Learjet 60 Pilot’s Manual
PM-123 6-7
Change 6
wing temperature indicator, a system switch, and associated aircraft
wiring. Electrical power for system operation is 28 VDC supplied
through the 3-amp WING HEAT circuit breaker on the copilot’s circuit-
breaker panel.
STAB WING HEAT SWITCH — WING HEAT FUNCTION
The wing anti-ice system is controlled through the STAB WING HEAT
switch located in the ANTI-ICE group on the center switch panel. The
switch has two positions: On (STAB WING HEAT) and OFF. When the
STAB WING HEAT switch is set On, the anti-ice shutoff and pressure
regulator valve control solenoid will close allowing pressure to build
within the valve reference chambers. The building pressure will open a
butterfly valve in the bleed-air airstream and allow heated air to flow
through the ducting into the wing diffuser tubes. The valve will main-
tain a regulated 15 (±2.5) psi bleed airflow providing the butterfly re-
mains open. In the event of an electrical system failure, the valve will
shut off the bleed-air flow and wing anti-ice protection will not be
available. Two sources of bleed air are used for wing anti-ice. In addi-
tion to the normal bleed-air supply (mixed low- and high-pressure), by-
pass circuits are activated which makes hotter bleed air from the
engines’ high pressure ports available for wing anti-icing. A tempera-
ture sensor will deactivate the bypass circuit if the respective high-pres-
sure duct becomes too hot. When the STAB WING HEAT switch is set
to OFF, the bypass circuits are deactivated. Additionally, the bypass
circuit is deactivated if the respective BLEED AIR switch is not ON or
the respective ENG FIRE PULL T-handle is pulled.
WING TEMP INDICATOR
The WING TEMP indicator, located on the center switch panel in the
ANTI-ICE group, is installed to provide a visual indication of the wing
leading edge temperature. The indicator receives input signals from the
wing temperature sensor installed on the inner surface of the left wing
leading edge. The indicator face is divided into three colored segments:
blue, green, and red. If the indicator pointer is in the blue segment,
wing leading edge temperature is cold enough for moisture to freeze on
the surface. If the indicator pointer is in the green segment, wing lead-
ing edge temperature is warm enough that moisture will not freeze on
the surface. If the indicator pointer is in the red segment, the wing lead-
ing edge is approaching an overheat condition and corrective action
must be taken. The wing anti-ice system should be energized whenever
flying through visible moisture and the WING TEMP indicator pointer
is in the blue segment.
Change 6
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