TM 55-1510-219-10 The system is controlled by a switch placarded RADOME ANTI-ICE-ON  located  on  the  overhead  control  panel.    A temperature  sensing  element  installed  in  the  discharge duct  measures  the  hot  air  temperature  as  it  leaves  the mixing  chamber.    When  the  hot  air  temperature  reaches 130 degrees Fahrenheit, the green RADOME HEAT light in  the  mission  caution/  advisory  panel  will  illuminate.    If the  air  temperature  exceeds  200  degrees  Fahrenheit,  a heat detection switch, located adjacent to the temperature sensing  element,  will  close  the  solenoid  shutoff  valves, and   the   yellow   RADOME   HOT   light   located   on   the mission    caution/advisory    panel    will    illuminate.        The shutoff    valves    will    automatically    open    after    the    air temperature cools to approximately 130 degrees Fahrenheit.    The  system  is  protected  by  a  7.    5  ampere circuit  breaker  placarded  RADOME  ANTI-ICE  located  on the overhead control panel. 2-54.        PROPELLER    ELECTROTHERMAL    ANTI-ICE SYSTEM. a. Description.      Electrothermal   anti-ice   boots   are cemented to each propeller blade to prevent ice formation or  to  remove  the  ice  from  the  propellers.    Each  thermal boot  consists  of  one  outboard  and  one  inboard  heating element,   and   receives   electrical   power   from   the   deice timer.      This   timer   sends   current   to   all   propeller   deice boots and prevents the boots from overheating by limiting the  time  each  element  is  energized.    Four  intervals  of approximately   30   seconds   each   complete   one   cycle. Current consumption is monitored by a propeller ammeter on    the    copilot's    subpanel.        Two    20-ampere    circuit breakers  placarded  PROP  ANTI  ICE  LEFT  and  RIGHT and  5-ampere  propeller  control  circuit  breaker  placarded PROP ANTI-ICE CONTR on the overhead circuit breaker panel   (fig.      2-26),   protect   the   propeller   electrothermal deice   system   during   manual   operation.      A   25   ampere circuit breaker placarded PROP ANTI-ICE AUTO, protects the system in automatic operation. b. Automatic   Operation.      A   control   switch   on   the overhead  control  panel  placarded  PROP  OFF  AUTO  is provided   to   activate   the   automatic   system.      A   deice ammeter on the center subpanel registers the amount of current  (14  to  18  amperes)  passing  through  the  system being  used.    During  AUTO  operation,  power  to  the  timer will   be   cut   off   if   the   current   rises   above   25   amperes. Current  flows  from  the  timer  to  the  brush  assembly  and then   to   the   slip   rings   installed   on   the   spinner   backing plate.  The slip rings carry the current to the deice boots on the propeller blades.  Heat from the boots reduces the grip  of  the  ice  which  is  then  thrown  off  by  centrifugal force,  aided  by  the  air  blast  over  the  propeller  surfaces. Power  to  the  two  heating  elements  on  each  blade,  the inner  and  outer  element,  is  cycled  by  the  timer  in  the following  sequence:    right  propeller  outer  element,  right propeller  inner  element,  left  propeller  outer  element,  left propeller  inner  element.    Loss  of  one  heating  element circuit on one side does not mean that the entire system must be turned off.  Proper operation can be checked by noting the correct level of current usage on the ammeter. An  intermittent  flicker  of  the  needle  approximately  each 30   seconds   indicates   switching   to   the   next   group   of heating elements by the timer. c. Manual  Operation.    The  manual  propeller  deice system is provided as a backup to the automatic system. A  control  switch  located  on  the  overhead  control  panel, placarded   PROP   INNER   OUTER,   controls   the   manual override   relays.      When   the   switch   is   in   the   OUTER position,  the  automatic  timer  is  overridden  and  power  is supplied to the outer heating elements of both propellers simultaneously.  The switch is of the momentary type and must be held in position until the ice has been dislodged from  the  propeller  surface.    After  deicing  with  the  outer elements, the switch is to be held in the INNER position to perform the same function for the inner elements of both propellers.  The loadmeters will indicate approximately a 5% increase of load per meter when manual prop deice is operating.  The prop deice ammeter will not indicate any load in the manual mode of operation. 2-55.  PITOT AND STALL WARNING 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. a. Pitot Heat.  Heating elements are installed in the pitot masts located on the nose.  Each heating element is controlled  by  an  individual  switch  placarded  PITOT  ON LEFT  or  RIGHT,  located  on  the  overhead  control  panel (fig.    2-18).    It  is  not  advisable  to  operate  the  pitot  heat system   on   the   ground   except   for   testing   or   for   short intervals  of  time  to  remove  ice  or  snow  from  the  mast. Circuit protection is provided by two 7.  5 amperes circuit breakers, placarded PITOT HEAT, on the overhead circuit breaker panel (fig.  2-26). 2-43