External Defog
There are two push-pull defog knobs located
on the left side of the pedestal. The top knob
(Figure 10A-8) is labeled “IN–NORMAL—
OUT–DEFOG,” and the bottom is labeled
“IN–PILOT & COPILOT—OUT–PILOT.” For
external use, pull the top knob out, then tog-
g l e t h e t h r e e - p o s i t i o n , s p r i n g - l o a d e d
DEFOG–OFF switch to the DEFOG position
for three to four seconds until the desired air-
flow is attained. Adjacent to the DEFOG
switch is an amber or blue light which illu-
minates anytime the defog shutoff valve is not
fully closed.
In the pilot’s defog nozzle is a thermal switch
which causes the red W/S O’HEAT light to il-
luminate when the temperature reaches 210ºF.
The light extinguishes when the temperature
drops to 180ºF. When the W/S O’HEAT light
illuminates, the defog system should be turned
off or the airflow decreased to prevent possi-
ble distortion to the windshield. To turn off the
defog system, toggle the DEFOG switch to
OFF until airflow has stopped, then push the
top knob in.
Internal Defog
Internal windshield defogging is supplied by
a continuous flow of conditioned cabin air
and requires no management.
A defog nozzle drain located on the right side
of the fuselage under the right windshield
drains condensation from the lines.
10A-8
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
Figure 10A-8. Defog Knob
