INTRODUCTION: We examined aircrew fatigue during the following flight duty periods (FDPs) mentioned in the European Union (EU) Flight Time Limitations (FTLs): night FDPs longer than 10 h and FDPs typical of disruptive schedules (early starts, late finishes, and nights). An alternative way of classifying night FDPs was also examined to reveal possible subcategories that warrant special attention.METHODS: A total of 392 aircrew members (96 women) representing 24 airlines participated in the study. Their FDPs were measured by a diary, sleep by the diary and wrist-actigraphy, and fatigue by the Karolinska Sleepiness Scale (KSS) over 14 consecutive days. The KSS ratings given at top of descent (TOD) served as the main outcome.RESULTS: The probability of high fatigue (KSS ≥ 7) at TOD was 0.41 and 0.32 during long (>10 h) and short night (≤10 h) FDPs, respectively. The corresponding value was 0.19 for early starts, 0.31 for late finishes, 0.34 for night FDPs, and 0.15 for day FDPs (reference). The main predictors of high fatigue were FDP's encroachment on the window of circadian low (WOCL, 02:00 h-05:59 h) and prior sleep. Within the night category, FDPs fully covering the WOCL showed the highest probability of high fatigue at TOD (0.42).DISCUSSION: Late finish and night FDPs warrant special attention in fatigue management. Within the night category, the same holds for FDPs that fully cover the WOCL. To manage fatigue, adjustments of the FTLs seem to be a limited strategy and therefore other measures, including maximizing preflight sleep, are needed.Sallinen M, van Dijk H, Aeschbach D, Maij A, Åkerstedt T. A large-scale European Union study of aircrew fatigue during long night and disruptive duties. Aerosp Med Hum Perform. 2020; 91(8):628-635.