When is a hot battery bus powered in a jet aircraft electrical system?

• A. Only when a charged battery is installed in the aircraft
• B. Only when the engine is running
• C. Only when external power is connected
• D. Only when the generator is online

Answer: (A)

A hot battery bus is kept energized by the aircraft’s main battery, supplying essential systems when other power sources aren’t available. It stays powered as long as the battery is connected and charged, so the presence of a charged battery is what lets it stay live. If there’s no charged battery, the hot battery bus can’t be energized, even if the engines are running or external power or generators are available. External power and generators feed other buses, but the hot battery bus relies on the battery voltage to stay on.