A Southwest Airlines flight was forced to divert and land before reaching its intended destination on Wednesday after a pane in one of the cabin windows was damaged in flight.

The Federal Aviation Administration said it was investigating what had caused the window, which was on an exit row, to break. The plane, which was traveling from Chicago to Newark, landed in Cleveland at 11:45 a.m., although the damage did not affect the pressure inside the plane, Southwest said.

The airline said that the Boeing 737 was taken out of service so that maintenance teams could investigate, and that it did not yet know exactly what had happened to the window.

In an email, Southwest said it regularly inspects windows on its aircraft for clarity and condition and replaces them as needed. The window that broke was last inspected in April.