What is a key requirement for aircraft at a non-tower airport?

At non-tower airports, pilots operating under IFR (Instrument Flight Rules) are required to notify Air Traffic Control (ATC) when they choose to cancel their IFR flight plan. This notification is crucial because it ensures that ATC is aware of a pilot’s change in operational status, which helps maintain overall air traffic safety and efficiency. By informing ATC, the pilot effectively communicates that they are no longer operating under IFR and may be transitioning to VFR (Visual Flight Rules), which may have different surveillance and separation requirements.

In other options, maintaining visual flight rules is not a requirement at all times at non-tower airports, as pilots can operate under IFR as well. Reporting to ATC at all times is generally not mandated except in specific circumstances. Filing a flight plan before every flight is not a hard requirement; while filing is encouraged for safety and coordination, it is not strictly necessary for all types of flights at non-tower airports.