January 1, 2004
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737-700 MAINTENANCE TRAINING MANUAL
IRS - TRAINING INFORMATION POINT - IRU DRIFT CRITERIA

General
You use the position error chart to find the IRU drift.
Time In Navigation Mode
To use the position error chart, you must know the time that the IRU was in the navigation mode. The time is on the vertical axis of the position error chart. If the flight crew did not do any new alignments, the time can be for multiple flight legs.
Drift Criteria
Use the drift from the CDU and the time in the navigation mode to find the drift on the position error chart.Maintenance Manual Procedure
NOTE:  To accomplish the following steps, each IRS mode select switch must remain in the NAV position at flight termination. This is to preserve the IRS position coordinates computed during flight. These coordinates are displayed on the POS REF 2/2 page.
Inertial Reference Residual Groundspeed Error Check
Groundspeed readout must be taken before the airplane has been stationary for three minutes. The system may zero the display after three minutes.
Set the SYS switch to the L position on the ISDU.
Set the DSPL switch to the TRK/GS position on the ISDU.
When the airplane is stationary, the ISDU display shows the residual groundspeed error.
Make sure these conditions do not occur:
-The residual groundspeed error is 15 knots or larger after each of two checks, one after the other. -The residual groundspeed error is 21 knots or larger at the end of one check.
If one of the above conditions occurs replace the ADIRU.
A34-28-300-071.fm
January 1, 2004
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737-700 MAINTENANCE TRAINING MANUAL
A34-28-300-071.fm
RADIAL POS ERROR (NMI)
40
35
30
25
20
15
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5
0

REPLACE - 1 FLIGHT  FLIGHTS REPLACE - 2 CONSECUTI VE 

OK 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 TIME IN NAV MODE (HOURS)

IRS - TRAINING INFORMATION POINT - IRU DRIFT CRITERIA

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COMMON DISPLAY SYSTEM
(CDS)

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