Pilot response to somatogravic illusion in a simulated environment: Implications for early instrument flight training

The somatogravic illusion, a vestibular misperception caused by linear acceleration in the absence of visual cues, poses a significant safety risk during flight, particularly under instrument meteorological conditions. Despite its operational relevance, current pilot training programs emphasize theoretical instruction and lack practical exposure to such illusions. This study aimed to assess the behavioral effects of the somatogravic illusion in a controlled simulator environment and to evaluate the potential for adaptation through repeated exposure. A total of 114 pilots were assigned to four groups based on IFR experience. Each participant completed two simulator sessions one week apart, each comprising flights with and without induced somatogravic illusions. Illusion induction was achieved using cabin pitch motion within a fixed-base disorientation trainer. Altitude trajectories during the illusion interval were extracted, L2-normalized, and analyzed using principal component analysis and hierarchical clustering. Cluster transitions were evaluated to identify adaptation patterns. Post-exposure questionnaires assessed perceptual awareness and training utility. Illusion exposure caused systematic suppression of climb performance, independent of IFR experience. Unsupervised clustering revealed two dominant trajectory patterns corresponding to affected and unaffected responses. In the second session, 32% of previously affected pilots transitioned to the unaffected cluster, indicating behavioral adaptation. Perceptual awareness of the illusion remained low (23%-29%), yet 95.6% of participants endorsed the inclusion of vestibular illusion scenarios in IFR training. Controlled simulator exposure to the somatogravic illusion elicits measurable disruptions in altitude control that are not mitigated by experience alone but can improve with brief, repeated exposure. The findings support the integration of illusion-focused modules into early instrument training to enhance resilience to spatial disorientation. The use of fixed-base simulators for such training is feasible and well-received by pilots.