TM 55-1510-219-10 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  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  left  landing  gear  saety  switch.    Circuit  protection  is provided    by    a    15-ampere    circuit    breaker,    placarded STALL WARN, on the overhead circuit breaker panel (fig. 2-26). 2-56.  PITOT AND STATIC SYSTEM. a. Description.  The pitot and static system supplies static pressure to two airspeed indicators, two altimeters, two    vertical    velocity    indicators,    and    ram    air    to    the airspeed   indicators.      This   system   consists   of   two   pitot masts (one located on each side of the lower position of the nose), static air pressure ports in the aircraft's exterior skin   on   each   side   of   the   aft   fuselage,   and   associated system  plumbing.    The  pitot  head  is  protected  from  ice formation by internal electric heating elements. b. Alternate Static Air Source.  An alternate static air line,    which    terminates    just    aft    of    the    rear    pressure bulkhead,  provides  a  source  of  static  air  for  the  pilot's instruments in the event of source failure from the pilot's static air line.  A control on the pilot's subpanel placarded PILOTS   STATIC   AIR   SOURCE,   may   be   actuated   to select either the NORMAL or ALTERNATE air source by a two position selector valve.  The valve is secured in the NORMAL position by a spring clip.  Refer to Chapter 7 for airspeed   indicator   and   altimeter   calibration   information when using the alternate air source. c. 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 OFFLDG 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. 2-57.  BRAKE DEICE SYSTEM. a. Description.      A   heated-air   brake   deice   system may be used on the ground or in flight with gear retracted or   extended.      When   activated,   hot   air   is   diffused   by means  of  a  manifold  assembly  over  the  brake  discs  in 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.      A   switch   on   the   overhead   control 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 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 light, and has a resetting  circuit  interlocked    with  the  gear  uplock  switch. When  the  system  is  activated,  the  BRAKE  DEICE  ON light should be monitored and the control 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  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 BLEED AIR FAIL lights may momentarily  illuminate  during  simultaneous  operation  of the  surface  deice  and  brake  deice  systems  at  low  N1 speeds.  If the lights immediately extinguish.  this may be disregarded. 2-44