TM 1-1510-224-10 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,   located   on   the   overhead circuit breaker panel (fig.  2-9). 2-57.  BRAKE DEICE SYSTEM. a. Description.    The  brake  deice  system  may  be used  in  flight  with  gear  retracted  or  extended,  or  on  the ground.    When  the  brake  deice  system  is  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,  when  brake  assemblies  which  are  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.      Hot   air   is 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.    A  switch  located  on  the  overhead control   panel   (fig.      2-15),   placarded    BRAKE   -   ON, controls  the  solenoid  valve  by  routing  power  through  a control module box under the aisle way floorboards.  The system is protected by a 5-ampere circuit breaker on the overhead   circuit   breaker   panel   (fig.      2-9),   placarded BRAKE  DE-ICE.    A  10-minute  timer  limits  operation  to avoid    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    N₁    speeds.        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   20C.        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  15C 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  boot  inflation,  select the  brake  deice  system  off.    Both  sources  of  pneumatic bleed air must be in operation during brake deice system use.    Select  the  brake  deice  system  off  during  single engine operation. 2-58.  FUEL SYSTEM ANTI-ICING. a. Description.        An    oil-to-fuel    heat    exchanger, located    in    each    engine    accessory    case,    operates continuously and automatically to heat the fuel sufficiently  to  prevent  freezing  of  any  water  in  the  fuel. No  controls  are  involved.    Three  external  fuel  vents  are provided  on  each  wing.    One  is  recessed  to  prevent  ice formation,  the  second  is  flush  mounted  so  that  no  ice can  collect  upon  it,  and  the  third  is  electrically  heated. Heating  is  controlled  by  two  toggle  switches  located  on the   overhead   control   panel,   placarded    FUEL   VENT, LEFT, RIGHT and ON (fig. 2-15).  They are protected by two  5-ampere  circuit  breakers,  placarded    FUEL  VENT HEAT,   LEFT,   and   RIGHT,   located   on   the   overhead circuit breaker panel (fig.  2-9). CAUTION To prevent overheat damage to electrically heated anti-ice jackets, the FUEL VENT heat switches should not be turned ON unless cooling air will soon pass over the jackets. b. Normal     Operation.          For     normal     operation, switches for the fuel vent anti-ice circuits are turned   ON as required during the BEFORE TAKEOFF procedures. 2-59.      WINDSHIELD   ELECTROTHERMAL   ANTI-ICE SYSTEM. a. Description.        Both    the    pilot's    and    copilot's windshields  are  provided  with  an  electrothermal  anti-ice system.      Each   windshield   is   part   of   an   independent electrothermal     anti-ice     system.          Each     system     is comprised of the windshield assembly with heating wires sandwiched     between     glass     panels,     a     temperature 2-59