AD/B737/291 Auxiliary Fuel Tank Float Switch (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/B737/291 Auxiliary Fuel Tank Float Switch 9/2006

Applicability:	Model 737-200, -300, and -400 series aeroplanes, equipped with auxiliary fuel tanks.
Requirement:	1.    Replace the existing fuelling float switch in the auxiliary fuel tank with a new, improved fuelling float switch, install a new liner system inside the float switch conduit in accordance with Part A of the Accomplishment Instructions of Boeing Service Bulletin (SB) 737-28A1192, Revision 2, dated 27 April 2006.
Note 1:  This Directive does not require doing the actions in Part B of the Accomplishment Instructions of Boeing Service Bulletin 737- 28A1192, Revision 2.
Replacements and conduit liner system installations accomplished before the effective date of this Directive in accordance with Boeing Alert Service Bulletin 737-28A1192, dated 27 March 2003; or Boeing SB 737-28A1192, Revision 1, dated 21 August 2003; are acceptable for compliance with the requirements of this Directive.
2.    Fuelling float switch part number (P/N) F8300-146 may not be installed on the auxiliary fuel tank of any aeroplane as a replacement spare.
Note 2:  FAA AD 2006-15-05 Amdt 39-14685 refers.
Compliance:	For Requirement 1 - Within 24 months after the effective date of this Directive.
For Requirement 2 - As of the effective date of this Directive.
This Airworthiness Directive becomes effective on 31 August 2006.

Background: The United States Federal Aviation Administration (FAA) has received reports of chafing of the direct-current-powered float switch wiring insulation in the centre fuel tank.  This Directive requires actions designed to prevent contamination of the fuelling float switch of the auxiliary fuel tank by moisture or fuel, together with chafing of the float switch wiring against the float switch conduit in the fuel tank, which could present an ignition source inside the fuel tank that could cause a fire or explosion.

James Coyne
Delegate of the Civil Aviation Safety Authority

21 July 2006