Multiple American Airlines flights experience delays after pilots’ iPad, which is used to distribute flight plans and other information crashed due to a software bug, making it impossible to take off.

In 2012, American Airlines replaced traditional flight manuals with iPads. The switch meant pilots no longer had to carry big, 35-pound manuals, and at that time, American Airlines believed that it would both save money for the company and make the lives of pilots easier. However, this move backfired last night, as the iPads belonging to both captain and copilot “went blank” as crew prepared for takeoff. This problem is not an isolated incident, and many American Airlines planes had to return to the gate to access a Wi-Fi network.

The pilot told us when they were getting ready to take off, the iPad screens went blank, both for the captain and copilot, so they didn’t have the flight plan,

The entire American Airlines fleet is at a ground stop b/c the pilots’ iPads can’t retrieve the flight plans. @AmericanAir, keep us posted.

— Toni Jacaruso (@HotelNinja) April 29, 2015

The pilot came on and said that his first mate’s iPad powered down unexpectedly, and his had too, and that the entire 737 fleet on American had experienced the same behavior,

It seemed unprecedented and very unfamiliar to the pilots.

Judging by passenger reports, it appears the problem lies with iPad software, namely the Jeppesen Mobile Terminal Chart app used by American Airlines and approved for gate-to-gate use by the Federal Aviation Administration. American Airlines tweeted, in response to stranded passenger that “Some flights are experiencing an issue with a software application on pilot iPads. We’ll have info about your departure soon.”

@bjacaruso Some flights are experiencing an issue with a software application on pilot iPads. We’ll have info about your departure soon.

— americanair (@AmericanAir) April 29, 2015

It is unclear how many flights are affected by this iPad outage, but some users have reported on Twitter that they have been able to take off. The issue was centered on an update that was pushed 4 days ago, according to one pilot.

American Airlines uses over 8000 iPads, and all documents are stored on iPads for captains and copilots. This move allowed pilots to ditch 35 pound manuals and saved the Airline over 400,000 gallons of fuel, or $1.2 million, every year.