TM 1-1510-218-10   3C-1 CHAPTER 3C AVIONICS  T1  T2 Section I.  GENERAL 3C-1.  DESCRIPTION. This    chapter    covers    the    avionics    equipment configuration  installed  in  C-12T1 and C-12T2 aircraft.   It     includes     a     brief     description     of     the     avionics equipment,  its  technical  characteristics,  capabilities, and  locations.    It  covers  systems  and  controls  and provides  the  proper  techniques  and  procedures  to  be employed  when  operating  the  equipment.    For  more detailed   operational   information,   consult   the   vendor manuals that accompany the aircraft's loose tools. 3C-2.  AVIONICS EQUIPMENT CONFIGURATION. The avionics configuration of the aircraft consists of    three    groups    of    electronic    equipment.        The communication    equipment    group    consists    of    the interphone and V/UHF, VHF, and HF communications transceivers  and  an  Emergency   Locator  Transponder (ELT).    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  group  includes  equipment  for  determining altitude, attitude, position, destination, range, bearing, heading, groundspeed, and drift angle. The transponder and radar group includes an identification, position,  a  emergency  tracking  system,  and  a  radar system to locate potentially dangerous weather areas.   A Ground Proximity Altitude Advisory System (GPAAS), Traffic Alert and Avoidance System (TCAS- II), and Stormscope are also installed. 3C-3.  POWER SOURCE. a.   DC    Power.        The    avionics    equipment    is supplied  with  DC  power  from  the  aircraft  battery,  left and  right  generators,  and  external  power.    Power  is routed  through  two  50-ampere  circuit  breakers  to  the avionics    power    relay,    which    is    controlled    by    the avionics master power switch, located on the overhead control  panel,  Figure  2-15.    Individual  system  circuit breakers and the associated avionics buses are shown in   Figure 2-28.      A   three-position   switch,   placarded AVIONICS    MASTER    POWER    ON    /    EXT    PWR, located on the overhead control panel controls a relay which applies power to two 35-ampere     circuit breakers, placarded   AVIONICS  MASTER  PWR  #1  / #2,   located   on   the   overhead   circuit   breaker   panel, Figure 2-16.  When the  AVIONICS MASTER POWER switch is set to the  ON  (center)  position,  the  avionics power   relay   is   de-energized   and   power   is   applied through   two   35-ampere   circuit   breakers,   placarded AVIONICS  MASTER  PWR  #1  /  #2,  located  on  the overhead circuit breaker panel. NOTE If  the  AVIONICS  MASTER  POWER  switch fails   to   operate,   power   to   the   individual avionics  circuit  breakers  can  be  provided by   pulling   the   5-ampere   circuit   breaker, placarded AVIONICS MASTER CONTR, located   on   the   overhead   circuit   breaker panel. In the off (aft) position, the relay is energized and power  is  removed  from  avionics  equipment.    When external  power  is  applied  to  the  aircraft,  the  avionics power    relay    is    normally    energized,    automatically removing   power   from   the   avionics   equipment.      To apply external power to the avionics equipment, move the  AVIONICS  MASTER  POWER  switch  to  the  EXT PWR position, which overrides the automatic avionics lockout   system.      This   will   de-energize  the  avionics power   relay   and   allow   power   to   be   applied   to   the avionics equipment. b.  AC   Power.      AC    power    for    the    avionics equipment  and  ac  engine  instruments  is  provided  by two   400 Hz   750   volt-ampere   single-phase  inverters.   During    normal    operation,    the    number    1    inverter supplies 115 Vac and 26 Vac to the number 1 avionics and    navigation    system    and    the    left    engine    ac instruments,   while   the   number   2   inverter   supplies 115 Vac  and  26  Vac  to  the  number  2  avionics  and navigation system and the right ac engine instruments.   If either inverter fails, the total ac load will be switched to    the    remaining    inverter    automatically,    unless    a ground fault exists.  The inverters are controlled by two switches, placarded INVERTER #1/ON and INVERTER  #2/ON,  located  on  the  overhead  control panel.