A passenger on the San Francisco-to-Boston flight Monday said he had just put in earbuds and started to doze off when he felt the plane shaking.

“All of a sudden I heard this violent vibration like I had never heard before,” Kevin Clarke said in an interview Tuesday.

Clarke said one of the pilots walked down the aisle of the main cabin, then returned to the cockpit and announced that the plane had minor damage to its right wing and the flight would be diverted to Denver.

Clarke opened his window shade and took video of the damage that was later broadcast on Boston 25 News. The 67-year-old, a ski-race announcer from Maine, was comforted that the pilot believed the plane was good enough to fly, but he began having doubts when the jet hit turbulence.

Clark began checking the wing repeatedly, until he decided that he just couldn’t look anymore.

“I was just going to pray that we made it to the other side of the turbulence,” he said.

United said the Boeing 757-200 carrying 165 passengers landed in Denver to “address an issue with the slat” on one of its wings. Slats are moveable panels on the front or leading edge of the wing and are used during takeoffs and landings. Chicago-based United did not say what caused the damage which left pieces of the slat torn away.

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

The plane landed safely in Denver, and passengers were put on a different plane and arrived later in the day in Boston, according to the airline.

The incident comes at a time of heightened passenger jitters after last month’s blowout of a door panel on an Alaska Airlines jetliner flying over Oregon. The National Transportation Safety Board said in a preliminary report that bolts designed to prevent the panel from moving were missing on the Boeing 737 Max 9 jet.