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EASA AIRWORTHINESS DIRECTIVE 

AD No : 2008-0077 

Date: 28 April 2008

No person may operate an aircraft to which an Airworthiness Directive applies, except in accordance with the 

requirements of that Airworthiness Directive unless otherwise agreed with the Authority of the State of Registry.

Type Approval Holder’s Name : 

TURBOMECA 

Type/Model designation(s) : 

ARRIEL 2B turboshaft engines 

TCDS Number: EASA E.001 

Foreign AD: Not applicable 

Supersedure: None 

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

Pressure Switch – Inspection/Replacement 

Manufacturer(s): Turboméca S.A. 

Applicability: ARRIEL 2B, 2B1 and 2B1A turboshaft engines, all serial numbers 

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 loss of internal components from the Hydro Mechanical Unit 

(HMU) low fuel pressure switch Hydra-Electric Part number 9 550 17 956 0 into 

the fuel system, have been reported on Arriel 2 engines. 

The loss of internal components from the low fuel pressure switch into the fuel 

system may lead to a rupture of the HP-LP pumps drive shaft shear pin, and 

thus to a possible uncommanded In-Flight Shut-Down (IFSD). On a singleengine helicopter, an uncommanded IFSD results in an emergency autorotation 

landing and in certain conditions may lead to an accident. 

The evaluation of this condition prompts the issuance of this Airworthiness 

Directive (AD), which requires the following actions for the HMUs installed on 

Arriel 2 single-engine applications in order to: 

 verify the part number of the low fuel pressure switch; 

 if installed, replace the low fuel pressure switch P/N 9 550 17 956 0 by an 

IN-LHC low fuel pressure switch P/N 9 550 17 199 0 or P/N 

9 550 17 913 0; 

 in case a Hydra-Electric switch P/N 9 550 17 956 0 is installed or may 

have been installed on the HMU, verify that no parts are found in the 

chamber of the HMU body where the base of the low fuel pressure switch 

has been installed. 
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Effective Date: 13 May 2008 

Compliance: Required as indicated, unless accomplished previously: 

No later than 30 September 2009, accomplish a one-time inspection of the HMU 

in accordance with paragraph 2 of the Turboméca Mandatory Service Bulletin 

(MSB) 292 73 2826 to identify the low fuel pressure switch installed on adjusted 

HMU. 

1. If a Hydra-Electric low fuel pressure switch P/N 9 550 17 956 0 is installed:

 1.1 Inspect low fuel pressure switch and chamber of the HMU body. 

1.1.1 If any parts from the low fuel pressure switch are missing or found in 

the HMU chamber, replace the HMU by a new or overhauled HMU 

equipped with an IN-LHC low fuel pressure switch. 

1.1.2 If not, replace only the low fuel pressure switch by an IN-LHC low 

fuel pressure switch. 

2. If an IN-LHC low fuel pressure switch P/N 9 550 17 199 0 or 

P/N 9 550 17 913 0 is installed:

2.1 If an IN-LHC low fuel pressure switch has been installed since new, repair 

or overhaul, no further action is required. 

2.2 If a Hydra-Electric switch P/N 9 550 17 965 0 has been or may have been 

installed: 

2.2.1 Inspect the chamber of the HMU body. 

2.2.2 If any parts are found in the HMU chamber, replace the HMU by a 

new or overhauled HMU equipped with an IN-LHC low fuel pressure 

switch. 

Ref. Publications: Turboméca Mandatory Service Bulletin 292 73 2826 – Original Issue, dated 13 

March 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 accept Alternative 

Methods of Compliance for this AD. 

2. This AD was posted on 20 March 2008 as PAD 08-037 for consultation until 

17 April 2008. No comments were received during this period. 

3. Enquiries regarding this AD should be referred to the AD Focal Point, 

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 TURBOMECA technical 

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