Delta Air Lines will test offering free Wi-Fi on 55 domestic daily flights this month. The tests will start on May 13th and last for two weeks, and they will allow users to do just about everything except stream video free of charge.

Delta calls the tests the “first step toward realizing its vision” of offering free, in-flight Wi-Fi, though it admits there will likely be “several more” phases before any actual rollout happens. Currently, JetBlue is the only US airline that offers free Wi-Fi.

While it hasn’t named the specific routes it will run the test on, Delta says short, medium, and long-haul routes are included. Customers who have tickets on the test flights will be notified ahead of time either by email or via the company’s mobile app.

Just 12 percent of passengers used Wi-Fi on Gogo-equipped flights in 2018

Offering free Wi-Fi in the air is a “highly complex” problem to solve, according to Delta, likely because removing fees could dramatically increase the number of people who use it, which, in turn, could stress the plane’s connection. As The Wall Street Journal points out, Gogo (which provides connectivity on Delta flights) recently reported in an SEC filing that just 12 percent of passengers used in-flight Wi-Fi in 2018. An increase in that number could choke a plane’s bandwidth and result in slower speeds.

Gogo also said in that filing that it’s already facing network capacity constraints in the US, and it expects demand to increase — especially if airlines decide to stop charging for in-flight Wi-Fi. Regardless of how long Delta takes to complete its tests, the airline’s ability to offer free in-flight Wi-Fi might largely depend on Gogo’s ability to build out its network. If Gogo can’t, Delta has the ability to walk away from its contract with the provider in favor of one of its competitors (like satellite company ViaSat), according to the filing.

Of course, Gogo makes a lot of its money by selling the bandwidth to airlines, so the company is deeply incentivized to make sure it can handle more users. Delta flights already accounted for 23 percent of Gogo’s revenue in 2018, and the service provider said it expects revenue from airlines to keep growing as they need more bandwidth to support free in-flight Wi-Fi.