TM 1-1510-218-10 3A-31 (4)   Knots/Minutes Display.    Digital  display  of time-to-station in minutes or groundspeed of aircraft in knots.  This information is accurate  only  if  the  aircraft is flying directly toward the ground station. (5)   DIM  Control.    Controls  intensity  of  digital readouts. d.  Normal Operation. (1)   Determining    Slant    Range    Distance    to Station. 1.   VOR  control  panel    –   Tune   required station. 2.   DME SEL switch – VOR-1 or VOR-2. 3.   DME MILES indicator – Read distance in nautical miles. (2)   Determining  Groundspeed  And  Time-To- Station. 1.   VOR  control  panel    –   Tune   required station. 2.   DME SEL switch – VOR-1 or VOR-2. 3.   DME indicator control switch – KTS. 4.   DME   knots/minutes   display   –   Read aircraft's   groundspeed   in   knots   and time-to-station in minutes. 3A-26.  GLOBAL POSITIONING S YSTEM (KLN 90B). For     information     on     the     Global     Positioning System, refer to Chapter 3, Paragraph 3-7. 3A-27.  AUTOPILOT SYSTEM (AP -106). a.   Description.      The   autopilot   system   is   an integral part of the flight control system.  The autopilot and  flight  director  have  a  common  computer  system.   When   the   autopilot   is   engaged,   the   flight   control system controls the aircraft and the pilot monitors the flight  path  by  observing  the  information  displayed  on the    pilot's    horizon    reference    indicator,    the    pilot's horizontal   situation   indicator,   and   the   flight   director system indicators.  The autopilot system can maintain a pre-selected attitude, maintain a barometric altitude, maintain an indicated airspeed, capture and maintain a desired  heading,  capture  and  maintain  a  pre-selected radio    course,    and    capture    and    maintain    an    ILS approach  to  published  minimums.    The  autopilot/flight director commands are selected by the autopilot mode selector panel located on the pedestal extension.  Roll rate  and  pitch  commands  can  be  given  to  the  system through  the  autopilot  pitch-turn  panel,  located  on  the pedestal   extension.      The   operating   status   of   the autopilot  is  indicated  on  the  autopilot/flight  director annunciator,  located  on  the  instrument  panel  directly above   the   pilot's   horizon   reference   indicator.      Two autopilot  control  switches  are  also  provided  on  each control   wheel.      One   is   placarded   PITCH   SYNC  & CWS,  pitch  synchronize  and  control  wheel  steering, and    the    other    is    placarded    DISC    TRIM/AP    YD, disconnect   trim/autopilot   yaw   damp.      The   autopilot system is protected by the 10-ampere  AP PWR circuit breaker located on the overhead circuit breaker panel. b.  Autopilot   Mode   Selector.      The   autopilot/ flight director commands are  selected  by  the  autopilot mode selector.  Selection is accomplished by pressing the  face  of  the  appropriate  push-on/push-off switch.   The  lateral  modes  are   HDG,  NAV,  APPR, and   B/C.   When not in a lateral mode the flight director command bars are biased  out  of  view.    The  vertical  modes  are ALT,  IAS  and  pitch,  and  are  all  hold  modes.    If  a vertical  mode  is  not  selected,  the  pitch  hold  mode  is automatically operational.  Selection of a mode causes the   legend   of   that   push-button  switch  to  illuminate.   The self-test switch on the lower right of the autopilot control panel acts as a lamp test when pressed.  For operation  at  night,  overall  illumination  of  the  autopilot mode selector and switches is adjusted by the console light control. c.   Controls   and   Functions,   Mode   Selector.   Refer to Figure 3A-19. (1)   HDG Switch/Indicator.  Engages heading mode.      Commands   aircraft   to   acquire   the   heading indicated by heading marker on pilot's HSI. (2)   NAV Switch/Indicator. Engages navigation mode. VOR-1 or VOR-2 selected commands intercept and track VOR radial selected on pilot's HSI. (3)   APPR Switch/Indicator. Engages approach mode.  Commands aircraft to intercept and track ILS inbound course. (4)   B C Switch/Indicator. Engages backcourse   mode.      Commands   aircraft   to   intercept backcourse ILS. (5)   AUTO    PILOT    TRIM    TEST    Indicator.   Illuminates when in test position.