True free flight applications exist only on a small scale in selected airspace operations where only the most well equipped aircraft operate, such as at high altitude by commercial airliners. There are many versions of free flight being conceived for the Next Generation Air Transportation System (NGATS). The free flight vision is expected to slowly emerge over the next 20–30 years as NGATS emerges from billions of dollars of development, testing, careful transition planning, training, and deployment of ground-based and airborne systems by all types of aircraft. Key elements of NGATS include the automatic dependent surveillance-broadcast (ADS-B) and what can be expected to be an ever-evolving, net-centric information application called the System Wide Information Management System or "SWIM".