# A Fuzzy Path Selection Strategy for Aircraft Landing on a Carrier
## 2 Problem Statement and Conceptual Model Establishment
### Essential Elements  
According to the problem description, there are several essential elements in the path section problem: the decision makers, the alternative landing paths and the contributing factors. The decision makers have been analyzed above, the remaining two are depicted later. 1. The alternative landing paths:  
Four landing path are regulated according to the atmospheric environment, the performance of the aircraft and the air traffic condition, as listed below. 1. \(l_{1}\): The weather, visibility, performance of aircraft and air traffic are suitable for landing. Under such conditions, the pilot lands the aircraft by vision. The aircraft flies counterclockwise following the rectangular route above the carrier, as shown in Figure 2.  
Figure 1: Description of the landing path selection problem. Figure 2: General view of alternative landing path \(l_{1}\). The carrier is located in the center of the right edge of the rectangle at this moment. If the aircraft keeps waiting for the landing command, it will fly counterclockwise following the rectangular path and will get in touch with the approaching operation person every time it passes the carrier to confirm the landing permission. 2. \(l_{2}\): The weather and visibility are both at a medium level, and the performance of the aircraft and the air traffic are suitable for landing. A safer landing path will be used when clouds appear between the height of 1000 and 3000 feet and cover more than 5/8 of the sky. It is dangerous for the pilot to land the aircraft by vision in this case due to the heaviness of clouds. Therefore, a landing path called \"Martial Pattern\" is set 15 miles away from the carrier to guarantee the landing safety, as shown in Figure 3. The aircraft will repeat the \"Martial Pattern\" until it is permitted to land. 3. \(l_{3}\): The weather and the visibility are both bad, but the performance of the aircraft and the air traffic are suitable for landing. It is also unsafe for the pilot to land the aircraft by vision under such conditions. Similarly, the \"Martial Pattern\" is set 15 miles away from the carrier, and the aircraft repeats the \"Martial Pattern\" before being permitted to land, as shown in Figure 4. Unlike in the case of \(l_{2}\), the aircraft does not have to fly a rectangular route around the carrier after receiving the landing permission. Instead, it approaches the carrier directly by gliding. 4. \(l_{4}\): Poor performance of aircraft or bad air traffic condition. In this case, as it is dangerous to land on the carrier, the pilot has to get in touch with the staff on land for an emergency landing. Figure 3: General view of alternative landing path \(l_{2}\). 2. The contributing factors:  
1) Weather  
It is often difficult to predict the sea weather because no obstacles exist above the sea, and the air flow above the sea is active. Therefore, the weather information is obtained by measuring the nearby weather condition continuously. Usually, \(l_{1}\)\(l_{2}\) and \(l_{3}\) are chosen for good, medium and bad weather, respectively. 2) Height of clouds  
Low clouds which cover a wide range of the sky will impair the vision of the pilot. Therefore \(l_{1}\) is preferred when there are few or no clouds. Otherwise, \(l_{2}\) or \(l_{3}\), which allow a higher safety standard, are preferred. 3) Visibility  
The visibility of the pilot will have an influence on the accuracy of landing. Good visibility often leads to the choice of \(l_{1}\) or \(l_{2}\). On the contrary, \(l_{3}\) or even \(l_{4}\) will usually be chosen under poor visibility. 4) Performance of the aircraft  
In daily training and scouting tasks, the aircraft is normally in good operating condition and will land on the carrier according to the command received. However, the aircraft may be damaged when accidents occur, and \(l_{4}\) will be the best choice in this case to guarantee the landing safety. 5) Air traffic  
This refers to the flyable space for the landing aircraft.