At what speed does a gas turbine APU generally operate?

A gas turbine Auxiliary Power Unit (APU) is designed to provide power and pneumatic support while an aircraft is on the ground and is often used during ground operations before engines are started. The APU operates at high efficiency, which is typically achieved at or near its rated speed. This rated speed is specific to the design and operating characteristics of the APU and is where it operates most effectively, delivering the necessary power output for systems like air conditioning and engine starting.

Operating at or close to this rated speed ensures that the APU can deliver optimal performance without stressing its components. This is crucial because maintaining a consistent and efficient operational speed allows the APU to function reliably and extend its service life. The design of an APU focuses on balancing performance and fuel efficiency, making rated speed the target under normal operational conditions.

Other options, while they may apply to different types of engines or systems, do not accurately reflect the standard operational characteristics of a gas turbine APU.