What are the two main components of the C-130J APU?

The two main components of the C-130J APU are the gas turbine engine and starter generator. The gas turbine engine is essential because it provides the necessary power to drive the APU, enabling it to function effectively. It operates on the principle of converting fuel into mechanical energy that can be used to generate electricity. The starter generator plays a critical role by both starting the APU and providing electrical power to the aircraft when it is on the ground and the main engines are not running. This combination of components allows the APU to fulfill its primary functions – providing electrical power and pneumatic air for engine starting and environmental control systems while the aircraft is on the ground.

Having only the fuel pump and air compressor would not capture the essential elements needed for generating electricity or starting operations, as would be the case with other combinations. The cooling system and control panel, although important for the APU's operation, do not serve as the foundational elements defining its primary purpose. Therefore, the identification of the gas turbine engine and starter generator as the main components accurately reflects the primary operational capabilities of the APU in the C-130J aircraft.