S 865-081
 (4)  Set the switches on the MSU to the ALIGN or NAV position.
 D.  Procedure
 S 865-082
 (1)  
Set the SYS DSPL switch on the ISDU to the L position.

 S 865-083

 (2)
Set and hold the DSPL SEL switch on the ISDU in the TEST position.

 NOTE: You must hold the DSPL SEL switch in the TEST position or
____ it will return to the TK/GS position and the test will stop. Run the test again if you do not see all the results of the test.
 (a)  
For seconds 0-2, make sure these indications occur: 1) All the segment and punctuation indicators on the ISDU come on. 2) The ALIGN, FAULT, ON DC, and DC FAIL annunciators on the left side of the MSU come on.

 3)  The IRS master cation light on the captain's side of the pilot's lightshield comes on.

 (b)  
For seconds 2-10, make sure the indications occur: 1) The ALIGN, FAULT, ON DC, and DC FAIL annunciators on the left side of the MSU go off. 2) The IRS master caution light on the captain's side of the pilot's light shield goes off.

 3)  All the segment and punctuation indicators on the ISDU go off.

 (c)  
Release the DSPL SEL switch on the ISDU.

 (d)  
Set the SYS DSPL switch on the ISDU to the R position.

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 (e)  Set and hold the DSPL SEL switch on the ISDU in the TEST position. 1) For seconds 0-2, make sure that these indications occur:
 a)  All the segment and punctuation indicators on the ISDU come on. b) The ALIGN, FAULT, ON DC, and DC FAIL annunciators on the right side of the MSU come on. c) The IRS master caution light on the first officer's side of the pilot's lightshield comes on. 2) For seconds 2-10, make sure that these indications occur: a) The ALIGN, FAULT, ON DC, and DC FAIL annunciators on the right side of the MSU go off. b) The IRS master caution light on the first officer's side of the pilot's lightshield goes off. c) All the segment and punctuation indicators on the ISDU go off.
 E.  Put the Airplane Back to Its Usual Condition
 S 865-092
 CAUTION:_______SOME SWITCHES MUST BE PULLED AND THEN TURNED. IF YOU TRY TO TURN THESE SWITCHES BEFORE YOU PULL THEM, YOU CAN DAMAGE THE SWITCH.
 YOU MUST MOVE THE CDU SWITCH TO THE OFF POSITION BEFORE POWER IS REMOVED FROM THE AIRPLANE. IF THE POWER IS REMOVED WITH THE IRU's ON, THE IRS WILL SWITCH TO BATTERY POWER AUTOMATICALLY AND A WARNING HORN WILL SOUND.
 (1)  
Turn the mode switches on the MSU to the OFF position.

 (2)  
Remove equipment cooling if it is not necessary (AMM 21-58-00/501).

 (3)
Remove electrical power if it is not necessary (AMM 24-22-00/201).

 S 865-085
 S 865-086
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 INERTIAL REFERENCE SYSTEM - DESCRIPTION AND OPERATION
_____________________________________________________
 1.  General (Fig. 1 and Fig. 2)_______
 A.  The inertial reference system (IRS) provides inertial navigation data to user systems. It uses a ring laser gyro instead of the conventional rate gyro to sense angular rate about the roll, pitch and yaw axes. The system is termed strapdown since its sensors are, in effect, directly mounted to the airframe.
 B.  The inertial reference system (IRS) includes two inertial reference units (IRU), one inertial system display unit (ISDU), one mode select unit (MSU), one master caution unit (MCU), two digital/analog adapters (DAA) and two radio digital distance magnetic indicators (RDDMI). The IRS provides the inertial navigation data and the inertial flight control data to other systems (Fig 2).
 C.  The main function of each IRU is to sense and compute linear accelerations and angular turning rates about the airplane's pitch, roll, and yaw axes. This data is used for pitch and roll displays and navigational computations.
　
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