{"id":"F2006B02320","name":"AD/ALF/6 - Replacement of Fuel By-Pass Valve In Dual Heat Exchanger","slug":"ad-alf-6-replacement-of-fuel-by-pass-valve-in-dual-heat-exchanger","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41550,"registerId":"commonwealth-F2006B02320-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/ALF/6 - Replacement of Fuel By-Pass Valve In Dual Heat Exchanger","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  AlliedSignal (Lycoming) Turbine Engines - ALF502 and LF507 Series\n\n \n\nAD/ALF/6 Replacement of Fuel By-Pass Valve In Dual Heat Exchanger\n\n\n6/87\n\n \n\nApplicability: ALF 502R series which have dual heat exchanger P/N 2-303-491-01 installed.\n\n \n\nRequirement: Remove from service or rework dual heat exchangers P/N 2-303-491-01 in accordance with Lycoming SB ALF 502R-79-0151 Rev 1.\n\n \n\nCompliance: Unless already accomplished within 100 flights after 4 June 1987 but not later than 31 July 1987.\n\n \n\nBackground:  This Directive is issued requiring the installation of a new fuel by-pass valve which will prevent engine fuel system icing when fuel load temperature at take-off is above 10º C.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument implements the stated original aim in the text: it targets ALF 502R engines with the specified dual heat exchanger and mandates either removal or rework to install a new fuel by-pass valve to address fuel-system icing when fuel temperature at take-off exceeds 10°C. The directive's requirements (Requirement) and compliance window (Compliance) remain aligned with that stated purpose (Background); no expansion or narrowing of scope beyond those elements is indicated in the provided text."},"complexity_factors":["Narrow applicability (only ALF 502R engines fitted with dual heat exchanger P/N 2-303-491-01) (Applicability)","Mandatory technical action tied to a single external document (Lycoming SB ALF 502R-79-0151 Rev 1) (Requirement)","Two discrete compliance options provided (remove from service or rework), requiring an operator choice (Requirement)","Dual timing constraint: a flight-based threshold (100 flights after 4 June 1987) plus an absolute calendar cap (not later than 31 July 1987) (Compliance)","Safety-critical context implies operational impact and potential scheduling pressure, though enforcement details are not specified in the text (Background; Compliance)"],"plain_english_summary":"This AD requires removal or rework of dual heat exchanger P/N 2-303-491-01 on AlliedSignal (Lycoming) ALF 502R engines within 100 flights of 4 June 1987 or by 31 July 1987. Affected aircraft owners/operators must pay and choose removal or rework per Lycoming Service Bulletin ALF 502R-79-0151 Rev 1; the measure is intended to prevent engine fuel‑system icing when fuel temperature at takeoff exceeds 10°C."},"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 engine component. It has not expanded beyond its original purpose of mandating replacement of a faulty fuel by-pass valve."},"complexity_factors":["Single, specific applicability criterion (one engine series with one specific part number)","Single requirement with two alternative actions (remove or rework)","Clear compliance deadline with simple conditional logic","No defined terms section","No cross-references to other legislation","Straightforward background explanation","Total length: approximately 150 words of substantive content"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). Think of it as a \"recall notice\" for aircraft parts, but legally binding.\n\n**What it does:** It requires owners or operators of specific AlliedSignal (Lycoming) ALF 502R turbine engines to replace or repair a faulty fuel by-pass valve in the dual heat exchanger system.\n\n**Who it affects:** Anyone operating aircraft with ALF 502R series engines that have a specific dual heat exchanger part (P/N 2-303-491-01) installed.\n\n**Why it matters:** The existing valve can cause dangerous ice buildup in the fuel system during take-off when fuel temperatures are above 10°C. Ice in fuel lines can starve the engine of fuel, potentially causing engine failure. The new valve prevents this icing problem.\n\n**What must be done:** Operators must either remove the affected heat exchangers from service or rework them following Lycoming's Service Bulletin ALF 502R-79-0151 Rev 1.\n\n**When:** The work had to be completed within 100 flights after 4 June 1987, but no later than 31 July 1987 (this is a historical directive from 1987)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-alf-6-replacement-of-fuel-by-pass-valve-in-dual-heat-exchanger","history":"/api/acts/ad-alf-6-replacement-of-fuel-by-pass-valve-in-dual-heat-exchanger/history","analysis":"/api/acts/ad-alf-6-replacement-of-fuel-by-pass-valve-in-dual-heat-exchanger/analysis","conflicts":"/api/acts/ad-alf-6-replacement-of-fuel-by-pass-valve-in-dual-heat-exchanger/conflicts","importantCases":"/api/acts/ad-alf-6-replacement-of-fuel-by-pass-valve-in-dual-heat-exchanger/important-cases","documents":"/api/acts/ad-alf-6-replacement-of-fuel-by-pass-valve-in-dual-heat-exchanger/documents"}}