Pilots test collision-avoidance system

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The Air Force's Automatic Air Collision Avoidance System successfully put two F-16 Fighting Falcons into automated maneuvers Aug. 7 to avoid collision during tests at Edwards Air Force Base, Calif.

Maj. James Less and Swedish air force Maj. Richard Ljungberg flew a specially equipped research aircraft during the maneuver, conducted on actual aircraft for the first time. Maj. Scott Wierzbanowski from the 46th Test Wing at Eglin Air Force Base, Fla., flew the other aircraft, a standard F-16.

The system is the world's first automated collision-avoidance system.

"During this milestone flight, the two aircraft repeatedly approached each other, and the Auto ACAS activated every time to separate them without pilot input," said Steve Markman, flight-test director at the Air Force Research Laboratory's air vehicles directorate.

"Midair collisions are a major cause of U.S. Air Force fighter aircraft losses, and an unfortunate consequence of the aggressive, highly dynamic environment of air-to-air combat and realistic training," Markman said.

"Collision-avoidance systems currently in use provide audio and visual guidance to pilots, who then must take manual action,” he said. “Such warnings work well for slow-maneuvering transport aircraft that must keep far apart, but are ineffective for the fighter pilot whose mission requires close-formation flying and aggressive maneuvering in the vicinity of other aircraft.

"Auto ACAS, by comparison, waits until the last possible instant ... until after the pilot missed his last chance to avoid a collision," Markman said. "When Auto ACAS takes control, it performs an aggressive maneuver to avoid the collision, then returns control to the pilot."

The system is not hardware, but "fail-safe" software in the aircraft's digital-avionics system, he said.

"Each Auto ACAS-equipped aircraft broadcasts its position and trajectory using a data link and receives identical information transmitted from other aircraft," Markman said. The computers aboard each aircraft compare the data and identify conflicting flight paths, he said.

"When a conflict is found, the two aircraft coordinate their escape maneuvers, and time them to begin at the last possible instant to avoid the collision,” he said. “Auto ACAS returns control to the pilot as soon as the aircraft begin to separate, typically in a second or two."

This flight continued a build-up testing process including ground simulation and single-ship flights against computer-generated, "virtual" targets, according to Markman.

"These targets were produced by a flight simulator on the ground and connected to an identical data link," he said. "In the air, the test aircraft responded to the simulated target as if it was a real aircraft and maneuvered to avoid it. This technique allowed engineers to verify that the computer algorithm worked properly and produced correct escape maneuvers without putting the aircraft at risk.

"The miss distance for this flight was intentionally set high," Markman said. "As pilots and engineers gain confidence in the system's operation, they gradually will decrease the distances."

An operational system should allow miss distances of only a few hundred feet, just enough to prevent the collision, he said.

The test program will fly additional flight-test sorties involving the two F-16s.

Accepting an automatic system that takes control from the pilot has been a major concern to engineers developing the Auto ACAS, according to Less. He said engineers writing the software and developing the test process understand pilots' concerns for such an automated system.

"Once the system is fully tested and implemented, any pilot who experiences an Auto ACAS activation will know that the system probably just saved his life," Less said. "I have no problem with that under such a situation, and I believe that Auto ACAS will be accepted by the fighter community."

The system includes modes to account for formation flight, allow un-piloted air vehicles to avoid piloted vehicles and use sensor inputs to avoid a collision with other aircraft not equipped with Auto ACAS, he said.

"This first Auto ACAS flight was the result of two years of hard work by dozens of engineers and test pilots from many government organizations and industry participants," said Don Swihart, AFRL Air Vehicles Directorate program manager. "Their efforts will result in many lives saved every year and reduce the loss of valuable military aircraft." (Courtesy of Air Force Materiel Command News Service)