(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 ADR function calculates airspeed and altitude etc.
(4)
The message 34-21020 shows when the ADIRU detects an internal fault of the ADR. The ADR fault also causes the status code 20 to show on the inertial system display unit (ISDU).
B. Possible Causes
(1)
ADMs
(2)
AOA sensors
(3)
Wiring problem
(4)
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 34-21-11)
(2)
(WDM 34-21-12, 34-21-22)
E. Initial Evaluation
(1)
For
the
applicable
ADIRS,
do
this
task:
ADIRS
BITE
Procedure,
34-21
TASK
801.
(2)
If other maintenance messages are shown on the CDU along with the 34-21020 message, then do the corrective tasks to remove those maintenance messages first.
(a)
After you clear the correlated maintenance messages, if the maintenance message 34-21020 does not show on the CDU, and the status code 20 does not show on the ISDU, and the FAULT light on the MSU goes off, then you corrected the fault.
(b)
After you clear the correlated maintenance messages, if the maintenance message 34-21020 continues to shows on the CDU, and the status code 20 shows on the ISDU, and the FAULT light on the MSU stays on, then do the Fault Isolation Procedure below.
EFFECTIVITY SIL ALL 34-21 TASK 839
D633A103-SIL BOEING PROPRIETARY -Copyright # Unpublished Work -See title page for details Page 272 Oct 15/2008
F. Fault Isolation Procedure
(1)
Do the air data inertial reference system self-test in this task: Air Data Inertial Reference System -Operational Test, AMM TASK 34-21-00-710-801.
(a)
If static and/or pitot ADM test is unsatisfactory, then do these steps.
1) Replace the static and/or pitot ADM as appropriate, these are the tasks: Pitot Air Data Module Removal, AMM TASK 34-21-04-000-801, Pitot Air Data Module Installation, AMM TASK 34-21-04-400-801, Static Air Data Module Removal, AMM TASK 34-21-04-000-802, Static Air Data Module Installation, AMM TASK 34-21-04-400-802. a) If static and/or pitot ADM test is satisfactory, then you corrected the fault. b) If the test is unsatisfactory, then continue.
(b)
If the test is satisfactory, then continue.
(2)
Do the test of the AOA sensor in this task: Angle of Attack Sensor -Inspection, AMM TASK 34-21-05-200-801.
(a)
If the test is unsatisfactory, then replace 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. 1) Re-run the test of the AOA sensor in this task: Angle of Attack Sensor -Inspection,
AMM TASK 34-21-05-200-801.
a) If AOA sensor test is satisfactory, then you corrected the fault.
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