TM 55-1510-219-10 (12) Designating fly-to-destinations or TACAN. 1. Data   selector   L/L   WYPT   or UTM WYPT, as required. 2. Waypoint thumbwheel Select destination number. (Observe number of destination waypoint appears in "TO" part of FROM-TO display.) 3. Data selector HDG DA. (Observe     present     aircraft     heading     appears,     to nearest  tenth  of  degree,  in  left  data  display;  also  drift angle, to nearest degree, appears in right data display.) 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. (13)    To fly selected INS course. 1. Pilot's  COURSE  INDICATOR switch INS. 2. Pilot's RMI select switch INS. 3. Horizontal Situation Indicators (pilot's   and/or   copilot's   HSI) Steer toward indicators. 4. CDU ALERT lamp Monitor. (Observe   illumination   approx   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.) (14) Aided TACAN operation. 1. Mode selector NAV. 2. Data selector DSRTK/STS. 3. Key "4" Press. (Observe right data display is "000004" and INSERT/ADVANCE pushbutton light is illuminated.) 4. INSERT/ADVANCE pushbutton Press. (Observe right data display is "1-XX4" and INSERT/ADVANCE pushbutton light is extinguished.) NOTE Every   15   seconds,   the   INS   will select next eligible TACAN station in sequence for 3-58 updating.  To be eligible, TACAN station range must   be   between   5   and   150   nmi and channel between 1 and 126. 5. Data    selector    L/L    WYPT    or UTM WYPT. 6. 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.) 7. To    monitor    station    selection Observe FROM-TO data display. (Observe   only   the   number   of   stations   eligible   for mixing will be displayed.  A "0" indicates that none of the 9 stations are eligible for selection.) 8. Monitor "TACAN 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. 9. To return INS display to normal.    Set  data  selector  to any  position  except  WYPT  or DIS/TIME. 10. To  monitor  progress  of  update 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: * One station must be at least 15 nmi off course. *   For   optimum   single   TACAN   station   updating, update   should   continue   until   aircraft   has   passed   the station. * For optimum dual TACAN updating, use one "off- track" TACAN station and one "on-track" station. *  For  optimum  multi-TACAN  station  updating,  the stations  should  be  evenly  distributed  in  azimuth  around the aircraft. 3-58