TAP003: Hydraulics

This week we take a look at the hydraulic systems we have on board and the best way to remember them.

The basics - The A320 has 3 independent, hydraulic systems. Green, Blue and Yellow. Each system has its own hydraulic fluid reservoir and all three of these reservoirs are automatically pressurised by bleed air from engine 1. If the bleed pressure is too low from engine 1, the system will automatically take air from the cross bleed duct. 

The systems normally operate at around 3000psi

A power transfer unit, commonly referred to as the PTU, enables the yellow system to pressurize the green system and vice versa. This allows the green system to be pressurised by the yellow system when no engines are running via the yellow electric pump. The power transfer unit comes into action automatically when the differential pressure between the green and the yellow systems is greater than 500 psi. The PTU does not transfer actual fluid between the green and yellow system, it can only transfer power.

The green system controls BOTH slats and flaps, the blue controls slats and the yellow flaps.

Reversers – green on the left controls Rev Eng 1 and yellow on the right controls Rev Eng 2.

Flight controls – the Rudder is nice and easy to remember as all 3 systems can power the rudder. The elevator is similar again, the green system on the left controls the left elevator and the yellow system on the right controls the right elevator. The blue system can control both as a backup. The ailerons buck the trend a little, the green and blue systems can power both. Blue is primary on the left aileron and green is primary on the right.

Ground Spoilers/Speed brake – This system uses all 3 hydraulic systems so at least 1 panel would be available in a dual hydraulics failure situation. There are 5 panels on each wing.

Andy's way to remember - panel 1 and 5, the two outer panels are powered by the green system, then the next 2 in, 2 and 4, are powered by the yellow system leaving a solitary panel 3 to be powered by the blue system.

Matt's way to remember (including ailerons) - Going from wing root to wing tip, GYBYG GB

Yaw Damper – follows a similar pattern, Yaw damper 1 on the left green system and yaw damper 2 on the right yellow system.

Landing gear is only powered by the green system. Normal braking is also on the green. Andy's way to remember is G for GOOD brakes. The alternate braking is on the Yellow system as well as the parking brake.

Nose wheel steering is on the green system BUT some older aircraft had it on the yellow system so check your aircraft.

Links & Resources

 Diagrams by Pierre-Michel Gasser - http://pmgasser.ch/

Matt's diagram for remembering the hydraulic systems