Improved Ground Collision Avoidance System for General Aviation Aircraft and UAVs

Armstrong Flight Research Center, Edwards, California

Controlled flight into terrain (CFIT) causes almost 100 deaths each year in the United States. Although warning systems have virtually eliminated CFIT for large commercial air carriers, the problem still remains for general aviation aircraft and unmanned aerial vehicles (UAVs). Existing systems are forced to rely on digital maps with low resolution/fidelity. They also require expensive equipment, limit the maneuvers to avoid collision, and frequently issue false alarms, causing pilots to ignore the safety system.

To address this problem, researchers developed a lifesaving system that accurately alerts pilots when a ground collision is imminent, and provides the maneuvers needed to avoid a crash. It offers enhanced vehicle performance modeling, more efficient data-handling methods, and user-friendly warning systems. The inexpensive, lightweight, and easy-to-install system can be incorporated into an app for tablets or other handheld/mobile devices, electronic flight bags (EFBs), and/or aircraft avionics systems. Designed to operate on a variety of aircraft with minimal modifications, similar systems have been successfully demonstrated on an F-16, a small UAV, and a Cirrus SR22 single-engine aircraft.

The system uses functionally partitioned software modules to sense a ground collision threat and specify multidirectional avoidance trajectories:

• Threat sensing includes data regarding geo-referenced position, aircraft climb and roll rates, velocity vector information, bank angle, performance parameters, horizontal winds, and ground proximity.
• A kinematic model computes predictions in three axes (roll, pitch, and speed), using these to derive range and ground track.
• The system simulates three-dimensional avoidance maneuvers ahead of the aircraft, producing three geo-referenced trajectories.
• The system then compares the three predicted trajectories to a terrain profile, determining ground clearance and selecting the appropriate avoidance maneuver and notifying the pilot.

The algorithms successfully balance precision and agility, including detailed models of flight dynamics, while maintaining a fast computational frame rate, enabling rapid reactions to changes in speed, aircraft attitude, and other quickly shifting parameters.

Furthermore, the system is greatly enhanced by patented high-fidelity digital terrain mapping algorithms. Typical ground collision avoidance systems rely heavily on digital terrain maps and sensors to detect a collision threat and plan an escape route. However, the standard compression ratio of 4:1 limited the number of maps that could be stored in the onboard flight control system. An innovative encoding algorithm was developed with a compression ratio of 5,000:1 as well as ultrafast (real-time), high-performance decoding. Its recursive, semi-regular, treebased compression utilizes linear regression geometric tiling, which is useful not only for aviation, but for any application that requires large databases of graphical information deployed via restricted environments (e.g., tablets, smartphones, embedded systems) where both significant compression and real-time local decompression are needed. The algorithms are described in “Global Elevation Data Adaptive Compression Algorithms” (DRC-009-008), Software Tech Briefs, Vol. 38, No. 9 (September 2014), p. 28.

This patent-pending improved ground collision avoidance system emerged from more than 25 years of collaboration between Armstrong Flight Research Center and the U.S. Air Force (USAF) as well as industry partners. A related system was successfully incorporated into the USAF’s F-16 fleet in 2014.

This work was done by Mark Skoog, Loyd Hook, and Kevin Prosser of Armstrong Flight Research Center. For more information, contact the Armstrong Technology Transfer Office at 661-276-3967. Refer to DRC-012-033.

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