EASA AD No.: 2009-0010 

EASA Form 110 Page 1/2 

EASA AIRWORTHINESS DIRECTIVE 

AD No.: 2009-0010 

Date: 20 January 2009 

Note: This Airworthiness Directive (AD) is issued by EASA, acting in accordance with 

Regulation (EC) No 216/2008 on behalf of the European Community, its Member States and 

of the European third countries that participate in the activities of EASA under Article 66 of 

that Regulation.

This AD is issued in accordance with EC 1702/2003, Part 21A.3B. In accordance with EC 2042/2003 Annex I, Part M.A.301, the 

continuing airworthiness of an aircraft shall be ensured by accomplishing any applicable ADs. Consequently, no person may operate 

an aircraft to which an Airworthiness Directive applies, except in accordance with the requirements of that Airworthiness Directive 

unless otherwise specified by the Agency [EC 2042/2003 Annex I, Part M.A.303] or agreed with the Authority of the State of Registry 

[EC 216/2008, Article 14(4) exemption]. 

Type Approval Holder’s Name : 

TURBOMECA 

Type/Model designation(s) : 

ARRIEL 2S1 turboshaft engines 

TCDS Number : EASA.E.001 

Foreign AD : Not applicable 

Supersedure : None 

ATA 73 Engine Fuel & Control - Digital Engine Control Unit (DECU) – 

Software Modification 

Manufacturer(s): Turboméca 

Applicability: ARRIEL 2S1 turboshaft engines, all serial numbers. 

These engines are known to be installed on, but not limited to, 

Sikorsky S-76C+ series twin-engine helicopters. 

Reason: During acceleration up to One Engine Inoperative (OEI) 30-second rating, one 

event of in-flight loss of full automatic control occurred on an Arriel 2S1 engine. 

The selection of OEI 30-second rating on engine 1 was triggered by the 

automatic detection of an OEI situation further to a transient deceleration of 

engine 2. The transient deceleration of engine 2 was caused by the untimely 

reset of its DECU. Once this reset was completed, engine 2 resumed its nominal 

operation. Afterwards the aircraft then continued its flight safely with its engine 1 

operating in manual control mode. 

The loss of full automatic control of engine 1 was caused by loss of steps of the 

stepper motor controlling the fuel metering valve inside the Hydromechanical 

Unit (HMU). 

It has been found that high accelerations, notably up to OEI 30-second rating, 

increase the risk of loss of steps of the HMU stepper motor. 

Therefore, this event has lead to the consideration of the following unsafe 

condition at aircraft level: In-flight loss of full automatic control of the engine 

induced by the loss of steps of the stepper motor during acceleration up to OEI 

30-second rating, further to an actual OEI situation on the other engine (such as 

a power loss event). 
EASA AD No.: 2009-0010 

EASA Form 110 Page 2/2 

It has been determined that the Arriel 2S1 is the only engine variant of the Arriel 

2 family affected by this potential unsafe condition. 

For the reason stated above, this AD requires, on DECUs of Arriel 2S1 engines, 

the application of modification TU109 - which is a software modification to 

version 11.01 - that increases the tolerance to loss of steps of the control 

system. This modification reduces significantly the risk of an in-flight loss of full 

automatic control due to loss of steps of the stepper motor, notably during 

engine accelerations up to OEI 30-second rating. 

Effective Date: 03 February 2009 

Required Action(s) 

and Compliance 

Time(s): 

Required as indicated, unless accomplished previously: 

(1) No later than 31 August 2010, perform an upgrade of the DECU software 

to version 11.01 to implement modification TU109 in accordance with the 

accomplishment instructions of Turboméca Mandatory Service Bulletin 

N° 292 73 2109 Version E. 

Previous upgrade of the DECU software to version 11.01 accomplished 

before the effective date of this AD, in accordance with the 

accomplishment instructions of Turboméca Mandatory Service Bulletin 

No. 292 73 2109 Version D, dated 30 November 2007, satisfy the 

requirements of paragraph (1) of this AD. 

NOTE: NEVER MIX ON A TWIN ENGINE HELICOPTER A POST TU109 

(DECU SOFTWARE AT VERSION 11.01) ENGINE WITH A PRE 

TU109 ENGINE (DECU SOFTWARE AT VERSION 8.08 OR 

EARLIER). 

(2) After 31 August 2010, No person shall install an ARRIEL 2S1 turbo shaft 

engine unless its DECU has software at version 11.01 or higher. 

Ref. Publications: Turboméca Mandatory Service Bulletin 292 73 2109 Version E, dated 17 

September 2008. 

The use of later approved revisions of this document is acceptable for 

compliance with the requirements of this AD. 

Remarks : 1. If requested and appropriately substantiated, EASA can approve 

Alternative Methods of Compliance for this AD. 

2. This AD was posted on 12 December 2008 as PAD 08-141 for 

consultation until 09 January 2009. No comments were received during 

the consultation period. 

3. Enquiries regarding this AD should be referred to the Airworthiness 

Directives, Safety Management & Research Section, Certification 

Directorate, EASA. E-mail ADs@easa.europa.eu 

4. For any question concerning the technical content of the requirements in 

this AD, please contact: 

TURBOMECA S.A. 

ARRIEL 2 Customer Support 

40220 Tarnos, France 

Fax: +33 5 59 74 45 15, or your usual or nearest TURBOMECA 

technical representative (refer to http://www.turbomeca-support.com)