ACSS, NASA plan UAS collision avoidance flight tests this summer

By Patrick C. Miller | March 30, 2017

Phoenix-based Aviation Communication & Surveillance Systems (ACSS) will this summer conduct another round of flight tests with its aircraft collision avoidance system for unmanned aircraft (ACAS Xu) at Edwards Air Force Base in California.

Late in 2016, ACSS—an avionics systems developer—worked with Northrop Grumman Corp., the Federal Aviation Adminstration (FAA), the Massachusetts Institute of Technology (MIT) Lincoln Laboratory and the Johns Hopkins University Applied Physics Laboratory to conduct successful flight tests at the Mojave Air and Space Port in Mojave, California.

Greg Boerwinkle, unmanned aircraft systems (UAS) program manager for ACSS, said flights with NASA from June to August this year will test an upgraded version of the algorithms and software developed for ACAS Xu by the Johns Hopkins lab.

“I think this is really going to open up a whole new avenue for the industry as far as being able to fly in the national airspace,” he said. “It will start with large UASs and evolve down to smaller UASs as we develop hardware that can be smaller and consume less power. For some of the medium-sized UASs, you’ll see this technology enabled more and more for commercial operations.”

The FAA is developing ACAS as a successor to the Traffic Alert and Collision Avoidance Warning System (TCAS) to support the objectives of its Next-Generation Air Transportation System Program (NextGen). ACSS has developed two ACAS variants for manned aircraft and the ACAS Xu for UAS.

All ACAS variants detect conflicts with intruder aircraft, issue resolution advisories and coordinate maneuvers with other collision avoidance systems. ACAS Xu is designed for UAS and other vehicles with new surveillance technologies and different performance characteristics.

Last year’s ACAS Xu flight tests were flown using Northrop Grumman’s optionally piloted Firebird aircraft with encounters against manned aircraft serving as intruders.

“For safety reasons, the Firebird was flown with a pilot onboard,” Boerwinkle said. “Having a pilot really gives us good safety mitigation. For the most part, that pilot is hands-off, recording data and making sure that the encounters are set up properly.”

A number of pre-planned encounters were flown, ranging from simple head-on encounters to complex multi-aircraft turning encounters at different altitudes and geometries.

“We put our system through its paces to make sure that every possible combination of aircraft encounter is accounted for,” Boerwinkle noted. “These also include what are called blunders, which means that if a pilot in a manned aircraft is not responding correctly to an alert or a climb or a dive command, the system can still be robust enough to reverse the logic and ultimately create a correct outcome to avoid a collision.”

According to Boerwinkle, NASA will be responsible for test organization during the flights this summer which will involve multiple aircraft, multiple intruders and multiple UAS. An improved version of the algorithms and software known as ACAS Xu Run 3 will be tested with the goal of integrating the technology into ACSS avionics.

“Once we have that integration done, we’ll take it out to our partners at General Atomics and Northrup Grumman, test it in their labs, do ground testing on their aircraft and ultimately conduct flight testing on the aircraft to make sure that the algorithms are operating correctly, that all the interfaces are working and that we are getting the expected outcomes from the system.”

Boerwinkle noted that ACSS has many years of experience in developing avionics for manned aircraft.

“The technology is essentially the same that we used for TCAS for manned aircraft, transponders and ADS-B,” he explained. “We are modifying what we know to enable a new mission area, a new capability. The technology is not a revolutionary leap, but a natural evolution of known technology.”