{"references": ["Pham H., Smolka S. A., Stoller S. D., Phan D., Yang Junxing, \"A Survey on Unmanned Aerial Vehicle Collision Avoidance Systems\", Cornell University Library, August 2015.", "FAA Washington DC, \"Nextgen implementation plan\", US Department of Transportation, 2013.", "Strobel A., Schwarzbach M., \"Cooperative Sense and Avoid: Implementation in Simulation and Real World for Small Unmanned Aerial Vehicles\", International Conference on Unmanned Aicraft Systems (ICAUS), Orlando, FL, USA, May 27-30, 2014.", "Kim K.-Y., Park J.-W., Tahk M.-J, \"UAV Collision Avoidance Using Probabilistic Method in 3-D\", International Conference on Control, Automation and Systems, COEX, Seoul, Korea, October 17-20, 2007.", "Park J.-W., Oh H.-D., Tahk M.-J., \"UAV Collision Avoidance Based on Geometric Approach\", SICE Annual Conference 2008, Tokyo, Japan, 20-22 August, 2008.", "Fu Y., Soupin P., Yu X., Zhang Y., Cole P., \"Sense and Collision Avoidance of Unmanned Aerial Vehicles Using Geometric Guidance and Flatness Approaches\", IEEE International Conference in Unmanned Aircraft Systems (ICAUS), Denver, Colorado, USA, June 9-12, 2015.", "Lin Y., Saripalli S., \"Sense and Avoid for Unmanned Aerial Vehicles using ADS-B\", IEEE International Conference on Robotics and automation, Seattle, WA, May 26-30, 2015.", "Lin Y., Saripalli S., \"Collision Avoidance for UAVs Using Reachable Sets\", IEEE International Conference on Unmanned Aircraft Systems (ICAUS), Denver, Colorado, USA, June 9-12, 2015.", "Albaker B.M., Rahim N.A., \"Autonomous unmanned aircraft collision avoidance based on geometric intersection\", Internal Journal of the Physical Sciences Vol. 6(3), pp. 391-401, February 4, 2011.\n[10]\tSaha S., Natraj A., Waharte S., \"A Real-Time Monocular Vision Based Frontal Obstacle Detection and Avoidance for Low Cost UAVs in GPS Denied Environment\", IEEE International Conference on Aerospace Electronics and Remote Sensing Technology (ICARES), Yogyakarta, 13-14 November, 2014.\n[11]\tBai H., Hsu D., Kochenderfer M. J., Lee W. S., \"Unmanned Aircraft Collision Avoidance using Continuous-State POMDPs\", Robotics: Science and Systems VII, Los Angeles, CA, USA, June, 2011.\n[12]\tRoelofsen S., Gillet D., Martinioli A., \"Reciprocal Collision Avoidance for Quadrotors Using On-Board Visual Detection\", IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Hamburg, Germany, September 28 \u2013 October 2, 2015.\n[13]\tRoelofsen S., Gillet D., Martinioli A., \"Distribute Deconflict Algorithm for Unmanned Aerial Vehicles with Limited Range and Field of View Sensors\", IEEE American Control Conference (ACC), Chicago, IL, July 1\u20133, 2015.\n[14]\tLai C.-K., Lone M., Thomas P., Whidborne J., Cooke A., \"On-Board Trajectory Generation for Collision Avoidance in Unmanned Aerial Vehicles\", IEEE Aerospace Conference 2011, Big Sky, MT, March 5-12, 2011.\n[15]\tYang X., Alvarez L. M., Bruggemann T., \"A 3D Collision Avoidance Strategy for UAVs in a Non-Cooperative Environment\", Journal of Intelligent & Robotic Systems, Volume 70, April, 2013.\n[16]\tMcfadyen A., Mejias L., Corke P., Pradalier C., \"Aircraft Collision Avoiodance using Spherical Visual Predective Control and Single Point Features\", Proceedings of IEEE/RSJ International Conference on Intelligent Robots and Systems, Tokyo, 2013.\n[17]\tBoyadzhiev K. N., \"Spirals and Conchospirals in the Flight of Insects\", The College Mathematics Journal, Volume 30, No. 1, January, 1999.\n[18]\tMcfadyen A., Mejias L., Corke P, Visual \"Serving Approach to Collision Avoidance for Aircraft\", 28th Congress of the International Council of the Aeronautical Sciences 2012, Brisbane Convention & Exhibition Centre, Brisbane, QLD, September 24-28, 2012.\n[19]\tTurner R., Lehmann R., Wadley J., Kidd D., Swihart D., \"Automatic Aircraft Collision Avoidance Algorithm Design for Fighter Aircraft\", Asia - Pacific International Symposium on Aerospace Technology, Jeju, Korea, November 13-15, 2012.\n[20]\tKochenderfer M. J., Holland J. E., Chryssanthacopoulos J. P., \"Next-Generation Airborne Collision Avoidance System\", Lincoln Laboratory Jounrnal, Volume 19, Number 1, 2012.\n[21]\tKochenderfer M. J., Chryssanthacopoulos J. P, Weibel R. E., \"A new approach for Designing Safer Collision Avoidance Systems\"\u00b8 Ninth USA/Europe Air Traffic Management Research and Development Seminar (ATM2011), Berlin, Germany, 2011.\n[22]\tOrefice M., Di Vito V., Corraro F., Fasano G., Accardo D., \"Aircraft Conflict Detection Based on ADS-B Surveillance Data\", IEEE Metrology for Aerospace, Benevento, Italy, 29-30 May, 2014.\n[23]\tOrefice M., Di Vito V., Garbarino L., Corraro F., Accardo D., Fasano G., \"Real-Time Validation of an ADS-B Based Aircraft Conflict Detection System\", AIAA SciTech 2015 Conference, Kissimmee, Florida, 5-9 January, 2015.\n[24]\tICAO, \"Rules of the Air\", Annex 2 to the Convention on International Civil Aviation, Tenth Edition, July, 2005.\n[25]\tMIDCAS-T-0017 \"D2.5.2-2 MID-air Collision Avoidance System (MIDCAS) Concept of Operations (CONOPS)\", 17 July, 2015."]}

This paper provides a description of a Collision Avoidance algorithm that has been developed starting from the mathematical modeling of the flight of insects, in terms of spirals and conchospirals geometric paths. It is able to calculate a proper avoidance manoeuver aimed to prevent the infringement of a predefined distance threshold between ownship and the considered intruder, while minimizing the ownship trajectory deviation from the original path and in compliance with the aircraft performance limitations and dynamic constraints. The algorithm is designed in order to be suitable for real-time applications, so that it can be considered for the implementation in the most recent airborne automatic collision avoidance systems using the traffic data received through an ADS-B IN device. The presented approach is able to take into account the rules-of-the-air, due to the possibility to select, through specifically designed decision making logic based on the consideration of the encounter geometry, the direction of the calculated collision avoidance manoeuver that allows complying with the rules-of-the-air, as for instance the fundamental right of way rule. In the paper, the proposed collision avoidance algorithm is presented and its preliminary design and software implementation is described. The applicability of this method has been proved through preliminary simulation tests performed in a 2D environment considering single intruder encounter geometries, as reported and discussed in the paper.