TM 1-1510-225-10 2-35 When  ice  protection  is  not  required,  the  vane and bypass door are  retracted  out  of  the  airstream  by placing    the    ice    vane    switches    in    the    RETRACT position.    The  green  annunciator  lights  will  extinguish. Retraction   should   be   accomplished   at   +15   °C   and above   to   assure   adequate   oil   cooling.      The   vanes should  be  either  extended  or  retracted;  there  are  no intermediate positions. If  for  any  reason  the  vane  does  not  attain  the selected  position  within  15  seconds,  a  yellow    L ICE VANE    or    R    ICE    VANE    light    illuminates    on    the caution/advisory  panel.    In  this  event,  a  mechanical backup system is provided, and is actuated by pulling the     T-handles     just     below     the     pilot's     subpanel, placarded ICE VANE EMERGENCY. b.  Manual   Extension   Pull   Left   Eng   /   Right Eng.  Airspeed reduction may be necessary to extend the    ice    vanes    manually.    Once    extended,    normal airspeed may be resumed. CAUTION Once the manual override system has been engaged (i.e., anytime the manual ice vane T-handle  has  been  pulled),  do  not  attempt to   electrically   extend   or   retract   the   ice vanes,    even    if    the    T-handle    has    been pushed  back  in,  until  the  override  linkage in     the     engine     compartment     has     been properly reset on the ground. When  the  vane  is  successfully  positioned  with the  manual  system,  the  yellow  annunciator  lights  will extinguish.        The    vane    may    then    be    retracted    or extended   with   the   manual   system.      During   manual system  use,  the  electric  switch  position  must  match the  manual  handle  position  for  a  correct  annunciator readout. 2-20.  ENGINE FUEL CONTROL SYSTEM. a.   Description.  The basic fuel system for each engine consists of an engine driven  fuel  pump,  a  fuel control unit, a fuel flow divider, a dual fuel manifold, 14 fuel  nozzles,  and  a  purge  system.    The  fuel  purge system  forces  residual  fuel  from  the  manifolds  to  the combustion chamber where it is consumed. b.  Fuel  Control  Unit.    The  fuel  control  unit  is mounted  on  the  accessory  case  of  the  engine.    The unit     is     a     hydro-pneumatic     metering     device     that determines  the  proper  fuel  flow  schedule  required  for the engine to produce the amount of power requested by   the   relative   position   of   the   associated   POWER lever.      The   control   of   developed   engine   power   is accomplished  by  adjusting  the  speed  of  the  engine- gas  generator  (N₁).  N₁  speed  is  controlled  by  varying the    amount    of    fuel    injected    into    the    combustion chamber through the fuel nozzles.  Engine shutdown is accomplished by moving the appropriate  CONDITION lever   to   the   full   aft   FUEL   CUTOFF  position,  which shuts off the fuel supply. 2-21.  POWER LEVERS. CAUTION Moving  the  POWER  lever  below  the  flight idle   gate   without   the   associated   engine running    may    re sult    in    damage    to    the reverse mechanism linkage. The   two   POWER   levers   are   located   on   the control pedestal and are placarded POWER.  Refer to Figure   2-11.      These   levers   regulate   power   in   the reverse,  idle  and  forward  ranges,  operating  so  that forward  movement  increases  engine  power.    Power control  is  accomplished  through  adjustment  of  the  N₁ speed   governor   in   the   fuel   control   unit.      Power   is increased  when  N₁  RPM  is  increased.    The   POWER levers  also  control  propeller  reverse  pitch.    Distinct movement  (pulling  up  and  then  aft  on  the  POWER lever)   by   the   pilot   is   required   for   operation   in   the ground  fine  and  reverse  ranges.    Forward  lever  travel range  is  designated   INCR  (increase),  supplemented by an arrow pointing forward.    R  Lever travel range is marked    IDLE,    LIFT,    GROUND    FINE,    LIFT,    and REVERSE.  T3 F3  Lever travel range is marked IDLE, LIFT, and  REVERSE.  A placard below the lever slots reads: CAUTION – REVERSE ONLY WITH ENGINES RUNNING.