High concentrations of carbon dioxide (CO2) were linked to a decrease in pilot performance in a simulator study that assessed the flying of maneuvers in flight deck atmospheres containing varying concentrations of CO2. The study, by the Harvard T.H. Chan School of Public Health, was published last week in the Journal of Exposure Science and Environmental Epidemiology.

The study “combines our aviation work with the work we have been doing on indoor environments and helps shine a light for the first time on the air quality of the cockpit and how it can affect pilot performance,” said principal researcher Joe Allen.

Research included a series of tests conducted in an A320 flight simulator with 30 airline pilots. During each test, researchers adjusted simulator CO2 levels to 700, 1,500, or 2,500 parts per million (ppm). Ventilation rates remained the same for each segment. The researchers took pilots through standard operations, as well as a set of more difficult procedures.

Performances diminished as CO2 concentrations rose. For example, “Five of the seven most difficult maneuvers (steep turns, rejected takeoff, circling to land, landing with slat malfunction, and collision avoidance) showed better performance at 700 ppm relative to 1,500 ppm,” the FAA-recommended level in the main cabin.

The study concluded that there is a “direct effect of carbon dioxide on performance, independent of ventilation.” However, Allen said, “In practice, CO2 is largely controlled through ventilation.” As such, Allen said he is hoping the study could help inform how the industry and regulators approach ventilation standards.