01-12-2012, 02:08 PM
Landing Gear and Brake System
1Landing Gear.pdf (Size: 315.74 KB / Downloads: 91)
Overview
Gear down and locked positions are indicated by three green lights located below the selector,
and a red “Warning Gear Unsafe” light is located at the top of the panel. An all-lights-out condition
indicates the gear is up.
To prevent inadvertent gear retraction, if the gear selector is placed in the “Up” position and
the airplane is on the ground, a “squat switch” located on the left main gear will prevent the hydraulic
pump from actuating when the master switch is turned on. On takeoff, when the landing gear strut
drops to its full retraction, the safety switch closes to complete the circuit which allows the hydraulic
pump to be activated to raise the landing gear when the gear selector is moved to the “Up” position.
During preflight check, be sure the landing gear selector is in the “Down” position and that the three
green indicator lights are illuminated. The gear should be retracted before VLO is reached. The
landing gear may be lowered at any airspeed up to VLE.
The hydraulic reservoir for landing gear operation is an integral part of hydraulic pump.
Access to the combination pump and reservoir may be gained through the panel located on the aft
hatshelf bulkhead in the baggage compartment.
The gear warning horn emits a 90 cycle per minute beeping sound in contrast to the stall
warning horn which emits a continuous sound.
Introduction
The PA-28 Arrow Series aircraft are equipped with retractable tricycle air-oil strut type landing
gear which are hydraulically operated by an electrically powered reversible pump.
Landing Gear System
The PA-28 Arrow Series aircraft are equipped with a retractable, tricycle, air-oil strut type
landing gear system that is hydraulically actuated by an electrically powered reversible pump. The
hydraulic pump is controlled by the landing gear selector knob, located on the instrument panel to the
left of the control quadrant. The gear extension / retraction speed is approximately seven seconds.
The emergency gear lever, when used for emergency extension of the gear, manually
releases hydraulic pressure to permit the gear to free-fall with spring assistance on the nose gear.
The lever must be placed in the downward position for emergency extension and held down on those
aircraft equipped with a lever return spring. On those aircraft not equipped with the spring, the lever
must be returned to the raised position before the gear can be retracted.
· Pressure Switch
o Turns the pump off when pressure reaches 1800 PSI during gear retraction
o If line pressure to the bottom of the actuators drops below 1800 PSI, the pressure
switch closes to start the pump and increase pressure to more than 1800 PSI
· High Pressure Control
o Is essentially a relief valve that is used during gear retraction if pressure in the lines
exceeds 2,250 psi. If for example the pressure switch was to fail and not turn the
pump off at 1800 psi, the high pressure control would allow fluid back into the reservoir
instead of over pressurizing the lines
· Low Pressure Control
o Is once again essentially a relief valve that is used during gear extension. If pressure
in the lines were to exceed 650 psi during gear extension, the low control pressure
would allow fluid back into the reservoir. The likely cause of this would be a down limit
switch malfunction. If the down limit switch was not to work, the hydraulic pump would
run infinitely. In this case, fluid would escape through the low pressure control.
· Thermal Relief
o A relief valve that is used when the gear is fully retracted. This relief valve allows fluid
to return to the reservoir. The likely cause of a pressure increase with the gear up
would be thermal expansion due to an increase in outside air temperature.
· Emergency Gear Valve
o Pressure relief valve located in the lines to hold gear up in the retracted position
o Opening will divert fluid to the reservoir from the high pressure lines