{"id":"F2006B02945","name":"AD/B737/46 - Engine Fire/Overheat Detection System","slug":"ad-b737-46-engine-fire-overheat-detection-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42287,"registerId":"commonwealth-F2006B02945-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/46 - Engine Fire/Overheat Detection System","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)  \nBoeing 737 Series Aeroplanes\n\nAD/B737/46 Engine Fire/Overheat Detection System 10/90\n\nApplicability: All model 737-300 and 737-400 series aircraft fitted with Kidde engine fire and overheat detection systems as listed in Boeing SB 737-26-1055 Revision 1.\n\nRequirement: Modify the engine fire and overheat detection system in accordance with Boeing SB 737-26-1055 Revision 1.\n\nNote: FAA AD 90-15-14 also refers.\n\nCompliance: Prior to 4 April 1992.\n\nBackground: Boeing have advised that multiple reports have been received from operators describing short circuits in the engine fire detection system which have resulted in false fire warnings. The problem has been attributed to contamination in the electrical connectors at the detector sensor unit. Action in accordance with this AD is necessary to reduce false fire warnings which may result in unnecessary engine shut down which could unduly jeopardise continued safe flight of the aircraft.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope matches the stated original intent: it targets specific 737-300/400 aeroplanes fitted with the identified Kidde detection systems and requires a Boeing-prescribed modification to address false fire warnings attributed to contaminated connectors (Applicability; Requirement; Background). The AD does not expand beyond correcting that identified defect or change the set of affected aircraft or required remedy as presented in the text."},"complexity_factors":["Requires executing a technical modification specified in an external document (Boeing SB 737-26-1055 Revision 1) rather than detailing the steps in the AD (Requirement).","Applies only to a subset of aircraft (737-300 and 737-400) fitted with specific Kidde detection systems, so applicability requires equipment-level identification (Applicability).","Safety-critical nature of the system increases the need for qualified maintenance and correct implementation (Background; Requirement).","Fixed compliance deadline creates scheduling pressure for operators and maintenance providers (Compliance).","Cross-reference to an FAA AD introduces potential coordination or harmonisation issues for operators that fly under multiple jurisdictions (Note)."],"plain_english_summary":"What this direction does (mechanically)\n\n- Applies to: All Boeing 737-300 and 737-400 aircraft that are fitted with Kidde engine fire and overheat detection systems listed in Boeing Service Bulletin (SB) 737-26-1055 Revision 1 (Applicability).\n- Requires: Operators must modify the engine fire and overheat detection system in accordance with Boeing SB 737-26-1055 Revision 1 (Requirement).\n- Timing: The required modification had to be completed before 4 April 1992 (Compliance).\n\nOfficial reason given\n\n- Boeing reported multiple operator incidents of short circuits in the engine fire detection wiring or connectors that produced false fire warnings. The fault was attributed to contamination in electrical connectors at the detector sensor unit. The AD states that the modification is necessary to reduce false fire warnings and the potential for unnecessary engine shutdowns (Background).\n\nWho decides and who pays\n\n- The Civil Aviation Safety Authority issued the directive under the Civil Aviation Regulations (header).\n- The aircraft operators of the affected 737-300/400 aircraft are the parties required to carry out the modification and therefore will bear the direct cost and downtime associated with the work (Requirement; Applicability).\n\nHow it changes behaviour and incentives\n\n- Operators must schedule the specified modification into their maintenance programmes and resources, or ground affected aircraft until the work is done (Requirement; Compliance). That creates an incentive to prioritise the modification during routine maintenance or plan extra downtime to meet the deadline.\n- Maintenance organisations that can perform the modification may receive additional work; operators that cannot perform the work in-house will contract it out (Requirement).\n\nCosts, trade-offs and implementation risks\n\n- Compliance cost and downtime: The AD does not state costs, but the operator incurs labour, parts and potential aircraft downtime to implement the SB-required modification (Requirement; Compliance).\n- Dependence on external technical material: The AD mandates compliance with a Boeing Service Bulletin; the AD does not include the modification steps itself, so operators must obtain and follow Boeing SB 737-26-1055 Revision 1 (Requirement). That creates a dependence on the manufacturer’s instructions for the exact technical remedy.\n- Safety benefit vs opportunity cost: The declared safety benefit is fewer false fire warnings and reduced risk of unnecessary engine shutdown (Background). The trade-off is that operators must allocate funds and maintenance time to achieve that benefit instead of using those resources elsewhere.\n- Implementation risk: If the modification is not carried out correctly or completely according to the Boeing SB, false warnings could persist. The AD sets a firm compliance date but does not describe verification steps beyond following the SB (Requirement; Compliance).\n- Cross-jurisdictional reference: The AD notes a related FAA airworthiness directive (FAA AD 90-15-14), indicating parallel regulatory action in the United States (Note).\n\nConcrete mechanics summarised\n\n- The AD mandates a manufacturer-specified modification to a safety-critical electrical detection system on a delimited set of aircraft, sets a compliance deadline, and relies on the Boeing Service Bulletin for the technical work required (Applicability; Requirement; Compliance). The stated objective is to reduce false fire warnings caused by contaminated electrical connectors at the detector sensor units (Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive with a single purpose. It has not expanded beyond its original intent of addressing a specific electrical fault in specific aircraft."},"complexity_factors":["Single, specific technical requirement with clear reference to external Boeing documentation","Narrow applicability limited to two aircraft models with specific equipment","No conditional logic, exceptions, or nested provisions","Only one defined applicability criterion and one compliance deadline","Straightforward background explanation without cross-references to other legislation beyond a single related FAA directive"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific repairs or modifications to aircraft.\n\n**What it does:**\nOrders airlines and aircraft operators to fix a dangerous electrical fault in the engine fire detection systems of certain Boeing 737 aircraft.\n\n**Who it affects:**\n- All Boeing 737-300 and 737-400 aircraft equipped with Kidde brand fire/overheat detection systems\n- Airlines and operators flying these specific aircraft models in Australia\n\n**The problem:**\nThe engine fire detection system was giving **false alarms** due to contaminated electrical connectors. This matters because:\n- Pilots might unnecessarily shut down a perfectly good engine mid-flight, creating a serious safety risk\n- False warnings erode trust in real emergency warnings\n\n**What must be done:**\nOperators must modify the fire detection system following Boeing's official repair instructions (Service Bulletin 737-26-1055 Revision 1).\n\n**Deadline:**\nAll modifications had to be completed before 4 April 1992.\n\n**Why it matters:**\nThis directive prevents potentially catastrophic situations where pilots might shut down working engines due to faulty warnings, which could compromise the aircraft's ability to fly safely."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-46-engine-fire-overheat-detection-system","history":"/api/acts/ad-b737-46-engine-fire-overheat-detection-system/history","analysis":"/api/acts/ad-b737-46-engine-fire-overheat-detection-system/analysis","conflicts":"/api/acts/ad-b737-46-engine-fire-overheat-detection-system/conflicts","importantCases":"/api/acts/ad-b737-46-engine-fire-overheat-detection-system/important-cases","documents":"/api/acts/ad-b737-46-engine-fire-overheat-detection-system/documents"}}