AD/B747/331 Frequency Converters (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.

Boeing 747 Series Aeroplanes

AD/B747/331 Frequency Converters 9/2005

Applicability:	Model 747-200F and -400 series aeroplanes as listed in Boeing Service Bulletin (SB) 747-25-3313, Revision 1, dated 15 May 2003.
Requirement:	Replace the frequency converter(s) used to supply electrical power to utility outlets (for the galley, medical equipment or personal computers) with modified frequency converter(s) in accordance with the Accomplishment Instructions of SB 747-25-3313, Revision 1.
Note 1:  SB 747-25-3313, Revision 1, refers to JAMCO Service Bulletin CAW74-25-1697, dated 7 June 2002, as an additional source of information for procedures to remove and install certain galley frequency converters.
Later revisions of the above Boeing SB, approved by the United States Federal Aviation Administration (FAA) as an Alternate Method of Compliance (AMOC) to FAA AD 2005-12-10, are considered acceptable for compliance with the equivalent Requirements of this Directive.
Note 2:  FAA AD 2005-12-10 Amdt 39-14126 refers.
Compliance:	Within 18 months after the effective date of this Directive.
This Airworthiness Directive becomes effective on 1 September 2005.
Background:	The FAA has received a report that a hard short condition between the frequency converter's output and its downstream circuit breakers will produce a continuous current that could cause the undersized output wiring to overheat.  This Directive requires the replacement of the frequency converter(s) used to supply electrical power for utility outlets (for the galley, medical equipment, or personal computers) with modified frequency converter(s).

This Directive is issued to prevent the overheating of the frequency converter's undersized output wiring, which could lead to the failure of a wire bundle and consequent adverse effects on other systems sharing the affected wire bundle.

David Villiers
Delegate of the Civil Aviation Safety Authority

21 July 2005