# Real-Time Safety Decision-Making Method for Multirotor Flight Strategies Based on TOPSIS Model
## 1 Introduction  
Multirotors have the characteristics of a vertical take-off and landing, simple mechanical structure, and easy maintenance, and have been widely used in many military and civil mission scenarios, such as search and rescue [1], package delivery [2], border patrol [3], military surveillance [4], and agricultural application [5]. At the same time, multirotors are flexible in flight, with hovering and slow-flying functions, and are used in electric power inspection [6], border surveillance [7], modern agriculture [8], forest fire control [9], flood control, and disaster resistance [10], playing an increasingly important role in other fields too. However, the failures of multirotors such as communication faults, sensor failures, and power system anomalies are inevitable [11, 12, 13, 14]. These failures may lead to mission interruption, multi-rotor crashes, and even casualties. To ensure flight safety, the decision-making module of the multirotor should prevent or reduce the adverse effects caused by failure. By studying the real-time decision-making method for the multirotor flight strategy and determining the next action of the multirotor, the multirotor can adapt to different flight tasks and different abnormal situations. To ensure the flight safety of themultirotor, it is necessary to grasp the motion state information in real-time and evaluate the safety level during the control process [15]. The flight strategy needs to be decided when the fault classification of the multirotor has a low grade. A flight safety decision-making method is built to prevent or mitigate the negative impact of failure as much as possible, and to provide a good safety guarantee for the multirotor [16]. The existing flight decision-making mainly focuses on mission decision-making of multirotor, with more research on path planning of multirotor and less research on safety decision-making [17]. Though the bi-level programming-based leader-follower decision-making model [18], influence diagrams-based decision-making model [19], artificial potential field decision-making method, and others can effectively solve the decision-making problem in UAV trajectory planning [20], they have not been successfully applied to the safety decision making of multirotors. At the same time, in multirotor flight safety evaluation decision making, the related research on multi-structure information is relatively scarce. In order to solve the above problems, this paper takes a multirotor as the main analysis object and puts forward a safety decision-making mechanism for the multirotor flight strategy, in which multiple types of information are processed and fused. According to the safety state level of the multirotor, the process of the safety manipulation strategy decision making of the multirotor is started, that is, when the result of the condition assessment is \"danger\" or even \"disaster\", it is necessary to adjust the control strategy according to the current various factors, and the choice of manipulation strategy is the safety decision of the multirotor. The real-time environment and flight status of the multirotor should be considered when making decisions on the flight strategy of the multirotor. Therefore, a flight safety strategy decision method of multirotors that takes both the real-time environment (electricity, obstacle, and wind interface) and the current flight state (disaster, danger, and slight failure) into account is proposed in this paper. In actual multi-attribute decision-making problems, decision-makers often prefer to use words such as \"very good\", \"poor\", and \"particularly poor\" to express their decision information. Therefore, [PERSON] [21] proposed the concept of language variables. Language variables are a useful tool in the field of multi-attribute decision making because they can better simulate the evaluation opinions given by decision experts [22].