TM 1-1510-223-10 (23)  Fast/slow   source   annunciator.      The   fast/ slow source annunciator (white) displays A/S. (24)  Lateral   mode   arm   annunciators.      Lateral mode arm function is annunciated on the EADI in white. Possible annunciations are NAV, APR, LOC, and BC. c. EADI   Amber   Caution   and   Failure   annunciators (fig. 3-10). (1) Same  attitude  source.    There  is  no  attitude source annunciated if the pilot and copilot are using their normal    attitude    sources.        Selecting    other    attitude sources  causes  the  new  source  to  be  annunciated  in white.  If  the  pilot  and  copilot  have  selected  the  same attitude source, that attitude source will be annunciated in amber on both EADI's. (2) Comparison    monitor.        The    comparison monitor compares selected pilot and copilot input data in the symbol generator. If the difference between the data exceeds    predetermined    levels,    the    out-of-tolerance symbol  will  be  displayed.  Table  3-2  shows  comparison monitor symbols and miscompare levels. NOTE When the compared pitch and roll attitude or glideslope and  localizer  signals  are  out  of  tolerance,  a  combined symbol (ATT or ILS) is displayed. (3) Radio altitude failure.  Radio altitude failure is  indicated  by  amber  dashes  replacing  the  numerical altitude  value,  and  the  removal  of  the  rising  runway radio altitude display from the EADI, if present (4) Decision height warning. If a DH potentiometer is open, or during self test, amber dashes will replace numerical values of decision height display. (5) Autopilot  status  messages.    The  following messages  may  appear  for  autopilot  status.    They  will replace the autopilot engage (AP ENG) annunciator: (a) AP ENG. Autopilot engaged. (b) AFCS?   Autopilot   wraparound   signal failure. (c) TCS  ENG.  Touch  control  steering  is engaged. (6) Flightdirector failure.  In the event of a flight director   failure,   an   amber   FD   FAIL   warning   will   be displayed on the EADI. (7) Air  data  command  failure.    If  an  air  data flight director mode has been selected, and the air data computer fails, amber dashes will replace the numerical values in the air data command display. (8) Common   symbol   generator.   When   in   the reversionary mode and one symbol generator is driving both  the  pilot's  and  copilot'  s  display  tubes,  an  amber reversionary warning is given to indicate the information source. d. EADI Red Failure Annunciations (fig 3-11). (1) Attitude failure.  If the attitude display, pitch scale, or roll pointer fail, they will be removed from the display, the attitude sphere will become blue, and a red ATT FAIL will be displayed on the EADI. (2) Glideslope, expanded Iocalizer, and rate- of- turn  failures.    If  the  glideslope,  expanded  localizer,  or rate-of-turn system fails, the pointer will be removed and a red X will be drawn through the scale. The letter G will remain  at  the  zero  deviation  position  to  identify  invalid glideslope information. (3) Internal failure.  If an internal failure occurs within the display system itself, the display will be blank A  failure  of  the  input/output  processor  will  be  indicated by  a  red  X  centered  on  the  display  with  a  SG  FAIL annunciated (fig. 3-12). 3-21. ELECTRONIC HORIZONTAL SITUATION INDICATOR (EHSI). a. Description.   The   electronic   horizontal   situation indicator    (fig.    3-13),    combines    several    displays    to provide   a   maplike   display   of   aircraft   position.   The indicator   displays   aircraft   displacement   relative   to   a VOR    or    TACAN    radial,    inertial    navigation    system guidance, and localizer and glideslope beam. The EHSI provides  the  following  full  and  partial  compass  display information: (1) Full compass displays Heading Course selection Course or azimuth deviation Distance Groundspeed To/from Desired track Bearing 3-28