Abstract:Liquid water content (LWC), median volume diameter (MVD), outside air temperature and other meteorological conditions are important meteorological factors affecting the intensity of aircraft icing, and are also the basic condition for measuring and evaluating whether the aircraft natural icing certification flight test meets the natiural icing certification flight test standard. The meteorological conditions of a domestic large passenger aircraft natural icing test flight on 22 January 2022 are analyzed based on multi-source meteorological data. The results show that the high-altitude weather background of this natural icing certification flight test was a latitudinal fluctuating airflow, cooperated with the cold air inversion near the surface, forcing the southwest warm and humid airflow in the middle and lower layers of the troposphere to lift northward, and forming a wide range of non-precipitation layered cloud system. The height of the cloud top in the test area developed from 3.0 km to 4.6 km, and an inversion layer existed in 1.3-3.5 km, with the lowest temperature at the cloud top being -14℃, no precipitation in the cloud, and the radar basic reflectivity＜15 dBz. The ambient temperature of the two times of fights penetrating the cloud and the standby flight in the cloud for 45 min hovering flights was from -10 to -7℃, with the relative humidity＞80%, and the scattering of water vapor flux＜-2.73×10-7 g·s-1·hPa-1·cm-2. This provided ideal temperature and water vapor conditions for the natural icing test flights, and a weak updraft of -0.2 Pa·s-1 in the middle and upper part of the cloud layer contributed to the growth of the supercooled cloud droplets. The DMT sounding data show that the supercooled cloud is inhomogeneous both vertically and horizontally, and that the supercooled cloud droplets were dominant inside the cloud, where the mean value of LWC was 0.23-0.27 g·m-3, and the mean value of MVD was 15.82-15.93 μm. So there are aircraft natural icing meteorological conditions in winter under the influence of the “inversion + inversion trough” weather system, which is conducive to carrying out aircraft natural icing certification tests in Shaanxi.