Which document is NOT required for flight as a pilot?

The flight plan is not a required document for flight as a pilot. While filing a flight plan is encouraged, especially for IFR flights, it is not mandatory in all circumstances. A flight plan serves to inform air traffic control of your intended route and provides a safety mechanism, as it allows authorities to track your progress and respond in case you do not arrive as expected.

On the other hand, having a valid pilot certificate is essential because it proves that you are qualified to operate the aircraft. A medical certificate is also required to ensure that you meet the necessary health standards to safely fly. Additionally, a radio license is required for certain types of operations, particularly if you're flying internationally or using specific radio frequencies. Therefore, while submitting a flight plan is highly beneficial, it’s the document that is not strictly mandated for a pilot to legally conduct a flight.