ANTI-AVOIDANCE SYSTEM IN WORKS.

Byline: Jim Skeen Staff Writer

EDWARDS AIR FORCE BASE - An international test team is trying to save lives by keeping fast-moving, high-performance jets from colliding with other aircraft.

Their objective is an automatic system that detects an approaching aircraft, calculates whether it is on a collision course and then changes its own aircraft's course faster than a human pilot could.

``The system would take away control from the pilot temporarily and do it at the last instant,'' said program manager Don Swihart.

The effort is led by engineers from Wright-Patterson Air Force Base in Ohio and includes aircraft engineers from Sweden, which is splitting the $12 million cost with the U.S. military.

The intent is to prevent accidents like one in 1987 in which a fast-moving Edwards T-38 trainer collided with a civilian Cessna over the Tehachapi mountains, killing four people.

More recently, in October 1997, two men aboard a T-38 were killed over Edwards when their jet was struck by an F-16 fighter whose pilot had made a hard turn to avoid hitting a flock of birds.

Engineers say they're trying to prevent mid-air collisions involving both conventional aircraft and UAVs - unmanned aerial vehicles, the computer-controlled or remote-controlled craft like the GlobalHawk and Predator spy planes that the American military is finding increasing use for.

There are existing collision-avoidance systems, but they require action by the pilots, who consider the alarms the systems emit to be a nuisance for formation flying or dog-fighting training.

``We want a nuisance-free system for very aggressive flight by military pilots,'' said Mark Skoog, an engineer assisting the flight test program.

Called the Automatic Air Collision Avoidance System, or Auto ACAS for short, the system under development is described as ``see-and-avoid.''

For the ``see'' portion of the testing, Edwards test aircraft will use a data link, a sort of flying computer modem, to exchange information on their location, direction and speed.

The Air Force is trying to develop optic sensors that would allow aircraft to ``see'' all aircraft.

About 90 percent of the aircraft flying in the United States already have devices called transponders to share information about their course and speed with other aircraft.

The ``avoid'' testing will try out a set of computer instructions to see if the system can tell an aircraft to make the proper changes at the proper times to its direction.

``The aircraft use data links to exchange information, and Auto ACAS uses this data to evaluate flight paths, determine closing rate and range, and keep them from approaching closer than 200 feet,'' said Ba Nguyen, chief engineer.

Test officials believe it is possible to allow aircraft to pass as close as 50 feet.

The testing is being done with two F-16 fighters, in a program that involves testing each aircraft separately, first to make sure the software is working properly and then to pit the system against ``virtual'' aircraft generated by a signal from a ground station.

``It avoids a virtual aircraft in the same fashion as a real aircraft,'' Skoog said.

The aircraft will then be flown together, but at different altitudes to maintain safety.

The testing is expected to run through early August.

Researchers are looking at a follow-on program in which the system is put together with an automatic ground collision-avoidance system tested at Edwards in the 1990s. That system automatically pulls an aircraft up if a pilot comes too close to the ground.

The test team includes the Air Vehicles Directorate at the Air Force Research Laboratory at Wright-Patterson, Sweden's Forsvaret Materielwerk, and the Test Pilot School at Edwards.

Skoog is an engineer with NASA's Dryden Flight Research Center, but is participating in the program because of his previous work as an Air Force engineer on the automatic ground avoidance system.

Portions of the Auto ACAS development were contracted to Lockheed Martin Aeronautics, Fort Worth, Texas; Boeing Co., St. Louis, Mo.; Saab AB, Linkoping, Sweden; Birhle Applied Research, Hampton, Va.; and Veridian Engineering, Buffalo, N.Y., and Dayton, Ohio.