TM 55-1510-222-10 control circuit is also protected by this circuit breaker.  If either  left  or  right  pitot  heat  is  on,  the  true  airspeed temperature probe heat will be on. CAUTION The 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. b.      Stall   Warning   Heat   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 in 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. 2-6). 2-56.  STALL WARNING SYSTEM. The stall warning system consists of a transducer, a lift computer, a 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. 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  right  subpanel.    Holding  this  switch  in  the  STALL WARN   TEST   position   actuates   the   warning   horn   by moving the transducer vane.  The circuit is protected by the  5-ampere  circuit  breaker,  placarded  STALL,  on  the overhead circuit breaker panel. 2-57.  BRAKE DEICE SYSTEM. a.      Description.      The   heated   air   brake   deice system   may   be   used   in   flight   with   gear   retracted   or extended, or on the ground.  When activated, hot air is diffused   by   means   of   a   manifold   assembly   over   the brake   discs   on   each   wheel.      Manual   and   automatic controls are provided.  There are two primary occasions which require brake deicing.  The first is when an aircraft has been parked in a freezing atmosphere allowing the brake   systems   to   become   contaminated   by   freezing rain,  snow,  or  ice,  and  the  aircraft  must  be  moved  or taxied.    The  second  occasion  is  during  flight  through icing conditions with wet brake assemblies presumed to be  frozen,  which  must  be  thawed  prior  to  landing  to avoid   possible   tire   damage   and   loss   of   directional control.  Hot air for the brake deice system comes from the   compressor   stage   of   both   engines   obtained   by means  of  a  solenoid  valve  attached  to  the  bleed  air system which serves both the surface deice system and the pneumatic systems operation. b.  Operation.  The switch in the overhead control panel, placarded BRAKE, controls the solenoid valve by routing  power  through  a  control  module  box  under  the aisleway floorboards.  The system is protected by the 5- ampere  circuit  breaker  in  the  overhead  circuit  breaker panel   placarded   BRAKE   DEICE.      A   10-minute   timer limits    operation    and    avoids    excessive    wheel    well temperatures  when  the  landing  gear  is  retracted.    The control   module   also   contains   a   circuit   to   the   green BRAKE  DEICE  ON  annunciator,  and  has  a  resetting circuit  interlocked  with  the  gear  uplock  switch.    When the    system    is    activated,    the    BRAKE    DEICE    ON annunciator should be monitored and the control switch selected     OFF     after     the     annunciator     extinguishes, otherwise,  on  the  next  gear  extension  the  system  will restart  without  pilot  action.    The  control  switch  should also  be  selected  OFF  if  deice  operation  fails  to  self- terminate    after    approximately    10    minutes.        If    the automatic  timer  has  terminated  brake  deice  operation after  the  last  retraction  of  the  landing  gear,  the  landing gear   must   be   extended   in   order   to   obtain   further operation of the system. (1) The  L  BL  AIR  FAIL  or  R  BL  AIR  FAIL annunciator may momentarily illuminate during simultaneous  operation  of  the  surface  and  brake  deice systems     at     low     N₁speeds.          If     the     annunciators immediately extinguish, they may be disregarded. (2) During  certain  ambient  conditions,  use  of the  brake  deice  system  may  reduce  available  engine power,   and   during   flight   will   result   in   a   TGT   rise   of approximately  20^o  C.    Applicable  performance  charts should be consulted before brake deice system use.  If specified  power  cannot  be  obtained  without  exceeding limits, the brake deice system must be selected off until after takeoff is completed.  TGT limitations must also be observed  when  setting  climb  and  cruise  power.    The brake  deice  system  is  not  to  be  operated  above  15^o  C ambient  temperature.    During  periods  of  simultaneous brake deice and surface deice operation, maintain 85% N₁   or   higher.      If   inadequate   pneumatic   pressure   is developed for proper surface deice 2-48