Loss of Detection by Engine-1 Loop-A AGB and Loop B

TASK 26-12-00-810-873-A
Loss of Detection by Engine-1 Loop-A AGB and Loop B

1. Possible Causes

DET-FIRE, CORE AGB LOOP A [4002WD1]
wiring
fire-electrical-harness loop-A
FDU-ENG1 [2WD1]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
TSM TASK 26-12-00-810-804-A	Loss of Detection by Engine-1 Loop B
TSM TASK 26-12-00-810-869-A	Loss of Detection by Engine-1 Loop-A Core and Loop B
AMM 26-12-00-200-802	Visual Inspection of the Engine Fire Detection System
AMM 26-12-00-710-002	Operational Test of the Engine Fire and Overheat Detection with the Centralized Fault Display System (CFDS)
ASM 261201
AWM 261205
AMM 26-12-17-000-802	Removal of the Forward Fire/Overheat Detector
AMM 26-12-17-400-802	Installation of the Forward Fire/Overheat Detector
AMM 26-12-34-000-001	Removal of the Engine Fire-Detection Unit (FDU)
AMM 26-12-34-400-001	Installation of the Engine Fire-Detection Unit (FDU)
AMM 26-12-61-000-802	Removal of the Loop-A Fire Harness and Electrical Rail Assembly
AMM 26-12-61-400-802	Installation of the Loop-A Fire Harness and Electrical Rail Assembly
AWM 715175

3. Fault Confirmation
Subtask 26-12-00-710-185-A ** ON A/C NOT FOR ALL

A. Test
(1) Do the operational test of the engine fire and overheat detection from the Multipurpose Control and Display Unit (MCDU) AMM 26-12-00-710-002.

4. Fault Isolation
Subtask 26-12-00-810-128-A ** ON A/C NOT FOR ALL

A. If the test confirms the fault:

If, on the PFR, the CHECK ENG1 FIRE LOOP A AGB fault message is shown, do not do the troubleshooting that follows but go to (Ref. TSM TASK 26-12-00-810-869).
Do a visual inspection of the core-AGB loop-A fire-detector (4002WD1) AMM 26-12-00-200-802.

(1) If the fire detector is damaged:

Replace the DET-FIRE, CORE AGB LOOP A [4002WD1] AMM 26-12-17-000-802 and AMM 26-12-17-400-802.

(2) If there is no visual damage:

Disconnect the electrical harness from the core-AGB loop-A fire-detector (4002WD1).
On the responder of core-AGB loop-A fire-detector (4002WD1), make sure that the resistance value is between 3078 ohms and 3402 ohms between pins A and C, ASM 261201.

(a) If the resistance values are out of the specified limits:

Replace the DET-FIRE, CORE AGB LOOP A [4002WD1] AMM 26-12-17-000-802 and AMM 26-12-17-400-802.
Connect the electrical harness to the core-AGB loop-A fire-detector (4002WD1).

(b) If the resistance values are in the specified limits:

Do a check of the wiring between the pins A and C of the core-AGB loop-A fire-detector (4002WD1) and the first terminal-block, AWM 261205 and AWM 715175.

1 If the wiring is not correct:

Do a check of the wiring between the first terminal-block and the fire-electrical-harness loop-A AWM 261205 and AWM 715175.

a If the wiring is not correct:

Repair it.
Connect the electrical harness to the core-AGB loop-A fire-detector (4002WD1).

b If the wiring is correct:

Replace the fire-electrical-harness loop-A AMM 26-12-61-000-802 and AMM 26-12-61-400-802.

2 If the wiring is correct:

Replace the FDU-ENG1 [2WD1] AMM 26-12-34-000-001 and AMM 26-12-34-400-001.
Connect the electrical harness to the core-AGB loop-A fire-detector (4002WD1).

Subtask 26-12-00-810-159-A ** ON A/C NOT FOR ALL

B. For the fault message related to engine-1 loop-B, refer to the (Ref. TSM TASK 26-12-00-810-804).

[Rev.8 from Aug 2018] 2026.04.04 04:27:15 UTC