Learjet 20 Series Pilot Training Manual page 321

to the copilot's instruments. The right rear static
port is connected with an alternate static port
inside the nose compartment to provide the
pressurization module or outflow valve with a
static source. The static source goes to the pres-
surization module on models with the Garrett
pressurization system, or to the outflow valve
on airplanes with the IDC pressurization sys-
tem. A static source inside the tailcone on all 20
series airplanes provides static pressure to the
cabin safety valve. Refer to Chapter 12,
"Pressurization," for additional information.
Two shoulder static ports are located on top
of the fuselage nose in front of the windshield.
These ports provide static pressure to the au-
topilot altitude controller on the air data sen-
s o r s a n d a n a l t i t u d e p r e s s u r e s w i t c h o n
airplanes with the Century III wing.
On airplanes SNs 24-138 and subsequent and
all 25 models, the two forward static ports on
each side are heated. Circuit protection is
through the PITOT HEAT circuit breakers.
On those airplanes with the Learjet Century
III RAS, the shoulder static ports are also
heated. Refer to Chapter 10, "Ice and Rain
Protection," for additional information.
An ALTERNATE STATIC SOURCE valve is
located below the pilot's instrument panel
(Figure 16-5) and connects the pilot's static
system to an alternate source located on frame
5. For normal operation, the lever remains
down (CLOSED); for alternate air, the lever
is moved up (OPEN).
When the ALTERNATE STATIC SOURCE
valve is positioned to OPEN, the pilot's static
instruments are connected to an alternate port
inside the unpressurized nose section. See the
AFM for corrections to be applied to the air-
speed and the altimeter when using the alter-
nate static source.
16-4
LEARJET 20 SERIES PILOT TRAINING MANUAL
FOR TRAINING PURPOSES ONLY
Figure 16-5. ALTERNATE STATIC SOURCE
Valve
AIR DATA SENSOR
An air data sensor is installed on airplanes
SNs 25-270 and subsequent and those air-
planes modified per AMK 81-12 (installation
of engine stall warning system). The air data
sensor is installed in the nose compartment just
forward of the nose wheel well box. It re-
ceives a static input from the shoulder static
ports. The pitot input is from the copilot's
p i t o t s y s t e m .
air data sensor provides altitude hold, alti-
tude rate, indicated airspeed, and Mach num-
ber output signals. High altitude and low
altitude switch outputs and synchronous air
data output are also available.
RAM-AIR TEMP GAGE
Ram-air temperature is displayed on the RAM
AIR TEMP gage, located on the copilot's sub-
panel (Figure 16-6). The gage is calibrated
in degrees Celsius. For conversion to outside
air temperature (OAT), refer to the Ram-Air
Outside Temperature Conversion figure in the
"Performance" section of the approved AFM.
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