Abstract:Ice on airplanes can cause serious accidents.SSA upper air cold vortex is one of the synoptic backgrounds that are prone to icing aircraft.SSIn order to understand the characteristics and mechanism of natural freezing of aircraft under the background of cold vortex, seven flight detections were conducted using Y-12 aircraft under the upper-air cold vortex in Hulunbuir in May 2021, with two moderate and two intense ice accumulation occurred respectively, the atmospheric environments suitable for aircraft icing detection are discussed.SCharacteristics and mechanism of aircraft icing are speculated based on data obtained from the DMT equipments carried by the aircraft for the two intense aircraft icing processes on May 31. The results show:S While the aircraft flying at altitudes of about 3.5~4.2 km, with the ambient temperature of -8~-4 ℃, intense aircraft ice accumulation occurred in the vapor saturated region in the southeast of the cold vortex. The averaged supercooled liquid water content(LWC) during high LWC value periods could reached as high as 0.25~1.04 g.m-3^{, l}eading to instantaneously aircraft icing,Sand the particle number concentration raising to 100~200 cm-3 for drops with mean effective drop diameter (MED) in the range of 15~100 μm. Particle images and their growth patterns in the southeast of the cold vortex were brought out. Finally, the atmospheric icing conditions in the southeast part of the cold vortex are discussed.