Most flight trackers require you to enter the name of an airline and a flight number to see its current departure and arrival time, with real-time updates if the flight is currently in the air. Some sites allow you to enter the departure and arrival locations to view a schedule, with some also displaying a map of the flight.
Flight tracking systems rely on a wide range of data to determine the status of flights, including live information as well as preset details filed by the pilot. Each departing plane must file a flight plan with the Federal Aviation Administration and both the airport from which it departs and the airport at which it plans to arrive. Many flight trackers, such as those on FlightAware.com and FlightStats.com, use this as the baseline for determining the original departure and arrival times for the flight. From this alone, it is possible to locate a flight using its flight number and the name of the airline.
Each flight time is subject to changes, such as a delay due to a technical issue or from a backup on the runway. Pilots and airports file updates to the original flight plans with new takeoff times, which reflect in the tools. While a plane is in flight, it periodically sends information about its speed and location to the airport so that it may monitor its arrival, which also appears in the tools.