Influence of Explanation Timing and Content on Passenger Trust and Risk Perception in Autonomous UAM

Securing passenger trust is critical to the successful adoption of autonomous urban air mobility (UAM). Although HMI-based information provision has been widely studied in aviation and automation, limited empirical evidence exists on passenger-facing explanation strategies for autonomous UAM. To address this gap, we conducted a VR-based UAM flight experiment with 40 participants and tested five conditions: a no-information baseline and four explanation strategies varying in timing and content. Participants experienced six in-flight events and provided repeated trust and risk ratings across 13 assessment time points. Results showed that pre-event explanations significantly increased trust and reduced risk perception relative to the baseline. Event-level analyses further indicated that, for some environmental events, particularly fog and gust, post-event explanations including both How and Why information were associated with relatively larger trust recovery. These findings suggest that UAM passenger HMIs should prioritize pre-event explanations when possible, while post-event explanations should include Why information to support trust recovery after unexpected aircraft responses.