THE HYDRAULIC SYSTEM

The Airbus basically have 3 systems of hydraulic , colour coded GREEN, BLUE and YELLOW. Refer to the overhead panel of this Airbus 340-600. At the HYD panel, the schematic diagram showed Eng 1 and 4 run the GREEN system, Eng 2 runs the BLUE and Eng 3 runs the YELLOW System. The engines driven pumps pressurized the hydraulic system to 3000 PSI. The GREEN used for Landing Gear operation, the Nosewheel steering and anti skid. The BLUE for the brakes and YELLOW for the Flaps. For flight controls servo, normally using GREEN but always backup by the YELLOW and the BLUE.

For the pilot, the system screen will show the status of the hydraulic system in flight. 1,2,3,4 represent the engines that run the hydraulic pumps for each system and there are 3 ELECtric pumps that can be used momentarily in the event of failure of the respective engine pump to provide sufficient pressure for the Landing gear, Flaps and Brakes. If all engines are failed, mean all engine driven pumps not working, the RAT, on the ENG 4 GREEN system will operate automatically to provide some pressure for the flight control and electric emergency generator.

RAT, the Ram Air Turbine is a small propeller that will pop out of the underneath right ring, and it is turned by the ram air, depending on the speed of the plane, higher speed , higher rotation, which in turn runs as a motor to pressurize the GREEN system.

So, next time you fly, you will feel safe because you know the systems always have backup in the event of failures.