TM 1-1510-218-10   3C-47 data  computer  functions  are  automatic  in  nature  and require no flight crew action. c.   Pilot's    Autopilot/Flight    Director    Switch/ Indicator.    An  alternate  action  autopilot/flight  director switch/indicator, placarded  AP FD 1 and  AP  FD  2, is located on the pilot's instrument panel, directly below the  glare  shield,  Figure  2-17.    This  switch  is  used  to select    which    autopilot/flight    director    computer    will control the aircraft flight servos. d.  Copilot's  Autopilot/Flight  Director  Number 2   Annunciator.      If   the   pilot   selects   AP   FD   2,   an annunciator placarded AP FLT DIR NO.  2, located on the copilot's instrument panel directly below the glare shield, will illuminate to alert the copilot that the No. 2 autopilot   flight   director   computer   is   controlling   the aircraft. NOTE The autopilot will disengage when transferring  between  the  pilot  and  copilot flight directors.  e.   Flight   Director   Mode   Selector   (MS-400).   The    flight    director/mode    selector    located    on    the pedestal  extension,  Figure  2-9,  provides  for  selection of  all  flight  director  modes  except  go-around (which is initiated by remote switches located on the left power lever and on the copilot's control wheel).  The top row of  split-light,  annunciated  push  buttons  contains  the lateral modes and the bottom row contains the vertical modes.        The    mode    buttons    will    illuminate    when manually  selected,  or  automatically  selected  through other modes.  The split-light, push-button annunciators illuminate  amber  for  armed  conditions  and  green  for captured.      When   more   than   one   lateral   or   vertical mode is selected, the flight director system automatically arms and captures the submode.  Mode annunciations are also presented on remote annunciator  blocks, located above both the pilot's and copilot's EADI,'s and on the pilot's EADI. f.    Autopilot   Modes   of   Operation.      Refer  to Figure 3C-20. (1)   Heading    Select    Mode    (HDG).         The heading select mode is selected by pressing the  HDG button  on  the  mode  selector.    In  the  HDG  mode  the flight     director     computer     provides     inputs     to     the command   cue   to   command   a   turn   to   the   heading indicated   by   the   heading   bug   on   the   EHSI.      The heading    select    signal    is    gain    programmed    as    a function   of   airspeed.      When    HDG   is   selected,   it overrides  the  NAV,  BC  APR,  and  VOR  APR  modes.   In  the  event  of  a  loss  of  valid  signal  from  the  vertical gyro  or  compass,  the  command  bar  on  the  EADI  is biased out of view. (2)   Navigation  Mode  (NAV).   The navigation mode    represents    a    family    of    modes    for    various navigation  systems  including  VOR,  localizer,  TACAN, and FMS 1 or FMS 2. (a)   VOR    Mode.        The   VOR   mode   is selected  by  selecting  the  radio  position  with  the  NAV Source Selector on the EFIS control panel and either VOR 1 or VOR 2, as selected by the   CRS 1/2 switch tuned  to  a  VOR  frequency  and  DME  greater  than  20 miles   from   the   station.      Prior   to   VOR   capture,   the command cue receives a heading select command as described    above    and    the    HDG    mode    switch    is illuminated   along   with   the   NAV   ARM  annunciators.   Upon VOR capture  the system automatically switches to the VOR mode,  HDG and  NAV  ARM annunciators extinguish, and NAV capture (NAV CAP ) annunciators will illuminate.  At capture, a command is generated to capture  and  track  the  VOR  beam.    VOR  deviation  is gain  programmed  as   a  function  of  distance  from  the station.          This     programming     corrects     for     beam convergence,   thus   optimizing   the   gain   through   the useful VOR range.  To use this feature, the DME must be tuned to the same VOR station as the NAV receiver that  is  feeding  the  flight  director  and  DME  hold  must not   be   selected.      The   course   error   signal   is   gain programmed  as  a  function  of  airspeed.    Crosswind washout  is  included,  which  maintains  the  aircraft  on beam   center   in   the   presence   of   crosswind.      The intercept    angle    and    DME    distance    are    used    in determining  the  capture  point  to  insure  smooth  and comfortable performance during bracketing. When  passing  over  the  station,  an  overstation sensor   detects   station   passage   removing   the   VOR deviation signal from the command until it is no  longer erratic.    While  over  the  station,  course  changes  may be  made  by  selecting  a  new  course  on  the  EHSI.    If the NAV receiver is not valid prior to the capture point, the lateral beam sensor will not trip and the system will remain  in  the  HDG  mode.    After  capture,  if  the  NAV receiver, compass data or vertical gyro go invalid, the ADI command cue will bias out of view.  Also, the  NAV CAP  annunciators  will  extinguish  if  the  NAV  receiver becomes invalid.