{"id":"F2006B09238","name":"AD/DHC-8/8 Amdt 4 - Flap Drive and Torque Sensing Systems","slug":"ad-dhc-8-8-amdt-4-flap-drive-and-torque-sensing-systems","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":53135,"registerId":"commonwealth-F2006B09238-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-8/8 Amdt 4 - Flap Drive and Torque Sensing Systems","content":"![](image.001.png)  \nBombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes\n\nAD/DHC-8/8\n\nAmdt 4\n\n  \nFlap Drive and Torque Sensing Systems 11/94\n\nApplicability: Model DHC-8 series, serial numbers 3 and subsequent, as indicated.\n\nRequirement: Part I. For aircraft serial numbers 3 through 177, and serial numbers 178 through 231, 233, 235, 237, and 243:\n\n    (a) Locate flap primary-drive torque tubes having part numbers and serial numbers listed in revised table 1 below:\n\nTABLE 1\n\nTORQUE TUBE P/N SERIES TORQUE TUBE S/N\n\n734187 125 through 171\n\n734378 129 through 150\n\n734380 127 through 166\n\n734382 211 through 322\n\n734384 153 through 188 and 226 through 235\n\n734386 195 through 286\n\n734388 160 through 177\n\n    (b) Determine whether torque tubes located by 1.(a) above have been re-identified with the service bulletin number indicated in Table 2 below.\n\nNote: For re-identification, the applicable service bulletin number may have been marked on the rod with indelible ink or on the identification plate adjacent to the part number.\n\n    (i) Torque tubes found to have been re-identified with the applicable service bulletin number do not require further action per Part 1 of this Directive.\n\n    (ii) Torque tubes not re-identified with the applicable service bulletin number must be inspected and reworked as required by Part I, Requirements 1(c) and (d), and 2 below.\n\n    (c) On the torque tubes located per Requirement 1.(b)(ii) above, remove the through bolt from the splined coupling(s) of each torque tube and, using a 10x magnifying glass, visually inspect the area around all holes for cracks.\n\nNote: Some torque tubes have one splined coupling, while others have two. If a splined coupling is found cracked, accomplish one of the following steps before further flight:\n\n    (i) Replace the splined coupling(s) in accordance with the accomplishment instructions in the appropriate Sundstrand service bulletin (see Table 2). Re-identify the torque tubes as indicated in the service bulletins.\n\nMarking the service bulletin number on the rod with indelible ink will satisfy this requirement; or,\n\n    (ii) Replace the particular torque tube with a serviceable unit.\n\n|                        | TABLE 2                 |                         |\n| ---------------------- | ----------------------- | ----------------------- |\n| Torque Tube P/N Series | Sunstrand SB NO         | Post-Mod Identification |\n| 734187                 | 734187-27-A2 Revision 1 | 27-A2                   |\n| 734378                 | 734378-27-A3 Revision 1 | 27-A3                   |\n| 734380                 | 734380-27-A2 Revision 1 | 27-A2                   |\n| 734382                 | 734380-27-A3 Revision 1 | 27-A3                   |\n| 734384                 | 734384-27-A2 Revision 1 | 27-A2                   |\n| 734386                 | 734386-27-A2 Revision 1 | 27-A2                   |\n| 734388                 | 734388-27-A1 Revision 1 | 27-A1                   |\n\n    (d) Upon reassembly, install the through bolt and torque to between 20 and 25 in- lb.\n\n    2. Unless already accomplished per Part I, Requirement 1.(c); replace all splined couplings on torque tubes located per Part I, Requirement 1.(b)(ii) above, in accordance with the accomplishment instructions in the appropriate Sundstrand service bulletin (Table 2). Re-identify the torque tubes as indicated in the service bulletins. Marking the service bulletin number on the rod with indelible ink will satisfy this requirement.\n\nPart II. For aircraft serial numbers 3 through 293:\n\n    Accomplish the following visual inspection of the flap primary-drive torque tube system and the flap secondary-drive flex shaft system:\n\n    (a) Extend flaps fully.\n\n    (b) Visually inspect the flap primary-drive torque tubes over their entire length for fracture, rubbing and wear.\n\n    (c) Torque tubes must be replaced before further flight if wear exceeds 0.25mm (0.010 inch) in depth or is present over more than 180 degrees around the circumference of the shafts.\n\n    (d) Visually inspect the flap secondary-drive flex drive for permanent deformation (kinks), or evidence of excessive heat (blueing of outer braided sheath, melting of outer plastic sheath, loss of blue anodic film on the casing ferrules).\n\n    (e) Damaged flex shafts must be replaced with serviceable flex shafts before further flight.\n\n    2. Accomplish the following:\n\n    (a) Perform an operational check of the torque sensor as per maintenance program task 2750/11. Refer to DASH 8 Maintenance Program Supplementary Information, PSM 1-8-7/1-83-7, Volume 2, Procedures-27.\n\n    (b) Any torque sensor found malfunctioning or jammed must be replaced with a serviceable unit before further flight.\n\nNote: The inspections required by Part II, Requirements 1 and 2 above may be terminated on aircraft that have complied with Part III of this Directive and which have incorporated both of the Boeing Canada/de Havilland modifications listed below:\n\n    (i) Modification No. 8/1473, Service Bulletin No. 8-54-16, ‘Nacelles \\- Flap Torque Tube - Introduction of Torque Tube Guard’.\n\n    (ii) Modification No. 8/0803, Service Bulletin No. 8-27-47, ‘Flight Controls \\- Flap Power Drive Unit - Replacement of Flow Regulator Valve’.\n\nPart III. For aircraft serial numbers 3 through 293:\n\nModify the wing flap system torque sensor in accordance with Boeing Canada/de Havilland Service Bulletin No. 8-27-61.\n\nNote: Transport Canada AD CF-89-09R4 refers.\n\nCompliance: Part I:\n\n    For aircraft serial numbers 3 through 177; within 300 hours time in service after 15 October 1992.\n\nFor aircraft serial numbers 178 through 231, 233, 235, 237 and 243; unless already accomplished, within 300 hours time in service after 13 October 1994.\n\n    2. Within 900 hours time in service after 15 October 1992\\. Part II:\n\n    Within 300 hours time in service after 19 April 1990 (the compliance date of the previous issue of this Directive), and thereafter at intervals not to exceed 300 hours time in service.\n\n    2. Within 600 hours time in service after 19 April 1990 (the compliance date of the previous issue of this Directive), and thereafter at intervals not to exceed 1200 hours time in service.\n\nPart III:\n\nWithin 2000 hours time in service or 9 months after 15 October 1992, whichever occurs first.\n\nThe compliance of the previous issue of this Directive remains unchanged except for the additional aircraft now included in Requirement Part I.\n\nThis Amendment is effective from 13 October 1994.\n\nBackground: There had been an incident of asymmetric flap where the caution light did not illuminate and the flap indicator remained at zero degrees. Investigation revealed that the primary drive shaft between the two port flaps and the splined coupling between the flap power unit and the starboard primary drive shaft had broken. Further, a secondary drive sensor failed to detect the shaft failure. A further investigation revealed that early serial number splined couplings received inadequate heat treatment. Amendment 1 required replacement of early couplings, a repetitive visual inspection of the flap systems, and an operational check of the torque sensor system.\n\nAmendment 2 extended the serial number range of torque tubes having had inadequate design and heat treatment, required modification of the wing flap system torque sensor, and required terminating action for the on-going repetitive inspections. Amendment 3 corrected a serial number error in Table 1.\n\nAmendment 4 is issued in response to a revision of the relevant Transport Canada AD which extends the serial number range of aircraft which require the inspections and possible replacement of splined torque tube couplings in accordance with Requirement Part I.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":7,"scope_assessment":{"changed":true,"description":"Amendment 4 extends the serial‑number range of aircraft and torque tubes subject to Part I inspections and possible splined‑coupling replacement (per Background and Part I applicability). It leaves prior compliance for already‑covered aircraft unchanged but adds additional aircraft that must now perform the specified inspections, rework/replacement, and comply with the stated timeframes."},"complexity_factors":["Multiple targeted serial‑number ranges with specific inclusions and exclusions (see Part I applicability and Table 1), increasing tracking and applicability complexity.","Cross‑referenced part numbers and serial‑number ranges in Table 1 requiring detailed parts identification.","Dependency on external manufacturer service bulletins for rework, re‑identification and replacement procedures (Table 2 and Sundstrand/Boeing Canada/de Havilland SB references).","Multiple, distinct compliance actions (visual inspection, magnified inspection of splined couplings, torque‑spec reassembly, operational torque‑sensor check, and modification) with different technical requirements.","Numeric acceptance criteria for wear and damage (0.25 mm depth; >180° circumferential wear) that require precision measurement and judgment (Part II c).","Several different compliance timeframes and recurring inspection intervals that vary by Part and serial‑number group (Parts I–III compliance schedule).","Two alternative remediation routes for cracked couplings (replace coupling per SB and re‑identify, or replace entire torque tube) and terminating action if specific structural/modification SBs are incorporated.","Recordkeeping/re‑identification requirement (marking service bulletin number on the rod or identification plate) adding administrative steps.","Interplay with foreign ADs (reference to Transport Canada AD CF‑89‑09R4) and prior amendments, requiring reconciliation of historical compliance records."],"plain_english_summary":"This directive requires operators of Bombardier (De Havilland) DHC‑8 aeroplanes in specified serial‑number ranges to locate, inspect, re‑identify, rework or replace flap primary‑drive torque tubes and splined couplings, carry out visual checks of flap and flex‑shaft systems, and modify the wing flap torque sensor per the listed service bulletins and torque/tolerance instructions. It affects aircraft owners/operators, who pay for inspections, parts and labour; sets concrete inspection thresholds and compliance timeframes; and extends the serial‑number range of aircraft now required to comply."},"kimi_summary":{"content_quality":"ok","complexity_score":6,"scope_assessment":{"changed":true,"description":"The original directive (implied by Amendment 1) addressed a specific manufacturing defect in early serial number torque tubes. Amendment 4 significantly expands the scope by extending the serial number range for Part I requirements to include additional aircraft (178 through 231, 233, 235, 237, and 243) that were previously excluded. The directive has evolved from addressing a limited production batch defect to a broader fleet-wide safety program encompassing repetitive inspections, sensor modifications, and terminating actions across nearly the entire early production run (serial numbers 3–293)."},"complexity_factors":["Multiple applicability groups based on aircraft serial numbers (3–177, 178–231/233/235/237/243, and 3–293) with different requirements for each","Cross-referencing between three distinct Parts (I, II, III) with interdependent requirements — Part II inspections can be terminated if Part III modifications are completed","Extensive use of manufacturer service bulletin references (Sundstrand SB numbers, Boeing Canada/de Havilland Service Bulletins 8-54-16, 8-27-47, 8-27-61)","Detailed part number and serial number tables (Table 1 and Table 2) that must be consulted to determine applicability","Nested conditional logic: applicability depends on serial number, which determines which Part applies, which determines whether re-identification exists, which determines whether inspection/rework is required","Multiple compliance deadlines varying by serial number range, effective date, and flight hours (300, 600, 900, 1200, 2000 hours, or 9 months)","Technical aviation terminology requiring specialized knowledge (torque tubes, splined couplings, flex shafts, anodic film, flow regulator valves)","Amendment history references (Amendments 1–3) that explain evolution but also create cognitive load in understanding current requirements"],"plain_english_summary":"This AD orders owners/operators of Bombardier DHC‑8 (Dash 8) aircraft, serial numbers 3–293, to inspect, replace and modify flap torque tubes, couplings and torque sensors after discovery of inadequate heat treatment that can cause cracks, coupling failure and asymmetric flap movement. The mandated inspections, part replacements and torque‑sensor modifications restore warning/drive integrity to prevent loss of control during takeoff or landing and expand protections to more aircraft found at risk."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-8-8-amdt-4-flap-drive-and-torque-sensing-systems","history":"/api/acts/ad-dhc-8-8-amdt-4-flap-drive-and-torque-sensing-systems/history","analysis":"/api/acts/ad-dhc-8-8-amdt-4-flap-drive-and-torque-sensing-systems/analysis","conflicts":"/api/acts/ad-dhc-8-8-amdt-4-flap-drive-and-torque-sensing-systems/conflicts","importantCases":"/api/acts/ad-dhc-8-8-amdt-4-flap-drive-and-torque-sensing-systems/important-cases","documents":"/api/acts/ad-dhc-8-8-amdt-4-flap-drive-and-torque-sensing-systems/documents"}}