Section VII. UTILITY SYSTEMS
Description. The defrosting system is an
integral part of the heating and ventilation system. The
system consists of two warm air outlets connected by
ducts to the heating system. One outlet is just below the
pilot's windshield and the other is below the copilot's
windshield. A push-pull control, placarded DEFROST
AIR, on the pilot' s subpanel, manually controls airflow
to the windshield. When pulled out, defrosting air is
ducted to the windshield. As the control is pushed in,
there is a corresponding decrease in airflow.
VENT BLOWER switches - As required
CABIN AIR MODE SELECT switch - AUTO.
CABIN AIR TEMP CONTROL rheostat - As
CABIN AIR, COPILOT AIR PILOT AIR, and
DEFROST AIR controls - As required.
Manual Operation. If the automatic temperature
control should fail to operate, the temperature of defrost
air and cabin air can be controlled manually by setting
the CABIN AIR MODE SELECT switch to the MAN
COOL position, then using the CABIN AIR MANUAL
TEMP switch to set the desired temperature. This
control is located on the overhead control panel (fig. 2-
13). Use the following procedure for manual operation:
PILOT and COPILOT AIR controls - In.
CABIN AIR and DEFROST AIR controls Out
CABIN AIR MODE SELECT switch - MAN
Cold air outlets - As required.
CABIN AIR MANUAL TEMP switch - As
SURFACE DEICING SYSTEM.
Description. Ice accumulation is removed from
each inboard and outboard wing leading edge, both
horizontal stabilizers, stabilons, and taillets by the
flexing of deice boots which are pneumatically actuated.
Engine bleed air from the engine compressor is used to
supply air pressure to inflate the deice boots, and to
supply vacuum through the ejector system. A pressure
the system from over inflation. When the system is not
in operation, a distributor valve keeps the boots held
down by vacuum supplied through the ejector systerm
Operation of the surface device system in
ambient temperatures below -40°C can
cause permanent damage to the deice
Under conditions where one bleed air
source is inoperative, sufficient bleed air
pressure for deice boot inflation may riot 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 N, and/or
decreasing aircraft altitude will increase
bleed air pressure.
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 its formation. For
the most 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.
Never cycle the system rapidly, this may
cause the ice to accumulate outside the
contour of the inflated boots and prevent ice
(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