AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section. Eurocopter SA 360 and SA 365 (Dauphin) Series Helicopters AD/DAUPHIN/78 Main Gearbox Bottom Plate 4/2005 TX Applicability: EUROCOPTER SA 360 C and SA 365 C, C1, C2, and C3 helicopters. 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. 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. 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. This Airworthiness Directive becomes effective on 23 February 2005. 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. James Coyne Delegate of the Civil Aviation Safety Authority 21 February 2005