switch is to be held in the INNER position to perform the
same function for the inner elements of both propellers.
The loadmeters will indicate approximately a 5% increase
of load per meter when manual propeller de-ice is
operating. The propeller de-ice ammeter will not indicate
any load in the manual mode of operation.
2-55. PITOT AND STALL WARNING HEAT SYSTEM.
Pitot heat should not be used for
more than 15 minutes while the
a. Pitot Heat. 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 on the overhead control panel
(fig. 2-12). It is not advisable to operate the pitot heat
system on the ground except for testing, or for short
intervals of time to remove ice or snow from the mast.
Circuit protection is provided by two 7 1/2 ampere circuit
breakers, placarded PITOT HEAT, on the overhead circuit
breaker panel (fig. 2-27). The INS true air speed probe
(air data probe) heat control circuit is also protected by
this circuit breaker. If either left or right pitot heat is on,
INS true airspeed probe heat will be on.
The heating elements protect the
stall warning lift transducer vane
and face plate from ice, however, a
buildup of ice on the wing may
change or disrupt the airflow and
prevent the system from accurately
indicating an imminent stall.
Stall Warning Heat. The lift transducer is
equipped with anti-icing capability on both the mounting
plate and the vane. The heat is controlled by a switch
located on the overhead control panel placarded STALL
WARN. The level of heat is minimal for ground operation
but is automatically increased for flight operation through
the landing gear safety switch. Circuit protection is
provided by a 15-ampere circuit breaker, placarded
STALL WARN, on the overhead circuit breaker panel (fig.
2-56. STALL WARNING SYSTEM.
The stall warning system consists of a transducer, a lift
computer, a warning horn, and a test switch. Angle of
attack is sensed by aerodynamic pressure on the lift
transducer vane located on the left wing leading edge.
When a stall is imminent, the output of the transducer
activates a stall warning horn. The system has preflight'
test capability through the use of a switch placarded
STALL WARN TEST OFF LDG GEAR WARN TEST on
the right subpanel. Holding this switch in the STALL
WARN TEST position actuates the warning horn by
moving the transducer vane. The circuit is protected by a
5-ampere circuit breaker, placarded STALL WARN, on
the overhead circuit breaker panel.
2-57. BRAKE DEICE SYSTEM.
Description. A heated-air brake deice system
may be used in flight with gear retracted or extended, or
on the ground. When activated, hot air is diffused by
means of a manifold assembly over the brake discs on
each wheel. Manual and automatic controls are provided.
There are two primary occasions which require brake
deicing. The first is when an aircraft has been parked in a
freezing atmosphere allowing the brake systems to
become contaminated by freezing rain, snow, or ice, and
the aircraft must be moved or taxied. The second
occasion is during flight through icing conditions with wet
brake assemblies presumed to be frozen, which must be
thawed prior to landing to avoid possible tire damage and
loss of directional control. Hot air for the brake de-ice
system comes from the compressor stage of both engines
obtained by means of a solenoid valve attached to the
bleed air system which serves both the surface de-ice
system and the pneumatic systems operation.
Operation. A switch on the overhead control
panel, placarded BRAKE DEICE, controls the solenoid
valve by routing power through a control module box
under the aisleway floorboards. When the switch is on,
power from a 5-ampere circuit breaker on the overhead
circuit breaker panel is applied to the control module. A
10-minute timer limits operation and avoids excessive
wheel well temperatures when the landing gear is
retracted. The control module also contains a circuit to
the green BRAKE DE-ICE ON annunciator light, and has
a resetting circuit interlocked with the gear unlock switch.
When the system is activated, the BRAKE DE-ICE ON
light should be monitored and the control switch selected
OFF after the light extinguishes otherwise, on the next
Change 2 2-44