In December 2020, the Federal Aviation Administration (FAA) announced the release of a new final rule, permitting operators of small unmanned aircraft systems (sUAS) to perform routine night operations. Public comments to the Notice of Proposed Rulemaking indicated potential safety concerns regarding a pilot’s ability to spot a low-altitude sUAS during nighttime conditions. Leveraging data from the FAA’s UAS Sighting Report Database, the research team evaluated the significance of aircraft encounters with UAS at night. Researchers conducted an inflight experiment in which 10 pilots performed an instrument approach to airport during nighttime conditions in which a multi-rotor sUAS presented a potential collision hazard. The sUAS was equipped with lighting visible for 3 miles with a sufficient flash rate to avoid a collision, as specified by the new regulation. Participants performed five approaches, with the sUAS flying different scripted encounter profiles. Participants were asked to indicate when they visually spotted the sUAS, with sighting data recorded via an onboard observer. Geolocation information from both the aircraft and sUAS were compared at the time of each reported sighting to assess visibility distance and orientation. The sUAS was successfully spotted during 30 percent (n = 12) of the testing passes. Hovering sUAS were spotted at the same rate as moving sUAS, however, sUAS in motion were spotted at a much greater range. Researchers noted disproportionately higher spotting rates occurred when the sUAS was oriented on the starboard side of the aircraft vs. the port side. It is believed that airport lighting systems may have obscured or otherwise camouflaged portside sUAS encounters. When asked to estimate distance to an encountered sUAS, most participants underestimated, perceiving the sUAS to be much closer than reality. Additionally, the researchers assessed the potential for the participants to initiate evasive maneuvers, based on the distance and closure rate of the aircraft and sUAS at the time of sighting. Based on the FAA’s Aircraft Identification and Reaction Time Chart, collision avoidance would only have been successful during 15 percent of encounters (n = 6). The research team recommends Remote Pilots employ vigilant traffic awareness during nighttime operations, and leverage use of ADS-B (In) technology and monitor Common Traffic Advisory Frequencies to maintain situational awareness—particularly when operating in proximity to airports.



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