetitive inspections for fuselage cracks at tailplane attachments."},"complexity_factors":["Single, specific aircraft type (Beagle B121 Pup series)","Clear applicability threshold (2,450 hours time in service)","Single compliance action (follow manufacturer service bulletin B121/86)","Simple recurring interval (every 50 hours time in service)","No defined terms section, no cross-references to other legislation, no conditional exceptions","Total length: approximately 150 words of substantive content"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order — issued by Australia's Civil Aviation Safety Authority for a specific type of light aircraft called the **Beagle B121 (Pup)**.\n\n**What it does:**\n- Requires owners and operators of these planes to inspect the rear fuselage (the tail section of the aircraft) for cracks near where the tailplane (horizontal stabiliser) attaches to the body of the plane.\n- The inspection must follow a specific technical bulletin from the manufacturer (British Aerospace).\n\n**Who it affects:**\n- Anyone who owns or operates a Beagle B121 Series 1, 2, or 3 aircraft that has flown more than **2,450 hours**.\n\n**What must be done:**\n- First inspection: within **50 hours of flying time** after 8 June 1984.\n- Repeat inspections: every **50 hours of flying time** thereafter.\n\n**Why it matters:**\nThe manufacturer discovered cracks developing in this area during normal use. If left unchecked, these cracks could compromise the structural integrity of the tail section — potentially leading to loss of control of the aircraft. This directive forces regular checks to catch problems before they become dangerous."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The text contains no indication that the AD’s scope has been altered from an earlier instrument. It specifically targets B121 series 1, 2 and 3 aeroplanes with more than 2,450 hours time in service and mandates actions in accordance with Service Bulletin B121/86 within and thereafter at 50‑hour intervals (Applicability; Requirement; Compliance). No amendment or expansion of scope is described in the provided text."},"complexity_factors":["Clear, narrowly defined applicability (B121 series 1–3 with >2450 hours) reducing scope ambiguity (Applicability).","Short, fixed compliance interval (every 50 hours) which is operationally demanding but straightforward to enforce (Compliance).","Dependence on an external document (Service Bulletin B121/86) for technical detail introduces execution complexity and reliance on that bulletin’s clarity (Requirement).","No detailed repair procedures or multiple conditional branches in the AD itself — technicians must consult the SB, so the AD text is concise (Requirement).","Administrative enforcement sits within established airworthiness directive regime, so legal/process complexity is low though monitoring workload may rise (header)."],"plain_english_summary":"### What this directive does\n\nThis airworthiness directive (AD) requires regular inspection and any necessary corrective action at the tailplane spar attachment area of certain Beagle B121 (Pup) aeroplanes. The AD applies only to B121 series 1, 2 and 3 aeroplanes that have accumulated more than 2,450 hours time in service (Applicability). The specific inspection and repair instructions are those set out in British Aerospace (Scottish Division) Service Bulletin No. B121/86 (Requirement).\n\n### Who it affects\n\n- Aircraft owners and operators of Beagle B121 series 1, 2 and 3 aeroplanes with more than 2,450 hours time in service (Applicability).  \n- Maintenance organisations that perform the inspections and any repairs required by the service bulletin (Requirement).\n\n### What you must do and by when\n\n- Carry out the actions described in the manufacturer’s Service Bulletin B121/86 (Requirement).  \n- Start within 50 hours time in service after 8 June 1984 and then repeat at intervals not exceeding 50 hours time in service (Compliance).\n\n### Why the AD was issued\n\nThe manufacturer reported that rear fuselage cracks had been found in service in the area of the tailplane attachment (Background). The AD implements the manufacturer’s service instructions so that operators inspect for, and fix, these cracks (Requirement).\n\n### Who pays and what behaviours change\n\n- The cost of the inspections and any corrective work falls on the aircraft owners/operators and their maintenance providers, because the AD makes compliance and any repairs mandatory (Applicability; Requirement; Compliance).  \n- Aircraft will spend additional time in maintenance for inspections every 50 hours; this increases direct maintenance hours and may change operational scheduling (Compliance).  \n- The AD delegates technical detail to the manufacturer’s service bulletin, so the content and method of corrective actions are determined by that bulletin rather than spelled out in the AD itself (Requirement).  \n\n### Compliance, enforcement and discretion\n\n- The directive is issued under the Civil Aviation Safety Authority and is part of the Schedule of Airworthiness Directives under Part 39 (header). Enforcement and oversight are conducted under those statutory arrangements.  \n- The AD requires compliance with the manufacturer’s service bulletin; it does not itself describe the specific inspection techniques or repair steps, creating a dependence on the manufacturer’s technical procedures (Requirement).  \n\n### Trade-offs, costs and implementation risks (mechanical, not political)\n\n- Benefit claimed by the manufacturer: detect and remedy rear fuselage cracks to address a structural risk identified in service (Background).  \n- Costs borne by operators: recurring inspection labour and any parts/repairs required by the service bulletin; increased maintenance downtime because inspections are required every 50 hours (Compliance).  \n- Implementation dependence: the AD refers operators to Service Bulletin B121/86 for the precise actions, so effective compliance depends on the clarity and applicability of that bulletin (Requirement).  \n- Monitoring and enforcement rely on the usual airworthiness directive surveillance framework administered by the Civil Aviation Safety Authority (header).\n\n### Net mechanical effect\n\nOperators of affected B121 aircraft must perform a short-interval inspection cycle (every 50 hours) and any corrective work specified by British Aerospace’s Service Bulletin B121/86. The directive narrows its reach to aircraft above a specific hours threshold (more than 2,450 hours) and uses the manufacturer’s technical guidance to define the remedial work (Applicability; Requirement; Compliance; Background)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bea-121-24-fuselage-angle-diaphragm-and-flange-at-tailplane-spar-attachments","history":"/api/acts/ad-bea-121-24-fuselage-angle-diaphragm-and-flange-at-tailplane-spar-attachments/history","analysis":"/api/acts/ad-bea-121-24-fuselage-angle-diaphragm-and-flange-at-tailplane-spar-attachments/analysis","conflicts":"/api/acts/ad-bea-121-24-fuselage-angle-diaphragm-and-flange-at-tailplane-spar-attachments/conflicts","importantCases":"/api/acts/ad-bea-121-24-fuselage-angle-diaphragm-and-flange-at-tailplane-spar-attachments/important-cases","documents":"/api/acts/ad-bea-121-24-fuselage-angle-diaphragm-and-flange-at-tailplane-spar-attachments/documents"}}