TM 1-1510-224-10 Section III.  ENGINES AND RELATED SYSTEMS 2-16.  ENGINES. The     aircraft     is     powered     by     two     PT6A-67 turboprop  engines,  rated  at  1200  SHP  each  (fig.  2-13). Each  engine  is  equipped  with  a  hydraulically  controlled, reversible,    constant-speed,    four-bladed,    full-feathering propeller.    The  engines  are  reverse-flow  free  turbines, and  each  employs  a  four-stage  axial  compressor  and  a single-stage    centrifugal    compressor    in    combination, driven  by  the  gas  generator  turbine.    The  gas  generator turbine  and  the  two  power  turbines  are  in  line  and  have opposite  rotations.    The  power  turbines  are  connected through     planetary     reduction     gearing     to     a     flanged propeller  shaft.    The  oil  tank,  filler  cap  and  dipstick  are an integral part of the engine. The  ram  air  supply  enters  the  lower  portion  of the  nacelle  and  is  drawn  in  through  the  aft  protective screens.    The  air  is  then  routed  into  the  compressor. After  the  air  is  compressed,  it  is  forced  into  the  annular combustion chamber and mixed with fuel that is sprayed in through 14 nozzles mounted around the gas generator case.      A   capacitance   discharge   ignition   unit   and   two spark  igniter  plugs  are  used  to  start  combustion.    After combustion, the exhaust passes through the compressor turbine and two stages of power turbines, then is routed through  two  exhaust  ports  near  the  front  of  the  engine. A  pneumatic  fuel  control  system  schedules  fuel  flow  to maintain  power  set  by  the  gas  generator  POWER  lever (fig.  2-14).    The  accessory  drive  at  the  aft  end  of  the engine   provides   power   to   drive   the   fuel   pumps,   fuel control,  oil  pump,  refrigerant  compressor  (right  engine), starter/generator,   and   the   tachometer   generator.      The reduction gearbox forward of the power turbine provides gearing    for    the    propeller    and    drives    the    propeller tachometer generator, the propeller overspeed governor, and the propeller primary governor. 2-17.  ENGINE COMPARTMENT COOLING. The  forward  engine  compartment,  including  the accessory  section,  is  cooled  by  air  which  enters  around the exhaust stack cutouts and through the gap between the propeller spinner and forward cowling, and exhausts through louvers in the upper forward and aft cowling. 2-18.  AIR INDUCTION SYSTEMS - GENERAL. Each   engine   and   oil   cooler   receives   ram   air ducted  from  separate  air  inlets  located  within  the  lower section    of    the    forward    nacelle.        Induction    system components   protect   the   power   plant   from   icing   and reduce the possibility of foreign object damage. 2-19.  FOREIGN OBJECT DAMAGE CONTROL. The   engine   has   an   integral   air   inlet   screen designed   to   obstruct   objects   large   enough   to   damage the compressor. 2-20.  ENGINE ICE PROTECTION SYSTEMS. a.      Inertial   Separator.      An   inertial   separation system   is   built   into   each   engine   air   inlet   to   prevent moisture  particles  from  entering  the  engine  inlet  plenum under  icing  conditions.    A  movable  vane  and  a  bypass door  are  lowered  into  the  airstream  when  operating  in visible moisture at 5 °C or colder, by energizing electrical actuators  with  the  switches,  placarded    #1 and   #2  ICE VANE CONTROL - ON, located on the overhead control panel  (fig.  2-15).    The  system  incorporates  an  electrical back-up  system  which  operates  identically  to  the  main system.    The  back-up  ice  vane  system  is  controlled  by two switches placarded   #1  and  #2  ICE  VANE  POWER SELECT - MAIN - STANDBY,  located  on  the  overhead control panel (fig. 2-15).  If the main system fails, placing the  switch  in  the   STBY   position   will   allow   use   of   the back-up    system.        Electrical    protection    is    provided through   two   5-ampere   circuit   breakers   placarded   ICE VANE CONTR MAIN and ICE VANE CONTR AUXILIARY,   located   on   the   overhead   circuit   breaker panel. b.      Engine   Ice   Protection   Systems   Operation. The  vane  deflects  the  ram  airflow  slightly  downward  to introduce   a   sudden   turn   in   the   airflow   to   the   engine. Because    of    their    greater    momentum    the    particles continue undeflected and are discharged overboard. Once    the    ice    vane    system    is    actuated,    the extended    position    of    the    vane    and    bypass    door    is indicated   by   green   annunciators,   placarded   #1   VANE EXT and #2 VANE EXT, located on the caution/advisory panel.    If  for  any  reason  the  vane(s)  do  not  attain  the selected position within 33 seconds, an amber  #1 VANE FAIL and/or   #2  VANE  FAIL  annunciator(s)  illuminates on   the   caution/   advisory   panel.      In   this   event,   the appropriate    #1   or    #2   ICE   VANE    POWER   SELECT switch should be placed in the  STBY  position.  Once the vane    is    successfully    positioned,    using    the    standby (STBY) system, the amber annunciator(s) will extinguish and  the  applicable  green  #1  VANE  EXT or   #2  VANE EXT annunciator(s) will illuminate. c.  Engine Anti-Ice System. (1)  Air inlet.   A  small  duct,  which  faces  into the exhaust flow in the left exhaust stack of each engine, diverts  a  small  portion  of  the  engine  exhaust  gases  to the engine air inlet lip.  The gases are circulated through the engine air inlet lip and then exhausted through a duct in  the  right  exhaust  stack.    The  continuous  flow  of  hot engine   exhaust   gases   heats   the   engine   air   inlet   lip, preventing     the     formation     of     ice.          Two     switches, placarded ENG INLET LIP HEAT #1  and  #2 (located on the  overhead  control  panel,  fig.  2-15),  operate  solenoid valves in the lip heat 2-29