{"id":"F2006B09121","name":"AD/DHC-6/33 Amdt 4 - Elevator Root and Nose Ribs","slug":"ad-dhc-6-33-amdt-4-elevator-root-and-nose-ribs","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115674,"registerId":"commonwealth-F2006B09121-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/DHC-6/33 Amdt 4 - Elevator Root and Nose Ribs","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)  \nDHC-6 (Twin Otter) Series Aeroplanes\n\nAD/DHC-6/33\n\nAmdt 4\n\n  \nElevator Root and Nose Ribs 4/92\n\nApplicability: Model DHC-6 series.\n\nRequirement: 1. Inspect the elevator root rib for cracks in accordance with de Havilland Service Bulletin 6/399 Revision E.\n\nIf cracking is present, incorporate de Havilland modification 6/1769 before further flight.\n\n2. Incorporate de Havilland modification 6/1769.\n\nNote: Transport Canada AD CF-82-21 R1 refers.\n\nCompliance: 1. At intervals not to exceed 600 hours time in service, until modification 6/1769 is incorporated.\n\n2. Prior to 1 January 1996 or 15 000 hours airframe time in service, whichever occurs later.\n\nThe compliance of the previous issue of this Directive was:\n\nUnless already accomplished, inspect within 200 hours time in service after 31 October 1983, with repeat inspections at intervals not exceeding 600 hours time in service until modification 6/1769 is incorporated.\n\nThis Amendment is effective from 2 April 1992.\n\nBackground: Cracking has occurred in the elevator root rib. Amendment 4 is issued to align this Directive with a revision of the relevant Country of Origin AD which requires terminating action in lieu of ongoing repetitive inspections.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This amendment narrows and clarifies the original directive rather than expanding it. Amendment 4 replaces ongoing repetitive inspections with a definitive 'terminating action' (modification 6/1769) that ends the inspection cycle. This is a refinement toward completion, not scope creep. The original 1983 directive required indefinite inspections; this 1992 amendment sets a clear endpoint."},"complexity_factors":["Single aircraft type applicability (DHC-6 series only)","Two straightforward compliance paths: repetitive inspection OR terminating modification","Clear cross-reference to Canadian aviation authority (Transport Canada AD CF-82-21 R1) for traceability","Simple conditional logic: 'If cracking is present, do X before further flight'","Minimal defined terms — relies on standard aviation terminology (time in service, airframe time)","Short document with single purpose (structural integrity of specific component)","Historical context provided but does not complicate current requirements"],"plain_english_summary":"This CASA airworthiness directive targets de Havilland DHC-6 Twin Otter aircraft after cracked elevator root and nose ribs were found. It mandates regular inspections and repairs where cracks are detected to prevent loss of pitch control.\n\nAll affected aircraft must have modification 6/1769 installed as the terminating action—by 1 January 1996 or at 15,000 total flight hours (whichever is later)—ending the need for repetitive inspections and aligning with Canadian standards."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Amendment 4 replaces the earlier one‑off initial inspection timing and continuing 600‑hour repeats (initial 200‑hour start after 31 Oct 1983) by explicitly requiring repetitive 600‑hour inspections until the incorporation of modification 6/1769 and mandating that modification as terminating action by 1 Jan 1996 or 15,000 airframe hours, thereby shifting from indefinite repetitive inspections toward a fixed terminating modification to align with the Country of Origin AD (Compliance; Background)."},"complexity_factors":["Reliance on external technical documents: de Havilland Service Bulletin 6/399 Revision E and modification 6/1769 (Requirement).","Multiple compliance timelines: 600‑hour inspection intervals until modification; final mandatory incorporation by 1 Jan 1996 or 15,000 airframe hours (Compliance).","Conditional work: immediate incorporation of mod 6/1769 if cracking is found before further flight (Requirement).","Reference to foreign AD (Transport Canada AD CF‑82‑21 R1) requiring alignment with Country of Origin actions (Background).","Technical inspection and repair work require qualified maintenance facilities and parts, creating practical compliance burdens for operators (implicit in Requirement/Compliance).","Change from previous directive wording (earlier initial 200‑hour inspection window replaced by ongoing 600‑hour intervals until terminating modification) increases regulatory history to track (Compliance; previous compliance)."],"plain_english_summary":"Requires operators of DHC‑6 (Twin Otter) aeroplanes to inspect the elevator root rib for cracking per de Havilland Service Bulletin 6/399 Rev E, to repeat inspections every 600 flight hours until modification 6/1769 is fitted, and to incorporate modification 6/1769 by 1 January 1996 or 15,000 airframe hours, whichever is later (Requirement; Compliance). Issued because cracking has occurred; owners/operators pay inspection and modification costs and approved maintenance organisations carry out the work."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-6-33-amdt-4-elevator-root-and-nose-ribs","history":"/api/acts/ad-dhc-6-33-amdt-4-elevator-root-and-nose-ribs/history","analysis":"/api/acts/ad-dhc-6-33-amdt-4-elevator-root-and-nose-ribs/analysis","conflicts":"/api/acts/ad-dhc-6-33-amdt-4-elevator-root-and-nose-ribs/conflicts","importantCases":"/api/acts/ad-dhc-6-33-amdt-4-elevator-root-and-nose-ribs/important-cases","documents":"/api/acts/ad-dhc-6-33-amdt-4-elevator-root-and-nose-ribs/documents"}}