The commercial aviation of European operators adheres to the rules of the EASA (European Union Aviation Safety Agency). These define maximum flight duty periods and minimum rest times to prevent excessive fatigue. The latter has been proven to have similar effects on psychomotor skills and reaction time as alcohol intoxication. However, this does not always work. This is due, for example, to schedules that define the maxima/minima as target objectives or the rigid algorithm for time zone acclimatization, from which maximum permitted flight duty times are derived. Other causes include departure delays, which may shift the flight duty period to a larger extent into the night without reducing the maximum flight duty time, or unforeseen disturbances during rest periods. Therefore, the Fatigue Risk Management has been introduced as an additional barrier, whose principles are summarized under Fatigue Awareness and Countermeasures.