AD/Arriel/35 HP/LP Pump Metering Unit Low Pressure Fuel Pump Impeller Drive (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/35 HP/LP Pump Metering Unit - Low
Pressure Fuel Pump Impeller Drive 11/2009

Applicability:

Turboméca S.A ARRIEL 2B, 2B1 and 2B1A turboshaft engines, which do not incorporate modification TU147.

Note 1:  These engines are known to be installed on, but not limited to Eurocopter
AS 350 B3 and EC 130 B4 helicopters; Changhe Z11 helicopters.

Note 2:  If the HP/LP Pump Metering Unit incorporates modification TU147, no action is required by this AD.

Note 3:  TU147 modification consists of bonding the LP fuel pump impeller with the impeller screw.

Requirement:

Perform a check of the transmissible torque between the LP pump impeller and the HP pump shaft in accordance with paragraph 2 of Turboméca Mandatory Service Bulletin (MSB) No. A292 73 2830.

-      If the check is compliant, apply the nominal tightening torque to the screw of the LP pump impeller.

-      If the check is not compliant, replace the HP/LP Pump Metering Unit with a pre-TU147 compliant unit or a post-TU147 unit.

The use of later approved updates of this document is acceptable for compliance with the requirement of this AD.

Note 4:  EASA AD 2009-0184 dated 14 August 2009 refers.

Compliance:

Within 500 Engine Flight Hours (EFH) from the effective date of this AD, but no later than 30 June 2010.

This Airworthiness Directive becomes effective on 22 October 2009.

Background:

Several events of uncoupling of the LP (Low Pressure) fuel pump impeller and the HP (High Pressure) fuel pump shaft have been reported on ARRIEL 2 engines which do not incorporate modification TU 147 (1).  In most cases the “low fuel pressure switch” enlightened, the pilot activated the aircraft booster pump in accordance with the Flight Manual Instructions and landed safely with no other incident.  One case, on a single-engine helicopter, led to a sudden engine power loss.

The uncoupling of the LP fuel pump impeller and the HP fuel pump shaft may lead to a limitation of engine power or, at worst, an uncommanded In-Flight Shut-Down (IFSD).  On a single-engine helicopter, the result may be an emergency autorotation landing.

James Coyne
Delegate of the Civil Aviation Safety Authority

2 September 2009