TM 1-1510-225-10 3A-40 b.  Selected Course.  Selected course is shown by  a  green  alphanumeric  display  located  toward  the bottom of the display.  In addition to the digital display, a downward pointing arrow on the heading tape shows the selected course. If the selected primary NAV sensor is an on-side sensor the digital readout and pointer will be displayed in  green.    If  an  on-side LNAV is the selected primary NAV sensor and it is in the approach mode, the digital readout  and  pointer  will  be  green.    If  the  en  route mode is selected, the readout and pointer will be cyan.   If an off-side sensor is selected, the digital readout and pointer will be yellow. c.   Heading    Marker    Selected    Heading.        A digital display of selected heading is displayed toward the  bottom  of  the  screen  to  the  right  of  center.    The selected heading is also shown by the orange heading marker on the heading tape. NOTE As     the     aircraft     heading     changes,     the heading   marker   will   follow   the   heading tape and may disappear from view. d.  Navigation    Source    Annunciation.        The primary navigation sensor is displayed on the left side of  the  display.    A  green  annunciation  indicates  an  on- side   approach   NAV   system   is   being   displayed.      A yellow annunciation indicates that a cross-side system has  been  selected.    Cyan  annunciations  apply  to  on- side non-approach  NAV  systems.    These  color  codes apply   to   the   NAV   source   annunciator   CRS   pointer, course deviation bar, CRS, and distance.  If both sides select the same navigation source a yellow box will be placed  around  the  navigation  source  annunciator  on both  sides  of  the  cockpit.    If  both  sides  select  their respective   cross-side   navigation   source,   both   NAV source annunciators will be yellow with no yellow box. e.   Lateral  Course  Deviation  Scale.    A  lateral course deviation scale, consisting of four white circles and a center diamond, is located at the bottom of the display.        The    course    deviation    scale    provides    a reference  for  the  course  deviation  bar  to  indicate  the centerline    of    the    selected    navigation    or    localizer course  in  relation  to  the  center  diamond.    The  course width displayed in the composite mode is identical to that typically shown on the EHSI. f.    Lateral  Course  Deviation  Bar.  The course deviation bar represents the centerline of the selected navigation   or   localizer   course.      If   invalid   or   failed primary   NAV   sensor   data   is   received   the   course deviation  bar  and  scale  will  be  removed  and  a  red  X will be annunciated. g.  To  /  From  Indicator.    A  white  TO  or  FR  is displayed   to   the   left   of   the   center   diamond   on   the lateral deviation scale when in non-ILS modes. h.  Distance Information.  Distance information is  shown  in  an  alphanumeric  display,  located  in  the lower  left  corner  of  the  display.    Distance  in  nautical miles  from  the  aircraft  to  the  selected  primary  NAV station  when  in  the  VOR,  TACAN,  or  ILS  mode,  or  to the waypoint in LNAV mode is displayed. i.    DME  HOLD.    When  DME  HOLD  is  selected the,  DME  distance  and  annunciator  color  changes  to white  and  remains  white  until  the  HOLD  function  is released.    The  sensor  identifiers  (ADF,  VOR,  or  ILS) retain   their   original   color.      The   HOLD   function   is additionally   annunciated   by   an   orange   H   displayed immediately  to  the  right  of  the  distance  information.   Groundspeed  and  time  to  station  are  not  displayed while DME HOLD is active. NOTE DME HOLD will not function when LNAV is the selected sensor. Once   DME   is   placed   in   HOLD,   its   distance continues to be displayed and is not affected when the primary NAV sensor is changed. 3A-23.  ELECTRONIC FLIGHT INSTRUMENT SYSTEM REVERSIONARY MODES. Three different reversionary modes of operation are    provided   for    use    in    the    event    of    a    system component    failure:    composite,    display    down,    and standby. a.   Composite Reversionary Mode. The composite   reversionary   mode   is   generally   used   to compensate for a failure of a display unit or the EADI section    of    the    symbol    generator.        Pressing    the respective pilot's or copilot’s composite switch indicator, placarded  CMPST, located on the instrument panel,  selects  the  composite  display  on  the  EADI  or EHSI.  The lower half of the  CMPST switch illuminates DISP to indicate that the composite reversionary mode has  been  selected.    Refer  to  Paragraph  3A-22  for  a description of the composite mode displays. b.  Display   Down   Reversionary   Mode.    The display  (EADI)  down  reversionary  mode  is  generally used  to  compensate  for  a  failure  of  the  EADI  display unit   or   the   EADI   section   of   the   symbol   generator.   Pressing  the  respective  pilot's  or  copilot’s   ADI switch indicator,  located  on  the  instrument  panel,  transfers the normal EADI display to the MFD.  The lower half of the  ADI switch illuminates DOWN to  indicate that the display down reversionary mode has been selected.