How is the APU bleed valve controlled?

The APU bleed valve is primarily controlled by the APU Electronic Control Unit (ECU). The APU ECU actively manages the operation of the APU, including the control of the bleed valve. This automated control allows the ECU to make rapid adjustments based on the operational needs of the aircraft, such as ensuring that sufficient bleed air is available for systems that require it, while also maintaining optimal performance and safety of the APU.

This system offers a level of precision and responsiveness that manual control by the pilot would not be able to achieve effectively, as the demands on the aircraft systems can change rapidly during flight. Automatic control by engine performance, as suggested by another option, does not directly pertain to the bleed valve operation, since the APU operates somewhat independently of the engines in terms of bleed air supply. Additionally, the flight control system is generally associated with the aircraft's aerodynamic control surfaces rather than operational control of the APU and its components.