TM 1-1510-225-10 3B-18 c.   EHSI Modes.    The  EHSI  allows  for  multiple display   formats.      See   Table   3B -3   for   the   display formats that are selectable from the control panel. Table 3B-3.  EHSI Display Modes MODE FORMAT HSI HSI (360° compass) HSI ARC (Partial 80° compass) MAP Map ARC (Partial 80° compass) Map (360° reference) Diagnostics MFD Status d.  EHSI    Outputs.         The    EHSI    outputs    the following to the flight director: (1)   HDG Datum. (2)   CRS Datum. (3)   LOC Tune if the course source is LOC. (4)   Lateral Deviation. (5)   Glideslope  Deviation  is  sent  to  the  flight director when it is available. (6)   Roll  Steering.    The  bottom  MFD  outputs roll steering to the flight director when the flight director is valid and the course source is FMS. e.   HSI Graphic Format.   The following graphics are utilized on the EHSI during the HSI Mode. (1)   Course   Readout/Label.      When   a   valid source  is  tuned,  the  course  selected  is  displayed  in white.  Next to the course readout is the label CRS or DTK in white letters.  The digital CRS or DTK readout is always associated with the course source. (a)  Radial   Source   (VOR).      The  course label    is    CRS    and    the    digital    course    readout    is independently controlled by each MFD control panel. (b)  FMS -800   Operation.      The   label   is CRS   when   the   primary   source   is   not   FMS.      If   the primary   source   is   tuned   to   FMS,   the   CRS   will   be replaced  with  Desired  Track  (DTK)  for  all  FMS  modes except TO / FROM mode (TACAN Emulation).  When FMS is the course source the course is automatically set by FMS. (c)  KLN 90B Operation.  Refer to  OBS / LEG switch in Paragraph 3D-20 for a description of the course readout. (2)   Message   Alert.      The   message   (MSG) alert appears whenever the FMS sends an alert to the MFD.  The yellow MSG alert indicates to the crew that they  should  look  at  FMS  on  the  selected  side  of  the cockpit [on-side/x (cross) side]. (3)   FMS -800     Heading     Bug.          The     FMS heading   bug   is   only   available   for   display   when   the FMS-800    is    the    NAV    source    and    the    FMS    is commanding   the   bug   to   be   displayed.      The   FMS heading  bug  is  white  and  travels  about  the  aircraft symbol  around  the  outer  edge  of  the  compass.    The center of the FMS heading bug indicates the selected heading  in  1  increments.    When  the  FMS  selected heading is set, the FMS NAV source label is replaced with  FHDG  1  in  white  letters.    If  the  FMS  selected heading  is  invalid,  unavailable,  or  the  primary  course source   is   not   FMS   1,   the   heading   bug   will   not   be displayed.        The    FMS    selected    heading    bug    is displayed    in    yellow    when    a    cross-side   source   is selected. (4)   Course    Deviation    Scale.        Four    white lateral   deviation   scale   dots   indicate   deviation   from course.    The  course  deviation  scale  rotates  about  the aircraft     symbol     such     that     the     scale     is     always perpendicular   to   the   selected   primary   course.      The maximum deviation is   2.5 dots.  When the selected course or source is invalid, the course deviation scale is removed from the display. The  EHSI  outputs  lateral  deviation  and  lateral deviation  validity  to  the  flight  director  and/or autopilot.   The  lateral  deviation  validity  signal  corresponds  with the  selected  course  source’s  lateral  deviation.    The lateral   deviation   output   flag   is   displayed   when   the lateral   deviation   for   the   selected   primary   navigation source  is  invalid  or  an  MFD  failure  results  in  bad  or failed lateral deviation output. (5)   Vertical   Deviation   Scale.      The   Vertical Deviation Scale, four small circles located on the right side  of  the  MFD  indicate  the  vertical  deviation  of  the aircraft. (6)   Vertical  Deviation  Pointer.    The  Vertical Deviation    Pointer,    represented    by    a    white    star, displays   the   deviation   with   respect   to  the  selected source. (7)   Lateral  Deviation  Bar.    The  center  of  the course   pointer   moves   laterally   with   respect   to   the aircraft symbol and the four white deviation scale dots to   indicate   lateral   deviation.      The   course   deviation scale   rotates   about   the   aircraft  symbol  so  that  the scale is always perpendicular to the selected primary course.