{"id":"F2006B03588","name":"AD/BEA 121/23 - Engine Mounting Structure","slug":"ad-bea-121-23-engine-mounting-structure","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":43173,"registerId":"commonwealth-F2006B03588-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BEA 121/23 - Engine Mounting Structure","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 121/23 Engine Mounting Structure 10/79\n\nApplicability: All Beagle B121 series 1 and 2, which have achieved 1000 hours time in service. Requirement:              Action in accordance with British Aerospace (Scottish Division) SB No. B121/81.\n\nCompliance: Inspect within 50 hours time in service after 27 August 1979 and thereafter at intervals not exceeding 50 hours time in service.\n\n \n\nBackground: The manufacturer reports that cases of engine mount cracking 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\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-issue airworthiness directive focused specifically on engine mount inspections for one aircraft type. It has not expanded beyond its original safety purpose. Airworthiness directives are inherently narrow in scope — they address specific defects in specific aircraft types."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 4 defined elements: applicability, requirement, compliance, and background","No cross-references to other legislation or regulations beyond the parent Civil Aviation Regulations 1998","Single, clear compliance pathway with no exceptions or conditional branches","No nested definitions or interpretive provisions","Straightforward temporal trigger (1000 hours time in service) and recurring interval (50 hours)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft.\n\n**What it does:**\nIt requires owners and operators of specific light aircraft (Beagle B121 \"Pup\" Series 1 and 2) to inspect the engine mounting structure for cracks.\n\n**Who it affects:**\n- Owners and operators of Beagle B121 Series 1 and 2 aeroplanes\n- Only applies to aircraft that have flown 1,000 hours or more\n\n**What must be done:**\n- **First inspection:** Within 50 flight hours after 27 August 1979\n- **Ongoing inspections:** Every 50 flight hours thereafter\n- **How:** Follow the manufacturer's Service Bulletin B121/81 (a technical instruction document from British Aerospace)\n\n**Why it matters:**\nThe manufacturer discovered cases of engine mount cracking in actual use. Since the engine mount holds the engine to the airframe, cracks could cause engine separation — a catastrophic failure. This directive forces proactive inspection before failures occur.\n\n**Key point:** This is a **retrospective safety mandate** — it applies to existing aircraft already in service, not just new ones."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The AD, as drafted here, sets a focused obligation: mandatory inspections for Beagle B121 series 1 and 2 aircraft meeting the 1,000 hour threshold, following British Aerospace SB No. B121/81, with a 50-hour inspection interval. There is no indication in the supplied text that the scope of affected aircraft, the actions required, or the inspection interval has been broadened or narrowed from the instrument’s own stated terms."},"complexity_factors":["Narrow applicability (specific aircraft model and series, and a clear 1,000 hours time-in-service threshold). [Applicability]","Single, well-defined required action referencing a single manufacturer Service Bulletin (no multiple options). [Requirement]","Short, fixed recurring compliance interval (inspect within 50 hours after specified date and every 50 hours thereafter) — creates an ongoing obligation but is procedurally simple. [Compliance]","Technical specifics of inspections and repairs are deferred to the Service Bulletin, which can add substantive technical complexity outside the AD text. [Requirement]","The AD does not quantify risk or enforcement details, leaving outcome uncertainty about costs and operational impact. [Background] [header reference]"],"plain_english_summary":"This AD requires owners/operators of Beagle B121 series 1 and 2 aeroplanes (at/after 1,000 hours TIS) to carry out the inspections and any corrective work specified in British Aerospace Service Bulletin B121/81. Inspections must begin within 50 hours TIS after 27 August 1979 and recur every 50 hours.\n\nIt was issued after the manufacturer reported engine‑mount cracking; operators bear the cost and mandatory compliance."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bea-121-23-engine-mounting-structure","history":"/api/acts/ad-bea-121-23-engine-mounting-structure/history","analysis":"/api/acts/ad-bea-121-23-engine-mounting-structure/analysis","conflicts":"/api/acts/ad-bea-121-23-engine-mounting-structure/conflicts","importantCases":"/api/acts/ad-bea-121-23-engine-mounting-structure/important-cases","documents":"/api/acts/ad-bea-121-23-engine-mounting-structure/documents"}}