{"id":"F2009L03830","name":"AD/DHC-8/120 Amdt 1 - Power Transfer Unit Overspeed","slug":"ad-dhc-8-120-amdt-1-power-transfer-unit-overspeed","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":81067,"registerId":"commonwealth-F2009L03830-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Bombardier (Boeing Canada/De Havilland) ","sectionType":"division","heading":"Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes","content":"### Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes\n\n| AD/DHC-8/120 Amdt 1 | Power Transfer Unit Overspeed | 12/2009 |\n| ------------------- | ----------------------------- | ------- |\n\n| Applicability: | Bombardier Inc. Models DHC-8-400, DHC-8-401 and DHC-8-402, Serial Numbers (S/N) 4001, 4003, 4004, 4006 and 4008 through 4184. |\n| -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement: | 1. Amend the Aeroplane Flight Manual (AFM), PSM 1-84-IA, by inserting Temporary Amendment (TA) No. 13, dated 14 July 2005, or later approved changes to this AFM temporary amendment.2. Advise all flight crew of the changes introduced by the AFM temporary amendment.Note 1: Aircraft S/N 4185 and subsequent have been removed from the applicability of this AD since an equivalent PTU control logic modification (consisting of both (a) Modsum 4-126354 and (b) Modsum 4-901472 or Modsum 4-901473) has been installed in production. As a result, it is permissible to amend AFM PSM 1-84-1A by removing TA No.13 for these specific aircraft S/Ns.3. Modify/rework the PTU control logic by incorporating Modsum 4-126425. Bombardier Service Bulletin (SB) 84-29-22, Revision A, dated 24 February 2009, or later revisions approved by the Chief, Continuing Airworthiness, Aircraft Certification, Transport Canada, provides approved instruction for incorporating Modsum 4-126425.Note 2: For Bombardier Inc. Models DHC-8-400, DHC-8-401 and DHC-8-402 Aircraft, SNs 4001, 4003, 4004, 4006 and 4008 through 4094, accomplishment in accordance with the original issue of Bombardier SB 84-29-22, dated 5 December 2008, also meets the intent of Requirement 2 of this AD.4. Amend AFM PSM 1-84-1A by removing TA No.13.Note 3: Transport Canada AD CF-2006-08R1 dated 31 August 2009 refers. |\n| Compliance: | For Requirements 1 and 2 - Remains unchanged as detailed in the original issue of this AD as: Within 14 days after the 31 May 2006 (the effective date of the original issue of this AD), unless previously accomplished. |\n\n| | For Requirement 3 - Within 6,000 flight hours of the effective date of this AD, unless previously accomplished.For Requirement 4 - Upon completion of SB 84-29-22, initial issue, dated5 December 2008, Revision A, or later revision approved by the Chief, Transport Canada. |\n| ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| | This Amendment becomes effective on 19 November 2009. |\n| Background: | Several cases have been reported where a loss of fluid in the No.2 hydraulic system has caused the power transfer unit (PTU) to over speed, resulting in pressure fluctuations and increased fluid flow within the No.1 hydraulic system. In one case, the hydraulic system control logic did not shut down the PTU and the over speed condition persisted, resulting in the illumination of the No.1 HYD FLUID HOT caution light.As an interim action to avoid possible loss of both the No.1 and No.2 hydraulic systems, the AFM has been revised to include pulling the HYD PWR XFER circuit breaker in the event of the loss of all hydraulic fluid in the No.2 hydraulic system.Amendment 1 of this AD mandates modification of the PTU control logic, including the provision of automatic PTU shutdown in the event of loss of fluid in the No. 2 hydraulic system. In addition, the applicability of the AD has been revised to remove aircraft S/N 4185 and subsequent, since an equivalent modification has been installed in production on these aircraft.The original issue of this AD became effective on 31 May 2006. |\n\n![](image.001.png) \nDavid Villiers \nDelegate of the Civil Aviation Safety Authority\n\n28 September 2009","sortOrder":0},{"sectionNumber":"AD/DHC-8/120 Amdt 1","sectionType":"part","heading":"AD/DHC-8/120 Amdt 1","content":"## AD/DHC-8/120 Amdt 1","sortOrder":1},{"sectionNumber":"Power Transfer Unit Overspeed","sectionType":"part","heading":"Power Transfer Unit Overspeed","content":"## Power Transfer Unit Overspeed","sortOrder":2},{"sectionNumber":"12/2009","sectionType":"part","heading":"12/2009","content":"## 12/2009","sortOrder":3}],"analysis":{"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"},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"Amendment 1 expands the original AD by mandating a permanent PTU control-logic modification (Modsum 4-126425) that provides automatic PTU shutdown on loss of No.2 hydraulic fluid, and it narrows applicability by removing aircraft S/N 4185 and subsequent because those aircraft already have an equivalent production modification. It also formalises AFM temporary-amendment procedures and links compliance to approved revisions of Bombardier SB 84-29-22."},"complexity_factors":["Technical modification to PTU control logic (Modsum 4-126425) requiring engineering/maintenance work and verification.","Multiple operator actions: AFM amendment insertion and later removal, flight crew notification, and physical system modification.","Staggered compliance timeframes (14 days for AFM/crew brief; 6,000 flight hours for control logic mod) increasing scheduling complexity.","Applicability carved by specific serial numbers; later S/Ns (4185 onward) excluded because production aircraft have equivalent mod — requires tracking serial-numbered fleet status.","Dependency on supplier service bulletins and regulatory approval: Bombardier SB 84-29-22 revisions must be approved by the Chief, Continuing Airworthiness, Aircraft Certification, Transport Canada.","Recordkeeping and procedural changes for operators: AFM temporary amendment insertion/removal and crew training create administrative burden.","Safety risk mitigation relies on correct installation and software/logic behaviour; residual implementation risk if modification or SB compliance is incomplete."],"plain_english_summary":"Requires operators of specified Bombardier DHC‑8‑400 series aeroplanes to amend the Aeroplane Flight Manual, brief flight crew, and modify the Power Transfer Unit (PTU) control logic so the PTU will automatically shut down if hydraulic fluid is lost from the No.2 system. The amendment also narrows applicability by excluding aircraft serial numbers 4185 and later that already have the production modification. It matters because it creates definite maintenance, training and compliance costs and sets firm deadlines for operators."},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This Amendment 1 remains tightly focused on the original safety issue (PTU overspeed). It adds the permanent hardware modification that was always intended as the final solution, and narrows applicability by excluding newer aircraft that already have the fix. This represents the natural progression of an AD from interim to final action, not scope creep."},"complexity_factors":["Multiple serial number ranges with different applicability rules (S/N 4001, 4003, 4004, 4006, 4008-4184 exempted vs 4185+)","Four distinct requirements with different compliance deadlines and dependencies","Cross-references to external documents: Bombardier Service Bulletin 84-29-22 (with revision levels), Transport Canada AD CF-2006-08R1, and specific Modsum numbers (4-126354, 4-901472, 4-901473, 4-126425)","Conditional logic: Requirement 4 compliance depends on completion of Requirement 3; Note 2 creates an alternative compliance path for specific serial numbers","Technical aviation terminology requiring domain knowledge (PTU, Modsum, AFM temporary amendments)","Amendment structure creates layered effective dates (original AD 31 May 2006, this Amendment 1 effective 19 November 2009)"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators of specified Bombardier DHC-8-400 series aircraft (S/N 4001, 4003, 4004, 4006, 4008–4184; newer S/N ≥4185 are exempt) to address a PTU overspeed fault that can occur after loss of No.2 hydraulic fluid and risk dual hydraulic failure.\n\nIt mandates an immediate temporary flight manual change and pilot brief (pull a circuit breaker) within 14 days, and installation of a permanent hardware Modsum 4-126425 within 6,000 flight hours, after which the temporary procedure is removed."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-8-120-amdt-1-power-transfer-unit-overspeed","history":"/api/acts/ad-dhc-8-120-amdt-1-power-transfer-unit-overspeed/history","analysis":"/api/acts/ad-dhc-8-120-amdt-1-power-transfer-unit-overspeed/analysis","conflicts":"/api/acts/ad-dhc-8-120-amdt-1-power-transfer-unit-overspeed/conflicts","importantCases":"/api/acts/ad-dhc-8-120-amdt-1-power-transfer-unit-overspeed/important-cases","documents":"/api/acts/ad-dhc-8-120-amdt-1-power-transfer-unit-overspeed/documents"}}