Fatigue can defeat the best pilots, procedures, and training—and if not properly managed can become a killer. For most of pilots’ professional lives, fatigue has been on the NTSB’s “Most Wanted” list. In fact, the Board has issued more than 200 safety recommendations to address the problem of human fatigue in all modes of transportation.

For a pilot, flying an aircraft requires complex human interaction, complete attention, and a high level of proficiency. However, according to the NTSB, all too often pilots and others performing safety-critical functions are impaired by fatigue stemming from insufficient or poor-quality sleep.

Fatigue is a tough topic. The only known preventive measure for fatigue is good rest. Trying to accommodate good rest and meet the demands of a 24/7 transportation system is tricky. Managing fatigue requires a three-pronged approach involving strategic planning using science-based scheduling practices, tactical countermeasures when needed, and a pilot’s responsibility to show up to a trip well rested and properly manage rest periods.  

The FAA defines fatigue as “a physical state of reduced mental or physical performance capability resulting from lack of sleep or increased physical activity that can reduce a flight crewmember’s alertness and ability to safely operate an aircraft or perform safety-related duties.” The challenge, according to the NTSB, is that the effects of fatigue often are not recognized until it’s too late.

In recent years, regulators such as FAA and EASA have established new science-based rules for flight and duty time limitations and now require commercial operators to employ a fatigue risk-management system (FRMS). Much of the science behind managing fatigue is based on defending the most critical period of the day—the window of circadian low (WOCL). WOCL is the time where humans are most vulnerable to sleepiness and is defined as the period between 2 a.m. and 5:59 a.m. in the time zone to which a pilot is acclimated.

Pilots flying at night or internationally operate in a perfect fatigue storm. International schedules, which typically involve long duty periods and like-nighttime flights, can also breach or skirt the WOCL. Crews flying these challenging schedules might feel the effects of fatigue manifested in either, or both, chronic or acute sleep loss and circadian rhythm disorders (desynchronoses).

Chronic sleep loss or sleep deprivation is the condition of not having enough sleep. It adversely affects the brain and cognitive function. Acute sleep loss occurs when sleep debt—the amount of sleep loss accumulated over time—is greater than six hours. Accumulated sleep debt can be zeroed out only by two nights of restorative sleep. To combat the onset of fatigue, pilots must show up to work without any sleep debt.

Circadian rhythm sleep disorders affect, among other things, the timing of sleep. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work or social needs.

The most common form of circadian rhythm sleep disorders is extrinsic (external) or circumstantial. Examples include jet lag (multiple time zones) and shift work (rotating shifts) sleep disorders. Other more serious circadian rhythm sleep disorders are intrinsic (internal) or “built in.” These examples are less common and more serious since the internal sleep patterns are out of sync with the normal biological clock or become variable throughout the day.

Strategic planning through science-based scheduling is the first line of defense against fatigue. Once in the cockpit, pilots might have to employ tactical countermeasures before the onset of fatigue, such as caffeine, conversation, or even water (to stay hydrated).

Some regulators—but not the FAA—endorse the use of controlled rest (CR) as a tactical countermeasure to mitigate fatigue. CR is a formal rest period during periods of low workload where one member of a non-augmented crew follows specific guidelines to take a brief nap on the flight deck.

Notably, the Flight Safety Foundation recently published a guide that not only endorses the practice but also establishes protocol for utilizing CR in an operation. The guide includes a checklist for pre/post CR and addresses the physiology of rest, sleep inertia, and other dos-and-don’ts.

Combating fatigue in around-the-clock, around-the-world operations is a significant challenge. Remember, the only known preventive measure for fatigue is good rest. While many regulators have begun implementing science-based scheduling regulations for commercial flight crews (in the U.S., cargo operators are exempt), these practices need to be extended to all operators and personnel in safety-sensitive operations. FRMSs are a great tool but should be fully integrated into an operator's SMS. Likewise, when the strategic plan falls apart, pilots should be allowed to employ countermeasures such as controlled rest.

Pilot, safety expert, consultant, and aviation journalist Stuart “Kipp” Lau writes about flight safety and airmanship for AIN. He can be reached by email.