Long-standing assumptions about the risk to life from drones colliding with people on the ground have been “overly conservative” according to the latest study released by the Alliance for System Safety of UAS through Research Excellence (ASSURE). Hundreds of impact tests and simulations were carried out by the ASSURE research team to assess the injury potential of small UAS (sUAS) of different material properties and construction over an 18-month study period. The final report of the FAA-sponsored study, released 14 August 2019, found “the Post Mortem Human Surrogate (PMHS) testing and analysis of the injury data strongly support our previous study’s assessment that the Range Commanders Council (RCC) probability of fatality data is overly conservative and largely not applicable to elastic sUAS. The preliminary injury thresholds for sUAS head impacts developed in our earlier work were also overly conservative.” The report also recommends addition PMHS testing to develop more accurate probability-based injury risk curves, similar to those used by the automotive industry, but relevant to the impact characteristics of sUAS. In the meantime, it recommends the FAA use the automotive based injury criteria called out in this report, as well as previously developed risk thresholds that have been further developed in this study, to assess when additional operational risk mitigations are required to reduce the probability of serious injury.
The team’s new research findings and data will help inform the FAA and industry of operational limitations for sUAS when operating over people. It will also provide new data from which sUAS design specifications may be developed to further reduce risk to people and property on the ground.
The goal for the FAA study was to assess injury potential of various sUAS of different material properties and construction. The team conducted fixed-wing and multi-rotor sUAS failure flight testing and aerodynamic modelling, full anthropomorphic test device (ATD) impact testing, simplified head and neck only ATD impact testing, PMHS impact testing, ATD and human-body model impact simulations, and high-fidelity head and neck only impact simulations. Over 512 impact tests and simulations were conducted using 16 different multi-rotor and fixed-wing sUAS, as well as various objects and payloads (batteries, wood blocks, etc.) with weights ranging from 0.71 to 13.2 lbs. Testing also included evaluation of heavier sUAS using mitigations to reduce potential for injury, such as sUAS under parachutes.
The ASSURE research team is led by the University of Alabama in Huntsville and including Mississippi State University, The National Institute for Aviation Research (NIAR) at Wichita State University, and The Ohio State University. David Arterburn, Director, Rotorcraft Systems Engineering and Simulation Center at The University of Alabama in Huntsville and principal investigator for the study said: “The Ground Collision Severity Evaluation does not seek to advocate for any new rules or regulations, but rather may inform the rulemaking process by increasing the body of scientific knowledge for the FAA, industry and UAS manufacturers. Rather than speculate on the possibility for injury, the new report also allows manufacturers access to sufficient data that could be used to create new industry consensus standards that reduce the potential of human injury risk for flight over people operations.”
The scope of earlier studies was limited to testing of a single vehicle, with a limited number of impact tests, and no correlation of the testing results to actual human injury.
“The research results give the FAA a better picture of potential injuries and their severity, based on established science,” said Stephen P. Luxion, Col (Ret.), Executive Director, ASSURE. “Earlier testing of injury data strongly supported our assessment that long-standing fatality data was overly conservative and largely not applicable to injuries resulting from impacts by more elastic sUAS. Additional testing was needed to develop a more accurate, science-based test methodology that may be used by the FAA, sUAS manufacturers, and operators of sUAS to evaluate the injury risk potential.”
Arterburn added: “The injury impacts conducted in the study were controlled impact tests of the worst case, using those variables capable of transferring the most energy to a human. Even in these controlled studies, slight variations of the vehicle orientation or location of impact with the human, just prior to impact, reduced the injury potential. These results showed that these worst-case impacts are very difficult to achieve, even under controlled impact test conditions.”
The complete report is available at http://www.assureuas.org/projects/deliverables/sUASGroundCollisionReport2017-2019.php.