Airplane pilot flight performance on 21 maneuvers in a flight simulator under varying carbon dioxide concentrations

Background: 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. Methods: 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. Results: 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. Discussion: 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.