The quality of the air in a cockpit can affect the way a pilot flies a plane.
If the air is stale and has higher levels of carbon dioxide, it makes it harder for pilots to make maneuvers and handle emergencies like engine failure on take-off, which could be fatal to passengers.
Higher levels of carbon dioxide can be caused by bleed air in the cabin, when engine oil or other harmful chemicals leak into the plane through faults in the plane’s engine seals.
In a study by Harvard scientists, published in the Journal of Exposure Science and Environmental Epidemiology, 30 commercial airline pilots flew an Airbus A320 simulator for an hour and a half at a time under varying air conditions.
The tests were supervised by a pilot examiner from the Federal Aviation Administration (FAA), the body in the USA that regulates the plane industry.
They were instructed to carry out 21 different flying maneuvers, including making a steep turn, recovering from stalling and circling a plane while maintaining a constant altitude.
Results showed that the pilots were more 60 percent likely to pass the tests when the concentrations of carbon dioxide in the air was 700 parts per million (ppm) in the air, compared with 2,500 ppm, the highest level in the test.
At 1,500 ppm they were 50 percent more likely to make the maneuvers successfully than at 2,500 ppm.
The scientists wrote: “Our testing conditions, and the results, therefore, do not necessarily reflect actual conditions in all planes nor do they necessarily reflect how pilots would perform during an actual flight.
“They do, however, suggest that there are important direct effects of carbon dioxide on pilot performance at concentrations that are occasionally observed on the flight deck and in the cabin.”
Investigator Piers MacNaughton, from the Harvard School of Public Health in the US, said: “Using a flight simulator gave us a unique opportunity to test the impact of extreme, but rare, events in aircraft.
“Our results suggest we need to know more about how air quality on the flight deck can be used to enhance pilot performance.”
