UAS in the NAS

Introduction

Unmanned aircraft systems (UASs) are proliferating worldwide over the last decade as their applications can bring about numerous benefits as opposed to traditional ways of doing things. However, in order to unleash their full potential, the sense and avoid (SAA) systems incorporated into the UASs must be able to demonstrate its ability to detect obstacles that are considered potential collision hazards in common airspace, and subsequently perform the required maneuvers to avoid any collision. In manned aircraft, transponders, radar and more importantly, the visual sight of the onboard human pilots to “see and avoid” are depended upon (Yu & Zhang, 2015). However, the absence of a human pilot in an unmanned aircraft necessitates the need for SAA systems to ensure safety in autonomous operations.

Manned vs Unmanned separation

There are significant differences in the operations of manned and unmanned aircraft. According to Austin (2010), manned aircraft which are more than 5,700kg or are authorized to carry more than 19 passengers, have transponders incorporated in traffic collision and avoidance system (TCAS). They transmit ADS-B signals to interrogate oncoming aircraft and obtain their range and bearing. At the same time, they can be flown under visual flight rules (VFR) or instrument flight rules (IFR). However, it is not always possible to incorporate such technologies into all types of UASs due to their equipment costs, weight and spatial requirements. 

Depending on the type of airspace, the separation requirements of aircraft differs. In controlled airspace, air traffic controllers give instructions to pilots of manned aircraft to keep a certain vertical and horizontal distance from other aircraft in the vicinity using radar (Planefinder, 2016). For UAS, onboard sensors, such as electro-optics, radar, or laser technology such as LiDAR, need to be incorporated and be able to detect other users in the proximity in order to avert any collision. However, since there is no pilot for UAS, one problem with such techniques is the inherent latency of the data link for any ground operator to receive the image and make corrective actions in any impending collision scenario.

Size and Type of UAS

            The airspace in which the UAS is allowed to operate will depend on its type and size. Depending on the certification of authorization from FAA in U.S., groups 1 and 2 small UASs may not have adequate payload capability to carry SAA equipment, and therefore may only be able to operate with LOS operation in uncontrolled airspace under 400 feet (FAA, 2016). Larger UASs, such as those in groups 3 to 5, may have sufficient payload capabilities to carry SAA equipment and therefore their integration into NAS may be made easier. Since different platforms (fixed wing, rotary, etc.) have different speed capabilities, UASs such as fixed wing types that can fly at faster speeds compared to rotary platforms, will require more robust SAA equipment to mitigate the effects of signal propagation latency and reaction times for obstacle avoidance.

Future Technology

            NASA, in collaboration with FAA, have recently announced the development of new technology that may enable large UASs to fly in the same airspace as manned aircraft (NASA, 2016). Tested extensively on the Predator B UAS, it has also shown to improve situational awareness using existing FAA infrastructure (NASA, 2016). With such progress in SAA technologies, other major challenges such as developing a robust communication, control and command system, and promulgating comprehensive regulatory standards will certainly path the way for full UAS integration into NAS soon.

References

Austin, R. (2010). Unmanned aircraft systems: UAVs design, development and deployment. West Sussex, UK: John Wiley & Sons.

FAA (2016, June 21). Summary of small unmanned aircraft rule (Part 107). Retrieved from https://www.faa.gov/uas/media/Part_107_Summary.pdf

NASA (2016, February 26). NASA licenses new communication technology for unmanned aircraft. Retrieved from http://www.nasa.gov/centers/armstrong/news/newsrelease/2016/16-03.html

Planefinder (2016). Radar separation in air traffic. Retrieved from https://planefinder.net/about/radar-separation-in-air-traffic/

Yu, X., & Zhang, Y. (2015). Sense and avoid technologies with applications to unmanned       aircraft systems: Review and prospects. Progress in Aerospace Sciences, 74, 152-166.    doi:10.1016/j.paerosci.2015.01.001