Flight plans are documents filed by a pilot or flight dispatcher with the local Air Navigation Service Provider (e.g. the FAA in the United States) prior to departure which indicate the plane's planned route or flight path. Flight plan format is specified in ICAO Doc 4444. They generally include basic information such as departure and arrival points, estimated time en route, alternate airports in case of bad weather, type of flight (whether instrument flight rules [IFR] or visual flight rules [VFR]), the pilot's information, number of people on board, and information about the aircraft itself. In most countries, flight plans are required for flights under IFR, but may be optional for flying VFR unless crossing international borders. Flight plans are highly recommended, especially when flying over inhospitable areas such as water, as they provide a way of alerting rescuers if the flight is overdue. In the United States and Canada, when an aircraft is crossing the Air Defense Identification Zone (ADIZ), either an IFR or a special type of VFR flight plan called a DVFR (Defense VFR) flight plan must be filed. For IFR flights, flight plans are used by air traffic control to initiate tracking and routing services. For VFR flights, their only purpose is to provide needed information should search and rescue operations be required, or for use by air traffic control when flying in a "Special Flight Rules Area." Route or flight paths Routing types used in flight planning are: airway, navaid and direct. A route may be composed of segments of different routing types. For example, a route from Chicago to Rome may include airway routing over the U.S. and Europe, but direct routing over the Atlantic Ocean. Airway or flight path Airway routing occurs along pre-defined pathways called flight paths. Airways can be thought of as three-dimensional highways for aircraft. In most land areas of the world, aircraft are required to fly airways between the departure and destination airports. The rules governing airway routing cover altitude, airspeed, and requirements for entering and leaving the airway (see SIDs and STARs). Most airways are eight nautical miles (14 kilometers) wide, and the airway flight levels keep aircraft separated by at least 1000 vertical feet from aircraft on the flight level above and below. Airways usually intersect at Navaids, which designate the allowed points for changing from one airway to another. Airways have names consisting of one or