TM 1-1510-224-10 WARNING Never  cycle  the  system  rapidly,  this may    cause    the    ice    to    accumulate outside   the   contour   of   the   inflated boots and prevent ice removal. 2-52.      FORWARD   GUARDRAIL   DUAL   DATA   LINK ANTENNA RADOME ANTI-ICE. The forward guardrail dual data link (GDDL) antenna radome    anti-ice    system    utilizes    engine    bleed    air    to prevent the formation of ice on the radome.  The system is   controlled   by   a   switch,   placarded   RADOME   -   ON, located  on  the  overhead  control  panel  (fig.    2-15).    The circuit    is    protected    by    a    7.5-ampere    circuit    breaker, placarded RADOME ANTI-ICE, located on the overhead circuit breaker panel (fig.  2-9). 2-53.  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   on the  overhead  control  panel  (fig.    2-15),  for  automatic  or manual control of the system. b. Automatic  Operation.      The   two   position   switch located on the overhead control panel, placarded  PROP AUTO   -   ON,    is    provided    to    activate    the    automatic system.  When the switch is placed 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 on the overhead  control  panel,  placarded   PROP  -  MANUAL  - ON,   controls   the   manual   override   relay.      When   the switch is held in the  ON  position,  the  automatic  timer  is overridden,     and     power     is     supplied     to     the     heating elements  of  both  propellers  simultaneously.    The  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  10%  increase  in load     while     the     manual     propeller     deice     system     is operating. 2-54.  PITOT HEAT SYSTEM. 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,  LEFT,  RIGHT and ON, located on the overhead control panel (fig.  2-15).  Circuit protection is provided by the two 7.5- ampere circuit breakers, placarded  PITOT  HEAT, on the overhead   circuit   breaker   panel   (fig.      2-9).      The   true airspeed  temperature  probe  heat  control  circuit  is  also protected  by  these  circuit  breakers.    If  either  left  or  right pitot   heat   is   on,   the   true   airspeed   temperature   probe heat will be on. 2-55.  STALL WARNING HEAT SYSTEM. CAUTION Heating    elements    protect    the    stall warning lift transducer vane and face plate from ice.  However, a buildup of ice    on    the    wing    may    change    or disrupt   the   airflow   and   prevent   the system from accurately indicating an imminent stall. The     lift     transducer     is     equipped     with     anti-icing capability on both the mounting plate and the vane.  The heat  is  controlled  by  a  switch,  located  on  the  overhead control  panel,  placarded    STALL  WARN.      The   level   of heat is minimal for ground operation, but is automatically increased   for   flight   operation   through   the   landing   gear safety   switch.      Circuit   protection   is   provided   by   a   15- ampere circuit breaker, placarded  STALL WARN, on the overhead circuit breaker panel (fig.  2-9). 2-56.  STALL WARNING SYSTEM. The stall warning system consists of a transducer, a lift  computer,  warning  horn,  and  a  test  switch.    Angle  of attack   is   sensed   by   aerodynamic   pressure   on   the   lift transducer  vane  located  on  the  left  wing  leading  edge (fig.  2-1 and 2-2).  When a stall is imminent, the output of   the   transducer   activates   a   stall   warning   horn.      The system  has  preflight  test  capability  through  the  use  of  a switch placarded STALL WARN TEST OFF LDG GEAR WARN   TEST   on    the    copilot's    subpanel    (fig.        2-8). 2-58