What must a pilot do when they want to cancel an IFR flight plan?

When a pilot wishes to cancel an IFR (Instrument Flight Rules) flight plan, the appropriate action is to notify Air Traffic Control (ATC). This request alerts the air traffic controllers that the pilot no longer intends to operate under IFR conditions, allowing them to update their traffic management systems accordingly and manage airspace effectively.

Notifying ATC is crucial because it ensures that the flight plan is removed from their system, freeing up resources and preventing any misunderstandings regarding the aircraft's status. This action can be taken at any point during the flight, including before departure or in-flight, as long as the pilot is in communication with ATC. Proper communication with ATC is essential for maintaining safety and efficiency in the air traffic control system.