(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)
If the residual groundspeed error is greater than 20 knots, replace the left IRU.
(5)
Set the SYS DSPL switch to the R position.
(6)
Do the procedure again for the right IRU.
B. Radial Position Error
(1) Figure 103 shows steps to measure the IRS radial position error. Radial position error shows the accuracy of the IRU. IRS radial position error is the distance between IRS computed position and the actual position of the airplane. Acceptable (or excessive) radial position error can be determined with the radial position error chart (Fig. 103). This chart shows acceptable and excessive radial position error as a function of hours in the NAV mode.
8. Prepare for Trouble Shooting
____________________________
A. Set the two mode selector switches on the IRS MSU (pilot's aft overhead panel) to the OFF position.
B. Supply electrical power (Ref 24-22-00/201).
CAUTION: MAKE SURE EQUIPMENT COOLING IS ON BEFORE YOU TURN ON THE ELECTRONIC
_______
SYSTEMS. IF YOU DO NOT, DAMAGE TO EQUIPMENT CAN OCCUR.
C. Supply equipment cooling air (Ref 21-58-00/501)
D. Make sure the systems that follow are operational:
(1) DADC (No. 1 and No. 2)
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A
737-300/400/500MAINTENANCE MANUAL
(2)
Captain's ADI and first officer's ADI
(3)
Captain's HSI and first officer's HSI
E. Make sure the LANDING GEAR LATCH & AIR/GND relay circuit breaker, on the P6 circuit breaker panel, is closed.
F. Close these circuit breakers on the P6 and P18 circuit breaker panels:
(1)
IRS (No. 1 and No. 2)
(2)
DAA (No. 1 and No. 2)
(3)
INST XFR
(4)
INST XFMR (No. 1 and No. 2)
(5)
COMPASS XFMR (No. 1, No. 2 and ALTN)
G. Make sure the ATTITUDE switch is in the NORMAL position.
H. Make sure the COMPASS switch is in the NORMAL position.
I. Set the captain's and first officer's HSI switches to the VOR/ILS position (P7 panel).
J. Set the two mode selector switches on the IRS MSU to the ALIGN position.
K. Input the present position latitude and longitude coordinates into each IRS. You can use the IRS ISDU or the FMS CDU.
NOTE: You can input local latitude and longitude after you set the mode
____ selector switches on the IRS MSU to the ALIGN or NAV position.
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A 737-300/400/500MAINTENANCE MANUAL
FLIGHT DECK EFFECT SIGNIFICANCE RECOMMENDED ACTION
FLASHING ALIGN LIGHT ON IRS MSU. IRU CANNOT ACHIEVE ALIGN-MENT WITHOUT ADDITIONAL OPERATOR ACTION. 1. 2. 3. 4. 5. ENTER KNOWN ACCURATE PRESENT POSITION. IF ALIGN LIGHT IS STILL FLASHING, RE-ENTER THE IDENTICAL POSITION ENTERED IN STEP 1. IF ALIGN LIGHT IS STILL FLASHING, PLACE MODE SELECTOR SWITCH TO OFF. WAIT UNTIL ALIGN LIGHT GOES OUT (APPROXIMATELY 30 SEC). ENSURE THAT AIRPLANE IS NOT MOVING AND REPEAT THE 10-MINUTE ALIGN PROCEDURE. REPLACE IRU IF FAULT LIGHT COMES ON.
ALIGN LIGHT ILLUMINATES STEADILY. ATT AND HDG FLAGS APPEAR ON FLIGHT INSTRUMENTS. AFTER 30 SECONDS, ATT FLAG DIS-APPEARS AND ALIGN LIGHT GOES OUT. ISDU DISPLAYS NO DATA OTHER THAN STATUS. ATTITUDE MODE HAS BEEN NOTE:____ NAV CAPABILITY IS LOST WHEN MODE SELECTOR SWITCH IS PLACED TO ATT. SELECTED. IF ATTITUDE MODE IS NOT DESIRED: PLACE MODE SELECTOR SWITCH TO OFF. WAIT UNTIL ALIGN LIGHT GOES OUT (APPROXIMATELY 30 SEC). RESTART THE 10-MINUTE ALIGNMENT PROCEDURE. IF ATTITUDE MODE IS DESIRED: ENTER MAGNETIC HEADING, USING THE ISDU, OR FMS CDU POS INIT PAGE 1/2. IF ISDU IS USED TO ENTER HEAD-ING, THE LETTER H MUST BE ENTERED FIRST. HEADING FLAGS WILL DISAPPEAR WHEN HEADING IS ENTERED.
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