Abstract: Since the end of the last century, aircraft icing phenomenon in supercooled large drop (SLD) icing conditions (14 CFR Part 25 Appendix O) have attracted much attention. The impact on flight safety is worse than atmospheric icing conditions (14 CFR Part 25 Appendix C). The promulgation of Amendment of FAR 25-140 and EASA CS-25 16 suc-cessively indicates that the implementation of SLD icing airworthiness compliance verification is a mandatory condi-tion for China's large civil aircraft to obtain European and American airworthiness certificates. The simulation of SLD icing conditions is a pre-requisite for the ground SLD icing test, and it is very important for the design of SLD anti-icing system and the verification of icing test. In this paper, the typical characteristics of the drop diameter distribution simulation under the icing conditions of SLD are analyzed, namely, large drop diameter span with bimodal distribu-tion and low liquid water content (LWC). The research and development of the simulation methods of drop diameter distribution under SLD icing conditions in the world's major icing research institutions in the past 30 years are re-viewed. It is found that the technology to simulate the drop diameter distribution for freezing drizzle (FZDZ) mainly goes through four stages: increasing the median volume diameter (MVD) of the spray, alternately producing MVD clouds with different sizes, regulating water pressure simultaneously producing clouds with different MVD, and us-ing two sets of independently controllable MVD cloud generation systems. Simulation on the drop diameter distribu-tion for freezing rain (FZRA) are even more challenging and are still in the initial stages of development. The main achievements are introduced and the problems are discussed. In terms of drop diameter and bimodal distribution, the current technology can basically simulate the drop diameter distribution of FZDZ. Although the LWC is generally high, it can meet certain experimental requirements. Although the simulation method for FZRA is not mature, it is possible to simulate the drop diameter distribution through cloud generation method mixing the controlled large drop and the spray. Finally, the research direction, key technical problems and solutions of drop diameter distribu-tion simulation in SLD icing conditions are proposed.

Key words: Aircraft ground tests, Aircraft icing conditions, Supercooled large drop, Drop diameter distribution, Simulation method, Double spray mixing, Single drop and spray mixing