Incorporating pilot mental stress into no-fly zone boundaries through a human factors approach to safe separation design in urban air mobility

The outer boundaries of the no-fly zones in urban air mobility (UAM) are defined through factors such as weather conditions, noise and navigation. This study aimed to include human factors into the spatial envelop design of no-fly zones in low-altitude airspace. A simulating experiment of electric vertical take-off and landing (eVTOL) flights based on four obstacle avoidance distances was conducted. Psychological, physiological and behavioral indicators were extracted to reflect stress levels and capture the distance showing the surge of stress. To calculate the individual overall stress from the three modalities of indicators, this study proposed a J-shape guided multi-feature fusion framework through extracting the properties of monotonic increasing and slope increasing from the J-shape relationship between stressors and stress to execute reliable individual-level fusion. The results showed that 65.91% of the participants showed stress surge on the 50-to-25-meter separation, while the 75-to-50-meter separation covered 86.36% participants. Robustness analysis tested the stability of the 75-meter separation under different fusion, modality, feature and weighting settings. Therefore, the 75-meter separation with corresponding time-to-collision (TTC) as 3.18 s was selected for an engineering design reference of human factors-driven safety separation. These conclusions bring a new human-centric design for safety assurance in UAM.