PSA Airlines Canadair Regional Jet Systems (PSA-CRJ) Practice Exam

What does the APU battery deplete if the DC Service switch is left on?

1. The emergency battery

2. The APU battery

3. The main aircraft battery

4. All onboard batteries

The correct answer is: The APU battery

The correct answer is that the APU battery is depleted if the DC Service switch is left on. The Auxiliary Power Unit (APU) battery is specifically designed to provide power for the APU, which is responsible for starting the aircraft's engines and supplying electrical power when the engines are off. When the DC Service switch is activated, it allows power to be drawn from the APU battery. If the switch remains on for an extended period without the APU running or the engines started, it can lead to the depletion of the APU battery. This is critical to remember, as a depleted APU battery could compromise the ability to start the APU or the main engines, potentially leading to operational issues. While the emergency battery and the main aircraft battery are also crucial for various aircraft operations, they are not directly affected by the DC Service switch's operation in the same way the APU battery is. Therefore, understanding the power management of the APU battery is essential for maintaining the readiness of the aircraft's electrical systems.