{"id":"F2006B03597","name":"AD/BEA 121/31 Amdt 1 - Main Spar Doubler at Main Landing Gear Attachment and Wing to Fuselage Main Spar Attachment Nuts","slug":"ad-bea-121-31-amdt-1-main-spar-doubler-at-main-landing-gear-attachment-and-wing-to-fuselage-main-spa","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":43188,"registerId":"commonwealth-F2006B03597-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/BEA 121/31 Amdt 1 - Main Spar Doubler at Main Landing Gear Attachment and Wing to Fuselage Main Spar Attachment Nuts","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)  \nBeagle B121 (Pup) Series Aeroplanes\n\nAD/BEA 121/31\n\nAmdt 1\n\n  \nMain Spar Doubler at Main Landing Gear Attachment and Wing to Fuselage Main Spar Attachment Nuts\n\n  \n6/98\n\nApplicability: Beagle B121 Series 1, 2, and 3 aircraft.\n\nRequirement: Action in accordance with British Aerospace Regional Aircraft Service Bulletin (SB) B121/105 and B121/106.\n\nNote: UK CAA AD 005-01-98 and AD 006-01-98 refer.\n\nCompliance: For SB B121/105:\n\nInitial Inspection- Aircraft that have recorded less than 1950 flying hours; accomplish before 2000 flying hours. Aircraft that have recorded 1950 flying hours or more, accomplish within 50 flying hours after 21 May 1998.\n\nRepeat Inspection \\- At intervals not to exceed 800 flying hours from initial accomplishment of SB B121/102, at Original issue or Revision 1.\n\nNote: Aircraft that have accomplished SB B121/102 at Original issue or Revision 1, comply with Repeat Inspection timescale only.\n\nFor SB B121/106: Within 100 flying hours after 21 May 1998\\. This amendment becomes effective on 21 May 1998.\n\nBackground: The UK CAA requires the actions specified in this Directive to determine the continuing airworthiness of the aircraft.\n\nAmendment 1 is issued in response to new CAA ADs which introduce structural inspections of the main spar doubler at the main landing gear attachment points and replacement nuts at the fuselage main spar fittings that have better torque retention.\n\nThe original issue of this Airworthiness Directive became effective on 27 March 1997.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This amendment remains tightly focused on its original purpose: ensuring structural integrity of the main spar and landing gear attachments on Beagle B121 aircraft. Amendment 1 simply updates the requirements to incorporate new UK safety information (additional inspections and improved nuts) without expanding beyond the original aircraft type or safety concern."},"complexity_factors":["Short, single-purpose document (approximately 250 words)","Only 3 defined applicability categories (Series 1, 2, and 3)","Two distinct compliance pathways based on flying hours accumulated","Cross-references to two UK Service Bulletins (SB B121/105 and B121/106) and two UK CAA Airworthiness Directives","Conditional logic for initial inspection timing (threshold at 1950 flying hours)","Nested note creating exception for aircraft already compliant with earlier service bulletin (SB B121/102)","Amendment structure requires understanding of \"original issue\" dated March 1997 versus current version dated May 1998"],"plain_english_summary":"This AD orders Australian owners/operators of Beagle B121 (Pup) Series 1–3 aircraft to inspect and maintain the main spar doubler and wing‑to‑fuselage attachment nuts — critical structural parts — to prevent possible wing separation. It mandates initial inspections (based on flying hours), repeat checks every 800 flight hours, and replacement of certain nuts with improved torque‑retaining versions. The requirements adopt UK CAA measures."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"Amendment 1 expands the original AD by introducing structural inspections of the main spar doubler at main landing gear attachment points and mandatory replacement of wing‑to‑fuselage main spar nuts with parts that have better torque retention (Background; Amendment 1). Applicability remains Beagle B121 Series 1–3 (Applicability). Compliance is prescribed through BAe Service Bulletins B121/105 and B121/106 with differentiated flying‑hour windows (including an 800‑hour repeat interval and 50‑hour short windows for aircraft at/above 1950 hours) (Requirement; Compliance). The costs and labour for inspections and replacements are imposed on aircraft operators; CASA enforces the directive by requiring actions 'in accordance with' the stated service bulletins (Requirement)."},"complexity_factors":["Technical scope: structural inspection of main spar doubler and mechanical part replacement (nuts) — requires engineering-level assessment and access to fittings (Background; Amendment 1).","Multiple referenced service bulletins: compliance is through SB B121/105 and SB B121/106, and repeat inspections reference SB B121/102 (Requirement; Compliance).","Time‑window complexity: different initial compliance windows depending on whether an aircraft has <1950 or ≥1950 flying hours, plus a 50‑hour short window after 21 May 1998 for high‑hour aircraft (Compliance: For SB B121/105).","Recurring interval: Repeat inspections mandated at intervals not to exceed 800 flying hours tied to accomplishment of SB B121/102 at specified issue/revision levels (Compliance).","Cross‑jurisdictional references: UK CAA ADs are cited as the motivating documents, creating interlocking regulatory references (Note; Background).","Applicability constraint: limited to Beagle B121 Series 1, 2, and 3 aircraft, which focuses obligation but concentrates costs on a small operator population (Applicability).","Effective and historic dates: original AD effective date and amendment effective date create retroactive compliance windows for some operators (original issue effective 27 March 1997; amendment effective 21 May 1998).","Operational burden: physical inspections and nut replacements impose direct maintenance time, parts cost, and record‑keeping on operators (Requirement; Compliance)."],"plain_english_summary":"This amendment applies to Beagle B121 Series 1–3 aircraft. It requires inspections of the main spar doubler at the main landing gear attachments and replacement of wing‑to‑fuselage main spar nuts with parts that retain torque better.\n\nOperators must follow British Aerospace Service Bulletins B121/105 and B121/106 within the stated flying‑hour windows (including an 800‑hour repeat interval and short-term windows around 1950 hours). The work and costs fall to aircraft operators."}},"importantCases":[],"_links":{"self":"/api/acts/ad-bea-121-31-amdt-1-main-spar-doubler-at-main-landing-gear-attachment-and-wing-to-fuselage-main-spa","history":"/api/acts/ad-bea-121-31-amdt-1-main-spar-doubler-at-main-landing-gear-attachment-and-wing-to-fuselage-main-spa/history","analysis":"/api/acts/ad-bea-121-31-amdt-1-main-spar-doubler-at-main-landing-gear-attachment-and-wing-to-fuselage-main-spa/analysis","conflicts":"/api/acts/ad-bea-121-31-amdt-1-main-spar-doubler-at-main-landing-gear-attachment-and-wing-to-fuselage-main-spa/conflicts","importantCases":"/api/acts/ad-bea-121-31-amdt-1-main-spar-doubler-at-main-landing-gear-attachment-and-wing-to-fuselage-main-spa/important-cases","documents":"/api/acts/ad-bea-121-31-amdt-1-main-spar-doubler-at-main-landing-gear-attachment-and-wing-to-fuselage-main-spa/documents"}}