DOC AIRBUS | TSM A320FFuel - A Leak is Shown by Discrepancies in the Fuel On Board (FOB) and Fuel Used (FU) Calculations During Flight
TASK 28-11-00-810-806-A
Fuel - A Leak is Shown by Discrepancies in the Fuel On Board (FOB) and Fuel Used (FU) Calculations During Flight
A. Referenced Information
3. Fault Confirmation
Subtask 28-11-00-710-056-A
Subtask 28-11-00-810-055-A ** ON A/C NOT FOR ALL
[Rev.8 from Aug 2018]
2026.04.04 04:39:24 UTC
Fuel - A Leak is Shown by Discrepancies in the Fuel On Board (FOB) and Fuel Used (FU) Calculations During Flight
WARNING:
OBEY THE FUEL SAFETY PROCEDURES.
1. Possible Causes- incorrect assembly
- damage
- fuel sealant
- unserviceable seal
- fuel tank leak
- engine fuel supply lines
- VALVE-LP FUEL, ENG 1 [12QM]
- VALVE-LP FUEL, ENG 2 [13QM]
engine/IDG cooling return to tank fuel lines - CHECK VALVE-FUEL RECIRCULATION, L [122QM]
- CHECK VALVE-FUEL RECIRCULATION, R [123QM]
- fuel bladder
A. Referenced Information
| REFERENCE | DESIGNATION |
|---|---|
| TSM TASK 28-13-00-810-801-A | Fuel - Leak Shows at Drain Mast |
| AMM 12-11-28-650-003 | Pressure Refuel with Automatic Control |
| AMM 12-11-28-650-004 | Pressure Refuel with Manual Control |
| AMM 12-11-28-650-007 | Use of Magnetic Level Indicators (MLI) |
| AMM 24-41-00-861-002 | Energize the Aircraft Electrical Circuits from the External Power |
| AMM 24-41-00-862-002 | De-energize the Aircraft Electrical Circuits Supplied from the External Power |
| AMM 28-11-00-280-002 | Structural Fuel Tank Leaks - General Information |
| AMM 28-16-00-710-002 | Operational Check of Fuel Recirculation Check Valve to Ensure Valve not Failed Open |
| AMM 28-16-42-000-001 | Removal of the Fuel Recirculation Check-valve |
| AMM 28-16-42-400-001 | Installation of the Fuel Recirculation Check-valve |
| AMM 28-24-41-000-001 | Removal of the LP Fuel Valve |
| AMM 28-24-41-400-001 | Installation of the LP Fuel Valve |
| AMM 28-25-00-650-001 | Pressure Defuel |
| AMM 28-25-00-650-003 | To Drain Remaining Fuel from the Wing Tanks and the Center Tank |
Subtask 28-11-00-710-056-A
A. Test
There is no fault confirmation test available for the values of Fuel On Board (FOB) and Fuel Used (FU) as used in the FOB and FU calculations. But, the airline operations, and the flight crew during flight, know the typical fuel load required for specfic flight legs. Thus all significant discrepancies must be investigated.
(1) Get as much data (as possible) about the fuel leak FOB/FU discrepancy and the subsequent steps of the unusual and/or emergency procedure used, from:
The FOB value is supplied from the FQIS.
If it is not shown degraded it can be accepted as correct for this TSM Task.
If necessary use one of the two sub-procedures that follow:
(a) The Refuel/Defuel:
1 Fully defuel the aircraft AMM 28-25-00-650-001 and AMM 28-25-00-650-003.
2 Refuel the aircraft AMM 12-11-28-650-003 or AMM 12-11-28-650-004.
3 Make a record of the fuel load put on the aircraft as shown by the tanker or fuel hydrant.
(b) Manual Magnetic Indicators (MMIs):
1 Use the MMI secondary direct-reading system to calculate the FOB when the aircraft is on the ground AMM 12-11-28-650-007.
(c) Compare the FOB values obtained from the FQIS and defuel/refuel, or MMIs.
(d) Troubleshoot if necessary:
1 Refer to the Fault Symptoms, at the front of the TSM and/or chapter 28, for the related Task number.
2 Do the applicable trouble shooting procedure related to the observation or failure message.
(3) Fuel Used (FU)
The FU data is supplied from each engines FADEC system.
The source of the data is a fuel flow sensor/transmitter mounted on each engine.
(a) Examine the PFR/CFDS(ENG) for a related flow sensor problem or message:
1 If a flow sensor problem or message is shown:
a Refer to the Fault Symptoms, at the front of the TSM and/or chapter 28, for the related Task number.
b Do the applicable trouble shooting procedure related to the observation or failure message.
2 If there is no fuel flow sensor problem or message shown, do the next step.
(4) Only continue with this procedure if you are sure that the FOB and FU values, at the time of the event, were correct.
4. Fault IsolationThere is no fault confirmation test available for the values of Fuel On Board (FOB) and Fuel Used (FU) as used in the FOB and FU calculations. But, the airline operations, and the flight crew during flight, know the typical fuel load required for specfic flight legs. Thus all significant discrepancies must be investigated.
(1) Get as much data (as possible) about the fuel leak FOB/FU discrepancy and the subsequent steps of the unusual and/or emergency procedure used, from:
- the aircraft technical log
- the flight crew.
The FOB value is supplied from the FQIS.
If it is not shown degraded it can be accepted as correct for this TSM Task.
If necessary use one of the two sub-procedures that follow:
(a) The Refuel/Defuel:
1 Fully defuel the aircraft AMM 28-25-00-650-001 and AMM 28-25-00-650-003.
2 Refuel the aircraft AMM 12-11-28-650-003 or AMM 12-11-28-650-004.
3 Make a record of the fuel load put on the aircraft as shown by the tanker or fuel hydrant.
(b) Manual Magnetic Indicators (MMIs):
1 Use the MMI secondary direct-reading system to calculate the FOB when the aircraft is on the ground AMM 12-11-28-650-007.
(c) Compare the FOB values obtained from the FQIS and defuel/refuel, or MMIs.
(d) Troubleshoot if necessary:
1 Refer to the Fault Symptoms, at the front of the TSM and/or chapter 28, for the related Task number.
2 Do the applicable trouble shooting procedure related to the observation or failure message.
(3) Fuel Used (FU)
The FU data is supplied from each engines FADEC system.
The source of the data is a fuel flow sensor/transmitter mounted on each engine.
(a) Examine the PFR/CFDS(ENG) for a related flow sensor problem or message:
1 If a flow sensor problem or message is shown:
a Refer to the Fault Symptoms, at the front of the TSM and/or chapter 28, for the related Task number.
b Do the applicable trouble shooting procedure related to the observation or failure message.
2 If there is no fuel flow sensor problem or message shown, do the next step.
(4) Only continue with this procedure if you are sure that the FOB and FU values, at the time of the event, were correct.
- if no data is available as to the location of the fuel leakage, do all of Para. 4.A.
- if the leakage is reported to come from a fuel tank, go to Para. 4.A., step (4)
- if the leakage is reported to come from an engine fuel supply pipe-line, go to Para. 4.A., step (5)
- if the leakage is reported to come from an engine/IDG cooling return (to tank) fuel pipe-line, go to Para. 4.A., step (6).
NOTE: This procedure is not a full list of all items/LRUs that can possibly leak (possible causes). It is only a guide to logical Trouble-shooting to find the source of the leak.
Subtask 28-11-00-810-055-A ** ON A/C NOT FOR ALL
A. Procedure
(a) Put a container (example, barrel - 42 gal.) under the aircraft at the position where the fuel comes from (example, the drain mast).
(b) Defuel the applicable/adjacent fuel tank, or if necessary, defuel the aircraft (all tanks) AMM 28-25-00-650-001.
(c) In accordance with the local regulations:
1 Remove all the spilt fuel.
2 Clean the fuel spillage from the aircraft.
3 Clean the fuel spillage from the area on the ground (hard standing).
(3) If you can see a small fuel leakage:
(a) If the leak is found from:
(4) Do the fuel tank leak checks and repair as necessary AMM 28-11-00-280-002.
(a) Do a manual refuel of the applicable tank when the repair is complete AMM 12-11-28-650-004.
(b) If there is remaining fuel leakage:
1 Make sure that it agrees with that given in AMM 28-11-00-280-002.
2 If necessary, do the repair again.
(5) Do a check for leaks (on the engine fuel supply lines ) in the areas that follow:
(a) The mounting plate between the front spar and the LP valve 1(2) AMM 28-24-41-000-001.
(b) The VALVE-LP FUEL, ENG 1 [12QM] ( VALVE-LP FUEL, ENG 2 [13QM] ) for external leakage.
1 Replace, if necessary AMM 28-24-41-000-001 and AMM 28-24-41-400-001.
(c) The engine 1(2) fuel feed-pipe (shrouded) from between the LP valves 1(2) and the aircraft to pylon (shrouded) connection.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel feed-pipe between the aircraft to pylon connection and the fluid disconnect panel.
(e) The engine 1(2) fuel feed-pipe between the fluid disconnect panel and the engine 1(2) fuel flow transmitter.
1 Replace all the unserviceable pipes and connections.
(f) If no leak can be seen in steps (a) thru (e):
1 Pressurize the engine 1(2) LP fuel feed supply as follows:
a Make sure that the L(R) wing tank contains a mimimum of 1000 kg (2200 lb) of fuel. If necessary, refuel the L(R) wing tank AMM 12-11-28-650-003.
b Energize the aircraft electrical circuits AMM 24-41-00-861-002.
c Open, safety and tag the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2) to open the LP valve 12QM (13QM).
d On the HYD/FUEL panel 40VU, push (in) the L(R) wing-tank fuel PUMP P/BSWs.
e Make sure that the OFF legends go off.
f Make sure that the FAULT legends momentarily come on and then stay off.
a On the HYD/FUEL panel 40VU, release (out) the L(R) wing-tank fuel PUMP P/BSWs.
b Make sure that the OFF legends come on.
c De-energize the aircraft electrical circuits AMM 24-41-00-862-002.
d Remove the safety clip and the tag and close the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2).
(g) At the next engine 1(2) start, and make sure that there are no fuel leaks in its fuel supply.
(6) Do a check for leaks (of theengine/IDG cooling return to tank fuel lines ) in the areas that follow:
(a) The mounting block/piping installation between the wing bottom skin and the fuel recirculation check valve L(R) AMM 28-16-42-000-001.
(b) The CHECK VALVE-FUEL RECIRCULATION, L [122QM] ( CHECK VALVE-FUEL RECIRCULATION, R [123QM] ) for external leakage AMM 28-16-42-000-001.
1 Replace, if necessary AMM 28-16-42-000-001 and AMM 28-16-42-400-001.
(c) The engine 1(2) fuel return-pipe between the aircraft to pylon connection (adjacent to check valve 122QM/123QM) and the fluid disconnect panel.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel return-pipe between the fluid disconnect panel and the engine IDG cooling fuel exit point AMM 28-16-00-710-002.
1 Replace all the unserviceable pipes and connections.
(e) Do the applicable Leak Test of the Fuel Recirculation Cooling System as follows:
(a) The first time:
1 Make an entry in the aircraft technical log to make a record of this procedure.
2 Return the aircraft to service.
3 Make a record in the aircraft log book for the flight crew, during the next flight, to:
a Monitor and record the initial FOB, the final or current FOB and the FU for fault confirmation of the original fuel leak.
b Compare the initial FOB with the sum of the final FOB and FU for calculated signs of a fuel leak (discrepancy).
(b) The second time:
1 Do the step (1) again in more detail.
3 Troubleshoot the data supplied by the systems that follow:
Subtask 28-11-00-810-055-K ** ON A/C NOT FOR ALL WARNING:
OBEY THE FUEL SAFETY PROCEDURES.
(1) Do a visual check, for a (obvious) fuel leak, at: - the lower surface of the aircraft wings
- the engine pylons and the overboard drains at the aft fairings
- the engine nacelles
- the fuselage adjacent to and below the wing box/center tank area
- the main landing gear bays
- the aircraft drain mast
- the hardstanding.
NOTE: The fuel leakage can be caused by incorrect assembly , damage , the natural deterioration of fuel sealant , or an unserviceable seal .
- if you can see a large fuel leakage, do step (2) and then (3)
- if you can see a small fuel leakage (seepage) or no fuel leakage, do step (3).
(a) Put a container (example, barrel - 42 gal.) under the aircraft at the position where the fuel comes from (example, the drain mast).
(b) Defuel the applicable/adjacent fuel tank, or if necessary, defuel the aircraft (all tanks) AMM 28-25-00-650-001.
(c) In accordance with the local regulations:
1 Remove all the spilt fuel.
2 Clean the fuel spillage from the aircraft.
3 Clean the fuel spillage from the area on the ground (hard standing).
(3) If you can see a small fuel leakage:
(a) If the leak is found from:
- the aircraft's drain mast, do the TSM procedure (Ref. TSM TASK 28-13-00-810-801)
- the pylon drains at the aft fairings, do step (5) and (6).
- the aircraft's main fuel tanks, do step (4).
(4) Do the fuel tank leak checks and repair as necessary AMM 28-11-00-280-002.
(a) Do a manual refuel of the applicable tank when the repair is complete AMM 12-11-28-650-004.
(b) If there is remaining fuel leakage:
1 Make sure that it agrees with that given in AMM 28-11-00-280-002.
2 If necessary, do the repair again.
(5) Do a check for leaks (on the engine fuel supply lines ) in the areas that follow:
(a) The mounting plate between the front spar and the LP valve 1(2) AMM 28-24-41-000-001.
(b) The VALVE-LP FUEL, ENG 1 [12QM] ( VALVE-LP FUEL, ENG 2 [13QM] ) for external leakage.
1 Replace, if necessary AMM 28-24-41-000-001 and AMM 28-24-41-400-001.
(c) The engine 1(2) fuel feed-pipe (shrouded) from between the LP valves 1(2) and the aircraft to pylon (shrouded) connection.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel feed-pipe between the aircraft to pylon connection and the fluid disconnect panel.
NOTE: The aft section of the pylon engine fuel feed pipe is shrouded. If the inner fuel pipe should leak the shroud (outer pipe) drains into the zone A compartment just forward of Rib 9. A fuel leakage can move across the floor of the compartment. The compartment has a drain installed and lets the fuel go overboard at the pylon aft fairing (through the top drain-pipe).
1 Replace all the unserviceable pipes and connections. (e) The engine 1(2) fuel feed-pipe between the fluid disconnect panel and the engine 1(2) fuel flow transmitter.
1 Replace all the unserviceable pipes and connections.
(f) If no leak can be seen in steps (a) thru (e):
1 Pressurize the engine 1(2) LP fuel feed supply as follows:
a Make sure that the L(R) wing tank contains a mimimum of 1000 kg (2200 lb) of fuel. If necessary, refuel the L(R) wing tank AMM 12-11-28-650-003.
b Energize the aircraft electrical circuits AMM 24-41-00-861-002.
c Open, safety and tag the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2) to open the LP valve 12QM (13QM).
d On the HYD/FUEL panel 40VU, push (in) the L(R) wing-tank fuel PUMP P/BSWs.
e Make sure that the OFF legends go off.
f Make sure that the FAULT legends momentarily come on and then stay off.
NOTE: The engine 1(2) LP fuel supplies are now pressurized.
2 Do the steps (6) (a) thru (e) again. a On the HYD/FUEL panel 40VU, release (out) the L(R) wing-tank fuel PUMP P/BSWs.
b Make sure that the OFF legends come on.
c De-energize the aircraft electrical circuits AMM 24-41-00-862-002.
d Remove the safety clip and the tag and close the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2).
(g) At the next engine 1(2) start, and make sure that there are no fuel leaks in its fuel supply.
(6) Do a check for leaks (of the
(a) The mounting block/piping installation between the wing bottom skin and the fuel recirculation check valve L(R) AMM 28-16-42-000-001.
(b) The CHECK VALVE-FUEL RECIRCULATION, L [122QM] ( CHECK VALVE-FUEL RECIRCULATION, R [123QM] ) for external leakage AMM 28-16-42-000-001.
1 Replace, if necessary AMM 28-16-42-000-001 and AMM 28-16-42-400-001.
(c) The engine 1(2) fuel return-pipe between the aircraft to pylon connection (adjacent to check valve 122QM/123QM) and the fluid disconnect panel.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel return-pipe between the fluid disconnect panel and the engine IDG cooling fuel exit point AMM 28-16-00-710-002.
1 Replace all the unserviceable pipes and connections.
(e) Do the applicable Leak Test of the Fuel Recirculation Cooling System as follows:
- for CFM engines (Ref. AMM TASK 73-11-50-360-00200)
- for IAE engines (Ref. AMM TASK 28-16-00-790-00100).
(a) The first time:
1 Make an entry in the aircraft technical log to make a record of this procedure.
2 Return the aircraft to service.
3 Make a record in the aircraft log book for the flight crew, during the next flight, to:
a Monitor and record the initial FOB, the final or current FOB and the FU for fault confirmation of the original fuel leak.
b Compare the initial FOB with the sum of the final FOB and FU for calculated signs of a fuel leak (discrepancy).
(b) The second time:
1 Do the step (1) again in more detail.
NOTE: Make sure that good lighting is available.
2 Do the steps (4) thru (6) again in more detail. 3 Troubleshoot the data supplied by the systems that follow:
- FOB - FQIS Chap. 28-42-00
- FU - FFIS Chap. 73-31-00.
A. Procedure
(a) Put a container (example, barrel - 42 gal.) under the aircraft at the position where the fuel comes from (example, the drain mast).
(b) Defuel the applicable/adjacent fuel tank, or if necessary, defuel the aircraft (all tanks) AMM 28-25-00-650-001.
(c) In accordance with the local regulations:
1 Remove all the spilt fuel.
2 Clean the fuel spillage from the aircraft.
3 Clean the fuel spillage from the area on the ground (hard standing).
(3) If you can see a small fuel leakage:
(a) If the leak is found from:
(4) Do the fuel tank leak checks and repair as necessary AMM 28-11-00-280-002.
(a) Do a manual refuel of the applicable tank when the repair is complete AMM 12-11-28-650-004.
(b) If there is remaining fuel leakage:
1 Make sure that it agrees with that given in AMM 28-11-00-280-002.
2 If necessary, do the repair again.
(5) Do a check for leaks (on the engine fuel supply lines ) in the areas that follow:
(a) The mounting plate between the front spar and the LP valve 1(2) AMM 28-24-41-000-001.
(b) The VALVE-LP FUEL, ENG 1 [12QM] ( VALVE-LP FUEL, ENG 2 [13QM] ) for external leakage.
1 Replace, if necessary AMM 28-24-41-000-001 and AMM 28-24-41-400-001.
(c) The engine 1(2) fuel feed-pipe (shrouded) from between the LP valves 1(2) and the aircraft to pylon (shrouded) connection.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel feed-pipe between the aircraft to pylon connection and the fluid disconnect panel.
(e) The engine 1(2) fuel feed-pipe between the fluid disconnect panel and the engine 1(2) fuel flow transmitter.
1 Replace all the unserviceable pipes and connections.
(f) If no leak can be seen in steps (a) thru (e):
1 Pressurize the engine 1(2) LP fuel feed supply as follows:
a Make sure that the L(R) wing tank contains a mimimum of 1000 kg (2200 lb) of fuel. If necessary, refuel the L(R) wing tank AMM 12-11-28-650-003.
b Energize the aircraft electrical circuits AMM 24-41-00-861-002.
c Open, safety and tag the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2) to open the LP valve 12QM (13QM).
d On the HYD/FUEL panel 40VU, push (in) the L(R) wing-tank fuel PUMP P/BSWs.
e Make sure that the OFF legends go off.
f Make sure that the FAULT legends momentarily come on and then stay off.
a On the HYD/FUEL panel 40VU, release (out) the L(R) wing-tank fuel PUMP P/BSWs.
b Make sure that the OFF legends come on.
c De-energize the aircraft electrical circuits AMM 24-41-00-862-002.
d Remove the safety clip and the tag and close the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2).
(g) At the next engine 1(2) start, and make sure that there are no fuel leaks in its fuel supply.
(6) Do a check for leaks (of theengine/IDG cooling return to tank fuel lines ) in the areas that follow:
(a) The mounting block/piping installation between the wing bottom skin and the fuel recirculation check valve L(R) AMM 28-16-42-000-001.
(b) The CHECK VALVE-FUEL RECIRCULATION, L [122QM] ( CHECK VALVE-FUEL RECIRCULATION, R [123QM] ) for external leakage AMM 28-16-42-000-001.
1 Replace, if necessary AMM 28-16-42-000-001 and AMM 28-16-42-400-001.
(c) The engine 1(2) fuel return-pipe between the aircraft to pylon connection (adjacent to check valve 122QM/123QM) and the fluid disconnect panel.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel return-pipe between the fluid disconnect panel and the engine IDG cooling fuel exit point AMM 28-16-00-710-002.
1 Replace all the unserviceable pipes and connections.
(e) Do the applicable Leak Test of the Fuel Recirculation Cooling System as follows:
(a) The first time:
1 Make an entry in the aircraft technical log to make a record of this procedure.
2 Return the aircraft to service.
3 Make a record in the aircraft log book for the flight crew, during the next flight, to:
a Monitor and record the initial FOB, the final or current FOB and the FU for fault confirmation of the original fuel leak.
b Compare the initial FOB with the sum of the final FOB and FU for calculated signs of a fuel leak (discrepancy).
(b) The second time:
1 Do the step (1) again in more detail.
3 Troubleshoot the data supplied by the systems that follow:
WARNING:
OBEY THE FUEL SAFETY PROCEDURES.
(1) Do a visual check, for a (obvious) fuel leak, at: - the lower surface of the aircraft wings
- the engine pylons and the overboard drains at the aft fairings
- the engine nacelles
- the fuselage adjacent to and below the center tank area
- the fuselage adjacent to and below the rear cargo compartment
- the main landing gear bays
- the rear cargo compartment
- the aircraft drain mast
- the hardstanding.
NOTE: The fuel leakage can be caused by incorrect assembly , damage , the natural deterioration of fuel sealant , an unserviceable seal , or a damaged fuel bladder .
- if you can see a large fuel leakage, do step (2) and then step (3)
- if you can see a small fuel leakage (seepage) or no fuel leakage, do step (3).
(a) Put a container (example, barrel - 42 gal.) under the aircraft at the position where the fuel comes from (example, the drain mast).
(b) Defuel the applicable/adjacent fuel tank, or if necessary, defuel the aircraft (all tanks) AMM 28-25-00-650-001.
(c) In accordance with the local regulations:
1 Remove all the spilt fuel.
2 Clean the fuel spillage from the aircraft.
3 Clean the fuel spillage from the area on the ground (hard standing).
(3) If you can see a small fuel leakage:
(a) If the leak is found from:
- the aircraft's drain mast, do the TSM procedure (Ref. TSM TASK 28-13-00-810-801)
- the pylon drains at the aft fairings, do step (5) and (6).
- the aircraft's main fuel tanks, do step (4).
(4) Do the fuel tank leak checks and repair as necessary AMM 28-11-00-280-002.
(a) Do a manual refuel of the applicable tank when the repair is complete AMM 12-11-28-650-004.
(b) If there is remaining fuel leakage:
1 Make sure that it agrees with that given in AMM 28-11-00-280-002.
2 If necessary, do the repair again.
(5) Do a check for leaks (on the engine fuel supply lines ) in the areas that follow:
(a) The mounting plate between the front spar and the LP valve 1(2) AMM 28-24-41-000-001.
(b) The VALVE-LP FUEL, ENG 1 [12QM] ( VALVE-LP FUEL, ENG 2 [13QM] ) for external leakage.
1 Replace, if necessary AMM 28-24-41-000-001 and AMM 28-24-41-400-001.
(c) The engine 1(2) fuel feed-pipe (shrouded) from between the LP valves 1(2) and the aircraft to pylon (shrouded) connection.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel feed-pipe between the aircraft to pylon connection and the fluid disconnect panel.
NOTE: The aft section of the pylon engine fuel feed pipe is shrouded. If the inner fuel pipe should leak the shroud (outer pipe) drains into the zone A compartment just forward of Rib 9. A fuel leakage can move across the floor of the compartment. The compartment has a drain installed and lets the fuel go overboard at the pylon aft fairing (through the top drain-pipe).
1 Replace all the unserviceable pipes and connections. (e) The engine 1(2) fuel feed-pipe between the fluid disconnect panel and the engine 1(2) fuel flow transmitter.
1 Replace all the unserviceable pipes and connections.
(f) If no leak can be seen in steps (a) thru (e):
1 Pressurize the engine 1(2) LP fuel feed supply as follows:
a Make sure that the L(R) wing tank contains a mimimum of 1000 kg (2200 lb) of fuel. If necessary, refuel the L(R) wing tank AMM 12-11-28-650-003.
b Energize the aircraft electrical circuits AMM 24-41-00-861-002.
c Open, safety and tag the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2) to open the LP valve 12QM (13QM).
d On the HYD/FUEL panel 40VU, push (in) the L(R) wing-tank fuel PUMP P/BSWs.
e Make sure that the OFF legends go off.
f Make sure that the FAULT legends momentarily come on and then stay off.
NOTE: The engine 1(2) LP fuel supplies are now pressurized.
2 Do the steps (6) (a) thru (e) again. a On the HYD/FUEL panel 40VU, release (out) the L(R) wing-tank fuel PUMP P/BSWs.
b Make sure that the OFF legends come on.
c De-energize the aircraft electrical circuits AMM 24-41-00-862-002.
d Remove the safety clip and the tag and close the C/B-1KC1 for engine 1 (C/B-1KC2 for engine 2).
(g) At the next engine 1(2) start, and make sure that there are no fuel leaks in its fuel supply.
(6) Do a check for leaks (of the
(a) The mounting block/piping installation between the wing bottom skin and the fuel recirculation check valve L(R) AMM 28-16-42-000-001.
(b) The CHECK VALVE-FUEL RECIRCULATION, L [122QM] ( CHECK VALVE-FUEL RECIRCULATION, R [123QM] ) for external leakage AMM 28-16-42-000-001.
1 Replace, if necessary AMM 28-16-42-000-001 and AMM 28-16-42-400-001.
(c) The engine 1(2) fuel return-pipe between the aircraft to pylon connection (adjacent to check valve 122QM/123QM) and the fluid disconnect panel.
1 Replace all the unserviceable pipes and connections.
(d) The engine 1(2) fuel return-pipe between the fluid disconnect panel and the engine IDG cooling fuel exit point AMM 28-16-00-710-002.
1 Replace all the unserviceable pipes and connections.
(e) Do the applicable Leak Test of the Fuel Recirculation Cooling System as follows:
- for CFM engines (Ref. AMM TASK 73-11-50-360-00200)
- for IAE engines (Ref. AMM TASK 28-16-00-790-00100).
(a) The first time:
1 Make an entry in the aircraft technical log to make a record of this procedure.
2 Return the aircraft to service.
3 Make a record in the aircraft log book for the flight crew, during the next flight, to:
a Monitor and record the initial FOB, the final or current FOB and the FU for fault confirmation of the original fuel leak.
b Compare the initial FOB with the sum of the final FOB and FU for calculated signs of a fuel leak (discrepancy).
(b) The second time:
1 Do the step (1) again in more detail.
NOTE: Make sure that good lighting is available.
2 Do the steps (4) thru (6) again in more detail. 3 Troubleshoot the data supplied by the systems that follow:
- FOB - FQIS Chap. 28-42-00
- FU - FFIS Chap. 73-31-00.