TM 1-1510-224-10 (12) Course     deviation     bar.        The    course deviation  bar  represents  the  centerline  of  the  selected VOR,  localizer,  or  TACAN  course,  or  inertial  navigation system (INS) track.  The aircraft symbol pictorially shows the aircraft's position in relation to the selected course or track. (a) VOR/TACAN.    When  the  selected navigation  source  is  a  VOR  or  TACAN  station  each  dot on   either   side   of   the   aircraft   symbol   represents   a   5 degree   deviation   from   the   centerline   of   the   course. When the selected navigation source is a localizer, each dot  represents  a  1  degree  deviation  from  the  centerline of  the  course.    When  the  selected  navigation  source  is the INS, each dot represents 3.75 nautical miles of cross track deviation. (b) Back   course   (BC).      When   back course    (BC)    mode    has    been    selected,    or    when    a localizer   frequency   has   been   tuned   and   the   selected course  is  more  than  90  degrees  from  aircraft  heading, course   deviation   will   automatically   reverse   to   provide proper   deviation   sensing   with   respect   to   the   course centerline.    The  course  deviation  bar  always  indicates the  location  of  the  course  centerline  relative  to  the  nose of the aircraft. (13) Groundspeed or time-to-go display. Depressing the GSPD/TTG  button  on  the  display  control panel will cause groundspeed or time-to-go to alternately be     displayed.          GSPD/TTG     information     is     always referenced to the active INS waypoint. (14) To-from  indicator.    An  arrowhead  (white triangular    box)    in    the    center    of    the    EHSI    indicates whether  the  selected  course  is  to  or  from  the  station  or waypoint.  The to-from annunciator will be removed from view during localizer operation. (15) Aircraft    symbol.        The    aircraft    symbol provides  a  quick  visual  cue  as  to  the  aircraft's  position with respect to the selected course and aircraft heading. (16) Preview course pointer.  A preview course pointer   (magenta)   is   provided   to   enable   the   pilot   to preview data prior to its use. The preview course pointer will be displayed if: INS is displayed as the navigation source on the EHSI. LNAV    is    the    lateral    capture    mode    (green) displayed on the  EADI. Selection of V/L or TCN on the display controller after the above two conditions have been met. The    preview    course    pointer    may    be    rotated around  the  heading  dial  using  the  remote  course  knob on  the  remote  instrument  control  panel,  located  on  the pedestal  extension  (fig.    3-14).    Each  time  the  preview course  pointer  position  is  changed  on  the  heading  dial with  the  remote  course  knob,  the  EHSI  digital  course display  will  show  the  preview  course  in  magenta  for  5 seconds, or until the course is changed again. The preview course deviation bar will respond to VOR, localizer, and TACAN signals as appropriate. Once the previewed navigation source is valid, if the    approach    mode    (for    localizer    or    ILS)    or    VOR approach mode (for VOR or TACAN) has been selected on   the   flight   director   mode   selector,   the   appropriate LOC, ILS, or NAV annunciator will be illuminated on the EADI. When   the   flight   director   determines   that   the capture point for the previewed mode has been reached, it will transition the flight director from LNAV mode to the capture  mode  of  the  previewed  navigation  source.    The preview   course   pointer   will   then   be   removed   and   the standard  course  pointer  will  be  slewed  to  the  previewed selected course. (17) Course    pointer.        The    course    pointer (yellow)  is  positioned  on  the  rotating  heading  dial  by  a remote    course    knob    on    the    remote    heading/course control panel, located on the pedestal extension (fig.  2- 12).  The course pointer is set to a magnetic bearing that coincides   with   the   desired   VOR   or   TACAN   radial,   or localizer course.  Once set, the course pointer maintains its   position   on   the   rotating   heading   dial   to   provide   a continuous  readout  of  course  error  to  the  flight  director computer.      Pulling   out   on   the   remote   course   knob (pedestal   extension,   fig.      2-14),   will   rotate   the   course pointer to center the course deviation bar. When  long  range  navigation  (INS)  is  selected, the course pointer becomes a desired track pointer.  The desired  track  pointer  will  be  positioned  on  the  rotating heading dial by the INS. (18) Heading  display.    The  heading  display  is a   digital   readout   of   the   heading   selected   by   the   blue heading  marker.    The  display  is  placarded  HDG  (white) with blue numerals. (19) Double-needle    bearing    pointer    source annunciator.    This  annunciator  displays  the  navigation source     supplying     information     to     the     double-needle bearing  pointer  (green).    This  display  is  marked  by  a green  diamond  with  the  navigation  source  displayed  in white  letters.    Possible  annunciations  are   ADF,  VOR2, INS, and TCN. (20) Single-needle     bearing     pointer     source annunciator.    This  annunciator  displays  the  navigation source     supplying     information     to     the     single-needle bearing pointer (blue).  This display is marked by a blue circle with 3-33