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Fatigue in the cockpit


Pay attention! Pilot awareness is important in recognizing the danger signs.

By Shawn Pruchnicki
ATP. CRJ 200

Length of workday, varying time zones, and varying shifts are contributors to pilot fatigue. These factors should be considered when scheduling flight department personnel.

The jet entered instrument meteorological conditions (IMC) upon descent. Automatic terminal information service (ATIS) reported that the ILS was out of service and that a VOR approach was in use.

The experienced Part 135 crew began the briefing. During the approach, on the second step-down segment, their vertical speed became excessive, and the ground proximity warning system (GPWS) alerted numerous times.

After a significant delay initiating the go-around, the aircraft struck rising terrain and was destroyed. The cockpit recorder revealed that the crew was too slow to recognize the warning and to initiate the escape. The subsequent NTSB investigation was unable to find any problems with the aircraft, ATC, navigation, training, or any medical problems.

The crew’s 72-hour history failed to reveal anything potentially contributory. The length of rest periods and the duty day for FAA Part 135 flight operations were within these limits.

So why would a highly experienced crew fly a state-of-the-art jet into the ground? NTSB’s investigation turned toward considering fatigue as a potential explanation.

The value of a good night’s sleep

As most of us moved beyond adolescence, we learned that 8 hours of sleep is what we need to be rested. In many cases, it seems like some of us need more, while others think they are fine with less. However, this is typically not true despite their claim to the contrary. Soon did we discover that not only was the length of the sleep period important – the quality of our sleep can affect how we feel and perform in the days following.

The quality of sleep and thus its adequacy can be affected by numerous factors, such as temperature, noise, physical comfort, security concerns, psychological state, and medication usage. And many of these factors are out of a pilot’s control while on trips. For decades, fatigue has been a constant fixture in everyday life, and this is especially true in the transportation sector.

Although all of us who fly under either FAR Part 121 or 135 are fortunately provided a degree of protection with regard to length of workday and rest period, the possible solutions to remaining rested during a trip are not so simple.

For example, despite what might appear to be a fatigue-reducing advantage such as a shorter duty day, a circadian disruption of even a few hours (a couple of time zones) can produce significant amounts of fatigue, with insidious effects on decision-making. In this example, it is not the length of the day that is the problem, but rather the ability to adjust to the new time zone and obtain sleep of both sufficient quantity and quality.

Circadian disruption, time on task, and time awake, are all well-known predicators for fatigue. In fact, being awake for 17 hours creates the same degree of cognitive impairment and reduced decision-making ability as having a blood alcohol concentration (BAC) of .05%. And worse, being awake for 21 hours equals a BAC of .1%.

Just as a reminder – FAA’s BAC limit is .04%. What were you doing the last time you had been awake for 17 or even 21 hours? Flying or driving perhaps? Although factors such as length of workday and varying time zones are widely recognized as contributing to fatigue, sleep researchers and accident investigators also understand the role that daily trips with varying start times may have on fatigue.

An example of a trip with different types of shift work would be a 5-day trip that starts with a pilot doing their first shift flying, then moving to third shift, and ending with a second shift flying. This rapid cycling shift work is well documented to be extremely fatiguing and a known dangerous practice in scheduling.

Other factors, such as the number of flight segments per day, the time of day when a duty period starts and ends, and the number of consecutive workdays, are all considerations that can determine our level of fatigue.

All of these factors must be examined during accident investigations, and considered proactively as scheduling tools. Over the decades, what started as a realization that longer working days and/or shorter sleep periods produce fatigue, has matured into a more comprehensive insight into what is really involved in understanding human fatigue.

Larger business jets have a dedicated flightcrew rest area. If you’re feeling fatigued enroute, let your crew mate handle the flight deck, take a break, and come back well rested to handle flight duties as a team again.

The effects of fatigue incognitive functioning

Our higher cognitive processing, such as decision-making, originates from the prefrontal cortex of the brain, which is highly vulnerable to the effects of fatigue and will impair those tasks that require executive cognitive functions.

The real danger here is that pilots may not be aware of this at first, but may eventually catch themselves making “silly” mistakes. There may be other explanations for these mistakes, but some degree of fatigue is a very real consideration and may not be apparent at first.

Although we are usually aware of our individual type of physical and psychological results from fatigue, some effects are more universal. For example, executive cognition functions that are critical to safe flight include plan development, adhering to procedures, assessing risks, and making timely judgements.

Increasing the danger even further, we may also experience a reduction in both speed and complexity of innovative thinking and decision-making capabilities. One of the most dangerous effects is the presence of plan continuation, meaning that, once a pilot starts a course of action, he/she is less likely to recognize the need to modify that decision, even when faced with what might appear to be overwhelming indications to do so.

How much fatigue is too much?

As professional pilots, we have all been taught that we should not fly when fatigued. However, what we are not taught is how fraught with complications this decision really is. For example, we never seem to hear about how fatigue is not bimodal. That is, it is not as simple as either we are fatigued or we are not.

Being fatigued is a continuum, and one could probably argue that we might be fatigued to some degree, no matter how slight our sleep reduction might be or how far we are into a workday. So, how much fatigue is too much? There is no easy answer. We all have flown fatigued to some extent, and calling in fatigued is not as easy as the regulator and our companies seem to make it.

As we were learning to fly, we were never taught how to handle a scenario where we start the flight feeling rested, but end up feeling overcome with fatigue enroute. What do you do then? We all seem to have our own strategies for dealing with this problem – even if we only think we’re dealing with the problem.

Again, as before, the regulator is silent on guidance or regulation. In many countries, strategic napping on the flight deck is allowed and planned for. The majority of the most meaningful flight fatigue research was performed by NASA and FAA. Yet, despite their findings, we are still waiting on guidance.

Finally, what could be considered of greatest concern – and perhaps most dangerous of all – is that we are terrible at assessing our own level of fatigue. The exact science behind this is beyond the scope of this article, but it has been established for decades. Probably, the next concern is that we might feel that we are used to flying fatigued and perform quite fine, even when exhausted, because, after all, we’ve never had an accident.

The problem is that accidents are multifactorial, and we may never know the next time fatigue may unexpectedly be the tipping point that makes an accident inevitable.


The solution to not flying fatigued of simply assessing your level and calling in, as recommended by the regulator, is overly simplistic. Awareness of the causes, cognitive effects, and symptoms will play a role in your assessment and will allow for a more informed decision.

One suggestion may be that, if you feel fatigued while flying, advise your crew mate, so that they can observe for fatigue-related behaviors. Maybe they should fly the approach, especially if it is night-time and/or IMC. Quite possibly, the most significant factor is our awareness that when we do feel tired we can be sure that we are actually more fatigued then we think we are. Make sure that you use this as part of your assessment. Moreover, by the time you feel severely tired/fatigued, this is a very dangerous situation. Don’t let fatigue be the final straw on tonight’s approach!

SteveShawn Pruchnicki has a PhD in Cognitive Engineering from Ohio State University. A former airline pilot and accident investigator, he now teaches safety and human factors at OSU, in addition to teaching and lecturing all over the world.