Methodological limitations

The limitations of this analysis correspond to the drone weather tolerances, weather reanalysis data, and their comparison to quantify flyability. The list of drone models we used to represent CDs and WRDs was not exhaustive; we considered the top 50 (for CDs) and top 500 (for WRDs) drone models based on the number of active commercial registrations of small UAS (< 25 kg) in the United States, which represented 69% (for CDs) and 85% (for WRDs) of total active commercial registrations as of 05 May 2020. There are likely other drone models that fit within the CD and WRD classes, but they were excluded from the analysis due one or more of the following: (1) at least one weather constraint parameter was not specified by the manufacturer; (2) the drone’s FAA commercial registration rank was higher than 50 (for CDs) and 500 (for WRDs); and (3) the drone was not commercially registered in the United States. Our analysis did not consider drone models that are unregistered or registered for recreational use in the United States, nor did we include drone models that are unregistered or registered in other countries.

The weather constraints representing the CD and WRD classes were directly compared to ERA5 weather data to quantify flyability, though there are several limitations associated with this comparison. The ERA5 parameters are generated by combining instantaneous modeled estimates that are spatially averaged within each grid cell and direct observations at point locations that reveal localized variations. Within a grid cell, there could be local weather conditions exceeding the operating envelope of a CD or WRD. However, due to the modeling and spatial resolution of ERA5 data, such conditions preventing flyability may not be represented. Furthermore, the weather parameters are inconsistent in terms of the altitudes at which they are modeled: 2 m, 100 m, and surface level for the air temperature, wind speed, and precipitation parameters, respectively. The 100 m wind speed data were used in the analysis (instead of ERA5 10 m wind speed data) because this altitude is more representative of drone operations based on factors such as areal coverage requirements for surveying, collision avoidance with vertical objects, and nationally mandated maximum flight altitudes for drones. Ideally, all three weather parameters would be modeled at 100 m. In addition to the three weather parameters and daylight parameter considered in this analysis, there are other parameters that constrain drone flyability, such as icing, fog, visibility, smoke, and dust. If additional constraint factors are considered, drone flyability estimates would likely be reduced. In summary, the flyability analysis is limited by: (1) the modeling and spatial resolution of the ERA5 data; (2) the inconsistent altitudes at which the ERA data parameters are modeled; and (3) the exclusion of additional factors that constrain drone flyability.