The U.S. aviation group charged with developing standards to enable unmanned aircraft to fly in unrestricted airspace has completed the first documents for key systems, but cautions they are limited in scope and application.
RTCA Special Committee (SC) 228 has released interim minimum operational performance standards (MOPS) for the detect-and-avoid (DAA) system and command-and-control (C2) data link. Final document release is planned for 2016, after verification and validation testing of system performance.
SC-228 was formed in 2011 after the disbandment of SC-203, an earlier group formed in 2004 to define overarching standards for UAS but discontinued because of lack of progress. SC-228 comprised nearly 500 members from government and industry.
The MOPS focus on an initial scenario: civil unmanned aircraft flying to and from Class A controlled airspace (above 18,000 ft.) under instrument flight rules. The DAA MOPS does not apply to small UAS (below 55 lb.) flying below 500 ft. The C2 MOPS applies to C- and L-band links, but not satcom.
The initial DAA MOPS will enable launch and recovery within Class D, E and G airspace, but excludes surface operations, flight within the airport visual flight rules (VFR) traffic pattern and operations in Class B or C airspace around airports. Operations in Class A and special-use airspace are outside SC-228’s scope.
The DAA MOPS specifies a collection of sensors on the UAS to detect other cooperative and uncooperative aircraft and software to provide the pilot in the ground control station with awareness of proximate traffic and suggest guidance on remaining well clear of other aircraft and avoid collisions.
The sensors are active Mode S surveillance and Automatic Dependent Surveillance–Broadcast (ADS-B) to detect aircraft with transponders and TCAS 2 collision-avoidance systems; and radar to detect other aircraft and validate ADS-B. A separate interim MOPS for the air-to-air radar also has been released.
The DAA MOPS include a control-station standard for controls and displays that allow the pilot-in-command to transit through Class D and E aircraft to/from 18,000 ft. and Class G uncontrolled airspace. The DAA specification allows both automatic and manual modes, but pilot-in-the-loop is the minimum with automatic and pilot-on-the-loop as optional.
The C2 MOPS, meanwhile, define the minimum performance standards for the control and non-payload communications data link. Functions include sending commands to the UAS, receiving information from the onboard DAA system and supporting pilot-to-ATC communications.
The system includes airborne and ground-based radios and antennas operating at 960-1164 MHZ (L-band) or 5030-5090 MHz (C-band). RTCA says the MOPS differ from other standards in that they have to include the propagation path between the ground and airborne radios.
Testing to support development of the DAA and C2 standards already has been conducted by NASA, the Air Force Research Laboratory and others. In September, NASA completed a third phase of intruder-encounter testing with its Ikhana UAS (General Atomics Predator B) equipped with a General Atomicsair-to-air radar, BAE Systems ADS-B and Honeywell TCAS.
According to the interim MOPS, the next phase in standards development will establish DAA system requirements needed to extend operations in Class E and G beyond transiting the airspace, and may include avoidance of other hazards such as terrain and weather.
“Further requirements will be developed to enable operations in the airport VFR traffic pattern or in Class B and C airspace,” the MOPS say. “Finally, requirements will be investigated that will permit UAS to accept visual separation clearances, conduct taxi operations and perform automatic DAA maneuvers.” Phase 2 of the C2 MOPS development would bring in satcoms.
Source: Aviation Week