Hydraulics

Question 1

Hydraulics

How many hydraulic systems are there ?

Answer 1

3

Left, right and center.

Question 2

Hydraulics

What are the differences between the left and the right hydraulic systems ?

Answer 2

None !

They are identical.

Question 3

Hydraulics

Which hydraulic system powers the landing gear actuation ?

Answer 3

The center hydraulic system.

Question 4

Hydraulics

Which hydraulic system powers the nose gear steering ?

Answer 4

The center hydraulic system.

Question 5

Hydraulics

What triggers a Hydraulic pump FAULT light ?

Answer 5

• Low pump pressure
• High pump fluid temperature
• Pump is selected OFF

Question 6

Hydraulics

What is the Hydraulic operating pressure ?

Answer 6

5000 psi

Question 7

Hydraulics

Under which conditions do the electric L and R demand pumps operate when in AUTO position ?

Answer 7

• LOW system pressure.
• For 3 minutes after both ENG start on the ground.
• From T-OFF thrust set to flaps retraction.
• From gear down or RA < 1000 ft to GS < 40 kts
• During thrust REV operations

Question 8

Hydraulics

How many pumps does the center Hydraulic system have and how are they driven ?

Answer 8

2 electric motor driven pumps (EMPs)

Question 9

Hydraulics

Which Center system pump operates as Primary ? Which as Demand ?

Answer 9

The FMC (Flight Management Computer) determines which pump operates as Primary based on calendar days :
C1 is primary on odd days
C2 is primary on even days

Question 10

Hydraulics

When does the Center PRIMARY pump operate ?

Answer 10

Continuously after the second engine is started.

Question 11

Hydraulics

When does the Center DEMAND pump operate ?

Answer 11

• LOW system pressure
• For 3 minutes immediately after both engines have been started.
• From T-OFF thrust set to RA > 2000 ft
• Flaps or slats in motion.
• During descent when landing gear down and RA < 2000 ft until GS < 60 kts.

Question 12

Hydraulics

What does the RAT provide when deployed ?

Answer 12

It provides hydraulic power to the primary flight control components connected to the center hydraulic system.

Question 13

Hydraulics

What does the UNLKD light indicate on the RAT switch ?

Answer 13

The RAT is not in the stowed position.

Question 14

Hydraulics

What does the white PRESS light indicate on the RAT switch ?

Answer 14

• The RAT is deployed.

* The CENTER system primary flight control hydraulic pressure is > 3000 psi.

Question 15

Hydraulics

What would cause automatic RAT deployment in flight ?

Answer 15

• Both engines have failed,
• All 3 HYD system pressures are LOW,
• Loss of all electrical power to CPT and F/O’s flight instruments,
• Loss of all 4 EMPs (Electric Motor Driven Pumps) and faults in the flight control system occur on approach,
• Loss of all 4 EMPs and an engine fails on take off or landing.

Question 16

Hydraulics

Once deployed, can the RAT be restowed in flight ?

Answer 16

NO

Question 17

Hydraulics

Which hydraulic system contains isolation functionalities ?

Answer 17

The center hydraulic system has isolation functionality to ensure key systems remain operational in the event of a hydraulic leak.

Question 18

Hydraulics

What does the hydraulic isolation system ensure ?

Answer 18

It ensures the flight crew can lower the landing gear and that nose wheel steering remains operational.

Question 19

Hydraulics

How many isolation valves does the isolation function use ?

Answer 19

3
• Nose gear isolation valve (NGIV)
• Reserve steering isolation valve (RSIV)
• Alternate extend isolation valve (AEIV not displayed on synoptic)

Question 20

Hydraulics

Can the isolation valves from the isolation function be operated manually by the crew ?

Answer 20

NO, all isolation valves operate automatically.

Question 21

Hydraulics

On the L and R hydraulic systems, what do the engine driven pump hydraulic supply shut off valves (SOVs) do ?

Answer 21

They are positioned between the reservoir and the engine driven pump (EDP) to isolate the pump from the hydraulic reservoir.

Question 22

Hydraulics

How are the left and right shut off valves (SOVs) triggered ?

Answer 22

Through their respective engine fire switch :
When pulled out :
• The SOV closes
• The EDP is depressurized.

Question 23

Hydraulics

How are the hydraulic reservoirs pressurized ?

Answer 23

By using pump outlet pressure.