A review of 182 major NTSB investigations completed between 1 January 2001 and 31 December 2012 found that 20% of these investigations identified fatigue as a probable cause, contributing factor, or a finding. The presence of fatigue varied between among the modes of transportation, ranging from 40% of highway investigations to 4% of marine investigations.
Using a standardized performance test in, both, sleep loss and alcohol consumption conditions, investigators could provide a blood alcohol concentration metric to compare results from the sleep loss condition. Results demonstrated that after 17 hours of continuous wakefulness, cognitive psychomotor performance decreased to a level equivalent to a blood alcohol concentration of 0.05%. After 24 hours of continuous wakefulness, performance was approximately equal to a blood alcohol concentration of 0.10%.(Dawson D and Reid K. Fatigue, alcohol and performance impairment. Nature, 388:235, 1997.)
Fatigue, sleep loss, and circadian disruption created by flight operations can degrade performance and alertness, we all know that. Scientific examination of these physiological considerations has established a direct relationship to errors, accidents, and safety, we all know that, too. But, despite that knowledge fatigue remains an ever present danger in flight operations.
Extensive data are available that clearly establish fatigue as a significant safety concern in all modes of transportation and in 24-hr shiftwork settings. However, there are other associated costs of fatigue, such as decreased performance and productivity, financial costs of accidents and reduced productivity, and potential liability issues.
Fatigue refers to a physiological state of reduced mental or physical performance capability in which there is a decreased capacity to perform cognitive tasks and an increased variability in performance. It is also associated with tiredness, weakness, lack of energy, lethargy, depression, lack of motivation, and sleepiness. Fatigue is an enabler of poor judgment and decision-making, slowed reaction times, and loss of situational awareness and control. It degrades a person’s ability to stay awake, alert, and attentive to the demands of controlling a vehicle safely. Therefore, fatigue can impair a crew member’s alertness and ability to safely operate an aircraft or perform safety-related duties and it is a risk factor for occupational safety, performance effectiveness, and personal wellbeing. To make matters worse, fatigue actually impairs the ability to judge just how fatigued a person really is.
Fatigue results from an imbalance between:
- The physical and mental exertion of all waking activities (not only duty demands); and
- Recovery from that exertion, which (except for recovery from muscle fatigue) requires sleep.
Moreover, fatigue is associated with sleep loss, extended wakefulness, high mental and/or physical workload (mental and/or physical activity), long unbroken periods of work (now known as ‘time-on-task’ fatigue), and circadian phase (performance and alertness levels are largely influenced by the complex interaction between sleep and the 24-hour biological clock).
The multiple flight legs, long duty hours, limited time off, early report times, less-than-optimal sleeping conditions, rotating and non-standard work shifts and jet lag pose significant challenges for the basic biological capabilities of pilots, crewmembers, and shift workers. Humans simply are not designed to operate under the pressured 24/7 schedules that often define aviation operations, whether the operations are short-haul commercial flights, long-range transoceanic operations, or around-the-clock and shift work operations.
For all the above managing fatigue is a very complex task that must go far beyond flight/duty/rest time limitations. All these factors preclude a simple solution. There is no a simple and unique one-size-fits-all approach strategy that works for everybody.
The complexity and diversity of operational requirements demand a variety of approaches. Concept development should be initiated to move beyond current flight/duty/rest regulatory schemes and toward operational models that provide flexibility and maintain the safety margin. Managing fatigue must take into account operational differences and differences among crewmembers.and requires a comprehensive approach that focuses on research, education, and training, technologies, treatment of sleep disorders, hours-of-service regulations, and on- and off-duty scheduling policies and practices.
Nonetheless, it is critical that the core human requirement for sleep be managed effectively and operations should reflect the fact that the basic properties of the circadian clock directly affect an operator’s performance, productivity, and safety.
Scientific evidence has remarked the vital importance of adequate sleep (not just rest) for restoring and maintaining all aspects of waking function and the importance of daily rhythms in the ability to perform mental and physical work and in sleep propensity (the ability to fall asleep and stay asleep). Therefore, pilots and other aviation personnel, particularly those performing overnight operations especially during the window of circadian low, must be deeply and recurrently trained about the physiology of sleep and circadian rhythm and the causes, effects and risks associated with fatigue as well as its prevention and mitigation strategies, personal responsibility during non-work periods, rest environments, and commuting and/or napping. The fatigue training should include personnel involved in crew scheduling and senior management too.
Ultimately, fatigue-related accidents can be avoided with a combination of science-based regulations, comprehensive fatigue risk management programs, and individual responsibility.
Being the first part of Fatigue, an ever-present danger, series.
Sources: 1. FATIGUE RISK MANAGEMENT SYSTEM (FRMS)IMPLEMENTATION GUIDE FOR OPERATORS. ICAO, IATA, IFALPA. July 2011
2. FAA Advisory Circular AC No: 120-100. Subject: Basics of Aviation Fatigue. Federal Aviation Administration, June 7th, 2010.
3. FROM LABORATORY TO FLIGHT DECK: PROMOTING OPERATIONAL ALERTNESS
Mark R. Rosekind, Ph.D.1, LCDR David F. Neri, Ph.D. 1,2, and David F. Dinges, Ph.D. 3
1NASA Ames Research Center, 2United States Navy Medical Service Corps, 3University of Pennsylvania School of Medicine.
4. NTSB Most wanted list 2016. Reduce Fatigue-Related Accidents. National Transportation Safety Board, January 2016.
By Laura Duque-Arrubla, a medical doctor with postgraduate studies in Aviation Medicine, Human Factors and Aviation Safety. In the aviation field since 1988, Human Factors instructor since 1994. Follow me on facebook Living Safely with Human Error and twitter@dralaurita. Human Factors information almost every day