In order to estimate the change trend of aircraft taking off and landing separation in case of low visibility, improve the efficiency of runway use and reduce flight delay, an aircraft taking off and landing separation model in airport category Ⅱ operation was proposed. Firstly, the taking off and landing operation procedures under the category Ⅱ operation were analyzed to detail the process of aircraft taking off, landing, lining up and vacating runway. Secondly, a taking off and landing model was established based on the category Ⅱ operational regulations. Then, the cellular structure was defined, the rule of avoiding deceleration and the condition of vacating runway were introduced, and a cellular automata model of aircraft taxing was defined. Finally, the control rules were abstracted as constraint conditions and the taking off and landing separations were quantified. An example of Urumqi airport was used to verify the simulation. The change trends of taking off and landing separation and separation standard deviation were obtained through computer numerical simulation by setting different values for parameters such as the ratio of aircraft type, the ratio of landing and taking off, the length of the critical area and the time of vacating. The experiments demonstrated that in categoryⅡoperation,the separation was large, with a peak of 228.6 s. The capacity for landing and taking off were only 60% and 90% of the normal operation conditions. The peak of separation standard deviation was 74 s, which was 1.64 times of normal situation. The vacating position was the main factor for the increase of continuous landing separation. Results showed that the model could quantify the influence of key factors on the taking off and landing separation. The simulation results are in line with the actual operation, and provides theoretical foundation for improving efficiency in categoryⅡoperation.
