Glen Rose Top Gun Human Fac. Join Leave Welcome to the Air Traffic Cafe' website. We Hope that you enjoy your visit. The pace of reports has picked up since May 8, when the FAA asked controllers to be more vigilant for spotting the anomalies.
Technical experts analyzing the radar data believe the physical environment is the likely cause.
The problem is the number of metal structures that reflect radio frequency signals, which is the usual cause of a ghost image, he said. But if after passing the aircraft, the outgoing SSR pulse bounces off a crane or a building and returns to the aircraft with sufficient energy, it can occasionally trigger another response from the aircraft transponder. The SSR uses the elapsed time from pulse to return to determine range and the antenna centerline to establish bearing. In a similar fashion, reflections from the primary radar can produce false returns. All big metropolitan areas may have this problem, Duffy said, but Chicago's O'Hare has been historically bad because of the city skyline surrounding it on all sides.