The parking brake system is used for temporary parking only.

The parking brake system is used to apply brake pressure for an extended length of time after the hydraulic systems have stopped. The parking brake system is also used to stop the aircraft if there is a hydraulic malfunction.

The parking brake system uses hydraulic pressure from the No. 3 brake accumulator for emergency operation. A shuttle valve is connected between each brake and the brake control valve to isolate the brake control function from the emergency/parking brake function.

The emergency/parking brake handle is used to control the emergency/parking brake valve. The handle is connected to a lever on the emergency/parking brake valve. The lever moves a piston in the valve that controls the pressure from the No. 3 brake accumulator to the brakes.

The Emergency Park Brake Metering Valve is located in the main landing gear wheel well area.

The meter valve receives mechanical inputs from the parking brake handle, and meters brake pressure to each of the main wheel brake through shuttle valves. The emergency/parking brake valve has a pressure port, a return port, a brake port and a fourth port connected to a pressure switch. The pressure port is connected to the hydraulic system No. 3 pressure line and bypasses the shutoff valve. The brake port is connected to the brake line and bypasses the brake control valve. The pressure switch connects to channel A and channel B of the brake control unit.

Springs in the metering valve provide artificial feel and return pressure to the park brake handle. Thermal relief protection is provided at 3,800 psi.

The pressure switch on the valve sends a signal to the brake control unit when the valve is used to operate the brakes. A lever on the emergency/parking brake valve moves a piston that controls the pressure that goes to the brakes. The emergency/parking brake handle is connected to the lever on the emergency/parking brake valve.

The Emergency Park Brake handle is mounted on the cockpit center pedestal. Full handle travel is approximately 45 degrees, where it mechanically latches in the park brake position.

A spring-loaded button, on the end of the handle, permits the handle to be released from the park brake position. A push/pull rod, and lever assembly to a ball bearing control cable mechanically link the handle. The cable transmits the park brake lever motion to the park brake metering valve.

The No. 3 brake accumulator is installed in the aft fuselage compartment.

It is installed upstream of the shutoff valve and contains pressurized hydraulic fluid. If hydraulic system No. 3 does not operate correctly, the accumulator will supply 3,000 psi system pressure. The No. 3 brake accumulator has sufficient fluid for six emergency brake operations. A pressure transducer on the accumulator sends brake pressure data to the brake control unit.

 The No. 3 hydraulic system brake pressure switch is installed in the center wing/fuselage compartment.

It is installed downstream of the parking brake valve and the hydraulic fuse. The No. 3 hydraulic system brake pressure switch has a pressure loaded mechanism and a dual pole switch. The No. 3 hydraulic system brake pressure switch sends parking brake message indications to (EICAS):

• PARK/EMER BRAKE ON – white status
• PARK/EMER BRAKE ON – amber (in flight)
• PARK/EMER BRAKE ON – red warning (takeoff configuration)

The switch is activated at hydraulic pressures above 170 psig.

The emergency/parking brake hydraulic fuse is installed in the center wing/fuselage compartment.

Hydraulic fuses are used to prevent loss of hydraulic fluid in the event of a brake line failure downstream. They are located between the brake control valve and the brake assemblies. At flow rates greater than 0.1 gpm, the fuse will close, preventing a further loss of fluid. The fuse will reset within 5 seconds of the input pressure being reduced to approximately 5 psi. An override lever is provided to carry out brake bleeding.

The emergency/parking brake pressure transducer is connected to the No. 3 hydraulic system and is installed in the rear fuselage on the valve manifold assembly. It has one hydraulic port and one electrical connector. The pressure transducer uses a Wheatstone bridge to change the hydraulic pressure at the input port into an electrical signal. The transducer sends a signal to the brake control unit.

Emergency brake operation is provided by pulling up on the emergency/park brake handle located on the center console. As the handle is pulled up, handle force and emergency/park brake metering valve pressure is progressively increased.

Pulling the handle travel, mechanically latches it in the park brake position. The park brake is released by pressing the unlock button on the handle and stowing it.

Hydraulic system No. 3 pressure from the park brake metering valve is directed to each brake by shuttle valves. Because the emergency parking brake pressure bypasses the brake control valves, no antiskid protection, locked wheel protection or touchdown protection are available.

The system No. 3 brake accumulator provides approximately six emergency brake applications or allows extended park brake operation.Accumulator pressure indication is provided to the EICAS by its pressure transducer. EICAS parking brake message indications are provided by the pressure switch mounted downstream of the hydraulic fuse.