WASHINGTON — That poorly ventilated conference room isn’t the only place with the potential for sick-air syndrome.
Airliner cockpits can also have levels of carbon dioxide elevated enough that in simulations it causes pilots to fail test maneuvers at higher rates than normal, a new Harvard University study has found.
The first-of-its-kind research suggests that current regulations aren’t adequate to assure there’s enough fresh air in airline flight decks and raises questions about whether even moderately elevated carbon dioxide levels could impact safety, said Joseph Allen, an assistant professor at Harvard’s School of Public Health and lead author of the study.
“It’s clear that the air quality in the cockpit can have an impact on performance,” Allen said. “It’s clear we haven’t been thinking about it too deeply in terms of the impact on pilot performance. Now that we know, I think we’re obligated to ask those next sets of questions and really understand it.”
In recent years, studies have shown that even an increase of a few hundred parts per million of carbon dioxide in the air we breath causes people to test lower for cognitive skills. But until the latest study, pilots and airline cockpits hadn’t been examined.
Normal levels in the atmosphere are 400 parts per million. Concentrations of the colorless, tasteless gas can rise in poorly ventilated spaces where people exhale it — such as crowded airliners.
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Carbon dioxide levels reached as high as 1,400 parts per million on five percent of airline flights the European Aviation Safety Agency tested, according to data it released last year. The average was 603 parts per million, just slightly higher than levels found in the air.
Airliners replenish oxygen in a plane at high altitudes by pulling in the thin air and pressurizing it, mostly by scooping it from the front end of jet engines.
Because earlier studies showed people performed more poorly on tests of brain function at levels as low as 1,000 parts per million, the researchers thought it would make sense to examine pilot skills and carbon dioxide.
Thirty airline pilots were recruited to fly multiple three-hour segments in a special flight simulator in which carbon dioxide levels could be manipulated. Performance on 21 maneuvers — ranging from making a steep turn to handling an emergency engine fire — decreased as carbon dioxide levels rose, according to the study. Flight examiners certified by the Federal Aviation Administration rated the pilots’ performance.
At 700 parts per million, pilots were 69 percent more likely to correctly perform the maneuvers compared to when they were breathing carbon dioxide at 2500 parts per million. At 1,500 parts per million, they were 52 percent more likely to pass compared to the higher level.
The study was published Wednesday in the Journal of Exposure Science & Environmental Epidemiology.
Allen, who is also co-director of Harvard’s Center for Climate, Health, and the Global Environment, 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.
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One of the maneuvers the pilots in the study were tested on was a simulated engine emergency, which was similar to the real situation on April 17 when debris from a jet on a Southwest Airlines Co. killed a passenger, Allen said.
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 allow for concentrations of carbon dioxide were drafted in 1996 before its effects 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.
(With assistance from Julie Johnsson.)
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