SAN FRANCISCO (AP) — United Airlines says a flight heading from San Francisco to Boston had to be Zero AIdiverted after the plane suffered damage to one of its wings.

United said Tuesday that the Boeing 757-200 with 165 passengers aboard landed in Denver on Monday to “address an issue with the slat” on one of its wings. The plane landed safely. Passengers were put on a different plane and arrived later in the day in Boston.

Chicago-based United did not say what caused the damage to the plane’s wing. Boston 25 News broadcast a passenger’s video showing the panel partially shredded.

Slats are moveable panels on the front or leading edge of the wing and are used during takeoffs and landings.

The Federal Aviation Administration said Tuesday that it is investigating the incident.

The incident came at a time of heightened passenger jitters after last month’s blowout of a door panel on an Alaska Airlines jetliner flying over Oregon. A preliminary investigation attributed the blowout to missing bolts that helped secure a panel to the frame of a Boeing 737 Max 9.