N1 Mismatch greater than 1% during Flex Take Off between Engine 1 and 2

TASK 77-00-00-810-859-A
N1 Mismatch greater than 1% during Flex Take Off between Engine 1 and 2

1. Possible Causes

PS12 sense line
fuel pump
engine identification plug
ECU [4000KS]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 72-23-00-000-006	Removal of the PS12 Line
AMM 72-23-00-000-040	Removal of the PS12 Line
AMM 72-23-00-280-002	Inspection/Check of the PS12 line
AMM 72-23-00-280-003	Inspection/Check of the PS12 Line
AMM 72-23-00-400-006	Installation of the PS12 Line
AMM 72-23-00-400-040	Installation of the PS12 Line
AMM 73-11-10-000-001	Removal of the Fuel Pump and Filter Assembly
AMM 73-11-10-000-003	Removal of the Fuel Pump and Filter Assembly
AMM 73-21-60-000-001	Removal of the Electronic Control Unit (ECU)
AMM 73-21-60-400-001	Installation of the Electronic Control Unit (ECU)

3. Fault Confirmation
Subtask 77-00-00-710-143-A ** ON A/C NOT FOR ALL

A. Test
(1) Not applicable, the fault is evident.

4. Fault Isolation
Subtask 77-00-00-810-116-A ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the crew observation: N1 mismatch during flex take off:
(1) Do the trouble shooting procedure on both engines.
(2) On each engine do a check of the PS12 line:

For absence of blockage or leaks AMM 72-23-00-280-003.
If leaks or absence of blockage are found, tighten unions or replace the PS12 sense line AMM 72-23-00-000-006 and AMM 72-23-00-400-006.
For dents, cracks or wear.
If you find any damage, replace the PS12 sense line AMM 72-23-00-000-006 and AMM 72-23-00-400-006.

(3) Make sure that all piping connections are correctly tightened. If they are loosen, tighten them.
(4) If you find no damage on the PS12 line:

disconnect the PS12 line from the ECU
blow filtered dry air or nitrogen from the ECU (4000KS) side fitting into the PS12 line to clear it in case of any blockage
clean the weep hole with a non metallic wire (max diameter: 0.5 mm).

(5) If the fault continues:

do a continuity check between the following pins of the J14 connector and make sure that the values are in accordance with the thrust rating of the engine installed (see the following table for identification of the different engines).

ENGINE FAMILY Pin number	DISCRETE (29 - 28) (16 - 28) (15 - 28)	PLUG TYPE
CFM56-5A1	0 0 1	OLD/NEW
CFM56-5A1F	0 1 0	OLD/NEW
CFM56-5A3	0 1 1	OLD/NEW
CFM56-5A4	1 0 0	NEW
CFM56-5A4F	1 0 1	NEW
CFM56-5A54	1 1 0	NEW
CFM56-5A5F4	1 1 1	NEW

(6) If the fault continues:

Replace the fuel pump AMM 73-11-10-000-001.

Subtask 77-00-00-810-116-B ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the crew observation: N1 mismatch during flex take off:
(1) Do the trouble shooting procedure on both engines.
(2) On each engine do a check of the PS12 line:

For absence of blockage or leaks AMM 72-23-00-280-002.
If leaks or absence of blockage are found, tighten unions or replace the PS12 sense line AMM 72-23-00-000-040 and AMM 72-23-00-400-040.
For dents, cracks or wear.
If you find any damage, replace the PS12 sense line AMM 72-23-00-000-040 and AMM 72-23-00-400-040.

(3) Make sure that all piping connections are correctly tightened. If they are loosen, tighten them.
(4) If you find no damage on the PS12 line:

disconnect the PS12 line from the ECU
blow filtered dry air or nitrogen from the ECU (4000KS) side fitting into the PS12 line to clear it in case of any blockage
clean the weep hole with a non metallic wire (max diameter: 0.5 mm).

(5) If the fault continues:

do a check of the engine LRU identification screen with the CFDS to see if the engine rating coded through the engine identification plug is correct.

(a) If the rating is not correct:

replace the engine identification plug .

(b) If the rating is correct:

replace the ECU [4000KS] AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(6) If the fault continues:

Replace the fuel pump AMM 73-11-10-000-003.

Subtask 77-00-00-810-116-C ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the crew observation: N1 mismatch during flex take off:
(1) Do the trouble shooting procedure on both engines.
(2) On each engine do a check of the PS12 line:

For absence of blockage or leaks AMM 72-23-00-280-003.
If leaks or absence of blockage are found, tighten unions or replace the PS12 sense line AMM 72-23-00-000-006 and AMM 72-23-00-400-006.
For dents, cracks or wear.
If you find any damage, replace the PS12 sense line AMM 72-23-00-000-006 and AMM 72-23-00-400-006.

(3) Make sure that all piping connections are correctly tightened. If they are loosen, tighten them.
(4) If you find no damage on the PS12 line:

disconnect the PS12 line from the ECU
blow filtered dry air or nitrogen from the ECU (4000KS) side fitting into the PS12 line to clear it in case of any blockage
clean the weep hole with a non metallic wire (max diameter: 0.5 mm).

(5) If the fault continues:

do a check of the identification connector (J14) through the CFDS engine LRU identification.
or
do a continuity check between the following pins of the J14 connector and make sure that the values are in accordance with the thrust rating of the engine installed (see the following table for identification of the different engines).

ENGINE FAMILY Pin number	DISCRETE (29 - 28)	DISCRETE (16 - 28)	DISCRETE (15 - 28)	PLUG TYPE
CFM56-5A1	0	0	1	OLD/NEW
CFM56-5A1F	0	1	0	OLD/NEW
CFM56-5A3	0	1	1	OLD/NEW
CFM56-5A4	1	0	0	NEW
CFM56-5A4F	1	0	1	NEW
CFM56-5A54	1	1	0	NEW
CFM56-5A5F4	1	1	1	NEW

(6) If the fault continues:

Replace the fuel pump AMM 73-11-10-000-001

Subtask 77-00-00-710-144-A ** ON A/C NOT FOR ALL

B. After the subsequent flight, make sure that the fault does not continue.

[Rev.8 from Aug 2018] 2026.04.04 04:37:33 UTC