60 Questions
Where is the circuit breaker for the hydraulic system located?
Battery bus circuit breaker panel
What happens when the circuit breaker placarded HYD SYS is open?
Pressure indication and HYD FL LO sensor are not available
What activates the emergency hydraulic system?
Pulling the emergency gear extension handle
What does the amber EHYD PX LO caution on the EICAS indicate?
Emergency accumulator pressure is below 2400 ±150 psi
What prevents the emergency system from bleeding back into the main system?
Check valve
What is the maximum fluid loss allowed in the event of an emergency hydraulic system leak?
20-30 cubic inches (0.5 quart)
What happens if the leak rate is below 0.25 GPM?
Main reservoir depletes until HYD FL LO caution illuminates
When does the EHYD PX LO caution extinguish?
When the system pressurizes
What is the fluid flow rate to the emergency accumulator restricted to?
Below 0.25 GPM
What is the only indication of the emergency accumulator's status?
Amber EHYD PX LO caution on the EICAS
Which component prevents damage from high system pressure in the hydraulic system?
Pressure relief valve
Where is the hydraulic system service bay located?
In the lower aft fuselage behind the right wing trailing edge
What does the fluid quantity indicator in the hydraulic system service bay show?
Level of hydraulic fluid
At what pressure does the hydraulic pump pressurize the normal system and emergency accumulator?
3000±120 psi.
What components can be powered by the hydraulic system when the pressure exceeds 1800 psi?
Landing gear, main gear doors, flaps, speed brake, and nose wheel steering
What color does the hydraulic pressure display change to when the pressure drops below 1800 psi?
Amber
What does the amber HYD FL LO caution on the EICAS display indicate?
Low hydraulic fluid level
How is the hydraulic fluid level checked in the hydraulic system service bay?
By comparing the position of the green indicating rod to marked indicator windows
What should be done if the fluid level is not FULL AC or FULL AD in the hydraulic system service bay?
Depressurize the emergency accumulator by pulling the manual pressure release handle
When should the hydraulic system be serviced?
When the accumulator is fully discharged and the fluid level indicates FULL AD
Where is the pressure relief valve located in the hydraulic system?
In the main and emergency systems
What is the capacity of the engine driven pump in the hydraulic system?
Approximately 5 quarts
What does the amber HYD FL LO caution on the EICAS display indicate?
The reservoir level has dropped below approximately 1 quart
What is the purpose of the manual pressure release handle in the hydraulic system service bay?
To release the pressurized fluid from the emergency accumulator back to the reservoir
What happens when the hydraulic pressure indicator drops below 1800 psi?
The hydraulic pressure display changes from white to amber
What components can be powered by the hydraulic system when the pressure exceeds 1800 psi?
Landing gear, main gear doors, flaps, speed brake, and nose wheel steering
What should be done if the fluid level is not FULL AC or FULL AD in the hydraulic system service bay?
Depressurize the emergency accumulator by pulling the manual pressure release handle
Where is the hydraulic system service bay located?
In the lower aft fuselage behind the right wing trailing edge
What is the purpose of the ground hydraulic power, sampling, and servicing connection in the hydraulic system service bay?
To provide power, sampling, and servicing for the hydraulic system
What does the fluid quantity indicator in the hydraulic system service bay show?
The level of hydraulic fluid in the power package reservoir
Which system is activated by pulling the emergency gear extension handle in the front cockpit?
Emergency hydraulic system
Which caution on the EICAS indicates that the emergency accumulator pressure has dropped below a certain level?
Amber EHYD PX LO caution
What is the purpose of the hydraulic fuse in the emergency system?
To limit fluid loss in the event of an emergency hydraulic system leak
What happens if the leak rate in the emergency system exceeds 0.25 GPM?
The system depletes the main reservoir until the HYD FL LO caution illuminates
What is the only indication of the emergency accumulator's status?
Amber EHYD PX LO caution on the EICAS
What is the maximum volume of fluid loss allowed in the event of an emergency hydraulic system leak?
20-30 cubic inches (0.5 quart)
What is the rate at which the fluid flow to the emergency accumulator is restricted?
Below 0.25 GPM
What happens when the circuit breaker placarded HYD SYS is open?
The pressure indication and HYD FL LO sensor is not available
What does the amber HYD FL LO caution on the EICAS indicate?
Insufficient fluid in the main reservoir
When should the light indicating the discharge of the emergency accumulator extinguish?
Before flight
Which circuit breaker provides power for the hydraulic system?
HYD SYS
What is the indication of the emergency accumulator's status?
EHYD PX LO caution
What happens when the emergency accumulator pressure drops below 2400 ±150 psi?
Amber EHYD PX LO caution illuminates
What prevents the emergency system from bleeding back into the main system?
Check valve
What is the maximum volume of fluid loss allowed in the event of an emergency hydraulic system leak?
20-30 cubic inches (0.5 quart)
What is the rate at which the fluid flow to the emergency accumulator is restricted?
Below 0.25 GPM
What is the color of the caution displayed on the EICAS when the emergency accumulator pressure drops below 2400 ±150 psi?
Amber
What should be done if the emergency accumulator is discharged?
Ensure light has extinguished prior to flight
What is the purpose of the hydraulic fuse in the emergency system?
To prevent a leak in the emergency system from depleting the main hydraulic system
When is the hydraulic system considered to have sufficient fluid to lower the landing gear and flaps using the main system?
When the HYD FL LO caution illuminates
Where is the hydraulic system service bay located?
In the lower aft fuselage
What is the capacity of the engine driven pump in the hydraulic system?
Approximately 5 quarts
What components can be powered by the hydraulic system when the pressure exceeds 1800 psi?
Landing gear, main gear doors, flaps, speed brake, and nose wheel steering
What happens when the circuit breaker placarded HYD SYS is open?
The hydraulic system loses all power
What does the amber HYD FL LO caution on the EICAS display indicate?
The hydraulic fluid level is low
What is the only indication of the emergency accumulator's status?
The green indicating rod
What does the amber EHYD PX LO caution on the EICAS indicate?
The emergency hydraulic system is malfunctioning
What happens if the leak rate is below 0.25 GPM?
The hydraulic system continues to operate normally
What should be done if the fluid level is not FULL AC or FULL AD in the hydraulic system service bay?
Depressurize the emergency accumulator
What is the purpose of the manual pressure release handle in the hydraulic system service bay?
To release the pressurized fluid from the emergency accumulator back to the reservoir
Study Notes
Hydraulic System
- The circuit breaker for the hydraulic system is placarded HYD SYS.
- When the HYD SYS circuit breaker is open, the system is shut down.
- The emergency hydraulic system is activated by pulling the emergency gear extension handle.
Emergency Hydraulic System
- The emergency hydraulic system is protected from bleeding back into the main system by a check valve.
- The system allows a maximum fluid loss of 0.25 GPM in the event of a leak.
- If the leak rate is below 0.25 GPM, the system will continue to operate.
- The amber EHYD PX LO caution on the EICAS indicates a low pressure in the emergency accumulator.
Hydraulic Pressure
- The hydraulic pump pressurizes the normal system and emergency accumulator to 3000 psi.
- When the pressure exceeds 1800 psi, the system can power flight controls, landing gear, and brakes.
- If the pressure drops below 1800 psi, the display changes to amber.
- The amber HYD FL LO caution on the EICAS indicates a low fluid level.
Hydraulic System Service Bay
- The hydraulic system service bay is located on the aircraft.
- The fluid quantity indicator shows the fluid level, which should be checked regularly.
- If the fluid level is not FULL AC or FULL AD, the level should be topped up.
- The service bay is also used for ground hydraulic power, sampling, and servicing connection.
Emergency Accumulator
- The emergency accumulator's status is indicated by the EHYD PX LO caution on the EICAS.
- If the pressure drops below 2400 ±150 psi, the caution will illuminate.
- The hydraulic fuse prevents damage from high system pressure.
- If the emergency accumulator is discharged, it should be serviced.
System Operation
- The hydraulic system is considered to have sufficient fluid to lower the landing gear and flaps using the main system when the level is FULL AC or FULL AD.
- The engine-driven pump has a capacity of 7.5 GPM.
- The system can be powered by the hydraulic system when the pressure exceeds 1800 psi.
Test your knowledge of hydraulic systems and their components with this quiz. Learn about the engine-driven pump, pressure relief valve, and other important features.
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