Ad/B737/293 - Master Dim and Test System Wiring (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 737 Series Aeroplanes

AD/B737/293 Master Dim and Test System Wiring 10/2006

Applicability:	Model 737-300, -400 and -500 series aeroplanes identified in Boeing Special Attention Service Bulletin (SB) 737-33-1132, Revision 2, dated 8 September 2005; and Model 737-600, -700, -700C, -800 and -900 series aeroplanes identified in Boeing SB 737-33-1133, Revision 3, dated 8 September 2005.
Requirement:	1.    Modify the wiring for the master dim test system in accordance with the Accomplishment Instructions of Special Attention SB 737-33-1132, Revision 2 (for Model 737-300, -400 and -500 series aeroplanes) and SB 737-33-1133, Revision 3 (for Model 737-600, -700, -700C, -800 and -900 series aeroplanes), as applicable.
2.    Accomplish the prior or concurrent actions specified in Table 1, as applicable.
Table 1 - Prior and/or Concurrent Actions
For:	Accomplish all actions associated with:	According to the Accomplishment Instructions of:
Group 57 aeroplanes identified in Special Attention SB 737-33-1132, Revision 2	Installing an engine instrument system (EIS), and	Boeing SB 737-77-1022, Revision 1, dated 26 October 1989
	Modifying the advisory system for the EIS	Boeing SB 737-77-1023, Revision 1, dated 9 November 1989
Group 37 and 46 aeroplanes identified in SB 737-33-1133, Revision 3	Installing wiring for the test system for the audio control panel lamp	Boeing SB 737-33-1121, Revision 1, dated 19 December 2002
Group 2 aeroplanes identified in Boeing SB 737-33-1121, Revision 1	Installing splice SP896	Boeing Service Bulletin 737-26A1083, Revision 1, dated 15 November 2001

Group 39 aeroplanes identified in SB 737-33-1133, Revision 3	Installing a smoke detection and fire extinguishing system in the cargo compartment		Boeing SB 737-26A1083, Revision 1
Group 59 aeroplanes identified in Special Attention SB 737-33-1132, Revision 2	Replacing the very high frequency (VHF) and high frequency (HF) communications panels with radio control panels		Boeing SB 737-23-1102, dated 3 June 1999
Actions accomplished before the effective date of this Directive in accordance with the service bulletins identified in Table 2 are considered acceptable for compliance with the corresponding actions specified in this Directive.
Table 2 - Previous Issues of Service Bulletins
Service Bulletin		Revision		Date
Special Attention SB 737-33-1133 SB 737-33-1133 SB 737-33-1133 Special Attention SB 737-33-1132 Special Attention SB 737-33-1132		Original Revision 1 Revision 2 Original Revision 1		19 December 2002 17 April 2003 4 December 2003 20 March 2003 4 March 2004
Later revisions of the above SB(s), approved by the United States Federal Aviation Administration (FAA) as an Alternate Method of Compliance (AMOC) to FAA AD 2006-15-18, are considered acceptable for compliance with the equivalent Requirements of this Directive.
Note:  FAA AD 2006-15-18 Amdt 39-14699 refers.
Compliance:	For Requirement 1 - Within 48 months after the effective date of this Directive.
For Requirement 2 - Prior to or concurrently with accomplishment of Requirement 1.
This Airworthiness Directive becomes effective on 28 September 2006.
Background:	The FAA has received a report that the master dim and test system circuit does not have wiring separation of the test ground signal for redundant equipment in the flight compartment.  This lack of separation could allow a single fault failure in flight to simulate a test condition and show test patterns instead of the selected radio frequencies on the communications panels, which could inhibit communication between the flight crew and air traffic control, affecting the continued safe flight of the aeroplane.

This Directive requires the modification of the wiring for the master dim and test system and for certain aeroplanes, related concurrent actions as necessary.

James Coyne
Delegate of the Civil Aviation Safety Authority

14 August 2006