NASA is evaluating ADS-B system’s ability to prevent collisions in a simulated urban environment, to assess if it could be used to track large volumes of air taxis operating at low altitudes in cities.
A challenge for ADS-B (Automatic Dependent Surveillance-Broadcast) systems operating in urban areas is consistent signal coverage.
ADS-B systems use GPS to broadcast an aircraft’s location, altitude, and other data to ground stations and other aircraft. Like losing a cell phone signal, air taxis flying through densely populated areas may have trouble maintaining ADS-B signals due to distance or interference.
If that happened, those vehicles would become less visible to air traffic control and other aircraft in the area, increasing the likelihood of collisions.
To simulate the conditions of an urban flight area and better understand signal loss patterns, NASA researchers established a test zone at NASA’s Armstrong Flight Research Center in Edwards, California, on Sept. 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 equipment configurations.
Researchers could pinpoint where signal dropouts occurred from the strategically placed ground stations in connection to the plane’s altitude and distance from the stations. This data will inform the future placement of additional ground stations to enhance signal coverage.
Brad Snelling, vehicle test team chief engineer for NASA’s Air Mobility Pathfinders project said, “Like all antennas, those used for ADS-B signal reception do not have a constant pattern. There are certain areas where the terrain will block ADS-B signals and depending on the type of antenna and location characteristics, there are also flight elevation angles where reception can cause signal dropouts,”
“This would mean we need to place additional ground stations at multiple locations to boost the signal for future test flights. We can use the test results to help us configure the equipment to reduce signal loss when we conduct future air taxi flight tests.”
Last September’s flights at NASA Armstrong built upon earlier tests of ADS-B in different environments. In June 2024, researchers at the Glenn Research Center in Cleveland flew the Pilatus PC-12 and found a consistent ADS-B signal between the aircraft and communications antennas mounted on the roof of the center’s Aerospace Communications Facility.
Data from the June flights at Glenn helped researchers plan the recent tests at NASA Armstrong. In December 2020, test flights performed 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.
NASA researchers are evaluating the data from these flight tests to understand the different signal transmission conditions and equipment needed for air taxis and drones to operate safely. The research results will inform the infrastructure design to support future air taxi communication, navigation, and surveillance research and to develop new ADS-B-like concepts for uncrewed aircraft systems, said NASA.
