AD/Arriel/26 Engine Electronic Control Unit Software (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/26 Engine Electronic Control Unit Software 6/2007 DM

Applicability:	Arriel 2B1 turboshaft engines, all serial numbers.
Note 1:  These engines are known to be installed on, but not limited to, Eurocopter AS 350 B3 and EC 130 B4 single-engine helicopters.
Requirement:	Either modify the engine electronic control unit (EECU) by downloading software version V5.02 (modification TU 144C), or replace the EECU with an EECU that has modification TU 144C incorporated.  Both actions are to be accomplished in accordance with Turbomeca Mandatory Service Bulletin 292 73 2144 dated 5 January 2007 or later approved revision.
Note 2:  EASA AD 2007-0085 refers.
Compliance:	At the next 100 hourly inspection, after the effective date of this Directive, but no later than 31 August 2007.
This Airworthiness Directive becomes effective on 5 April 2007.
Background:	Two cases of flame-out have been reported on Arriel 2B1 engines: one when lowering collective pitch on ground at landing and one when switching from Flight Position to Idle Position on ground.  Both flame-out events are explained as follows:
in case of stepper motor loss of steps to a value below the "level 1 failure" detection threshold, the fuel flow of the anti flame-out limit can be reduced, the reduction can be sufficient to cause an engine flame-out when decreasing rapidly the demand for power (it can therefore also happen in flight).

This condition may lead to an uncommanded in-flight shut-down.  On a single-engine helicopter, the result may be an emergency autorotation landing or, at worst, an accident.  To prevent this, software version 5.02 (TU 144C) increases the anti flame-out limit in the event of small stepper motor loss of steps (below the "level 1 failure" detection threshold).

David Punshon
Delegate of the Civil Aviation Safety Authority

2 April 2007