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Hydraulic System (Technical Notes)

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PostPosted: Mon Aug 06, 2012 5:56 pm    Post subject: Hydraulic System (Technical Notes) Reply with quote

QTY Display

Displays system reservoir quantity as a percentage of the normal service level (1.00 is the normal service level).

Left and Right Hydraulic System Demand Pumps (electric)

• In the AUTO position, the L and R demand pumps operate for takeoff, landing, and when system or primary pump pressure is low. In the ON position, the demand pump runs continuously. In the AUTO position the right demand pump operates continuously when the airplane is on the ground.

Center Hydraulic System Primary Pumps (electric)

Arrow On the ground:

• With only a single ground power source (including the APU) the C2 pump will not run if the C1 pump is selected.

• The pump will not be load shed if one engine generator is operating, or the following sources are operating:

- primary external power and secondary external power
- APU generator and primary external power

Arrow In flight:

The C2 pump may be load shed by the electrical load management system when the following conditions exist:

• all other electric pumps are running

• there is a single source of electrical power

• generator capacity is exceeded

The pump will start automatically when the conditions that shed the pump no longer exist.

Center Hydraulic System Demand Pumps (air driven)

• If both air–driven pumps are selected to ON, only air–driven pump C1 operates; the two air–driven pumps cannot operate simultaneously when both are selected ON.

Center Hydraulic System Non–Normal Operation

If center hydraulic system quantity is sensed to be low and airspeed is greater than 60 knots the:

• alternate brakes are isolated from the center system and remain operable using reserve fluid

• nose gear actuation and steering are isolated

• leading edge slats are isolated and not allowed to operate in the primary (hydraulic) mode

The leading edge slats are reconnected to the center hydraulic system and allowed to operate in primary mode when:

• center hydraulic fluid quantity recovers to normal for 5 seconds, and

• the system determines that both engines have been running for more than 30 seconds

Nose gear actuation and steering are reconnected when:

• airspeed decreases below 60 knots, or

• hydraulic pressure to the center system flight controls is low, or

• the landing gear is selected down, both engines are normal, and both engine–driven pumps are providing pressure


The RAT provides hydraulic and electrical power throughout the flight envelope.

In flight, the RAT deploys automatically if:

• both engines are failed and center system pressure is low, or

• both AC transfer busses are unpowered, or

• all three hydraulic system pressures are low

The ram air turbine (RAT) can provide hydraulic power to the center hydraulic system primary flight control components only.


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