Which of the following is normally responsible for powering the DC BUSES when the Battery Switches are AUTO on a cold aircraft?

Which of the following is normally responsible for powering the DC BUSES when the Battery Switches are AUTO on a cold aircraft?

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

Answer: (A)

When a cold aircraft is powered on with the Battery Switches in AUTO, the DC distribution is supplied from the aircraft battery. The battery feeds the DC BAT BUS, which in turn energizes the DC BUSES, and it also powers the DC ESS BUS to keep critical systems alive. This arrangement ensures essential equipment can operate and the start sequence can proceed even before any generators (APU or engine) are online. The other options would require an AC source or generator output to reach the DC Buses, which isn’t the normal source during a cold soak with the battery in AUTO.

When a cold aircraft is powered on with the Battery Switches in AUTO, the DC distribution is supplied from the aircraft battery. The battery feeds the DC BAT BUS, which in turn energizes the DC BUSES, and it also powers the DC ESS BUS to keep critical systems alive. This arrangement ensures essential equipment can operate and the start sequence can proceed even before any generators (APU or engine) are online. The other options would require an AC source or generator output to reach the DC Buses, which isn’t the normal source during a cold soak with the battery in AUTO.