AD/B737/347 Centre Wing Tank Autoshutoff 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/B737/347 Centre Wing Tank Autoshutoff Wiring 1/2009 TX

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:	1.    Carry out the autoshutoff system wiring test as follows:
a.     Remove electrical power from the aeroplane.
b.    Open the following circuit breakers, and install collars and ‘DO-NOT-CLOSE’ tags on the circuit breakers.
i.     Circuit breaker (CB) C3012, XFR BUS 2 SECT 2, on the P92 panel.
ii.     CB C3002, XFR BUS 1 SECT 2, on the P91 panel.
iii.    CB C1639, Fuel Auto S/O BST PUMP CTR TNK L AC, on the P6-3 panel.
c.     Verify continuity between TB5060F in terminal 5 and the bus side terminal of CB C1639 in the P6-3 circuit breaker panel.
d.    Check that wire number W0040-6402-14 is installed in terminal 5 of TB5060F.
e.     Remove the tags and collars from the following circuit breakers and close the circuit breakers.
i.     CB C3012, XFR BUS 2 SECT 2, on the P92 panel.
ii.     CB C3002, XFR BUS 1 SECT 2, on the P91 panel.
iii.    CB C1639, Fuel Auto S/O BST PUMP CTR TNK L AC, on the P6-3 panel.
f.     Supply electrical power to the aeroplane.
g.     Verify the voltage at CB C1639 is 115 volts alternating current +/- 5 volts.

h.     Test the autoshutoff system as follows:

i.     On P5-4 panel, switch Bus Transfer to OFF.

ii.     Using only one power source (auxiliary power unit (APU) or an engine generator), power only AC Bus 1 with no power to AC Bus 2.

iii.    Carry out the “Centre Tank Boost Pump Auto Shutoff Functional Test” in accordance with paragraphs 9.A. through 9.G. of the Boeing
737-600/700/800/900 Aircraft Maintenance Manual task
28-22-00-720-805, Revision 37, dated 15 October 2008.  Paragraphs 9.H. and 9.I. of the functional test should not be carried out.

2.    If, during the Requirement 1.c. continuity verification, there is no continuity; or if, during the Requirement 1.d. check, the wire is found not installed in TB5060F terminal 5, trace wire W0040-6402-14 from CB C1639 and re-terminate the other end of the wire to TB5060F terminal 5.  After re-terminating the wire, repeat the actions specified Requirement 1.c and 1.d and then complete the remainder of Requirement 1.

3.    If the voltage is not within the limits specified in Requirement 1.g., repeat the actions specified in Requirement 1.a. through Requirement 1.g.

4.    If the autoshutoff test fails the Requirement 1.h.iii. test, accomplish either of the following:

A.   Carry out all applicable maintenance actions in accordance with Chapter 28, Section 28-22 of the Boeing 737-600/700/800/900 Fault Isolation Manual, Revision 37, dated 15 October 2008, and repeat the Requirement 1.h.iii. test; or

B.    Deactivate the left-hand fuel pump of the centre wing tank (CWT) as specified below.

Deactivation of the left-hand fuel pump of the CWT and operation in accordance with Item 28-02, ‘Fuel Boost Pumps (Centre Tank),’ of the Boeing
737-100/200/300/400/500/600/700/800/900 Master Minimum Equipment List (MMEL), Revision 52, dated 29 April 2008, may be accomplished in lieu of Requirement 1 of this Directive until the left-hand fuel pump of the CWT is reactivated.  If the pump is deactivated, dispatch under this configuration is allowed for 10 days.  For aeroplanes on which the left-hand fuel pump of the CWT is deactivated under the provision of this paragraph - Prior to further flight after reactivating the pump, do the autoshutoff system wiring test and applicable corrective actions specified in Requirements 1, 2, 3 and 4 of this Directive.

Accomplishing the installation of the power failed ‘ON’ protection system (ie uncommanded pump “ON” protection system) for the centre tank fuel boost pump in accordance with Boeing ASB 737-28A1248, dated 21 December 2006; or Revision 1, dated 9 January 2008; terminates the Requirement 1 autoshutoff system wiring test.

5.    Submit a report of the findings (both positive and negative) of the Requirement 1 actions to Boeing via e-mail at [email protected]; or via fax at [phone].  The report must include: a description of the test failure; a description of the action taken to correct the failure; the total number of flight cycles/flight hours accumulated on the aeroplane at the time of inspection; and the date of accomplishment of Boeing ASB 737-28A1206 and total number of flight hours/flight cycles accumulated on the aeroplane on the date of accomplishment of that service bulletin.

Note:  FAA Emergency AD 2008-24-51 refers.

Compliance:

For Requirement 1 - Within 48 hours elapsed time after receipt of this Directive or prior to further flight, whichever occurs later.

For Requirement 2 - Before further flight.

For Requirement 3 - Before further flight.

For Requirement 4 - Within 48 hours elapsed time after receipt of this Directive or before further flight, whichever occurs later.

For Requirement 5 -

       If the test is accomplished after receipt of this directive - Submit the report within 10 days after accomplishing the test.

       If the test was accomplished prior to receipt of this Directive - Submit the report within 10 days after receipt of this Directive.

This Airworthiness Directive becomes effective on 20 November 2008.

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.

James Coyne
Delegate of the Civil Aviation Safety Authority

20 November 2008