The call comes in at 3 a.m., waking you from sleep on your sixth night of a seven-night hitch. A rollover accident on a country road has left the driver critically injured, and dispatch requests helicopter transport to the local hospital.
After checking the weather and conducting a preflight, you have the rotors turning within 12 minutes of the call. However, according to fatigue and sleep study data, you aren’t fully awake. And you may not be for a while.
At Verticon 2026, Federal Aviation Administration (FAA) engineering research scientist Dr. Hannah Baumgartner shared findings from a new FAA-sponsored study, Benchmarking Fatigue in U.S. Helicopter Air Ambulance Pilots. One of the findings emphasized sleep inertia — the time it takes to become fully alert after being woken.
The study showed that sleep inertia in helicopter air ambulance (HAA) pilots varies depending on when the pilot wakes, the cumulative days worked prior to the event, and the length and quality of sleep throughout the hitch. In this scenario, sleep inertia could last from 15 minutes in a best-case case to an hour or more if the pilot is significantly fatigued.
Establishing a benchmark
Sponsored by the FAA and supported by the National EMS Pilots Association (NEMSPA) and the Air Medical Operators Association (AOMA), this new study was initiated to provide deeper insight into HAA operations and fatigue, with potential use in future rulemaking.
“A few years ago, [the] Part 135 Pilot Rest and Duty Rules Aviation Rulemaking Committee was looking at 135 duty and rest limitations, and one of the key things that came from that group was an understanding that air ambulance operates differently than 135 and it should be looked at separately,” Baumgartner said.
“While there is some research on fatigue in helicopter air ambulance operations, it’s mostly in Scandinavia and Europe where they operate differently than us. We have operators working in many different environments, in many time zones, different places that get different amounts of light during the day. It’s a big swath to cover. We needed to conduct our own study that takes that into account.”
The study included data collected from 125 U.S. helicopter emergency medical services (HEMS) pilots across 21 operators — representing roughly one-third of the country’s HAA operators.
Participating pilots were evenly divided among daytime-only pilots working 7-on/7-off shifts, nighttime-only pilots working 7-on/7-off shifts, and a mixed-shift group rotating between days and nights, whether on 7-on/7-off or 3-on/4-off schedules. The research team was particularly interested in the mixed-shift scenarios to determine any differences in fatigue compared to strictly day- or night-shift pilots.
The study assessed three key areas of fatigue — cumulative fatigue, particularly over long consecutive shifts; circadian disruption, especially during the 2 to 6 a.m. window of circadian low; and sleep inertia when pilots are woken from sleep.
Paid for their time, the pilots participated in both subjective and objective data collection to measure fatigue in these areas. They kept daily sleep diaries and provided sleepiness assessments throughout the day and after every mission. They also wore activity watches, completed psychomotor vigilance tests (PVT) — the gold standard in fatigue research — to measure reaction time, and took the NASA Task Load Index after each flight to assess workload throughout their shifts.
Data was collected over a 13-day period per pilot: three pre-hitch baseline days, seven on-duty days, and three post-hitch recovery days.
Cumulative fatigue: the seven-day toll
One of the study’s most significant findings was the measurable buildup of fatigue across a standard seven-day hitch, Baumgartner said. Pilot reaction speeds on the PVT slowed steadily from day one through day seven, becoming especially apparent by day four. At the same time, pilots displayed cognitive lapses that increased at a similar rate.
“These are akin to sitting at a stoplight, and when it turns green, you are not responding fast enough,” she said of cognitive lapses. “It illustrates degraded alertness.”
The cumulative fatigue finding was nothing new to the industry.
“One of our HEMS pilots told us they have a checkbox on their flight risk assessment that asks if it is day four or later of their duty,” Baumgartner said. “Day four is exactly the statistically significant day we found, so that backs it up completely.”
The subjective data gathered at the same time told a different story, however. While pilots showed decreased response times in the objective data, they reported no change in their self-assessments.
“We’re not great at assessing our own sleepiness and fatigue levels,” she added. “We need to double-question ourselves sometimes and make sure we really are OK.”
The window of circadian low and sleep inertia
Flights occurring between 2 and 6 a.m. — the window of circadian low, when the human body most needs sleep and vigilance is at its lowest — painted a stark picture. Across the board, slower PVT speeds, more cognitive lapses, and higher sleepiness and fatigue ratings were recorded during this period compared to other nighttime flights. Baumgartner emphasized these effects compound with time on shift.
Pilots woken from sleep to respond during this period also experience a higher level of sleep inertia, the neurological state of impaired cognition following sudden awakening. Under normal circumstances, it might last 15 minutes. For a pilot more than four days into a hitch and waking during the circadian low, it could last an hour or more, she said.
Feedback from study participants highlighted they already recognized this timeframe as high risk through experience. “By far my most dangerous time on night shift is immediately after getting up to answer a call,” one wrote anonymously.
In light of this, another respondent suggested that pilots could be given a short period to fully wake before deciding whether to take a call.
Nolan Crawford of the FAA’s Air Transportation Division agreed: “Waking up in the middle of the night, two or three o’clock in the morning, answering the phone, trying to get my head together, trying to read the weather, all of that probably takes an extra minute or two more than it does on the day shift. Take that into account. If we can’t do it safely, should we really be moving the patient?”
Another stark danger
On June 24, 2019, a Boston MedFlight helicopter overflew the hospital before returning to land. After an investigation, the FAA determined the pilot had fallen asleep during the flight. Fortunately, he woke up, and the flight concluded normally with no incident or injury. Fatigue was determined to be a contributing factor. It turns out, this is not an isolated incident.
The HAA pilot study asked pilots several direct questions in an anonymous survey. One was, “How often do you nod off during flight?” Strikingly, 30% reported it happens “rarely” or “sometimes.” The survey also showed that about 85% of pilots identified the return-to-base leg of a call as when they felt most fatigued.
Baumgartner emphasized the true figures are likely higher, given the natural reluctance to self-report.
Crawford recalled observing a fellow pilot’s head droop as they flew a medevac mission together over open water in the military. “It made me stop and think,” he said. “If I’m seeing that in him, am I missing it in myself?”
To address these extreme signs of fatigue, Baumgartner emphasized that a cultural shift is needed alongside regulatory direction. “Normalize the conversation. You see this and you know that you’re not alone. Talk to your other pilots. Normalize saying, ‘That was a bad one — I shouldn’t have done that.’ Keep each other accountable,” she said.
What the industry can do now
While there was no significant difference in fatigue between day, night, and mixed-shift pilots, the findings still showed a measurable level of fatigue in HAA operations. However, it is not deeply concerning.
“I think fatigue is managed very well in this industry,” Baumgartner said. “We didn’t find horrible, scary things. We found things that can be fixed.”
She outlined several concrete, near-term recommendations operators can implement to reduce fatigue risk. These include incorporating day-of-hitch count into preflight risk assessment tools to flag increased fatigue, explicitly identifying operations during the window of circadian low, and building in a formal stand-down period of several minutes between receiving a call and wheels-up on night shifts — giving pilots time to overcome sleep inertia before entering the cockpit.
Crawford extended this guidance to the full crew: flight nurses and medics, he noted, face the same physiological vulnerabilities as pilots and deserve equal consideration in fatigue management systems.
A full technical report from the study is expected in the coming months, pending FAA review. Additional analyses are planned, including a deeper examination of workload, night vision goggle operations, and multi-leg flights, Baumgartner said.
With new data shedding light on fatigue in HAA operations, the conversation is gaining momentum. Stay tuned for a deeper discussion in an upcoming episode of the Valor Flight Crew Podcast.
Excellent article. I am currently conducting M.S. Aviation research at the University of North Dakota on fatigue management in Canadian helicopter operations under CARs 702, 703, and 704.
This FAA-sponsored HAA fatigue study appears highly relevant, particularly the findings related to cumulative fatigue, circadian low, sleep inertia, and mixed-shift operations.
If the full technical report becomes publicly available after FAA review, I would be very interested in reading it. I would also appreciate any guidance on how to contact the research team or access future publications from the study.
Thank you for sharing this important work.