A United Airlines flight diverted to Salt Lake City last week after an object struck the plane’s windshield at 36,000 feet, causing it to crack and injuring the pilot, according to the airline and officials. 

Data from flight tracking website Flight Radar24 shows the plane was 36,000 feet in the air when an object hit the windshield. The flight then descended to a lower altitude, following standard protocol, before making an emergency landing at Utah’s Salt Lake City International Airport.

“This is an extraordinary situation in terms of the glass being able to create any damage at all to the people in the cockpit, and what it might have hit at 36,000 feet. That’s really the great puzzle,” said ABC News aviation analyst John Nance.

The windshield is being transported to the National Transportation Safety Board’s laboratory as it investigates what caused the windshield to crack.

Aircraft windshields are designed with multiple layers to be able to sustain damage caused by things like a bird strike, weather or even debris, but experts say it’s rare for it to be a bird strike that high in the sky.

“You’re talking about a bird at that altitude. It’s very, very rare to say the least, you’re talking about maybe a drone, a weather balloon, anything of that nature that has enough mass to be able to cause this kind of shattering,” said Nance.

Heather Ramsey, a college student and a passenger onboard, said she first noticed something was weird about 50 minutes into the flight, even before any announcements, when she overheard one of the flight attendants sharply raising her voice and telling the other to stop the service and get to the back of the cabin.

Shortly after, Ramsey said the pilot made an announcement of the flight diverting. 

“The aircraft has collided with an object and a window in the cockpit has shattered, so we need to make an emergency landing in Salt Lake City,” Ramsey told ABC News, recalling the pilot’s message.

United Airlines said the Boeing 737-MAX 8 with 134 passengers landed safely in Utah “to address damage to its multilayered windshield.” Officials said the pilot was treated for minor injuries. 

The images of the cracked windshield were first shared on social media by aviation account JonNYC.

The airline said passengers were accommodated on another aircraft to Los Angeles later that day and United is working with its team to return the plane to service.

Kerem Inal, Sam Sweeney and Clara McMichael contributed to this report.