Loss of Detection by Engine-1 Loop-B Pylon

TASK 26-12-00-810-853-A
Loss of Detection by Engine-1 Loop-B Pylon

1. Possible Causes

DET-FIRE, ENG 1 PYLON LOOP B [4WD1]
HARNESS-FIRE DET, ENG 1 PYLON LOOP B STUD A [41WD1]
HARNESS-FIRE DET, ENG 1 PYLON LOOP B STUD C [42WD1]
wiring
FDU-ENG1 [2WD1]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
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 261207
AMM 26-12-16-000-803	Removal of the Pylon Fire Detector
AMM 26-12-16-400-803	Installation of the Pylon Fire 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 26-12-63-000-801	Removal of the Pylon Fire-Detector Harness
AMM 26-12-63-400-801	Installation of the Pylon-Fire Detector Harness

3. Fault Confirmation
Subtask 26-12-00-710-156-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 26-12-00-810-108-A ** ON A/C NOT FOR ALL

A. If the test confirms the fault:

Do a visual inspection of the engine-1-pylon loop-B fire-detector (4WD1) AMM 26-12-00-200-802.

(1) If the fire detector is damaged:

Replace the DET-FIRE, ENG 1 PYLON LOOP B [4WD1] AMM 26-12-16-000-803 and AMM 26-12-16-400-803.

(2) If there is no visual damage, do a visual inspection of the pylon fire-detector harnesses (41WD1) and (42WD1):
(a) If one or more pylon fire-detector harness(es) is (are) damaged:

Replace it (them):
. For HARNESS-FIRE DET, ENG 1 PYLON LOOP B STUD A [41WD1] AMM 26-12-63-000-801 and AMM 26-12-63-400-801
. For HARNESS-FIRE DET, ENG 1 PYLON LOOP B STUD C [42WD1] AMM 26-12-63-000-801 and AMM 26-12-63-400-801.

(b) If there is no visual damage on the pylon fire-detector harnesses:

Disconnect the pylon fire-detector harnesses (41WD1) and (42WD1) from the engine-1-pylon loop-B fire-detector (4WD1).
On the responder, make sure that the resistance value is between 4275 ohms and 4725 ohms between pins A and C, ASM 261201.

1 If the resistance values are out of the specified limits:

Replace the DET-FIRE, ENG 1 PYLON LOOP B [4WD1] AMM 26-12-16-000-803 and AMM 26-12-16-400-803.

2 If the resistance values are in the specified limits:

Do a continuity test of the wiring of the pylon fire-detector harnesses (41WD1) and (42WD1) AWM 261207.

a If there is no continuity:

Replace it (them):
. For HARNESS-FIRE DET, ENG 1 PYLON LOOP B STUD A [41WD1] AMM 26-12-63-000-801 and AMM 26-12-63-400-801.
. For HARNESS-FIRE DET, ENG 1 PYLON LOOP B STUD C [42WD1] AMM 26-12-63-000-801 and AMM 26-12-63-400-801.

b If there is continuity:

Do a check of the wiring between the first terminal-block and the pylon fire-detector harnesses (41WD1) and (42WD1), AWM 261207.

* If the wiring is not correct:
* - Repair it (them).
* - Connect the pylon fire-detector harnesses (41WD1) and (42WD1) to the engine-1-pylon loop-B fire-detector (4WD1).

* 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 pylon fire-detector harnesses (41WD1) and (42WD1) to the engine-1-pylon loop-B fire-detector (4WD1).

Subtask 26-12-00-710-157-A ** ON A/C NOT FOR ALL

B. Do the test given in Para. 3.

[Rev.8 from Aug 2018] 2026.04.04 04:27:12 UTC