Which hydraulic system(s) can be powered by the PTU?

The Power Transfer Unit (PTU) on the A320 serves as an important component in the hydraulic system, primarily designed to enhance redundancy and ensure operational capability. The PTU can transfer hydraulic power from one system to another, specifically from the green hydraulic system to the yellow hydraulic system, thereby allowing for the operation of essential systems when one hydraulic source might be weakened or lost.

The ability to power both the green and yellow systems is crucial during many operational scenarios, such as when the yellow system is low on pressure, ensuring that critical flight controls, landing gear, and other hydraulic-reliant systems remain functional. This capability enhances the safety and reliability of the aircraft's hydraulic operations. Therefore, the correct answer highlights the versatility of the PTU in maintaining hydraulic pressure across both systems as needed.