TM 1-1510-223-10 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    N,    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   200C.      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  150°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 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 eng;ne 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 and RIGHT ON (fig.  2-13).  They are protected by two  5-ampere  circuit  breakers,  placarded  FUEL  VENT HEAT   L'FT,   RIGHT,   located   on   the   overhead   circuit breaker panel (fig.  2-7). 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 sensor attached  to  the  glass,  an  electrothermal  controller,  two relays,  a  control  switch,  and  two  circuit  breakers.    The two switches, placarded WINDSHIELD, PILOT, NORMAL   OFFHIGH   and   WINID   SHIELD,   COPILOT, NORMAL  OFF  HIGH,  located  on  the  overhead  control panel (fig.  2-13), 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  50-ampere  circuit  breaker,  which are not accessible to the flight crew. To help prevent windshield cracking, windshield heat should be placed in NORMAL  position  for  at  least  15  minutes prior to using the HIGH position. 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   HIGH   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 HIGH position, heat is provided at a higher    watt    density    to    a    smaller    portion    of    the windshield.      The   lever   lock   switch   feature   prevents inadvertent    switching    to    the    HIGH    position    during system shutdown 2-60. PRESSURIZATION SYSTEM. a. Description.     A  mixture  of  bleed  air  from  the engines and ambient air is available for pressurization to the cabin at a rate of approximately 10 to 17 pounds per 2-51