Imagine boarding your four-hour flight from Salt Lake City to Washington DC. You reach cruising altitude and begin to really settle in, recline your seat, and get ready to nap or watch tv or read a book. And then all of a sudden you hear over the loudspeaker to remain calm — the plane is suddenly diverting to Denver International Airport.

On Friday, April 1, that very situation happened after pilots made the decision to divert to Denver when the cockpit windshield cracked at 30,000 feet. The crack happened about 90 minutes into the flight, and it diverted in about 10 minutes.

A photo posted by passenger Kirk Knowlton on Twitter shows the cracked windshield. No glass fell from the plane, as these windshields tend to be about two inches thick and have several layers. The crew said the crack happened “spontaneously.”

“They kept coming on saying for everyone to stay calm, to be calm, and we were calm so being told to stay calm while we were calm made us feel a little panicky,” passenger Rachael Wright told KUTV.

Shortly after the crew of Delta Flight 760 “declared an emergency due to a cracked windshield,” the flight landed safely at Denver International Airport around 11 AM, according to The New York Times

“Delta flight 760 from Salt Lake City to Washington D.C. experienced a maintenance issue mid-flight. Out of an abundance of caution, the flight crew diverted into Denver and the plane landed routinely. Our team worked quickly to accommodate customers on a new plane, and we sincerely apologize for the delay and inconvenience to their travel plans,” Delta said in a statement.

Although it’s unclear whether the cabin lost pressure, airplanes are designed to remain safe with a shattered or cracked windshield and pilots are prepared to descend to reduce pressure and divert to the closest airport if necessary.