Hydraulics

Question 1

The following systems receive hydraulic power:

Answer 1

flight controls,

leading edge slats,

trailing edge flaps,

landing gear, wheel brakes,

nose and main gear steering

and thrust reversers.

Question 2

Hydraulic power is distributed to the flight control system to allow sufficient aircraft control with

Answer 2

only one functioning hydraulic system.

Question 3

Primary pumps pressurize each system during most operations.

Demand pumps are employed

Answer 3

during high load phases of flight and to provide system redundancy.

Question 4

Reservoirs requiring refilling display

Reservoir low quantity is displayed as

Reservoir over-full shown as

Answer 4

a white RF.

LO.

OF.

OF and RF are inhibited in flight.

Question 5

The shutoff switches are for ground maintenance use only and are not required for any flight crew

Answer 5

normal or non-normal procedures.

Question 6

The demand pumps augment hydraulic power during high load

system demands and also

Answer 6

provide redundancy should the primary pump fail.

Question 7

The center hydraulic system power is used to

Answer 7

retract and extend the landing gear and provide nose and main gear steering.

The alternate brakes, the reserve brakes,

the leading edge slats, and the trailing edge flaps

all receive hydraulic power exclusively from the center system.

Question 8

The center hydraulic system has two electrically

Answer 8

driven primary pumps.

Question 9

Two air-driven demand pumps

(powered by bleed air) augment the center system during

Answer 9

high load system demands and when pressure is low.

Question 10

Back-up hydraulic power to the center system flight controls is

Answer 10

supplied by the Ram Air Turbine.

Question 11

The Ram Air Turbine is located

Answer 11

on the underside of the aft fuselage.

Question 12

To further increase redundancy in the hydraulic system, the Ram Air Turbine, (RAT) can

Answer 12

be deployed automatically or manually.

Question 13

The RAT extends into the airflow providing hydraulic power to the center system’s primary flight controls only.

The RAT is capable of providing hydraulic and electrical power throughout the flight envelope. In flight it will deploy automatically if:

Answer 13

both engines have failed and C-HYD system pressure is low,

or both AC transfer busses are unpowered,

or all three HYD system pressures are low.

Question 14

With the primary pump switches ON, each engine driven pump pressurizes

Answer 14

its system when the respective engine is running.

Question 15

The FAULT light illuminates to show

Answer 15

low pump pressure,

excessive fluid temperature,

or the pump switch is off.

Question 16

With AUTO selected, the demand pump operates when

Answer 16

system or primary pump pressure is low or when required by control logic.

Question 17

The demand pump selector’s AUTO position

controls the electrically driven demand pumps.

If the AUTO function fails, or if required by a non-normal procedure —

Answer 17

the demand pump should be selected ON.

The pump will run continuously.

Question 18

The demand pump also operates when control logic anticipates

With AUTO selected, both the left and right demand pumps operate during

Answer 18

a large system demand.

takeoff and landing phases.

Question 19

In the AUTO position, the right demand pump operates

Answer 19

continuously when the airplane is on the ground.

Question 20

In the AUTO position, system logic

commands the center demand pumps to operate

As the landing gear is selected down, system logic commands

Answer 20

in anticipation of gear retraction.

a demand pump to operate.

Question 21

Once the center system primary flight control hydraulic pressure

is greater than

Answer 21

1,500 psi, the Ram Air Turbine pressure light illuminates green.

Question 22

Selecting both center system demand pumps ON results in

Answer 22

only the C1 pump operating.

Both center demand pumps

cannot operate together in the ON position

due to system logic.

Question 23

When excessive fluid temperature is sensed in either

a primary or a demand pump, a

Answer 23

FAULT light appears in the associated pump switch

or below the demand selector.

Question 24

When low left primary pump pressure is sensed, a

Answer 24

caution level EICAS message is generated.

Question 25

The hydraulic system has a great deal of pump redundancy.

Therefore, the most likely cause for low system pressure

Answer 25

is loss of fluid quantity.

Question 26

he center hydraulic system is unique in its ability to

When a low fluid quantity is sensed,

Answer 26

isolate certain components when low fluid quantity is sensed.

both isolations valves close.

The C1 primary pump and the ALTN / RSV BRAKES

are now isolated from the rest of the system.

Question 27

Let’s look at what happens when the leak is in the main part of the system.

In this case, quantity is indicated as 0.00,

the actual fluid level has stopped at

Answer 27

standpipe level.

System pressure remains low.

Note that the C1 PRIM pump receives fluid below the standpipe level.

Question 28

If center system pressure drops to a low value,

the left isolation valve will re-open.

Note: that in this case, the C1 PRIM pump can provide pressure to the ALTN / RSV BRAKES and under certain conditions to NOSE GEAR STEERING (after landing with the airspeed below 60 kt).

Answer 28

re-open.

Note: that in this case, the C1 PRIM pump can

provide pressure to the ALTN / RSV BRAKES

and under certain conditions to NOSE GEAR STEERING

(after landing with the airspeed below 60 kt).

Question 29

The left isolation valve also opens

Answer 29

after landing when airspeed decreases below 60 kt.

The center ELEC C1 pump

can now provide pressure to NOSE GEAR STEERING.