When the Battery Switches are selected to AUTO on a cold aircraft the ___________ is powered by the Batteries.

When the Battery Switches are selected to AUTO on a cold aircraft the ___________ is powered by the Batteries.

• A. APU Generator
• B. DC BAT BUS and DC ESS BUS
• C. Engine Generators
• D. AC Bus 1

Answer: (B)

When the Battery Switches are in AUTO on a cold aircraft, the power that comes from the batteries feeds the essential DC power network. The main battery directly powers the DC BAT BUS, and the emergency or essential DC BUS is supplied to keep the critical systems alive if any other power sources aren’t yet online. This arrangement ensures avionics, flight control computers, and essential instrumentation have power before the engines or APU generators come up. The APU generator or engine generators only provide electrical power once their respective source is running, which isn’t the case on a cold aircraft. The AC Bus 1 is normally supplied by AC sources (engine or APU generators) or via an inverter, not directly by the batteries.

When the Battery Switches are in AUTO on a cold aircraft, the power that comes from the batteries feeds the essential DC power network. The main battery directly powers the DC BAT BUS, and the emergency or essential DC BUS is supplied to keep the critical systems alive if any other power sources aren’t yet online. This arrangement ensures avionics, flight control computers, and essential instrumentation have power before the engines or APU generators come up.

The APU generator or engine generators only provide electrical power once their respective source is running, which isn’t the case on a cold aircraft. The AC Bus 1 is normally supplied by AC sources (engine or APU generators) or via an inverter, not directly by the batteries.