As Unmanned Aerial Systems (UAS) become more prevalent in the United States, a safe and effective method of National Airspace System (NAS) integration is needed to prevent stifling the new industry. The method should include Group 1 through 5 UAS and all varieties of aircraft configuration.
Figure 1. US Department of Defense UAS group descriptions. Reprinted from DoD UAS Airspace Integration Plan , by the UAS Task Force, 2011.
Understanding the Problem
The Federal Aviation Administration (FAA) is charged with maintaining control of the NAS, and does so with operating regulations, operator qualifications, and airworthiness certifications (FAA, 2016). The Department of Defense (DoD), commercial, and public research entities require access to the NAS for numerous missions, however FAA regulation has lagged UAS industry growth, creating a roadblock for many military and civil operations. The root of the problem lies in safe traffic separation between manned and unmanned aircraft, all with a wide variety of equipage standards. In airspace classes A and B, responsibility for separation lies with air traffic control (ATC) using primary and secondary radar systems. In airspace classes C through G, a UAS will face the challenge of integrating with optionally or non-participating aircraft. Instrument or visual flight rules (IFR or VFR) overlay additional considerations. Under IFR, aircraft are separated by positive (ATC personnel) or procedural control (published departure, arrival, or approach procedures). Under VFR, pilots are responsible for their own separation, optionally participate with ATC depending on the airspace class, and are the most challenging airspace user for UAS to share with. The following solutions encapsulate a phased approach that starts with systems technologically closer to NAS access and working towards full UAS access.
IFR Solution
This solution is most readily implemented with Group 4 and 5 UAS, as many of them already meet (or have the space and power available for) the IFR equipment requirements in Federal Aviation Regulation (FAR) 91.205 (FAA, 2009). Medium and high altitude UAS would transition to Class A airspace using procedural control measures (such as a climb corridor) recommended by the DoD UAS Integration Task Force (2011) that would separate non-participating manned aircraft by charting the control measures as special use airspace. Once above FL180, UAS would not differ from manned aircraft in operation or control. One UAS specific condition is loss of command and return links. Large UAS have robust lost-link programming capabilities which would be leveraged to maintain the aircraft in a safe and predictable state. In the terminal environment, lost-link UAS would follow a predetermined path similar to a missed approach procedure. During en route phases, lost-link UAS would follow either a path provided in a procedure similar to a Standard Terminal Arrival, or fall back on the same guidance for manned aircraft that lose contact with ATC (maintain last assigned, then expected, then filed). In any case, the burden of ensuring safe lost-link separation would rest with an appropriately trained and certified UAS pilot. This IFR solution has the benefit of requiring very little aircraft modification, can be implemented with today’s technology, and allows large UAS to access the NAS soonest in order to accomplish critical missions and begin adding to the collective knowledge base. The costs are increased workload on air traffic control, administrative functions to create the procedures given above, and establishment of additional Class B airspaces in areas with high UAS traffic.
VFR Solution
A VFR solution would allow UAS access to all airspace classes in the NAS, but is the most difficult to implement technologically. Significant research has been done to allow UAS to satisfy the “see and avoid” FAA requirement for VFR flights. The most successful to date has been demonstration of autonomous and pilot directed collision avoidance using a fusion of Automatic Dependent Surveillance-Broadcast (ADS-B), Traffic Collision Avoidance System (TCAS), and onboard air-to-air radar. This allows separation from close range TCAS-equipped aircraft, close range ADS-B/Out-equipped aircraft with onboard ADS-B/In functions, and non-participating aircraft. Additionally, a UAS equipped with a Universal Access Terminal would receive traffic and weather data from ground stations, adding redundancy. The only shortfall of such an all-inclusive system is the cost in size, weight, and power supply which would exclude Group 3 and below vehicles. UAvionics has marketed a micro ADS-B receiver weighing only 1.5 grams that provides autopilots or ground control stations with participating traffic information within 100 miles (sUAS News, 2016). The most promising solution for separating light UAS from non-participating traffic lies in vision based systems that combine multi-spectral sensors with image processing algorithms to detect moving objects (Novik, 2014). The challenge vision based systems will face is providing the same detection probability as a human pilot in an extremely wide range of ambient lighting and atmospheric conditions. For Group 1 UAS, even vision systems and micro receivers may impose an unacceptable sacrifice in payload. Since they weigh less than 20lbs, a risk analysis should be conducted to determine the probability of collision with manned aircraft and whether the consequences would exceed that of bird strikes.
Conclusion
This short essay has defined the challenging problem of operating manned and unmanned traffic in the NAS in the context of airspace classes and flight rules. The DoD is poised to access the NAS with large UAS, as it has established internal practices to satisfy the technology, training, and certification needed for integration. Rapid integration of these assets will not only accomplish vital defense, training, and disaster response missions, but pave the way for commercial and public operations. Technical solutions for lightweight UAS were summarized, along with the inspiration to conduct risk analysis, since a 100% perfect solution may not be required and will likely constrain development.
References
Federal Aviation Administration. (2016). National Airspace System. Retrieved November 10, 2016, from http://www.faa.gov/air_traffic/nas/
Federal Aviation Administration. (2009, August 21). Federal Aviation Administration. Retrieved November 10, 2016, from http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgFar.nsf/FARSBySectLookup/91.205
Federal Aviation Administration. (2016, May 10). Equip ADS-B Research. Retrieved November 11, 2016, from https://www.faa.gov/nextgen/equipadsb/research/
Merlin, P. (2015, January 25). NASA, FAA, Industry Conduct Initial Sense-and-Avoid Test. Retrieved November 11, 2016, from http://www.nasa.gov/centers/armstrong/Features/acas_xu_paves_the_way.html
Novick, D. (2014, January). Image Processing Primer Document for Autonomous Vehicle Competitions. Retrieved November 11, 2016, from http://www.robotx.org/
SUAS News. (2016). UAvionix Introduces Micro ADS-B Receiver For Small Drone Collision Avoidance - sUAS News. Retrieved November 11, 2016, from http://www.suasnews.com/2016/04/43057/
UAS Task Force. (2011, March). (United States of America, Department of Defense, Airspace Integration Integrated Product Team). Retrieved November 7, 2016, from http://www.acq.osd.mil/sts/docs/DoD_UAS_Airspace_Integ_Plan_v2_(signed).pdf
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