10 - Aircrew Fatigue and Circadian Rhythmicity

Abstract

This chapter highlights aircrew fatigue and circadian rhythmicity. In the early days of aviation, fatigue was viewed primarily as a function of total flight time and workload intensity. Such a view was certainly reasonable given that most flying was accomplished during the day. With the advent of frequent night flying and transoceanic aircraft, the need has arisen for a more comprehensive view of pilot fatigue. Flight time and workload cannot account for the increases in fatigue experienced by crews operating throughout the night or across multiple time zones. The additional factor of biological rhythmicity must be considered. Similarly, the effectiveness of flight crew rest time cannot be separated from the influence of the internal biological clock that programs bodies to behave differently at different times of the day. On the other hand, circadian rhythms are known to exist throughout human physiology. These rhythms have a period of about 24 hours and are seen as measurable and stable daily fluctuations—sometimes greater than 50% of the daily mean—in variables such as body temperature, blood pressure, heart rate, sensory acuity, adrenal gland output, brain neurotransmitter levels, and cell division. Circadian rhythms are also manifested in a variety of human behaviors when measured by standard techniques at different times of day. Significant rhythmic variations can be seen in overall flying skill and in each independent flight parameter as a function of the time of day, with poorer performance prevailing during the early morning hours.