Which of the following is NOT a main component of the C-130J APU?

The main components of the C-130J APU (Auxiliary Power Unit) include the engine, control system, and fuel system. The APU serves as a small turbine engine capable of providing electrical power and bleed air for starting the aircraft engines and running essential systems when the aircraft is on the ground or in situations where main engines are not operating.

The engine of the APU is crucial as it generates the necessary power, while the control system manages and monitors the operations of the APU to ensure it functions correctly and safely. The fuel system supplies the APU engine with the fuel it needs to operate.

On the other hand, the landing gear is not part of the APU system. The landing gear is associated with the aircraft's primary structure, allowing it to take off, land, and taxi on the ground. Thus, identifying the landing gear as not being a main component of the APU is correct, as it serves a different and separate function from those provided by the APU.