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

Leaving the DC Service switch on overnight depletes the APU battery. The DC Service switch is designed to supply power to various aircraft systems when the engines or auxiliary power unit (APU) are not running. If this switch is left on for an extended period, such as overnight, it draws power from the APU battery to maintain the necessary systems. Since the APU battery is not being charged during this time—without the APU running to replenish its charge—the battery gradually loses its charge and may become depleted.

This understanding is critical for operational safety and ensuring that the aircraft's systems can function correctly when needed. Proper management of auxiliary power systems is essential to prevent situations where the battery power is insufficient for starting the APU or running critical systems.