## 3 Data Analysis
### Two-Factor ANOVA on Controller Situational Awareness Related Indicators
#### 3.2.2 Analysis of Heart Rate Variability Parameters in Air Traffic Controllers  
The psychological load significantly affects the incidence of human mistakes, since both extremely high and low psychological loads may result in the oversight of essential information [31]. This is especially important during the operation of remote tower controllers because safety depends on the controllers' ability to take appropriate actions. Mental stress triggers physiological changes in the heart and peripheral blood vessels. Stress influences heart rate, and heart rate variability (HRV) accurately measures the degree of alterations in cardiac rhythms. Heart Rate Variability (HRV) is an effective metric for evaluating the equilibrium between the sympathetic and parasympathetic nervous systems. Consequently, examining heart rate patterns may provide insights about personal psychological and physiological alterations, facilitating the evaluation of mental stress via HRV values [32]. This research used Kubios software (Kubios HRV 2.2) to examine the time-domain and frequency-domain characteristics of participants' heart rates, namely SDNN, NN50, LF, HF, and RMSSD. The specific values are shown in Table 4.  
We performed a two-way ANOVA on the SDNN findings and found that neither the tiredness state (F = 0.624, \(p\) = 0.439) nor the controller qualifications (F = 2.002, \(p\) = 0.172) significantly influenced the SDNN parameter. Moreover, there was no notable interaction between the tiredness state and controller qualifications (F = 0.00, \(p\) = 0.987). The interplay between fatigue levels and controller qualifications significantly influenced the SDNN parameter. The SDNN index denotes the standard deviation of normal-to-normalintervals and serves as a sensitive measure of sympathetic nerve activity. As mental stress increases, this indication often declines. Figure 4a illustrates that when the tiredness levels of distant tower controllers fluctuate, both seasoned and novice controllers show a declining trend in SDNN, with trainees seeing a somewhat lesser decline compared to their experienced counterparts. A two-way ANOVA of the NN50 data revealed a significant main impact of the tiredness state (F = 5.256, \(p\) = 0.033), although the influence of controller qualifications (F = 0.661, \(p\) = 0.426) on the NN50 parameter was not significant. Furthermore, there was no notable interaction between the tiredness state and controller qualifications (F = 0.100, \(p\) = 0.755). The NN50 index denotes the proportion of consecutive R-R interval differences over 50 ms and serves as a sensitive measure for evaluating parasympathetic nerve activity. As mental stress rises, this measure often diminishes. Figure 4b shows that when the tiredness levels of distant tower controllers change, both experienced and trainee controllers show a decreasing trend in NN50. However, the decrease in NN50 for trainees is not as strong as it is for experienced controllers. A two-way ANOVA for the LF findings indicated that neither tiredness state (F = 0.017, \(p\) = 0.899) nor controller qualifications (F = 0.014, \(p\) = 0.908) had a significant impact on the LF parameter. We observed no significant interaction between tiredness state and controller qualifications (F = 0.106, \(p\) = 0.749). The impact of controller qualifications on the LF parameter was significant. Most people use the LF index to assess brain function, as it indicates low-frequency sympathetic nervous system activity. This indication tends to rise with increasing mental stress. Figure 4c illustrates that when the tiredness levels of remote tower controllers fluctuate, both experienced and trainee controllers have a declining trend in LF, whereas trainee controllers exhibit an upward trend in LF data. A two-way ANOVA on the HF data revealed a significant main impact of the tiredness state (F = 6.631, \(p\) = 0.018), although the influence of controller qualifications (F = 0.613, \(p\) = 0.443) on the HF parameter was not significant.