{"id":"F2006B04837","name":"AD/CA25/6 - Gazelle Exhaust System","slug":"ad-ca25-6-gazelle-exhaust-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44638,"registerId":"commonwealth-F2006B04837-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CA25/6 - Gazelle Exhaust System","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 (Hedaro) CA25 Series Aeroplanes\n\nAD/CA25/6 Gazelle Exhaust System 2/97\n\nApplicability: CA25N Gazelle aircraft serial numbers up to and including CA25N042 not incorporating Helitech Engineering Order HEO-143.\n\nRequirement: To detect cracking of the exhaust system which may result in exhaust gas leakage and/or failure of the exhaust system, carry out an inspection of the exhaust system in accordance with the requirements of Skyfox Aviation Service Bulletin (SB) Number 14.\n\nCompliance: Effective 30 January 1997; unless previously accomplished, within 50 hours time in service and thereafter at intervals not to exceed 100 hours time in service.\n\nBackground: This Directive has been issued to require inspection of the exhaust system. The requirement follows advice from the aircraft manufacturer of several incidents of cracking in the area where the exhaust manifold inlet tube enters the muffler chamber.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive's scope is limited to CA25N Gazelle aeroplanes up to serial CA25N042 not incorporating HEO-143 and requires repeated inspections as specified. That scope aligns with the instrument's stated purpose (to detect cracking reported by the manufacturer where the exhaust manifold inlet enters the muffler chamber) and does not indicate any expansion or narrowing beyond that stated intent within the text (Applicability; Requirement; Background; Compliance)."},"complexity_factors":["Reference to an external document (Skyfox Aviation Service Bulletin Number 14) for the required inspection procedure increases operational complexity.","Applicability limited by serial-number cutoff (CA25N up to and including CA25N042) requires checking aircraft records.","Exemption for aircraft incorporating Helitech Engineering Order HEO-143 requires verifying modification status.","Recurring inspection intervals (initial at 50 hours TIS, then every 100 hours TIS) create ongoing compliance burdens and scheduling needs.","The Directive mandates action but does not itself contain technical inspection steps or repair actions, requiring reliance on the Service Bulletin."],"plain_english_summary":"What this instrument does (mechanics)\n\n- This Airworthiness Directive requires owners/operators of certain Skyfox Aviation (Hedaro) CA25N Gazelle aeroplanes to inspect the aircraft exhaust system. The inspections must be done in accordance with Skyfox Aviation Service Bulletin Number 14 (Requirement).\n- The rule applies to CA25N Gazelle aeroplanes with serial numbers up to and including CA25N042 unless the aircraft already incorporates Helitech Engineering Order HEO-143 (Applicability).\n- The inspection regime is mandatory from 30 January 1997. If not already done, the first inspection must occur within 50 hours time in service and then repeated at intervals not exceeding 100 hours time in service (Compliance).\n\nWhy this was issued (stated purpose)\n\n- The Directive was issued after the aircraft manufacturer advised of several incidents of cracking where the exhaust manifold inlet tube enters the muffler chamber. The Directive’s stated aim is to detect cracking that could cause exhaust gas leakage and/or failure of the exhaust system (Background). This is the explicit rationale recorded in the instrument.\n\nWho pays and who decides\n\n- Owners/operators of affected CA25N aircraft are the parties required to act: they must arrange and pay for the inspections called for by the Directive (Applicability; Requirement; Compliance). The Civil Aviation Safety Authority is the regulator issuing the mandatory direction.\n\nIncentives, trade-offs and compliance burden\n\n- Incentive to comply: compliance reduces the risk of undetected cracking that the manufacturer linked to exhaust leakage or failure (Background). Non-compliance would leave that risk unaddressed and would breach the airworthiness directive.\n- Direct costs to operators: arranging the inspection (and any follow-up work identified by the inspection) will impose maintenance costs and aircraft downtime. The instrument specifies inspection timing in hours-in-service (initial at 50 hours, thereafter every 100 hours), which translates to recurrent operating disruption and expenditure (Compliance).\n- Administrative and implementation tasks: operators must obtain and follow Skyfox Aviation Service Bulletin Number 14 to perform the inspection as directed (Requirement). The Service Bulletin is an external document referenced by the Directive; the Directive does not reproduce the inspection procedure itself.\n\nDiscretion, enforcement and operational effects\n\n- The Directive prescribes a mandatory inspection procedure location (the referenced Service Bulletin). The regulator enforces compliance with the Directive; the instrument does not set out discretionary waivers or alternative compliance paths within its text (Requirement; Compliance).\n- The rule narrows the set of affected aircraft by serial number and by whether Helitech Engineering Order HEO-143 has been incorporated, so owners must check configuration and serial-number status to determine applicability (Applicability).\n\nEffects on private-market actors\n\n- The requirement creates predictable demand for inspection services and any remedial maintenance that follows an inspection. Independent maintenance organisations capable of performing the Service Bulletin inspection can offer those services.\n- The Directive constrains private choice of when to continue operating an affected aircraft without inspection: operators must schedule inspections to meet the specified hours-in-service windows (Compliance). The instrument does not itself specify repair actions or costs; those follow from inspection findings and the Service Bulletin's procedures (Requirement).\n\nImplementation risks and opportunity costs\n\n- Implementation depends on access to and correct interpretation of Skyfox Aviation Service Bulletin Number 14; operators who cannot obtain or interpret the Service Bulletin face practical risk of non-compliance or incorrect inspections (Requirement).\n- The recurring inspection intervals imply an ongoing maintenance cost stream and operational planning requirement for affected aircraft. Time and money spent complying are opportunity costs relative to other uses of the aircraft or maintenance resources (Compliance).\n\nSource references within the instrument: Applicability; Requirement; Compliance; Background."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating exhaust system inspections."},"complexity_factors":["Single, specific mechanical issue (exhaust cracking)","Narrow applicability: only one aircraft model series (CA25N), specific serial number range, with one clear exemption (HEO-143)","Simple compliance structure: one-time initial inspection plus recurring interval","No defined terms section — uses standard aviation terminology","No cross-references to other legislation or regulations beyond the parent Civil Aviation Regulations 1998","Single requirement referencing an external technical document (Service Bulletin 14)","No conditional logic, exceptions to exceptions, or nested provisions"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). Think of it like a compulsory recall notice, but for aircraft rather than cars.\n\n**What it does:** It requires owners and operators of specific Skyfox Aviation CA25N Gazelle light aircraft to inspect their exhaust systems for dangerous cracks. The inspections must follow a specific technical procedure laid out in \"Service Bulletin Number 14\" from the manufacturer.\n\n**Who it affects:** Owners and operators of CA25N Gazelle aircraft with serial numbers up to CA25N042, **unless** their plane has already been modified according to \"Helitech Engineering Order HEO-143\" (a specific repair or upgrade).\n\n**Why it matters:** Cracks in the exhaust system can leak dangerous carbon monoxide into the cockpit and cabin, or cause the exhaust system to fail completely — both potentially fatal situations. The directive was triggered after the manufacturer reported several cases of cracking where the exhaust pipe enters the muffler.\n\n**What must be done:**\n- **First inspection:** Within 50 hours of flying time after 30 January 1997 (or immediately if already past that date)\n- **Ongoing checks:** Every 100 hours of flying time thereafter\n- **How:** Follow the manufacturer's Service Bulletin Number 14 exactly"}},"importantCases":[],"_links":{"self":"/api/acts/ad-ca25-6-gazelle-exhaust-system","history":"/api/acts/ad-ca25-6-gazelle-exhaust-system/history","analysis":"/api/acts/ad-ca25-6-gazelle-exhaust-system/analysis","conflicts":"/api/acts/ad-ca25-6-gazelle-exhaust-system/conflicts","importantCases":"/api/acts/ad-ca25-6-gazelle-exhaust-system/important-cases","documents":"/api/acts/ad-ca25-6-gazelle-exhaust-system/documents"}}