(2)
In order to remove power from the IRUs, set the mode selector switch on the IRS MSU to OFF, instead of opening circuit breakers.
(3)
Make sure that the airplane is not moved during alignment.
(4)
When you clear a malfunction code, you may cause another malfunction code to be shown. You should then clear this new malfunction code.
(5)
The IRS Malfunction Codes (Fig. 102) are applicable to the left and/or right IRS.
6. BITE Procedure______________
A. Malfunctions or failures of the IRS system can also be identified by the use of the FMS BITE (Built-In Test Equipment) procedures, contained in Chapter 22.
B. The FMS BITE is started and controlled through the FMCS CDU. The CDU is the flight compartment control and display for actuating and evaluating FMCS, DFCS, A/T, EFIS, and IRS BITE (Ref 22-01-10, FMS BITE - D&O). Once the test has been started from the CDU, the system under test will transmit plain text messages to be shown on the CDU. In response to the messages, the operator can set flight compartment controls, and/or do data entries through the CDU. Test pass or failure is shown on the CDU display.
C. Do the IRS BITE trouble shooting per 22-05-10, IRS BITE - T/S.
NOTE: Trouble shooting procedures for FMCS, DFCS, A/T, and EFIS are in
____
these sections:
FMCS BITE - T/S, 22-02-10
DFCS BITE - T/S, 22-03-10
A/T BITE - T/S, 22-04-10
EFIS BITE - T/S, 22-07-10
D. After you have completed all BITE tests, push the INIT REF key on the FMCS CDU to exit the BITE mode.
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A 737-300/400/500MAINTENANCE MANUAL
7. IRS Accuracy Criteria
_____________________
A. Residual Groundspeed Error
NOTE: Groundspeed readout must be taken before the airplane has been
____ stationary for three minutes. The system may zero the display after three minutes.
(1)
Set the SYS DSPL switch to the L position on the ISDU.
(2)
Set the DSPL SEL switch to the TK/GS position on the ISDU.
(3)
When the airplane is stationary, the ISDU display shows the residual groundspeed error.
(4)
Replace the left IRU (Ref 34-28-31/401) if one of these conditions occurs:
(a)
The residual groundspeed error is 15 knots or larger after each of two consecutive checks.
(b)
The residual groundspeed error is 21 knots or larger at the end of one check.
(5)
Set the SYS DSPL switch to the R position.
(6)
Do the procedure again for the right IRU.
B. Radial Position Error
NOTE: The mode select switch must stay in the NAV position at the end of
____
the flight and also during this procedure.
(1)
Push the RTE key on the CDU.
(a) Make sure that the RTE page shows.
(2)
Put the airport identification into the CDU scratchpad.
(3)
Push line select key (LSK) 1R on the CDU.
(a) Make sure that the airport identification shows as the destination.
(4)
Put the gate latitude and longitude into the CDU scratchpad.
NOTE: Do not put spaces between the latitude and longitude.
____
(5) Push the LEGS key on the CDU.
(a) Make sure that the LEGS page 1/1 shows.
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737-300/400/500MAINTENANCE MANUAL
(6)
Push LSK 1L on the CDU.
(a) Make sure that an identification point for the airplane position shows.
(7)
Push the INIT/REF key on the CDU.
(a) Make sure that the PERF INIT page shows.
(8)
Push the LSK adjacent to <INDEX.
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