What is Mode-S/ADS-B

	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.
	The UK Civil Aviation Authority (CAA) has required IFR flights operating as General Air Traffic (GAT) within designated UK Mode S airspace (London TMA) to be Mode S equipped from 31 March 2005, with a 2-year transition period until 31 March 2007, as per AIC 49/2005 (Yellow 171). Additionally, the CAA is about to begin a Regulatory Impact Assessment to mandate Mode S (Elementary) carriage outside of current designated Mode S airspace from 31 March 2008, with a proposed 2-year transition period to 31 March 2010.