* Radar: This is the most common and primary method. Ground-based radar stations emit radio waves that bounce off aircraft, providing information about their location, altitude, and speed.

* ADS-B (Automatic Dependent Surveillance-Broadcast): This system uses transponders on aircraft that broadcast their position, altitude, speed, and other data directly to ground stations and other aircraft.

* Satellite-based tracking: Systems like the FAA's NextGen program use satellites to track aircraft, especially over remote areas where ground-based radar coverage is limited.

* FLIGHT TRACKING WEBSITES: These websites, like Flightradar24, FlightAware, and others, use data from ADS-B and other sources to provide real-time tracking of aircraft.

It's important to note that the specific tracking systems used vary depending on the country, airspace, and the type of aircraft.