TM  55-1510-221-10 indicate  over  400  PSI.  If  the  pressure  exceeds  400 vided  with  a  cord  for  connecting  with  the  micro- PSI,  a  malfunction  of  the  pressure  reducer  is  indi- phone  jack.  To  test  mask  and  hose  integrity,  the cated.   Whenever   oxygen   is   inhaled,   a   blinker-vane individual  places  the  supply  control  lever  on  the  reg- slides   into   view   within   the   flow   indicator   window, ulator  control  panel  to  the  ON  position,  puts  on  and showing  that  oxygen  is  being  released.  When  oxygen adjusts  his  mask,  selects  TEST  MASK  position,  and is  exhaled,  the  blinker  vane  vanishes  from  view. checks  for  leaks. NOTE Check  to  insure  that  the  OXYGEN  SUP- PLY  PRESSURE  gage  registers  adequate pressure  before  each  flight.  When  oxygen is  in  use,  a  check  of  the  supply  pressure should  be  made  at  intervals  during  flight to   note   the   quantity   available   and   to approximate   the   supply   duration.   The outside  temperature  is  reduced  as  an  air- craft  ascends  to  higher  altitudes.  Oxygen cylinders  thus  cooled  by  temperature change  will  show  a  pressure  drop.  This type  of  drop  in  pressure  will  raise  again upon  return  to  a  lower  or  warmer  alti- tude.   A   valid   cause   for   alarm   would   be the rapid loss of oxygen pressure when the aircraft  is  in  level  flight  or  descending; should   this   condition   arise,   descend   as rapidly  as  possible  to  altitude  which  does not  require  the  use  of  oxygen. W A R N I NG Pure  oxygen  will  support  combustion.  Do not  smoke  while  oxygen  is  in  use. W A R N I N G If  any  symptoms  occur  suggestive  of  the onset  of  hypoxia,  immediately  set  the emergency  pressure  control  lever  to  the EMERGENCY   position   and   descend below  10,000  feet.  Whenever  carbon monoxide  or  other  noxious  gas  is  present or  suspected,  set  the  dilutor  control  lever to  100%  OXYGEN  and  continue  breath- ing   undiluted   oxygen   until   the   danger   is past. e. Oxygen  masks.  Oxygen  masks  for  the  pilot and  copilot  are  provided  as  personal  equipment.  To connect  a  mask  into  the  oxygen  system,  the  individ- ual   connects   the   line   attached   to   the   mask   to   the flexible  hose  which  is  attached  to  the  cockpit  side- wall.   The   microphone   in   the   oxygen   mask   is   pro- f.  Normal Operation. Oxygen     pressure     is maintained  at  all  times  to  the  regulator  control  pan- els  if  the  cylinder  shut-off  valves  are  on  and  if  there is  pressure  in  the  cylinders.  Each  individual  places the   supply   lever   (green)   on   his   regulator   control panel  to  the  ON  position,  and  the  diluter  lever (white)  to  the  NORMAL  OXYGEN  position. g.  Emergency  Operation.  For   emergency   oper- ation,  the  affected  crew  member  selects  the  EMER- GENCY  position  of  the  emergency  pressure  control lever  (red)  on  his  regulator  control  panel.  This  selec- tion   provides   100%   oxygen   at   a   positive   pressure, regardless  of  the  position  of  the  diluter  control  lever on  his  panel. h.  First  Aid  Operation.  A  first  aid  oxygen mask  is  installed  in  the  aft  cabin  area  as  a  supple- mental  or  emergency  source  of  oxygen.  The  mask  is stowed  behind  an  overhead  cover  placarded  FIRST AID  OXYGEN  -PULL.  Removing  the  cover  allows the  mask  to  drop  out  of  the  container,  exposing  a manual  control  valve,  which  releases  oxygen  to  the mask  when  placed  in  the  ON  position.  After  using the  mask,  the  manual  valve  in  the  container  must  be turned  OFF  before  stowing  the  mask  and  replacing the  cover. 2-63.  WINDSHIELD  WIPERS. a. Description. Two   electrically   operated windshield  wipers,  are  provided  for  use  at  takeoff, cruise  and  landing  speed.  A  rotary  switch  (fig.  2-12) placarded   WINDSHIELD   WIPER,   located   on   the overhead   control   panel,   selects   mode   of   windshield wiper   operation.   An   information   placard   above   the switch   states:   DO   NOT   OPERATE   ON   DRY GLASS.   Function   positions   on   the   switch,   as   read clockwise,  are  placarded:  PARK  -  OFF  -  SLOW  - FAST.  When  the  switch  is  held  in  the  spring-loaded PARK  setting,  the  blades  will  return  to  their  normal inoperative  position  on  the  glass,  then,  when released,  the  switch  will  return  to  OFF  position  ter- minating   windshield   wiper   operation.   The   FAST and   SLOW   switch   positions   are   separate   operating speed   settings   for   wiper   operation.   The   windshield wiper   circuit   is   protected   by   one   lo-ampere   circuit breaker,  placarded  WSHLD  WIPER,  located  on  the overhead  circuit  breaker  panel  (fig.  2-26). 2-51