Aircrew: Repeated Sleep Loss and the Accumulation of Fatigue

Introduction: It is commonly assumed that two undisturbed nights of recovery reset the fatigue to normal. This is also the assumption in mathematical models designed to predict fatigue from work schedules which lacks long-term recovery processes. However, there is almost no research done on the effect of repeated sleep deprivation/sleep loss across longer periods of time. It is possible that fatigue/sleepiness accumulates across repeated bouts of sleep loss. Such findings should affect work hour regulations and mathematical models predicting fatigue from work schedules. The present study focused on aircrew, and the purpose was to study the association between repeated sleep loss and accumulation of fatigue across work rosters, and to derive metrics that can be used to improve the performance of mathematical models in predicting fatigue. As an indicator of sleep loss, we used the encroachment of work (roster based) on the window of circadian low – WOCL (timing between 0200–0600), since that was available directly from collected roster data.