{"id":"F2008L01626","name":"AD/DHC-6/75 - Wing Front Spar Adapter Assembly","slug":"ad-dhc-6-75-wing-front-spar-adapter-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":73872,"registerId":"commonwealth-F2008L01626-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"DHC-6 (Twin Otter) Series Aeroplanes","sectionType":"division","heading":"DHC-6 (Twin Otter) Series Aeroplanes","content":"### DHC-6 (Twin Otter) Series Aeroplanes\n\n| AD/DHC-6/75 | Wing Front Spar Adapter Assembly | 6/2008 |\n| ----------- | -------------------------------- | ------ |\n\n| Applicability: | Model DHC-6, all series aircraft, fitted with wing box part numbers C6W1002-1/-3 and subsequent or R.W. Martin, Inc (FAA STC No. SA00160LA or Canadian STC No. SA96-65) Re-Life Wing Box part number WR6-1002-59 or -61, incorporating a part number C6WM1027-1 or -3 Front Spar Adapter Assembly. |\n| -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement: | 1. For wing boxes incorporating C6WM1027-1 front spar adapter assembly with 10 or more years of service:a. Incorporate Viking Service Bulletin (SB) 6/541 (installation of inspection holes in Lower Wing Assembly), dated 1 October 2007, or later Transport Canada approved revision; and then perform a visual inspection of front spar adapter assemblies in accordance with accomplishment instructions in SB 6/540 dated 1 October 2007, or later Transport Canada approved revision. For R.W. Martin Wing Box part numbers, perform the visual inspections in accordance with R.W. Martin SB 00160/2 Revision A, dated 15 November 2007, or later Transport Canada approved revision.b. If a cracked front spar adapter assembly is detected during any inspection, before further flight, replace the adapter assembly with a new adapter (part number C6WM1027-3) in accordance with Viking SB 6/542 dated1 October 2007, or later Transport Canada approved revision. For R.W. Martin Wing Box part numbers, contact R.W. Martin for replacement instructions.2. Incorporate task C57-10-18 of the DHC-6 Corrosion Prevention and Control Manual, PSM 1-6-5, into the Transport Canada approved maintenance schedule.Replacement of the front spar adapter assembly in accordance with Requirement 1.b., and the incorporation of the new task C57-10-18 into the Transport Canada approved maintenance schedule in accordance with Requirement 2, constitutes terminating action to this Directive.Note: Transport Canada AD CF-2007-31 refers. |\n| Compliance: | 1. Unless the initial requirement is already accomplished, within 180 days after 5 June 2008. Repeat the Requirement 1.a. visual inspection at intervals not to exceed 1,200 flight hours, 2,400 flight cycles, or 12 months, whichever occurs first. |\n\n| | 2. Unless already accomplished, within 90 days after 5 June 2008. |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| | This Airworthiness Directive becomes effective on 5 June 2008. |\n| Background: | There have been reports of inter-rivet cracking on several wing front spar adapter assemblies (part number C6WM1027-1) on the horizontal and vertical flanges. It was determined that the cracking was caused by stress corrosion in the short transverse grain initiated by local riveting induced stress. This Directive mandates modification and inspection of the wing front spar adapter fitting and replacement of cracked fittings. |\n\n![](image.001.png) \nDavid Villiers \nDelegate of the Civil Aviation Safety Authority\n\n21 April 2008","sortOrder":0},{"sectionNumber":"AD/DHC-6/75","sectionType":"part","heading":"AD/DHC-6/75","content":"## AD/DHC-6/75","sortOrder":1},{"sectionNumber":"Wing Front Spar Adapter Assembly","sectionType":"part","heading":"Wing Front Spar Adapter Assembly","content":"## Wing Front Spar Adapter Assembly","sortOrder":2},{"sectionNumber":"6/2008","sectionType":"part","heading":"6/2008","content":"## 6/2008","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":6,"scope_assessment":{"changed":false,"description":"The Directive's scope is focused on addressing reported inter‑rivet stress‑corrosion cracking of front spar adapter assemblies by mandating inspection, modification, replacement and an added maintenance task for the listed wing boxes and adapter parts. It does not broaden applicability beyond the specific parts/STCs and actions set out in the 'Applicability' and 'Requirement' text (Applicability; Requirement; Background)."},"complexity_factors":["Technical specificity of affected components and modifications — named part numbers and STCs determine applicability (Applicability).","Multiple alternate service instructions and manufacturers referenced (Viking SBs 6/540–6/542 and R.W. Martin SB 00160/2) requiring operators to follow the correct source for their installation (Requirement 1.a–1.b).","Two distinct corrective paths: modification/inspection and mandatory replacement if cracking is found (Requirement 1.a–1.b).","Addition of a new recurring maintenance task into a Transport Canada‑approved schedule (task C57-10-18) — requires regulator interaction and paperwork (Requirement 2).","Mixed compliance metrics for recurring inspections: flight hours, flight cycles, or months — operators must track multiple usage counters (Compliance).","Short initial compliance windows (90–180 days) combined with ongoing intervals create operational scheduling pressure (Compliance).","Termination clause: replacement plus maintenance-schedule incorporation constitutes terminating action — requires coordination to confirm completion (Requirement 1.b and Requirement 2).","Operator cost and logistics: procurement of replacement parts (C6WM1027-3), potential AOG downtime, and labour for inspections/modification (Requirement 1.b and Background).","Regulatory cross-reference to Transport Canada AD CF-2007-31 and requirement to use Transport Canada approved revisions increases regulatory coordination (Requirement text and Note)."],"plain_english_summary":"This Airworthiness Directive requires operators of DHC-6 (Twin Otter) aeroplanes fitted with specified wing box/front spar adapter assemblies to install inspection access, carry out recurring visual inspections, add a corrosion-prevention task to the maintenance schedule, and replace any cracked adapter with a new part. It affects aircraft owners and maintenance organisations who must meet the Directive's deadlines and update their Transport Canada‑approved maintenance programme because of reported stress‑corrosion cracking in the adapter assemblies."},"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":4,"scope_assessment":{"changed":false,"description":"This is a standard, targeted Airworthiness Directive addressing a specific safety-critical defect in a particular aircraft type. The scope remains precisely focused on the wing front spar adapter assembly cracking issue as originally identified. There is no evidence of scope creep; the directive follows the typical format for mandatory continuing airworthiness information."},"complexity_factors":["Multiple overlapping applicability criteria involving both original manufacturer (Viking/de Havilland) and supplemental type certificate (STC) holder (R.W. Martin) parts","Dual compliance pathways requiring reference to different service bulletins depending on wing box manufacturer (Viking SB 6/540 and 6/541 vs R.W. Martin SB 00160/2)","Conditional logic: different requirements based on whether adapter has 10+ years service, whether initial requirement already accomplished, and whether cracks are detected","Nested compliance intervals: 180-day initial deadline with recurring intervals of 1,200 hours/2,400 cycles/12 months (whichever first), plus separate 90-day deadline for maintenance schedule update","Cross-reference to Canadian aviation authority (Transport Canada AD CF-2007-31) indicating harmonised international regulatory action","Technical terminology requiring aviation engineering knowledge (stress corrosion, short transverse grain, inter-rivet cracking, flanges)"],"plain_english_summary":"This CASA Airworthiness Directive requires operators of certain de Havilland DHC-6 Twin Otter aircraft to inspect the front spar adapter assembly (C6WM1027-1) for stress-corrosion cracking and replace any cracked parts with the improved C6WM1027-3. It targets aircraft with those adapters (including some R.W. Martin replacement wing boxes), especially units in service 10+ years, because undetected cracks can threaten wing integrity.\n\nCompliance also adds a recurring corrosion-prevention maintenance task; completing the replacement and task removes the aircraft from the AD."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-75-wing-front-spar-adapter-assembly","history":"/api/acts/ad-dhc-6-75-wing-front-spar-adapter-assembly/history","analysis":"/api/acts/ad-dhc-6-75-wing-front-spar-adapter-assembly/analysis","conflicts":"/api/acts/ad-dhc-6-75-wing-front-spar-adapter-assembly/conflicts","importantCases":"/api/acts/ad-dhc-6-75-wing-front-spar-adapter-assembly/important-cases","documents":"/api/acts/ad-dhc-6-75-wing-front-spar-adapter-assembly/documents"}}