Hydraulic System

Question 1

After engine start, under what circumstances would you expect the left or right demand pumps to run?

Answer 1

• System low pressure
• On the ground, 3 minutes after second engine start
• Takeoff thrust set to flaps retracted
• From gear down or RA less than 1000’ to GS less than 40kts
• During thrust reverser operations

Question 2

After engine start, under what circumstances would you expect the center demand pump to run?

Answer 2

• System low pressure
• On the ground, 3 minutes after second engine start
• Takeoff thrust set to RA >2000’
• From gear down and RA less than 2000’ to GS less than 60kts
• Flaps or slats in motion

Question 3

Why does the center system have an isolation feature?

Answer 3

To preserve system functionality in the event of a leak, allowing crew to be able to lower landing gear and have nose gear steering on landing roll.

Question 4

When does the RAT deploy automatically?

Answer 4

• Both engines have failed
• All three hydraulic system pressures are low
• Loss of all electrical power to the CPT & FO flight instruments
• Loss of all 4 EMP’s and faults in the flight control system occur on approach.
• Loss of all 4 EMP’s and an engine fails on takeoff or landing.

Question 5

When will a hydraulic pump FAULT light illuminate?

Answer 5

• Low primary pump pressure
• Excessive pump fluid temperature
• Pump is selected off

Question 6

Will a hydraulic pump shutdown/stopped by system logic (i.e. Before engine start etc) cause the FAULT light to illuminate?

Answer 6

No. A pump manually selected OFF will illuminate the FAULT light.

Question 7

With the C1 demand pump switch selected on, when will the pump run?

Answer 7

Continuously

Question 8

Which systems are powered by the center hydraulic system?

Answer 8

• Flaps/Slats
• Landing gear actuation
• Nose wheel steering
• Flight controls

Question 9

Which systems are powered by the Left and Right hydraulic systems?

Answer 9

Flight controls and the respective side thrust reverser

Question 10

Will the OF and RF indications show in the air?

Answer 10

No, only on the ground

Question 11

Below what value will the hydraulic pressure display in amber in the synoptic display?

Answer 11

Below 3000psi

Question 12

When does the RAT “PRESS” light illuminate?

Answer 12

When the system pressure for the flight controls is higher than 3000psi

Question 13

What determines which Center pump will be primary and which will be demand?

Answer 13

Day of the week from the FMC

Question 14

Below what pressure is an EMP displayed in amber as failed on the synoptic display? EDP?

Answer 14

EMP - amber below 2000psi

EDP - amber below 2150psi

Question 15

Which hydraulic systems have an isolation functionality?

Answer 15

Center system only

Question 16

What is the purpose of the accumulators in the hydraulic systems?

Answer 16

• Absorb pressure changes during operation

- Keep positive bootstrap pressure in system when pumps do not operate. This prevents pump cavitation on startup.

Question 17

How are the hydraulic systems cooled?

Answer 17

By heat exchangers in the main fuel tanks.

Each system has one heat exchanger in its respective tank, Center system has one heat exchanger in each tank.

Question 18

What is the purpose of the reservoir suction shutoff valve in the left and right systems?

Answer 18

• Ensures system doesn’t lose all hydraulic fluid if there is a leak in the tubing to the EDP.
• Fluid will be shut off to EDP ensuring EMP has enough remaining in the tubing to operate flight controls.

Question 19

What is the purpose of the reservoir suction shutoff valve in the center system?

Answer 19

• Ensures system doesn’t lose all hydraulic fluid if there is a leak in the tubing to the EMP C2. (MLG and flight controls)
• Fluid will be shut off to EMP C2 ensuring EMP C1 has enough remaining in the tubing to operate nose wheel steering and flaps.

Question 20

Where can hydraulic quantity and pressure be monitored?

Answer 20

Can be monitored on STATUS display or hydraulic synoptic display.