CHICAGO (CBS) — A Southwest Airlines flight heading from Chicago to Newark was diverted to Cleveland on Wednesday, after a window cracked on the plane.

FAA spokeswoman Elizabeth Cory told CNN that Southwest flight 957 from Midway to Newark landed safely in Cleveland, after a report of an issue with a window aboard the aircraft.

Southwest Airlines said the crew decided to land in Cleveland “for maintenance review of one of the multiple layers of a window plane,” and said pilots did not declare an emergency before landing.

Spokeswoman Brandy King confirmed a window cracked, but said the plane never lost cabin pressure, and there were no other mechanical issues.

“The aircraft has been taken out of service for maintenance review, and our local Cleveland Employees worked diligently to accommodate the 81 Customers on a new aircraft to Newark. The Safety of our Customers and Employees is our number one focus each and every day,” the airline said in a statement.

Several passengers shared pictures of a broken window in the plane’s emergency exit door on social media.

Passengers said they could hear the window crack.

“The outside panel, the outside pane of the exit row window actually cracked, and was damaged,” passenger Stephen Poon told CBS 2’s Vince Gerasole. “We didn’t lose any cabin pressure. There was no safety concerns. It was just a matter of controlling the emotions in the cabin, and some of the passengers who had freaked out, and didn’t really understand what was taking place.”

Poon said pilots and flight attendants calmed passengers down and explained what had happened before landing in Cleveland. Passengers were placed on another plane to Newark within an hour of landing in Cleveland.

DePaul University transportation expert Joe Schwieterman said, while cockpit windows occasionally crack as a result of bird strikes, it’s a mystery so far what caused a side window to crack on the Southwest flight.

“We’re wondering if there was perhaps debris from the airplane, but the initial inspections say there was not. Birds are a possibility; getting caught up in the thrust. But we’re scratching our heads a bit on this one,” he said.

No injuries were reported.

The incident comes a few weeks after a woman was killed when she was partially sucked out of a window after an engine failure.

Vince Gerasole