This might be the scariest thing I've ever read in a Harvard study, at least on the surface. It's about how stale air aboard commercial aircraft could actually be making pilots less safe and prone to errors.

Before we dive in, let's stipulate something important: Air travel is safer than it's ever been, at least in the United States. The only fatal incident aboard a plane since 2009, which was the Southwest tragedy in April, clearly didn't involve pilot error or fatigue.

But if you're flying often, and if you've ever been put off by the stale air aboard commercial airplanes, you'll want to pay attention to this.

Here's the Harvard study, the practical results, and the reason why this story might seem familiar to you even though the study itself is brand new.

21 different flying maneuvers

It's self-evident that an airplane's atmosphere can be stale, but Harvard scientists have been studying precisely how much usable oxygen there is in the air that we breathe onboard, at 35,000 feet--and how it affects people.

To that end, they recruited 30 commercial airline pilots, and asked them to fly three-hour simulations in an Airbus A320 simulator through 21 different flying maneuvers. The scientists manipulated the air quality that the different aircrews were exposed to, and tracked their performance.

Among the maneuvers they were asked to perform were both common and rare tasks, like circling at a consistent altitude, reacting to a single engine failure at takeoff, and recovering from a stall. 

The more concentrated the carbon dioxide (CO2) levels were in the air they breathed, the less effectively they performed these crucial maneuvers.

Worse air, worse performance

To understand the CO2 levels we're talking about here, let's use a baseline of between 1,000 ppm and 2,500 ppm, which is the range the scientists previously used in a study of how people's perform in office buildings depending on how much CO2 is in the air.

In short, as you might expect, the less carbon dioxide in the air, the better the pilots performed. Among the results:

Pilots who flew under simulated conditions of 700 CO2 ppm (meaning air with a lot of oxygen), were "69 percent more likely to receive a passing grade on a maneuver" than when they flew under conditions with 2,500 CO2 ppm.

Meantime, pilots who flew under simulated conditions of 1,500 CO2 ppm were 52 percent more likely to pass the tests than those in the 2,500 ppm conditions.

There wasn't any statistical difference between 700 and 1,500 ppm, the scientists say. In real life, the scientists said, "average CO2 levels on the flight deck are less than 800 ppm," which is good news.

"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," they added in a press release.

Bleed air and fume events

Of course, high levels of CO2 aren't the only things that can pollute the air quality aboard commercial airliners.

Earlier this year, we explored a study of British pilots that found that when chemicals like "engine oil, hydraulic fluid, or even deicing fluid" accidentally get pumped into the cabin as a result of a recirculation process involving "bleed air," it can have a potentially severe effect on pilot safety.

That phenomenon is called a "fume event," and the study found that the results could be stunning, "including full or partial incapacitation of two pilots." 

We don't need to panic about these air quality issues, scientists say, but they do warrant further study and keeping an eye on.

"Flying is safe, no question," said Joseph Allen, an assistant professor at Harvard and the principal investigator of the CO2 levels 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 Harvard study was published last week in the Journal of Exposure Science & Environmental Epidemiology.

Published on: Aug 12, 2018