industry Onboard Traffic Systems Keeping the Other Guy Out of My Window! S T O R Y O Avidyne’s TAS600 Series combines transponder and ADS-B signals to maximize situational awareness. 32 avionics news B Y J O H N D . R U L E Y nboard traffic awareness and collision avoidance arose from tragedy. A series of midair collisions between airliners and other aircraft beginning in 1956 made clear that the prevailing “empty sky” theory of operation was no longer viable as traffic density increased. The Civil Aeronautics Authority (today’s Federal Aviation Administration) responded with the imposition of positive control zones and worked with industry to develop onboard traffic alert systems. Several technologies were investigated, and consensus was eventually reached on a system based on transponder interrogation. In 1978, another midair collision involving an airliner led the FAA administrator to demand action, leading to the first Traffic Alert and Collision Avoidance System. The U.S. Congress eventually passed legislation mandating TCAS on air carrier aircraft. In the 30-plus years since, the original transponder-based • july 2013