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VISTA F-16 will test airborne safety system

February 11, 2003 (by Lieven Dewitte) - The U.S. Air Force Test Pilot School, with the support from neighboring NASA Dryden Flight Research Center, is breaking new ground with an innovative research project intended to help prevent midair collisions.
Flight testing of the Automatic Air Collision Avoidance System, known as Auto ACAS, is scheduled to take off in March. Testing could prove the potential of this revolutionary concept; its ability to see and avoid aircraft on an airborne collision course.

This project is designed as a four-session technology evaluation planned to last through July. Session 1, in the March timeframe, is a systems check -- a chance to demonstrate that the Auto ACAS can be properly incorporated into an aircraft and work with all other systems. Session II, proposed for May, is the initial data-collection phase using the Variable-stability, In-flight Simulation and Test Aircraft F-16 to fly against a virtual target.

Session III, projected for June, is a second systems check using a production F-16 Fighting Falcon from Eglin Air Force Base, Fla.

Session IV, anticipated for July, is the end result -- an opportunity to test Auto ACAS in scenarios using both the VISTA and a production F-16.

Throughout these four sessions, TPS officials will conduct approximately 30 missions, each one engineered to test the Auto ACAS design.

Auto ACAS is an algorithm -- a set of instructions and computer code, explained Maj. Jim Less, TPS Auto ACAS project pilot. Developed by Boeing and Saab, the algorithm decides when an avoidance maneuver is required; it predicts the recovery flight path, evaluates other aircraft flight paths and determines the best escape maneuver. The auto pilot executes the avoidance maneuver based on the aircraft's limits and disengages as soon as the flight paths deconflict.

"Basically, the algorithm is doing the 'see and avoid'," said Mark Skoog, NASA Dryden Auto ACAS technical adviser and flight test director.

To safely test this capability without forcing two aircraft to enact a midair collision, the ACAS team will primarily use simulators.

"We'll have a computer on the ground running a simulation program," said Less. "This program will be connected to a data link, and the information will be sent up to the aircraft. The pilot will see a virtual airplane in his path through a helmet-mounted sight."

According to Skoog, the aircraft will think the simulated plane is real and try to avoid it.

"In other words, this simulation program will allow us to test Auto ACAS without putting people or aircraft in danger," said Skoog.

The simulation program will not only be used for safety reasons, but will also aid in test efficiency.

"It is easier to set up a virtual target in the exact right place at the exact right time, than it is to coordinate the positions of two separate aircraft," said Jeff Chen, TPS Auto ACAS project engineer. "Using a virtual plane, we will be able to accomplish more runs and collect more data points."

Auto ACAS is a big undertaking for the test pilot school, said Less.

"TPS doesn't usually tackle projects of this nature," he said. "We are ultimately involved because the school owns a one-of-a-kind F-16 reserved for curriculum sorties and projects."

The VISTA F-16 has a number of extra computers with the ability to change the aircraft's flying qualities, as well as the displays and electronics, explained Less. Also, Auto ACAS can be directly loaded from a computer into the VISTA Simulation System. These unique characteristics make this aircraft critical to the ACAS program.

With the VISTA's ability to maneuver like a variety of aircraft, and with the generic design of the ACAS algorithm, this program is getting a lot of attention from the unmanned aerial vehicle community, he said.

"At some point during testing, we are going to the fly the VISTA as a UAV in order to demonstrate Auto ACAS's versatility -- a quality many are interested in," said Less.

The Swedish government has expressed its interest by coming on board as an equal partner in the effort.

"At $14 million, the Swedes are funding half the program, while the Air Force Research Lab is sponsoring the U.S. portion," said Less.

The Swedish Government's involvement stems from an earlier cooperative venture on the Advanced Concept Technology Demonstration of the Automatic Ground Collision Avoidance System.

"When the Auto GCAS program concluded in 1999, the Swedes wanted to embark on another joint project," said Skoog. "So we started looking into Auto ACAS. The first official contract and design was produced ... in October 2000."

In the end, this product will be both Swedish and U.S. Air Force property.

"It is government-owned software, and will be available for use by any government agency," explained Skoog.

This does not mean TPS testing will result in the actual production of the system.

"We are out to prove an idea, prove that Auto ACAS works," said Less. "This is the very beginning -- baby steps. If we can help prevent midair collisions, we can eliminate a lot of fatalities and loss of aircraft."

Unfortunately, midair collisions do occur.

"The U.S. military probably has five or six per year," Less added, "and we'd like to bring those numbers down. Although there's a lot more work to be done, saving lives is well worth the effort and the cost."