One passenger reported smelling something burning, and saw a crew member carrying a fire extinguisher to the cockpit. Others reportedly took pictures of flames in the cockpit.
The flight left from New York’s JFK Airport on its way to Los Angeles. It landed at Dulles at 9:36 p.m.
Passenger Phil Lobel said flight attendants went over emergency instructions with passengers in the exit rows. Upon landing, he said about a half-dozen emergency vehicles were waiting on the tarmac.
He also said there were some celebs onboard, but did not specify who. But Entertainment Tonight said that Ashley Olsen was on the flight with her boyfriend. ET also said that "Californication" actress Pamela Adlon and "Jersey Boys" actor Jarrod Spector also were on the flight.
More than 100 passengers and six crew members were onboard. They all got off the plane safely.
About an hour after the plane landed, Lobel received an e-mail from United apologizing for the "experience" he had on the flight.
A spokeswoman for the Federal Aviation Administration did not immediately return a call for comment.