A Southwest Airlines flight was forced to make an unscheduled landing in Cleveland on Wednesday after passengers reported that an emergency exit window cracked while the plane was in the air.

Southwest Airlines said the flight, from Chicago’s Midway Airport to Newark Liberty International, had 81 passengers aboard. It was diverted to Cleveland Hopkins International Airport ” . . . for a maintenance review of one of the multiple layers of a window pane,” airline officials said. The plane landed without incident. There were no other problems reported with the plane or its engines.

“The aircraft did not lose pressurization, and we have no reports that the aircraft cabin was open,” officials said, adding that the plane landed uneventfully in Cleveland and was taken out of service for a maintenance review. The passengers were put on another Southwest flight and arrived in Newark just after 1 p.m., the airline said.

The airline said that aircraft windows are made of multiple panes and that the crack was in the outer pane. Data from the Federal Aviation Administration, which is investigating Wednesday’s incident, suggests that these types of window failures in Boeing 737’s are rare – only 26 times in the plane’s worldwide service history. Boeing began manufacturing the 737 in 1967.

A spokeswoman at Cleveland International said the Southwest Airlines jet landed at the airport around 11 a.m. She said no injuries were reported. According to a report published on the website DansDeals, an unidentified passenger aboard the plane tweeted the above image. The traveler said he heard a loud crack after something apparently hit the window and shattered it. He said passengers seated in the row “ran away” and others on the flight were “crying hysterically.”

The incident comes just a few weeks after a Southwest Airlines jet was forced to make an emergency landing in Philadelphia after one of the aircraft’s engines failed, sending shrapnel into the plane and shattering a window. One passenger, Jennifer Riordan of Albuquerque, was partially pulled out of the window. She was pulled back into the aircraft by other passengers but later died. It was the first passenger fatality on a U.S. carrier since 2009 and the first in Southwest’s 51-year history.