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.