{"id":"F2006B03210","name":"AD/B747/316 - Prevention of Mineral Deposits on Fire Shutoff Switches","slug":"ad-b747-316-prevention-of-mineral-deposits-on-fire-shutoff-switches","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42582,"registerId":"commonwealth-F2006B03210-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/316 - Prevention of Mineral Deposits on Fire Shutoff Switches","content":"![](image.001.png)\n\n![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\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 747 Series Aeroplanes\n\nAD/B747/316 Prevention of Mineral Deposits on\n\nFire Shutoff Switches\n\n  \n13/2004\n\nApplicability: Model 747SP, 747-200B, -200C, -200F, -300, -400, -400D and -400F series aeroplanes listed in Boeing Alert Service Bulletin (ASB) 747-26A2274, Revision 1, dated 9 January 2003.\n\nRequirement: 1. Perform a functional test of the auxiliary power unit (APU) and engine fire shutoff switches, in accordance with ASB 747-26A2274 Revision 1.\n\n    2. If any fire shutoff switch fails during any functional test required by Requirements 1 or 5.a., replace the switch with a new or serviceable switch, in accordance with the ASB 747-26A2274 Revision 1.\n\n    3. Replace all APU and engine fire shutoff switches that have not been previously replaced per Requirement 2 with new or serviceable switches, in accordance with ASB 747-26A2274 Revision 1.\n\n    4. If Lucas flight deck humidifier part number part number (P/N) M01AA0101, M01AB0101, M01AB0102 or M01AB0103 is optionally deactivated, replace all APU and engine fire shutoff switches with new or serviceable switches in accordance with ASB 747-26A2274 Revision 1.\n\n    5. If Lucas humidifier, P/N M01AA0101, M01AB0101, M01AB0102 or M01AB0103 is reactivated after the effective date of this Directive carry out the following:\n\n    Action in accordance with Requirement 1.\n\n    b. Action in accordance with Requirement 3.\n\nActions accomplished before the effective date of this Directive per Boeing Alert Service Bulletin 747-26A2274, dated 29 August 2002, are considered acceptable for compliance with the corresponding action specified in this Directive.\n\nNote: FAA AD 2004-20-16 Amdt 39-13821 refers.\n\nBoeing 747 Series Aeroplanes\n\nAD/B747/316 (continued)\n\nCompliance: For Requirement 1 - At the later of the compliance times specified below and thereafter at intervals not to exceed 18 months unless Lucas humidifiers P/N M01AA0101, M01AB0101, M01AB0102 or M01AB0103 is optionally deactivated:\n\n    Within 18 months after the original issue of a Certificate of Airworthiness, or\n\n    b. Within 90 days after the effective date of this Directive.\n\nFor Requirement 2 \\- Before further flight and thereafter at intervals not to exceed 36 months unless Lucas humidifier P/N M01AA0101, M01AB0101, M01AB0102 or M01AB0103 is optionally deactivated.\n\nFor Requirement 3 - Within 36 months after the effective date of this Directive and thereafter at intervals not to exceed 36 months unless Lucas humidifier P/N M01AA0101, M01AB0101, M01AB0102 or M01AB0103 is optionally deactivated.\n\nFor Requirement 4 \\- Before further flight immediately after the deactivation.\n\nFor Requirement 5.a. \\- Within 18 months after reactivating the humidifier and thereafter at intervals not to exceed 18 months.\n\nFor Requirement 5.b. \\- Within 36 months after reactivating the humidifier and thereafter at intervals not to exceed 36 months.\n\nThis Airworthiness Directive becomes effective on 23 December 2004.\n\nBackground: Boeing advised that during routine maintenance checks some engine fire control circuits were found to be faulty due to switch internal continuity failures. The humidified air being provided by the LUCAS Humidifier was identified as the source of mineral build up on APU and engine fire control switch contacts leading to failure of the switches to discharge fire suppressant in the affected area. This could result in an uncontrolled fire that could spread to the strut, wing, or aft body of the aeroplane.\n\nThis action is intended to address the identified unsafe condition by preventing the possibility of mineral build-up on the APU and engine fire shutoff switches.\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 11 November 2004\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 1 December 2004.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The AD remains focused on the single safety issue identified in the Background: mineral build-up from specific humidifiers causing fire shutoff switch failures. The requirements (tests, replace-on-failure, fleet replacement, and rules tied to humidifier deactivation/reactivation) are all directed at correcting that condition. The text permits prior compliance under an earlier Boeing ASB but does not add requirements unrelated to the core unsafe condition. Therefore the measure has not grown significantly beyond its original safety purpose."},"complexity_factors":["Applicability limited to specific Boeing 747 variants listed in Boeing ASB 747-26A2274 Revision 1 (narrow scope reduces complexity).","Multiple distinct mandatory actions (Requirements 1–5) with different triggers (routine test, failed test, fleet replacement, humidifier deactivation/reactivation).","Several different compliance timeframes: 90 days, 18 months, 36 months, and 'before further flight' (nested timing rules increase reading complexity).","Conditionals tied to the operational status of specific Lucas humidifier part numbers (deactivated vs reactivated), creating branching compliance paths (Requirement 4 and 5).","Cross-references to an external technical document (Boeing ASB 747-26A2274 Revision 1) for procedural detail and to an FAA AD (Note), requiring readers to consult additional materials.","Allowance that earlier compliance under a prior ASB is acceptable (introduces backward-looking compliance recognition).","Technical term set (APU, fire shutoff switch, \"new or serviceable\") but few formal statutory definitions in the AD itself (moderate technical but limited legal drafting complexity)."],"plain_english_summary":"**What this directive does (in plain English)**\n\n- This is an Airworthiness Directive (a mandatory safety order for aircraft operators) that targets specific Boeing 747 variants (see \"Applicability\").\n- It requires operators to test and, where necessary, replace the auxiliary power unit (APU) and engine fire shutoff switches because mineral deposits from certain cabin humidifiers can form on the switch contacts and cause them to fail. A failed switch could prevent fire suppressant release and allow a fire to spread (Background).\n\n**Who it affects**\n\n- Owners and operators of the listed Boeing 747 models (747SP, 747-200B/C/F, 747-300, 747-400 series) named in the Boeing Alert Service Bulletin (ASB) referenced in the AD (Applicability).\n- Maintenance organisations and engineers who must perform the functional tests and replacements in accordance with Boeing ASB 747-26A2274 Revision 1 (Requirement 1–5).\n- Suppliers of replacement switches and parts that must provide \"new or serviceable\" units per the ASB (Requirements 2–4).\n\n**What must be done (mechanics of compliance)**\n\n- Functional test: Perform a functional test of the APU and engine fire shutoff switches in accordance with the Boeing ASB (Requirement 1).\n- Immediate replacement if failed: If any switch fails a functional test (either the periodic test or after humidifier reactivation), it must be replaced with a new or serviceable switch before further flight (Requirement 2).\n- Fleet replacement: Replace any switches that have not previously been replaced per Requirement 2 with new or serviceable switches within 36 months and then at 36‑month intervals (Requirement 3).\n- Humidifier deactivation/reactivation rules: If the listed Lucas humidifier part numbers are optionally deactivated, operators must replace all APU and engine fire shutoff switches immediately before further flight following that deactivation (Requirement 4). If one of those humidifiers is reactivated after the AD comes into force, the operator must do the functional test (Requirement 5.a) and replace switches per Requirement 3 (Requirement 5.b).\n- The AD requires that the work be done in accordance with Boeing ASB 747-26A2274 Revision 1. Actions done earlier under the original ASB dated 29 Aug 2002 are acceptable for compliance with the corresponding AD actions (last paragraph of Requirement).\n\n**When the tests and replacements must happen (summary of compliance timing)**\n\n- Functional test (Requirement 1): within the later of (a) 18 months after first Certificate of Airworthiness, or (b) 90 days after the AD's effective date; then repeat at intervals not exceeding 18 months unless the listed Lucas humidifiers are deactivated (Compliance).\n- Replacement after a failed test (Requirement 2): before further flight and then at intervals not exceeding 36 months unless the humidifier is deactivated (Compliance).\n- Replacement of all switches not previously replaced (Requirement 3): within 36 months after the AD effective date and then every 36 months unless the humidifier is deactivated (Compliance).\n- Replacement required immediately before further flight if a humidifier is deactivated after the AD takes effect (Requirement 4 — Compliance).\n- If humidifier is reactivated, the test and replacement cycles in Requirements 5.a and 5.b apply (Compliance).\n\n**Why CASA says it matters (purpose claim)**\n\n- CASA’s stated purpose is to prevent mineral build-up on switch contacts caused by humidified air from the listed Lucas humidifiers, which was identified as the source of earlier switch continuity failures discovered during maintenance. The mineral build-up could prevent the switches from discharging fire suppressant, increasing the risk of an uncontrolled fire spreading from engine/APU areas (Background).\n\n**Testing that purpose against incentives, costs and trade-offs**\n\n- Who pays: aircraft operators bear the direct cost — labour, parts (new or serviceable switches), aircraft downtime and scheduling to perform tests and replacements (Requirements 1–3; Compliance).\n- Incentives created: the AD explicitly links requirements to the presence or absence of specific humidifier units (Requirements 4 and 5). That creates an operational incentive for some operators to deactivate the listed humidifiers to reduce inspection frequency and replacement obligations (the AD reduces some recurring obligations when humidifiers are deactivated). Conversely, reactivation triggers tests and replacement obligations (Requirement 5 and Compliance). The directive therefore alters operators' cost–benefit when choosing whether to operate those humidifiers.\n- Compliance burden and implementation risk: the AD relies on operators and maintenance organisations to carry out periodic functional tests and to source \"new or serviceable\" switches per the Boeing ASB. This imposes logistics (parts availability), maintenance scheduling, and recordkeeping burdens. If replacement parts are scarce, this could extend aircraft downtime or create non‑compliance risk (Requirement 2; Requirement 3; Compliance).\n- Trade-offs and opportunity costs: operators must weigh passenger comfort and cabin environment (if humidifiers are in use) against maintenance costs and inspection frequency. Deactivating humidifiers reduces maintenance burdens but may affect cabin humidity control and related operational considerations.\n- Concentrated vs diffuse impacts: costs are concentrated on the operators of the listed Boeing 747 models and maintenance providers; the safety benefit (reduced risk of fire spread) is distributed across aircraft occupants and the flying public.\n- Reliance on external documents: the AD requires compliance with Boeing ASB 747-26A2274 Revision 1 and notes acceptability of actions done under the earlier ASB — meaning operators must follow a manufacturer document to satisfy the regulatory mandate. The AD also cross‑references FAA AD 2004-20-16 (Note).\n\n**Bottom line**\n\n- The directive mandates recurring functional testing and periodic replacement of APU and engine fire shutoff switches on certain Boeing 747s to eliminate mineral-deposit related failures attributed to specific Lucas humidifiers. Operators must follow the Boeing ASB, bear the costs of testing and replacement, and face operational choices about continuing to use the listed humidifiers (Requirements 1–5; Compliance; Background)."},"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"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope — addressing a specific unsafe condition (mineral deposits on fire shutoff switches) on specific Boeing 747 models. The various requirements and conditional timelines all serve this single safety purpose rather than expanding into broader operational or maintenance areas."},"complexity_factors":["Multiple interdependent requirements (Requirements 1-5) with cross-references between them (e.g., Requirement 5 references Requirements 1 and 3)","Conditional compliance timelines that vary based on aircraft history (Certificate of Airworthiness date vs. directive effective date)","Complex conditional logic around the Lucas humidifier status — different rules apply if it's active, deactivated, or reactivated","Variable recurring intervals (18 months vs 36 months) depending on which requirement and humidifier status","Reference to external technical document (Boeing ASB 747-26A2274 Revision 1) for actual implementation details — the AD doesn't specify the technical steps itself","Nested exceptions: the 'unless' clauses creating alternative compliance paths if humidifiers are deactivated"],"plain_english_summary":"This AD requires operators of specific Boeing 747 series to address mineral deposits from a Lucas flight-deck humidifier that can disable fire shutoff switches. It mandates recurring functional tests, prompt replacement of failed switches, and eventual replacement of all affected switches (with restart/test rules if the humidifier is reactivated), per Boeing ASB 747-26A2274.\n\nIt’s a life‑safety measure to ensure fire suppression will work in an engine/APU emergency."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-316-prevention-of-mineral-deposits-on-fire-shutoff-switches","history":"/api/acts/ad-b747-316-prevention-of-mineral-deposits-on-fire-shutoff-switches/history","analysis":"/api/acts/ad-b747-316-prevention-of-mineral-deposits-on-fire-shutoff-switches/analysis","conflicts":"/api/acts/ad-b747-316-prevention-of-mineral-deposits-on-fire-shutoff-switches/conflicts","importantCases":"/api/acts/ad-b747-316-prevention-of-mineral-deposits-on-fire-shutoff-switches/important-cases","documents":"/api/acts/ad-b747-316-prevention-of-mineral-deposits-on-fire-shutoff-switches/documents"}}