The number and size of multi-airport systems are growing worldwide. Due to the limited resources in the terminal area, there is a certain interdependency between the operation of neighbouring airports, resulting in operational inefficiencies of multi-airport systems. In order to estimate the limitations of correlation on multi-airport systems, a statistical analysis framework was proposed to analyze the capacity loss of multi-airport systems as a whole by taking Beijing terminal area as an example. Firstly, the theoretical capacity of each airport in the Beijing terminal area was calculated according to the model, and the actual capacity of each airport under independent operation was further determined. Secondly, the robust Pareto capacity envelopes of three airports and the terminal area were estimated based on historical operation data of Beijing terminal area. Finally, the actual capacity loss of each airport and multi-airport system was quantified based on the independent operation capacity and related operating capacity. Suggestions and references are provided for further improving the operational efficiency of multi-airport terminal areas.