Unmanned

Sagetech Demonstrates Successful Test of DAA System Using ACAS Algorithms

By Kelsey Reichmann | August 2, 2021
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Sagetech Avionics has completed a successful test of its detect and avoid (DAA) system that uses ACAS algorithms to provide collision avoidance for unmanned aircraft systems (UAS). (Sagetech)

Sagetech Avionics has completed a successful test of its detect and avoid (DAA) system that uses ACAS algorithms to provide collision avoidance for unmanned aircraft systems (UAS), the company announced on July 27. 

The technology was tested as part of a Phase 1 STTR contract from the AFWERX’s Agility Prime, Tom Furey, CEO of Sagetech told Aviation Today. The technology can be used in commercial or military applications to enable beyond visual line of sight (BVLOS) UAS flights. 

“What we're trying to do is put technology on the aircraft so that we can trust it to go where the operator can't see the environment that it's in and it can operate without a visual observer,” Furey said. “So aircraft can operate beyond visual line of sight of the operator right now, unmanned aircraft, but often the FAA requires them to have a visual observer, so somebody is always looking out for traffic around that drone. This technology will enable, and is capable right now of enabling, the drone itself to recognize traffic around it and to avoid it.” 

This technology uses the next generation of the Federal Aviation Administration’s (FAA) alert and collision avoidance system, TCAS, Furey said. TCAS uses transponder frequencies and Automatic Dependent Surveillance Broadcast (ADS-B) to coordinate between manned aircraft to avoid collisions. The new system, ACAS X, improves on TCAS technology and can be used by other types of aircraft. 

“TCAS is designed for, call it a 777 or an Airbus A320 or something like that, it provides cooperative collision avoidance, but it expects ground speed greater than 100 knots, it expects the ability of the aircraft to climate 2,500 feet per minute, and now you've got unmanned aircraft that can't do those things and helicopters have never been able to do those kinds of things,” Furey said. “So ACAS X has versions, not only ACAS XA, which is just like TCAS from for normal commercial aircraft or whatever, but it has ACAS XU that's been approved, and that's for a larger fixed-wing aircraft greater than 55 pounds.” 

Furey said that the FAA is also working on different versions of ACAS for UAS under 55 pounds — ACAS SXU — and electric vertical takeoff and landing (eVTOL) aircraft — ACAS XR.

During these demonstrations, Sagetech was able to work with the TCAS program office to implement ACAS XR logic onto a very small device, Furey said. 

“We have a small transponder and then an interrogator that validates ADS-B,” Furey said. “So this was the first time we were able to take all of that, put it in the air, and do a flight test to see how the logic is working.” 

Sagetech ran two different types of flight trials for this: manned and unmanned. They first trialed the technology on two manned Piper Archers with one aircraft’s pilot following guidance from the system that was relayed through a passenger, Furey said. 

“There's two types of warnings or commands if you will,” Furey said. “So the first is, if it recognizes that there's an aircraft that's a potential risk of collision but not anything imminent, it gives what's called a remain well clear advisory. So then the pilot...gets a warning that says hey you better remain well clear of this thing. So our device did that.”

The second command happens within what Furey calls “the well-clear bubble.” 

Sagetech's software provides traffic display and ACAS collision avoidance. (Sagetech)

“The logic defines a kind of an aspirin-shaped bubble around every aircraft that is its safety bubble called the remain well clear volume, and if it looks like that is going to be penetrated, then it gives what's called a collision avoidance maneuver or a resolution advisory that you now have to follow,” Furey said. 

The manned test was successful, so Sagetech moved onto unmanned testing with a UAV Factory Penguin C UAS, Furey said. The UAS, which is about 55 pounds, flew against a Cessna 172. 

“The system performed as expected, as well,” Furey said. “So, the system was put through multiple encounter sets. When expected, the system provided the ground control operator with the symbology that said ‘hey, you've got a potential collision, you should remain clear.’ Then, sometimes purposely, we drove that encounter set to that imminent collision situation where it gave the collision avoidance command that says you have to do this to avoid a collision. So in all cases, the logic appeared to do what it was supposed to.” 

Furey said one of the big takeaways from the demonstration was the ability to provide a much smaller system that could be used in smaller aircraft. 

“From our perspective what we proved is that we can appropriately shrink the size of these systems,” Furey said. “So a TCAS box might be the size of cinder block and weigh 10 or 15 pounds, you can't put that on a small drone.” 

Sagetech’s system was able to fit inside the Penguin UAS resembles a small box the size of an iPhone with a little computer attached, which Furey said will eventually be included inside the small box. 

This system can be used for commercial or military applications. Furey said the company is able to modify the system for military applications like including its military IFF product which is essentially an encrypted transponder that can tell a drone if an aircraft is friendly or not. 

Furey said the company is now working to incorporate new sensors on the DAA system like radar, EO/IO camera input, or acoustic input that could allow the system to recognize and avoid traffic even if the other aircraft is not equipped with a transponder. 

While Sagetech is working on improving its own products, Furey said that DAA technology is not the only critical technology involved in BVLOS flight. 

“The holy grail, right, is beyond visual line of sight flight of unmanned aircraft and collision avoidance, detect and avoid, is a critical technology for that,” Furey said. “We're also working to make sure that we can appropriately equip aircraft onboard with this technology, right, and that's because in theory, you could control all airspace from the ground, however, the challenges there are safety and risk. So not only is detect and avoid critical technology command and control is a critical technology.” 

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