(3)  
CLR (clear) pushbotton - When pressed before ENT is pressed, removes entered data from display.

 (4)  
ENT (enter) pushbutton - When pressed, enters data input via data entry pushbuttons into the INU.

 (5)  
Data entry pushbuttons - When pressed, enter data in the display line indicated between entry line markers.

 (6)  
HLD (hold) pushbutton - When pressed, freezes present position display, except in waypoint select modes where it is used to insert a blank waypoint.

 (7)  
EXP (expand) pushbutton - Expands selected display categories.

 (8)  
Display slew pushbuttons - Enable slewing of appropriate lines of display. Normally, display will advance one line each time push-button is pressed or when continuously pressed will continuously slew.

 (9)  
Data display select pushbuttons - Allow display of particular data category.

 (10)
 ALR (alert) annunciator - Comes on at a preset time before airplane reaches each approaching To waypoint. When INS is in automatic mode, goes out to indicate that a leg change has been made automatically; when INS is in manual mode, flashes to indicate that a leg change must be made manually.

 (11)
 OFS (offset) annunciator - Comes on when INS is in the offset or parallel track mode.

 (12)
 WRN (warn) annunciator - Comes on when system malfunction occurs.

 (13)
 BAT (battery) annunciator - Comes on when INS is operating on 28 vdc backup power.

 11. VHF Navigation Control Panel (Fig. 8)
____________________________
 A.  Each VHF navigation control panel includes switch/indicators, frequency selector knobs and a frequency display.
 EFFECTIVITY
 AIRPLANES WITH LTN-72RL OR  CONFIG LTN-92 INS  01 Page 24  Apr 25/91

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ATTITUDE SPHERE

INCLINOMETER
INDICATOR
Attitude Director Indicator
Figure 10

EFFECTIVITY

 CONFIG 3
AIRPLANES WITH LTN-72RL OR
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LTN-92 INS
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 B.  A segmented light bar display indicates the VHF frequency. The light bars are checked when the DISPLAY TEST switch is pressed.
 C.  The INS APRCH switch/indicator, when operated, enables the INS to be used for non-precision R-NAV approaches. When the NORM switch/indicator is operated the INS is restored to normal operation
 D.  The AUTO switch/indicator, when operated, enables the INS to automatically tune the VHF navigation receiver and DME interrogator. When the MAN switch/indicator is operated the control panel frequency selector knobs are used to manually tune the VHF and DME.
 12. Inertial Navigation Unit
________________________
 A.  The inertial navigation units (INU), one for each INS, are installed in individual mounting trays on main equipment center shelf E2-6 (Fig. 1). Each INU weighs approximately 60 pounds and consists of a computer and digital subsystem, platform and platform electronics, synchro repeaters and an integral power supply. A temperature control and sensing circuit maintains required environmental conditions. Mounted on the front panel of each INU are an elapsed time indicator and a magnetically latched fault indicator. Any failure that causes the CDU WRN annunciator 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.
 B.  If the 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.
 C.  The INU inertial platform is the source of north-south and east-west acceleration signals for the INS. The INU digital computer uses the acceleration signals to compute the actual track, ground speed, and position coordinates of the airplane. The digital computer stores the desired route coordinates, computes steering commands to automatically guide the airplane along the desired flight path, and computes airplane crosstrack deviation.
 13. Battery Unit
____________
 A.  The battery unit (BU) provides auxiliary power to initiate INS turn on and to supply essential power to maintain INS operation when the 115-volt input power is interrupted or drops below the required voltage. The battery unit contains 19 nickel-cadmium cells which are connected in series to furnish 24 volts dc. A 20-ampere circuit breaker on the front of the battery unit protects it from excessive current flow if a short circuit develops. The battery unit will sustain INS operation for periods of up to 15 minutes.
　
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本文鏈接地址：747飛機維護手冊AMM CHAPTER 34 - NAVIGATION 第34章導航2(133)