A Model of Human Harm from a Falling Unmanned Aircraft: Implications for UAS Regulation

This paper quantifies the human harm, in the form of fatalities and skull fractures, which could occur as a result of an unmanned aircraft falling from a height. The analysis is used to establish the maximum height at which an unmanned aircraft can be flown over people to achieve a level of safety consistent with the rate of ground fatalities from General Aviation. The maximum height is dependent on the aircraft mass and the population density of people on the ground below. The results are used to inform a critical evaluation of recent recommendations from the FAA-chartered “Unmanned Aircraft Systems (UAS) Registration Task Force (RTF) Aviation Rulemaking Committee (ARC)” and the “Micro Unmanned Aircraft Systems Aviation Rulemaking Committee”. The recommendations from these committees derive from assumptions that do not reflect the risks of flying over groups of people, and particularly over crowds. The New Zealand CAA’s rules allowing flight over people who have granted consent are also considered, and this paper recommends that maximum height limits should be specified even when consent has been granted. The New Zealand CAA, in some instances, grant approvals to fly over people without consent, and parachutes are one factor considered in granting such an approval. The ability of parachutes to effectively reduce the speed of descent is analyzed, and it is shown that for lighter aircraft a parachute may allow operation over relatively dispersed groups of people. Finally, UAS reliability is analyzed, and it is found that a 10 fold increase in reliability over that assumed by the UAS RFT ARC does not alter the maximum height at which an unmanned aircraft can be safely operated