0171 Fatigue Risk Management in Aviation: Optimal Planning of Sleep Opportunities During 24-Hour Layovers Through Biomathematical Modeling

Abstract Introduction When switching between daytime and nighttime flying or during transmeridian trips, flight crew may encounter layovers that are ~24h in duration. Managing sleep during these layovers is challenging: Sleeping early helps to recover from the prior duty period, while sleeping late helps to prepare for the next one, and circadian rhythmicity constrains when sleep is possible. We used computer simulations based on the two-process model (TPM) of sleep/wake regulation to explore optimal 24h layover sleep strategies. Methods We simulated all possible sleep schedules during 24h layovers with 4h–8h total sleep opportunity, scheduled in 1h increments as consolidated sleep opportunity or split between two sleep opportunities of ≥2h duration and ≥2h apart. For each simulated sleep schedule, and for all possible layover start times in 1h steps, we tracked the homeostatic and circadian processes of the TPM across the 24h layover and a subsequent 12h duty period. Initial homeostatic sleep pressure at the layover start was assumed to be 0.62 or 0.85 (moderate or considerable prior wakefulness). Evaluated at 30min resolution, the model marked when sleep would occur during the scheduled sleep opportunities, based on homeostatic pressure exceeding the lower TPM circadian threshold (i.e., sleep was biologically plausible). The model also flagged when, outside of scheduled sleep opportunities, homeostatic pressure exceeded the upper circadian threshold (i.e., effort required to stay awake). Additionally, we calculated the peak level of sleepiness (homeostatic sleep pressure minus circadian wake pressure) during the subsequent 12h duty period. Results Among all simulated 24h layover sleep schedules the most (compared to least) effective ones yielded ~25%–50% reductions in peak sleepiness during the subsequent 12h duty period. For ≥6h total sleep opportunities, irrespective of 24h layover start time, optimal sleep scheduling involved split sleep with one sleep period near the start and another near the end of the layover. For ≥7h total sleep opportunities, regardless of initial homeostatic state (0.62, 0.85), none of the optimal sleep schedules were flagged as requiring effort to stay awake. Conclusion Biomathematical simulations for scheduling of sleep during 24h layovers suggest that optimal planning entails ≥7h, split sleep opportunities. Support (if any) Federal Express Corporation