{"id":"F2006B08371","name":"AD/CESSNA 400/88 - Horizontal Stabiliser Front Spar Attachment Bolt Retaining Nuts","slug":"ad-cessna-400-88-horizontal-stabiliser-front-spar-attachment-bolt-retaining-nuts","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115789,"registerId":"commonwealth-F2006B08371-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 400/88 - Horizontal Stabiliser Front Spar Attachment Bolt Retaining 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)  \nCessna 400 Series Aeroplanes\n\nAD/CESSNA 400/88 Horizontal Stabiliser Front Spar\n\nAttachment Bolt Retaining Nuts\n\n  \n2/86 TX\n\nApplicability: Model 425 with S/Nos 425-0002 to 425-0236 and Model 441 with S/Nos 441-0001 to\n\n441-0354.\n\nRequirement: 1. Visually inspect horizontal stabilizer front spar attachment bolt retaining nuts (P/N NAS 1291-8) for cracking.\n\n2. Replace left and right horizontal stabilizer attachment bolt retaining nuts (P/N NAS 1291-8) in accordance with the instructions contained in CESSNA SB No CQB 85-25R1. Replacement parts must be NAS 1291-8 nuts purchased from the Cessna supply division after 22 November 1985.\n\nCompliance: 1. Within 10 hours time in service after 16 January 1986.\n\n2\\. a. For applicable aircraft manufactured after 1 January 1984 or which have replaced the horizontal stabilizer after 1 January 1984 or which have replaced the front spar attachment bolt retaining nuts after 1 January 1984, within 10 hours time in service after 16 January 1986.\n\n2. b. For all other applicable aircraft, within 100 hours time in service after\n\n16 January 1986 or at the next scheduled inspection for Maintenance Release issue after 16 January 1986 whichever is the later.\n\nBackground: The manufacturer reports that one or both of the horizontal stabilizer front spar attachment bolt retaining nuts may be broken or subject to failure due to hydrogen embrittlement.","sortOrder":0}],"analysis":{"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"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope — addressing a specific manufacturing defect in a single component on specific aircraft models. There is no evidence of scope creep; it remains tightly focused on the hydrogen embrittlement issue in the horizontal stabiliser attachment nuts."},"complexity_factors":["Single, specific mechanical issue addressed (one part, one failure mode)","Limited applicability — only two aircraft models with defined serial number ranges","Straightforward two-step requirement (inspect, then replace)","Simple conditional compliance structure based on manufacturing/repair date","No cross-references to other legislation or complex defined terms","Background explanation is concise and technical but accessible"],"plain_english_summary":"This Airworthiness Directive requires urgent inspection and replacement of the NAS 1291-8 retaining nuts that secure the horizontal stabiliser on specified Cessna 425 (s/n 425-0002–425-0236) and 441 (s/n 441-0001–441-0354) airplanes. Manufacturer found hydrogen embrittlement can cause these nuts to crack and fail, risking loss of the stabiliser and catastrophic control loss. Compliance deadlines are immediate (short flight-hour windows) depending on aircraft age."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD maintains a focused scope: it applies only to the listed Cessna 425 and 441 serial-number ranges and prescribes inspection and replacement actions per the manufacturer's service bulletin. It does not expand applicability or alter the nature of the remedial steps set out in the instrument (see Applicability; Requirement; Compliance; Background)."},"complexity_factors":["Narrow applicability by model and serial-number ranges (Applicability) — limits affected fleet but requires checking operator records.","Immediate short-term inspection deadline: within 10 hours TIS after 16 January 1986 (Compliance: 1) — operational scheduling pressure for active aircraft.","Staggered replacement deadlines tied to manufacture/maintenance dates (Compliance: 2.a & 2.b) — creates conditional compliance pathways based on aircraft history.","Prescriptive replacement procedure reference to Cessna SB CQB 85-25R1 (Requirement: 2) — operators must obtain and follow the manufacturer’s service bulletin.","Mandatory source for replacement nuts (NAS 1291-8) purchased from Cessna supply after 22 November 1985 (Requirement: 2) — procurement constraint that may affect parts availability and cost.","Safety hazard identified as hydrogen embrittlement causing cracking (Background) — implies risk of concealed or brittle failures, motivating conservative remedial action."],"plain_english_summary":"Requires owners/operators of specified Cessna 425 and 441 aeroplanes to perform a prompt visual inspection of the horizontal stabiliser front spar attachment bolt retaining nuts and to replace them with NAS 1291-8 parts obtained from the Cessna supply division per Cessna SB CQB 85-25R1. The directive responds to manufacturer reports of cracking from hydrogen embrittlement and imposes short, model-dependent deadlines that create immediate maintenance and parts‑procurement obligations for affected operators."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-400-88-horizontal-stabiliser-front-spar-attachment-bolt-retaining-nuts","history":"/api/acts/ad-cessna-400-88-horizontal-stabiliser-front-spar-attachment-bolt-retaining-nuts/history","analysis":"/api/acts/ad-cessna-400-88-horizontal-stabiliser-front-spar-attachment-bolt-retaining-nuts/analysis","conflicts":"/api/acts/ad-cessna-400-88-horizontal-stabiliser-front-spar-attachment-bolt-retaining-nuts/conflicts","importantCases":"/api/acts/ad-cessna-400-88-horizontal-stabiliser-front-spar-attachment-bolt-retaining-nuts/important-cases","documents":"/api/acts/ad-cessna-400-88-horizontal-stabiliser-front-spar-attachment-bolt-retaining-nuts/documents"}}