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 39.1 (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/B737/221 Potable Water Pressure Relief Valve 4/2004 Applicability: Model 737-100, -200, -200C, -300, -400, and -500 series aeroplanes; line numbers 1 through 2696 inclusive. Requirement: 1. For those aeroplanes listed in the effectivity section of Boeing Service Bulletin (S/B)737-38-1029, Revision 1, dated August 19, 1993, on which the modification of the potable water pressurization system specified in the service bulletin has not been accomplished: 1. Modify the potable water pressurization system; in accordance with Boeing S/B 737-38-1029, dated June 6, 1991; or Revision 1 dated 19 August 1993 except for the following: i Do not reinstall the existing pressure relief valve having part number (P/N) 520A6DB50. ii Do not perform the leak test procedures specified in the referenced service bulletin. b. Install a new pressure relief valve having P/N RV05-362, in accordance with Boeing S/B 737-38A1047, Revision 2, dated July 18, 2002 or earlier revisions. 2. For those aeroplanes listed in the effectivity section of Boeing S/B 737-38-1029, or Revision 1; on which the modification of the potable water pressurization system specified in that service bulletin has been accomplished: remove the existing pressure relief valve from the potable water tank, and replace the valve with a new pressure relief valve having P/N RV05-362; in accordance with Boeing S/B 737-38A1047 Revision 2 or earlier revisions. 3. For all other aeroplanes having line numbers 1 through 2523 inclusive: remove the existing pressure relief valve from the potable water tank, and replace the valve with a new pressure relief valve having P/N RV05-362, in accordance with Boeing S/B 737-38A1047, Revision 2 or earlier revisions. Boeing 737 Series Aeroplanes AD/B737/221 (continued) 4. For aeroplanes having line numbers 2524 through 2696 inclusive: remove the existing pressure relief valve from the potable water tank and replace the valve with a new pressure relief valve having P/N RV05-362, in accordance with Boeing S/B 737-38A1038, Revision 2, dated September 25, 1997 or earlier revisions. 5. Do not install any pressure relief valve having P/N 520A6DB50, 520A6DB60, or D524TP6D60 on any aeroplane. Note: FAA AD 2003-26-08 Amdt 39-13405 refers. Compliance: For Requirements 1 through 4: Unless previously accomplished, within 18 months after the effective date of this Directive. For Requirement 5: From the effective date of this Directive. This Airworthiness Directive becomes effective on 15 April 2004. Background: The pressure relief valve fitted to the potable water tank can malfunction due to corrosion and maintenance actions. As a result, rupture of the potable water tank during flight that could result in structural damage to the aeroplane and its inability to sustain flight loads. This Directive requires the replacement of the relief valve with an improved design that is corrosion resistant and cannot be adjusted. James Coyne Delegate of the Civil Aviation Safety Authority 4 March 2004 The above AD is notified in the Commonwealth of Australia Gazette on 24 March 2004.