{"id":"F2006B02503","name":"AD/AS 355/49 - Single-Pole Circuit Breakers","slug":"ad-as-355-49-single-pole-circuit-breakers","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41759,"registerId":"commonwealth-F2006B02503-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AS 355/49 - Single-Pole Circuit Breakers","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)  \nEurocopter AS 355 (Twin Ecureuil) Series Helicopters\n\nAD/AS 355/49 Single-Pole Circuit Breakers 3/99\n\nApplicability: Model AS 355 helicopters, versions E, F, F1, F2 and N equipped with the following single-pole circuit breakers manufactured by Crouzet:\n\n| Location                                       | Rating  | Part Number |\n| ---------------------------------------------- | ------- | ----------- |\n| Emergency Flotation Gear Optional Installation | 5 Amp   | 84 400 032  |\n|                                                | 10 Amp  | 84 400 034  |\n| Other Optional Installations                   | 1 Amp   | 84 400 028  |\n|                                                | 3 Amp   | 84 400 031  |\n|                                                | 7.5 Amp | 84 400 033  |\n|                                                | 15 Amp  | 84 400 035  |\n|                                                | 20 Amp  | 84 400 036  |\n\nTwo types of Crouzet circuit breakers may have been delivered under Eurocopter Part Number (P/N) 704A36-6120-XXX (X indicates any digit). These circuit breakers are either P/N 84 400 XXX or SP4696-XX. This Directive is only applicable to P/N 84 400 XXX circuit breakers.\n\nNote 1: The circuit breakers are known to be installed on helicopters delivered between 24 April 1995 and 31 August 1996. The circuit breakers may also be installed on helicopters delivered prior to 24 April 1995 or after 31 August 1996 if circuit breakers have been replaced on optional installations since 24 April 1995 or if an optional installation was fitted between 24 April 1995 and 31 August 1996.\n\nRequirement: 1. Check the functioning of all circuit breakers, listed in the above table, that are fitted to installations listed in paragraph 1D1 of Eurocopter AS 355 Mandatory Service Bulletin (SB) 01.00.44 date code 98-47.\n\n    2. Apply the procedures detailed in paragraph 2B of the SB to all the circuit breakers for the remaining installations.\n\n    3. Test each circuit breaker held as spares that has a part number listed in this airworthiness directive by applying a torque load and checking the circuit breaker in accordance with the directions given in paragraphs 2B(1) and 2B(2) of the SB.\n\n    4. The use of circuit breakers bearing the part numbers listed in this Airworthiness Directive is prohibited.\n\nNote: DCAG AD 98-510-055(A) refers.\n\nCompliance: 1. Within 200 hours time in service but no later than 26 June 1999.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n    2. Prior to 1 January 2000.\n\n    3. Prior to installation.\n\n    4. From 31 December 1999.\n\nThis Airworthiness Directive becomes effective on 25 March 1999.\n\nBackground: This AD is issued to check for any loss of electrical continuity for single-pole circuit breakers bearing the part numbers listed. During testing by the OEM a loss of electrical continuity was discovered between the terminals of the circuit breaker in the engaged position. This loss was found to be due to deterioration of the circuit breaker operation brought about by excessive torque loading during installation.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive addresses a specific manufacturing/installation defect (loss of continuity caused by excessive torque) in a narrowly defined set of circuit breakers and prescribes inspection, testing and a ban on future use of those listed part numbers. The measures (inspect installed units, test spares, and prohibit the parts) are consistent with the original safety‑remedial purpose; the AD does not materially expand beyond fixing that defect. The only scope extension is a pragmatic applicability note that reaches circuit breakers replaced or fitted inside a specified date window even if the helicopter’s delivery date falls outside that window — this broadens which aircraft are covered but does so to capture affected installations rather than to change the AD’s fundamental purpose."},"complexity_factors":["Single narrow subject (single‑pole circuit breakers) with explicit part numbers (7 listed 84 400 XXX part numbers).","Cross‑reference to one Mandatory Service Bulletin (Eurocopter SB 01.00.44) for procedural detail rather than embedding test procedures in the AD (dependency on external doc).","Applicability includes model list (AS 355 E/F/F1/F2/N) and date‑range notes creating limited extension beyond initial delivery window (adds conditional applicability).","Multiple discrete actions with clear sequencing: inspect installed units, apply SB procedures to remaining installations, test spares, and prohibit future use (4 numbered requirements).","Several separate compliance deadlines (within 200 hours but no later than 26 June 1999; prior to 1 January 2000; prior to installation; prohibition from 31 December 1999) introduce calendar/time‑in‑service conditions.","Reference to an alternative Crouzet part number (SP4696‑XX) and a Eurocopter P/N (704A36‑6120‑XXX) with a clarifying exclusion (only 84 400 XXX are covered) — a small additional interpretive step for maintainers.","Relies on OEM testing findings (Background) — factual but requires implementers to accept OEM causation for the required remedial steps."],"plain_english_summary":"**What this directive does (mechanically)**\n\n- Requires owners/operators of certain Eurocopter AS 355 models (E, F, F1, F2 and N) that have specific single‑pole Crouzet circuit breakers (part numbers 84 400 028, 84 400 031, 84 400 032, 84 400 033, 84 400 034, 84 400 035, 84 400 036) to inspect and test those breakers, test any spares, and stop using those part numbers. (Applicability; Requirement 1–4.)\n\n- Directs operators to follow the detailed test and inspection procedures set out in Eurocopter Mandatory Service Bulletin SB 01.00.44 (paragraphs cited in the AD). That includes a functional check of installed breakers, torque‑load and continuity tests for spares, and application of the SB’s step‑by‑step method for remaining installations. (Requirement 1–3.)\n\n- Prohibits use or installation of circuit breakers bearing the listed 84 400 XXX part numbers from 31 December 1999 onward. (Requirement 4; Compliance.)\n\n**Who this affects**\n\n- Aircraft owners/operators of Eurocopter AS 355 series (E, F, F1, F2, N) fitted with the specified Crouzet single‑pole circuit breakers.\n- Maintenance organisations and engineers who perform inspections, testing, and installations on those helicopters.\n- Parts suppliers and logistics managers responsible for spares inventory, because spares with the listed part numbers must be tested before use and then are banned from future installation.\n- The Civil Aviation Safety Authority (CASA) as the enforcing authority for compliance.\n\n**Why it matters (safety and mechanical risk)**\n\n- The manufacturer found that some of these Crouzet circuit breakers can lose electrical continuity in the engaged position due to deterioration caused by excessive torque during installation. A loss of continuity means an electrical circuit can open unexpectedly, which can disable systems that rely on that breaker.\n- The AD’s mechanical effect is to detect affected units (through inspection and tests) and to remove the listed part numbers from service to prevent recurrence. (Background; Requirement.)\n\n**Who pays, who decides, and what behaviour changes**\n\n- Owners/operators pay for the inspections, testing, any replacement parts and associated aircraft downtime. Maintenance organisations will charge for labour and testing equipment use.\n- Maintenance organisations and the operator decide how to schedule inspections and replacements, but they must use the test procedures in SB 01.00.44 to comply. CASA enforces compliance with the AD’s deadlines. (Requirement; Compliance.)\n- Behaviour changes: maintenance staff must perform functional checks on installed breakers within the specified time window, perform torque/load and continuity tests on spares before use, and cease installing the banned part numbers after the prohibition date.\n\n**Costs, incentives, trade‑offs and implementation issues**\n\n- Direct costs: labour for inspection/testing, potential replacement breakers (purchase and inventory write‑offs for banned spares), and aircraft downtime while work is done. These are borne by operators.\n- Incentives: operators have a safety and regulatory incentive to replace suspect parts promptly; suppliers of compliant replacement breakers benefit from increased demand. Maintenance providers may see higher billable work in the short term.\n- Trade‑offs: the AD prioritises electrical reliability and safety over the short‑term cost of inspections/replacements. Operators face an opportunity cost in maintenance scheduling and asset availability.\n- Implementation risks: if replacement breakers are scarce or records of prior replacements are incomplete, operators may face delays or uncertain applicability (the AD covers breakers delivered or fitted during a defined date range but also reaches units replaced later). The AD cross‑references the Eurocopter Service Bulletin, so correct application depends on access to and correct interpretation of that SB.\n- Compliance burden: moderate — the directive lists specific part numbers and directs use of a single SB for procedures, but requires testing of installed units and spares and removal of the parts from future use.\n\n**Concentrated benefits and diffuse costs**\n\n- Concentrated benefit: suppliers/manufacturers of approved replacement breakers and maintenance providers that perform the corrective work will gain business. \n- Diffuse cost: many operators share the cost of inspections, testing and replacements, and incur aircraft downtime.\n\n(References in the AD: Applicability; Requirement paragraphs 1–4; Compliance dates; 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":3,"scope_assessment":{"changed":false,"description":"This is a targeted safety directive addressing a specific technical defect in identified aircraft components. The scope remains precisely focused on the circuit breaker fault discovered during OEM testing, with no evidence of scope creep beyond the original safety issue."},"complexity_factors":["Multiple compliance deadlines (4 separate timelines for different actions)","Cross-reference to external technical document (Eurocopter Service Bulletin 01.00.44) without reproducing its contents","Specific part number identification requiring technical knowledge to locate components","Conditional applicability based on manufacturing dates and replacement history","Reference to foreign airworthiness directive (DCAG AD 98-510-055(A)) without explanation"],"plain_english_summary":"This CASA Airworthiness Directive orders owners/operators of Eurocopter AS 355 E/F/F1/F2/N helicopters fitted with certain Crouzet single‑pole circuit breakers (part numbers beginning 84 400) to inspect, test, or replace them because they can fail to conduct when switched on—risking critical systems like emergency flotation. Initial checks and tests are required promptly, spares must be tested before installation, and use of the affected breakers is banned after 31 December 1999 (replacement completed by 1 January 2000)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-as-355-49-single-pole-circuit-breakers","history":"/api/acts/ad-as-355-49-single-pole-circuit-breakers/history","analysis":"/api/acts/ad-as-355-49-single-pole-circuit-breakers/analysis","conflicts":"/api/acts/ad-as-355-49-single-pole-circuit-breakers/conflicts","importantCases":"/api/acts/ad-as-355-49-single-pole-circuit-breakers/important-cases","documents":"/api/acts/ad-as-355-49-single-pole-circuit-breakers/documents"}}