# Human Factors Analysis of Air Traffic Safety Based on HFACS-BN Model
## 3 Theoretical Development  
### Network Construction  
Since 1980, 142 aviation accidents/incidents worldwide related to ATC human factors have been recorded in \"Skybrary,\" accounting for more than 13.6% of the 1045 aviation accidents/incidents in the database in the same period. SKYbrary was initiated by EUROCONTROL in partnership with International Civil Aviation Organization (ICAO), The Flight Safety Foundation and The UK Flight Safety Committee, and work with the Federal Aviation Administration (FAA) to upload the outputs of the Commercial Aviation Safety Team (CAST) to provide reference materials for safety managers. As shown in Figure 5, the time-frequency distribution shows that the number of aviation accidents/incidents related to ATC human factors is on a sharp rise, which is understandable because the leading cause of aviation accidents has shifted from technical problems to human factors; moreover, the number of aircraft fleet and flight frequency are also increasing. The analysis and identification of ATC human factors provide practical insights for organizations on aviation safety and ATC performance management, especially in understanding which key human factors have a significant impact on the performance of controllers, to further improve ATC work and the safety of ATC operations.  
Figure 6 shows the category of ATC human factors and the frequency of each human factor according to Skybrary statistics in 142 aviation accidents/incidents worldwide from 1980 to 2019. As we can see, a total of 14 human factor tags were behind 142 aviation accidents/incidents, and all human factor tags occurred 410 times; where 94 accidents/incidents related to procedural noncompliance and 92 accidents/incidents related to ineffective monitoring, while only 2 and 1 accidents/incidents related to stress and ATC team coordination, respectively. Note that this is because the human factors behind every aviation accident/incident are complex and diverse, as in the case of the 4 April 2016 accident, a Boeing 737-800 crew taking off in normal night visibility from Jakartz Halim were unable to avoid an ATR 42-600 undertow, which had entered their runway after ambiguity in its clearance. Both aircraft sustained substantial damage and caught fire but all those involved escaped uninjured. The accident report involves four kinds of human factor tags, including the ATC clearance error, ATC  
Figure 5: The number of aviation accidents/incidents related to air traffic control (ATC) human factors from 1980 to 2019.  
unit coordination, ineffective monitoring, and procedural noncompliance, hence all human factor tags occurred 410 times.  
Generally, the ATC performance model is a complex system with tightly coupled relationships between nodes. Combined with the opinions of experts in the aviation field, Figure 7 shows the \"ATC Performance\" model in this paper, which contains four sequential paths affecting the performance of ATC, namely \"Organizational Influence\", \"Unsafe Supervision\", \"Preconditions for Unsafe Acts\", and \"Unsafe Acts\", and each influence path contains human factors at the corresponding level.  
Figure 6: Distribution of ATC human factor tags in aviation accidents/incidents from 1980 to 2019.  
Figure 7: ATC performance model.  
In order to better illustrate each node in the ATC performance model, Table 1 describes the source and detailed interpretation of human factors. It is worth mentioning that the ATC human factor tags from Skybrary are not very comprehensive, and most of them are distributed on the two levels of unsafe acts and the preconditions of unsafe acts. However, some human factors related to organizational influence, such as organizational climate, safety culture, or resource allocation, are difficult to be directly recorded in the accident report. However, in previous studies [4; 33; 34], these factors did affect ATC performance. Therefore, some nodes in the model are not involved in the accident report mentioned above, which are derived from references and expert opinions.