EASA AD No : 2009-0091 

EASA Form 110 Page 1/2 

 

EASA AIRWORTHINESS DIRECTIVE 

AD No.: 2009-0091 

Date: 04 May 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 2B1/2B1A turboshaft engines 

TCDS Number : EASA E.001 

Foreign AD : Not applicable 

Supersedure : This directive supersedes AD 2007-0126, dated 07 May 2007. 

ATA 73 Engine Fuel & Control – Hydro Mechanical Unit (HMU) Constant 

Delta Pressure Valve Diaphragm – Replacement 

Manufacturer(s): Turboméca S.A 

Applicability: All ARRIEL 2B1 and 2B1A turboshaft engines, which do not incorporate 

modification TU157. 

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

Eurocopter AS 350 B3 and EC 130 B4 helicopters. 

Reason: Several cases of rupture of the constant delta pressure (delta-P) valve 

diaphragm were reported on ARRIEL 2B1 engines, due to 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). 

On a single-engine helicopter, the result may be an emergency landing. 

In order to reduce the probability of a diaphragm rupture due to fabric 

wear, AD 2007-0006 was issued, requiring periodical replacement of all 

diaphragms having logged more than 2 000 operating hours since new. 

After the issuance of EASA AD 2007-0006, no further case of rupture of 

the constant delta-P valve diaphragm was reported on ARRIEL 2B1 

engines. However several additional diaphragms returning from service 

were inspected by Turboméca, and some signs of wear were detected on 

diaphragms having logged less than 2 000 hours. Based on the inspection 

results, it was decided to decrease this limit from 2 000 hours to 1 500 

hours in order to further reduce the probability of delta-P diaphragm 

rupture. This was the reason for issuing EASA AD 2007-0126 which 
EASA AD No : 2009-0091 

EASA Form 110 Page 2/2 

 

superseded AD 2007-0006. 

Since the issuance of AD 2007-0126 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. 

This AD supersedes AD 2007-0126 by retaining the same requirements 

as in AD 2007-0126 except that: 

 In addition to the ARRIEL 2B1 engines, applicability is extended to the 

ARRIEL 2B1A engines, which share the same HMU design. 

 Applicability is limited to ARRIEL 2B1 and 2B1A engines which do not 

incorporate modification TU157. 

Effective Date: 18 May 2009 

Required Action(s) 

and Compliance 

Time(s): 

The following measures are made mandatory from the effective date of 

this AD, unless accomplished previously: 

If the engine does not incorporate modification TU157 and the Adjusted 

HMU has operated 1 500 operating hours since one of the following, 

whichever occurs later : 

 New 

 Overhaul 

 Incorporation of SB 292 73 2105 (all issues) 

 Incorporation of SB 292 73 2818 (all issues) 

replace the Adjusted HMU and return it to a Repair Centre for replacement 

of the constant delta-P valve diaphragm, in accordance with the 

instructions of Turboméca Mandatory Service Bulletin 292 73 2818 

Version C. 

NOTE: If the engine incorporates modification TU157, no action is required. 

Ref. Publications: 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. 

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

Alternative Methods of Compliance for this AD. 

2. This AD was posted on 20 February 2009 as PAD 09-045 for 

consultation until 20 March 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: 

TURBOMÉCA S.A. 

ARRIEL 2 Customer Support, 40220 Tarnos, France 

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

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