A cost effective satellite-based surveillance system has been installed in 21 airports in the country to help controllers track aircraft more accurately and enhance air space capacity. The ADS-B system will help controllers track aircraft more accurately and thereby reduce spacing between two aircraft and enhance air space capacity, Mr V Somasundaram, Board Member (Air Navigation Services), AAI, told reporters here last evening. The new system will give alert every second as against the 5 seconds alert in the conventional approach radar. Approach radars currently cost Rs 10 crore while ADS-B costs only one tenth of this, he said. Already, 21 stations have been covered and all the 120 airports under the ambit of Airports Authority of India, would be covered within the next one year in a phased manner. The new system at Trichy International Airport will be commissioned within the next one month. The swath area of Trichy system is about 250-300 air km. As a result, Madurai does not require such a system, he said. The data generated by ADS-B will be monitored through integrated air space management system at Chennai and Thiruvananthapuram. On the long pending commissioning of GAGAN (Geo Augmented Navigation System) in the country, Mr Somasundaram said this will hopefully be commissioned by December end pending initial clearance from DGCA. The test run will take place and DGCA is expected to give its full clearance by June-July next, he added.