This paper develops an alternative to the ground risk model provided by JARUS SORA. Key inconsistencies in the SORA ground risk model are identified, specifically ground risk continuing to increase when there is no further increase in fatality probability.

Population density is a critical component of UAS ground risk. Definitions of population density adopted by various regulatory jurisdictions are reviewed. A categorisation of population density is developed based on official statistics categories for New Zealand. This categorisation is more granular than that provided by SORA, enabling a more nuanced assessment of risk.

A ground risk model is then developed using a modified version of the model presented in Shelley (2016). Key changes to that model include use of realistic population density categories, modifications to the fatality model, and presentation of the results as an ordinal Risk Score. The Risk Score varies by population density, impact energy, and the size of the UAV.

An implication of the model is that operations over controlled ground areas do not require any additional hazard controls, including airworthiness controls, as the risk to people is already zero. The model does not suggest particular hazard controls, but does provide admit an obvious interpretation of how hazard controls can reduce the quantitative risk level.

Finally, potential reasons for regulators adopting the SORA are identified, including the need for legitimation by appeal to the authority of an international group. The model presented here provides a more coherent and logical framework than SORA, which can be used to provide alternative risk assessments while satisfying regulators’ needs for legitimation.



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