ATR 72 600 Hydraulic System

Overview of the Hydraulic System

System Description

• The aircraft features two independent hydraulic systems, designated as blue and green, which operate simultaneously during normal operations.

• Main components of the hydraulic system are located in the left landing gear fairing, including pumps, accumulators, connectors, and a main reservoir.

• Each hydraulic system is pressurized by an AC-powered electric pump delivering 3,000 PSI; blue pump uses AC bus one while green uses AC bus two.

Auxiliary Pump Functionality

• The blue system has an auxiliary DC-powered pump for ground use when no power is available; it operates at 1/3 output compared to main pumps.

• The auxiliary pump activates automatically if blue system pressure drops below 1,500 PSI under specific conditions (gear down and engine running).

Hydraulic Reservoir Details

Reservoir Specifications

• The common hydraulic tank has a total capacity of 9.6 liters with a sight gauge indicating fluid levels; refill line indicates minimum required fluid level at 8.5 liters.

• Fluid is added through a filler cap using approved brands like Skyrol LD4 and H Jet 4; each compartment in the tank holds up to 4 liters.

Monitoring and Indicators

• Low-level lights on the hydraulic power panel alert when fluid in any compartment drops below 2.5 liters; master caution lights also activate.

• Two clogging indicators monitor filters for particles that could cause blockages but do not provide cockpit warnings.

Green Hydraulic System Operations

Pressure Monitoring

• The green hydraulic system's electric pump outputs normal pressure of 3,000 PSI; low-pressure light illuminates if pressure falls below 1,500 PSI.

• An overheat condition occurs if return line temperature exceeds 121°C; associated alerts trigger on multiple displays.

Accumulator Role

• A nitrogen-charged accumulator acts as a shock absorber against pressure surges and assists during high demand on the green system.

Blue Hydraulic System Operations

Pressure Management

• Similar to the green system, the blue hydraulic pump operates at 3,000 PSI with monitoring for low-pressure conditions triggering alerts.

Auxiliary Pump Functionality

• The blue auxiliary pump boosts pressure on the ground when engines are off; it can run without power if certain conditions are met (e.g., one engine running).

Cross-feed Valve Mechanism

Interconnection Between Systems

• Both systems can interconnect via a cross-feed valve controlled by a push button on the hydraulic power panel to restore pressure if one fails.

Safety Features

• If either reservoir compartment drops below critical levels (2.5 L), cross-feed functionality is inhibited to prevent further loss of fluid from both systems.

Control Panel Overview

Hydraulic Power Panel Functions

• Located on the flight deck overhead panel, this controls all aspects of both hydraulic systems with visual indicators for operational status displayed clearly.