Mode S is a Secondary Surveillance Radar (SSR) technique with a selective interrogation of aircraft with its unique 24-bit worldwide address. This enables a unique identification of aircraft removing the risk of confusion due to overlapping signals.

Mode S operates in the same Radio Frequency (1030-1090 MHz) band as conventional SSR systems.

Mode-S employs airborne transponders to provide altitude and identification data, with ADS-B adding global navigation data typically obtained from a GPS receiver

The position and identification data supplied by Mode S/ADS-B broadcasts are available to pilots and air traffic controllers.

Mode S/ADS-B data updates rapidly, is very accurate and provides pilots and air traffic controllers with common air situational awareness for enhanced safety, capacity and efficiency. Further, It can provide a cost-effective solution for surveillance coverage in non-radar airspace.