4.  
DME ___ DME RNAV enabled/dual DME

 5.  
DME VOR DME RNAV enabled/dual DME and VOR

 6.  
DME XXX DME RNAV enabled/dual DME, VOR inhibited

 7.  
DME VOR XXX RNAV enabled/DME and VOR, DME 2 inhibited

 Update status 4, 5 and 6 are possible only if VOR/DME No. 1 and VOR/DME No. 2 are tuned to different stations.
 C.  The INS updating annunciators on the pilot's and copilot's panels change from black to green when the systems are being updated in status 3 thru 8, and remain green for 1 minute after degradation to status 2.
 D.  Providing VOR/DME No. 1 and VOR/DME No. 2 are tuned to different stations, a system in a multiple installation can be upgraded to DME ____ DME or DME VOR DME while a second system in the installation is in any status including RNAV not enabled.
 E.  The INS applies a series of validity or reasonableness checks to the VORTAC station signals. If these tests fail, advisory codes are displayed on line 5 of the CDU display. If more than one test fails, the failure codes cycle periodically on line 5. If the code is slewed between the entry line markers of the CDU display and the CDU EXP pushbutton is pressed, the codes and brief explanations are displayed.
 6.  Triple System Mixing
____________________
 EFFECTIVITY

 AIRPLANES WITH LTN-72RL OR  CONFIG LTN-92 INS  01 Page 18  Apr 25/91

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ENTRY LINE ALPHANUMERIC MARKER PUSHBUTTON

LED MATRIX DISPLAY

CLEAR

PUSHBUTTON ENTER
PUSHBUTTON
WARN

ALERTANNUNCIATOR ANNUNCIATOR
BATTERY

OFFSETANNUNCIATOR

ANNUNCIATOR

DATA ENTRY DISPLAY PUSHBUTTONS

PUSHBUTTONS

HOLD PUSHBUTTON
EXPAND
BRIGHTNESS PUSHBUTTON
CONTROLS
SLEW PUSHBUTTONS

INS Control Display Unit
Figure 7

EFFECTIVITY
AIRPLANES WITH LTN-72RL OR
 CONFIG 3 LTN-92 INS
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 A.  When three inertial navigation systems are installed, triple mixing of the three systems' present position may be enabled. This provides a mixed present position which is displayed on each system's CDU when the display is on the position page. MIX is indicated on the CDU UPDATE MODE page. The unmixed present position of each system can be displayed on its CDU by pressing the HLD pushbutton.
 B.  When the TMIX and the RNAV (Triple Mix and the Radio Navigation) update modes are enabled at the same time, the INS automatically shifts between triple mixing and RNAV, depending on the RNAV status. The normal update would be the RNAV mode. If the VOR/DME signals are degraded, the INS will automatically shift to the TMIX mode. When VOR/DME signals return to acceptable levels, the INS will automatically shift back to RNAV.
 C.  Triple mixing disregards large position errors between one system and the other two systems. If the present position of one system differs from the other two by more than 35 nautical miles (50 nautical miles after 8 hours in NAV mode), or the ground speed differs by more than 50 knots, action/malfunction codes will be set. Triple mixing is inhibited if either of these conditions occurs.
 7.  Approach Mode
_____________
 A.  VORTAC (VOR/DME) radio position updating allows the INS to be used for non-precision R-NAV approaches.
 8.  INS Warning Annunciation
________________________
 A.  The INS generates warning signals that are applied to the MSU, CDU and airplane instruments to annunciate INS malfunctions. The annunciations are as follows:
 (1)  
MSU BATT annunciator - INS battery voltage below 20 volts.

 (2)  
CDU BAT annunciator - INS operating on INS battery.

 (3)  
CDU WRN annunciator - INS malfunction.

 (4)  
Attitude valid - INS pitch or roll flag signal to airplane instruments.

 (5)  
Heading valid - INS heading flag signal to airplane instruments.

 (6)  
Navigation valid - INS navigation flag signal to airplane instruments.

 B.  A CDU WRN annunciation indicates that INS action and malfunction code(s) exist. These action and malfunction codes can be displayed on the CDU. The action codes identify recommended actions that should be taken to remedy a problem, which is identified by an accompanying malfunction code.
 9.  Mode Selector Unit (Fig. 6)
__________________
 A.  The mode selector unit (MSU) is used to control the application of power to the INS and to select the standby (STBY), alignment (ALIGN), navigation (NAV), and attitude reference (ATT REF) modes of operation. There are three MSU units installed at the pilots' overhead panel (Fig. 1) to control the operation of INS No. 1, 2 and 3 systems. Each unit contains a mode selector switch, two annunciators, ALIGN (or READY NAV) and BATT, and a remote access switch labeled OFF, TEST and BIAS (for program control) located behind a removable access cover. The mode selector is heavily detented in the NAV position to prevent inadvertent shutdown in flight.
　
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