During which operations does the APU provide electrical power for systems in the C-130J?

The Auxiliary Power Unit (APU) in the C-130J is crucial for providing electrical power during ground operations. Ground operations encompass various activities such as starting the main engines, performing maintenance checks, and during pre-flight preparations. The APU supplies the necessary power to the aircraft’s electrical systems when the main engines are not running, ensuring that essential systems like avionics and cabin air conditioning remain operational.

During flight phases such as takeoff and landing, the aircraft's electrical power comes primarily from the main engines through the generators. While the APU can provide power during flight, its primary role is during ground operations to ensure the aircraft can be fully functional and ready for flight without relying solely on the engines. This makes it essential for pre-flight checks and preparations.

The answer reflects the APU's role effectively, emphasizing its importance outside of flight phases, particularly during ground operations when the aircraft is stationary and not receiving power from the engines.