{"id":"F2006B04904","name":"AD/CESSNA 120/4 - Aileron Support Ribs","slug":"ad-cessna-120-4-aileron-support-ribs","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44748,"registerId":"commonwealth-F2006B04904-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# AIRWORTHINESS DIRECTIVE\n\n![](image.001.png)\n\n![](image.001.png)  \nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\nCessna 120 and 140 Series Aeroplanes","sortOrder":0},{"sectionNumber":"AD/CESSNA 120/4 Aileron Support Ribs 5/2","sectionType":"part","heading":"AD/CESSNA 120/4 Aileron Support Ribs 5/2003","content":"# AD/CESSNA 120/4 Aileron Support Ribs 5/2003\n\nApplicability: Model 120 and 140 aircraft, serial numbers 8001 through 10209.\n\nRequirement: Inspect the aileron support ribs for indications of buckling or cracking, particularly in the narrow part of the web at the aft edge of the lightening hole and in the top flange just forward of the doubler plate. Replace any damaged support rib with Cessna parts 0422200-2 (left) and 0422200-3 (right), which are made of 0.051- inch material and have a shorter lightening hole.\n\nNote: FAA AD 47-43-06 and Cessna Service Letter No. 46 refers.\n\nCompliance: Within 100 hours time in service or 12 months after 15 May 2003, whichever occurs first, and thereafter at intervals not to exceed 100 hours; and whenever the aircraft is tied down and subjected to high winds without the controls having been locked; until Cessna parts 0422200-2 and 0422200-3 are installed.\n\nThis Airworthiness Directive becomes effective on 15 May 2003.\n\nBackground: The FAA requires inspection of the aileron support ribs until modified.\n\n![](image.002.jpeg)  \n\nDavid Alan Villiers\n\nDelegate of the Civil Aviation Safety Authority 4 April 2003\n\n![](image.001.png)","sortOrder":1}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"This directive remains focused on the original safety objective: identify and mitigate buckling/cracking of the aileron support ribs on the specified Cessna 120/140 serial-number range. It requires inspections until the specified replacement parts are installed (a terminating modification). It does not broaden the regulated subject matter beyond that original purpose, add unrelated requirements, or expand the affected fleet beyond the stated serial-number range."},"complexity_factors":["Short, single-issue directive focused on one component (aileron support ribs)","Narrow applicability: two models and a single serial-number range (8001–10209)","Single terminating action specified by two exact OEM part numbers (0422200-2 and 0422200-3)","Multiple simple compliance triggers: time-in-service (100 hours), calendar time (12 months), and exposure to high winds when tied down","Cross-reference to FAA AD and a Cessna Service Letter (adds minor external-document reliance)","No nested exceptions or extensive definitions; straightforward inspection/replace structure"],"plain_english_summary":"**What this directive does (mechanics)**\n\n- **Applies to** Cessna Model 120 and 140 aeroplanes with serial numbers 8001 through 10209. (Applicability)\n- **Requires** regular inspections of the aileron support ribs for buckling or cracking, paying attention to the narrow part of the web at the aft edge of the lightening hole and the top flange just forward of the doubler plate. Replace any damaged rib with the specified Cessna parts: 0422200-2 (left) and 0422200-3 (right). These replacement parts are thicker (0.051-inch material) and have a shorter lightening hole. (Requirement)\n- **Timing**: Do the first inspection within 100 hours time-in-service or within 12 months after 15 May 2003 (whichever comes first). After that, inspect at intervals not to exceed 100 hours. Also inspect whenever the aircraft is tied down and exposed to high winds without the controls being locked. Continue these inspections until the specified replacement parts are installed. (Compliance)\n- **References**: The directive cross-references FAA AD 47-43-06 and Cessna Service Letter No. 46. (Note)\n\n**Who pays and who decides**\n\n- The aircraft owner/operator pays for inspections, any repairs, parts, and associated downtime. Maintenance organisations or individual mechanics contracted by the owner perform the work.\n- The Civil Aviation Safety Authority (CASA) delegate issued the directive and sets the compliance rule. The directive specifies that installing the identified Cessna parts is the terminating action for the inspection requirement. (Requirement / Compliance)\n\n**Why it matters (purpose-claim and practical test)**\n\n- The stated purpose is to correct an unsafe condition (risk of buckling or cracking in the aileron support ribs) that could affect flight control integrity. (Background / Requirement)\n- Practical trade-offs and consequences:\n  - Immediate cost: periodic inspection labour and possible replacement parts if damage is found. Owners who do not replace ribs will face recurring inspections (every 100 hours) and the extra inspections after high-wind events. (Compliance)\n  - Longer-term option: installing the specified Cessna replacement ribs ends the recurring inspection obligation (installation is the terminating modification). That creates an incentive to pay the one-time cost to avoid ongoing inspection costs. (Requirement / Compliance)\n  - Supply and compliance risk: the directive specifies OEM part numbers, so availability and cost of those Cessna parts determine how quickly operators can adopt the terminating modification. If parts are scarce or expensive, operators may choose recurring inspections instead. (Requirement)\n\n**Implementation, compliance burden and market effects**\n\n- Compliance burden is operational and financial on aircraft owners/operators: hourly inspection labour, potential part purchase, and aircraft downtime. (Compliance / Requirement)\n- The directive channels replacement work to qualified maintenance providers; this can create business for independent maintenance shops and parts suppliers, but it also ties the terminating action to specific OEM parts, which restricts substitute-part options unless approved. (Requirement)\n- The directive does not create new regulatory permissions or limits on operations aside from the inspection/replacement mandate; it does not alter operator licensing, airspace access, or broader commercial competition. It does change maintenance costs and procedures for the affected fleet. (Applicability / Requirement)\n\n**Practical notes for operators**\n\n- If your aircraft is within the serial-number range, schedule the first inspection promptly within the required 100 hours or by the 12-month date. Keep records of inspections and any replacements (standard maintenance practice). (Compliance)\n- Consider the cost of repeated inspections versus the one-time cost of installing the thicker, shortened-lightening-hole ribs; installing the specified parts removes the inspection requirement. (Requirement / Compliance)\n\n(References: Applicability; Requirement; Compliance; Background.)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope. It addresses a specific structural defect in specific aircraft models as identified by the FAA, with no expansion beyond the original safety purpose of preventing aileron control failure."},"complexity_factors":["Single, specific mechanical component addressed (aileron support ribs)","Clear applicability criteria (two specific aircraft models, defined serial number range)","Straightforward inspection requirement with visual check for two specific damage types","Simple compliance timeline (100 hours/12 months, then recurring 100 hours)","Single trigger condition for additional inspection (high winds without control locks)","Only two replacement part numbers specified","No nested definitions, cross-references to other legislation, or conditional exceptions","Background section is minimal (one sentence referencing FAA requirement)"],"plain_english_summary":"This CASA safety order targets Cessna 120/140 aircraft (S/N 8001–10209), requiring owners and maintenance engineers to inspect aileron support ribs for cracks or buckling around lightening holes and replace them with thicker Cessna parts if damaged. \n\nInspections are due within 100 flight hours or 12 months of 15 May 2003, then every 100 hours; an extra check is required after being tied down in high winds without locks. Inspections cease once upgraded ribs are fitted."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-120-4-aileron-support-ribs","history":"/api/acts/ad-cessna-120-4-aileron-support-ribs/history","analysis":"/api/acts/ad-cessna-120-4-aileron-support-ribs/analysis","conflicts":"/api/acts/ad-cessna-120-4-aileron-support-ribs/conflicts","importantCases":"/api/acts/ad-cessna-120-4-aileron-support-ribs/important-cases","documents":"/api/acts/ad-cessna-120-4-aileron-support-ribs/documents"}}