Internal Fuel Leak Which Causes a Fuel Imbalance or a Discharge From a NACA Vent During Taxi or Flight

TASK 28-21-00-810-825-A
Internal Fuel Leak Which Causes a Fuel Imbalance or a Discharge From a NACA Vent During Taxi or Flight

WARNING: OBEY THE FUEL SAFETY PROCEDURES.

1. Possible Causes

L(R) FULL SENSOR 23QJ1(2)
L(R) UNFULL SENSOR 24QJ1(2)
L(R) UNFULL SENSOR 25QJ1(2)
L(R) UNFULL SENSOR 26QJ1(2)
L(R) FULL SENSOR 27QJ1(2)
L(R) SURGE SENSOR 28QJ1(2)
FLSCU1(2) 7(9)QJ
VALVE-AIR RELEASE, L WING TK [86QM]
VALVE-AIR RELEASE, R WING TK [87QM]
L (R) engine LP fuel supply line VALVE ASSY-SUCTION, FUEL PUMP
OUTLET (CHECK) VALVE, Part of CANISTER-FUEL PUMP, L(R) WING TK OUTER 1QM(4QM)
OUTLET (CHECK) VALVE, Part of CANISTER-FUEL PUMP, L(R) WING TK INNER 2QM(3QM)
engine LP fuel feed pipes and connections between the wing front spar tank wall and the wing Rib 1 tank wall

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 28-21-00-280-001	Check Suction Valves For Full and Free Movement
AMM 28-21-00-710-011	Operational Leak Test of the Air Release Valve Float
AMM 28-21-00-790-001	Leak Test of the Main Fuel-Pump-System Pipelines
AMM 28-21-41-000-001	Removal of the Low Pressure (LP) Air-Release-Valve 86QM(87QM)
AMM 28-21-41-400-001	Installation of the Low Pressure (LP) Air-Release-Valve 86QM(87QM)
AMM 28-21-52-000-004	Removal of the Check Valve of the Fuel Pump Canister
AMM 28-21-52-400-004	Installation of the Check Valve of the Fuel Pump Canister
AMM 28-46-00-740-001	Functional (BITE) Test

3. Fault Confirmation
Subtask 28-21-00-710-089-B ** ON A/C NOT FOR ALL

A. Prerequisite Test

NOTE: If there are any failed LRUs in the FLSS, this test is necessary to find and to show them. This is because the FLSS Bite test is only done when the aircraft is electrically powered up and the FLSS defect report transferred to the Post Flight Report (PFR) at take off.

This procedure is based on actual aircraft malfunctions:

that did not give any reported WARNINGS or MESSAGES on the PFR
where the fuel imbalance was seen by the flight crew before a FUEL imbalance advisory was given.

(1) Do the Functional (BITE) Test of the FLSS AMM 28-46-00-740-001.
(2) Examine the FLSS STATUS page for the messages that follow:

L(R) FULL SENSOR 23QJ1(2)
L(R) UNFULL SENSOR 24QJ1(2)
L(R) UNFULL SENSOR 25QJ1(2)
L(R) UNFULL SENSOR 26QJ1(2)
L(R) FULL SENSOR 27QJ1(2)
L(R) SURGE SENSOR 28QJ1(2)
FLSCU1(2) 7(9)QJ.

(a) If:

none of the messages given are shown, do Para. 3.B.
one or more of the messages given are shown, trouble shoot the identified LRU(s) before you do Para. 3.B.

Subtask 28-21-00-710-075-B ** ON A/C NOT FOR ALL

B. Operational Test
(1) Go to the Operational Leak Test of the Air Release Valve Float AMM 28-21-00-710-011.

NOTE: The engine feed system (internal to the collector cell) has a suction valve with a controlled leak rate when in the closed position.
The suction valve has a number of slots in the valve seat. These slots let fuel go (escape from) between the clack valve and the valve seat. The fuel flow generated through the slots (controlled leak) is to prevent the formation of ice in the mouth of the suction valve. This is necessary because a proportion of water can be in the fuel.
The maximum permitted flow of the controlled leak is 210 kg (460 lb)/hour.

(a) If the left side fuel quantity was more than the right side (or fuel was discharged from the left side NACA vent):

do the AMM TASK with the PUMP-FUEL No. 1, CTR TK (37QA).

NOTE: During this test procedure fuel from the center tank is pressurized by the PUMP-FUEL No. 1, CTR TK (37QA). This fuel pressure is then applied to the ENG 1 (aircraft left side) LP fuel supply line to test for a leak.

(b) If the right side fuel quantity was more than the left side (or fuel was discharged from the right side NACA vent):

do the AMM TASK with the PUMP-FUEL No. 2, CTR TK (38QA).

NOTE: During this test procedure fuel from the center tank is pressurized by the PUMP-FUEL No. 2, CTR TK (38QA). This fuel pressure is then applied to the ENG 2 (aircraft right side) LP fuel supply line to test for a leak.

(2) If this is the first time this failure occurred and the related engine LP fuel supply line operates as specified:

more maintenance steps are not necessary.

(3) If the related engine LP fuel supply line does not operate as specified or this is the second/subsequent failure:

go to Para. 4.

Subtask 28-21-00-710-089-C ** ON A/C NOT FOR ALL

C. Prerequisite Test

that did not give any reported WARNINGS or MESSAGES on the PFR
where the fuel imbalance was seen by the flight crew before a FUEL imbalance advisory was given.

(1) Do the Functional (BITE) Test of the FLSS AMM 28-46-00-740-001.
(2) Examine the FLSS STATUS page for the messages that follow:

L(R) FULL SENSOR 23QJ1(2)
L(R) UNFULL SENSOR 24QJ1(2)
L(R) UNFULL SENSOR 25QJ1(2)
L(R) UNFULL SENSOR 26QJ1(2)
L(R) FULL SENSOR 27QJ1(2)
L(R) SURGE SENSOR 28QJ1(2)

NOTE: If a surge tank sensor becomes wet during normal operation it will cause the ECAM warning FUEL L(R) WING TK OVERFLOW and the applicable flight crew instructions to be given.

FLSCU1(2) 7(9)QJ.

(a) If:

none of the messages given are shown, do Para. 3.B.
one or more of the messages given are shown, trouble shoot the identified LRU(s) before you do Para. 3.B.

Subtask 28-21-00-710-075-A ** ON A/C NOT FOR ALL

D. Operational Test
(1) Go to the Operational Leak Test of the Air Release Valve Float AMM 28-21-00-710-011.

(a) If the left side fuel quantity was more than the right side (or fuel was discharged from the left side NACA vent):

do the AMM TASK with the R PUMP-FUEL No. 1 (22QA).

NOTE: During this test procedure fuel from the right wing tank is pressurized by the R PUMP-FUEL No. 1 (22QA). This fuel pressure is then applied (through the open crossfeed valve) to the ENG 1 (aircraft left side) LP fuel supply line to test for a leak.

(b) If the right side fuel quantity was more than the left side (or fuel was discharged from the right side NACA vent):

do the AMM TASK with the L PUMP-FUEL No. 1 (21QA).

NOTE: During this test procedure fuel from the left wing tank is pressurized by the L PUMP-FUEL No. 1 (21QA). This fuel pressure is then applied (through the open crossfeed valve) to the ENG 2 (aircraft right side) LP fuel supply line to test for a leak.

(2) If this is the first time this failure occurred and the related engine LP fuel supply line operates as specified:

more maintenance steps are not necessary.

(3) If the related engine LP fuel supply line does not operate as specified or this is the second/subsequent failure:

go to Para. 4.

4. Fault Isolation
Subtask 28-21-00-810-075-B

A. Procedure
(1) Replace the VALVE-AIR RELEASE, L WING TK [86QM] ( VALVE-AIR RELEASE, R WING TK [87QM] ) AMM 28-21-41-000-001 and AMM 28-21-41-400-001.
(2) If the fault continues, do a check of the L(R) suction valve for full and free movement AMM 28-21-00-280-001.
(3) Make sure that the clack valve closes against the valve seat correctly when in the closed position.
(4) If necessary, replace the L (R) engine LP fuel supply line VALVE ASSY-SUCTION, FUEL PUMP.
(5) If the fault continues, do a check of, and replace if necessary the:

OUTLET (CHECK) VALVE, Part of CANISTER-FUEL PUMP, L(R) WING TK OUTER 1QM(4QM) AMM 28-21-52-000-004 and AMM 28-21-52-400-004
OUTLET (CHECK) VALVE, Part of CANISTER-FUEL PUMP, L(R) WING TK INNER 2QM(3QM) AMM 28-21-52-000-004 and AMM 28-21-52-400-004.

(6) Do the test given in Para. 3.B.
(7) If the fault continues, examine the related engine LP fuel feed pipes and connections between the wing front spar tank wall and the wing Rib 1 tank wall .
(8) Repair all unserviceable fuel pipes and connections.
(9) Do the Leak Test of the Fuel-Pump-System Pipeline (Left(Right) Wing and Fuselage only) AMM 28-21-00-790-001.

[Rev.8 from Aug 2018] 2026.04.04 04:28:37 UTC