SUMMARYThis study employs exploratory and confirmatory factor analysis to identify key risk factors in air traffic control (ATC) influencing aviation safety and to explore the correlational relationships among constructs from the perspectives of air traffic controllers. A total of 57 potential risk factors are first proposed based on the framework of SHEL, namely software, hardware, environment, and liveware, by referring to a review of the related literature and observing local issues in Taiwan. Interviews are then conducted with some 232 Taiwan air traffic controllers and supervisors. Exploratory factor analysis is first performed to determine the item-factor assignment and develop an initially proposed framework. Next, confirmatory factor analysis is performed to test the construct validity. The correlational relationships among constructs are further investigated. The results reveal that 26 of the 57 potential risk factors studied can be characterized as key risk factors. These factors are associated with five constructs -constitutional framework, human error, system interface, external communications, and controller capabilities and physical conditions. Based on the identified key factors and the tested correlational relationships among constructs, appropriate countermeasures are proposed for mitigating ATC risks.