{"id":"F2006B08554","name":"AD/CHA/27 - Exhaust Stack 'Y' Junction","slug":"ad-cha-27-exhaust-stack-y-junction","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":51355,"registerId":"commonwealth-F2006B08554-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\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\n![](image.001.png)  \n\nAmerican Champion (Aeronca, Bellanca) Series Aeroplanes","sortOrder":0},{"sectionNumber":"AD/CHA/27 Exhaust Stack 'Y' Junction 12/","sectionType":"part","heading":"AD/CHA/27 Exhaust Stack 'Y' Junction 12/2003","content":"# AD/CHA/27 Exhaust Stack 'Y' Junction 12/2003\n\nApplicability: Aeronca 7AC aeroplanes with Serial Number (S/N) prior to No. 7AC-6797 and 11AC aeroplanes with S/N prior to No. 11AC-1697 fitted with mild steel exhaust stacks part numbers 7-485 and 7-486.\n\nRequirement: Visually inspect the exhaust stacks in the vicinity of the \"Y\" junction for evidence of burning or flaking, tap with a hammer for evidence of soft spots, and inspect to determine whether the stack is obstructed in any way in accordance with Champion Aircraft Corporation service helps and hints #25 Revision 1.\n\nNote: FAA AD 47-30-05 refers.\n\nCompliance: At repetitive intervals not to exceed 50 flight hours from the effective date of this Directive.\n\nThis Airworthiness Directive becomes effective on 27 November 2003.\n\nBackground: Difficulty in the manufacture of the mild steel “Y” stacks has lead to failure of the stacks through cracking, burning, and obstruction of the “Y” stack. Failure of the stack can lead to exhaust gases entering the cabin and/or carburettor heater muffs.\n\n![Signature of Jim Coyne Delegate of the Civil Aviation Safety Authority](image.002.png)  \n\nJim Coyne\n\nDelegate of the Civil Aviation Safety Authority 14 October 2003\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 5 November 2003.","sortOrder":1}],"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"},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD is narrowly focused on correcting an identified unsafe condition with mild-steel exhaust \"Y\" stacks (cracking, burning, obstruction). It requires inspection and corrective action and does not expand into unrelated regulatory areas or add additional regulatory mechanisms (e.g. mandated replacements, design changes, or economic measures). The directive aligns with the original safety-focused purpose described in the background and does not materially change scope beyond requiring repetitive inspections per the manufacturer's guidance."},"complexity_factors":["Short, single-issue instrument focused on one component (exhaust \"Y\" junction).","Limited applicability: two aircraft models with serial-number cut-offs and two specific part numbers.","One recurring compliance obligation (inspect every ≤50 flight hours).","Single external reference to the manufacturer's Service Helps and Hints #25 Revision 1.","Cross-reference to FAA AD 47-30-05 (informational only).","No nested exceptions, few defined terms, and no conditional branching beyond applicability."],"plain_english_summary":"**What this directive does (mechanics)\n\n- Requires owners/operators of certain American Champion (Aeronca, Bellanca) light aeroplanes to perform repeated visual and physical inspections of the mild-steel exhaust \"Y\" junction on specified aircraft models.\n- The inspections must follow Champion Aircraft Corporation Service Helps and Hints #25 Revision 1 (the manufacturer's inspection guidance). (Requirement)\n- Inspections must be repeated at intervals not exceeding 50 flight hours. (Compliance)\n\nWhich aircraft are affected\n\n- Aeronca 7AC aeroplanes with serial numbers before 7AC-6797 and\n- Aeronca 11AC aeroplanes with serial numbers before 11AC-1697\n- Only those fitted with mild-steel exhaust stacks part numbers 7-485 and 7-486. (Applicability)\n\nWhy the rule exists (stated reason)\n\n- The background states manufacturing difficulties with the mild-steel \"Y\" stacks have led to cracking, burning, and obstruction of the junction. Failure can allow exhaust gases into the cabin or carburettor heater muffs — a potential safety hazard. (Background)\n- The directive also cross-references an earlier FAA airworthiness directive (FAA AD 47-30-05). (Note)\n\nWho pays, who decides, and what changes in behaviour\n\n- Who pays: aircraft owners/operators pay for the inspections and any repairs or replacements discovered by the inspection (labour and parts). If a maintenance provider is used, the operator pays that provider. (Requirement; Compliance)\n- Who decides: the Civil Aviation Safety Authority (CASA) delegate issued the directive; the owner/operator must comply. Maintenance personnel follow the manufacturer's service document to carry out the inspections. (Opening paragraph; Requirement)\n- Behaviour change required: owners/operators must add a recurring maintenance task (inspect the Y junction every ≤50 flight hours), and must repair or replace stacks if defects are found. Aircraft may be grounded until a safe condition is restored.\n\nCosts, incentives, trade-offs and implementation considerations (assessment)\n\n- Direct costs: recurring inspection labour every 50 flight hours and potential parts and replacement costs if stacks show cracking, burning, soft spots or obstruction. The directive does not prescribe a replacement part or retrofit, only inspection and corrective action per the service document. (Requirement; Compliance)\n- Incentives: Frequent inspections lower the risk of unseen failure but increase ongoing maintenance cost and time between flying. Operators with low utilisation pay the same inspection burden in calendar terms if they reach 50 flight hours slowly; high-utilisation operators face more frequent inspection events.\n- Opportunity costs: Time spent on inspections is time aircraft are unavailable for flight; funds spent on repairs cannot be spent elsewhere. There is no compensating subsidy in the directive.\n- Implementation risk and compliance burden: The directive relies on visual/physical inspection methods (tap with a hammer to detect soft spots) and on maintenance personnel following the referenced service help document. That creates modest reliance on operator/technician judgement and on the availability of the service instruction. The AD does not create a complex compliance regime but does require consistent record-keeping to demonstrate inspections occurred at the required intervals.\n- Bureaucratic discretion: The AD is issued under CASR subregulation 39.1(1), which allows the CASA delegate to require corrective action for unsafe conditions. The AD itself specifies the required inspection and interval; there is limited discretion in the text for operators beyond following the service instruction and taking corrective action if defects are found. (Opening paragraph)\n- Effects on private enterprise: The directive increases maintenance workload and potential parts demand for operators of the affected models. Independent maintenance organisations can provide inspections and repairs; there is no restriction on who may perform the work beyond following the service instruction.\n\nReference points in the directive: Applicability, Requirement, Compliance, Background, Note (FAA AD reference).**"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"N/A — this is a discrete, targeted safety directive addressing a specific manufacturing defect in specific aircraft. No scope creep evident."},"complexity_factors":["Single, specific aircraft type and serial number range","Only two part numbers affected","Straightforward inspection procedure (visual, hammer tap, obstruction check)","Single compliance interval (50 flight hours, repetitive)","No nested exceptions, conditional logic, or extensive cross-referencing","References only one external document (manufacturer's service hint) and one related FAA AD"],"plain_english_summary":"This CASA Airworthiness Directive mandates recurring inspections of mild-steel exhaust stacks (P/Ns 7‑485, 7‑486) on older American Champion/Aeronca 7AC and 11AC aeroplanes (serials before listed thresholds). Owners must visually and physically check the exhaust “Y” junction per the manufacturer’s Service Helps and Hints #25 Rev 1, every 50 flight hours, because cracking, burning-through, or blockage can leak carbon monoxide into the cabin or impair carb heat. Effective 27 Nov 2003."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cha-27-exhaust-stack-y-junction","history":"/api/acts/ad-cha-27-exhaust-stack-y-junction/history","analysis":"/api/acts/ad-cha-27-exhaust-stack-y-junction/analysis","conflicts":"/api/acts/ad-cha-27-exhaust-stack-y-junction/conflicts","importantCases":"/api/acts/ad-cha-27-exhaust-stack-y-junction/important-cases","documents":"/api/acts/ad-cha-27-exhaust-stack-y-junction/documents"}}