{"id":"F2006B09716","name":"AD/F27/149 - Fuel Differential Pressure Switches","slug":"ad-f27-149-fuel-differential-pressure-switches","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115893,"registerId":"commonwealth-F2006B09716-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F27/149 - Fuel Differential Pressure Switches","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)  \n![](image.002.png)  \nFokker F27 Series Aeroplanes\n\nAIRWORTHINESS DIRECTIVE\n\n![](image.002.png)\n\n![](image.002.png)  \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 CAR 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 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| AD/F27/149     | Fuel Differential Pressure Switches                                    | 3/2000TX |\n| -------------- | ---------------------------------------------------------------------- | -------- |\n| Applicability: | Model F27 Mk 100 through Mk 700 series aeroplanes, all serial numbers. |          |\n\nRequirement: 1. Inspect the installed fuel differential pressure switches and attaching fuel pressure sensing lines for proper installation in accordance with Fokker Service Bulletin (SB) F27/28-63 dated November 21, 1999.\n\n2. Re-install, in accordance with Fokker SB F27/28-63 dated November 21,1999, any fuel differential pressure switches and/or fuel pressure sensing lines found incorrectly installed during the above inspection.\n\nNote: RLD AD (BLA) 1999-154 dated November 30, 1999 refers.\n\nCompliance: 1. Within one calendar month after the effective date of this directive.\n\n2. Before further flight.\n\nThis Airworthiness Directive becomes effective on 2 February 2000.\n\nBackground: Recent instances have occurred where the fuel differential switch was installed upside down which can result in inadvertent cross-connection of the fuel pressure sensing lines inhibiting the function of the fuel filter icing warning system. This could leave an ice-blocked fuel filter undetected, leading to fuel starvation and engine flame-out.\n\n![Signature of Eugene Paul Holzapfel, Delegate of the Civil Aviation Safety Authority.](image.003.png)  \n\nEugene Paul Holzapfel\n\nDelegate of the Civil Aviation Safety Authority 29 January 2000\n\n![](image.002.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 2 February 2000.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The directive's scope aligns with its stated intent: it targets incorrect installation of fuel differential pressure switches and sensing lines on Fokker F27 Mk100–Mk700 aircraft and mandates inspection and correction per the manufacturer SB. It does not broaden obligations beyond inspection and remedial re‑installation, and applies to all serial numbers within the specified models (Applicability; Requirement; Compliance)."},"complexity_factors":["Narrow, clearly defined applicability (F27 Mk100–Mk700, all serial numbers) reduces scope complexity (Applicability).","Technical implementation depends on following a manufacturer Service Bulletin (Fokker SB F27/28‑63), creating a dependency on external technical instructions (Requirement).","Short statutory compliance timeframe (inspection within one calendar month; corrections before further flight) creates scheduling and operational pressure for operators (Compliance).","Maintenance action requires access to aircraft fuel‑system components and competent maintenance personnel, imposing direct cost and logistical burden on operators (Requirement; Compliance).","Regulatory force: issued under CAR 1998 subregulation 39.1(1), so non‑compliance has legal consequences (preamble/signature).","Cross‑reference to related foreign ADs (RLD AD (BLA) 1999‑154) may require operators to reconcile multiple directives."],"plain_english_summary":"Requires operators of Fokker F27 Mk100–Mk700 aeroplanes to inspect fuel differential pressure switches and attached pressure sensing lines and to reinstall any incorrect installations in accordance with Fokker Service Bulletin F27/28‑63. (Applicability; Requirement; Compliance.) The inspection must occur within one calendar month and corrections made before further flight. (Compliance.) Operators pay for the inspections and repairs; the CASA delegate issued the directive. The action addresses the risk that an upside‑down switch can cross‑connect lines and disable the fuel‑filter icing warning, risking engine flame‑out. (Background.)"},"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope: addressing a specific mechanical installation error on a specific aircraft type. There is no evidence of scope creep — it does not expand to other aircraft systems, other aircraft types, or broader operational requirements beyond the immediate safety-critical fix."},"complexity_factors":["Very short document (approximately 300 words)","Only 2 substantive requirements (inspect and reinstall if needed)","Single defined applicability (Fokker F27 Mk 100-700 series)","No nested exceptions or conditional logic — straightforward 'if found incorrect, fix it' structure","Single cross-reference to Fokker Service Bulletin and one note referencing a Dutch aviation authority directive","Clear, unambiguous compliance deadlines with no alternative methods or escalations"],"plain_english_summary":"This Airworthiness Directive requires owners and operators of Fokker F27 Mk100–Mk700 aircraft to inspect fuel differential pressure switches and sensing lines because some were installed upside down, cross-connecting lines and disabling the fuel-filter blockage warning. Inspections must be done promptly (within the AD’s compliance window) and any incorrect installations corrected before the aircraft flies, preventing undetected fuel starvation, engine flame-out, and potential loss of control."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f27-149-fuel-differential-pressure-switches","history":"/api/acts/ad-f27-149-fuel-differential-pressure-switches/history","analysis":"/api/acts/ad-f27-149-fuel-differential-pressure-switches/analysis","conflicts":"/api/acts/ad-f27-149-fuel-differential-pressure-switches/conflicts","importantCases":"/api/acts/ad-f27-149-fuel-differential-pressure-switches/important-cases","documents":"/api/acts/ad-f27-149-fuel-differential-pressure-switches/documents"}}