AVOIDING AIRCRAFT IN THE SKY GLOBAL TEAM TESTS SOFTWARE.

Byline: Jim Skeen Staff Writer

EDWARDS AIR FORCE BASE - An international test team is wrapping up a series of tests of software intended to save lives by automatically steering fast-moving, high-performance jets away from collisions with other aircraft.

Two F-16 fighters flew a variety of potential collision courses to see if the Automatic Air Collision Avoidance System, or Auto ACAS, would separate the aircraft.

Each time the system maneuvered the aircraft without action by the pilot. In one test, the jets flew nearly head-on, each flying over 500 mph. The aircraft came within 200 feet of each other.

``We have a lot of numbers to go through,'' said Mark Skoog, the program's flight test director. ``Things worked. We didn't hit one another, and we still have two jets to show for it.''

The intent of the $12 million program is to develop technologies to prevent accidents like one in 1987 in which a fast-moving Edwards T-38 trainer jet 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 midair collisions involving both conventional aircraft and UAVs - unmanned aerial vehicles, the computer-controlled or remote-controlled craft like the Global Hawk 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.

``Auto ACAS, by comparison, waits until the last possible instant - until after the pilot missed his last chance to avoid a collision,'' said Steve Markman, program flight test director at the Air Force Research Laboratory's Air Vehicles Directorate. ``When Auto ACAS takes control, it performs an aggressive maneuver to avoid the collision, then returns control to the pilot.''

Auto ACAS is described as ``see-and-avoid.'' For the ``see'' portion of the testing, Edwards test aircraft used a data link to exchange information on their location, direction and speed.

The Air Force is trying to develop optic sensors that would allow pilots 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 is trying 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.

A total of 10 flights were flown with both F-16s, with all but one flight involving ``cooperative'' targets. In a cooperative situation, data is passed between the aircraft via a data link, and both aircraft maneuvered cooperatively to avoid the collision.

In one noncooperative flight, no information was exchanged and one of the fighters had to monitor the other aircraft with a radar.

Prior to the test flights, more than 1,000 simulations were conducted on the ground and there were close to 300 flights in which one aircraft flew against ``virtual'' target aircraft generated by a computer on the ground.

The testing of Auto ACAS will continue with one of the F-16s simulating an unmanned aircraft. The aircraft will fly against a virtual F-16 target. The test team plans to conduct tests of the aircraft against multiple virtual targets, as well.

Both the military and the National Aeronautics and Space Administration are interested in a see-and-avoid capability for unmanned aircraft.

The military is interested in flying such aircraft in formation and in the possibility of air refuelings for such aircraft.

NASA is about to start an effort called ``Access 5,'' in which the agency will look at what technologies, procedures and policies need to be in place to allow unmanned aircraft to share the national airspace. Unmanned aircraft are now limited to restricted ranges.

The test team includes the Air Vehicles Directorate at the Air Force Research Laboratory at Wright-Patterson Air Force Base, Ohio; Sweden's Forsvaret Materielwerk; NASA Dryden Flight Research Center; and the Test Pilot School at Edwards, which ran the flight tests.

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.

Jim Skeen, [phone]

james.skeen(at)dailynews.com