from the temperature sensor and the temperature
selector and supplies open and close signals, as
appropriate, to the vent suit temperature control
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 pilots
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.
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
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
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