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 NOTE: If the mode selector is moved out of NAV mode, the system
____ must be realigned on the ground in a static position.
 (5)  ATT REF - Provides pitch and roll attitude signals and a platform heading output. No navigation capability is available thus the CDU is blank because the computer is de-energized. Platform will remain properly oriented with local vertical because the accelerometers provide analog precission signals to the gyros. ATT REF must be manually selected by the operator.
 NOTE: The attitude outputs are not reliable for 3 minutes after
____ selecting ATT REF unless airplane attitude and speed remains constant. The initial selection of ATT REF places the system in a high-gain leveling mode and airplane maneuvers should be kept to a minimum for the 3-minute period.
 (6)  
The READY NAV Annunciator comes on when system alignment has been completed and mode selector may be set to NAV position. READY NAV light goes out when NAV position is selected. The annunciator has press-to-test capability.

 (7)  
The BATT Annunciator comes on when 28-volt dc backup battery voltage has decreased below 20 volts dc. Also the WARN light comes on and the system should be turned off. The annunciator has press-to-test capability.

 4.  Control/Display Unit (Fig. 8)
____________________
 A.  Three control/display units (CDU) are used to enter present position and waypoint coordinates, to control track selection, and to display navigation data generated by the system. The control/display units for INS No. 1 and 2 are located on the forward control stand electronic panel. The CDU for INS No. 3 is located on the aft control stand electronic panel (Fig. 1). The CDU power supply, which operates from 28 volts dc supplied by the INU power supply, provides 5-volt dc output for the electronics and lamps of the digital displays.
 B.  The left and right numerical displays (Fig. 8) read out navigation data selected for monitoring by the display selector or data to be inserted into the computer. Data insertion is accomplished when the INSERT pushbutton is pressed. The display of meaningful data depends upon certain controlling system functions, such as mode of operation, initial track established, or minimum ground speed. These functions are identified in the description of the display selector. For an explanation of the navigation terms monitored by the display selector (Fig. 3).
 EFFECTIVITY AIRPLANES WITH LTN-72 INS  
  CONFIG  01 A Page 21  Apr 25/86

34-41-00
 C. The primary functions and CDU indications are as follows:
 (1)  
The left and right numerical displays provide visual readouts of various data quantities selected with the display selector switch (Fig. 9).

 (2)  
The ALERT annunciator comes on 2 minutes before reaching each waypoint. Thirty seconds before reaching the waypoint, the ALERT light goes out in automatic operation or starts flashing in manual operation and continues to flash until a manual track change is performed. The ALERT light will not come on until ground speed is greater than 250 knots.

 (3)  
The BATT annunciator comes on when system automatically transfers to 28-volt dc backup power due to 115-volt ac power interruption or failure. Battery operation is limited to approximately 15 minutes.

 (4)  
The WARN annunciator comes on steady to indicate a system malfunction or flashes when incorrect present position coordinates have been entered or to indicate system degradation.

 (a)  During the attitude slew test procedure, the WARN lamp flashes continuously when the attitude slew test connector is inserted in J4 on the front of the INU. The WARN lamp remains lit until the attitude slew test connector is removed.

 (5)  
Data Keyboard provides 10 keys (0-9) to enter present position and waypoint coordinates, from/to waypoints, desired crosstrack offset, and track hold into display register. The CLEAR key clears accumulated contents of display register. The N, E, S, and W keys are used when entering latitude or longitude and the L and R keys are used when entering desired crosstrack offset. The DTK key is used to initiate INS track hold mode and the 1 key to initiate desired crosstrack offset mode.

 (6)  
HOLD Pushbutton, when pressed, holds present position readout on left and right numerical displays with display selector set to POS (position).

 (7)  
Display Selector selects data for presentation on the left and right numerical displays (Fig. 9).

 (8)  
The DIM control controls intensity of numerical displays and FROM/TO displays lamps.

 (9)  
When the INSERT pushbutton is illuminated, the INS is ready for insertion of data. Pressing the INSERT pushbutton, transfers the display register contents, selected on the keyboard, into the computer.
　
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