AD/Dauphin/94 Main Rotor Drive (Cth)
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/94 | Main Rotor Drive | 1/2008 TX |
Applicability: | EUROCOPTER AS 365 N2, AS 365 N3, EC 155 B, EC 155 B1, SA 360 C, |
Requirement: | 1. Accomplish the checks, inspections and replacements, of the Main Gearbox (MGB) as necessary, at the threshold and intervals as indicated in and in accordance with the instructions of EUROCOPTER AS365N Alert Service Bulletin (ASB) No. 05.00.48 Revision 1, SA366 ASB No. 05.33 Revision 1, SA360/365C ASB No. 05.26 Revision 1 or EC155 ASB No. 05A007 Revision 1, as applicable to type/model helicopter. 2. Do not install a spare MGB on a helicopter as a replacement part unless the MGB has been inspected in accordance with instructions of EUROCOPTER AS365N Alert Service Bulletin (ASB) No. 05.00.48 Revision 1, SA366 ASB No. 05.33 Revision 1, SA360/365C ASB No. 05.26 Revision 1 or EC155 ASB No. 05A007 Revision 1, as applicable to type/model helicopter. The use of later revisions of the referenced documents is acceptable for compliance with the requirements of this AD. Note: EASA Emergency AD 2007-0288-E dated 15 November 2007 refers. |
Compliance: | 1. From the effective date of this AD. 2. After the effective date of this AD. |
| This Airworthiness Directive becomes effective on 21 November 2007. | |
Background: | In 2004, cracks were discovered in the web of the MGB planet gear carrier. The two affected MGB units had been removed for overhaul/repair, subsequent to the detection of metal chips at the magnetic plugs. This phenomenon can be detected by metal chips at the magnetic plug. Investigation of the first case showed a failure of the head of a screw that secures the sun gear bearing. |
| The screw head was caught by the planet gear/fixed ring gear/sun gear drive train. The second case was discovered and did not seem to be associated with any other failure. To address the unsafe condition, EUROCOPTER published ALERT TELEX documents for the types affected, containing instructions to check the magnetic plug of the MGB after the last flight of each day, without exceeding 10 flying hours, and a check of the MGB planet gear carrier as soon as one or more chips are found. A further case of crack in a planet gear carrier of a MGB installed on an EC155 helicopter has been reported. Examination of the crack revealed a progressive fatigue failure of the planet gear carrier initially caused by a machining non-conformity (scoring) in the blend radius between a pin and the web. An additional analysis showed, however, that the time limit of 265 hours that was assigned to the first inspection of the planet gear carrier, can no longer guarantee safe flight. The established interval of the inspection is not invalidated as the analysis also showed that the non-conformity does not affect the crack growth rate. This AD supersedes the requirements previously detailed in AD/DAUPHIN/74 and AD/DAUPHIN/77 but requiring the initial inspection/check of the MGB planet gear carrier, irrespective of the accumulated operating hours. Subsequently AD/DAUPHIN/74 and AD/DAUPHIN/77 will be cancelled. |
David Punshon
Delegate of the Civil Aviation Safety Authority
16 November 2007
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