## 3 Construction of an Evaluation Indicator System for Spare Parts Support Capacity  
The evaluation of civil aircraft spare parts support capacity refers to assessing the matching degree between the actual situation of civil aircraft spare parts ordering, storage, and supply capacities and their expected capacities. This aims to ensure that spare parts are supplied adequately and timely during the operation of civil aircrafts and can meet the needs of aircraft repair and maintenance. This evaluation usually includes the consideration of spare parts inventory level, supply chain management, delivery efficiency, spare parts availability, exchange rate, cost-effectiveness, etc. Through the evaluation of spare parts support capacity, airlines and aircraft maintenance organizations can better manage their spare parts inventory, improve maintenance efficiency, reduce operating costs, and ensure the safety and reliability of aviation devices. To facilitate the follow-up study, considering the coverage, independence, practicability, and systematic characteristics that evaluation indicators should contain, four levels--task capability indicator, emergency support capacity indicator, cost-effectiveness indicator, and service capacity indicator--were selected to establish an evaluation indicator system for the spare parts support capacity of civil aircrafts, specifically as shown in Figure 1.  
Task capability indicator. The task capability indicators mainly include the annual operating hours of an aircraft, aircraft sortie intensity, and aircraft integrity rate. The longer the annual operating hours, the higher the operating frequency of the aircraft, and the higher the requirements for the spare parts support capacity. Therefore, longer annual operating hours of the aircraft indicate a stronger spare parts support capacity. The aircraft sortie intensity reflects the task execution frequency of an aircraft within unit time, and a high aircraft sortie intensity means that a stronger spare parts support capacity is needed to  
Figure 1: Evaluation indicators for spare parts support capacity of civil aircrafts. ensure the timeliness and adequacy of spare parts supply. The aircraft integrity rate reflects the ability of an aircraft to keep a good operating state within a certain time, and a high aircraft integrity rate generally manifests a relatively effective and sufficient spare parts support capacity. Emergency support capacity indicator. Emergency support capacity indicators mainly include emergency spare parts supply time and emergency spare parts supply satisfaction rate. The emergency spare parts supply time refers to the time from the demand for spare parts proposed until the actual supply time in case of aircraft failure or emergency maintenance. The shorter the emergency spare parts supply time, the better the spare parts support capacity. The emergency spare parts supply satisfaction rate means the ratio of the number of spare parts supplied to the number of spare parts demanded in case of emergencies, and a higher emergency spare parts satisfaction rate reflects a better spare parts support capacity. Cost-effectiveness indicator. Cost-effectiveness indicators include the recovery rate of used spare parts, the utilization rate of spare parts repair, and the total value of spare parts in stock. The recovery rate of used aircraft spare parts refers to the proportion of used spare parts recovered and reused in aircraft maintenance. The higher the proportion, the stronger the spare parts support capacity. The utilization rate of aircraft spare parts repair refers to the proportion of used spare parts that are put into use again through repair and maintenance. Similarly, the higher the proportion, the better the spare parts support capacity. The total value of aircraft spare parts in stock refers to the total value of spare parts held by the aircraft. If the total value of spare parts in stock is reasonably controlled, enterprises can reduce capital occupation and costs while ensuring spare parts supply.