Which hydraulic system(s) provides pressure for the ALTERNATE brakes?

The hydraulic system that provides pressure for the alternate brakes is the yellow hydraulic system. The A320 aircraft uses the yellow hydraulic system specifically for alternate braking when the normal braking system, which relies on the green hydraulic system, is inoperative or unavailable.

In the normal configuration, the green hydraulic system is responsible for pressure and operation of the main brakes. However, during specific failures where the green system's pressure is lost, the aircraft’s design allows the yellow system to take over the brake function, ensuring safety and operational capability.

The other hydraulic systems – green, blue, and a combination of green and yellow – do not provide the necessary pressure for alternate braking functions. Understanding the role of the yellow hydraulic system in alternate braking is crucial for effective operation and safety management in the aircraft systems.