Flight plans are specific information relating to the intended flight of an aircraft that is filed orally or in writing with an FSS or an ATC facility. They are usually filed by pilots or a flight dispatcher with the local Civil Aviation Authority prior to departure. Flight plans include information specific to the flight the aircraft is about to depart on, such as departure and arrival points, estimated time en route, alternate airports in case of bad weather, type of flight (which could be either IFR or VFR), the pilot's name, and the number of people on board.
In most countries, flight plans are required to file flights under IFR (instrument flight rules) rules. However, flight plans are not typically filed under VFR (visual flight rules) unless the aircraft is crossing national borders. Despite this, pilots are always encouraged to file flight plans whenever they fly, as this could help to alert search and rescue parties if the flight is overdue.
Flight plans are also used by air traffic controllers to initiate tracking and routing services for flights conducted under IFR rules. The routes used on flight plans can be constructed by using airways, navigational aids, or direct routing (most often used in conjunction with GPS). In addition, flight plans may also contain SIDs (standard instrument departures) or STARS (standard terminal arrival routes), which are both procedures and checkpoints used to enter and exit the airway system.