The aviation standards organization supporting the FAA in developing the technical criteria for allowing large unmanned aircraft systems (UAS) to fly in civilian airspace has achieved a “significant milestone” in that effort. Preliminary requirements for airborne collision avoidance and communications with the ground have been completed, RTCA announced on October 2.

The “interim” documents establish minimum operational performance standards—or MOPS—for “detect and avoid” and command and control, core functions the FAA will require for unmanned aircraft to fly with manned aircraft in unrestricted airspace. RTCA, formerly known as the Radio Technical Commission for Aeronautics, expects to produce final standards next summer after verification testing of the requirements.

RTCA standards are incorporated by the FAA in its regulatory and advisory documents, and provide guidance to designers and manufacturers in building and certifying equipment.

Under RTCA’s auspices, a committee of industry and government experts designated Special Committee 228 (SC-228) has been at work since 2013 developing detect-and-avoid and command and control, or C2, requirements for large unmanned aircraft—not the small drones that have been much in the news lately. The resulting interim documents “focus on an initial scenario: the operation of civil unmanned aircraft ‘to’ and ‘from’ Class A airspace” the layer of airspace above 18,000 feet, RTCA said.

“This is a historic milestone on the path to integrating UASs into the airspace in a safe and efficient manner,” RTCA president Margaret Jenny said of the preliminary standards. “It would not have been possible without the hard work and dedication of the leaders and participants of SC-228, as well as the guidance and support of the Department of Defense, FAA and NASA.”

The RTCA release followed a September 16 announcement by NASA that it has completed a third phase of detect-and-avoid flight tests of its Ikhana unmanned aircraft at Armstrong Flight Research Center, part of Edwards Air Force Base, Calif. Those tests, which resume next spring, are informing the standards development effort.

NASA, the FAA and industry partners have flown the five-ton Ikhana, a variant of the General Atomics MQ-9 Reaper, in “scripted encounters” with manned aircraft over the Mojave Desert. “Depending on the specific scenario, either Ikhana detected one or more approaching aircraft and sent an alert to its remote pilot to take action, or Ikhana itself took action on its own by flying a programmed maneuver to avoid a collision—an aviation first,” NASA said.

The Ikhana was fitted with a detect-and-avoid system consisting of a prototype General Atomics electronically scanned radar, an automatic dependent surveillance-broadcast transponder from BAE Systems, and a second-generation Honeywell traffic alert and collision avoidance system, or TCAS, computer. Honeywell also provided software that fused the operations of the three sensors and a specially instrumented King Air “intruder” aircraft for the scripted encounters.

“That ends that particular phase, but we’ve got some other work, both internally funded as well, that we’re going to continue to push,” said Bob Witwer, Honeywell Aerospace vice president for advanced technology. “I think both we and our customers are really excited about the product space that we’re targeting.”