Which of the following is NOT a component of an APU?

The correct answer highlights that the fuel manifold system is not a component of an Auxiliary Power Unit (APU). An APU is typically designed to provide power and pneumatic services to an aircraft while it is on the ground or during low-power operations by using components that serve specific functions necessary for its operation.

The main components of an APU include the compressor assembly, which is responsible for compressing air for the combustion process; the accessory drive assembly, which provides drive power for various auxiliary systems; and the power turbine, which converts the energy from the combustion process into mechanical energy for use. Each of these components plays a critical role in the efficient functioning of the APU, contributing to its capability to generate power and provide pneumatic services.

While the fuel manifold is essential in supplying fuel to engines, its role is distinct from the APU's primary function and structure, thereby making it not a direct component of the APU itself. Understanding the specific components that constitute an APU is crucial for comprehending how it operates and integrates into the aircraft systems.