mission antennas. Pressure regulated bleed air from
both engines supply pressure to inflate or heat the
boots. To assure operation of the system, in the event
of failure of one engine, a check valve is incorporated in
the bleed air line from each engine to prevent loss of
pressure through the compressor of the inoperative
engine. Inflation and deflation phases are controlled by
b. Antenna Deice System Switch. The antenna
deice system is controlled by a switch placarded
ANTENNA, SINGLE CYCLE MANUAL located in the
overhead control panel (fig. 2-13). The switch is spring
loaded to return to the off position from the SINGLE
CYCLE or MANUAL position. When the switch is set to
the single position, the system will run through one
timed inflation-deflation cycle. When the switch is held
in the MANUAL position the boots will inflate and remain
inflated until the switch is released.
Forward Wide Band Data Link Antenna Radome
Anti-Ice. The forward wide band data link antenna
radome anti-ice system utilizes engine bleed air to
prevent the formation of ice on the radome. The system
is controlled by the switch placarded RADOME located
in the overhead control panel. The circuit is protected by
the 7 1/2-ampere circuit breaker placarded RADOME
ANTI-ICE, located in the overhead circuit breaker panel
d. Operation. 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 1/8 to 1/4 inch of ice to form on the boots
before attempting the 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 removal.
2-54. 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 in the overhead control panel for automatic or
manual control of the system.
b. Automatic Operation. The two position switch
located in the overhead control panel, placarded PROP
AUTO ON, is provided to activate the automatic system.
Upon placing the switch to the ON position the timer
diverts power through the brush block and slip ring to all
heating elements on one propeller. Subsequently, the
timer then diverts power to all heating elements on the
other propeller for the same length of time. This cycle
will continue as long as the switch is in the ON position.
The system utilizes a metal foil type single heating
element, energized by DC voltage. The timer switches
every 90 seconds, resulting in a complete cycle in
approximately 3 minutes.
c. Manual Operation. The manual propeller deice
system is provided as a backup to the automatic
system. The spring-loaded control switch located in the
overhead control panel, placarded PROP MANUAL ON,
controls the manual override relay. When holding the
switch in the ON position the automatic timer is
overridden, and power is supplied to the heating
elements of both propellers simultaneously. This switch
is of the momentary type and must be held in position
for approximately 90 seconds to dislodge ice from the
propeller surface. Repeat this procedure as required to
avoid significant buildup of ice, which will result in: a
loss of performance, vibration, and impingement of ice
upon the fuselage. The propeller deice ammeter will not
indicate a load while the propeller deice system is being
utilized in the manual mode. However, each aircraft
loadmeter will indicate an approximate 4% increase in
load while the manual prop deice system is operating.
2-55. PITOT AND STALL WARNING HEAT SYSTEM.
Pitot heat should not be used for more
than 15 minutes while the aircraft is on
the ground. Overheating may damage
the heating elements.
Heating elements are installed in both pitot masts,
located on the nose. Each heating element is controlled
by an individual switch placarded PITOT ON LEFT or
RIGHT, located in the overhead control panel (fig. 2-13).
Circuit protection is provided by the two 7.5-ampere
circuit breakers, placarded PITOT HEAT, on the
overhead circuit breaker panel (fig. 2-6). The true
airspeed temperature probe heat