a. Description. The pitot tube and stall warning
vane have electrical heating elements to prevent icing.
On aircraft equipped with electronic
Each heating elements is controlled by a 5-ampere,
timers, cycle switching occurs very
circuit-breaker type switch, located on the left subpanel,
rapidly and may or may not be
detectable as a flicker of the ammeter
These timers cannot be
manually stepped through cycles by
b. Normal Operation. When the pitot heat switch is
in the LH (up) position, the heating element in the
energizing the system on/off switch.
exposed position of the pitot tube is energized. The
PITOT (down) position shuts the pitot heating element
Heating may begin at any phase in the cycle depending
off. The stall warning heat switch activates the healing
on the timer position when the switch was turned off
element in the stall warning vane when the switch is in
from previous use. If ammeter readings are above or
the STALL WARN (up) position. The HEAT (down)
below the operating limits, propeller unbalance may
position of the switch shuts off the vane heating element.
occur when operating in icing conditions.
In the event of overload, the circuit breaker element of
either switch will disconnect the respective heating
2-55. Pitot and Static System.
circuit, tripping the switch toggle to a down position. To
reset power to a healing circuit, move the respective
The pitot and static system
toggle switch to the up position.
supplies static pressure to two airspeed indicators, two
altimeters two vertical velocity indicators, and ram air to
2-57. Fuel System Anti-Icing.
the airspeed indicators. This system consists of a single
pilot tube attached to the underside of the left wing
An oil-to-fuel heat exchanger,
leading edge, static air pressure ports in the aircraft's
located on each engine accessory case, operates
exterior skin on each side of the aft fuselage, and
continuously and automatically to heat the fuel
associated system plumbing.
The pitot head is
sufficiently to prevent freezing of any water in the fuel.
protected from ice formation by internal electric heating
No controls are involved. One external fuel vent on each
elements. Refer to Pitot and Stall Warning Heat System,
wing serves both the nacelle and wing tanks and is
protected against icing by externally attached electric
heat elements, controlled by the 5-ampere circuit
b. Emergency Static Air Source.
A knob type
breaker switch placarded HEAT-FUEL VENTS-LEFT,
control valve located at the upper right corner of the
and the 7.5-ampere circuit breaker switch placarded
instrument panel permits the selection of an alternate
static air pressure source. It is placarded EMERGENCY
STATIC AIR SOURCE, NORM OFF.
operating position (NORMAL, OFF) supplies static air
pressure from the external pressure ports on the aft
When required, static pressure may be
obtained from the alternate source by rotating the control
To prevent overheat damage to
electrically heated anti-ice jackets,
using the emergency static air source, refer to chapter 7.
FUEL VENT HEAT switches should
not be turned ON unless cooling air
2-56. Pitot and Stall Warning Heat System.
will soon pass over the jackets.
b. Normal Operation. For normal operation, HEAT
switches for the FUEL VENTS anti-ice circuits are turned
ON as required during the BEFORE TAKEOFF
FUEL CONTROL HEAT switches are
Pitot or stall warning heat should not
turned ON during the STARTING ENGINES procedures.
be used for more than 15 minutes
while the aircraft is on the ground.
Overheating may damage the heating
Change 6 2-39