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This article is the ninth in a series on landmark events in aviation since Flight Safety Foundation was founded in 1945.
When Charles Lindbergh made his 33-hour trans-Atlantic flight in 1927, fatigue was perhaps his greatest challenge. He fought off sleep for much of the flight, occasionally dozing off and waking again, seconds — or, sometimes, minutes — later.
In the decades that followed, fatigue has remained a challenge for pilots, and they — along with operators, regulators, researchers, and other safety advocates in the aviation community, including Flight Safety Foundation — have sought reliable methods of ensuring that flight crewmembers remain alert in the skies.
The basic dictionary definition of fatigue is “extreme tiredness.”
A more detailed definition from the International Civil Aviation Organization (ICAO) describes “a physiological state of reduced mental or physical performance capability resulting from sleep loss, extended wakefulness, circadian phase,1 and/or workload (mental and/or physical activity) that can impair a person’s alertness and ability to perform safety-related operational duties.”
Further elaboration, in Flight Safety Foundation’s 1997 “Principles and Guidelines for Duty and Rest Scheduling in Corporate and Business Aviation,” developed by the FSF Fatigue Countermeasures Task Force, warned of the “insidious” nature of fatigue, which “can cause even the most conscientious pilots to exceed reasonable duty limits and thus risk the safety of their aircraft, their passengers, and themselves.”
The Aerospace Medical Association (AsMA), in a 2009 position paper, attributed pilot fatigue to a variety of working conditions: “unpredictable work hours, long duty periods, circadian disruptions, and insufficient sleep that are commonplace in both civilian and military flight operations.”2
Effects of fatigue are “often underappreciated,” the paper said, adding, “Compared to people who are well-rested, people who are sleep deprived think and move more slowly, make more mistakes and have memory difficulties. These negative effects may and do lead to aviation errors and accidents.”
Flying While Fatigued
Multiple surveys have found pilots reporting that they have been sleepy or fatigued during flight.
A 2021 study by Swiss researchers of 406 pilots found that, even though they were working fewer hours than the legal limit, 45 percent of short-haul pilots said they had experienced “severe fatigue” and 32 percent reported “high fatigue.” Of long-haul pilots, 35 percent reported “severe fatigue” and 37 percent, “high fatigue.”3
A 2021 report in the Journal of Aviation Technology and Engineering identified 20 fatigue-related accidents and incidents between 1993 and 2016.4
According to a 2021 report in Frontiers in Physiology, various studies in recent decades have determined that fatigue has factored in 21 to 23 percent of major aviation accidents.5
Among those accidents, the report said, was the May 22, 2010, crash of an Air India Express Boeing 737 in Mangalore, India, which killed 158 of the 166 passengers and crew. The accident report from the Indian Ministry of Civil Aviation said the captain was asleep for the first 100 minutes of the 125-minute flight and included repeated references to the sound of the captain’s snoring on the cockpit voice recorder. The report said the probable cause of the accident was the captain’s failure to discontinue the unstabilized approach, and a contributing factor was the captain’s “prolonged [period of] sleep during flight, which could have led to sleep inertia.”
Several years later, fatigue was cited for contributing to a July 17, 2017, incident in which the crew of an Air Canada Airbus A320 lined up to land on a taxiway instead of a parallel runway at San Francisco International Airport, overflying two airliners awaiting takeoff clearances and descending to 60 ft before initiating a go-around. At the time of the incident, just before midnight, the captain had been awake for 19 hours. The U.S. National Transportation Safety Board (NTSB) said in its final report on the accident that the probable cause was the crew’s misidentification of the taxiway as the intended landing runway but that contributing factors included the captain’s fatigue “due to circadian disruption and length of continued wakefulness.”
Fatigue also figured in the Feb. 12, 2009, crash of a Colgan Air Bombardier DHC-8 in Clarence Center, New York, U.S., that killed all 49 passengers and crew and one person on the ground. The NTSB said the probable cause was the captain’s “inappropriate response to the activation of the stick shaker, which led to an aerodynamic stall,” but the board’s final report also said that the pilots’ performance likely was impaired by fatigue and subsequent legislation required the creation of new flight and duty time requirements.
Regulatory Limits
Over the decades, the aviation community has implemented numerous programs intended to help pilots remain alert.
Lindbergh’s self-designed effort, as he wrote years later in an account of his transoceanic flight, involved “letting one eyelid close at a time while I prop the other open with my will. My whole body argues dully that nothing, nothing life can attain, is quite so desirable as sleep.”6
Within a few years, civil aviation authorities intervened with regulatory efforts aimed at limiting monthly flight time. In 1931, the U.S. Commerce Department implemented a 110-hour limit, which was reduced three years later to 85 hours a month. In the decades that followed, the limits were adjusted periodically, and requirements were added to guarantee not only a limit for flight hours but also requirements for rest time.
These flight time limitation (FLT) plans eventually were supplemented with fatigue risk management systems (FRMS), which were intended not only to provide for crews to be well-rested throughout their flights but also to offer proactive and reactive interventions. ICAO describes FRMS as “a data-driven means of continuously monitoring and maintaining fatigue-related safety risks, based on scientific principles and knowledge as well as operational experience that aims to ensure relevant personnel are performing at adequate levels of alertness.”
An FRMS gathers and analyzes data involving crewmember alertness and operational performance. Critical elements of FRMS include fatigue management training, a crew fatigue-reporting system; fatigue-risk-based scheduling rules; and a fatigue safety action group to monitor the effectiveness of fatigue risk management controls and FRMS.
The first official use of FRMS was in 1995, when the New Zealand Civil Aviation Authority (CAA) began allowing operators to either comply with standard FTL requirements or to receive CAA approval for a variation designed to address additional factors that might be associated with fatigue.
Program Adoptions
In the years that followed, most nations and most operators adopted some form of fatigue management, and in some cases, specific fatigue-fighting programs were developed for specific operations.
For example, the Foundation, working with the National Business Aviation Association, produced “Principles and Guidelines for Duty and Rest Scheduling in Corporate and Business Aviation” in 1997. The document, updated in 2014 as Duty/Rest Guidelines for Business Aviation, cited business aviation components that can include shift work, night work, irregular and unpredictable work schedules, and time zone changes and noted that they “challenge human physiology and can result in performance-impairing fatigue and an increased risk to safety.”
In 2003, the Foundation published recommendations on operational guidelines, regulatory requirements and supporting research requirements for sleep and rest requirement for pilots on ultra-long-range flights — those lasting 16 hours or longer. In general, the recommendations called for airlines to develop ULR operational plans using a scientifically based method and to obtain approval for their plans from civil aviation authorities.
In 2018, the Fatigue Countermeasures Working Group — with more than two dozen members, including Flight Safety Foundation — issued Controlled Rest on the Flight Deck: A Resource for Operators, which discussed scientific research suggesting that a well-designed, monitored procedure of controlled rest on the flight deck could reduce fatigue-related safety risks and help pilots manage their fatigue.
In 2020, the Foundation, along with ICAO, the International Federation of Air Line Pilots’ Associations, and the International Federation of Helicopter Associations, released the Fatigue Management Guide for Helicopter Operators, which expanded explanations of the workings of fatigue management to helicopter operations.
Today, operators often incorporate an FRMS into their safety management system (SMS), with both systems based on data analysis and scientific principles that take into account not only the need for pilots to obtain adequate sleep but also the ways that a fatigued pilot can present a safety risk to flight operations, ICAO says.
In Doc 9966, Manual for the Oversight of Fatigue Management Approaches, ICAO says, “The FRMS approach represents an opportunity … to use advances in scientific knowledge to improve safety, use resources more efficiently and increase operational flexibility.”
Fatigue management, ICAO says, is a shared responsibility, with civil aviation authorities providing an acceptable regulatory framework, operators providing safe work schedules, and individuals arriving at work “fit for duty, including making appropriate use of non-work periods to obtain sleep.”
Notes
- ICAO defines the circadian body clock as a “neural pacemaker in the brain that monitors the day/night cycle … and determines our preference for sleeping at night. Shift work is problematic because it requires a shift in the sleep/wake pattern that is resisted by the circadian body clock, which remains ‘locked on’ to the day/night cycle.”
- Caldwell, John A.; Mallis, Melissa M.; Caldwell, J. Lynn; Paul, Michel A.; Miller, James C.; Neri, David F. for the Aerospace Medical Association Fatigue Countermeasures Subcommittee of the Aerospace Human Factors Committee. “Fatigue Countermeasures in Aviation.” Aviation, Space, and Environmental Medicine Volume 80 (January 2009): 29–59.
- Venus, Marion; Holtforth, Martin Grosse. “Short and Long Haul Pilots Rosters, Stress, Sleep Problems, Fatigue, Mental Health and Well-Being.” Aerospace Medicine and Human Performance Volume 92 (October 2021): 786‒797.
- Olaganathan, Rajee; Holt, Timothy B.; Luedtke, Jackie; Bowen, Brent D. “Fatigue and Its Management in the Aviation Industry, With Special Reference to Pilots.” Journal of Aviation Technology and Engineering Volume 10 (Issue 1): 45–47.
- Wingelaar-Jagt, Yara Q.; Wingelaar, Thijs T.; Riedel, Wim J.; Ramaekers, Johannes G. “Fatigue in Aviation: Safety Risks, Preventive Strategies, and Pharmacological Interventions.” Frontiers in Physiology Volume (Sept. 6, 2021). doi: 10.3389/fphys.2021.712628
- Lindbergh, Charles A. In “The Spirit of St. Louis.” Charles Scribner’s Sons, 1953. Quoted in multiple sources.
