UAS in the National Airspace System

As the number of UAVs in civilian airspace continues to increase at a rather rapid rate, consideration for collision avoidance is critical not only with structures but with manned aircraft as well. The development of the collision avoidance technology plays an imperative role in the integration process of UAS in the NAS, which has yet to be successfully achieved. Researching the progression of the technology has proven to be as compounded as the actual development and implementation itself.     
            Safety of the civil airspace is the challenge that UAS have with integration into the NAS. In 2014, the Federal Aviation Administration (FAA) reported approximately 25 near-midair collisions reported by ATC, private pilots, and commercial pilots in or around airports in the span of five months (Whitlock, 2014). The development of collision avoidance technology is imperative for NAS integration as well as enabling growth in the UAS industry.  Researches at the MITRE Corp. indentified a generic process model for developing collision avoidance technology. The model consists of a five-step process where:
1) Aircraft uses surveillance to sense other aircraft
2) Risk is identified
3) Appropriate avoidance maneuver is determined
4) Maneuver is performed and lastly
5) UAV returns to the original course (Lacher, Maroney, & Zeitlin, 2007). 
Utilizing current technology such as ADS-B or TCAS, which will be discussed in more detail later in this study, is an option for monitoring and maintaining separation while new technology or partnering with current technology such as that being used by NASA and their Ikhana UAS is another possible route. The Ikhana UAS, following the five-step process, uses a prototype radar system consisting of three primary Detect-and-Avoid (DAA) sensors working together with airborne and ground-based computers (National Aeronautics and Space Administration [NASA], 2015).
            The size of the UAV is proving to be challenging, as the smaller UAVs are limited in payload capacity. With the increase in development of micro and nano UAVs, the limitation to using traditional methods such as radar is drastically increased and cause for concern (SkyTech, 2016). Speed capabilities of the UAV also contribute to the limiting compatibility of collision avoidance technology. Detecting an extremely slow aircraft is difficult in and of itself, but detecting a high speed UAV “requires a much quicker reaction time from sense and avoid technology in order to avoid collisions, thus creating an even greater hurdle to implementing the technology” (SkyTech Event, 2016). So the complexity in collision avoidance design is coupled with the FAA requirements as well as compatibility with the vast number of different UAS designs that currently exist. 
            Technology currently being utilized by manned aircraft for collision avoidance is the Automatic Dependent Surveillance-Broadcast (ADS-B) or the Traffic Collision Avoidance Systems (TCAS). Both systems transmit aircraft information such as altitude, distance from other aircraft, and speed while operating independently from the ground based Air Traffic Controller (ATC). ADS-B is a satellite-based surveillance system that transmits the aircrafts information to Air Traffic Controller (ATC) displays and also to nearby aircraft (Federal Aviation Administration [FAA], 2016). TCAS Processors us pressure altitude, radar altitude, and isolated aircraft status inputs to provide radar depiction to other aircraft and ATC for collision avoidance alerting (FAA, 2011). Even as these systems provide adequate collision avoidance for manned aircraft, the disadvantage for UAVs is that the equipment will prove obsolete until all aircraft are equipped with them so in the meantime research on other options is being carried out (SkyTech Event, 2016).
            In summation, the complexity of developing new or utilizing current collision avoidance technology is high and is intertwined with compatibility requirements and FAA regulations. Safety of the NAS is a huge driving force for implementation of the technology for the goal of the integration into civil airspace.  New technology is currently being explored by agencies such as NASA and has been exhibited with successful flights and avoidance maneuvers of the Ikhana UAS. Current technology such as ADS-B and TCAS are options but will not be effective until every aircraft, manned and unmanned, is equipped with the technology and they are adjusted to be compatible with UAVs of various sizes and speeds. The complex and exciting nature of this technology makes for thrilling aspirations and flight tests but unfortunately does not delay the dire need to successfully integrate UAS into the NAS sooner rather than later.
  
References
Federal Aviation Administration [FAA]. (2011. February 28). Introduction to TCAS II Version 7.1. Retrieved from http://www.faa.gov/documentLibrary/media/Advisory_Circular /TCAS%20II%20V7.1%20Intro%20booklet.pdf  
Federal Aviation Administration [FAA]. (2016, July 27). Automatic Dependent Surveillance-Broadcast (ADS-B). Retrieved from http://www.faa.gov/nextgen /programs/adsb/ 
Lacher, A., Maroney D., & Zeitlin, A. (2007). Unmanned Aircraft Collision Avoidance-Technology Assessment And Evaluation Methods. The MITRE Corporation. Retrieved from https://www.mitre.org/sites/default/files/pdf/07_0095.pdf
National Aeronautics and Space Administration [NASA]. (2015, September 16). NASA, Industry Complete Third Phase of UAS Flight Testing. Retrieved from https://www.nasa.gov/centers/armstrong/features/detect_and_avoid.html
SkyTech Event. (2016). Sense and Avoid The Technology to Watch. Retrieved from http://www.skytechevent.com/#!Sense-and-Avoid-The-Technology-to-Watch/c1leh/559bb52c0cf2361ae7868374
Whitlock, C. (2014, November 26). Near-collisions between drones, airliners surge, new FAA reports show. The Washington Post. Retrieved from https://www.washingtonpost.com /world/national-security/near-collisions-between-drones-airliners-surge-new-faa-reports-show/2014/11/26/9a8c1716-758c-11e4-bd1b-03009bd3e984_story.html


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