Mass threshold for ’harmless’ drones

Today it is possible to buy small and cheap drones in toy stores, supermarkets, and on numerous online shops. Often, these drones are very lightweight and are flown in backyards, sport fields, parking lots, and such places. They typically pose no lethal threat to people in the vicinity of the drone. Nonetheless, in many countries such drones are regulated by aviation rules that does not (sufficiently well) distinguish between these drones and the larger hobby or professional drones. Consequently such small drones are flown illegally. This has prompted some national aviation authorities to consider a form of ‘harmless’ category, which ideally should be based on a mass threshold. To aid such a classification this work proposes a mass threshold of 250 g, below which, we argue, it is reasonable to classify drones as ‘harmless’ in the sense that the expected fatality rate is equivalent to that of manned aviation. In this work we combine a series of models and methods to provide a foundation for giving a mass threshold. The approach is probabilistic and focuses on the relation between mass and human injury in the case of small drones. The approach is also parameterized such that readers can substitute other probabilities and conduct their own calculations, possibly determining a different mass threshold. </jats:p