{"id":"F2006B04828","name":"AD/CA21/9 - Carburettor Heat Modification Number 7/97","slug":"ad-ca21-9-carburettor-heat-modification-number-7-97","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44629,"registerId":"commonwealth-F2006B04828-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CA21/9 - Carburettor Heat Modification Number 7/97","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\nAD/CA21/9 Carburettor Heat Modification Number 7/97 12/98 TX\n\nApplicability: All Skyfox CA22A aircraft fitted with ROTAX 912 engines.\n\nRequirement: Embody Skyfox modification Number 7/97 in accordance with the manufacturer’s instructions.\n\nCompliance: Within 10 flying hours or 30 days, whichever is the sooner, of the effective date of this directive.\n\nThis directive becomes effective on 18 September 1998.\n\nBackground: ROTAX powered Skyfox CA22A aircraft suffer from excessive RPM drop when carburettor heat is selected. Skyfox modification 7/97 was released in October 1997 to correct this unsatisfactory characteristic. This is considered to be a safety of flight issue and this Directive is issued to ensure that all Skyfox CA22A aircraft are modified expediently.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive implements Skyfox modification Number 7/97 for all affected CA22A aircraft with ROTAX 912 engines, consistent with the stated purpose in the Background to correct an excessive RPM drop when carburettor heat is selected. The text neither widens nor narrows that technical scope beyond requiring embodiment per the manufacturer’s instructions within the stated compliance timeframe (Applicability; Requirement; Compliance; Background)."},"complexity_factors":["Narrow technical scope: applies only to Skyfox CA22A aircraft fitted with ROTAX 912 engines (Applicability).","Single concrete action required: embody a specific manufacturer modification (Requirement).","Short, fixed compliance window increases operational pressure: 10 flying hours or 30 days (Compliance).","Reliance on the manufacturer’s instructions for technical detail creates an external dependency for compliance (Requirement).","Safety-critical context increases practical urgency but does not add legal complexity in the directive text (Background)."],"plain_english_summary":"# What this directive does\n\n- Mechanically, the Civil Aviation Safety Authority requires that Skyfox modification Number 7/97 (a change to the carburettor heat system) be fitted to every Skyfox CA22A aircraft that has a ROTAX 912 engine. (Applicability; Requirement)\n- Operators must carry out the modification \"in accordance with the manufacturer’s instructions.\" (Requirement)\n- The modification must be completed within 10 flying hours or 30 days from the directive’s effective date, whichever comes first. The directive became effective on 18 September 1998. (Compliance)\n\n# Why this was issued (official rationale)\n\n- The directive cites an operational problem: ROTAX-powered Skyfox CA22A aircraft experience an excessive RPM drop when carburettor heat is selected. Skyfox issued modification 7/97 in October 1997 to correct that characteristic, and CASA issued this Directive to ensure the modification is applied promptly on all affected aircraft. (Background)\n\n# Who decides and who acts\n\n- The Civil Aviation Safety Authority (CASA) issued the directive. (header)\n- The directive requires embodiment of the manufacturer’s modification according to the manufacturer’s instructions; that is, the manufacturer provides the technical method and operators or their maintenance providers must perform it. (Requirement)\n\n# What the directive does not say (important practical notes)\n\n- The directive does not specify who pays for the modification or any associated downtime or parts. (No such provision in Requirement or Compliance)\n- The directive does not set out enforcement, penalty, or inspection arrangements in the text provided. (Not stated)\n- The directive does not quantify the modification’s cost, the expected downtime for each aircraft, or whether independent maintenance providers must be authorised beyond following the manufacturer’s instructions. (Not stated)\n\n# Practical trade-offs and implementation points to consider (based on the directive’s wording)\n\n- Compliance burden and timing: affected aircraft must be modified quickly (10 flying hours or 30 days); operators will need to schedule work within that window. (Compliance)\n- Technical discretion: the directive delegates the detailed technical method to the manufacturer’s instructions; the manufacturer’s document therefore determines technical scope and the actionable checklist. (Requirement)\n- Effects on private choice and enterprise: the directive compels operators to have the modification performed (Requirement). The text does not discuss effects on prices, competition between maintenance providers, or ownership rights. (Not stated)\n\n# Net effect in plain language\n\n- If you operate a Skyfox CA22A with a ROTAX 912 engine, this directive required you to have modification 7/97 installed per the manufacturer’s instructions within the stated short deadline. The stated reason is to correct an excessive RPM drop when carburettor heat is selected, which CASA treated as a safety-of-flight issue. (Applicability; Requirement; Compliance; Background)\n"},"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 a known manufacturer modification to prevent dangerous engine behaviour."},"complexity_factors":["Single, clearly defined applicability criterion (Skyfox CA22A + ROTAX 912 engine)","Single, unambiguous compliance action (install Modification 7/97 per manufacturer's instructions)","Simple time-based compliance trigger (10 hours/30 days from effective date)","No defined terms section, no cross-references to other legislation, no conditional exceptions","Total length: approximately 150 words","Straightforward factual background with clear safety rationale"],"plain_english_summary":"**What this is:** An Airworthiness Directive (AD) — essentially a mandatory safety order issued by Australia's aviation safety regulator (CASA) to fix a specific mechanical problem in certain light aircraft.\n\n**Who it affects:** Owners and operators of **Skyfox CA22A aircraft** powered by **ROTAX 912 engines**. These are small, two-seat recreational/training aeroplanes (also known as Calair or Hedaro models).\n\n**What the problem is:** When pilots activate the carburettor heat system (used to prevent ice forming in the engine's fuel system), these aircraft experience an **excessive drop in engine RPM** (revolutions per minute). This is dangerous because it means the engine loses too much power when the pilot needs to use this safety feature.\n\n**What must be done:** Aircraft owners must install **\"Modification Number 7/97\"** — a factory-designed fix released by Skyfox in October 1997. This must be done following the manufacturer's instructions exactly.\n\n**When it must be done:** Within **10 flying hours OR 30 days** (whichever comes first) from **18 September 1998**.\n\n**Why it matters:** Carburettor icing can cause engine failure. If applying the fix for icing causes dangerous power loss, pilots face a horrible choice: risk ice buildup or risk stalling the engine. This directive forces a safety upgrade to eliminate that dilemma."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ca21-9-carburettor-heat-modification-number-7-97","history":"/api/acts/ad-ca21-9-carburettor-heat-modification-number-7-97/history","analysis":"/api/acts/ad-ca21-9-carburettor-heat-modification-number-7-97/analysis","conflicts":"/api/acts/ad-ca21-9-carburettor-heat-modification-number-7-97/conflicts","importantCases":"/api/acts/ad-ca21-9-carburettor-heat-modification-number-7-97/important-cases","documents":"/api/acts/ad-ca21-9-carburettor-heat-modification-number-7-97/documents"}}