Preferential Scheduling


Importance of scheduling to prevent pilot fatigue

Preventing fatigue in pilots in the past has been mainly based on restricting the total amount of work hours in a given period. Recently there has been more focus on fatigue that is accumulated in the short-term, caused by hours of work that conflict with the normal circadian rhythm of a crew. This more recent focus is due to a series of studies by NASA on crew fatigue in flight operations, providing a guide in the scheduling of duty and rest in commercial aviation.

Government regulations and industrial rules to prevent fatigue

Most governments prevent fatigue by limiting the hours worked and dictating the rest that is required before and after duty. They can also limit the amount of duty according to the time of day and time zone, make changes to the total time on duty in terms of flight sectors operated as take-offs and landings induce a greater workload than cruise flight. In addition to government regulations, there are the more restrictive industrial rules put in place unique to an airline’s operational environment. These rules may focus on issues such as the number of successive night duties, landings versus length-of-duty period and grouped or patterned time off scheduling.

Examples of schedule-related fatigue

The following examples illustrate some of the conditions that lead to fatigue in crew. There are also government regulations, industrial and airline rules, and scheduling methods in place to reduce or prevent fatigue in the aircrew, which is added to each example as they apply.

1. Duty period and time zones. A crew starts work in the afternoon in America and then arrives in Europe in the morning, local time. The crew then need to rest during daylight hours in a noisy environment, finishing in the evening, and then with added rest in the night to minimize fatigue the next morning. This would be when their normal sleep period begins. Because their circadian rhythms have not had time to adjust to the different time zones, departing from Europe in the morning would be the same as arriving at work at midnight to work through the night.

There is a limit to the length of duty period and number of sectors operated when there has been insufficient rest.

2. Continuous night duties. This creates the same problems of fatigue when it is not possible to achieve a full and complete rest outside normal circadian rhythms. Family and social commitments also put pressure on this situation. Also, an added problem is when the crew begins a series of days off, returning to their normal sleep cycle, but this occurs just after their bodies have finally adjusted their internal clock for the night duties.

Restrictions are enforced, such as limiting the number of consecutive duties, reducing the duty period length as the number of consecutive duties increases, and increasing the rest requirements before and after duty.

3. Work schedule opposing normal circadian rhythm. Pilots who perform best in the morning are scheduled to work at night, or those who prefer to rest late and rise late are scheduled for an early morning shift. This creates “sleep deficit” leading to accumulated fatigue, having a harmful effect on crew members and preventing them from correctly performing safety-related tasks

Early and late duty periods are spread out evenly through the use of monthly crew schedules mixing flight duties

Preferential Scheduling

In terms of creating crew schedules to prevent fatigue, the focus is on the distribution of duties and time-off periods. Some schedules create a balance in the number of early and late trips flown by each pilot. Other schedules use a set of “line blocks” which expands on the techniques used by the government and industry to limit crew fatigue. However, this does not allow for the importance of matching duty periods with a crew member’s circadian rhythm. A recent development known as preferential scheduling allows crew to alter their schedule to follow their preferences for duty, time off, pattern of work and co-workers. This reduces the possibility of undesirable schedules and matches it with their circadian rhythms, further helping to reduce fatigue and clashes with personal commitments. It is impossible to match an exact schedule to what all crew members desire, however it does increase the overall suitability of the schedule.

Other factors that can be used in combination with preferential scheduling to prevent fatigue include such things as getting as much rest as possible before a trip, maintaining a healthy lifestyle and avoiding or limiting alcohol, caffeine and tobacco. There are also a number of ways to prevent fatigue once on duty, including a well lit workplace, controlled intake of caffeine, keeping the body moving, taking short naps and following a proper diet.


Chittick, J. (1998). Preferential scheduling for aircrew can help address problem of short-term accumulated fatigue. Retrieved November 4, 2011 from

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