International Civil Aviation Organization Annex 6, Operation of aircraft prescribes the relevant definitions concerning the flight time limitations. It also gives guidance on the establishments of the limitations. In establishing limitations concerning the flight time limitations the size of the crew, whether the aircraft is equipped with a horizontal rest facility, traffic density, navigational and communication facilities, the biological rhythms, number of flight cycles, aircraft performance and weather conditions are taken into account. The European Union states that the maximum daily flight duty period is 13 hours. There are several exceptions to this rule. The minimum amount of rest at a pilot’s home base is at least 12 hours or the duration of the precious duty period, whichever is the greatest. Same rule counts outside the pilots home base only the minimum rest period is at least ten hours. The national legislation specifies the 18 ‘white spots’ remained from the European Union. The extension on the maximum daily flight duty period which is given when the aircraft is equipped with a rest facility is one of them.

Human factors are the most restrictive aspect concerning the flight time limitations. Over 20% of the aviation accidents are related to fatigue. The most dangerous type of fatigue in the aviation industry is chronic fatigue. A flight exists out of different flight phases with flight phase specific workloads. During take-off and approach the workload of the airline pilots increases compared to the other flight phases. The biological rhythms of a human person are hard to adjust when traveling through several time zones. In general it takes one day per one hour time difference to adjust to the daily rhythm at destination. A good night of sleep can provide a maximum of eight sleep credits. One sleep credit is equal to two hours of activity. Meaning that a person is able to have an activity period of maximum 16 hours before he/she is creating a sleep deficit.