Which document is essential for a pilot operating under IFR?

A flight plan is essential for a pilot operating under Instrument Flight Rules (IFR) because it serves several critical functions in the aviation system. When flying under IFR, the pilot must file a flight plan with air traffic control (ATC) to communicate the intended route, altitude, and any relevant details about the flight. This document provides vital information to air traffic controllers, enabling them to manage air traffic effectively and maintain safety.

The flight plan also ensures that the pilot receives the necessary clearances and instructions from ATC throughout the flight, facilitating communication and coordination during IFR operations. Moreover, without a filed flight plan, a pilot cannot legally operate under IFR, as it is a regulatory requirement. This necessity underscores the importance of the flight plan in ensuring safe and efficient operation within the controlled airspace.

While other documents like a flight route clearance, medical certificate, and aircraft registration are important for various aspects of aviation operations, they do not specifically fulfill the requirement of IFR operations in the same way that a flight plan does.