Passengers on a Boston-bound plane witnessed a troubling sight mid-flight on Tuesday.

A United Boeing 757-200 was diverted to a Denver airport after passengers noticed the wing of the plane beginning to come apart during the flight.

United Flight 354 was carrying 165 passengers from San Francisco to Boston on February 20 when portions of the plane’s right wing began to dislodge. Passenger footage captured during the plane’s descent and obtained by RAWSALERTS shows pieces missing from the slat on the wing’s leading edge.

Kevin Clarke, one of the passengers on the plane who filmed the incident, told Boston 25 that he had noticed bird strike forms on the plane as he began to board.

“I’m like, ‘Bird strike? That’s not good,'” said Clarke. “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.”

Clarke said that there was a brief moment of panic; however, the pilot quickly inspected the damage, taking pictures before communicating with the ground of the situation. The pilot then directed the plane to Denver, Colorado.

Upon landing, crews immediately came to inspect the damage, and passengers were placed on another flight, arriving safely in Boston three hours later than scheduled. Clarke said United handled the incident well and that he was glad to have arrived in Boston safely.

The exact cause of the wing damage is currently unknown.

Boeing has seen several recent issues regarding the construction of its line of 737 Max jets. An employee working at the company’s fuselage factory in Renton documented two improperly drilled holes, leading to the discovery of 50 more like it, as previously reported by The Dallas Express.