General Atomics Aeronautical System, Inc. (GA-ASI), the maker of the Predator and Reaper Unmanned Aerial Vehicles (UAVs) has successfully completed the first of several flight tests of a prototype Sense and Avoid (SAA) system that allows a UAV to operate safely around other aircraft in flight. This marked the first time the entire system – consisting of a radar, transponder, and traffic alert system – worked together as a “system of systems” to detect the various types of aircraft it might encounter in the air.

The FAA and international agencies have long insisted that UAVs have their own “sense and avoid” systems onboard that can detect other nearby aircraft and instruct either the onboard autopilot or the ground-based remote operator of the UAV how to avoid a collision. The lack of this ability is a major reason why UAVs are not permitted to fly over much of the United States, and are restricted to special airspace that has been set aside just for that use. The addition of an SAA system to a UAV paves the way for them to operate in airspace with manned air traffic.

“We are working closely with the FAA, NASA, the U.S. Department of Homeland Security [DHS], and our industry alliances to advance the safe and efficient integration of unmanned aircraft systems into domestic and international airspace,” said Frank W. Pace, president, Aircraft Systems Group, GA-ASI. “Our Sense and Avoid capability is a key part of that goal, and we continue to make ongoing progress towards this end.”

The technology demonstrated during General Atomics' flight test does not rely on optical detection, and would be able to operate in any weather. It combines three integrated systems – the BAE Systems’ AD/DPX-7 Identification Friend-or-Foe (IFF) transponder with Automatic Dependent Surveillance – Broadcast (ADS-B) receiver; the GA-ASI-developed Due Regard Radar (DRR); and Honeywell’s TPA-100 Traffic Collision Avoidance System or TCAS.

During the test, the system had 40 pre-planned encounters with other air traffic, including some not being tracked by Air Traffic Control. The test was conducted from the Gray Butte Flight Operations Facility near Palmdale, California, a facility on the edge of the Mojave Desert and located just south of Edwards Air Force Base. The test aircraft was a Predator B model.

The three onboard systems were able to track two participating “intruder” aircraft that acted as targets for the exercise. The onboard software fused the data into a single set of tracking information that was relayed to the Conflict Prediction and Display Systems (CPDS) in front of the Predator’s ground-based pilot.

Modern aircraft have a variety of means to “see” each other in the air. It is still legal in certain areas of the US to fly with no radio at all – and even no electrical system in the aircraft. Sailplanes and gliders have no onboard power except for batteries, and ultralights can fly in uninhabited areas. The UAV SAA system would use its radar to see these targets.

General Aviation aircraft, such as Cessnas and Pipers, carry transponders, which are special radios that automatically respond when “interrogated,” or sent a special signal. Air Traffic Control normally uses transponders to tell aircraft apart on radar as each aircraft has its own code that it responds to. The TCAS – Traffic Collision Avoidance System – uses these transponders to detect the other aircraft.

The newest method is ADS-B, where each aircraft sends out its own GPS position once a second to all the other aircraft in the area. The FAA has mandated that most aircraft will have ADS-B transmitters by 2020, which will make it possible to track aircraft from space.

Since aircraft flying today may have no transponder, a current-style radar transponder, or a new, modern ADS-B radio (or some combination thereof), the General Atomics See and Avoid system uses all three techniques to detect other aircraft. The company reported that all possible combinations of radios, aircraft, and sensors were tried in the flight test.

This test is a follow-on to other individual tests conducted previously. In October of last year, the company flew the ADS-B component on a Guardian UAV, the version of the Predator being flown by the US Border Patrol, while the DRR radar flew on the Predator B in February 2013. Follow up tests are planned to continue to validate the operation of the combined system.

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