## 4 Experiments and Results
### Results and Analysis
#### 4.2.2 Determination of the Number of Diverted Flights  
The types of bad weather classified using a fuzzy mathematics calculation method are presented in Table 3.  
The route directions of routes are expressed by waypoints at critical points in each sector. The relationship between the routes and the waypoints at Yinchuan Hedong International Airport is presented in Table 4. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type of** & & \\
**Bad Weather (_a_)** & **Specific Meaning** & **Weather-Influence Coefficient \((W_{a})\)** \\ \hline
1 & High echo intensity and high cloud base (including cloudy weather) & 0.19 \\
2 & High cloud base and low–high echo intensity (including cloudy weather) & 0.27 \\
3 & High echo intensity and middle cloud base (including cloudy weather) & 0.39 \\
4 & Low cloud base and high echo intensity (including cloudy weather) & 0.51 \\
5 & High visibility and low echo intensity (including high blowing and floating dust weather) & 0.21 \\
6 & Echo intensity in high visibility (including high blowing and floating dust weather) & 0.32 \\
7 & Echo intensity in moderate visibility (including high blowing and floating dust weather) & 0.41 \\
8 & Moderate visibility and high echo intensity (including high blowing and floating dust weather) & 0.48 \\
9 & Low visibility and high echo intensity (including high blowing and floating dust weather) & 0.59 \\
10 & Low precipitation and low echo intensity (including thunderstorms) & 0.57 \\
11 & Echo intensity in moderate precipitation (including thunderstorms) & 0.72 \\
12 & High precipitation and high echo intensity (including thunderstorms) & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Weather-influence coefficients for various types of bad weather. \begin{table}
\begin{tabular}{c c} \hline \hline
**Bad Weather Rating** & **Types of Bad Weather** \\ \hline
1 & 11, 12 \\
2 & 4, 8, 9, 10 \\
3 & 1, 2, 3, 5, 6, 7 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Classification of severe-weather grades. The data for 2019 were imported into the AIRTOP software model on a daily basis for the simulations. The air traffic flow in each route was determined, as was the flow distribution ratio according to the flow passing through the inbound and outbound waypoints. The statistical results are shown in Figure 8.  
According to the statistical results, the inbound and outbound flights of Yinchuan Hedong International Airport accounted for 51.21% and 48.79% of the total flights, respectively. The flow distribution ratio on each route could be obtained by combining the inbound and outbound flow distribution for each route waypoint. The specific distribution is presented in Table 5. \begin{table}
\begin{tabular}{c c} \hline
**Route Path Number** & **Path** \\ \hline R1 & Exit in the direction of OPULI \\ R2 & Exit in the direction of DOXED \\ R3 & Exit in the direction of DOMVA \\ R4 & Exit in BELIP direction \\ R5 & Go in the direction of OPULI \\ R6 & Advance in the direction of AGVEN \\ R7 & Heading in the direction of IDGOB \\ R8 & LUVKO heading in \\ \hline \end{tabular}
\end{table} 
Table 4: Route classification. Figure 8: Flow distribution for approach and departure. **(a)** Departure flow distribution, (**b**) Approach flow distribution. According to the position of the boundary points for the approach and departure routes, the flight-restricted area of each route was determined in the AIRTOP model. Simulations were performed based on the annual takeoff and landing operations at Yinchuan Hedong International Airport in 2019, and different restricted areas were designed according to the flow direction of the inbound and outbound routes. The specific design details are shown in Figure 9.  
The opening hours of restricted areas are set according to when bad weather occurs, and the blocking degree of restricted areas is defined according to the route-availability values. The flight arrivals and departures in 2019 were simulated according to the route-availability values calculated under different grades of bad weather.