FCOM: 29 - Hydraulic Flashcards
What is the difference between a pump fail and a loss of fluid on the green system?
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.
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If the blue hydraulic pump overheats, will this affect the RAT?
No. The blue system is normally pressurised by an electric pump, but the RAT is a seperate hydraulic pump.
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When will the RAT deploy?
Can the RAT power the blue hydraulic system if the fluid is lost?
No.
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When does the PTU begin to operate?
When the difference in pressure between the yellow and green systems is >500 PSI.
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What are the main considerations for a G+B hydraulic failure?
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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What are the main considerations for a G+Y hydraulic failure?
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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What are the main considerations for a B+Y hydraulic failure?
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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Name the sources of power for each of the hydraulic systems.
Green: Engine driven pump
Blue: Electric pump, RAT
Yellow: Engine driven pump, electric pump, hand crank
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What are the main services provided by the green system?
- Landing gear
- Slats
- Flaps
- Normal braking
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What are the main services provided by the blue system?
- Emergency generator
- Slats
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What are the main services provided by the yellow system?
- Flaps
- Nosewheel steering
- Alternate braking
- Parking brake
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In flight, why does the green hydraulic reservoir quantity show lower than the blue and yellow systems?
Because the actuators are filled with hydraulic fluid under pressure in order to raise the landing gear.
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What is the purpose of the hydraulic priority valves?
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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What services are upstream of the priority valves?
Green:
* Landing gear
* Slats & flaps
Blue:
* Emergency generator
* Slats
Yellow:
* Flaps
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What is the purpose of the hydraulic accumulators?
These maintain a constant pressure in the system by absorbing transient demands.
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How are the accumulators pressurised?
Using bleed air from engine 1. If this pressure is too low, bleed air is taken from the crossbleed duct.
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Explain the purpose of the PTU.
This transfers power from the green system to the yellow system, and vice versa.
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What is the typical system pressure of the three hydraulic systems?
3000 PSI
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What pressure would you expect to see when the RAT is powering the blue system?
2500 PSI
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At what PSI does the system pressure indicate amber?
1450 PSI
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Of the dual hydraulic failures, which in your opinion is worst and why?
G+Y is potentially the worst, because the manual trim is unusable and controllability on the ground is severely impaired.
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Which of the dual hydraulic failures maintains the aircraft in normal law?
B+Y
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Why is the gear gravity extension used on the blue and yellow dual hydraulic failure?
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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