The risk of exposure to Covid-19 on aircraft is very low for masked passengers, according to a study by the U.S. Transportation Command, which is part of the Department of Defense.
United Airlines participated in the study, and CEO Scott Kirby said during the carrier’s quarterly earnings call that the results were “the most significant announcement to have come out” regarding safety aboard aircraft.
“Because the airflow is from the ceiling to the floor and is not spreading amongst the customers and because the air circulation is every two to three minutes going through [high-efficiency particulate air]-grade filters with 50 percent air from the outside, there is no place indoors that is anywhere close to that,” Kirby said.
Transportation Command researchers in late August, simulated a Covid-19 infected passenger onboard United Airlines’ Boeing 767-300 and 777-200 twin-aisle aircraft, using mannequins with and without face masks.
The researchers released more than 300 aerosols over eight days and conducted in-flight, simulated in-flight and on-the-ground testing, according to the study. Fluorescent tracer particles were released at intervals of two seconds to stimulate breathing for a minute during ground and in-flight tests. Real-time fluorescent particle sensors were placed throughout the aircraft at the breathing zone of passengers to measure concentration over time, and DNA-tagged aerosol tests were performed along with surface sample collections from high-touch areas like armrests and seatbacks.
The tests found that the aerosol rapidly diluted within the aircraft, with particles detectable within the cabin for less than six minutes on average.
“For comparison, a typical American home takes around 90 minutes to clear these types of particles from the air, according to Transportation Command. The high air exchange coupled with high efficiency particulate air (HEPA) filtration of all recirculated air, means a commercial aircraft’s air supply system provides protection greater than the design standards for a patient isolation room or a hospital operating room.”
The testing assumed that mask wearing is continuous among passengers and that the number of infected individuals is low.
TransCom commander and liaison for the test’s operation Joe Pope said in a statement, “While the tests did have some limitations, specifically it only considered a single infected passenger and did not attempt to gather data reflecting passenger movement about the cabin, the results are encouraging. For both the 777 and 767 airframes, the calculations show about 54 flight hours are required for cumulative inhalation of an assumed infectious dose.”
Before TransCom released its test results, Delta CEO Ed Bastian during the carrier’s earnings call said, “We carry at Delta over 1 million people a week and have had no documented transmission onboard any of our aircraft.”
Like Kirby, Bastian cited the International Air Transport Association data when commenting on aircraft safety: “There have only been 44 documented cases of suspected Covid transmission onboard an aircraft, and virtually all of them were in the early months of the pandemic before masks and revised safety protocols came into existence.”
To conduct the study, TransCom partnered with Boeing, United, Defense Advanced Research Projects Agency, Zeteo Tech, S3i and the University of Nebraska’s National Strategic Research Institute.