One of the newest ATC techniques is multilateration, where several small unattended receiving stations are dispersed around an airport to monitor transponder and TCAS transmissions from aircraft in the area. The received signals are then computer processed to pinpoint the exact location and identity of each aircraft. This data is then displayed to tower controllers to give them a much more accurate and faster updated local traffic picture than radar.

Multilateration is particularly valuable when integrated with the tower’s display from the airport surface-detection equipment (ASDE) at large airports, since it adds specific aircraft identification tags to the otherwise unidentifiable “skin paints” of objects moving on the surface. The FAA’s next-generation ASDE-X will incorporate multilateration in its basic design.

Many airports in North America, Europe and Asia have installed multilateration systems, built primarily by two U.S. companies–Sensis and Rannoch. But not all installations are used to monitor traffic movements at major hubs. At a recent conference, Rannoch president Alexander Smith noted that smaller airports have used the system’s recording capability to identify which aircraft broke local noise ordinances.

More recently, airport managers have discovered another non-ATC benefit. The system’s ID tagging capability can ensure that every aircraft is billed for any applicable fees. Manually logged movement records at busy smaller fields have missed many aircraft–possibly as many as 30 percent.