T.M. Detwiler

If only it were an April Fools’ joke: On Monday, hundreds of flights were delayed after a brief software glitch affected U.S. airlines Delta, Southwest, United, American, Alaska, and JetBlue. The issue was due to a third-party, non-FAA system called AeroData, which some airlines use to determine the plane’s weight and balance data, which is necessary for takeoff.

"Much like any software that any company would use, you would hope that your provider has developed adequate backup processes so that if the primary system fails, a backup system kicks in almost instantaneously," says Henry Harteveldt, travel industry analyst and the president of Atmosphere Research Group. "Clearly, that didn't happen."

After implementing an internal ground stop for 40 minutes on Monday morning, Southwest said it was anticipating “scattered flight delays” and that customers should check with the airline for the latest updates. Delta, meanwhile, cited a “brief third-party technology issue” that affected some Delta Connection flights and said it was working to “resolve some resulting delays.” United, which had “about 150” delays, advised travelers check the website for the most up-to-date information. American, Alaska, and JetBlue have all said they are working with customers.

If “technology problems cause headaches for fliers” sounds familiar, it is: Last week, travelers on JetBlue, American, and Alaska flights were stuck in long lines after Sabre, an airline reservations company, went down for 30 minutes.

Despite the length of this outage (relatively short) and the number of delays (relatively small), the AeroData outage has brought to light some of the unknowns of air travel, including a pilot’s pre-launch plan and keeping track of where—and how much—luggage is placed. (Entering incorrect baggage weights, as seen in the case of Southwest, is dangerous.) It’s also shown, once again, just how dependent airlines are these entrusted systems to do some of their most important work.

So where does AeroData fit into takeoff—and what power does the FAA have? Harteveldt says in this case, it helps to think of the FAA as a traffic cop. "They don’t directly employ AeroData," he says. "AeroData works directly with the airlines. But the airlines have to file their flight plans with the FAA, and weight and balance data is a component of that flight plan." In other words: If you're an airline that uses AeroData to crunch your weight and balance information and that system is suddenly no longer available to you, you won't get clearance to fly, because you can't provide that required information. (This also explains why airlines that don't use AeroData had no issues; other weight-and-balance technology systems include Evinta, LodeStar, and Jeppesen.)