(h)  If the tests in the installation tasks for the instrument landing system and the integrated standby flight display are satisfactory, and the G/S or LOC flag does not show on the integrated standby flight display, then you corrected the fault.
-------------------------END OF TASK ---------------------------
809. HDG Flag on the Integrated Standby Flight Display -Fault Isolation
A.  Description
(1)  The HDG flag shows when there is a loss of magnetic heading function.
B.  Possible Causes
(1)  ADIRU.
EFFECTIVITY

34-24 TASKS 808-809
SIL ALL
Page 206 D633A103-SIL Jun 15/2008

(2) Integrated Standby Flight Display.
C.  Circuit Breakers
(1)  These are the primary circuit breakers related to the fault:
CAPT Electrical System Panel, P18-1
Row Col Number Name
E 5 C01009 ADIRU LEFT DC
E 7 C01007 ADIRU LEFT AC

CAPT Electrical System Panel, P18-2
Row Col Number Name
D 8 C01551 ISFD

E 8 C00425 ADIRU LEFT EXC
D.  Related Data
(1)
(SSM 34-24-15).

(2)
(WDM 34-24-15).

E.  Initial Evaluation
(1)  Make sure that these circuit breakers are closed:
CAPT Electrical System Panel, P18-1
Row Col Number Name
E 5 C01009 ADIRU LEFT DC
E 7 C01007 ADIRU LEFT AC

CAPT Electrical System Panel, P18-2
Row Col Number Name
D 8 C01551 ISFD

E 8 C00425 ADIRU LEFT EXC
(2)  
If the HDG flag does not show on the integrated standby flight display, then there was an intermittent fault.

(3)  
If the HDG flag shows on the integrated standby flight display, then do the Fault Isolation Procedure below.

F. Fault Isolation Procedure
(1)  
Do this task: Air Data Inertial Reference System -Alignment from the ISDU, AMM TASK 34-21-00-820-802 or Air Data Inertial Reference System -Alignment from the FMC CDU, AMM TASK 34-21-00-820-801.

(a)  
If the HDG flag does not show on the integrated standby flight display, then you corrected the fault.

(b)  
If the HDG flag shows on the integrated standby flight display, then continue.

(2)
Replace the left air data inertial reference unit, M1749.
These are the tasks:
Air Data Inertial Reference Unit Removal, AMM TASK 34-21-01-000-801,
Air Data Inertial Reference Unit Installation, AMM TASK 34-21-01-400-801.

(a)  
If the test in the installation task for the air data inertial reference unit is satisfactory and the HDG flag does not show on the integrated standby flight display, then you corrected the fault.

(b)  
If the HDG flag shows on the integrated standby flight display, then continue.

(3)
Replace the integrated standby flight display, N226. These are the tasks: Integrated Standby Flight Display Removal, AMM TASK 34-24-02-000-801, Integrated Standby Flight Display Installation, AMM TASK 34-24-02-400-801.

(a)  
If the test in the installation task for the integrated standby flight display is satisfactory and the HDG flag does not show, then you corrected the fault.

(b)  
If the HDG flag shows on the integrated standby flight display, then continue.

(4)  
Do this check of the wiring between the left air data inertial reference unit and the integrated standby flight display:

(a)  
Remove the air data inertial reference unit, M1749. To remove it, do this task: Air Data Inertial Reference Unit Removal, AMM TASK 34-21-01-000-801.

(b)  
Remove the integrated standby flight display, N226. To remove it, do this task: Integrated Standby Flight Display Removal, AMM TASK 34-24-02-000-801.
　
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