Operation
Antiskid operation requires:
• The ANTISKID switch must be on.
• The airplane must be moving at least
5 mph.
Above 5 mph, with the ANTISKID switch ON
and brakes applied, the printed circuit board
receives and analyzes wheel speed inputs from
the transducer on each main wheel (Figure 14-
12). If the wheel deceleration rate is higher than
a predetermined limit, the applicable solenoid-
operated antiskid valve will individually regulate
braking force on the corresponding brake by
releasing braking pressure into the return line.
Four green ANTI-SKID GEN lights (24-112 and
subsequent) will illuminate at approximately 5
mph to indicate wheel generator operation. A
fault in the system is indicated by the respective
ANTI-SKID GEN light extinguishing. All four
lights go out if power to the circuit board is lost
or if the ANTI-SKID switch is OFF. An ANTI-
SKID TEST switch is provided on the test
switch panel forward of the thrust levers. For
system testing, refer to the approved AFM.
The brakes may be applied in flight to break up
suspected accumulations of ice on the brakes.
At low taxi speeds (5 mph or less), the antiskid
system is inoperative, and the ANTI-SKID GEN
lights will be out.
EMERGENCY BRAKES
Emergency airbrakes are provided for use in the
event of normal brake system failure. Antiskid
protection, differential braking, and parking
brakes are not available while using the emer-
gency brakes.
To apply brakes with the emergency system, the
EMER BRAKE handle (see Figures 14-11 and
14-12) must be carefully pushed down until the
desired braking force is obtained. This meters
pressure from the emergency air bottle through
four shuttle valves to the brake assemblies in
proportion to handle movement. A maximum of
600 psi may be applied. Releasing the handle
stops flow from the bottle and allows applied air
pressure to be vented overboard, releasing
the brakes.
PARKING BRAKES
Normal hydraulic system pressure from either
engine-driven pump or the auxiliary pump can
be used to set the parking brakes. Pulling the
PARK BRAKE handle on the left side of the
power lever quadrant mechanically closes both
parking brake valves (see Figures 14-11 and 14-
12). The closed valves allow pressure from the
pilot or copilot brake valves to be trapped in the
brake assemblies.
To set the parking brakes, pull the PARK
BRAKE handle rearward. Pedal pressure may be
applied during or after handle movement.
Setting the parking brake on model 25 airplanes
(see Figure 14-11) disconnects the antiskid sys-
tem and prevents inadvertent loss of brake pres-
sure. Failure to fully release the parking brake
may result in the antiskid not being operational.
To release the parking brakes, the PARK
BRAKE handle must be pushed fully forward.
NOSEWHEEL STEERING
GENERAL
Two types of electrically operated nosewheel
steering systems are installed: with or without
variable authority. System components include a
DC steering actuator, a computer-amplifier, rud-
der pedal followups, and switches for system
engagement. In addition, airplanes with variable
authority steering utilize signals from the wheel
speed transducers. AC and DC power are sup-
plied through NOSE STEER circuit breakers on
the pilot’s and copilot’s circuit-breaker panels.
Airborne, the nosewheel steering system is deen-
ergized by the squat switch on airplanes without
a relay box.
14-14
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
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