NASA Tests Air Traffic Surveillance Technology Using Its Pilatus PC-12 Aircraft

As air taxis, drones and other innovative aircraft enter U.S. airspace, aircraft location systems will be critical to ensuring air traffic safety.

The Federal Aviation Administration (FAA) requires aircraft to report their location to other aircraft and air traffic control in real time using the Automatic Dependent Surveillance-Broadcast (ADS-B) system. NASA is currently evaluating the ability of the ADS-B system to prevent collisions in a simulated urban environment. Using NASA’s Pilatus PC-12 aircraft, researchers are investigating how these systems can handle the demands of air taxis flying at low altitudes through cities.

When operating in urban areas, a particular challenge for ADS-B systems is consistent signal coverage. Like losing a cell-phone signal, air taxis flying over densely populated areas may have trouble maintaining an ADS-B signal due to distance or interference. If this happens, those vehicles become less visible to air traffic control and other aircraft in the area, increasing the chance of collision.

To simulate urban flight field conditions and better understand signal loss patterns, NASA researchers set up a test area at NASA’s Armstrong Flight Research Center in Edwards, California, on September 23 and 24, 2024.

Flying in the agency’s Pilatus PC-12 in a grid pattern over four ADS-B stations, researchers collected data on signal coverage from multiple ground locations and instrument configurations. The researchers were able to trace where signal dropouts occurred from strategically placed ground stations in relation to the aircraft’s altitude and distance from the stations. This data will inform future placement of additional ground stations to increase signal boosting coverage.

“Like all antennas, the antenna used for ADS-B signal reception does not have a constant pattern,” said Brad Snelling, chief engineer for the vehicle test team for NASA’s Air Mobility Pathfinder Project. “There are certain areas where terrain will block ADS-B signals and, depending on the characteristics of the antenna type and location, there are also flight elevation angles where reception can cause signal dropouts,” Snelling said. “This will mean that we will need to place additional ground stations in several locations to boost the signal for future test flights. We can use the test results to help us configure the equipment to minimize signal loss when we conduct future air taxi flight tests.

NASA Armstrong’s September flights were based on the first tests of ADS-B in a variety of environments. In June, researchers at NASA’s Glenn Research Center in Cleveland flew a Pilatus PC-12 and found a consistent ADS-B signal between the aircraft and the roof-mounted communications antenna. Center’s Aerospace Communications Facility. Data from these flights helped researchers at NASA Armstrong plan recent tests. In December 2020, test flights conducted under NASA’s Advanced Air Mobility National Campaign used an OH-58C Kiowa helicopter and ground-based ADS-B stations at NASA Armstrong to collect baseline signal information.