As air taxis, drones, and other innovative aircraft enter U.S. airspace, systems that communicate an aircraft’s location will be critical to ensure air traffic safety.

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

When operating in urban areas, one particular challenge for ADS-B systems is consistent signal coverage. Like losing cell-phone signal, air taxis flying through densely populated areas may have trouble maintaining ADS-B signals due to distance or interference. If that happens, those vehicles 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 were able to 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 future placement of additional ground stations to enhance signal boosting coverage.  

“Like all antennas, those used for ADS-B signal reception do not have a constant pattern,” said Brad Snelling, vehicle test team chief engineer for NASA’s Air Mobility Pathfinders project. “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,” Snelling said. “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.”

The September flights at NASA Armstrong built upon earlier tests of ADS-B in different environments. In June, researchers at NASA’s 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 these flights helped researchers plan out 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’s research in ADS-B signals and other communication, navigation, and surveillance systems will help revolutionize U.S. air transportation. Air Mobility Pathfinders researchers will evaluate the data from the three separate flight tests to understand the different signal transmission conditions and equipment needed for air taxis and drones to safely operate in the National Air Space. NASA will use the results of this research to design infrastructure to support future air taxi communication, navigation, and surveillance research and to develop new ADS-B-like concepts for uncrewed aircraft systems.

NASA recently began a series of flight tests with partners to answer an important aviation question: What will it take to integrate remotely piloted or autonomous planes carrying large packages and cargo safely into the U.S. airspace? Researchers tested new technologies in Hollister, California, that are helping to investigate what tools and capabilities are needed to make these kinds of flights routine.  

The commercial industry continues to make advancements in autonomous aircraft systems aimed at making it possible for remotely operated aircraft to fly over communities – transforming the way we will transport people and goods. As the Federal Aviation Administration (FAA) develops standards for this new type of air transportation, NASA is working to ensure these uncrewed flights are safe by creating the required technological tools and infrastructure. These solutions could be scaled to support many different remotely piloted aircraft – including air taxis and package delivery drones – in a shared airspace with traditional crewed aircraft. 

“Remotely piloted aircraft systems could eventually deliver cargo and people to rural areas with limited access to commercial transportation and delivery services,” said Shivanjli Sharma, aerospace engineer at NASA’s Ames Research Center in California’s Silicon Valley. “We’re aiming to create a healthy ecosystem of many different kinds of remotely piloted operations. They will fly in a shared airspace to provide communities with better access to goods and services, like medical supply deliveries and more efficient transportation.”  

During a flight test in November, Reliable Robotics, a company developing an autonomous flight system, remotely flew its Cessna 208 Caravan aircraft through pre-approved flight paths in Hollister, California. 

Although a safety pilot was aboard, a Reliable Robotics remote pilot directed the flight from their control center in Mountain View, more than 50 miles away.

Congressional staffers from the United States House and Senate’s California delegation joined NASA Deputy Associate Administrator for Aeronautics Research Mission Directorate, Carol Caroll, Ames Aeronautics Director, Huy Tran, and other Ames leadership at Reliable Robotics Headquarters to view the live remote flight.

Researchers evaluated a Collins Aerospace ground-based surveillance system’s ability to detect nearby air traffic and provide the remote pilot with information in order to stay safely separated from other aircraft in the future. 

Initial analysis shows the ground-based radar actively surveilled the airspace during the aircraft’s taxi, takeoff, and landing. The data was transmitted from the radar system to the remote pilot at Reliable Robotics. In the future, this capability could help ensure aircraft remain safely separated across all phases of fight.   

While current FAA operating rules require pilots to physically see and avoid other aircraft from inside the cockpit, routine remotely piloted aircraft will require a suite of integrated technologies to avoid hazards and coordinate with other aircraft in the airspace.  

A radar system for ground-based surveillance offers one method for detecting other traffic in the airspace and at the airport, providing one part of the capability to ensure pilots can avoid collision and accomplish their desired missions. Data analysis from this testing will help researchers understand if ground-based surveillance radar can be used to satisfy FAA safety rules for remotely piloted flights. 

NASA will provide analysis and reports of this flight test to the FAA and standards bodies. 

“This is an exciting time for the remotely piloted aviation community,” Sharma said. “Among other benefits, remote operations could provide better access to healthcare, bolster natural disaster response efforts, and offer more sustainable and effective transportation to both rural and urban communities. We’re thrilled to provide valuable data to the industry and the FAA to help make remote operations a reality in the near future.”  

Over the next year, NASA will work with additional aviation partners on test flights and simulations to test weather services, communications systems, and other autonomous capabilities for remotely piloted flights. NASA researchers will analyze data from these tests to provide a comprehensive report to the FAA and the community on what minimum technologies and capabilities are needed to enable and scale remotely piloted operations. 

This flight test data analysis is led out of NASA Ames under the agency’s Air Traffic Management Exploration project. This effort supports the agency’s Advanced Air Mobility mission research, ensuring the United States stays at the forefront of aviation innovation.