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. Flight plans 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 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 usually 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.
For flights conducted under IFR rules, flight plans are also used by air traffic controllers to initiate tracking and routing services. 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.