What are the three main sections of an APU?

The correct choice highlights that the three main sections of an Auxiliary Power Unit (APU) are the compressor, power, and accessory drive sections.

The compressor section is responsible for drawing in ambient air and compressing it, which is crucial for the APU to produce the necessary power and pneumatic energy. The power section generates the power required to operate the APU and can include the combustion chamber and turbine, converting fuel energy into mechanical energy. Finally, the accessory drive section is vital as it provides the necessary mechanical connections to drive various components that are essential for the operation of the APU and the aircraft systems, such as the fuel pumps and generators.

Understanding these sections is fundamental for anyone working with APUs in aviation, as each plays a critical role in the overall function and performance of the system. This knowledge is essential for troubleshooting, maintenance, and operation of these units.