{"id":"F2006B04825","name":"AD/CA21/6 - Life Limited Components","slug":"ad-ca21-6-life-limited-components","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44626,"registerId":"commonwealth-F2006B04825-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CA21/6 - Life Limited Components","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)  \nSkyfox Aviation (Calair/Hedaro) CA21 and CA22A Series Aeroplanes\n\n| AD/CA21/6      | Life Limited Components                                                     | 3/96 |\n| -------------- | --------------------------------------------------------------------------- | ---- |\n| Applicability: | All CA21 and CA22A aircraft.                                                |      |\n| Requirement:   | The following components are to be retired from service at the times shown: |      |\n\nComponent Maximum Time in Service\n\nWing Front and Rear Spars 4000 Hours Wing Lift Struts and Carry-Through Structure 4000 Hours Horizontal Stabiliser Spar 8000 Hours All Other Structure, Except Doors and Fairings 8000 Hours\n\nCompliance: As specified in the Requirement, with effect from 29 February 1996.\n\nBackground: The fatigue life limits in this Directive are the best estimates, based on stress and fatigue analyses supplied by the manufacturer.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope: setting fatigue life limits for specific structural components of two specific aircraft models. There is no evidence of scope creep or expansion beyond this original safety purpose."},"complexity_factors":["Very short document (under 200 words)","Only 4 defined component categories with simple hour-based thresholds","No cross-references to other legislation or regulations","No conditional logic, exceptions, or nested provisions","Single compliance date with no phased implementation","Plain tabular format for requirements"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It applies to all **Skyfox Aviation CA21 and CA22A series aircraft** (light aeroplanes).\n\n**What it does:**\nThe Directive sets **strict retirement deadlines** for critical structural parts of these planes. Once a component reaches its maximum allowed flight hours, it must be permanently removed from service — no exceptions.\n\n**The affected parts and their limits are:**\n- **Wing spars** (front and rear): 4,000 hours\n- **Wing lift struts and carry-through structure**: 4,000 hours  \n- **Horizontal stabiliser spar**: 8,000 hours\n- **All other structure** (except doors and fairings): 8,000 hours\n\n**Why it matters:**\nThese limits exist because metal parts weaken over time due to **fatigue** (tiny cracks that develop from repeated stress during flight). The manufacturer provided stress and fatigue analyses showing these components have finite safe lifespans. Ignoring this Directive would risk structural failure in flight.\n\n**Who must comply:**\nOwners and operators of CA21 and CA22A aircraft. The rule took effect on **29 February 1996**."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The instrument's scope, as stated, is to set retirement life-limits for named structural components on all CA21 and CA22A aircraft (Applicability; Requirement). The text provides those limits and an effective date; nothing in the supplied instrument indicates the scope described differs from the original stated purpose (Background; Compliance)."},"complexity_factors":["Narrow applicability: covers only Skyfox CA21 and CA22A aeroplanes (Applicability).","Limited number of explicit, fixed retirement limits listed in a simple table (Requirement).","Administrative requirement to track component hours and schedule retirements (Requirement; Compliance).","No alternate compliance procedures or exemptions provided in the text — binary retirement rule reduces regulatory complexity but raises operational logistics complexity (Requirement).","Underlying limits are estimates from manufacturer analyses, introducing technical uncertainty that could require engineering judgment outside the text (Background)."],"plain_english_summary":"What this instrument does (mechanically)\n\n- It requires that specific structural components on Skyfox Aviation (Calair/Hedaro) CA21 and CA22A aeroplanes be removed from service after a set number of hours in service. The affected components and their retirement times are: wing front and rear spars — 4,000 hours; wing lift struts and carry-through structure — 4,000 hours; horizontal stabiliser spar — 8,000 hours; and all other structure except doors and fairings — 8,000 hours. (Requirement)\n- The rule applies to all CA21 and CA22A aircraft. (Applicability)\n- The requirement is effective from 29 February 1996. (Compliance)\n- The airworthiness limits are based on stress and fatigue analyses supplied by the manufacturer. (Background)\n\nWho is affected\n\n- Owners and operators of CA21 and CA22A aeroplanes must ensure the listed components are retired at the specified hours. (Applicability; Requirement)\n- Maintenance organisations and parts suppliers that service those types will be involved in removing and replacing retired components. (Requirement)\n\nWhy it matters (stated purpose and practical implications)\n\n- The directive sets mandatory retirement life-limits for key structural parts. The document states the limits are the best estimates from the manufacturer’s stress and fatigue analyses (Background). That is the stated safety rationale. (Background)\n\nPractical consequences, incentives and implementation mechanics (source-grounded)\n\n- Who pays: Owners/operators are responsible for taking components out of service when the specified hours are reached and for the costs of replacing or repairing affected parts. This follows from the Requirement applying to all listed aircraft and components. (Applicability; Requirement)\n- What must be done: Operators must track time-in-service for the listed components and schedule their retirement and replacement in accordance with the hours given. The directive prescribes retirement at the stated hours without offering alternative procedures or exceptions in the text. (Requirement)\n- Compliance timing: The retirement obligations applied from 29 February 1996. Operators in service at that date must follow the timetable from that effective date. (Compliance)\n- Discretion and decision-making: The instrument sets fixed retirement hours. No discretionary exemption, alternate life-extension process, or administrative waiver is included in the text provided. The directive is issued under the Civil Aviation Regulations framework (Part 39 — Schedule of Airworthiness Directives). (header; Requirement)\n- Sources of uncertainty and implementation risk: The background notes the limits are estimates based on manufacturer analyses, indicating the limits rely on modelling and the manufacturer’s data rather than on long-term empirical service experience alone. That introduces estimation uncertainty into the retirement timetable. (Background)\n- Effects on maintenance market and operations: Removing parts at fixed life-limits creates predictable demand for replacement parts and labour for CA21/CA22A aircraft. Maintenance providers will perform the work; supply of parts and downtime for aircraft operation will be the immediate operational considerations for affected owners/operators. (Requirement)\n\nSummary statement\n\nThis airworthiness directive mechanically mandates retirement-at-hours for specific structural components on all Skyfox CA21/CA22A aircraft, effective 29 February 1996, based on manufacturer fatigue and stress analyses. The directive assigns compliance responsibilities to owners/operators (tracking hours and replacing parts) and creates predictable maintenance demand for the affected fleet. (Applicability; Requirement; Compliance; Background)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-ca21-6-life-limited-components","history":"/api/acts/ad-ca21-6-life-limited-components/history","analysis":"/api/acts/ad-ca21-6-life-limited-components/analysis","conflicts":"/api/acts/ad-ca21-6-life-limited-components/conflicts","importantCases":"/api/acts/ad-ca21-6-life-limited-components/important-cases","documents":"/api/acts/ad-ca21-6-life-limited-components/documents"}}