AD/Arriel/24 Amdt 2 Constant Delta Pressure Valve Diaphragm (Cth)
AIRWORTHINESS DIRECTIVE
On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/ARRIEL/24 Amdt 1 and issues the following 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.
Turbomeca Turbine Engines - Arriel Series
| AD/ARRIEL/24 Amdt 2 | Constant Delta Pressure Valve Diaphragm | 7/2009 |
Applicability: | Turbomeca ARRIEL 2B1 and 2B1A turboshaft engines which do not incorporate modification TU157. Note 1: These engines are known to be installed on, but not limited to, Eurocopter (formerly Aérospatiale) AS 350 B3 and EC 130 B4 helicopters. |
Requirement: | Replace the Adjusted HMU and return it to a Repair Centre for replacement of the constant delta-P valve diaphragm, in accordance with Turboméca Mandatory Service Bulletin 292 73 2818 Version C dated 29 January 2009. The use of later approved revisions of this document is acceptable for compliance with the requirements of this AD. Note 2: EASA AD 2009-0091 dated 4 May 2009 refers. This AD supersedes EASA AD 2007-0126. |
Compliance: | If the adjusted HMU has operated 1,500 flight hours since one of the following, whichever occurs later:
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| This Amendment becomes effective on 2 July 2009. | |
Background: | This AD was prompted by several reported cases of rupture of the constant delta pressure valve diaphragm on ARRIEL 2B1 engines, due to the wear of the delta-P diaphragm fabric. Rupture can result in the loss of the automatic control mode of the helicopter, accompanied with a deterioration of the behaviour of the auxiliary back-up mode (emergency mode). In order to reduce the probability of a diaphragm rupture, this AD requires the removal from service of all the delta Pressure valve diaphragms logging more than 1,500 hours since new. |
| The original issue of this AD required the replacement of parts at 2,000 flight hours. A review of the return parts prompted a reduction of the interval down to 1,500 flight hours to further reduce the possibility of delta-P rupture. Since amendment 1 of this AD Turboméca has released modification TU157 which consists in modifying the pressure relief valve of the HMU by introducing a damping device into the valve. Introduction of this device has demonstrated to decrease the pressure fluctuations in the system, therefore reducing significantly the risk of wear of the delta-P diaphragm fabric. This will delete the need for a periodical replacement of the delta-P diaphragm before overhaul of the HMU. The modification TU157 is therefore considered as the terminating action for this AD. Amendment 1 of this AD became effective 30 August 2007. The original issue of this AD became effective on 23 January 2007. |
James Coyne
Delegate of the Civil Aviation Safety Authority
22 May 2009
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