{"id":"F2006B02921","name":"AD/B737/225 - Proximity Switch Electronics Unit","slug":"ad-b737-225-proximity-switch-electronics-unit","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42263,"registerId":"commonwealth-F2006B02921-current","compilationNumber":null,"startDate":"2026-04-01","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\nBoeing 737 Series Aeroplanes","sortOrder":0},{"sectionNumber":"AD/B737/225 Proximity Switch Electronics","sectionType":"part","heading":"AD/B737/225 Proximity Switch Electronics Unit 6/2004","content":"# AD/B737/225 Proximity Switch Electronics Unit 6/2004\n\nApplicability: Model 737-600, \\-700, \\-700C, \\-800, and \\-900 series aeroplanes, as listed in Boeing Alert Service Bulletin (ASB) 737-32A1343 dated 26 July 2001.\n\nRequirement: 1. Remove Proximity Switch Electronics Unit (PSEU) part number (P/N) 285A1600-2 or 285A1600-3 and replace it with a PSEU P/N 285A1600-4, in accordance with the Accomplishment Instructions of ASB 737-32A1343.\n\n2. PSEU P/N 285A1600-2 or 285A1600-3 may not be installed on any aeroplane as a replacement part.\n\nNote: FAA AD 2004-07-10 Amdt 39-13554 refers.\n\nCompliance: For Requirement 1 \\- Within 18 months after the effective date of this Directive.\n\nFor Requirement 2 - As of the effective date of this Directive. This Airworthiness Directive becomes effective on 10 June 2004.\n\nBackground: This Directive requires replacement of the PSEU with a new, improved unit. This action is necessary to prevent a malfunction of the aural warning for the landing gear, leading the crew to open the circuit breaker for the aural warning horn which stops the operation of other aural warnings of malfunctions in other systems and, thus, could jeopardize a safe flight and landing.\n\n![Signature of James Coyne, Delegate of the Civil Aviation Safety Authority.](image.002.png)  \n\nJames Coyne\n\nDelegate of the Civil Aviation Safety Authority 27 April 2004\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 19 May 2004.","sortOrder":1}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive’s scope aligns with its stated safety aim: it mandates replacement of specified PSEU part numbers on the Boeing 737 models listed in the Boeing ASB (Applicability; Requirement; Background). There is no text in this instrument that expands or narrows applicability beyond that stated purpose."},"complexity_factors":["Single, specific hardware swap: clear technical action to replace PSEU P/N 285A1600-2/ -3 with P/N 285A1600-4 (Requirement 1).","Immediate prohibition on using old parts: older PSEUs may not be installed from the effective date (Requirement 2; Compliance).","Fixed compliance window: replacement must occur within 18 months of the Directive’s effective date (Compliance).","Applicability limited to listed Boeing 737 submodels; operators must check ASB 737-32A1343 to confirm applicability (Applicability).","Procedure delegated to Boeing Alert Service Bulletin for accomplishment instructions, creating dependence on manufacturer documentation (Requirement 1).","Safety‑critical context: failure mode affects aural warnings and can lead crew actions that disable multiple warnings, increasing operational risk if unaddressed (Background).","Low regulatory discretion in text: few conditional exemptions or alternative means of compliance are set out, increasing compliance certainty but limiting flexibility (Requirement/Compliance).","Operational cost and logistics: fleet owners bear parts, labour and downtime costs within a short scheduling window (Requirement/Compliance)."],"plain_english_summary":"This Directive requires removal of Proximity Switch Electronics Units (PSEU) P/N 285A1600-2 or -3 and replacement with P/N 285A1600-4, and forbids fitting the older units. It applies to Boeing 737-600/700/700C/800/900 series listed in Boeing ASB 737-32A1343 (Applicability). The stated purpose is to prevent a landing‑gear aural‑warning malfunction that could cause crews to open an aural‑warning circuit breaker and disable other warnings (Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope: mandating replacement of a specific faulty component in specific aircraft models. There is no evidence of scope creep; the directive does exactly what its title and background suggest — addresses a known unsafe condition in the PSEU units."},"complexity_factors":["Very short document (approximately 250 words)","Only 2 substantive requirements with clear, unambiguous language","Single applicability criterion referencing an external Boeing document","No defined terms section — all technical terms are explained in context or are standard aviation part numbers","No nested exceptions or conditional logic beyond the basic applicability and compliance timing","Linear structure: Background → Applicability → Requirement → Compliance — no cross-references between sections"],"plain_english_summary":"Australia’s aviation regulator requires operators of certain Boeing 737-600/700/700C/800/900 series to replace faulty Proximity Switch Electronics Units (PSEU p/n 285A1600-2/ -3) with the improved p/n 285A1600-4 per Boeing Alert Service Bulletin 737-32A1343.  \n\nThe swap must be completed within 18 months of the directive (effective 10 June 2004); installing the old units is banned immediately. It prevents false landing-gear warnings that could lead crews to disable multiple critical alarms."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-225-proximity-switch-electronics-unit","history":"/api/acts/ad-b737-225-proximity-switch-electronics-unit/history","analysis":"/api/acts/ad-b737-225-proximity-switch-electronics-unit/analysis","conflicts":"/api/acts/ad-b737-225-proximity-switch-electronics-unit/conflicts","importantCases":"/api/acts/ad-b737-225-proximity-switch-electronics-unit/important-cases","documents":"/api/acts/ad-b737-225-proximity-switch-electronics-unit/documents"}}