Why the airline industry might want to lower cockpit CO2 levels

Pilots are much more likely to pass flight manoeuvers when carbon dioxide concentrations are low.
New research found the quality of air in the cockpit can affect a pilot's flight performance. (AFP/Getty Images)
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Air quality and pilot performance

Piloting a commercial aircraft is a high stakes job. And now there's new research showing that the quality of air in the cockpit can affect a pilot's flight performance.

Joseph Allen is the lead author of the new study and assistant professor of exposure assessment science at Harvard T.H. Chan School of Public Health in Boston.

"The key takeaway from our study is that the air quality, specifically carbon dioxide in the cockpit, was associated with the pilot's ability to perform complex maneuvers," he said. "It's no different from air quality in our office impacting our ability to work."

The double-blind experiment

Allen and his team arrived at their findings by setting up a double-blind experiment with 30 active commercial airline pilots. They were asked to fly three, three-hour segments in flight simulators and perform a series of 21 manoeuvres without the aid of autopilot.

Randomized amounts of carbon dioxide were pumped into the simulators so that cockpit concentrations were either 700 parts per million, 1,500 ppm, or 2,500 ppm. And each pilot flew one flight at each level during the course of the study.

Carbon dioxide levels in airplane cabins are much higher than cockpit levels, which may be inadequate to protect the health of the flight crew and passengers, according to a National Research Council report. (AFP/Getty Images)

While this was happening, a Federal Aviation Administration-designated pilot examiner was monitoring and scoring the pilots on each of their manoeuvres. But neither party knew the carbon dioxide levels during the simulations.

"We tested these extreme events like what happens with a rejected takeoff when you have a single engine fire or what happens if there's a potential for a mid-air collision." said Allen. "They don't happen all that often thankfully, but nonetheless, they're tied back to real-world issues or events that have happened, and our study was testing how the air quality in the cockpit contributes to the pilots performance in the event of one of these rare mishaps."

That tells us that with everything else happening, all the training and all these other things we do to to make sure flights are safe, the air quality matters too. But unfortunately, it tends to be an afterthought when we think of pilot performance.- Joseph Allen

Now, it bears mentioning that the average carbon dioxide level in the cockpit is actually on the lower end of the test, at around 700 to 800 ppm, according to the only research paper on cockpit carbon dioxide levels. Allen acknowledged the limitation, but points out that five per cent of the measurements in the research paper are above 1,300 ppm, the medium level tested in his own study. And occasionally, it can reach up to even 2,000 ppm.

In the cabins, where the passengers sit, the carbon dioxide levels are much higher. It's typically 1,800 ppm, and during boarding, it can get as high as 2,500 ppm, said Allen. To give you a sense of what those numbers mean, we can compare them to outdoor carbon dioxide concentrations which are about 400 ppm, while indoor building levels are usually kept under 1,000 ppm.

Lower is better

What they found was that pilots were much more likely to pass manoeuvres at lower carbon dioxide concentrations: they were 69 per cent more likely to pass at 700 ppm when compared against 2,500 ppm; and they were 52 per cent more likely to pass at 700 ppm when compared against 1,500 ppm. 

"That tells us that with everything else happening, all the training and all these other things we do to to make sure flights are safe, the air quality matters too," said Allen. "But unfortunately, it tends to be an afterthought when we think of pilot performance."

Allen's prior research on workers in office buildings found a striking decline in workers' cognitive function when exposed to slightly higher levels of CO2 than typical office levels. (AFP/Getty Images)

The genesis of this study comes from Allen's prior research on workers in office buildings. He found a striking decline in their cognitive function when exposed to slightly higher levels of carbon dioxide than typical office levels, even at the 1,000 ppm level, which is within most buildings' ventilation standards.

"We immediately made the connection to try to understand how these results from office workers might relate to what's happening on an airplane," he said. "Our goal really here is to understand the factors that we can manipulate in terms of air quality to optimize pilot performance during a flight and what happens in those cases when the air quality is less than optimal."

In the latter case, he showed that under high carbon dioxide concentrations, pilots performed worse, especially during stressful manoeuvres that require immense focus and skill to perform right.

Are current ventilation standards in planes adequate?

So are the air quality standards on airplanes good enough? Do we need a revamp to optimize pilots' performance and to prevent disasters?

According to Allen, the current regulation on planes was set half a century ago, and nothing substantive has changed since then.

The U.S. National Research Council has noted in a 2002 report that these established regulations may be inadequate to protect the health of the flight crew and passengers, Allen pointed out. "It's an area where there's a debate happening about what's the proper level of ventilation."

To worsen the outlook, there's also pressure to lower ventilation rates, which would increase carbon dioxide levels in an effort to conserve energy in buildings and planes, Allen said. This would lead to a whole host of changes that include not only increases the carbon dioxide concentrations in the air, but also body odour and other chemicals that increase the volatile organic compounds, which have long-term health effects.

Allen strongly advises decision makers to take these factors into consideration before making changes.