UAS Operations Above 400 Feet

By Patrick C. Miller | February 12, 2015

The news was late in coming, but what the U.S. Federal Aviation Administration, NASA, General Atomics and Honeywell accomplished in flight tests during the last two months of 2014 was truly groundbreaking in terms of opening the U.S. skies to the commercialized use of unmanned aerial systems.

Much attention has been focused on the use of small UAS below 400 feet where the early commercial applications of the technology such as package delivery are likely to occur and, in the case of aerial videography, are already occurring.

However, the heavy hitters in the UAS world have their sights set on operating larger, longer-range piston-powered, turbine-powered and even solar-powered unmanned aerial vehicles (UAV) in the same airspace as manned commercial and civil aircraft. Before that can happen, effective and reliable sense-and-avoid technology must be developed to keep manned and unmanned systems safe distances apart.

This is why the flight tests conducted last November and December at the NASA Armstrong Flight Research Center at Edwards, California, are of vital importance to integrating UAS into the national airspace. NASA’s Ikhana research UAV—a Predator B converted for civilian use—was fitted with the FAA's experimental Airborne Collision Avoidance System for Unmanned Aircraft (ACAS Xu), which uses a sensor fusion algorithm developed by Honeywell.

The Ikhana flew 170 separate encounters with two manned aircraft and a General Atomics Predator B—never facing more than one “intruder” aircraft at a time. One of the milestone accomplishments was the first successful collision avoidance test between two UAVs.

I spoke to Heather Maliska, deputy project manager at Armstrong, and Mauricio Rivas, NASA’s Ikhana project manager, about the flight testing. Rivas told me the Ikhana was never required to make any abrupt or dramatic maneuvers to avoid a conflict with an aircraft playing the part of an intruder.

Maliska said there were a few instances in which the Ikhana responded to an encounter that caused her to think about the reaction, but understanding how the algorithm works provided an explanation to the event. The flight tests will also give the FAA a wealth of data to study, she noted.

I also spoke to Brandon Suarez, a project engineer with General Atomics, about the tests. He emphasized that although the sense-and-avoid technology is designed for UAS, there is a pilot on the ground controlling the aircraft. And just like a manned aircraft, the UAV pilot can communicate with FAA air traffic control to put the aircraft on a safe course in the event it needs to maneuver to avoid a conflict.

There will be more flight testing of the FAA’s ACAS Xu sense-and-avoid system this year and next year as the Radio Technical Commission for Aeronautics (RTCA) Special Committee 228 works to develop minimum operational performance standards for UAS. Maliska stressed that finalizing these standards is an essential component in fielding technology that enables the FAA to safely integrate the UAS operating above 400 feet into the national airspace.

While the FAA is frequently criticized for dragging its feet on UAS commercialization, a great deal of important work is being done and positive results are being accomplished without being widely recognized. Let’s hope the agency continues down a path that succeeds in opening the entire sky to the safe use of UAS, a path that’s generating positive results.