ACAS Xu provides plug-and-play interfaces for radar and EO sensors. “Tracks come in in an appropriate way. Xu accepts them and uses them in the algorithm,” Suarez says. ACAS-X has separate surveillance and resolution modules (in TCAS they are intertwined, making it difficult to modify). “ACAS X can be updated more frequently for changes in airspace and operations. From an unmanned aspect, operations have changed in ways never imagined for TCAS, and this allows Xu to accommodate less-maneuverable aircraft.”
Several projects have shown the suitability of ADS-B for sense-and-avoid between cooperating aircraft. Last August in Argentia, Newfoundland, R3Engineering (R3E) conducted what it says was the first ADS-B-based fully autonomous collision-avoidance test, followed in April by further flights at Yuma Proving Ground, Ariz., involving two L-3 TigerShark UAVs equipped with its All-Weather Sense-and-Avoid System.
The Yuma tests represented a border-patrol mission, the system using ADS-B to build a track on the intruder and—when 60-70 sec. from a collision—linking directly to the autopilot, initiating a circle maneuver to resolve the conflict, then returning control to the autopilot to continue the patrol. “You need an autonomous maneuver,” says Dick Healing, chief technology officer.
The next series of tests will involve non-cooperative traffic and R3E is working with the Navy to integrate ground primary-radar data into the system in the same way as ADS-B, to provide a non-cooperative capability without onboard radar. “We want to compare the accuracy of ADS-B to data derived from radar,” Healing says.
“Can we use ADS-B data for sense-and-avoid? Definitively. It provides excellent data on where you are and where you are headed,” says Mark Askelson, principal investigator at UND for the project with Mitre, NASA and Draper. “We can have EO or radar capability and ADS-B as well. We are going to need redundancy in sense-and-avoid.”
“We need to do experimentation and get data to look at. Our main purpose is to conduct simulation and flight tests to generate data for the standards committee to consider,” says Lacher. “Also we recognize any solution will need to be evaluated and we need a capability for that. Mitre in partnership with NASA Langley is developing a simulation-to-flight framework to evaluate algorithms in simulation, then in flight. This is needed by the community to make a safety determination.”