Recent studies suggest that carbon dioxide has an impact on cognitive function performance of office workers at concentrations previously thought to be benign (1000–2500 ppm). The only available data for CO2 on the flight deck indicate that the average CO2 concentrations are typically <1000 ppm, but the 95th percentile concentration can be as high as 1400 ppm, depending on airplane type.
We recruited 30 active commercial airline pilots to fly three 3-h flight segments in an FAA-approved flight simulator with each segment at a different CO2 concentration on the flight deck (700, 1500, 2500 ppm). CO2 concentrations were modified by introducing ultra-pure CO2 into the simulator; ventilation rates remained the same for each segment. The pilots performed a range of predefined maneuvers of varying difficulty without the aid of autopilot, and were assessed by a FAA Designated Pilot Examiner according to FAA Practical Test Standards. Pilots and the Examiner were blinded to test conditions and the order of exposures was randomized.
Compared to segments at a CO2 concentration of 2500 ppm, the odds of passing a maneuver as rated by the Examiner in the simulator were 1.52 (95% CI: 1.02–2.25) times higher when pilots were exposed to 1500 ppm and 1.69 (95% CI: 1.11–2.55) times higher when exposed to 700 ppm, controlling for maneuver difficulty, Examiner and order of maneuvers.
Examiner rating captured a wider range of performance indicators than output from the flight simulator, which can characterize only a few quantitative aspects of the flight performance. More broadly, these findings suggest that there is a direct effect of carbon dioxide on performance, independent of ventilation, with implications for many other indoor environments that routinely experience CO2 concentrations above 1000 ppm.
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We thank the pilots for volunteering to participate in this study, AFG for support with the flight simulator, and the three FAA Designated Flight Examiners. We also acknowledge the reviewers for their thoughtful review of this manuscript. This research was supported by a gift from United Technologies to the Center for Climate, Health and the Global Environment (C-CHANGE) at the Harvard T.H. Chan School of Public Health. United Technologies provided feedback on the study design, but they were not involved in the data collection, data analysis, data interpretation, data presentation, or drafting of the manuscript. Dr. MacNaughton’s time was supported by NIEHS environmental epidemiology training grant 5T32ES007069-35.
Conflict of interest
The authors declare that they have no conflict of interest.
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