{"id":"F2006B02546","name":"AD/AT/18 - Parking Brake Valve","slug":"ad-at-18-parking-brake-valve","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41802,"registerId":"commonwealth-F2006B02546-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AT/18 - Parking Brake Valve","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)  \nAirtractor AT-300, 400 and 500 Series Aeroplanes\n\nAD/AT/18 Parking Brake Valve 5/97\n\nApplicability: All model AT-250, AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-402,\n\nAT-501 and AT-502 series aircraft not fitted with Scott P/N 4500A-2 parking brake valve.\n\nRequirement: Unless previously carried out, replace Gerdes P/N A-850-5 or Cleveland P/N 60-9, as applicable, parking brake valve with Scott P/N 4500A-2 parking brake valve in accordance with Snow Engineering Co. Service Letter #76, dated December 12, 1988.\n\nNote: FAA AD 96-24-08 Amdt 39-9833 refers.\n\nCompliance: At next scheduled maintenance release issue after 31 May 1997, or by 31 December 1997, whichever occurs first.\n\nThis Airworthiness Directive becomes effective on 24 April 1997.\n\nBackground: Advice has been received that during flight the parking brake valve lever can slip from the OFF to the ON position and has caused several aircraft to overturn when landing.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive remains tightly scoped to its original purpose: addressing a specific mechanical defect in a defined set of aircraft. There is no evidence of scope creep — it does not expand to other aircraft types, other brake systems, or unrelated maintenance requirements."},"complexity_factors":["Single, unambiguous requirement (replace one specific part with another specific part)","Only 9 aircraft models listed in applicability section","Clear compliance deadline with simple 'whichever occurs first' logic","Single cross-reference to FAA directive for background context only","No defined terms section, no nested conditions, no exceptions","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 a specific type of agricultural aircraft.\n\n**What it does:**\n- **Targets:** Air Tractor AT-250, AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-402, AT-501 and AT-502 series aeroplanes — these are crop-dusting and firefighting planes commonly used in rural Australia.\n- **The problem:** The parking brake valve (a mechanical part that keeps the brakes engaged when the plane is parked) can accidentally slip from \"OFF\" to \"ON\" during flight. If this happens, the brakes lock up on landing, causing the aircraft to flip over. Several accidents have already occurred.\n- **The fix:** Owners must replace the faulty Gerdes or Cleveland parking brake valves with a safer Scott model (part number 4500A-2), following specific instructions from Snow Engineering.\n- **Deadline:** The replacement must happen by whichever comes first — the next routine maintenance check after 31 May 1997, or by 31 December 1997.\n\n**Who it affects:**\n- Owners and operators of these specific Air Tractor aircraft that don't already have the safer valve installed.\n- Maintenance engineers who service these planes.\n\n**Why it matters:**\nThis is a **life-critical safety measure**. The directive addresses a known defect that has already caused multiple aircraft to overturn. Non-compliance risks catastrophic accidents during landing."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD applies to the listed Airtractor models not already fitted with Scott P/N 4500A-2 and mandates a specific part replacement. It does not expand beyond that set of aircraft or require additional unrelated modifications. The Applicability and Requirement together define the scope; the AD therefore does not change or widen the scope from its stated intent in the instrument itself (Applicability; Requirement)."},"complexity_factors":["Narrow applicability to a specific set of Airtractor models (Applicability).","Requirement ties compliance to a specific replacement part number (Scott P/N 4500A-2) and to removal of specific existing part numbers (Gerdes P/N A-850-5 or Cleveland P/N 60-9) (Requirement).","Implementation depends on following an external technical document (Snow Engineering Co. Service Letter #76), which must be obtained and followed (Requirement).","Compliance timing is linked to maintenance scheduling or a fixed calendar deadline, requiring operational coordination (Compliance).","Potential logistical factors: availability of the specified replacement valve and workshop time for installation affect practical compliance effort (implicit in Requirement and Compliance)."],"plain_english_summary":"This AD mandates replacing certain Gerdes (A-850-5) or Cleveland (60-9) parking-brake valves on specified Airtractor models with Scott P/N 4500A-2, per Snow Engineering Service Letter #76, because lever slippage in flight has caused landing overturns. It affects owners/operators of listed AT‑250/300/400/500 series aircraft not already fitted with the Scott valve, who must complete the swap at the next maintenance release after 31 May 1997 or by 31 Dec 1997 and bear parts and labor costs."}},"importantCases":[],"_links":{"self":"/api/acts/ad-at-18-parking-brake-valve","history":"/api/acts/ad-at-18-parking-brake-valve/history","analysis":"/api/acts/ad-at-18-parking-brake-valve/analysis","conflicts":"/api/acts/ad-at-18-parking-brake-valve/conflicts","importantCases":"/api/acts/ad-at-18-parking-brake-valve/important-cases","documents":"/api/acts/ad-at-18-parking-brake-valve/documents"}}