# Human Factors Analysis of Air Traffic Safety Based on HFACS-BN Model
## 4 Results
### BN Inference  
The process of finding the key factors is a top-down probabilistic diagnosis. In Figure 7, the value of the final target variable \"ATC Performance\" is replaced by 1, and the posterior probability of all parent nodes can be obtained; that is, the so-called bottom-up diagnosis. Here, the probability of \"ATC Performance = Bad\" is set to 1 to obtain the posterior probability of all nodes. The higher the posterior probability of human factors, the greater the contribution of this factor to aviation accident risk.  
Figure 8 shows the marginal probability distribution of the four levels in the HFACS model. Unsafe acts had the greatest influence on ATC Performance (79.4%), while preconditions for safe acts contributed the least (40.3%).  
Apparently, as shown in Figure 9, unsafe acts contributes the most to the overall risk of accidents, including violations and air traffic control errors, with a posteriori probability of 71.3% and 52.6%, respectively. This means that the respondents believe that these human factors are most likely to be present in air accidents involving controllers. The second group of factors with more considerable influence belong to unsafe supervision, and preconditions of safe acts level include inadequate supervision, ATCOs states, whose posterior probabilities range between 40% and 65%. The contributions of the other levels to the ATC performance are similar (23%-35%), in which the supervision violation at  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Node**} & \multirow{2}{*}{**State**} & **P (ATC** & \multirow{2}{*}{**State**} & **P (ATC** & \multirow{2}{*}{**State**} & **P (ATC** & **Increased** \\  & & & **= Good)** & & & **= Good)** & **Percent** \\ \hline
1 & Training & poor & 0.633 & normal & 0.656 & good & 0.662 & 4.58\% \\
2 & Physical Fatigue & poor & 0.645 & normal & 0.657 & good & 0.661 & 2.48\% \\
3 & Mental State & poor & 0.647 & normal & 0.658 & good & 0.662 & 2.32\% \\
4 & Ineffective Monitoring & yes & 0.654 & - & / & no & 0.669 & 2.29\% \\
5 & ATC Software/Hardware & poor & 0.650 & normal & 0.657 & good & 0.660 & 1.54\% \\
6 & Failed to Enforce Regulations & yes & 0.652 & - & / & no & 0.661 & 1.38\% \\
7 & Failed to Correct Inappropriate Acts & yes & 0.652 & - & / & no & 0.661 & 1.38\% \\
8 & ATC/Flight Crew Cooperation & poor & 0.652 & normal & 0.658 & good & 0.661 & 1.38\% \\
9 & ATC Communication & poor & 0.652 & normal & 0.659 & good & 0.661 & 1.38\% \\
10 & Noise & high & 0.652 & normal & 0.658 & low & 0.661 & 1.38\% \\
11 & Safety Culture & poor & 0.652 & normal & 0.659 & good & 0.660 & 1.23\% \\
12 & Air-Ground Communication Interference & serious & 0.653 & normal & 0.658 & slight & 0.661 & 1.23\% \\
13 & Visibility & poor & 0.653 & normal & 0.658 & good & 0.661 & 1.23\% \\
14 & Lack of Supervision Plan & yes & 0.653 & - & / & no & 0.660 & 1.07\% \\
15 & Team Human Resource Allocation & poor & 0.654 & normal & 0.659 & good & 0.661 & 1.07\% \\
16 & ATC clearance error & yes & 0.655 & - & / & no & 0.662 & 1.07\% \\
17 & Procedural Noncompliance & yes & 0.657 & - & / & no & 0.664 & 1.07\% \\
18 & Operation/Decision Error & yes & 0.654 & - & / & no & 0.660 & 0.92\% \\
19 & Poor Management Discipline & yes & 0.654 & - & / & no & 0.660 & 0.92\% \\
20 & Salary and Reward & low & 0.655 & middle & 0.659 & high & 0.661 & 0.92\% \\
21 & ATCO Misspeaking & yes & 0.655 & - & / & no & 0.660 & 0.76\% \\
22 & Emergency Mishandling & yes & 0.655 & - & / & no & 0.660 & 0.76\% \\
23 & Nonstandard Flight Progress Strip & yes & 0.656 & - & / & no & 0.660 & 0.61\% \\
24 & Distraction & yes & 0.656 & - & / & no & 0.660 & 0.61\% \\
25 & Use Nonstandard Terms & yes & 0.657 & - & / & no & 0.660 & 0.46\% \\ \hline \hline \end{tabular}
\end{table}
Table 5: Computation results of changing states of influence factors.  
the level of unsafe supervision and the organizational climate at the level of organizational influence contribute the least to the performance (posterior probabilities are less than 25%).