Learjet 20 Series Pilot Training Manual page 302

The pilot-operated normal pitch trim and emer-
gency pitch trim systems are electrically inde-
pendent systems. Mode selection (normal or
emergency) is made with the P TRIM selector
switch (Figure 15-7). On model 23 airplanes,
emergency trim is available with the P TRIM
switch in either NORM or EMER position. On
all subsequent airplanes, emergency trim is
available with the P TRIM switch in EMER
position only.
Normal pitch trim is controlled through either of
the control wheel trim switches; emergency
pitch trim is controlled through the EMERGEN-
CY PITCH trim toggle switch on the aft end of
the pedestal (Figure 15-7).
All airplanes other than model 23 incorporate a
two-speed NORMAL trim motor and an audible
clicker that signals trim in motion. On these air-
planes, trim occurs at the normal rate when the
flaps are extended 3º or more. With the flaps up
(or extended less than 3º), trim occurs at approx-
imately 1/4 the normal rate (slow trim). An
amber PITCH TRIM OVSP annunciator illumi-
nates if trim occurs at the normal rate with flaps
up or extended less than 3º. The trim in motion
clicker indicates movement of the horizontal sta-
bilizer and sounds whenever the stabilizer is in
motion for longer than one second with the flaps
extended less than 3º.
Autopilot operation uses the emergency motor to
adjust pitch trim.
Horizontal stabilizer position is displayed on the
pitch trim indicator.
Stabilizer Actuator
The stabilizer actuator is operated by either of
two DC-powered motors. The normal trim motor
and control circuits are powered through the
PITCH circuit breaker. The emergency trim
motor and control circuits are powered through
the EMERG TRIM circuit breakers.
The emergency trim motor operates at approxi-
mately 1/2 the speed of the normal trim motor.
LEARJET 20 SERIES PILOT TRAINING MANUAL
FOR TRAINING PURPOSES ONLY
P TRIM Selector Switch
The P TRIM (pitch trim) selector switch pro-
vides the normal and emergency mode selections
(Figure 15-7). In the NORM position, normal
pitch trim is available from both of the control
wheel trim switches. In the OFF position, both
trim motors and control circuits are deenergized.
In the EMER position, emergency pitch trim is
available from the EMERGENCY PITCH trim
switch (Figure 15-7). The pilot's normal trim
function is rendered inoperative.
The EMERGENCY PITCH trim switch is
spring-loaded to the center position.
The autopilot utilizes the emergency trim motor
with the P TRIM selector switch in the NORM
or EMER position; however, if either control
wheel trim switch is actuated with the arming
button depressed (Figure 15-7) or if the EMER-
GENCY TRIM switch is actuated, the autopilot
disengages. On model 23 airplanes, actuating the
pitch trim switch without arming disengages the
autopilot.
In the event of normal pitch trim runaway on air-
planes with the two-speed trim system, depress-
ing and holding the wheel master switch will
stop both the normal and the emergency trim
motors. On model 23 airplanes, the emergency
trim is not interrupted.
It is not a requirement that takeoff trim be set
within the green band for takeoff. Trim settings
forward of the green band should be used for
takeoff at aft center-of-gravity loadings. Trim
settings near the aft portion of the green band
should be used for takeoff at forward cg load-
ings. However, in no event should takeoff be
attempted with the TAKE-OFF TRIM annuncia-
tor illuminated.
The TAKE-OFF TRIM annunciator is disabled
in flight by the squat switch.
FlightSafety
international
15-11