Ad/B737/347 Amdt 1 - Centre Wing Tank Autoshutoff Wiring (Cth)

AIRWORTHINESS DIRECTIVE

On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/B737/347 and issues the following 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/B737/347 Amdt 1 Centre Wing Tank Autoshutoff Wiring 18/2011

Applicability:

Model 737-600, -700, -700C, -800 and -900 series aeroplanes, on which Boeing Alert Service Bulletin (ASB) 737-28A1206 dated 11 January 2006 has been accomplished.

Requirement:

Perform the actions as detailed in FAA Emergency AD 2008-24-51.

Compliance:

Date remains unchanged to that detailed in the original issue of this directive.

Despite the new AD/B737/347 Amdt 1, an exclusion or an alternate method of compliance that was in force before the coming into effect of AD/B737/347 Amdt 1 continues to be in force.

This Amendment becomes effective on 30 September 2011.

Background:

The United State’s Federal Aviation Administration (FAA) received a report of failure of the left-hand fuel pump of the CWT to shut off after being selected “OFF” by the flightcrew during flight on a Boeing Model 737-700 aeroplane.  Subsequent to that report, the failure was found on two additional aeroplanes.  Information indicates that the autoshutoff system appears to function normally; however, when the flightcrew manually turns off the CWT pump switches, that action turns off the right-hand pump, but re-energizes the left-hand pump due to incorrect wiring.  The low-pressure lights turn off, incorrectly indicating to the flightcrew that power to both pumps has been removed.  The failure condition results in continual running of the left-hand fuel pump without indication to the flightcrew, which could lead to localized overheating of parts inside the fuel pump, and which could produce an ignition source inside the fuel tank.

Investigation revealed that incorrect wiring could occur on airplanes on which an autoshutoff system was installed in accordance with Boeing ASB 737-28A1206.  Functional tests conducted in accordance with that service bulletin are not adequate to detect the incorrect wiring condition.

This Directive is issued to prevent extended dry-running of the fuel pump, which could lead to localized overheating of parts inside the fuel pump, and which could produce an ignition source inside the fuel tank.

This amendment deletes the original text of the AD and incorporates the original FAA AD by reference.  This was done to facilitate easier cross referencing to FAA AD 2011-18-03 Amdt 39-16785 which details the terminating actions for the requirements of this AD.

The original issue of this AD became effective on 20 November 2008.

Alternative methods of compliance for AD 2008-24-51 that are approved by the FAA are acceptable as a means of compliance against this AD.

Mike Higgins
Delegate of the Civil Aviation Safety Authority

5 September 2011