NOTE Navigation   information   is   now   available from  the  INS  for  display  on  the  pilot  and co-pilot  RMI’s  and  on  the  pilot  and  copi- lot  HSI’s,  as  determined  by  the  COURSE INDICATOR   and   RMI   select   switches. (8.) 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   light   -   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. (9.)   Aided   TACAN   operation: NOTE If   high   accuracy   alignment wait  for  the  READY  NAV selecting  NAV  mode. is   required, light   before 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  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  1  and  126. 5.   Data   selector   -   L/L   WY   PT   or UTM  WY  PT. TM  55-1510-221-10 6. Keys  “7“  and  “9“-  Press  simulta- neously.   Observe   channel   number of  the  TACAN  station  being  used for  navigation  flashes  on  and  off. Data   displays   indicate   coordi- nates  of  station  selected  via  thum- bwheel. 7.   To   monitor   station   selection   - Observe   FROM-TO   data   display. Observe  only  the  number  of  sta- tions   eligible   for   mixing   will   be displayed.   A   “0“   indicates   that none  of  the  9  stations  are  eligible for  selection. 8.   Monitor   “INS   UPDATE“   annun- ciator. 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  min- utes   elapse   without   an   update,   the   “NO INS  UPDATE“  annunciator  will  illumi- nate. 9.  To  return  INS  display  to  normal -  Set  data  selector  to  any  position except  WYPT  or  DIS/TIME. 10. 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  sta- tion  criteria  should  be  observed: 11. 12. 13. 14. One   station   must   be   at   least   15 nm  off  course. For   optimum   single   TACAN updating,   update   should   continue until   aircraft   has   passed   the   sta- tion. F o r    o p t i m u m    d u a l    T A C AN updating, use   one “off-track“ TACAN   station   and   one   "on- track“   station. For  optimum  multi-TACAN  sta- tion  updating,  the  stations  should 3-61