TM 55-1510-220-10 NOTE Check to insure that the OXYGEN SUPPLY 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 aircraft ascends to higher altitudes. Oxygen cylinders thus cooled by temperature   change   will   show   a pressure drop.  This type of drop in  pressure  will  rise  again  upon return    to    a    lower    or    warmer altitude.    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. (b) Emergency  pressure  control  lever.    The emergency   pressure   control   lever   (red),   is   placarded EMERGENCY     NORMAL     TEST     MASK,     has     three positions.  Two positions control oxygen consumption for the individual using oxygen, and the remaining position serves   for   testing   hose   and   mask   integrity.      In   the EMERGENCY  position,  the  control  lever  causes  100% oxygen to be delivered at a safe, positive pressure.  In the   NORMAL   position,   the   lever   allows   delivery   of normal  or  100%  oxygen,  depending  upon  the  selection of  the  diluter  control  lever.    In  TEST  MASK  position, 100% oxygen at positive pressure is delivered to check hose and mask integrity. (c) Diluter control lever. CAUTION When    not    in    use,    the    diluter control lever should be left in the 100% OXYGEN position to prevent regulator contamination. The    diluter    control    lever    (white),    placarded    100% OXYGEN  NORMAL  OXYGEN,  selects  either  normal  or 100%    oxygen,    but    acts    to    select    only    when    the emergency  pressure  control  lever  is  in  the  NORMAL position. (d) Supply  control  lever.    The  supply  control lever   (green),   placarded   ON   OFF,   turns   the   oxygen supply on or off at the regulator control panel. b. Oxygen  masks.    Oxygen  masks  for  the  pilot, copilot  and  mission  operators  are  provided  as  personal equipment.  To connect a mask into the oxygen system, the individual connects the line attached to the mask to the   flexible   hose   which   is   attached   to   the   cockpit sidewall.      The   microphone   in   the   oxygen   mask   is provided   with   a   cord   for   connecting   with   the   helmet microphone jack.< To test mask and hose integrity, the individual    places    the    supply    control    lever    on    the regulator  control  panel  to  the  ON  position,  puts  on  and adjusts   his   mask,   selects   TEST   MASK   position,   and checks for leaks. c. Normal Operation. Oxygen pressure is maintained at all times to the regulator control panels 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. d. Emergency Operation. For emergency operation,    the    affected    crew    member    selects    the EMERGENCY    position    of    the    emergency    pressure control  lever  (red)  on  his  regulator  control  panel.    This selection provides 100% oxygen at a positive pressure, regardless of the position of the diluter control lever on his panel. e. First Aid Operation.  A first aid oxygen mask is installed in the toilet compartment as a supplemental or emergency   source   of   oxygen   (100%).      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. 2-62.  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 2-52