GPS & ADS-B Risks for UAS (A44_A11L.UAS.86)
Unvalidated or unavailable Automatic Dependent Surveillance-Broadcast (ADS-B) and Global Position Systems (GPS) data poses security and safety risks to automated Uncrewed Aircraft Systems (UAS) navigation and to Detect and Avoid (DAA) operations. Erroneous, spoofed, jammed, or drop outs of GPS data may result in uncrewed aircraft position and navigation being incorrect. This may result in a fly away beyond radio control, flight into infrastructure, or flight into controlled airspace. Erroneous, spoofed, jammed, or drop outs of “ADSB-In” data may result in automated uncrewed aircraft being unable to detect and avoid other aircraft or result in detecting and avoiding illusionary aircraft. For automated DAA, a false ADS-B track can potentially be used to corral the uncrewed aircraft to fly towards controlled airspace, structures, terrain, and so on. This research is necessary to enable safe and secure automated small UAS (sUAS) navigation and DAA operations. Goals for the project include reports and recommendations useful for Federal Aviation Administration (FAA) policy development and UAS standards development. It is expected that this information will be used to better understand the risks and potential mitigations, and to help the FAA to reassess and refine FAA policy with respect to validation of ADS-B data.
The A44 team has completed the testing, analysis, and demonstration of mitigations reports and has made final recommendations which fulfills Task 5 for the A44 ASSURE project. Select mitigation strategies and test plans were chosen from previous reports. This report prioritizes the mitigations in Task 2 for further analysis based on those that show the most promise for reducing risks while remaining cost effective and implementable. These test plans were developed in the Task 3 report. The Task 4 report placed particular emphasis on testing mitigations that support sUAS operations. The use of simulated flight data is a significant source of the test data used for evaluation. Full reports can be found in the appendices of this document.
The integrity of ADS-B and GPS navigation systems were tested to detect threats to the integrity and/or reliability of the data. These risks include dropped, erroneous, spoofed, and jammed data from GPS and/or ADS-B systems. Several mitigation schemes were flight and simulation tested based on their potential effectiveness in jamming and spoofing conditions. The mitigation schemes tested are cellular signal navigation, the Eichelberger’s Collective Detection (ECD) method, optical flow, and geomagnetic navigation. Previous results indicate that these have an overall high effectiveness rating, while having varying effectiveness in the individual factors scored.
The UAS anomalies section focused on using ADS-B data sets to identify ADS-B anomalies that would result in ceasing operations and identify the scenarios that are most common. The data analyzed was collected by using flight test operations at University of Alaska Fairbanks (UAF) as well as from a unique case study of public use ADS-B data from the Dallas Fort Worth airport. Additional metrics are recommended for ADS-B reception quality and the distance and altitudes of the ADS-B receiver and transmitting aircraft. The DFW case clearly illustrated the possibility of extended loss of ADS-B signals and the subsequent need for mitigation strategies. Flight tests were developed to record and utilize nearby Long Term Evolution (LTE)/4G cellular signals to inform a Global Navigation Satellite System (GNSS)-independent positioning solution from a UAS-based receiver. The findings show precise cellular signal positioning approaches have strong potential for mitigating risk in UAS operations and should be considered a supporting navigation aide. For the spoofing chapter, the ECD method was studied in a simulation environment to produce preliminary data to assess its effectiveness. The research efforts have shown the viability and unique capabilities of ECD to detect spoofed signals, mitigate the false and true signals, and recover the true signals. A functional GPS simulation model has been created as an initial step in establishing ECD validity. The evaluation of the capabilities, advantages, and limitations of optical flow and geomagnetic navigation techniques were tested using both flight and simulated data. These algorithms have demonstrated significant potential in improving the accuracy and robustness of navigation systems.
A significant takeaway from the work completed is that industry standards bodies need mitigate the potential risks with better safeguards and protections from GPS and ADS-B dropout/jamming/spoofing events. All the mitigations investigated show the ability to increase the safety of sUAS operations, yet none are currently fully vetted or mandated by standards bodies. While several mitigation schemes were studies, there are more in development with new technologies and continued studies are needed to fully evaluate their potential. This is especially true for operations that were not investigated including small high drone densities managed by UAS traffic management via UTM, large UAS operations, UAS carrying hazardous cargo, UAS receiving ATC services, or future remotely piloted urban air mobility aircraft with passengers where the risks may be larger and new risks may emerge such as disruption to traffic management operations.
William H. Semke, Ph.D.
Associate Dean | Professor
College of Engineering and Mines
University of North Dakota