{"id":"F2006B02891","name":"AD/B737/19 - Engine Overheat, Fire Detection and Fire Extinguishing Systems","slug":"ad-b737-19-engine-overheat-fire-detection-and-fire-extinguishing-systems","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42233,"registerId":"commonwealth-F2006B02891-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/19 - Engine Overheat, Fire Detection and Fire Extinguishing Systems","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 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Boeing 737 Series Aeroplanes\n\n \n\n# AD/B737/19 Engine Overheat, Fire Detection and\n\nFire Extinguishing Systems\n\nApplicability: All 737-200, -300 and -400 aeroplanes.\n\n \n\nRequirement: “FIRE EXTINGUISHER BOTTLE CROSS-CONNECTION”\n\n \n\n1. The routing of the electrical wiring to the fire extinguisher bottles is to be\n\n\n# 3/89\n\npermanently modified in such a manner that inadvertent cross-connection of any explosive squib electrical connectors is impossible.\n\n \n\nNote: Boeing Service Letter 737-SL-24-57 refers.\n\n \n\nENGINE OVERHEAT, FIRE DETECTION AND FIRE EXTINGUISHING SYSTEMS\n\n \n\n2.    737-200 series aircraft. Carry out a functional check of each system in accordance with Boeing Telex M-7272-89-0532 dated 31 January 1989.\n\n \n\n3.    737-300 and -400 series aircraft. Carry out a functional check of each system in accordance with Boeing Telex M-7272-89-0530 dated 31 January 1989.\n\n \n\nNote 1: Operators of models 737-300 and -400 series aircraft that have completed a functional check of one engine’s overheat and fire detection system, and a continuity check of the second engine’s overheat and fire protection system to comply with FAA AD 89-01-51 dated 11 January 1989, are only required to complete the functional check on the second engine, and the “Fire Extinguishing Wire” portion of the functional test procedure detailed in Boeing Telex M-7272-89-0530 (Requirement 3 above).\n\n \n\nNote 2: Boeing have superseded Telex 0156 with 0530.\n\n \n\nNote 3: FAA Telegraphic AD T89-03-51 refers to Requirements 2 and 3.\n\n \n\nCompliance: Requirement 1: Within 25 days from 7 February 1989.\n\n \n\n2 and 3: Within 25 days from 7 February 1989, and thereafter before next flight following any maintenance action involving engine overheat, fire detection and/or fire extinguishing systems which could possibly result in cross-connection or mis- connection of any system wiring or plumbing.\n\n \n\nBackground: Requirement 1: Boeing have advised that the possibility exists that the electrical connectors for the fire bottle explosive squibs can be cross-connected. Under some circumstances this could result in the fire extinguisher bottle being dispensed to both engines simultaneously. Note that unlike, Boeing Service Letter 737-SL-24-57, applicability is not limited to a specific line position number.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\nRequirements 2 and 3: There have been reports in the last several months of improperly installed wiring and/or plumbing in the engine and cargo compartment Fire Protection System on various model Boeing aircraft. Whilst the cause of these problems has not been identified in each case, the FAA has determined that, due to design similarity or common production lines, these conditions are likely to exist on other fire protection systems of other Boeing aircraft not covered by previous AD action, and that as a precautionary measure, checks must be performed on specified aircraft.\n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This directive maintains its original narrow scope: addressing specific wiring and fire protection system issues on Boeing 737-200/300/400 aircraft. The applicability note explicitly limits it to these models, and the requirements remain tightly focused on the cross-connection risk and functional checks identified in the background."},"complexity_factors":["Short, single-purpose directive with only 3 numbered requirements","Limited to specific aircraft models (737-200, -300, -400)","Contains 3 explanatory notes but these clarify rather than complicate","References external documents (Boeing Service Letter, Telexes, FAA ADs) but provides sufficient standalone detail","Simple compliance structure: two deadlines, one conditional trigger (post-maintenance)","No defined terms section, no nested exceptions, no conditional logic beyond the maintenance-action trigger"],"plain_english_summary":"This CASA Airworthiness Directive mandates wiring modifications and functional checks on Boeing 737‑200/‑300/‑400 fire protection systems to eliminate the risk that fire extinguisher bottle connectors can be cross‑connected, which could cause both engines to be discharged and leave one unprotected. It affects owners/operators of these Australian‑registered aircraft and requires permanent rewiring and detection-system checks within the specified 25‑day compliance window to prevent catastrophic fire protection failure."},"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"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This AD expands the scope beyond the Boeing Service Letter in at least one explicit way: the AD’s applicability is not limited to a particular line position (as Boeing SL 737-SL-24-57 was), so CASA’s requirement applies to all 737-200, -300 and -400 aircraft rather than a narrower subset. It also bundles both a mandatory permanent wiring reroute requirement and model‑specific functional checks, and adds an ongoing post‑maintenance checking obligation; together these elements broaden the regulatory reach compared with a single vendor service letter that offered guidance for a limited set of aircraft."},"complexity_factors":["Three discrete requirements (Requirement 1; Requirements 2 and 3) with separate actions","References to Boeing Service Letter 737-SL-24-57 and Boeing Telexes M-7272-89-0532 and M-7272-89-0530 for procedural detail","Conditional relief in Note 1 tied to prior compliance with FAA AD 89-01-51","Two background rationales describing different problem sources (wiring cross‑connection risk; reports of improper installation)","Time‑limited initial compliance (25 days from 7 Feb 1989) plus an ongoing conditional requirement (checks before next flight after any maintenance that could affect systems)","Cross‑references to FAA telegraphic AD T89-03-51 and FAA AD 89-01-51"],"plain_english_summary":"**What the directive does (mechanical changes)\n\n- Requires a permanent rerouting of the electrical wiring to the engine fire‑extinguisher bottles so that the explosive squib connectors cannot be inadvertently cross‑connected (Requirement 1).\n- Requires functional checks of the engine overheat, fire detection and fire extinguishing systems on affected aeroplanes, carried out to Boeing telex procedures (Requirements 2 and 3).  \n\nWho it applies to\n\n- All Boeing 737-200, 737-300 and 737-400 series aircraft (the AD’s applicability statement).  \n\nWhen it must be done\n\n- The permanent wiring modification (Requirement 1) must be completed within 25 days from 7 February 1989.  \n- The functional checks (Requirements 2 and 3) must be completed within the same 25‑day window, and thereafter must be done before the next flight following any maintenance that could cause wiring or plumbing mis-connection of the fire/overheat systems.\n\nHow it must be done (procedural references)\n\n- The wiring reroute is to be done so that inadvertent cross‑connection of squib electrical connectors is impossible; Boeing Service Letter 737-SL-24-57 is referenced for guidance.\n- Functional checks must follow Boeing Telex M-7272-89-0532 (for 737-200) or M-7272-89-0530 (for 737-300/-400).  Note 1 provides partial relief for some 737-300/-400 operators who already complied with an FAA AD (they may only need to finish the remaining checks).\n\nWhy the regulator required this (official rationale)\n\n- Boeing warned that squib connector cross‑connection is physically possible and, in some circumstances, could cause a fire‑extinguisher bottle to discharge into both engines at once (background to Requirement 1).\n- Reports of improperly installed wiring and/or plumbing in engine and cargo fire systems on various Boeing aeroplanes prompted the FAA to require checks; CASA adopted equivalent action for the 737 models named (background to Requirements 2 and 3).\n\nWho pays, who decides, and what behaviour changes\n\n- Who pays: aircraft operators (airlines, lessors, or maintenance account holders) pay for the wiring modification, any replacement parts, labour and downtime.  \n- Who decides: licensed maintenance organisations or approved maintenance personnel carry out the permanent wiring reroute and the functional/continuity checks, using Boeing telex/service letter procedures; the operator must schedule and ensure compliance within the set timeframes.  \n- Behaviour changes required: operators must (a) arrange a permanent wiring routing change to eliminate the risk of squib cross‑connection; (b) perform initial functional checks within the compliance window; and (c) include the specified functional/continuity checks as a mandatory post‑maintenance check whenever maintenance could affect those systems.\n\nCosts, incentives, trade‑offs and implementation risks\n\n- Direct costs: labour, parts (if re‑routing requires new harnesses/fasteners/protection), and aircraft out‑of‑service time while the work and checks are completed. There is also administrative cost to document compliance.  \n- Incentives: the rule creates a strong safety incentive for operators to ensure wiring is routed and secured correctly and to improve post‑maintenance verification. It also creates an incentive for maintenance providers to adopt stricter wiring discipline to avoid repeat post‑maintenance checks.  \n- Trade‑offs/opportunity costs: aircraft unavailable for revenue service during modification/checks; resources diverted from other maintenance tasks.  \n- Implementation risk and compliance burden: the directive relies on operators following Boeing telex/service letter procedures; variations in workmanship or interpretation of the telex could leave residual risk. The ongoing requirement to check systems after any maintenance that could affect wiring/plumbing imposes a recurring compliance burden and operational discipline requirement.  \n- Concentrated benefits and diffuse costs: safety benefits accrue to passengers, crew and the operator in the form of reduced risk of inadvertent dual bottle discharge; direct costs are concentrated on the aircraft operator that must perform the modification and checks.\n\nNotes and conditional relief\n\n- Note 1: Operators of 737-300/-400 aircraft who already completed specified checks under FAA AD 89-01-51 may only need to complete the remaining functional checks and the ‘‘Fire Extinguishing Wire’’ portion of the telex procedure.\n- The AD cross‑references Boeing telexes and an FAA telegraphic AD; operators must consult those documents for procedural detail.\n\nIn short: the directive mandates a physical wiring change to prevent explosive‑squib cross‑connection and requires initial and recurring functional checks of engine fire/overheat and extinguisher systems, with tight initial compliance timing and ongoing post‑maintenance checks.**"}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-19-engine-overheat-fire-detection-and-fire-extinguishing-systems","history":"/api/acts/ad-b737-19-engine-overheat-fire-detection-and-fire-extinguishing-systems/history","analysis":"/api/acts/ad-b737-19-engine-overheat-fire-detection-and-fire-extinguishing-systems/analysis","conflicts":"/api/acts/ad-b737-19-engine-overheat-fire-detection-and-fire-extinguishing-systems/conflicts","importantCases":"/api/acts/ad-b737-19-engine-overheat-fire-detection-and-fire-extinguishing-systems/important-cases","documents":"/api/acts/ad-b737-19-engine-overheat-fire-detection-and-fire-extinguishing-systems/documents"}}