TM 55-1510-222-10 mission  antennas.    Pressure  regulated  bleed  air  from both   engines   supply   pressure   to   inflate   or   heat   the boots.  To assure operation of the system, in the event of failure of one engine, a check valve is incorporated in the  bleed  air  line  from  each  engine  to  prevent  loss  of pressure   through   the   compressor   of   the   inoperative engine.  Inflation and deflation phases are controlled by distributor valves. b.    Antenna  Deice  System  Switch.    The  antenna deice    system    is    controlled    by    a    switch    placarded ANTENNA,   SINGLE   CYCLE   MANUAL   located   in   the overhead control panel (fig. 2-13).  The switch is spring loaded  to  return  to  the  off  position  from  the  SINGLE CYCLE or MANUAL position.  When the switch is set to the   single   position,   the   system   will   run   through   one timed  inflation-deflation  cycle.  When  the  switch  is  held in the MANUAL position the boots will inflate and remain inflated until the switch is released. c. Forward Wide Band Data Link Antenna Radome Anti-Ice.      The   forward   wide   band   data   link   antenna radome   anti-ice   system   utilizes   engine   bleed   air   to prevent the formation of ice on the radome. The system is  controlled  by  the  switch  placarded  RADOME  located in the overhead control panel. The circuit is protected by the  7  1/2-ampere  circuit  breaker  placarded  RADOME ANTI-ICE, located in the overhead circuit breaker panel (fig. 2-6). d.      Operation.      Deice   boots   are   intended   to remove  ice  after  it  has  formed  rather  than  prevent  its formation.      For   the   most   effective   deicing   operation, allow at least 1/8 to 1/4 inch of ice to form on the boots before attempting the removal.  Very thin ice may crack and cling to the boots instead of shedding. NOTE Never   cycle   the   system   rapidly,   this may    cause    the    ice    to    accumulate outside   the   contour   of   the   inflated boots and prevent ice removal. 2-54.  PROPELLER ELECTRIC DEICE SYSTEM. a.      Description.      The   propeller   electric   deice system   includes:   electrically   heated   deice   boots,   slip rings and brush block assemblies, a timer for automatic operation,  ammeter,  circuit  breakers  for  left  and  right propeller and control circuit protection, and two switches located  in  the  overhead  control  panel  for  automatic  or manual control of the system. b.  Automatic Operation.  The two position switch located in the overhead control panel, placarded PROP AUTO ON, is provided to activate the automatic system. Upon  placing  the  switch  to  the  ON  position  the  timer diverts power through the brush block and slip ring to all heating  elements  on  one  propeller.    Subsequently,  the timer then diverts power to all heating elements on the other propeller for the same length of time.  This cycle will continue as long as the switch is in the ON position. The   system   utilizes   a   metal   foil   type   single   heating element, energized by DC voltage.  The timer switches every   90   seconds,   resulting   in   a   complete   cycle   in approximately 3 minutes. c.  Manual Operation.  The manual propeller deice system   is   provided   as   a   backup   to   the   automatic system.  The spring-loaded control switch located in the overhead control panel, placarded PROP MANUAL ON, controls  the  manual  override  relay.    When  holding  the switch    in    the    ON    position    the    automatic    timer    is overridden,    and    power    is    supplied    to    the    heating elements of both propellers simultaneously.  This switch is  of  the  momentary  type  and  must  be  held  in  position for  approximately  90  seconds  to  dislodge  ice  from  the propeller  surface.  Repeat  this  procedure  as  required  to avoid  significant  buildup  of  ice,  which  will  result  in:  a loss  of  performance,  vibration,  and  impingement  of  ice upon the fuselage.  The propeller deice ammeter will not indicate a load while the propeller deice system is being utilized  in  the  manual  mode.    However,  each  aircraft loadmeter  will  indicate  an  approximate  4%  increase  in load while the manual prop deice system is operating. 2-55.  PITOT AND STALL WARNING HEAT SYSTEM. a. Pitot Heat. CAUTION Pitot heat should not be used for more than 15 minutes while the aircraft is on the ground.  Overheating may damage the heating elements. Heating elements are installed in both pitot masts, located on the nose.  Each heating element is controlled by  an  individual  switch  placarded  PITOT  ON  LEFT  or RIGHT, located in the overhead control panel (fig. 2-13). Circuit   protection   is   provided   by   the   two   7.5-ampere circuit    breakers,    placarded    PITOT    HEAT,    on    the overhead   circuit   breaker   panel   (fig.   2-6).      The   true airspeed temperature probe heat 2-47