TM 55-1510-220-10 23. To return INS to normal display modes, momentarily  set  data  selector  to  LUL POS. (7). Designating fl-to destinations on TACAN. (a) Press waypoint change. (b) Insert new TO-FROM waypoints. (c) Press INSERT/ADVANCE. NOTE Navigation information is now available   from   INS   for   display   on pilot's     RMI     and     on     pilot's     and copilot's     HSI's     as     determined     by COURSE INDICATOR switches. (8) After  NA  V  READY  annunciator  illuminates,  place mode selector to NA V. NOTE Do not pull up on mode selector when switching   to   NAV.      Pulling   causes overshooting   into   the   ATT   position which  invalidates  the  alignment  and alignment must be restarted. (9) To fly selected course: (a) Pilot's COURSE INDICATOR switch INS. (b) Pilot's RMI select switch INS. (c) Horizontal  situation  indicators  (pilot's  and/or copilot's HSI) Steer toward indicators. (d) CDU  ALERT  annunciator  Monitor.    Observe illumination approximately 1.3 minutes before reaching    point    for    automatic    leg    switch. Indicator  flashes  on  and  off  after  passing  a waypoint, if AUTO-MAN switch is in MAN. (10) Aided TACAN operation: (a) Mode selector NAV. (b) Data selector DSRTK/STS. (c) Key  "4"  Press.    Observe  right  data  display  is "000004"    INSERT/ADVANCE    pushbutton annunciator is illuminated. (d) INSERT/ADVANCE pushbutton Press. Observe right data display is      "1-XX4"      and      INSERT/  ADVANCE pushbutton annunciator is extinguished. NOTE Every  30  seconds,  the  INS  will  select next eligible TACAN station in sequence for updating.  To be eligible, TACAN station range must be between  5  and  150  nm  and  channel between I and 126. (e)     Data selector UL  WY  PT or UTM WY PT. (f) Keys    "7"    and    "9"    Press    simultaneously. Observe    channel    number    of    the    TACAN station  being  used  for  navigation  flashes  on and off.  Data displays indicate coordinates  of station  selected  via thumbwheel. (g) To   monitor   station   selection   Observe   TO- FROM    data    display.        Observe    only    the number of stations eligible for mixing will be displayed.  A "O" indicates that none of the 9 stations are eligible for selection. (h) Monitor INS UPDATE annunciator. NOTE Mixing will not be annunciated if: (a) TACAN    control    is    inappropriately set; (b) TACAN station data loaded in error;  (c)  aircraft  look-down  angle  is greater than 30'; (d) horizontal ground distance is less than two times the  altitude.    When  2  minutes  elapse without    an    update,    the    NO    INS UPDATE annunciator will illuminate. (i) To   return   INS   display   to   normal   Set   data selector   to   any   position   except   WYPT   or DIS/TIME. (j)     To  monitor  program  of  mix  Set  data  selector to   DSRTK/STS.      (Observe   Accuracy   Index (AI) will decrement to "0".) NOTE To  insure  favorable  geometry  during the    update    process,    the    following TACAN    station    criteria    should    be observed: Change 5        3-61