How many batteries are required to start the APU?

How many batteries are required to start the APU?

• A. Only APU Batt
• B. Only Main Batt
• C. Both
• D. Neither

Answer: (C)

Starting an APU requires power to both spin the starter and power the control/electrical systems during the sequence. The starter draws a large surge of current, while the APU’s control electronics and related avionics need a solid power source to operate correctly during start. Using both the APU battery and the main aircraft batteries provides enough current for the starter and keeps the control systems energized, giving a reliable start with redundancy. If only one source were used, you risk insufficient current or loss of control power, potentially preventing the APU from starting.

Starting an APU requires power to both spin the starter and power the control/electrical systems during the sequence. The starter draws a large surge of current, while the APU’s control electronics and related avionics need a solid power source to operate correctly during start. Using both the APU battery and the main aircraft batteries provides enough current for the starter and keeps the control systems energized, giving a reliable start with redundancy. If only one source were used, you risk insufficient current or loss of control power, potentially preventing the APU from starting.