If the main and essential buses lose power, which bus is designed to continue powering critical instruments and basic flight functionality?

• A. Standby/EMERGENCY Bus
• B. Essential Bus
• C. Main Bus
• D. Battery Bus

Answer: (A)

Redundancy in aircraft electrical systems ensures essential instruments stay powered when primary power is lost. The Standby/EMERGENCY Bus is the dedicated backup path that remains energized even if both main and essential buses lose power. It typically draws from a separate power source, such as a standby generator or an emergency battery, and is wired to the critical flight instruments needed for basic attitude, airspeed, and altitude reference, along with essential flight functionality. This arrangement gives the pilot enough information and control capability to maintain safe flight and reach a suitable landing while power restoration or emergency procedures are pursued.