Final answer:
The FMS header of an aircraft typically defaults to a preflight or initialization page upon power-up, where pilots are prompted to enter or confirm essential flight data.
Step-by-step explanation:
The question refers to the behavior of an aircraft's Flight Management System (FMS) when it is powered up. The FMS header on power-up will typically default to a preflight or initialization page. This page often displays information related to the aircraft's current status, and it prompts the pilot to enter or confirm data such as the flight plan, weight and balance, fuel, and navigation databases. It is crucial for pilots to check this information and make sure it is updated and accurate before commencing with further preparations for the flight. The exact appearance and information on the initialization page can vary depending on the aircraft and FMS manufacturer.