## 6 Simulation and Verification of Operation Procedure in Apron U-Shaped Area
### Experimental Results and Comparative Analysis
#### 6.2.1 Comparison of Different Indices of U-Shaped Area
(**a**) Relationship between Flight Quantities and Conflict Probabilities Using Different Operation Program; (**b**) Relationship between Flight Quantities and Conflict Resolution Times Using Different Operation Program; (**c**) Relationship between Flight Quantities and Average Maximum Traffic Volume Using Different Operation; (**d**) Relationship between Flight Quantities and Saturation Using Different Operation Program. 50 vehicles/h, the maximum traffic volume per unit time is one vehicle for the exclusive operation procedure, two vehicles for the partition-shared operation procedure, and four vehicles for the global-shared operation procedure. When the flight volume is less than 35 vehicles/h, there is no difference in the saturation of the U-shaped area corresponding to the three operation procedures. When the flight volume increases from 35 to 50 vehicles/h, the saturation corresponding to the exclusive, partition-shared and global-shared operation procedures increases by 11.4%, 20%, and 42.7%, respectively. This is due to the different degrees of restriction of the three operation procedures. The exclusive operation procedure only allows one aircraft to taxi in the U-shaped area, which is much lower than the actual capacity of the U-shaped area, leading to low saturation and its resource utilization is not high. In contrast, the global-shared operation procedure allows aircraft to reach the limit of operation as much as possible while maintaining the safety separation, so the apron saturation is high and the resource utilization is relatively high. Figure 10 shows the total fuel consumption and carbon emissions of the aircraft in the three operating procedures at different flight flows. When the flight traffic is small, the difference in fuel consumption and carbon emission of the three operation procedures is small. As the traffic volume increases, the fuel consumption and carbon emission of the three operating procedures increase. The total fuel consumption and carbon emission of the three operation procedures increase when the flight flow reaches 30 to 50 vehicles/h. Compared with the global-shared operation procedure, the trend of increase is more significant for the exclusive and the partition-shared operation procedure, in which the total fuel consumption and carbon emission of the exclusive, partition-shared and global-shared operation procedure increase by 35.6%, 30.4%, and 23.9%, respectively. When the flight volume is 50 flights/h, the capacity and traffic flow ratios are 96.1%, 86.2%, and 82.0% for the exclusive, partition-shared, and operation procedures, respectively, and compared with the global-shared operation procedure, the average daily fuel consumption of a single aircraft increases by 3.6 kg and 2.4 kg for the exclusive and partition-shared operation procedures, respectively, and the average daily carbon emission of a single aircraft increases by 16.7 kg and 11.0 kg respectively, which translates into an increase of 1.2 tons and 0.8 tons of carbon emissions in a year. Figure 10: Aircraft Fuel Consumption and Carbon Emissions under Different Procedures and Flight Frequencies. The Critic method is used to objectively assign weights to conflict indices and resource utilization indices to further analyze the comprehensive evaluation indices of the U-shaped area. Figure 11 shows the comprehensive evaluation results of each of the three operation procedures for 1000 simulations at increasing flight flows, and Figure 12 shows the trend of the comprehensive evaluation indices with simulated flight flows under the three operation procedures. It can be seen that the performance of the global-shared operation procedure is completely superior to the other two procedures, and the advantage becomes more and more significant as the flight traffic increases.