Overview Safety is a very important consideration for all glider pilots. There are several approaches to collision avoidance that are commonly used in sailplanes.
Transponders - When queried by air traffic control they transmit the aircraft's altitude and other parameters. That data, along with positional data from the radar, can be used to route traffic around you. Transponders greatly enhance safety in congested areas. Also, most large aircraft are equipped with TCAS which, independent of any ground inputs, performs surveillance of nearby aircraft to provide information on the position and altitude of these aircraft so the collision avoidance algorithms can perform their function.
Collision Avoidance Systems - These are passive systems that listen to data transmitted by nearby aircraft transponders. Nearby transponder-equipped aircraft are detected and ranged, and the altitude is decoded. The range, relative altitude and (for some units) direction of the nearest traffic is displayed and an alert is sounded when the range and relative altitude are less than preset minimum values. Some systems provide direction information so the pilot knows where to look for the traffic. These systems can be very small and much lower cost than a transponder.