Final answer:
The PTU operates in AUTO mode in an aircraft's HYD Panel to balance hydraulic pressure and maintain necessary functions. It kicks in during engine start or shutdown and transfers fluid between hydraulic systems.
Step-by-step explanation:
The PTU (Power Transfer Unit) operates in AUTO mode in an aircraft's HYD (Hydraulic) Panel. It activates when there is a pressure difference between the hydraulic systems, especially during engine start or shutdown. The PTU functions to transfer hydraulic fluid between the systems to maintain balance and prevent excessive pressure fluctuation.
For example, in a dual-engine aircraft, if one engine shuts down, the PTU will start to operate automatically to compensate for the pressure loss and ensure that all necessary hydraulic functions are maintained.
It's important to note that not all aircraft have a PTU or it may behave differently based on the aircraft's design and hydraulic system configuration.