While in flight, which electrical buses are powered with only one generator online?

The correct choice reflects that when only one generator is running, the Essential and Main electrical buses are the ones typically powered. The Essential bus provides necessary power for critical systems needed for safe flight operations, while the Main bus supplies power to non-essential systems that are still important for routine operations.

In the event that only one generator is operational, these specific buses are prioritized to ensure that vital systems remain powered, thereby maintaining safety and functionality during the flight. This is crucial in scenarios where redundancy is necessary for critical operations, and thus, the Essential and Main buses are designed to operate under such conditions. The Auxiliary bus, however, may not receive power under this configuration, as it is not prioritized the same way the Essential and Main buses are in terms of operational capability with reduced generator availability.

Understanding the logic behind the distribution of electrical power in an aircraft helps in comprehending the overall operational dependencies and safety protocols that are in place for flight operations.