When must a flight plan or flight itinerary be filed?

Filing a flight plan or flight itinerary is typically required when an aircraft is departing for a distance that exceeds 25 nautical miles from the point of departure. This requirement ensures that air traffic services can monitor and assist aircraft that are operating outside of the immediate vicinity of an airport.

By establishing a flight plan for distances greater than 25 nautical miles, pilots can facilitate search and rescue operations in case of emergencies, as well as ensure the safety of air traffic operations by providing information about the flight's intended route, destination, and estimated times of arrival. This level of planning and notification helps maintain a structure within the air traffic system, especially in areas where commercial or other aircraft may be in operation.

The distances specified in the other choices (10 NM, 50 NM, and the stipulation of controlled airspace) do not align with the regulatory requirements set forth by aviation authorities regarding flight plan filing, making ‘greater than 25 NM from the point of departure’ the correct answer.