LOUISVILLE — As viral videos of a man being forced off a United Airlines flight to Louisville Sunday evening keep racking up views, the company's CEO has spoken up about this "upsetting event."

United Airlines CEO Oscar Munoz said what happened Sunday on United Express Flight 3411 at O'Hare International Airport was "an upsetting event" for everyone at the company.

"I apologize for having to re-accommodate these customers. Our team is moving with a sense of urgency to work with the authorities and conduct our own detailed review of what happened," he said. "We are also reaching out to this passenger to talk directly to him and further address and resolve this situation."

The video, posted by Audra D. Bridges at 7:30 p.m. Sunday, was taken from an aisle seat on a commercial airplane that appears to be preparing to take flight. The 31-second clip shows three men wearing radio equipment and security jackets speaking with a man seated on the plane. After a few seconds, one of the men grabs the passenger, who screams, and drags him by his arms toward the front of the plane. The video ends before anything else is shown.

A United spokesperson confirmed in an email Sunday night that a passenger had been taken off a flight in Chicago.

"Flight 3411 from Chicago to Louisville was overbooked," said the spokesperson. "After our team looked for volunteers, one customer refused to leave the aircraft voluntarily and law enforcement was asked to come to the gate.

"We apologize for the overbook situation. Further details on the removed customer should be directed to authorities."

Passengers were told at the gate that the flight was overbooked and United, offering $400 and a hotel stay, was looking for one volunteer to take another flight to Louisville at 3 p.m. Monday. Passengers were allowed to board the flight, Bridges said, and once the flight was filled those on the plane were told that four people needed to give up their seats to standby United employees who needed to be in Louisville on Monday for a flight. Passengers were told that the flight would not take off until the United crew had seats, Bridges said, and the offer was increased to $800, but no one volunteered.

Then, she said, a manager came aboard the plane and said a computer would select four people to be taken off the flight. One couple was selected first and left the airplane, she said, before the man in the video was confronted.

Bridges said the man became "very upset" and said that he was a doctor who needed to see patients at a hospital in the morning. The manager told him that security would be called if he did not leave willingly, Bridges said, and the man said he was calling his lawyer. One security official came and spoke with him, and then another security officer came when he still refused. Then, she said, a third security official came on the plane and threw the passenger against the armrest before dragging him out of the plane.

United Airlines spokesperson Erin Benson offered additional details about what happened during an interview with the Courier-Journal Monday afternoon.

United partners with other companies for some regional flights, Benson said, and Flight 3411 was operated by Republic Airline. Benson said four crew members, who were Republic employees, needed seats on the plane so they could catch another flight in Louisville in order to prevent another United flight from being canceled. If the crew members missed their flight in Louisville, she said it would have had a "domino effect" and impacted other customers.

Benson confirmed that United offered people on Flight 3411 some compensation if they were willing to take another plane, but she wasn't able to provide further details about what offers were made. In cases like this where United doesn't get as many volunteers as it needs, the airline selects passengers who must take a different flight instead, she said. As for how those people are selected, she said United typically follows a related U.S. Department of Transportation procedure and did so in this situation.

Two customers on Flight 3411 left the plane when they were asked, but the man who eventually was forcibly removed from the plane was asked to leave repeatedly "and refused to do so," Benson said.

"These instances are rare, but when they do happen the next step is to involve law enforcement, which is what we did," she said.

Benson said United Airlines staff called the Chicago Police Department for assistance. But Officer Laura Amezaga, a spokesperson for Chicago PD, said Chicago police officers were not involved in the incident on board Flight 3411. Amezaga told the Courier-Journal to contact the Chicago Department of Aviation for more information.

The Chicago Department of Aviation said Monday afternoon that it had placed the security officer who pulled the man out of his seat on leave pending a “thorough review” of the situation.

The aviation department said in an emailed statement that the incident wasn’t in accordance with its standard operating procedure and the officer’s actions “are obviously not condoned by the Department.”

The department confirmed that all three men who were seen on video talking to the man who was removed from the flight were aviation security officers.

Benson could not provide details regarding whether a fourth person was asked to get off of the United flight to make room for the crew members who needed to board the plane.