(a)  34-21023 AOA SIGNAL FAIL

(2)  
The maintenance message is identical for the left and right air data inertial reference systems (ADIRS). The left ADIRS maintenance message is shown on the ADIRS L BITE page on the control display unit (CDU). The right ADIRS maintenance message is shown on the ADIRS R BITE page on the CDU.

(3)  
The angle of attack (AOA) sensors measure and convert angle of attack to electrical signals. These electrical signals go to the ADIRUs.

(4)  
This message shows when the ADIRU receives an invalid signal from the angle of attack (AOA) sensor.

(5)  
This fault causes the status code 23 to show on the inertial system display unit (ISDU).

EFFECTIVITY

34-21 TASKS 813-814
SIL ALL
Page 226 D633A103-SIL Oct 15/2008

(6)  This fault causes the SPD flag to show on the airspeed indicator and the ALT flag to show on the altimeter indicator.
B.  Possible Causes
(1)  
AOA sensor, T433 (left) or T437 (right)

(2)
Wiring between the AOA sensor and the ADIRU

(3)
ADIRU, M1749 (left) or M1752 (right)

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
E 8 C00425 ADIRU LEFT EXC

F/O Electrical System Panel, P6-1
Row Col Number Name
C 14 C01008 ADIRU RIGHT AC
C 15 C00426 ADIRU RIGHT EXC
C 17 C01010 ADIRU RIGHT DC

D.  Related Data
(1)
(SSM 34-21)

(2)
(WDM 34-21)

E.  Initial Evaluation
(1)  
For
the
applicable
ADIRS,
do
this
task:
ADIRS
BITE
Procedure,
34-21
TASK
801.

(2)  
If the maintenance message does not show on the CDU, and the status code does not show on the ISDU, then there was an intermittent fault.

(3)  
If the maintenance message shows on the CDU and the status code shows on the ISDU, then do the Fault Isolation Procedure below.

F. Fault Isolation Procedure
(1)
Replace the applicable AOA sensor.
These are the tasks:
Angle of Attack Sensor Removal, AMM TASK 34-21-05-000-801,
Angle of Attack Sensor Installation, AMM TASK 34-21-05-400-801.

(a)  
For
the
applicable
ADIRS,
do
this
task:
ADIRS
BITE
Procedure,
34-21
TASK
801.

(b)  
If the maintenance message does not show on the CDU and the status code does not show on the ISDU, then you corrected the fault.

(c)  
If the maintenance message shows on the CDU and the status code shows on the ISDU, then continue.

(2)  
Do this check of the wiring between the applicable ADIRU and the AOA sensor:

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

(b)  
Remove the AOA sensor. To remove it, do this task: Angle of Attack Sensor Removal, AMM TASK 34-21-05-000-801.

(c)  
For the left ADIRU and left AOA sensor, do a wiring check between these pins of connector D10015 for the AOA sensor and connector D3687A for the ADIRU:

EFFECTIVITY SIL ALL  34-21 TASK 814 
D633A103-SIL BOEING PROPRIETARY -Copyright # Unpublished Work -See title page for details  Page 227 Oct 15/2008 

　
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