ATA 29 HYDRAULIC SYSTEM
The aircraft is equipped with three continuously hydraulic systems, BLUE, GREEN and YELLOW. Eachsystem is supplied from its own hydraulic reservoir. Normal system operating pressure is 3000 PSI. There is no possibility to transfer hydraulic fluid from one system to another.• Green system (System 1)
- The green system is pressurized by an engine driven pump installed at engine 1.
• Blue system (System 2)
- The blue system is pressurizedby an electric pump.
- A Ram Air Turbine (RAT) driven pump is provided for emergency use.
• Yellow system (System 3)
- The yellow system is pressurized by a pump driven byengine 2.
- An electric pump allows the yellow system to be pressurized.
This enables ground operations when the engines are stopped.
- A handpump can be used to supplythe yellow system in order to operate the cargo doors when no electrical power is available.
The hydraulic fluid is maintained clean by filters.
• HP filters oneach system, on the reservoir filling system and on normal braking system.
• Return filters on each line.
• Case drain filters on engine and blue electric pumps permit themonitoring of wear by detection of particles in the filters.
Power Transfer Unit
A bidirectional Power Transfer Unit enables the green system to be powered by the yellowsystem or vice versa, without fluid transfer.
In flight, with only one engine running, the PTU is automatically activated when the differential pressure between the greenand yellow system is higher than 500 psi (34 bar).
On ground, when the engines are shut down, the PTU allows the green system to be pressurized using the yellow electric pump.