Which component of the APU allows for control over its operational state?

The control unit is the critical component of the Auxiliary Power Unit (APU) that manages and oversees its operational state. It functions by receiving input from various sensors and systems, allowing it to regulate the APU’s start, operation, and shutdown processes. The control unit processes this data to maintain optimal performance, ensuring the APU operates within safe limits and under specified conditions.

Through the control unit, technicians can monitor APU performance metrics and make necessary adjustments, which is vital for reliability and efficiency. While other components such as the main fuel pump, exhaust system, and starting motor play essential roles in the APU’s overall functionality, they do not provide the same level of control over the operational status of the unit itself. The control unit is distinctly responsible for enabling and controlling the APU's operational states, which is why it stands out as the correct answer.