This discussion only touches the surface of the link between fatigue and stress in shift work such as UAS operations, and is a starting point for policy sharing between manned and unmanned aircraft organizations when it comes to fatigue and stress.

Fatigue and stress are related in many ways, here I will discuss just a few of them.  The long term effects of fatigue can be seen in the co-morbidities reported by Culpepper (2010): metabolic, gastrointestinal, cardiovascular, mood and anxiety issues have all been linked to problems caused by long term shift work, they are also symptoms of long term stress. In addition, chronic stress can disturb sleep patterns already compromised by working against natural circadian rhythms.  Research has shown that a complete lack of sleep is fatal (Pinel,2011). 

The hormone cortisol (one of many glutocorticoids released by the anterior pituitary in a natural stress response) serves a natural function to arouse an individual from sleep in a normal circadian rhythm (Drake, 2010; Pinel 2011).  This dual function of cortisol is a biological connection between fatigue and stress.  Circadian dsynchonization (a waking cortisol signal sent during the shift worker’s scheduled sleeping time) creates a biological stress on an organism and can underlay stress caused by the challenges and pressures of work performance (Drake, 2010). Stress and fatigue are so closely related that Pinel laments the lack of sleep studies that control for stress and vice versa (2011).  Even more problematic for UAS operators, research has shown that executive function, such as might be required to control a UAS, is the most vulnerable cognitive ability to long term chronic stress (Arnsten, Mazure & Sinha, 2012), as might be caused by shift work disorder.

UAS and manned aircraft share sources of stress caused by both vigilance tasks and acute events (Wickens, Lee, Liu and Becker, 2004), such as emergencies and offensive missions.  UAS operations involve long term (over months or years) shift work (manned aviation shift work is also a concern but varies by organization and mission, and is limited to some degree by vehicle maintenance cycles and refueling requirements); manned aviation involves the physical stresses associated with being in the aircraft at high altitudes, exposed to dynamic forces such as vibrations and aerodynamics.  In both cases, careful management of qualified personnel in number (allowing for coverage of mission schedules without compromising crew rest requirements) and shift schedules are paramount to addressing this dual threat to aviation safety.  This idea highlights one area that UAS communities would do well to learn from manned aviation:  strict adherence to established crew rest requirements by both the organization and the operator can preserve a protection against long term fatigue. The difference in motivation on the part of the operator is that the UAS operator does not encounter physical danger when fatigued, so the motivation to alter daily activities to observe crew rest is less salient.  Study in motivation and organizational psychology can suggest policies to encourage compliance with crew rest guidelines and regulations in UAS operators.  

Arnsten, A.,Mazure, C.M., and Sinha, R. (2012).  Everyday stress can shutdown the brain’s chief command center. Scientific American, 306(4). 48-53.

Culpepper, L. (2010).  The social and economic burden of shift work disorder. Supplement to The Journal of Family Practice. 59 (1), S3-S11.

Drake, C. (2010). The characterization and pathology of circadian rhythm sleep disorders. Supplement to The Journal of Family Practice. 59 (1), S12-S17. 

Pinel, J.P. (2011).  Biospychology. Boston, MA: Allen & Bacon.

Wickens, C. D., Lee, J. D., Liu, Y., Gordon Becker, S.E. (2004).  An Introduction to Human Factors Engineering. Upper Saddle River, New Jersey: Pearson Education.