{"id":"F2006B09184","name":"AD/DHC-8/29 - Anti-Collision Strobe Light Power Supplies","slug":"ad-dhc-8-29-anti-collision-strobe-light-power-supplies","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":52963,"registerId":"commonwealth-F2006B09184-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-8/29 - Anti-Collision Strobe Light Power Supplies","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)  \nBombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes\n\nAD/DHC-8/29 Anti-Collision Strobe Light Power Supplies 11/93\n\nDM\n\nApplicability: DHC-8 Series 100 and 300 aircraft with serial numbers 3 through 214 inclusive, which do not have Modification 8/1273 incorporated.\n\nRequirement: 1. Action in accordance with Part B of the Accomplishment Instructions Bombardier Regional Aircraft Division de Havilland Dash 8 Alert Service Bulletin A8-33-33 dated 31 May 1993.\n\n    2. Incorporate Modification 8/1273 in accordance with Bombardier Regional Aircraft Division de Havilland Dash 8 Service Bulletin 8-33-19 Revision A dated 31 May 1993.\n\nNote: Transport Canada AD CF-93-20 dated 3 August 1993 refers.\n\nCompliance: 1. Prior to further flight after 6 September 1993 if any of the following faults have been experienced:\n\n    With landing gear up and locked, one or more of the landing gear green locked down advisory lights illuminate continuously or intermittently.\n\n    b. With landing gear down and locked prior to or after landing, one or more of the green locked down advisory lights illuminate intermittently.\n\n    c. The above indications may also be accompanied by one or more of the following:\n\n    (i) Continuous or intermittent illumination of the gear selector lever advisory light.\n\n    (ii) Continuous or intermittent illumination of one or more of the red gear unsafe advisory lights.\n\n    (iii) Fluctuation of the cabin pressurisation rate needle.\n\n    2. Prior to 31 March 1994.\n\nNote: Incorporation of Modification 8/1273 is considered termination for the maintenance actions specified by Requirement 1.\n\nBackground: The aircraft manufacturer has received reports indicating that the white anti-collision light power supply units (pre-modification 8/1273) may develop a fault which produces a strong parasitic electromagnetic emission. This emission, when coupled into the wiring of the proximity switch electronics unit (PSEU), can adversely affect operation of associated systems as follows:\n\n    flashing of the landing gear locked down advisory lights during cruise,\n\n    b. fluctuation of cabin pressurisation rate needle during cruise,\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n    c. retraction and extension of roll and ground spoilers during ground operation,\n\n    d. nose gear steering inoperative after landing, and\n\n    e. normal wheel brakes not available below 35-40 knots.\n\nCompliance with this Directive will alleviate the possibility of electromagnetic interference causing incorrect operation of the PSEU.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive is tightly targeted at a specific technical fault: electromagnetic emissions from pre‑modification strobe light power supplies affecting the Proximity Switch Electronics Unit and related systems. The actions required (fault-driven maintenance and a retrofit modification) are proportionate to that technical problem. There is no sign in the text that the instrument expanded beyond that original technical purpose — it prescribes remedial inspections and a definitive design change and includes a deadline and termination condition. Therefore the scope has not materially grown beyond the original safety-fix intent described in the Background."},"complexity_factors":["Short, focused Airworthiness Directive with narrow applicability (DHC-8 Series 100 & 300, serials 3–214)","Two mandatory actions only: (1) fault-driven maintenance per Alert Service Bulletin A8-33-33 Part B; (2) retrofit Modification 8/1273 per Service Bulletin 8-33-19 Rev A","Conditional compliance windows: immediate action required if specified faults observed (before next flight after 6 Sep 1993); universal retrofit deadline (31 Mar 1994)","Cross-references to two external Bombardier service documents and one foreign AD (Transport Canada AD CF-93-20)","Defined technical terms and components (e.g. PSEU, strobe light power supply, parasitic electromagnetic emission) create some technical interpretation needs for maintainers","Termination clause linking mandatory maintenance to retrofit (incorporation of Mod 8/1273 terminates Requirement 1)"],"plain_english_summary":"**What this instrument does (mechanics)\n\n- Applies to: De Havilland (Bombardier) DHC-8 Series 100 and 300 aeroplanes, serial numbers 3 through 214, that have not already had Modification 8/1273 fitted. (See \"Applicability\".)\n\n- Requires two things for affected aeroplanes:\n  - Requirement 1: Carry out the maintenance actions set out in Part B of Bombardier Alert Service Bulletin A8-33-33 (31 May 1993). These are inspections/maintenance steps to address symptoms that indicate a fault. (The Alert SB is the technical instruction referenced by the Directive.)\n  - Requirement 2: Incorporate Modification 8/1273 by following Bombardier Service Bulletin 8-33-19 Revision A (31 May 1993). Fitting this modification removes the need for the repetitive maintenance actions in Requirement 1.\n\n- When to comply (deadlines):\n  - If certain operational faults are observed (see list below), the maintenance actions in Requirement 1 must be done before the next flight after 6 September 1993. Those faults include, for example, landing-gear green advisory lights flashing in cruise, intermittent green lights when gear is down, illumination of other gear advisory lights, or fluctuation of the cabin pressurisation rate needle.\n  - In any case, Modification 8/1273 must be incorporated by 31 March 1994.\n\n- Safety rationale (background): The manufacturer reported that the white anti-collision strobe light power supply units (pre-modification 8/1273) can develop a fault producing strong parasitic electromagnetic emissions. Those emissions can couple into the wiring of the Proximity Switch Electronics Unit (PSEU) and cause incorrect operation of several systems (examples listed below). The Directive says complying will reduce the risk of electromagnetic interference (EMI) causing incorrect PSEU operation.\n\nWho is affected\n\n- Aircraft owners/operators of the specified DHC-8 Series 100 and 300 aeroplanes (serials 3–214) that have not already installed Modification 8/1273.\n- Maintenance organisations and engineers who must perform the inspections, repairs or the modification in accordance with the referenced Bombardier service/alert bulletins.\n\nWhy it matters (concrete effects and risks)\n\n- The Directive addresses an electromagnetic interference (EMI) fault originating in a strobe-light power supply. The manufacturer linked that EMI to incorrect indications and loss of normal function in systems linked to the PSEU. The listed potential effects include:\n  - flashing of landing-gear \"green locked down\" advisory lights during cruise;\n  - fluctuation of the cabin pressurisation rate needle during cruise;\n  - ground-only retraction/extension of roll and ground spoilers;\n  - nose gear steering inoperative after landing;\n  - normal wheel brakes not available below 35–40 knots.\n\n- Mechanically, the AD forces operators either to perform immediate fault-driven maintenance (Requirement 1) or to install a design modification (Requirement 2) by a set date. Installing the modification ends the ongoing maintenance obligation.\n\nCosts, incentives, trade-offs and implementation considerations\n\n- Who pays: aircraft owners/operators bear the direct costs (parts, labour, aircraft downtime) of inspections, corrective work and the retrofit modification. Maintenance organisations perform the work under contract and charge labour and parts.\n\n- Who decides: the Civil Aviation Safety Authority (via the Airworthiness Directive) requires compliance; operators decide scheduling and which approved maintenance organisation will perform the work, provided the work follows the referenced Bombardier service documents.\n\n- Behaviour changes required: operators must (a) act immediately to perform the diagnostic/maintenance actions if the listed faults occur, and (b) schedule and fit Modification 8/1273 by the specified calendar date. Once the modification is fitted, the recurring maintenance requirement in Requirement 1 is terminated.\n\n- Compliance burden: the AD cross-references two Bombardier technical documents; operators must obtain and follow those documents. The burden includes cost of parts for the modification, labour and aircraft out-of-service time. The AD does not specify cost or exact labour hours — those are in the service bulletins and commercial quotes.\n\n- Implementation risk and practical trade-offs: scheduling the modification may cause aircraft downtime and affect operations; immediate inspections required by observable faults can ground an aircraft until resolved (the AD requires action before next flight if faults are seen). There is a potential operational substitution effect: operators might prefer to retrofit all affected aeroplanes quickly to avoid recurring inspections.\n\n- Effects on maintenance providers and market for spares: the AD creates short-term demand for the modification parts and authorised engineering capacity. Independent approved maintenance organisations can perform the work if they follow the service instructions and have necessary approvals; the AD itself does not restrict who may perform the work beyond existing maintenance approval frameworks.\n\n- Enforcement and termination: incorporation of Modification 8/1273 is expressly stated to terminate the maintenance actions required by Requirement 1.\n\nSource claims and testing them against costs and incentives\n\n- The instrument claims (in Background) that a fault in pre‑mod power supplies can create strong parasitic electromagnetic emissions that upset the PSEU and associated systems (paragraphs under \"Background\"). That claim justifies both immediate fault-driven action and a retrofit modification. The costs implied by that choice are (a) short-term inspections/repairs when faults occur, and (b) the one-off retrofit cost and downtime for the modification. The Directive trades those operator costs against the safety benefit of removing an EMI source that can cause erroneous system behaviour.\n\n- The AD centralises the safety decision: CASA mandates the technical solution by referencing the manufacturer service bulletins rather than prescribing alternative fixes. That directs operators toward the manufacturer-designed modification, concentrating demand for parts and certified labour on suppliers that can carry out the service to the required standard.\n\nBottom line\n\n- If you operate one of the affected DHC-8 aircraft without Modification 8/1273, you must perform specified maintenance immediately if the listed faults occur and must fit the modification by the deadline. The measure aims to remove an EMI source that has been reported to cause incorrect operation of PSEU-linked systems. The direct costs fall on operators and their maintenance providers; fitting the modification ends the need for the recurring maintenance actions called for when faults are seen."},"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":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope. It addresses a specific electromagnetic interference issue identified by the manufacturer and remains tightly focused on the strobe light power supply fault and its cascading effects on the proximity switch electronics unit. There is no evidence of scope creep; the directive does not expand into unrelated systems or impose broader operational restrictions beyond the specific technical fix required."},"complexity_factors":["Single, specific technical subject matter (strobe light power supplies)","Limited applicability (specific aircraft series and serial number range)","Clear two-part compliance structure with specific deadlines","References to external technical documents (Service Bulletins) rather than reproducing complex procedures inline","Straightforward conditional logic (if symptoms present → immediate action; all aircraft → deadline action)","Minimal defined terms (only standard aviation abbreviations like PSEU)","Single termination condition (Modification 8/1273 installation)"],"plain_english_summary":"This Airworthiness Directive orders operators of Bombardier DHC‑8 Series 100 and 300 aircraft (serials 3–214, unless fitted with Modification 8/1273) to remedy a faulty anti‑collision strobe power supply that can emit electromagnetic interference and trigger false warnings, pressure swings, loss of steering/brakes, or unintended spoiler deployment. Aircraft showing symptoms are grounded until repaired, and all affected planes must be corrected by 31 March 1994 to prevent runway/landing hazards."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-8-29-anti-collision-strobe-light-power-supplies","history":"/api/acts/ad-dhc-8-29-anti-collision-strobe-light-power-supplies/history","analysis":"/api/acts/ad-dhc-8-29-anti-collision-strobe-light-power-supplies/analysis","conflicts":"/api/acts/ad-dhc-8-29-anti-collision-strobe-light-power-supplies/conflicts","importantCases":"/api/acts/ad-dhc-8-29-anti-collision-strobe-light-power-supplies/important-cases","documents":"/api/acts/ad-dhc-8-29-anti-collision-strobe-light-power-supplies/documents"}}