AD/AB139/8 Generator Control Unit (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.

Agusta AB139 and AW139 Series Helicopters

AD/AB139/8 Generator Control Unit 5/2009

Applicability:	All AB139 and AW139 helicopters, all serial numbers (S/N) except for S/N 31002 to S/N 31004 and S/N 31007.
Requirement:	1.    Remove the number 1 and 2 generator control unit (GCU) part number (P/N) 1152550-3 and replace with GCU P/N 1152550-5 or, as an alternative, with two generator control units P/N 1152550-4, in accordance with the instructions of Agusta Bollettino Tecnico 139-133 dated 20 February 2009 or later revision approved by the European Aviation Safety Agency (EASA).
The two installed GCUs must have the same P/N at all times (ie two P/N 1152550-4 or two P/N 1152550-5).
2.    GCUs P/N 1152550-3 may not be installed as a replacement spare on any helicopter.
Note:  EASA AD 2009-0042 refers.
Compliance:	For Requirement 1 - Within six months after the effective date of this Directive.
For Requirement 2 - After the effective date of this Directive.
This Airworthiness Directive becomes effective on 7 May 2009.
Background:	EASA has advised that laboratory tests performed on a new a GCU model under development have shown a potential fault in the overvoltage protection of the currently installed generator control units P/N 1152550-3.  This condition, if not corrected, could adversely affect the electrical power generation and distribution system functionalities.

James Coyne
Delegate of the Civil Aviation Safety Authority

27 March 2009