Which component provides power to the STBY BUS when main power is unavailable?

Which component provides power to the STBY BUS when main power is unavailable?

• A. APU
• B. Main Battery
• C. Standby Battery
• D. Left Mission Bus

Answer: (C)

Power continuity for essential flight instruments is guarded by a dedicated standby source. The Standby Battery is wired specifically to feed the STBY BUS when the main electrical system loses power, so critical indicators and flight crew information remain available even with no engine or APU power. In this setup, the standby battery is designed for that exact role—providing limited-duration power to the STBY BUS to keep essential systems alive. The APU can supply electrical power to the aircraft’s main buses when needed, but it isn’t the source that feeds the STBY BUS during a main-power loss. The main battery supports other electrical loads, not the dedicated standby bus, and the left mission bus is a distribution path, not a power source for the standby bus. So, the component that keeps the STBY BUS powered when main power is unavailable is the Standby Battery.

Power continuity for essential flight instruments is guarded by a dedicated standby source. The Standby Battery is wired specifically to feed the STBY BUS when the main electrical system loses power, so critical indicators and flight crew information remain available even with no engine or APU power.

In this setup, the standby battery is designed for that exact role—providing limited-duration power to the STBY BUS to keep essential systems alive. The APU can supply electrical power to the aircraft’s main buses when needed, but it isn’t the source that feeds the STBY BUS during a main-power loss. The main battery supports other electrical loads, not the dedicated standby bus, and the left mission bus is a distribution path, not a power source for the standby bus.

So, the component that keeps the STBY BUS powered when main power is unavailable is the Standby Battery.