TM 55-1510-220-10 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   L   BL   AIR   FAIL   or   R   BL   AIR   FAIL annunciator   lights   may   momentarily   illuminate   during simultaneous  operation  of  the  surface  de-ice  and  brake de-ice    systems    at    low    N1    speeds.        If    the    lights immediately extinguish, they may be disregarded. (2) During certain ambient conditions, use of the brake de-ice system may reduce available engine power, and during flight will result in a TGT rise of approximately 20° C.        Appropriate    performance    charts    should    be consulted  before  brake  de-ice  system  use.    If  specified power  cannot  be  obtained  without  exceeding  limits,  the brake   de-ice   system   must   be   selected   off   until   after takeoff   is   completed.      TGT   limitations   must   also   be observed   when   setting   climb   and   cruise   power.      The brake  de-ice  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  terminate  after  approximately  10  minutes following  gear  retraction,  the  system  must  be  manually selected off.  During periods of simultaneous brake deice and surface de-ice 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.  2-27). 2-58.  FUEL SYSTEM ANTI-ICING. a. Description.        An    oil-to-fuel    heat    exchanger, located     on     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.    Two  external  fuel  vents  are  provided  on each wing.  One is recessed to prevent ice formation; the other is electrically heated and is controlled by two toggle switches  on  the  overhead  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.    2-27).    Each fuel control unit is protected against ice.  The pneumatic governing for each fuel control unit is electrically heated, and   protected   by   two   7   1/2-ampere   circuit   breakers located  on  the  overhead  circuit  breaker  panel  placarded FUEL  CONTR  HEAT,  LEFT  or  RIGHT  (fig.    2-27).  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 VENTS anti-ice circuits are turned ON as required during the BEFORE TAKEOFF procedures (Chapter 8). 2-59.      WINDSHIELD   ELECTROTHERMAL   ANTI-ICE SYSTEM. a. Description. Both pilot and copilot 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  sensor attached  to  the  glass,  an  electrothermal  controller,  two relays,  a  control  switch,  and  two  circuit  breakers.    Two switches, placarded WSHLD ANTI-ICE NORMAL OFF HI PILOT, COPILOT, located on the overhead control panel (fig.  2-12) control system operation.  Each switch controls one   electrothermal   windshield   system.      The   circuits   of each system are protected by a 5-ampere circuit breaker and a 50ampere circuit breaker which are not accessible to  the  flight  crew.    The  50-ampere  circuit  breakers  are located   in   the   power   distribution   panel   under   the   floor ahead  of  the  main  spar.    The  5-ampere  circuit  breakers are located on panels forward of the instrument panel. b. Normal    Operation.        Two    levels    of    heat    are provided  through  the  three  position  switches  placarded NORMAL  in  the  aft  position,  OFF  in  the  center  position, and HI after lifting the switch over a detent and moving it to the forward position.  In the NORMAL position, heat is provided for the major portion of each windshield.  In the HI position, heat is provided at a higher watt density to a smaller portion of the wind- 2-45