CO2 a threat to pilot performance? Need information on cockpit air quality

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Carbon Dioxide Levels can Negatively Impact Pilot Performance

Harvard Study finds Degradation as CO2 levels increase

Acknowledges Lack of Data on Air Quality of Cockpits

CO2 is a colorless, odorless gas which aviation has devoted considerable efforts to reduce, if not eliminate, from aircraft operations.

Joseph Allen, Assistant Professor of Exposure Assessment Science, Department of Environmental Health,  Harvard T.H. Chan School of Public Health, has identified the potential (and it is important to not his study does not conclude that it is present hazard) that CO2 levels inside a cockpit may effect pilot performance.  Allen research focuses on Healthy Buildings-to transform design and construction of indoor spaces by revealing how ventilation, temperature, lighting, and noise affect health. The team he leads has found evidence that indoor air quality, in a variety of settings, influences job performance



“I think the real danger within the scientific community can be that we talk just amongst ourselves,” Allen said in discussing his interdisciplinary approach. “We can always fall into that trap. But I think that’s the beauty of the field of public health …. We’re encouraged to not just do the science but get that all the way to implementation.” The larger study of workplace environments, human performance and CO2 made the following general conclusion:

“Participants’ cognitive function was significantly affected in all nine areas tested, including focused-activity levels, information usage, and strategy. Crisis-response scores were 97 percent higher at the green office setting compared with that of conventional office space, and 131 percent higher at the green+ office setting.”

[table is ILLUSTRATIVE, not from the Allen studies]

In an interview about the applicability, Dr. Allen made the following important comments which limit any inappropriate response to his preliminary work:

“Allen took pains to say that air travel is extremely safe. There has been only one passenger death on a U.S.-registered airline in more than nine years and there’s never been any evidence linking routine carbon dioxide levels to a crash.

However, several of the few recent fatal accidents that have occurred involved puzzling lapses in pilot performance, according to accident investigation agencies. One example was when a captain on a Colgan Air flight made a series of abrupt maneuvers in 2009 near Buffalo, causing a perfectly good commuter plane to plunge to the ground, killing 50.

At the very least, Allen said, regulation agencies like the FAA might want to study the issue and compare the growing research on the effects of carbon dioxide with the existing U.S. regulations on aircraft design.

‘The goal is to optimize conditions for a safe flight,’ he said, ‘and the air in the cockpit has to be a part of that conversation.’

Current U.S. regulations governing aircraft air quality were drafted in 1996 before the effects of concentrations of carbon dioxide on human performance were known. It allows more than 10 times the levels found in the atmosphere, or 5,000 parts per million.

According to the limited data available, the air in most aircraft is below that ceiling. But there are indications that carbon dioxide can spike. Tests of air in aircraft passenger cabins show carbon dioxide levels typically climb to 2,000-2,500 parts per million during loading and unloading, when a plane’s ventilation system is operating at lower capacity.

‘There’s virtually no information on the air quality in the cockpit. It’s the one place where it seems we really would want to know about the most,’ Allen said.”

Here is Dr. Allen’s article as published by  from Harvard T. H. Chan School of Public Health.

Commercial airline pilots were significantly better at performing advanced maneuvers in a flight simulator when carbon dioxide (CO2) levels on the flight deck (cockpit) were 700 parts per million (ppm) and 1500 ppm than when they were 2,500 ppm, according to new research led by Harvard T.H. School of Public Health. The study indicates that CO2 levels directly affect pilots’ flight performance.

“Flying is safe, no question,” said Joseph Allen, assistant professor of exposure assessment science and principal investigator of the study. “The entire flight experience is designed around a culture of ‘safety first.’ Optimizing air quality on the flight deck must continue to be a part of that safety equation.”

The study was published online Wednesday, August 8, 2018 in the Journal of Exposure Science & Environmental Epidemiology.


Previous research led by Allen and colleagues found that, in office buildings, CO2 concentrations between 1,000 ppm and 2,500 ppm—levels once thought to be benign—negatively impact the cognitive function of employees. For the new study, they wanted to determine if higher CO2 levels on the flight deck would impair a pilot’s ability to perform advanced maneuvers and manage emergency situations, such as a single-engine failure during takeoff.

The researchers recruited 30 male commercial airline pilots and split them into teams of two. Each team was asked to perform three 3-hour-long flight simulations that consisted of 21 maneuvers of varying degrees of difficulty without the aid of autopilot. Both pilots on each team took a 90-minute turn as the flying pilot during each simulation. CO2 levels were randomized to either 700 ppm, 1,500 ppm, or 2,500 ppm, and each pilot flew one flight at each CO2 level over the course of the study. A Federal Aviation Administration (FAA) Designated Pilot Examiner monitored and asesseallsimulations, and the pilots and the FAA examiner were unaware of the CO2 levels during the simulations.

The findings showed that the pilots were 69% more likely to receive a passing grade on a maneuver when CO2 levels were 700 ppm compared with 2,500 ppm. When CO2 levels were 1,500 ppm, the pilots were 52% more likely to successfully perform a maneuver than when CO2 levels were 2,500 ppm. When the researchers compared the difference in pilot performance at 700 ppm and 1,500 ppm, the difference was not statistically significant, but they did find that pilots were more likely to successfully perform some of the most difficult maneuvers at the lower CO2 level. The study also found that the negative effects of CO2 on flight performance became more pronounced the longer the pilots were in the simulator.





[graph is ILLUSTRATIVE, not from the Allen studies]

While data on CO2 levels on flight decks are limited, previous research has shown that average CO2 levels on the flight deck are less than 800 ppm. However, they have been measured as high as 2,000 ppm on the flight deck and even higher in the cabin during the boarding process, depending on the type of airplane and other factors. While the FAA has regulations pertaining to airplanes’ environmental control systems, the National Research Council has suggested that current standards for ventilation rates on flight decks may be inadequate.

“Using a flight simulator gave us a unique opportunity to test the impact of extreme, but rare, events in airplanes,” said Piers MacNaughton, research fellow and one of the investigators on the study. “Our results suggest that we need to know more about how air quality on the flight deck can be used to enhance pilot performance.”

This article has been republished from materials provided by Harvard T. H. Chan School of Public Health. Note: material may have been edited for length and content. For further information, please contact the cited source.

Airplane pilot flight performance on 21 maneuvers in a flight simulator under varying carbon dioxide concentrations. Joseph G. Allen, Piers MacNaughton, Jose Guillermo Cedeno-Laurent, Xiaodong Cao, Skye Flanigan, Jose Vallarino, Francisco Rueda, Deborah Donnelly-McLay & John D. Spengler. Journal of Exposure Science & Environmental Epidemiology (2018),







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