A Boston-bound flight out of San Francisco Monday evening experienced a scary mid-flight situation after a visible chunk of a wing flap tore off, necessitating an emergency landing in Denver.

The incident happened on United Flight 354 out of SFO Monday, which was flown by a Boeing 757-200 jet. One passenger with a clear view of the wing from his seat, Kevin Clarke, sent video of the damaged wing flap to his wife, Kimberly, who posted it to Facebook.

As Clarke tells Boston 25 News, there may have been some issue with a bird strike on the jet's earlier flight — he said he saw FAA bird strike forms being filled out on the jetway as he boarded.

"I’m like bird strike? That’s not good," Clarke tells the station. "We take off, I heard this loud buzzing noise, and then it faded away so I didn’t think much of it, and all of a sudden the pilot is coming back, so I threw my window open, peeked out the window and the whole leading edge of the wing was destroyed."

United has confirmed to the SF Chronicle only that there was "an issue with the slat on the wing of the aircraft."

Clarke says that there was some panic onboard the plane at first, as passengers saw what had happened to the wing, "but the pilot had come back, looked at it, took some pictures of it, talked to the guys on the ground, said yup, proceed to Denver [they said], shouldn’t be a problem."

Airline safety has been topping the news in recent months, particularly after that harrowing incident involving a blown-out piece of fuselage on an Alaska Airlines jet flying out of Portland last month. That prompted an investigation that found possible widespread issues with "door plugs" installed on Boeing's 737-Max 9 aircraft.

There still has been no fatal crash involving an American air carrier since 2009, however emergency landing incidents like these have been making the news with alarming frequency — and a December report by the New York Times found that staffing shortages in air traffic control towers has led to an even more alarming number of close calls on runways and in the air.

Related: Close Calls on SFO Runways Are Just Tip of the Iceberg In Broader National Trend