{"id":"F2005L00361","name":"AD/DAUPHIN/78 - Main Gearbox Bottom Plate","slug":"ad-dauphin-78-main-gearbox-bottom-plate","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":33992,"registerId":"commonwealth-F2005L00361-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Eurocopter SA 360 and SA 365 (Dauphin) S","sectionType":"division","heading":"Eurocopter SA 360 and SA 365 (Dauphin) Series Helicopters","content":"### Eurocopter SA 360 and SA 365 (Dauphin) Series Helicopters\n\n| AD/DAUPHIN/78 | Main Gearbox Bottom Plate | 4/2005 TX |\n| ------------- | ------------------------- | --------- |\n\n| Applicability: | EUROCOPTER SA 360 C and SA 365 C, C1, C2, and C3 helicopters.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Inspect the Main Gearbox (MGB) bottom plate for cracks, in accordance with paragraph 2.B. of EUROCOPTER SA 360/365 Alert Service Bulletin No. 05.25 or later DGAC approved revisions.2. In case of any cracks found, remove the MGB.Note 1: DGAC N° UF-2005-036 approved under EASA reference No 2005-1825 dated 17 February 2005 refers.                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |\n| Compliance:    | 1. Inspection:(a) For any MGB having never been overhauled or repaired and having logged less than 26,900 cycles:At the latest at 26,900 cycles, then at intervals of no more than 55 flying hours.(b) For any MGB having never been overhauled or repaired and having logged 26,900 cycles and more:At the latest at the ALF-check (check after the last flight of the day) as from the effective date of this Directive, then at intervals of not more than 55 flying hours.(c) Newly overhauled or newly repaired MGBs:At the latest at the ALF-check as from the effective date of this Directive, then at intervals of no more than 55 flying hours.(d) For MGBs held as spares:At the intervals specified in compliance paragraph 1(a) or 1(b) or 1(c) as is applicable, before installation in a helicopter. |\n\n|             | 2. Removal:Before further flight.Note 2: The MGB bottom plate is a component that is not subject to follow-up in service. It is therefore not possible to follow up the specific cycles of this component on MGBs on which the plate may have been replaced upon overhaul or repair of the MGB.                                                                                                                                                  |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n|             | This Airworthiness Directive becomes effective on 23 February 2005.                                                                                                                                                                                                                                                                                                                                                                              |\n| Background: | This Directive is issued following a case of a crack discovered in the MGB bottom plate of an AS 365 N2 helicopter. The crack was detected in the web of the MGB bottom plate, in the immediate vicinity of the attachment of one of the laminated pads, and ran to the inside of the MGB bottom plate and then on the MGB casing. In time, the growth of the crack can lead to the loss of the rotor torque-to-structure transmission function. |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n21 February 2005","sortOrder":0},{"sectionNumber":"AD/DAUPHIN/78","sectionType":"part","heading":"AD/DAUPHIN/78","content":"## AD/DAUPHIN/78","sortOrder":1},{"sectionNumber":"Main Gearbox Bottom Plate","sectionType":"part","heading":"Main Gearbox Bottom Plate","content":"## Main Gearbox Bottom Plate","sortOrder":2},{"sectionNumber":"4/2005 TX","sectionType":"part","heading":"4/2005 TX","content":"## 4/2005 TX","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":false,"description":"The directive responds to a specific crack in the MGB bottom plate and confines requirements to inspection and removal of that component on listed helicopter models; it does not broaden requirements to other parts or additional models beyond those named (Background; Applicability; Requirement)."},"complexity_factors":["Multiple applicability categories (SA 360 C and SA 365 C, C1, C2, C3) increasing tracking scope (Applicability).","Different compliance triggers depending on MGB history: never overhauled and <26,900 cycles; ≥26,900 cycles; newly overhauled/repaired; and spares (Compliance 1(a)–(d)).","Recurring short inspection interval (every ≤55 flying hours) creating operational and maintenance scheduling impact (Compliance).","Removal before further flight if cracks are found creates immediate out-of-service costs and potential substitutions (Requirement 2).","Reference to an external service bulletin and a foreign authority approval (EUROCOPTER Alert SB No. 05.25; DGAC/EASA references) requires operators to follow externally maintained material (Requirement/Note 1).","Traceability issue: MGB bottom plate is not separately tracked in service, complicating cycle accounting after overhauls or plate replacement (Note 2 / Compliance).","Safety-driven specificity (single component and failure mode) reduces legal ambiguity but raises inspection granularity."],"plain_english_summary":"Mandates inspections of the main gearbox (MGB) bottom plate for cracks on Eurocopter SA 360 C and SA 365 C/C1–C3 helicopters, using Eurocopter Alert Service Bulletin No. 05.25; any cracked MGB must be removed before further flight. The directive sets recurring inspections (initial timing depends on overhaul/cycle status, then at intervals not exceeding 55 flying hours) and was issued after a crack was found that could break the rotor torque-to-structure transmission."},"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":3,"scope_assessment":{"changed":false,"description":"This is a targeted safety directive addressing a specific mechanical defect in a defined aircraft component. The scope remains precisely limited to the identified safety risk (MGB bottom plate cracking) and specified helicopter models, consistent with the standard purpose of Airworthiness Directives."},"complexity_factors":["Multiple conditional compliance pathways based on gearbox maintenance history (4 distinct categories in paragraph 1)","Technical aviation terminology requiring specialised knowledge (ALF-check, flight cycles, MGB, DGAC, EASA references)","Cross-reference to external technical document (Eurocopter Alert Service Bulletin No. 05.25)","Nested applicability conditions combining aircraft model, component history, and flight hours/cycles","Regulatory reference chain (DGAC approval under EASA reference) creating dependency on foreign aviation authority documentation"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's aviation regulator (CASA) for specific helicopter models.\n\n**What it does:**\nOrders owners and operators of certain Eurocopter Dauphin helicopters (SA 360 C and SA 365 C, C1, C2, C3 models) to **inspect the main gearbox bottom plate for cracks** and **remove the gearbox immediately if any cracks are found**.\n\n**Why it matters:**\nA cracked bottom plate can cause the helicopter to lose rotor power transmission — essentially, the rotor could stop working properly, leading to catastrophic failure. This directive was triggered after a crack was discovered in one helicopter that could have grown and caused loss of rotor torque transmission.\n\n**Who must comply:**\n- Operators of the specified Dauphin helicopter models\n- Maintenance organisations holding these gearboxes as spare parts\n\n**Key requirements:**\n- **Inspection timing depends on the gearbox's history:**\n  - Never overhauled/repaired with under 26,900 flight cycles: inspect by 26,900 cycles, then every 55 flying hours\n  - Never overhauled/repaired with 26,900+ cycles: inspect at the next \"after last flight of the day\" check, then every 55 flying hours\n  - Newly overhauled or repaired gearboxes: inspect at the next \"after last flight of the day\" check, then every 55 flying hours\n  - Spare gearboxes: inspect before installation according to the above rules\n- **If cracks found:** Remove the gearbox before the helicopter flies again\n\n**The catch:** The bottom plate isn't tracked individually in service records, so operators can't tell if a plate was replaced during previous overhauls — they must follow the inspection schedule regardless."}},"importantCases":[],"_links":{"self":"/api/acts/ad-dauphin-78-main-gearbox-bottom-plate","history":"/api/acts/ad-dauphin-78-main-gearbox-bottom-plate/history","analysis":"/api/acts/ad-dauphin-78-main-gearbox-bottom-plate/analysis","conflicts":"/api/acts/ad-dauphin-78-main-gearbox-bottom-plate/conflicts","importantCases":"/api/acts/ad-dauphin-78-main-gearbox-bottom-plate/important-cases","documents":"/api/acts/ad-dauphin-78-main-gearbox-bottom-plate/documents"}}