{"id":"F2006B04943","name":"AD/CESSNA 150/45 - STOL Conversion Wing Stall Fence","slug":"ad-cessna-150-45-stol-conversion-wing-stall-fence","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44797,"registerId":"commonwealth-F2006B04943-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 150/45 - STOL Conversion Wing Stall Fence","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)  \nCessna 150, F150, 152 & F152 Series Aeroplanes\n\nAD/CESSNA 150/45 STOL Conversion Wing Stall Fence 10/96\n\nApplicability: Any model fitted with \"Bush Conversions Inc.\" Short Take Off and Landing (STOL) kit installed in accordance with FAA STC SA1371SW.\n\nRequirement: Measure the height of the wing stall fence at the trailing edge. If the height exceeds\n\n32.5 mm (1.28 inches) install a smaller fence in accordance with a scheme approved pursuant to CAR35 through a District Office of the Authority.\n\nNote 1. FAA AD 96-12-23 refers.\n\nNote 2. The diagram below is extracted from the FAA AD for guidance.\n\n![](image.002.png)  \n\nCompliance: Within 100 hours time in service after 12 September 1996.\n\nBackground: This Directive is issued to prevent modified aircraft from entering a stall condition due to excessive stall fence height, which could result in loss of control of the aircraft.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted airworthiness directive addressing a specific safety defect in a specific aircraft modification. It has not expanded beyond its original purpose of addressing the stall fence height issue."},"complexity_factors":["Single, specific applicability criterion (one STC number)","One simple measurement requirement (32.5mm threshold)","Single compliance deadline (100 hours time in service)","No defined terms section","No cross-references to other legislation beyond a single CAR reference and FAA AD citation","Straightforward conditional logic: IF height > 32.5mm THEN replace","Total length: approximately 150 words"],"plain_english_summary":"This is a **safety order** (called an \"Airworthiness Directive\") issued by Australia's aviation safety regulator for specific Cessna aeroplanes.\n\n**What it does:**\n- Targets Cessna 150, F150, 152 and F152 aircraft that have been modified with a special \"Bush Conversions\" STOL kit (a kit that helps planes take off and land in short distances)\n- Requires owners/operators to **measure the height of a small wing attachment called a \"stall fence\"** at the trailing edge of the wing\n- If that fence is **taller than 32.5mm**, it must be replaced with a smaller one using an approved modification scheme\n\n**Who it affects:**\n- Owners and operators of affected Cessna aircraft with this specific STOL modification\n- Maintenance engineers who work on these aircraft\n\n**Why it matters:**\n- A stall fence that's too tall can cause the aircraft to **stall unexpectedly** (lose lift and potentially crash)\n- This directive prevents accidents by ensuring the modification doesn't make the plane unsafe\n- Compliance is mandatory within 100 hours of flying time after 12 September 1996\n\n**Key terms explained:**\n- **STOL** = Short Take-Off and Landing (ability to use short runways)\n- **Stall fence** = A small vertical fin on the wing that helps control airflow and prevent stalls\n- **CAR35** = Civil Aviation Regulation 35 (the rules for aircraft modifications)\n- **FAA STC** = American aviation approval for the modification kit"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive defines a focused, technical change limited to aircraft fitted with the specified Bush Conversions STOL kit (Applicability). It requires measurement and conditional replacement of the stall fence above a precise height threshold (Requirement) to be completed within a stated time window (Compliance). The text provides no indication that the scope has been broadened or altered from its original technical intent."},"complexity_factors":["Narrow technical requirement (single measurement and threshold of 32.5 mm)","Clear applicability limited to aircraft with a specific STC (FAA STC SA1371SW) (Applicability)","Mandatory follow-up action only if measurement exceeds threshold (Requirement)","Administrative approval required under CAR35 via a District Office (adds procedural complexity and potential delay) (Requirement)","Fixed and near-term compliance window (100 hours TIS after 12 Sep 1996) (Compliance)"],"plain_english_summary":"### What this directive does (mechanics)\n\n- It applies to Cessna 150, F150, 152 and F152 aeroplanes that have had the \"Bush Conversions Inc.\" STOL (Short Take Off and Landing) kit installed under FAA STC SA1371SW. (Applicability)\n- The owner/operator must measure the height of the wing stall fence at the trailing edge. If the measured height is greater than 32.5 mm (1.28 inches) the operator must install a smaller fence. Installation must follow a scheme that is approved under CAR35 via a District Office of the Civil Aviation Authority. (Requirement)\n- The work must be done within 100 hours time in service after 12 September 1996. (Compliance)\n\n### Who pays and who decides\n\n- Aircraft owners/operators pay for the measurement and, if required, for the replacement fence and its installation. (Requirement)\n- The Civil Aviation Authority (via a District Office) approves the replacement scheme under CAR35 and so decides whether a proposed replacement method meets the directive’s requirements. (Requirement)\n\n### Why the directive was issued (official rationale)\n\n- The directive states it is intended to prevent modified aircraft from entering a stall condition due to excessive stall fence height, which could result in loss of control. (Background)\n- The directive cross-references FAA AD 96-12-23 and provides an FAA-derived diagram for guidance. (Note 1, Note 2)\n\n### Effects, trade-offs and implementation considerations\n\n- Compliance actions: owners/operators must measure the fence height and, when height exceeds 32.5 mm, arrange for installation of an approved smaller fence. This creates a direct compliance cost (measurement, parts, labour). (Requirement, Compliance)\n- Administrative burden and discretion: installation must follow a scheme approved under CAR35 through a District Office of the Authority. That creates an administrative step and relies on the Authority’s approval process and timelines. (Requirement)\n- Operational risk mitigation vs. cost: the stated safety benefit (reduced stall risk) is the claimed benefit; the concrete trade-off is the cost and time to inspect and possibly modify many aircraft versus the incremental change in stall behaviour the smaller fence produces. (Background, Requirement)\n- Market effects and suppliers: the directive channels demand for replacement fences and approved installation schemes through authorised approval processes, which may affect independent maintenance providers and parts suppliers who must work under an approved scheme or seek approval. The text does not prescribe a supplier. (Requirement)\n- Compliance timing and opportunity cost: the 100-hour time-in-service window after the specified date sets a short-term compliance timeline that pushes owners/operators to prioritise the inspection and any rectification within that flight-time budget. Scheduling inspections and maintenance within that window represents an opportunity cost for operators. (Compliance)\n- Implementation risks: accurate measurement of the fence height is required to determine compliance; discrepancies in measurement technique or tools could create compliance disputes. Availability of an approved scheme or parts could delay rectification. (Requirement)\n\n### Concrete behavioural change required\n\n- Inspect: measure the trailing-edge height of the stall fence. (Requirement)\n- Replace if necessary: install a smaller fence when height > 32.5 mm, only using a scheme approved under CAR35 via a District Office. (Requirement)\n- Timing: complete the above within 100 hours TIS after 12 September 1996. (Compliance)\n\n(References in parentheses point to the relevant parts of the directive: Applicability, Requirement, Compliance, Background, Note 1, Note 2.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-150-45-stol-conversion-wing-stall-fence","history":"/api/acts/ad-cessna-150-45-stol-conversion-wing-stall-fence/history","analysis":"/api/acts/ad-cessna-150-45-stol-conversion-wing-stall-fence/analysis","conflicts":"/api/acts/ad-cessna-150-45-stol-conversion-wing-stall-fence/conflicts","importantCases":"/api/acts/ad-cessna-150-45-stol-conversion-wing-stall-fence/important-cases","documents":"/api/acts/ad-cessna-150-45-stol-conversion-wing-stall-fence/documents"}}