TM 1-1510-218-10 3C-15 distress  frequencies  of  121.5  and  243.0  MHz.    The radiated signal is modulated with an audio swept tone. b.  ELT Controls and Functions. (1)  ON  /  ARM  /  OFF  Switch  (Located  on ELT). (a)  ON    –     Turns     set     on,     initiating emergency signal transmission. (b)  ARM    –    Establishes    a    readiness state to start automatic emergency signal transmission when forces on the ELT exceed a preset threshold. (c)   OFF – Turns set off. (2)  Remote RESET / AUTO / XMIT Switch. (a)  AUTO  –   Arms   the   set   to   operate automatically upon impact. (b)  XMIT – Turns set on. (c)   RESET  –  In  the  event  the  ELT  is accidentally triggered, pushing the switch to the reset position five times within 3 seconds will deactivate the transmitter  and  return  the  set  to  the  armed  (AUTO) condition. Section III.  NAVIGATION 3C-12.  DESCRIPTION. The   navigation   equipment   group   provides   the pilot  and  copilot  with  the  instrumentation  required  to establish  and  maintain  an  accurate  flight  course  and position,  and  to  make  an  approach  on  instruments  in Instrument   Meteorological   Conditions   (IMC).      The navigation     configuration     includes     equipment     for determining    attitude,    position,    destination,    range, bearing, heading, and groundspeed. 3C-13.  FLIGHT DISPLAY SYSTEM (FDS-255). a.  System   Overview.        The    Flight    Display System   (FDS-255),   is   a   replacement   for   existing electromechanical   Attitude   Direction   Indicator   (ADI) and Horizontal Situation Indicator (HSI) flight instruments. The   top   and   bottom   displays   are   physically identical.      The   top   display   is   configured    as   an Electronic  Attitude  Direction  Indicator  (EADI)  and  the bottom    display    is    configured    as    an    Electronic Horizontal Situation Indicator (EHSI). The MFD provides all of the internal diagnostics, data    processing,    and    hardware    configuration    to provide the following display modes. (1)  HSI.    Full  compass  rose  (360 )  or  HSI ARC which includes course needles, a bearing needle, heading bug, etc. (2)  MAP.      A   centered   360 MAP   or   an expanded compass rose segment (80 ).  Both of these modes include the current set of waypoints and course legs. (3)  ADI.    Provides  aircraft  attitude  pitch  and roll, lateral deviation, and vertical deviation. (4)  Primary  Flight  Display  (PFD).    ADI  and HSI combined on one display as a reversionary mode upon failure of a display. (5)  Diagnostics.      Provides   Multi   Functional Display (MFD) status pages. b.  External Aircraft Controls. (1)  Reversionary Switch (ALT ADI). Reversionary    switches    are    external    push    button switches   allowing   the   operator   to   place   the   EADI information on the bottom display.  The pilot’s switch is located  on  the  lower  left  portion  of  the  dash  panel under the Turn and Slip Indicator.  The copilot’s switch is located on the lower right portion of the dash panel under  the  Vertical  Speed  Indicator.    The  switch  has two positions, normal and reversionary.  In the normal position  the  top  display  is  an  EADI  and  the  bottom display is an EHSI.  In the reversionary position the top display   blanks   and   the   bottom   display   becomes   a PFD. (2)  OBS  /  LEG  Switch.    The  OBS  /  LEG switch  places  the  FMS  2  KLN  90B  in  either  LEG  or OBS mode.  The OBS / LEG switch is located on the top center portion of the dash panel to the right of the altitude select panel.  While in LEG mode the KLN 90B continuously updates the desired course in order to fly a   great   circle   route   between   the   FROM   and   TO waypoints.  If the leg selection is made and FMS 2 is selected  as  the  primary  navigation  source,  the  digital course  label  displays  DTK.    While  in  OBS  mode  the pilot’s   MFD   control   panel   updates   the   course   and sends  the  manually  selected  course  to  the  KLN  90B. If the OBS selection is made and FMS 2  KLN 90B  is selected as the course source, the digital course label displays   CRS   and   reflects   the   pilot’s   control   panel course selection.