The objective of the research project All-weather Drone is to investigate the effects of defined severe weather conditions (rain, snow and in-flight icing) on the operation of multicopters with 25 kg maximum take-off weight and the implications on performance and, hence, safety of flight. As part of the project detection capabilities (hardware-based sensors and software-algorithm) are developed and investigated for flight of multicopters in such weather conditions together with ice protection systems. Regulatory recommendations are derived from the project work to ensure that aviation authorities have a data-based framework in which to assess the risks associated with UAS operations in severe weather conditions. Additionally, market and industry relevant aspects are researched and incorporated into the project work to leverage the outcome. Given that limited research has been conducted in this field, the lack of civil weather-related certification specifications and rules for operation of multicopter UAS, as well as the absence of specific technical detection and protection solutions, the innovative character of the project is high.