{"id":"F2011L01126","name":"AD/DHC-1/31 Amdt 3 - Fin Rear Spar","slug":"ad-dhc-1-31-amdt-3-fin-rear-spar","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":86933,"registerId":"commonwealth-F2011L01126-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"De Havilland DHC-1 (Chipmunk) Series Aer","sectionType":"division","heading":"De Havilland DHC-1 (Chipmunk) Series Aeroplanes","content":"### De Havilland DHC-1 (Chipmunk) Series Aeroplanes\n\n| AD/DHC-1/31 Amdt 3 | Fin Rear Spar | 13/2011 |\n| ------------------ | ------------- | ------- |\n\n| Applicability: | English production (C1), all models, and Portuguese (T Mk 20) production models.                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n| -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | Inspect the fin structure for cracks and corrosion in accordance with paragraphs 2.4, 3.6 and 4 of British Aerospace Technical News Sheet (TNS) CT (C1) No. 156 Issue 5 or later revision published by British Aerospace Aerostructures Limited.Conduct dye penetrant inspections in accordance with CAO 108.10.Modification H283 performed in accordance with Note 1 of TNS No. 156 Issue 5 terminates the requirement for the inspections described in paragraph 3.                                                                                |\n| Compliance:    | Inspect at intervals not to exceed 3 years or 600 hours, whichever occurs first.Compliance with Amendment 1 constitutes compliance with this Amendment.                                                                                                                                                                                                                                                                                                                                                                                              |\n|                | This Amendment becomes effective on 23 June 2011.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |\n| Background:    | British Aerospace has reported that cracks have been found in the fin rear spar at a number of critical locations, and that corrosion has been found in the internal fin structure.This amendment includes the Portuguese manufactured (T Mk 20) in the applicability of this AD. A recent review indicates that the inspection required by this AD is applicable to this model.Amendment history:Amendment 1 incorporated Issue 4 of TNS No. 156, which revised paragraph 5 inspection interval from 6 years or 600 hours, to 3 years or 600 hours. |\n\n|     | Amendment 2, effective 30 July 2010, incorporated Issue 5 or later revision of TNS No. 156. |\n| --- | ------------------------------------------------------------------------------------------- |\n\n![](image.001.png)  \nGlen Steemson  \nDelegate of the Civil Aviation Safety Authority\n\n17 June 2011","sortOrder":0},{"sectionNumber":"AD/DHC-1/31 Amdt 3","sectionType":"part","heading":"AD/DHC-1/31 Amdt 3","content":"## AD/DHC-1/31 Amdt 3","sortOrder":1},{"sectionNumber":"Fin Rear Spar","sectionType":"part","heading":"Fin Rear Spar","content":"## Fin Rear Spar","sortOrder":2},{"sectionNumber":"13/2011","sectionType":"part","heading":"13/2011","content":"## 13/2011","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":"Scope was broadened from earlier versions by explicitly adding Portuguese-manufactured T Mk 20 aircraft to applicability (Background). Amendment 1 shortened the inspection interval from 6 years/600 hours to 3 years/600 hours (Background/Amendment history). Amendment 2 incorporated TNS Issue 5 (Background). The requirement can be terminated for an individual aircraft if modification H283 is performed as described in Note 1 of TNS No.156 Issue 5 (Requirement), creating an operational incentive to elect the modification and shift costs from recurring inspections to a one‑off change."},"complexity_factors":["External-document dependence: Mandates compliance with British Aerospace Technical News Sheet (TNS CT (C1) No.156 Issue 5 or later) and CAO 108.10 (Requirement) — operators must obtain and follow those technical procedures.","Termination-by-modification clause: Modification H283 (per Note 1 of TNS No.156 Issue 5) removes the inspection obligation (Requirement) — creates a cost/benefit decision for owners between a one‑off modification and recurring inspections.","Dual interval metric: Inspection frequency set as the lesser of 3 years or 600 flight hours (Compliance) — requires tracking flight hours and calendar scheduling.","Expanded applicability: Portuguese T Mk 20 models explicitly added to applicability (Applicability/Background) — enlarges the regulated fleet.","Amendment and versioning history: Multiple amendments (Amendment 1, 2, 3) and references to Issue 4/5 of the TNS (Background/Amendment history) — requires checking historical changes to know current obligations.","Clear enforcement date: This Amendment effective 23 June 2011 (Compliance) — operators must be aware of the effective date for compliance planning.","Who bears costs & operational burden: Owners/operators bear inspection and modification costs and scheduling burden (Requirement/Compliance) — affects maintenance budgets and downtime."],"plain_english_summary":"Requires owners/operators of De Havilland DHC-1 (Chipmunk) English production (C1) and Portuguese T Mk 20 aircraft to inspect the fin rear spar and internal fin for cracks and corrosion using British Aerospace TNS CT (C1) No.156 Issue 5 procedures and dye‑penetrant inspection per CAO 108.10. Inspections must be done every 3 years or 600 flight hours. Installing modification H283 as set out in the TNS ends the recurring inspection requirement."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"Originally applied only to English production models. Amendment 3 expanded scope to include Portuguese-manufactured T Mk 20 models after review showed the safety issue affected these aircraft too. This represents a modest expansion of regulatory coverage to address newly identified risk in similar aircraft variants."},"complexity_factors":["Single, specific technical requirement referencing external document (British Aerospace TNS No. 156 Issue 5)","Conditional termination clause (Modification H283 exempts ongoing inspections)","Simple applicability criteria limited to two specific production models","Straightforward compliance interval (3 years/600 hours, whichever first)","No nested definitions or extensive cross-referencing to other legislation","Amendment history included but does not complicate current obligations"],"plain_english_summary":"This AD mandates regular inspections of the tail fin structure on English-built De Havilland DHC‑1 Chipmunk C1s and Portuguese T Mk 20s to detect cracks and corrosion, following British Aerospace Technical News Sheet CT (C1) No. 156 Issue 5. It affects owners, operators and maintenance organisations of those aircraft.\n\nCatch­ing fin rear-spar cracks and internal corrosion prevents possible tail structural failure and loss of control; inspections stop if modification H283 has already been embodied."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dhc-1-31-amdt-3-fin-rear-spar","history":"/api/acts/ad-dhc-1-31-amdt-3-fin-rear-spar/history","analysis":"/api/acts/ad-dhc-1-31-amdt-3-fin-rear-spar/analysis","conflicts":"/api/acts/ad-dhc-1-31-amdt-3-fin-rear-spar/conflicts","importantCases":"/api/acts/ad-dhc-1-31-amdt-3-fin-rear-spar/important-cases","documents":"/api/acts/ad-dhc-1-31-amdt-3-fin-rear-spar/documents"}}