TM  55-1510-221-10 2-55.  STALL  WARNING  SYSTEM. The  stall  warning  system  consists  of  a  trans- ducer,  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   a   5-ampere   circuit   breaker,   placarded STALL   WARN,   on   the   overhead   circuit   breaker panel. 2-56. BRAKE DEICE SYSTEM. a. Description.   A  heated-air  brake  deice  sys- tem  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   auto- matic  controls  are  provided.  There  are  two  primary occasions   which   require   brake   deicing.   The   first   is when  an  aircraft  has  been  parked  in  a  freezing  atmo- sphere   allowing   the   brake   systems   to   become   con- taminated  by  freezing  rain,  snow,  or  ice,  and  the  air- craft  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  sole- noid   valve   attached   to   the   bleed   air   system   which serves  both  the  surface  deice  system  and  the  pneu- matic  systems  operation. b. Operation.   A  switch  on  the  overhead  con- trol   panel,   placarded   BRAKE   DEICE,   controls   the solenoid   valve   by   routing   power   through   a   control module   box   under   the   aisleway   floorboards.   When the  switch  is  on,  power  from  a  5-ampere  circuit breaker   on   the   overhead   circuit   breaker   panel   is applied  to  the  control  module.  A  lo-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  light,  and  has  a resetting   circuit   interlocked   with   the   gear   uplock switch.  When  the  system  is  activated,  the  BRAKE DElCE  ON  light  should  be  monitored  and  the  con- trol  switch  selected  OFF  after  the  light  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 2-44 to  self-terminate  after  10  minutes.  If  the  automatic timer  has  terminated  brake  deicer  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  lights  may  momentarily  illumi- nate  during  simultaneous  operation  of  the  surface deice  and  brake  deice  systems  at  low  N₁   speeds.  If the  lights  immediately  extinguish,  they  may  be  disre- garded. (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°C.   Appropriate   perfor- mance  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°C  ambient  temperature. The  system  is  not  to  be  operated  for  longer  than  10 minutes   (one   deicer   cycle)   with   the   landing   gear retracted.  If  operation  does  not  automatically  termi- nate  after  approximately  10  minutes  following  gear retraction,  the  system  must  be  manually  selected  off. During  periods  of  simultaneous  brake  deice  and  sur- face  deice  operation,  maintain  85%  N₁   or  higher.  If inadequate  pneumatic  pressure  is  developed  for proper  surface  deicer  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.   Circuit   protection   is   provided   by a   5-ampere   circuit   breaker,   placarded   BRAKE DEICE,  on  the  overhead  circuit  breaker  panel  (fig. 2-26). 2-57.  FUEL  SYSTEM  ANTI-ICING. a.   Description.   An   oil-to-fuel   heat   exchanger, located  on  each  engine  accessory  case,  operates  con- tinuously   and   automatically   to   heat   the   fuel   suffi- ciently  to  prevent  freezing  of  any  water  in  the  fuel. No   controls   are   involved.   Two   external   fuel   vents are  provided  on  each  wing.  One  is  recessed  to  pre- vent   ice   formation;   the   other   is   electrically   heated and  is  controlled  by  two  toggle  switches  on  the  over- head   control   panel   placarded   FUEL   VENT   ON, LEFT  and  RIGHT  (fig.  2-12).  They  are  protected  by two  5-ampere  circuit  breakers,  placarded  FUEL VENT  HEAT,  RIGHT  or  LEFT,  located  on  the overhead  circuit  breaker  panel  (fig.  2-26).  Each  fuel control  unit  is  protected  against  ice.  The  pneumatic governor  for  each  fuel  control  unit  is  electrically heated,   and   protected   by   two   7   1/2-ampere   circuit