N1 Mismatch between Engine 1 and Engine 2

TASK 73-00-00-810-873-A
N1 Mismatch between Engine 1 and Engine 2

1. Possible Causes

HMU-1 (4000KC1)
HMU-2 (4000KC2)

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 72-00-00-200-026	Inspection/Check of the PS3 Line
AMM 72-00-00-220-001	Inspection of the PS3 Line Connections
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 73-21-10-000-001	Removal of the Hydromechanical Unit (HMU)
AMM 73-21-10-000-002	Removal of the Hydromechanical Unit (HMU)
AMM 73-21-10-400-001	Installation of the Hydromechanical Unit (HMU)
AMM 73-21-10-400-002	Installation of the Hydromechanical Unit (HMU)
AMM 73-29-00-710-040	Operational Test of the FADEC on the ground (with Engine Motoring)

3. Fault Confirmation
Subtask 73-00-00-710-192-A ** ON A/C NOT FOR ALL

A. Test
(1) Not applicable, you cannot confirm this fault on the ground.

4. Fault Isolation
Subtask 73-00-00-810-123-A ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the crew observation: N1 Mismatch between Engine 1 and Engine 2
(1) Make sure that the PO fitting on the ECU (4000KS) is clear and not clogged.

Do an operational test of the FADEC 1 (2) A (B) on the ground (with engine motoring) AMM 73-29-00-710-040.

(2) After the flight crew report, if the mismatch occurs at take-off:
(a) Do the trouble shooting procedure on the engine with the lowest N1 actual.
(b) On this engine, do a check of the PS12 line to make sure that it is not cracked and/or broken AMM 72-23-00-280-003.
(3) After the flight crew report, if the mismatch occurs at climb:
(a) Do the trouble shooting procedure on the engine with the highest N1 actual.
(b) On this engine, do a check of the PS12 line to make sure that it is not cracked and/or broken AMM 72-23-00-280-003.
(4) Do a check of the PS3 line AMM 72-00-00-220-001.
(5) Replace the HMU-1 (4000KC1) ( HMU-2 (4000KC2)) AMM 73-21-10-000-001 and AMM 73-21-10-400-001.

Subtask 73-00-00-810-123-B ** ON A/C NOT FOR ALL

A. If the fault symptom is identified by the crew observation: ENG 1 or 2 - Incorrect power at/after take-off (N1 mismatch):
(1) Make sure that the PO fitting on the ECU (4000KS) is clear and not clogged.

Do an operational test of the FADEC 1 (2) A (B) on the ground (with engine motoring) AMM 73-29-00-710-040.

(2) After the flight crew report, if the mismatch occurs at take-off:
(a) Do the trouble shooting procedure on the engine with the lowest N1 actual.
(b) On this engine, do a check of the PS12 line to make sure that it is not cracked and/or broken AMM 72-23-00-280-002.
(3) After the flight crew report, if the mismatch occurs at climb:
(a) Do the trouble shooting procedure on the engine with the highest N1 actual.
(b) On this engine, do a check of the PS12 line to make sure that it is not cracked and/or broken AMM 72-23-00-280-002.
(4) Do a check of the PS3 line AMM 72-00-00-200-026.
(5) Replace the HMU-1 (4000KC1) ( HMU-2 (4000KC2)) AMM 73-21-10-000-002 and AMM 73-21-10-400-002.

Subtask 73-00-00-710-193-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 04:35:12 UTC