What information is critical when filing a flight plan?

The critical information when filing a flight plan is the flight route and estimated time of arrival. This information is essential for several reasons. First, the flight route provides the air traffic control (ATC) with a clear understanding of the planned path for the aircraft, allowing them to manage air traffic effectively and ensure safety in the skies. It facilitates coordinated traffic flow and helps in minimizing the risk of mid-air collisions.

Second, the estimated time of arrival (ETA) is crucial for ATC, as it aids in scheduling other flights, emergency response planning, and overall traffic management at busy airports. Knowing the ETA helps in determining the best time to provide clearance for takeoff and landing.

While other elements like a passenger list and preferred flight altitude may be relevant for specific operational considerations, they are not as foundational to the safe and efficient management of air traffic as the flight route and ETA. A pilot's favorite airport is not pertinent to flight planning and does not impact safety or coordination. Therefore, including clear and accurate flight route and ETA details is vital for maintaining organized and safe aviation operations.