(1)
INU

(2)
CDU

IF -play, ensure WPT 0 is not selected. blank corresponding numerical dis-Pressing N, S, E, W key does not 

or STBY). mode selector switch to ALIGN (NAV selector switch is set to WPT and Still not OK, check that display 

Pressing one or more keys does not cause corresponding readout on dis-play, replace CDU.
Left and right displays are not within |0.2 arc minute of inserted data, replace in sequence:
(1)
INU

(2)
CDU

EFFECTIVITY
 AIRPLANES WITH LTN-72 INS     CONFIG  01 A Page 128  Aug 25/87

34-41-00
PROCEDURE 16

ATED. DISPLAYS NOT CORRECT WHEN DATA SELECTOR SET TO XTK/TKE AND SPECIFIC TRACKS INITI-
(2) INU (Ref 34-41-03) (1) CDU (Ref 34-41-02) in sequence: data is not inserted in INS, replace and INSERT lamps do not go out and When INSERT key is pressed, TK CHG  to selections keyed in, replace CDU. FROM/TO display does not correspond 
Left displays are not as specified for tracks 12 and 21, replace in sequence: (2) CDU (1) INU 

PROCEDURE 17

EFFECTIVITY AIRPLANES WITH LTN-72 INS  
  CONFIG  01 A Page 129  Aug 25/87

34-41-00
PROCEDURE 18

SYSTEM MALFUNCTIONS WITH DATA SELECTOR SET TO WIND POSITION.

simulated (Ref 34-12-00, A/T), replace in sequence: Left and right data displays remain blank at true airspeeds in excess of 170 knots (2) CDU (Ref 34-41-02) (1) INU (Ref 34-41-03) 

PROCEDURE 19

SYSTEM MALFUNCTIONS WITH DATA SELECTOR SET TO DRS TK/STS 

(2) INU (Ref 34-41-03) (1) CDU (Ref 34-41-02) Replace in sequence: 

EFFECTIVITY
 AIRPLANES WITH LTN-72 INS     CONFIG  01 A Page 130  Aug 25/87
34-41-00
PROCEDURE 20

PROCEDURE 21

EFFECTIVITY AIRPLANES WITH LTN-72 INS  
  CONFIG  01 A Page 131  Aug 25/87

34-41-00
PROCEDURE 22

PROCEDURE 23

SYSTEM MALFUNCTIONS FOLLOWING REVERSION FROM NAV MODE TO ATT MODE OF OPERATION

Ensure INU rack cooling air blower is operating, replace INU, CDU. 

EFFECTIVITY
 AIRPLANES WITH LTN-72 INS     CONFIG  01 A Page 132  Aug 25/87
34-41-00
 INERTIAL NAVIGATION SYSTEM - TROUBLE SHOOTING
_____________________________________________
 1.  General
_______
 A.  The following trouble shooting procedures are based on performance of the system operational test and are presented in tree-type format. The test steps (heavy-line box) are connected by arrows to show the OK condition path. When all steps in the OK condition path check out, the system is operable.
 B.  When a test step does not check out, follow the NOT OK line to the box containing the trouble symptom. Turn to the procedure indicated and continue to follow a single line by analyzing the results of each test step until the required corrective action is determined. Perform the specified corrective action, then repeat the step at which the failure was encountered.
 C.  All trouble shooting procedures are based on the assumption that wiring is OK and that electrical power is available. If the corrective action in the procedure does not correct the problem, check wiring using the wiring diagram.
 D.  The CDU BAT annunciator illuminates when the INS is operating on the 28 volts dc backup battery.
 E.  The MSU BATT annunciator and CDU WRN annunciator illuminate when the 28 volt dc backup battery voltage is less than 20 volts.
 F.  On airplanes with LTN-92 INS, a WRN annunciation indicates that INS action/malfunction messages exist. The action and malfunction messages can be displayed on the CDU. The action messages identify recommended actions that should be taken to correct the problems indicated by the malfunction messages.
 G.  On airplanes with LTN-72RL INS, a CDU WRN annunciation indicates that INS action/malfunction code(s) exist. The action and malfunction codes can be displayed on the CDU. The action codes identify recommended actions that should be taken to correct a problem identified by an accompanying malfunction code.
 H.  Any failure that causes the WRN annunciator on the CDU to come on will also trip the INU fault indicator from the normal white indication to a yellow indication. Two conditions (not failures) will cause the WRN annunciator to come on but will not trip the fault indicator. These are low battery voltage (indicated by MSU BATT annunciator illuminating) and recycling from ATT mode to any other mode except OFF. If primary 115-volt ac power source should fail, fall below, or go above preset levels, a power monitor will automatically switch the system to the backup battery.
　
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