from the temperature sensor and the temperature selector and supplies open and close signals, as appropriate,  to  the  vent  suit  temperature  control valve. The  vent-air  flow  controllers,  as  the  name implies, control the flow of air from the vent-air system  ducting  to  the  personnel  services  dis- connects  and  the  seat  cushion  or  the  vent connection   of   the   antiexposure   suit.   One controller is provided for each crew member. The controller   has   an   inlet   connector,   an   outlet connector,   and   a   thumbwheel-operated   flow controller. The thumbwheel shaft connects to a rotating plug, which gradually opens or closes off the outlet port as it rotates up to a maximum of 180 degrees. The flow controller will be fully open when turned to the full counterclockwise position. The  temperature  selector  is  a  thumbwheel- operated  potentiometer,  located  on  the  pilot’s console, aft of the flow controller thumbwheel. One temperature selector serves both vent suit outlets.  The  thumbwheel  is  numbered  1  through 14,  and  the  console  is  labeled  HOT  and  COLD. Turning  the  thumbwheel  clockwise  to  the  lower numbered settings lowers the temperature of vent- air   system   air.   Counterclockwise   movement towards the hot position and the higher numbered settings increases the temperature. Response  to  temperature  changes  initiated  by repositioning  the  temperature  selector  thumb- wheel  will  be  noticeable  at  the  disconnect  outlet within a few seconds after making a selection change. When the aircraft is in a stabilized flight condition  (maintaining  a  steady  altitude),  the temperature of vent air will be monitored and controlled   within   a   ±2°F   tolerance   of   the temperature  selected  by  the  temperature  selector thumbwheel.   When   the   aircraft   is   changing altitude, the temperature is maintained within a ±  10°F  tolerance. The  thermal  switch  senses  any  abnormally high temperatures not compensated for by the temperature sensor and will provide a signal, via the cabin and vent suit temperature controller, to the temperature control valve to drive it towards the closed position. The  system  pressure  relief  valve  protects  the system from accidental overpressurization. The relief valve will open as necessary to prevent vent- air system ducting pressure from exceeding 10 psi. The check valve prevents conditioned air from backing  up  into  the  environmental  control  system ducting. Cooled air flows through the check valve, is mixed with the appropriate amount of hot bleed air, and is forced into the vent-air system ducting. DEICE/ANTI-ICING  SYSTEMS On days when there is visible moisture in the air, ice can form on aircraft leading edge surfaces at  altitudes  where  freezing  temperatures  start. Water droplets in the air can be supercooled to below freezing without actually turning into ice unless they are disturbed in some manner. This unusual occurrence is partly due to the surface tension  of  the  water  droplet  not  allowing  the droplet to expand and freeze. However, when air- craft   surfaces   disturb   these   droplets,   they immediately turn to ice on the aircraft surfaces. The ice may have a glazed or rime appearance. Glazed ice is smooth and hard to detect visually. Rime ice is rough and easily noticed. Frost  is  formed  as  a  result  of  water  vapor being turned directly into a solid. Frost can form on  aircraft  surfaces  in  two  ways.  First,  it  can accumulate on aircraft parked in the open over- night when the temperature drops below freezing and  proper  humidity  conditions  exist.  Second,  it can form on aircraft surfaces, caused by flying at  very  cold  altitudes  and  descending  rapidly into warm, moist air. In this case, frost deposits will result before the structure warms up because of the marked cooling of air adjacent to the cold skin. Ice  or  frost  forming  on  aircraft  create  two basic hazards: (1) the resulting malformation of the airfoil, which could decrease the amount of lift; and (2) the additional weight and unequal formation  of  the  ice,  which  could  cause  un- balancing  of  the  aircraft,  making  it  hard  to control.  Enough  ice  to  cause  an  unsafe  flight condition can form in a very short period of time, thus some method of ice prevention or removal is necessary. Presently there are two methods for removing or preventing ice. One method, deicing, employs a mechanical system to break up and remove the ice after it has formed. The second method, anti- icing,   uses   heated   bleed   air   to   prevent   the formation of ice. Deicing systems are common to older  aircraft,  and  are  now  generally  being replaced  by  anti-icing  systems. Deice Boot Systems The deice system for the wing, horizontal, and vertical stabilizer leading edges of E-2 aircraft is an example of a typical deice boot system. The system removes accumulated ice from the wing surfaces through the use of rubber deice boots, which are bonded to the leading edges. The cells 1-7