Pilot’s Manual
PM-126A III-1
TABLE OF CONTENTS
Hydraulic System ..................................................................................... 3-1
Firewall Shutoff Valves ......................................................................... 3-2
Source Selector Valve............................................................................. 3-2
AUX HYD Pump Control ..................................................................... 3-2
Main/Auxiliary System Pressure........................................................ 3-3
Brake Accumulator Pressure........................................................... 3-4
Hydraulic Ground Service.................................................................... 3-4
Hydraulic System Page......................................................................... 3-5
HYD System Page (Figure 3-1) ............................................................ 3-5
Hydraulic System Schematic (Figure 3-2) ..........................................3-7
Landing Gear System................................................................................ 3-9
Landing Gear Control Switch .............................................................. 3-9
Landing Gear Extension/Retraction Schematic (Figure 3-3) ........ 3-11
Landing Gear Position Lights ............................................................ 3-12
Landing Gear Warning System.......................................................... 3-13
Landing Gear Free Fall................................................................... 3-14
Nose Wheel Steering System.............................................................. 3-15
Nose Steer Switch ........................................................................... 3-16
Wheel Brake Control /Anti-Skid System............................................. 3-17
Touchdown Protection ........................................................................ 3-17
Emergency/Parking Brake................................................................. 3-18
Anti-Skid Switch .................................................................................. 3-19
Wheel Brake Control/Anti-Skid System Schematic
(Figure 3-4)....................................................................................... 3-21
SECTION III
HYDRAULICS &
LANDING GEAR
Pilot’s Manual
PM-126A 3-1
SECTION III
HYDRAULICS &
LANDING GEAR
HYDRAULIC SYSTEM
The aircraft hydraulic system supplies hydraulic pressure for operation
of the aircraft landing gear, brake, flap, spoiler/spoileron and thrust reverser
systems. Hydraulic fluid flows from the main hydraulic reservoir
through two firewall shutoff valves to the main engine-driven
hydraulic pumps for distribution to the required systems upon demand.
The hydraulic system has both a main and auxiliary source of hydraulic
power. These sources are totally separate up to the source selector
valve. An auxiliary dc motor-driven hydraulic pump is installed to provide
auxiliary hydraulic pressure to the brake system through the
brake source shuttle valve and to the landing gear and flap system
through the source selector valve in the event of a malfunction. The
auxiliary hydraulic system only provides pressure for the brake system
while the aircraft is on the ground.
A 260 cu. in. (4261 cc) reservoir supplies hydraulic fluid to the main and
auxiliary hydraulic systems. The reservoir is designed with a separation
wall (partition) to contain fluid for either the main or auxiliary system.
Reservoir pressure is maintained at approximately 20 psi (138 kPa)
by bleed air supplied through a pressure regulator. A bleed air pressure
relief valve releases pressure in excess of 20 psi (138 kPa), and a vacuum
relief valve prevents negative pressure in the reservoir. A thermal shutoff
valve prevents high energy bleed air (>390° F [199° C]) from entering
the reservoir in the event of a hydraulic line failure.
The main and auxiliary hydraulic pumps will each maintain a nominal
pressure of 3000 psi (20,685 kPa) for their applicable systems. A precharged
(1500 psi [10,343 kPa]) hydraulic accumulator is installed to
dampen and absorb pressure surges within the main hydraulic system.
A separate brake accumulator, fed by the auxiliary system, maintains
pressure for the emergency/parking brakes. Two high-pressure filters
and two return filters prevent hydraulic fluid contamination within the
main and auxiliary systems. These filters incorporate bypass valves
which will open in the event they become clogged. A hydraulic pressure
relief valve, installed between the high-pressure and return lines
in both the main and auxiliary system filters, will open to relieve pressure
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