Fairer Air

In 2011, about 20 percent of U.S. flights were at least 15 minutes behind schedule. Such delays irritate passengers, and in 2010 they cost airlines an estimated $6.5 billion.

But Federal Aviation Administration (FAA) rules for managing ground delays and air traffic, which minimize aggregate system delays nationwide, leave some airlines with more delays than others.

Now MIT researchers have developed a new method that would keep system-wide delays virtually constant while distributing the delays more evenly among airlines. They found that letting airlines extensively swap schedule slots with each other—and setting limits on the amount of time any flight could be delayed—is more fair without sacrificing efficiency.

Sloan professor of management Dimitris Bertsimas and Shubham Gupta, SM ’10, PhD ’12, formerly of MIT’s Operations Research Center, tested their model using data from the 55 biggest U.S. airports and the five biggest airlines on six randomly selected days in 2004, 2005, and 2006—more than 30,000 flights in all.

When they simulated what air traffic would have looked like on those six days using their technique, they found that the aggregate delays in the entire system were virtually unchanged. On none of the six days did those totals differ from the actual results by more than 1.0 percent, and the mean difference was 0.1 percent. Bertsimas also notes that the computational side of the proposed system is fast enough to work in real time. A paper detailing the researchers’ findings was published in the journal Transportation Science.

“The price of fairness is small,” says Bertsimas. And that price is well worth it: “If a system is viewed as not fair, it is not stable,” he says.