TM 1-1510-225-10 3C-1 CHAPTER 3C AVIONICS  F3 Section I.  GENERAL 3C-1.  DESCRIPTION. This section covers electronic equipment installed  in  the  C-12F3  aircraft.    It  provides  a  brief description    of    each    system,    associated    controls, indicators, and operating procedures.  ANG aircraft are equipped with HF radio provisions only.  The HF radio equipment,    cockpit    voice    recorder    and    flight    data recorder    discussed    are    not    installed    in    the    ANG aircraft. 3C-2.  AVIONICS EQUIPMENT CONFIGURATION. The   communication   group   is   comprised   of   an interphone  system  connected  to  a  dual  audio  control panel  with  separate  controls  for  the  pilot  and  copilot that  interface  with  VHF,  UHF,  and  HF  communication units.    The  navigation  group  provides  the  pilot  and copilot  with  instrumentation  to  establish  and  maintain an  accurate  flight  course  and  to  make  an  approach under    Instrument    Meteorological    Conditions    (IMC).   Equipment   for   determining   aircraft   altitude,   position, range  and  bearing  to  destination,  groundspeed,  and drift   angle   is   installed.      A   flight   control   system   is provided   with   autopilot   capabilities.      Separate   flight director   indicators   serve   the   pilot   and   copilot.      A transponder,   emergency   locator   transmitter,   cockpit voice  recorder,  crash  data  recorder  with  an  integral underwater acoustic beacon (pinger), Ground Collision Avoidance  System  (GCAS),  and  Data  NAV  weather radar are also installed. 3C-3.  POWER SOURCE. a.     DC Power. The avionics equipment receives  dc  power  from  the  28  Vdc  buses.    These buses  feed  through  three  30-ampere  circuit  breakers on   the   avionics   circuit   breaker   panel   to   respective avionics  power  relays.    Each  power  relay  connects power   to   circuit   breakers   that   protect   the   individual avionics   equipment.      A   5-ampere   circuit   breaker, placarded  AVIONICS  MASTER,  feeds  power  to  the AVIONICS MASTER POWER switch on the pilot’s left outboard subpanel. The AVIONICS MASTER POWER  switch  controls  three  avionics  power  relays.   If    the    switch    is     OFF,    the    relays    remain    open withholding    power    from    avionics    equipment.        DC (battery)  power  for  isolated  operation  of  the  UHF  and COMM  1  radios  and  pilot’s  audio  system  is  provided via  an  auxiliary  dc  bus.    Power  to  the  auxiliary  bus  is provided    through    two    aux    power    relays    and    is controlled by a two-position switch, placarded  DC AUX BUS, located under the gang bar with the battery and generator  switches.    An  external  power  receptacle  is located under the right wing outboard of the nacelle. b.    AC Power Source.  Two inverters sharing a common control switch, placarded  INVERTER  NO. 1  / OFF / NO. 2, on the pilot’s outboard subpanel, supply single  phase 26 Vac and 115 Vac power.  Each 115 Vac circuit is protected by a 10-ampere circuit breaker and  a  backup  5-ampere fuse.  Each 26 Vac circuit is protected by a 5-ampere circuit breaker.  Separate 50- ampere  current  limiters  on  the  main  dc  power  panel supply dc power to operate the inverters. Section II.  COMMUNICATIONS 3C-4.  COMMUNICATIONS EQUIPMENT GROUP DESCRIPTION. The   communication   group   is   comprised   of   an interphone  system  connected  to  a  dual  audio  control panel,  with  separate  controls  for  the  pilot  and  copilot which interface with VHF, UHF, and HF communication units. 3C-5.  MICROPHONES. Hand held, boom, and oxygen mask microphones can be utilized in the aircraft. a.     MIC   NORMAL   Switch.      Selects   boom   or hand held microphone. b.    OXYGEN MASK Switch. Selects microphone in oxygen mask. c.     The MIC Push Switch.    Control wheel/hand held   microphone   routes   voice   from   microphone   to selected transmitter when pressed. 3C-6.  AUDIO CONTROL PANEL. a.     Description.      A  dual  audio  control  on  the instrument  panel,  shown  as  Figure  3C-1, serves both