AD/Arriel/24 Constant Delta Pressure Valve Diaphragm (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.

Turbomeca Turbine Engines - Arriel Series

AD/ARRIEL/24 Constant Delta Pressure Valve Diaphragm 3/2007 DM

Applicability:

Turbomeca ARRIEL 2B1 turboshaft engines.

Requirement:

Replace the constant delta P diaphragm in accordance with Turbomeca Mandatory Service Bulletin No. A292 73 2818, original issue or later DGAC approved revision.

Note:  EASA AD 2007-0006 dated 9 January 2007 refers.

Compliance:

For Hydro Mechanical Unit (HMU) that has operated more than 2000 hours since new, overhaul or incorporation of SB 292 73 2105, no later than 28 February 2007.

After 28 February 2007, upon accumulating 2000 operating hours since new, overhaul, incorporation of SB 292 73 2105 or incorporation of SB 292 73 2818.

This Airworthiness Directive becomes effective on 23 January 2007.

Background:

This AD is 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 2,000 hours since new.

James Coyne
Delegate of the Civil Aviation Safety Authority

22 January 2007