Facing the Challenges of Supercooled Large Droplet Icing: Results of a Flight Test Based Joint DLR-Embraer Research Project

Today’s airplanes are well equipped to cope with most common icing conditions. However, some atmospheric conditions consisting of supercooled large droplets (SLD) have been identified as cause of severe accidents over the last decades as existing countermeasures even on modern aircraft are not necessarily effective against SLD-ice. In 2014, the new Appendix O to the certification regulations (FAR Part 25 / CS-25) had been issued to guarantee the safe operation of future airplane when encountering SLD conditions. But as the SLD topic is quite new for the majority of aircraft manufacturers and research institutes in a same way, DLR (German Aerospace Center) and Embraer established a joint research cooperation in 2012 to obtain a better understanding of the distinct influences of SLD-ice shapes on aircraft characteristics and to evaluate proper ways for future airplane certification under App. O. Furthermore, one additional scientific goal of the cooperation was to develop and test new tools for the in-flight monitoring of aircraft characteristics as well as the on-board identification of simulation models. During the 4 years of the project, a distinct way to better understand icing-induced degradations on a specific aircraft was followed: first, data of the clean aircraft was gathered in flight test to identify a dynamic simulation model as base for the subsequent evaluations. Second, data of test flights with artificial App. C ice configurations were analyzed and used for the development of distinct modifications of the base aircraft simulation model; a first evaluation of the icing-induced changes of aircraft characteristics was conducted. Third, after the generation of SLD-ice shapes, wind tunnel testing and flight clearance, a second flight test campaign with these artificial SLD-ice shapes delivered the data for an additional model modification and identification. The results of the final data and model evaluation provide the observable degradation of SLD-ice in flight, which is well comparable to results obtained from the App. C ice configurations.