FCOM: 29 - Hydraulic

Question 1

What is the difference between a pump fail and a loss of fluid on the green system?

Answer 1

A pump fail is recoverable using the PTU, which transfers power from the yellow system to the green system.
A loss of fluid renders the system unrecoverable.

05/11/24

Question 2

If the blue hydraulic pump overheats, will this affect the RAT?

Answer 2

No. The blue system is normally pressurised by an electric pump, but the RAT is a seperate hydraulic pump.

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Question 3

When will the RAT deploy?

Question 4

Can the RAT power the blue hydraulic system if the fluid is lost?

Answer 4

No.

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Question 5

When does the PTU begin to operate?

Answer 5

When the difference in pressure between the yellow and green systems is >500 PSI.

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Question 6

What are the main considerations for a G+B hydraulic failure?

Answer 6

Cruise:
* Alternate law, no protection
* Fuel consumption increased

Approach:
* Cat 1 only
* Slats jammed, flaps slow
* No autothrust
* Extend flaps using the VFE next -5 technique
* Landing gear gravity extension
* Direct law after gear extended

Landing
* Sluggish handling (only 1 elevator and 2 spoilers per wing, and no ailerons)
* Alternate braking only

Go around
* No gear retraction
* Maintain slats/flaps configuration if remaining in circuit

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Question 7

What are the main considerations for a G+Y hydraulic failure?

Answer 7

Cruise:
* Alternate law, no protection
* Fuel consumption increased
​
Approach:
* Cat 1 only
* Slats slow, flaps jammed
* Extend flaps using the VFE next -5 technique
* Landing gear gravity extension
* Direct law after gear extended, with no pitch trim available
​
Landing
* No stabiliser or pitch trim. Pitch authority reduced.
* No reverser
* Braking is on yellow accumulator only
* No nosewheel steering
​
Go around
* No gear retraction
* Maintain VAPP speed, due to pitch trim being unusable

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Question 8

What are the main considerations for a B+Y hydraulic failure?

Answer 8

Cruise:
* Normal law remains
* Fuel consumption increased

Approach:
* Cat 1 only
* Slats & flaps slow
* Landing gear gravity extension

Landing
* Sluggish handling (only 1 elevator and 2 spoilers per wing, and no ailerons)
* Braking is normal
* No nosewheel steering

Go around
* No gear retraction
* Maintain slats/flaps configuration if remaining in circuit

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Question 9

Name the sources of power for each of the hydraulic systems.

Answer 9

Green: Engine driven pump
Blue: Electric pump, RAT
Yellow: Engine driven pump, electric pump, hand crank

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Question 10

What are the main services provided by the green system?

Answer 10

• Landing gear
• Slats
• Flaps
• Normal braking

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Question 11

What are the main services provided by the blue system?

Answer 11

• Emergency generator
• Slats

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Question 12

What are the main services provided by the yellow system?

Answer 12

• Flaps
• Nosewheel steering
• Alternate braking
• Parking brake

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Question 13

In flight, why does the green hydraulic reservoir quantity show lower than the blue and yellow systems?

Answer 13

Because the actuators are filled with hydraulic fluid under pressure in order to raise the landing gear.

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Question 14

What is the purpose of the hydraulic priority valves?

Answer 14

If the pressure in the system gets too low, the priority valves cut off the hydraulic supply to heavy demand users.

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Question 15

What services are upstream of the priority valves?

Answer 15

Green:
* Landing gear
* Slats & flaps

Blue:
* Emergency generator
* Slats

Yellow:
* Flaps

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Question 16

What is the purpose of the hydraulic accumulators?

Answer 16

These maintain a constant pressure in the system by absorbing transient demands.

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Question 17

How are the accumulators pressurised?

Answer 17

Using bleed air from engine 1. If this pressure is too low, bleed air is taken from the crossbleed duct.

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Question 18

Explain the purpose of the PTU.

Answer 18

This transfers power from the green system to the yellow system, and vice versa.

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Question 19

What is the typical system pressure of the three hydraulic systems?

Answer 19

3000 PSI

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Question 20

What pressure would you expect to see when the RAT is powering the blue system?

Answer 20

2500 PSI

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Question 21

At what PSI does the system pressure indicate amber?

Answer 21

1450 PSI

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Question 22

Of the dual hydraulic failures, which in your opinion is worst and why?

Answer 22

G+Y is potentially the worst, because the manual trim is unusable and controllability on the ground is severely impaired.

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Question 23

Which of the dual hydraulic failures maintains the aircraft in normal law?

Answer 23

B+Y

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Question 24

Why is the gear gravity extension used on the blue and yellow dual hydraulic failure?

Answer 24

Because the landing gear extension is upstream of the priority valve and can be accomplished by gravity, rather than placing a heavy demand on the one remaining hydraulic system.

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Question 25

What is the purpose of extending the landing gear at 200kt with the green and blue system failure?

Answer 25

If the landing gear is extended at 200kt, this puts the aircraft into direct law sooner and provides much better controllability.

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Question 26

Why in the green and yellow failure is Flaps 3 selected before the gear is selected down?

Answer 26

In order to be stabilised at VAPP so that you can be in trim for the approach.

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Question 27

Which hydraulic systems power the ailerons?

Answer 27

Green & blue

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