NASA Study Highlights Short Haul Pilot Fatigue Issues

Fatigue is an ongoing safety concern for airline pilots, largely due to the realities of 24-hour operations. Fatigue arises from sleep deficiency and circadian disruption and impairs attention, concentration, and decision-making, increasing the risk of operational errors. While several studies have investigated pilot fatigue, especially related to jet lag, few have examined fatigue in short-haul operations, leaving an information gap in this large segment of operations.

Short-haul schedules often require pilots to work during their biological night, when they’d otherwise be asleep, leading to circadian disruption. Prior studies typically focused on characterizing single aspects of circadian disruption, like overnight flying (red-eyes) or early departures, rather than assessing the cumulative impact of circadian disruption across a trip. Because airline schedules often involve consecutive flight duty periods (FDPs) with varying start and end times, understanding how these patterns affect fatigue, performance, sleep, and recovery is important for developing effective fatigue-mitigation strategies.

About the Study

Our NASA team collaborated with Drs. Hannah Baumgartner and Thomas Nesthus at the Civil Aerospace Medical Institute (CAMI), Dr. Amanda Lamp at Washington State University, and Dr. Laura Barger at Harvard Medical School to study fatigue in short-haul operations. To ensure relevance to the pilot community, we conducted a focus-group study with short-haul airline pilots. Pilots identified circadian disruption, including red-eyes and circadian swaps (i.e., switching between early starts and late finishes, or vice versa), as a top concern. Based on these findings, and to better understand how circadian disruption impacts short-haul operations, we conducted a large in-flight study to evaluate fatigue, sleepiness, performance, and sleep during circadian-disrupted trips versus nondisrupted trips.

We worked with four U.S. airlines and their labor unions to distribute information about the study. Interested pilots contacted us, and we screened them to determine whether they’d be scheduled for the trips of interest. To be eligible to participate, pilot volunteers had to be willing to collect data for up to three days before and after a trip without circadian disruption (defined as at least two consecutive FDPs, none of which were scheduled to start or end between midnight and 6:59 a.m. relative to home-base time zone) and a trip with circadian disruption. Although the term red-eye is widely used, it can be hard to define. For our study, we considered a red-eye as an FDP operated through the window of circadian low (WOCL, 2:00 a.m. to 5:59 a.m.) relative to the pilot’s home-base time zone or the departure/destination local time zone. We defined circadian swaps as at least one FDP that started between midnight and 6:59 a.m. relative to home-base time zone, followed by at least one FDP ending between midnight and 6:59 a.m., or vice versa, on consecutive duty days.

Each eligible pilot was sent a data-collection kit that included an iPod equipped with the NASA Psychomotor Vigilance Task (PVT)+ application. Our NASA team designed the NASA PVT+ app to make it easy to collect real-world data. The app included several background questionnaires to help us understand the characteristics of our study volunteers. We asked about daily sleep quality and causes of sleep disruption (e.g., hotel noise, temperature issues), fatigue and sleepiness throughout the day, workload, hassle factors, and fatigue countermeasures utilized during flights. The app also prompted pilots to take a five-minute PVT performance test, a simple reaction-time test that’s an objective indicator of fatigue. We asked pilots to take the PVT before and after duty, and prior to the top of descent, during each flight. The app included a number of other types of data collection, including information on meal timing, exercise, turn time, “van” time, and other concerns that pilots told us in the focus groups were important to capture—and that we’ll evaluate in future analyses of this research.

In total, 159 pilots from four airlines completed the study, contributing approximately 8,000 PVTs and fatigue ratings over 1,921 flights and 2,406 days, making this the largest and most comprehensive study of short-haul operations to date. The pilots reported an average FDP length of approximately 8.5 hours, with an average individual flight length of about 2.75 hours. We were somewhat surprised to find that the average time off between duty was approximately 17 hours, with very few trips involving minimum rest (10 hours per FAR Part 117). After further investigating this finding, we learned that the airlines that helped us recruit pilots have many negotiated scheduling agreements that go beyond regulatory limits.

What We Found

When we compiled all of the data to assess fatigue, alertness, and performance by time of day, we found that the highest fatigue and sleepiness ratings and lowest PVT performance occurred during nighttime hours. In particular, performance and ratings slumped between about 1 a.m. to 4 a.m. home-base time, which, perhaps not surprisingly, corresponds approximately to the WOCL.

On circadian-disrupted trips, we found that pilots slept about 30 minutes less overall and took more naps of longer duration than on nondisrupted trips. This is likely because the disrupted FDPs (i.e., red-eyes or circadian swaps) would have interfered with the pilots’ ability to sleep at night. Many studies have shown that trying to sleep during the day results in less sleep because the circadian rhythm actively promotes wakefulness. As a result, even when a person is very tired from being awake all night, it’s unlikely that sleep of equivalent quantity and quality can be achieved during the day as compared to at night. Similarly, staying up late or getting up early for a swap means that a pilot would need to go to bed early or try to sleep late to obtain enough sleep, but it’s difficult to maintain sleep at times when one would usually be awake.

It’s also difficult to remain awake and fully alert during times when one would normally be asleep. It’s likely that insufficient sleep, coupled with working during the night, contributed to our finding that pilots had a small but statistically significant increase in fatigue and sleepiness and a decrease in performance during circadian-disrupted trips compared to nondisrupted trips. These results suggest that existing mitigations such as regulatory duty-hour limits, scheduling negotiations, and best practices employed by pilots, such as napping while off duty, are likely helping to reduce the impact of circadian disruption. However, our findings also highlight the importance of ongoing evaluation and determination of best practices for fatigue risk management.

Finally, we found that pilots performed worse, felt more fatigued, and slept more after all trips compared to before the trip, although these differences were also small. These findings highlight the importance of having ample time to recover between trips of any type.

Future Exploration

In summary, this dataset provides a rich source of information for exploring many issues related to fatigue in short-haul operations. We’re grateful to the pilots who volunteered for our study and look forward to conducting additional analyses to explore other concerns they raised. Future analyses will examine additional variables captured in this study, including factors identified by pilots during the focus groups. Our findings from this first analysis suggest a small but significant reduction in

From Flight Deck Insight to Data-Driven Conclusions: Why Pilot Input Is Paramount to Meaningful Research 

By Capt. Doug Marchese (JetBlue), Chair, ALPA Flight Time/Duty Time Committee

To better understand how circadian disruption impacts short-haul operations, NASA, in collaboration with the Civil Aerospace Medical Institute (CAMI), Harvard Medical School, and Washington State University, conducted a large in-flight study to evaluate various aspects of pilot fatigue. The agency’s use of U.S. airline pilots underscores its understanding of the importance of listening to frontline employees and demonstrates NASA’s respect for the input of those who fly the line each and every day.

Many of the study’s findings align with what we, as pilots, know from experience. For example, we sleep less overall and take longer-duration naps while off duty when our circadian rhythms have been disrupted and sleeping during the day is less restorative than at night. The data from the study strongly indicates that pilots place significance on proper planning to ensure maximum piloting performance and to seek opportunities for rest.

The study also references scheduling practices that push legal limits to the edge. This type of scheduling removes flexibility when things don’t go as planned, prevents proper recovery from sleep loss, and doesn’t consider the daily workload challenges that affect pilots.

Scheduling trips so that they align with pilots’ fatigue-mitigation strategies can only lead to more rested pairings, less-fatiguing schedules, and safer skies. It’s imperative that we consider the physiological needs of pilots when developing the system in which they operate. Workload challenges are real, and the fact that certain trips can reduce mental and physical performance demonstrates that there’s still much to learn about the interconnectivity among sleep science, mental workload, and physical performance. For pilots, improving access to educational materials on these connections is paramount.

In Canada, ALPA is launching a significant flight-time/duty-time campaign to support our Canadian ALPA members in their quest to ensure that fatigue regulations are implemented, consistently applied, and rigorously enforced.

The fatigue study from NASA and its partners highlights how we can better educate both pilots and operators to schedule, value, and ensure that our recovery environments are the best they can be. We can’t allow our safety record since the implementation of 14 CFR Part 117 to lead us down a path of complacency. This study underscores the importance of continued vigilance and improvement. Studies like this one, and the collaboration among airlines, unions, NASA, CAMI, and universities, enable us to dive deeper into fatigue issues and continuously improve Fatigue Risk Management Systems.