A team of U.S. university researchers have warned that airlines seeking to minimize COVID-19 transmission risk by boarding from the rear of the aircraft could actually be substantially increasing the probability of COVID-19 infection.

“Our analysis indicates that airlines that changed to a back-to-front boarding policy erred, exposing passengers to substantially higher infection risk than their original procedures. This result shows that good intention is not a substitute for good science when it comes to determining policies,” Florida State University department of computer science affiliated professor Ashok Srinivasan said. 

Preliminary findings from the study, performed by a team of researchers at Embry-Riddle Aeronautical University, Arizona State University, Florida State University and University of West Florida, suggest that one-zone randomized boarding—in which passengers enter randomly through one entry point in the aircraft—could be around 50% more effective than boarding from the rear. 

This is because back-to-front boarding can lead to bottlenecks, increasing the risk of transmission, according to Embry-Riddle associate professor of aerospace engineering Dr. Sirish Namilae. 

“While back-to-front boarding has been instituted by some airlines to try and reduce contact between people, our [computer] simulations show that high-density clusters can form, as people stow their luggage, while other passengers are still pushing toward the back of the aircraft,” Namilae said.

The study, which is yet to be peer-reviewed, looked at the number of “person-minutes” of contact where passengers are within six feet of one another. The researchers then ran roughly 16,000 supercomputer simulations—varying the number of passengers, their walking speed and proximity—and then tested this in different boarding scenarios, including front-to-back, back-to-front, through six boarding zones and random boarding through one zone.

Unsurprisingly, a positive correlation was found between person-minutes and infection risk.

“It turns out, the one-zone random boarding model eventually results in a lower number of contacts,” Namilae said. “Other patterns tend to increase the time a passenger waits in close proximity to fellow travelers.”

The simulations, based on a full-capacity Airbus A320, revealed 43,000 person-minutes of contact in the random-boarding model. This compares with 60,000 person-minutes for six-zone boarding and 90,000 person-minutes for back-to-front boarding. The highest number of person-minutes came from front-to-back model.

“Airlines should either revert to their earlier boarding process—or adopt the better random process,” Srinivasan said, if the research is confirmed. 

The study also suggested that keeping middle seats free significantly reduces infection risk. This will come as a blow to the industry, which has been promoting other prevention measures, such as face coverings.

Likewise, flying multiple smaller aircraft—rather than one higher-capacity flight—was also shown to reduce the risk of infection.

“Economics are a consistent consideration in these simulations,” the team said. “The key, however, is finding a middle ground and ... that conversation has to begin with the boarding process.” 

Namilae described boarding as one of the “critical aspects” that contributes to disease transmission during air travel. “Any steps we can take to reduce the spread would help,” he said.