Fuel Pumps - Center Tank Pump 1 and Center Tank Pump 2 Operate Incorrectly in Auto Mode When Slats Extended More Than 16 Degrees

TASK 28-21-00-810-819-A
Fuel Pumps - Center Tank Pump 1 and Center Tank Pump 2 Operate Incorrectly in Auto Mode When Slats Extended More Than 16 Degrees

WARNING: OBEY THE FUEL SAFETY PROCEDURES.

WARNING: WHEN YOU DO WORK ON THE FUEL SYSTEM WIRING, YOU MUST USE TEST EQUIPMENT THAT IS APPROVED (REFER TO INTERNATIONAL OR NATIONAL SPECIFICATIONS FOR INTRINSICALLY SAFE TEST EQUIPMENT: EN50020, UL913 OR EQUIVALENT). TEST EQUIPMENT THAT IS NOT APPROVED CAN CAUSE FIRE OR AN EXPLOSION.

1. Possible Causes

P/BSW-CTR TK/MODE SEL [48QA]
SLAT/FLAP CONTR.COMP. [21CV]
SLAT/FLAP CONTR.COMP. [22CV]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
TSM TASK 28-21-00-810-813-A	Fuel Pumps - Center Tank Fuel Pump No. 1 (Left Side) 37QA System Malfunction
TSM TASK 28-21-00-810-814-A	Fuel Pumps - Center Tank Fuel Pump No. 2 (Right Side) 38QA System Malfunction
AMM 27-51-34-000-001	Removal of the SFCC
AMM 27-51-34-400-001	Installation of the SFCC
AMM 27-80-00-866-004	Extending the Slats on the Ground
AMM 27-80-00-866-005	Retracting the Slats on the Ground
AMM 28-21-00-720-001	Functional Test of the Center-Tank Fuel Control
ASM 282103
ASM 282104

3. Fault Confirmation
Subtask 28-21-00-710-068-B ** ON A/C NOT FOR ALL

A. Test
(1) Do the Functional Test of the Center-Tank Fuel Control AMM 28-21-00-720-001, where it is applicable to Auto Mode operation:

if the two center tank pumps operate correctly, in auto mode, no more maintenance work is necessary
if one center tank pump only does not operate correctly, do the applicable trouble shooting procedure (Ref. TSM TASK 28-21-00-810-813) or (Ref. TSM TASK 28-21-00-810-814)
if the two center tank pumps do not operate correctly, do the fault isolation procedure in Para. 4.A.

4. Fault Isolation
Subtask 28-21-00-810-068-B ** ON A/C NOT FOR ALL

A. Procedure

NOTE: During AUTO mode, the two center tank pumps must not operate when the slats are extended to 16 degrees, or more.

(1) Make sure that the flaps are set to the same condition as when the fault occured. If necessary extend AMM 27-80-00-866-004 or retract AMM 27-80-00-866-005 the flaps.
(2) At the overhead FUEL panel:
(a) Make sure that:

the P/BSW-CTR TK/MODE SEL/AUTO (48QA) is set to AUTO (MAN light is off) ASM 282104
the P/BSW-FUEL/CTR TK/PUMP 1 (33QA) is set to ON ASM 282103
the P/BSW-FUEL/CTR TK/PUMP 2 (34QA) is set to ON ASM 282103.

(b) Loosen the panel-fastners and pull down the panel, to get access to the rear of the panel.
(c) Do a check for 28 VDC at pin B1 and B3 of P/BSW-CTR TK/MODE SEL/AUTO ASM 282104:

if 28VDC is at pin B3, do step (4)(a)
if 28VDC is not at pin B1, do step (4)(b)
if 28VDC is at pin B1, but not pin B3, do the next step.

(3) Replace the P/BSW-CTR TK/MODE SEL [48QA] .
(a) Make sure there is 28VDC at pin B1 and pin B3.
(b) Do the test in Para. 3.A.:

if the fault continues, do the next step.

(4) From the result of the voltage checks in step (2)(c):
(a) If 28VDC is at pin B3, do a check and replace as necessary the wiring/connectors between pin B3 and terminal block 202VT ASM 282104.
(b) If 28VDC is not at pin B1, do a check and replace as necessary the wiring/connectors between pin B1 and C/B FUEL/CTR TK/AUTO/CTL (47QA) ASM 282104.
(5) Put the overhead FUEL panel back to its original condition.
(a) Do the test in Para. 3.A.:

if the fault continues, do the next step.

(6) Replace SLAT/FLAP CONTR.COMP. [21CV] AMM 27-51-34-000-001 and AMM 27-51-34-400-001, then do the next step.

NOTE: When the slats are extended to more than 16 degrees, the SFCC-1 and SFCC-2 each supply a ground to the center tank fuel pumps auto control relays. If one SFCC does not supply a ground, this fault will not show until the opposite SFFC or wiring becomes unserviceable. Thus if this ground is not supplied there must two faults, one in each SFCC or its related wiring.

(7) Do a check and replace as necessary the wiring/connectors between terminal block 1853VT and the two SFFCs ASM 282104:

if the wiring/connectors are OK, do step (9)
if a repair is done, do the next step

(8) Do the test in Para. 3.A.:

if the fault continues, do the next step.

(9) Replace SLAT/FLAP CONTR.COMP. [22CV] AMM 27-51-34-000-001 and AMM 27-51-34-400-001.
(10) Do the test given in Para. 3.A.

[Rev.8 from Aug 2018] 2026.04.04 04:28:36 UTC