One of the vital tenets of a strong safety culture is open reporting free from reprisal. Not only does this facilitate improvement in training and policy, but safety-conscious pilots also can learn from the situations and mistakes others have found themselves in. Through my work on multiple aviation safety action programs (ASAPs) and avid reading of my airline’s published incident reports, I like to think I have learned a substantial amount from the experience of others.
One of the most common contributing factors in these reports was fatigue. On top of that, there was a general sentiment that before whatever event occurred that warranted the report, the pilot felt that they were mostly fit for flight. It was only after an error occurred or circumstances arose that heightened their workload when the pilot realized that fatigue was affecting their ability.
While operating under Part 91, there are next to zero limits on flight or duty times. Flying can often feel like a welcome break after a long day at work or other activities. The onus is completely on us to determine our limits in an environment that is extremely dynamic and unpredictable. Let’s review how fatigue accumulates and how to recognize, prevent and mitigate the threats that arise when flying tired.
Fatigue Factors
We have all experienced fatigue, but the definition from the FAA expands on the operational effects: “In lay terms, fatigue can simply be defined as weariness. However, from an operational standpoint a more accurate definition might be: ‘Fatigue is a condition characterized by increased discomfort with lessened capacity for work, reduced efficiency of accomplishment, loss of power or capacity to respond to stimulation, and is usually accompanied by a feeling of weariness and tiredness.’”
Generally, fatigue can be sorted into sorted into mental and physical as well as chronic and acute. In aviation, we typically consider mental fatigue, although if you are so physically fatigued you are concerned that you should not be operating an aircraft, those concerns should be honored. Chronic fatigue is the result of prolonged stressors and several days of reduced rest. Full recovery from a state of chronic fatigue can take days of rest and proper sleep.
Acute fatigue is more closely related to short-term sleep issues, duration of wakefulness and time of day. From the FAA’s advisory circular AC 120-103, Fatigue Risk Management Systems for Aviation Safety, “Less than 8 hours sleep in the last 24 hours, being awake longer than 17 hours, and working between midnight and 0600 are associated with acute fatigue in the average person.” A good night’s rest should alleviate the symptoms of acute fatigue.
We generally associate fatigue with a sleep deficit, but the reality is complex. If you are interested in a deep dive of the subject of fatigue, check out the study, Quantifying Energy and Fatigue: Classification and Assessment of Energy and Fatigue Using Subjective, Objective, and Mixed Methods towards Health and Quality of Life, by Natalie Leah Solomon and Vlad Manea. It highlights several additional factors that can contribute to fatigue: age, physical condition, diet, timing of most recent meal, mental status, psychological condition and health status.
Consider a scenario where a pilot had a fine night of sleep last night, but rushed to the airport to fly home after a stressful day at work. Because the last meeting ran long, the pilot did not have time to grab a bite to eat on the way to the airport. Factor in the drier air at altitude, adding potential dehydration as a physiological contribution to fatigue. We can all imagine the potential performance degradation that could face this pilot as the flight drags on.
According to the FAA’s Fatigue in Aviation brochure, any fatigued person will exhibit these same problems:
- Sleepiness
- Difficulty concentrating
- Apathy
- Feeling of isolation
- Annoyance
- Increased reaction times
- Slower high-level functions
- Decreased vigilance
- Memory problems
- Task fixation
- Increased task errors
The trick is applying the above symptoms to day-to-day life as well as flying. I mention recognition outside of flying because in a perfect world, a pilot would realize they are fatigued prior to departure and adjust accordingly. Some fatigue “red flags” that would make me concerned about fitness for flight could pop up on the drive to the airport.
Hazards of Fatigue
Flying is an exercise of manual dexterity, information processing, decision-making and communication. Put simply, it is a juggling act. Fatigue negatively affects our ability to carry out tasks. The lack of compatibility here is obvious, but it really compounds. Flying fatigued results in slower response times, increased errors and lapses in judgment, to name a few. If these occur, often the pilot ends up task-saturated and behind the aircraft, having to catch up while still feeling the effects of fatigue that contributed to being behind the aircraft in the first place.
For example, if a pilot experiences microsleeps (elaborated in the sidebar below) on the highway or makes a wrong turn on a familiar route, they should consider their fatigue levels before even beginning to preflight. I firmly believe that resisting so-called operational pressure is one of the foundational tenets of safe, considerate airmanship. I say operational pressure in reference to get-there-itis, student or friends/family wanting to fly, employer pressure…anything giving you pause when faced with the decision to cancel a flight. It is extremely difficult to make the call to send everyone home disappointed, but it is magnitudes better than incurring undue risk flying fatigued.
Long story short, if you are questioning your fitness for flight due to fatigue, trust your instincts and use sound judgement, even in the face of whatever pressures are compelling you to complete your mission.
Recognizing fatigue symptoms while flying is important, despite there being fewer options for mitigation once airborne. This varies person to person, like most physiological factors. For example, I know I am starting to hit my limits when I forget frequencies that were just given to me or I struggle with two- and three-part clearances from ATC.
Obviously, these happen to everyone time to time, but I can usually tell I am working harder to remember, repeat and execute ATC’s orders. I naturally speak too quickly for my own good, so when I am fatigued, I frequently stumble over my words. The first signs may be completely different for you. Knowing yourself and your own limitations is paramount.
The term “microsleep” refers to very short periods of sleep, measured in seconds, not minutes or hours. Most of us have experienced or witnessed this sensation, a brief head nod lasting 15 seconds or less before snapping awake. Generally, the biggest risk factors for microsleep Is lack of proper rest combined with a monotonous task, such as driving on an empty highway, but it can occur in fully rested individuals.
If you are heading to the airport and struggle to stay awake, exercise extreme caution when choosing whether to continue operating heavy machinery like an airplane. Dozing off in cruise happens. Missed radio calls and drifting from altitude are definite signs that intervention is needed. Try to eat or drink something, reduce cabin temperature and busy yourself with something to stay occupied but not distracted. Review Notams, read the emergency checklist/QRH…whatever it takes to stay engaged while monitoring the aircraft’s flight path.
Mitigation
Step one to mitigate fatigue is prevention. Get sufficient high-quality sleep every night, avoid stress and long periods of wakefulness. Easy, right? Since this is the real world and our best efforts can still leave us fatigued, we should mention some strategies when faced with flying while less than well rested. If you have a few hours before departure, adjusting the time to facilitate a nap or just some rest can make a world of difference. Canceling is always an option.
If you find yourself in the nebulous zone of feeling less than 100 percent but not so fatigued that you are unfit to fly, there are short-term solutions to mitigate symptoms. Caffeine, exercise or a nutritious meal can help temporarily shake that tired feeling, with a huge emphasis on temporarily. Often a cup of coffee can lure a pilot into a false sense of security, providing a fleeting energy boost only to find themselves dozing off during the approach and landing phase.
If you do find yourself fatigued in flight, the most common tips for risk mitigation apply.
Don’t rush: Rushing leads to mistakes even when everyone is in tip-top shape. Slow down, and methodically complete checklists and procedures. If necessary, make time by stopping the aircraft on the ground, or asking ATC for a hold or box vectors in flight.
Trust, but verify: The best method to trap errors is to catch them as early as possible. If you experience any doubts about the aircraft’s state or what is being expected of you by ATC, ask.
It has come up in passing during the body of this article, but it’s worth elaboration. Commercial aviation has a slew of challenges to maintaining fitness of flight day to day. Long duty days, time zone changes requiring circadian swaps, dehydrating cabin air, scheduling changes…it can all add up. Fittingly, most commercial aviation is operated in consistent environments, with advanced aircraft flown by at least two pilots.
While general aviation operations do not aren’t subjecting themselves to circadian swaps day to day, it is often single pilot in aircraft with minimal or no automation. Shooting an approach to minimums after spending hours at altitude with no break is a classic recipe for fatigue, all while demanding a higher workload. Always consider the physiological effects a flight will have at the end of the flight while assessing fatigue levels during your preflight. Proper hydration is one mitigation as is using supplemental oxygen, especially at night.
Aviate, Navigate, Communicate: Often unexpected, high-workload situations (think a published missed or mechanical failure) occur, and during the post mortem of the event, the pilot realized fatigue was a contributing factor to errors committed.
Consider a busy approach combined with the list of degraded functions fatigue creates. Now mix in going around, configuring the aircraft, communicating with ATC, pointing the aircraft in the right direction…it’s easy to see how wrong turns happen, how flaps get oversped or other common errors occur on a missed approach. If you aviate, then navigate, then communicate; it helps simplify the process for a fatigued brain.Are You Safe?
Fatigue can adversely affect a pilot’s ability on a level similar to anything else on the FAA’s IMSAFE checklist. Unlike some more obvious detractors—alcohol or illness, for example—fatigue is something that can really sneak up on us. Humans are notoriously poor judges of their own fatigue levels, so vigilance is required to ensure that we are always operating the aircraft as close to the top of our game as possible.
