Learjet 60 Pilot’s Manual
PM-123 6-5
Change 6
continually heated by bleed air flowing between their double-wall
construction. The low pressure compressor inner stator and nacelle in-
let are heated by bleed air when the associated NAC HEAT switch is on.
The engine air temperature (T
T0) and pressure (PT) sensors are anti-iced
by integral electrical heating elements. Each engine anti-ice system is
independently operated and consists of T
T0/PT sensor heating ele-
ments, a nacelle inlet anti-ice control valve (controls flow to the nacelle
inlet lip), an engine anti-ice control valve (controls flow to the low-pres-
sure compressor inner stator), a pressure switch, a control switch, a
NAC HT light, and associated aircraft wiring and bleed-air plumbing.
Control circuits are powered by 28 VDC supplied through the 7.5-amp
L and R NAC HEAT circuit breakers on the pilot’s and copilot’s circuit
breaker-panels respectively.
NAC HEAT SWITCHES
The left and right engine and nacelle inlet anti-ice systems are indepen-
dently controlled through the NAC HEAT switches in the ANTI-ICE
group on the center switch panel. Each NAC HEAT switch has two
positions: On (L or R) and OFF. When a NAC HEAT switch is placed in
the On (L or R) position, the associated TT0/PT sensor elements will be
energized and the associated engine and nacelle inlet anti-ice control
valves will open. Engine bleed air will flow through the open valves to
the low pressure compressor inner stator and nacelle inlet lip. Since the
control valves are energized closed, engine and nacelle inlet anti-ice
protection will still be available in the event of an electrical system
failure.
NAC HT LIGHTS
The amber L and R NAC HT lights on the glareshield annunciator pan-
el provide the crew with visual indication of an engine or nacelle inlet
anti-ice system malfunction. The lights are operated by a pressure
switch in the associated nacelle inlet bleed air plumbing and a proxim-
ity switch built into the engine anti-ice control valve. Illumination of a
NAC HT light when the associated NAC HEAT switch is in the On
position, indicates that insufficient pressure is being applied to the
nacelle inlet or the engine anti-ice control valve has failed to open.
Illumination of a NAC HT light, when the associated NAC HEAT
switch is in the OFF position, indicates that bleed-air pressure is being
applied to the nacelle anti-ice system due to a malfunction of the
nacelle anti-ice control valve.
The green NAC HT light on the glareshield annunciator panel provides
the crew with visual indication that either nacelle heat switch is On.
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