TM 1-1510-224-10 NOTE Under conditions where one bleed air source is inoperative, sufficient bleed air  pressure  for  deice  boot  inflation may  not  be  available.    Prior  to  deice boot   inflation,   check   the   regulated bleed air pressure gage for     a minimum   of   16   PSI.      If   insufficient pressure exists, increasing engine N1 and/or   decreasing   aircraft   altitude  - will increase bleed air pressure. b. Operation. WARNING To ensure adequate bleed air pressure  to  the  deice  boots,  do  not simultaneously   actuate   surface   and antenna deice systems in the manual mode. (1) Deice   boots   are   intended   to   remove   ice after it has formed rather than prevent ice formation.  For the  mdst  effective  deicing  operation,  allow  at  least  1/2 inch  of  ice  to  form  on  the  boots  before  attempting  ice removal.  Very thin ice may crack and cling to the boots instead of shedding. WARNING Never cycle the system rapidly.  This may    cause    the    ice    to    accumulate outside   the   contour   of   the   inflated boots and prevent ice removal. (2) A     two     position     deice     switch     on     the overhead  control  panel,  placarded  SURFACE,  controls the  deicing  operation.    The  switch  is  spring  loaded  to return  to  the  off  position  from  SINGLE  CYCLE  AUTO  or MANUAL.    When  the  SINGLE  CYCLE  AUTO  position  is selected,  the  distributor  valve  opens  to  inflate  the  wing boots.      After   an   inflation   period   of   approximately   6 seconds,  an  electronic  timer  switches  the  distributor  to deflate the wing boots and a 4 second inflation begins in the    horizontal    stabilizer,    stabilon,    and    taillet    boots. When  these  boots  have  inflated  and  deflated,  the  cycle is complete. (3) If    the    switch    is    held    in    the    MANUAL position, the boots will inflate simultaneously and remain inflated   until   the   switch   is   released.      The   switch   will return to the off position when released.  After the cycle, the boots will remain in the vacuum hold down condition until again actuated by the switch. (4) Either    engine    is    capable    of    providing sufficient bleed air   for   all   requirements   of   the   surface   deice   system. Check  valves  in  the  bleed  air  and  vacuum  lines  prevent backflow    through    the    system    during    single    engine operation.    Regulated  pressure  is  indicated  on  a  gage, placarded   PNEUMATIC   PRESSURE,   located   on   the center subpanel. 2-51.  ANTENNA DEICING SYSTEM. a. Description.          The     antenna     deicing     system removes  or  prevents  ice  accumulation  on  the  mission antennas.      Pressure   regulated   bleed   air   is   used   to supply    pressure    to    inflate    the    boots.        To    assure operation  of  the  system  in  the  event  of  failure  of  one engine, a check valve is incorporated in the bleed air line from each engine to prevent loss of pressure through the compressor   of   the   inoperative   engine.      Inflation   and deflation phases are controlled by distributor valves. WARNING To ensure adequate bleed air pressure  to  the  deice  boots,  do  not simultaneously   actuate   surface   and antenna deice systems in the manual mode. NOTE Under conditions where one bleed air source is inoperative, sufficient bleed air  pressure  for  deice  boot  inflation may  not  be  available.    Prior  to  deice boot     inflation,     check     PNEUMATIC PRESSURE gage for a minimum of 16 PSI.      If   insufficient   pressure   exists, increasing engine N₁ and/or decreasing aircraft altitude will increase bleed air pressure. b. Antenna   Deice   System   Switch.      The   antenna deice    system    is    controlled    by    a    switch,    placarded ANTENNA,  MANUAL  SINGLE  CYCLE  AUTO,  located on the overhead control panel (fig.  2-15).  The switch is spring   loaded   to   return   to   the   off   position   from   the SINGLE CYCLE AUTO or MANUAL position.  When the switch is set to the  SINGLE  CYCLE  AUTO position, the system    will    run    through    one    timed    inflationdeflation cycle.  When the switch is held in the  MANUAL  position the  boots  will  inflate  and  remain  inflated  until  the  switch is released. c. Operation.    Deice  boots  are  intended  to  remove ice after it has formed rather than prevent ice formation. For  the  most  effective  deicing  operation,  allow  at  least 1/8   to   1/4   inch   of   ice   to   form   on   the   boots   before attempting removal.  Very thin ice may crack and cling to the boots instead of shedding. 2-57