After energizing the EICAS, how long must you wait before starting the APU?

The correct answer is based on the requirement to ensure the Engine Indication and Crew Alerting System (EICAS) is fully operational before starting the Auxiliary Power Unit (APU). Waiting for 30 seconds after the EICAS has been energized allows the system to complete its initialization and perform necessary self-checks. This step is critical because it ensures that all indicators and alerts are functioning correctly, providing the crew with accurate information regarding aircraft systems.

Starting the APU too soon could result in insufficient system readiness, which might prevent the EICAS from properly monitoring and displaying critical data. The 30-second wait is a standard procedure that helps maintain operational safety and reliability of the systems during initial startup.