4. CABIN AIR, COPILOT AIR, PILOT AIR,
temperature control should fail to operate, the
temperature of defrost air and cabin air can be
controlled manually by setting the CABIN TEMP
MODE switch to the MAN HEAT position, then using
the MANUAL TEMP switch to set the desired
temperature. This control is located on the copilot's
subpanel. Use the following procedure for manual
1. PILOT and COPILOT AIR Controls In.
2. CABIN AIR and DEFROST AIR Controls
3. CABIN TEMP MODE Switch MAN
4. Cold Air Outlets As required.
5. MANUAL TEMP Switch As required.
2-52. SURFACE DEICING SYSTEM.
a. Description. Ice accumulation is removed
from each inboard and outboard wing leading edge
and both horizontal stabilizers by the flexing of deice
boots that are pneumatically actuated. Bleed air is
used to supply air pressure to inflate the deice boots
and to supply vacuum through the ejector system. A
pressure regulator protects 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 system.
Operation of the surface deice 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 not
be available. Prior to deice boot inflation,
check the regulated bleed air pressure
gauge for a minimum of 16 psi. If
insufficient pressure exists, increasing
altitude will increase bleed air pressure.
(1) Deice Boots. Deice boots are intended to
remove ice after it has formed rather than prevent ice
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
(2) Deice Switch. A two position deice
switch, placarded DEICE CYCL, on the pilot's
subpanel, controls the deicing operation. The switch is
spring loaded to return to the off position from SINGLE
(a) SINGLE Position. When the SINGLE
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 a
4-second inflation begins in the horizontal stabilizer,
stabilon, and taillet boots. When these boots have
inflated and deflated, the cycle is complete.
(b) MANUAL Position. If the switch is
held in the MANUAL position, the boots will inflate
simultaneously and remain inflated until the switch is
released. The switch will return to the OFF position
when released. After the cycle, the boots will remain
in the vacuum hold down condition until again actuated
by the switch.
(3) Bleed Air. Either engine is capable of
providing sufficient bleed air for all requirements of the
surface deice system. Check valves in the bleed air
and vacuum lines prevent backflow through the
system during single engine operation. Regulated
PNEUMATIC PRESSURE, located on the copilot's
2-53. PROPELLER ELECTRIC DEICE SYSTEM.
a. Description. The propeller electric deice
system includes electrically heated deice boots, slip
rings and brush block assemblies, a timer for
automatic operation, ammeter, circuit breakers for left
and right propeller and control circuit protection, and
two switches located on the pilot's subpanel, for
automatic or manual control of the system.