Which buses are affected during the first level of integrity?

The correct answer is that the essential bus and avionics 1 bus are affected during the first level of integrity.

In aircraft systems, the integrity levels refer to the availability and reliability of critical systems or buses. The essential bus is responsible for powering critical systems needed for safe operation, while the avionics 1 bus typically supplies power to primary avionics equipment that is crucial for navigation and communication.

During the first level of integrity, the systems powered by these buses remain operational, ensuring that essential functions can still be performed in the event of partial system failures. This is key to maintaining aircraft safety and operational capability under adverse conditions.

In contrast, the other options include buses that, while important, do not specifically relate to this first integrity level scenario, thereby underscoring the critical nature of the essential bus and avionics 1 in ensuring reliability of key systems during operational challenges.