Videos posted to Twitter and Facebook show a man being pulled out of his seat and down the aisle of the plane by three security officers. The incident prompted massive outrage and a federal investigation.

Videos showed a man being dragged off a United Airlines plane after the flight was overbooked — prompting massive outrage on social media and, hours later, a federal investigation. Tyler Bridges via Storyful Videos posted to Twitter and Facebook show a man being pulled out of his seat and down the aisle of the plane by three security officers. The incident occurred on Flight 3411, which was waiting to take off at Chicago O'Hare Airport for Louisville, Kentucky.

Audra Bridges, who said she was on the plane and posted video to Facebook, told the Courier-Journal the flight was overbooked by four people. Bridges said passengers were allowed to board the flight but were later told four people would need to give up their seats for four United employees who were needed in Louisville on Monday. She said no passengers volunteered, so a manager came aboard and said passengers would be randomly selected and asked to leave.

@United overbook #flight3411 and decided to force random passengers off the plane. Here's how they did it:

When asked to leave, the man in the video became "very upset" and said he was a doctor who had patients to see the next day, Bridges said. A manager then told him security would be called if he refused to leave the plane. Three security guards then removed him from his seat while other passengers yelled in disgust.

Another passenger, Jayse D. Anspach, posted a series of tweets about the incident. Twitter: @JayseDavid

Anspach tweeted that the doctor was later allowed back on the plane and appeared to have a "bloody face." @united @CNN @FoxNews @WHAS11 Man forcibly removed from plane somehow gets back on still bloody from being removed Footage of the clearly distressed man returning to his seat was posted on Twitter by Tyler Bridges.

Another video from the flight showed the man bloodied, apparently saying "they kill me" over and over. #flythefriendlyskies @united no words. This poor man!!

By Monday evening, the Department of Transportation said it was reviewing whether United followed consumer protection regulations. "The Department of Transportation (USDOT) remains committed to protecting the rights of consumers and is reviewing the involuntary denied boarding of passenger(s) from United Express flight 3411 to determine whether the airline complied with the oversales rule," a spokesperson said. "The Department is responsible for ensuring that airlines comply with the Department’s consumer protection regulations including its oversales rule. While it is legal for airlines to involuntary bump passengers from an oversold flight when there are not enough volunteers, it is the airline’s responsibility to determine its own fair boarding priorities."

When asked about the incident, United Airlines released the following statement: Flight 3411 from Chicago to Louisville was overbooked. 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.

When asked why the airline had the man forcibly removed, and whether that was standard procedure in cases of overbooked flights, United refused to comment. Instead they told BuzzFeed News all further questions should be referred to Chicago Police. BuzzFeed News contacted Chicago Police and were told to contact the Chicago Department of Aviation. When BuzzFeed News contacted the Chicago Department of Aviation, the call was transferred to a TSA message bank. A TSA spokesperson later told BuzzFeed News they were not involved and to contact Chicago Police.

The Chicago Police Department eventually released a statement saying, in part, that the 69-year-old passenger "fell," causing his head to strike "an armrest causing injuries to his face." Chicago Police statement confirms officers forcibly removed a passenger who refused to leave an oversold @united fl… https://t.co/RVvi67BmH8 The Chicago Department of Aviation later announced that one of their officers involved in the incident was placed on leave. "The incident on United flight 3411 was not in accordance with our standard operating procedure and the actions of the aviation security officer are obviously not condoned by the Department," a department statement read. "That officer has been placed on leave effective today pending a thorough review of the situation."

Later on Monday, the CEO of the airline issued a statement apologizing for "having to re-accommodate" customers, adding that the airline is conducting its own detailed review of the incident. United CEO response to United Express Flight 3411.

Munoz also sent a letter to United employees, saying that while he regretted the situation, he believed United staff had followed established procedures. "Our employees followed established procedures for dealing with situations like this," he said. "While I deeply regret this situation arose, I also emphatically stand behind all of you, and I want to commend you for continuing to go above and beyond to ensure we fly right. I do, however, believe there are lessons we can learn from this experience, and we are taking a close look at the circumstances surrounding this incident. Treating our customers and each other with respect and dignity is at the core of who we are, and we must always remember this no matter how challenging the situation."

.@united @courierjournal Overnight, United's CEO emailed staff to say the airline had "no choice" but to call offic… https://t.co/ZFfkOsSc6H

The technical term for kicking passengers off oversold flights is "involuntarily denied boarding," and there's a whole section of the Code of Federal Regulations (CFR) that spells out how airlines are required to deal with these sorts of situations. First, airlines are required to do everything they can to ensure "the smallest practicable number of persons holding confirmed reservation space" are kicked off a flight against their will. In a situation where there aren't enough people willing to volunteer, federal regulations state that airlines must have a seating priority policy "written in such manner as to be understandable and meaningful to the average passenger" laying out how they choose which paying customers will be removed from a flight. Airlines must make sure that their priority boarding policy "shall not make, give, or cause any undue or unreasonable preference or advantage to any particular person or subject any particular person to any unjust or unreasonable prejudice or disadvantage in any respect whatsoever." Examples of factors that can make you higher or lower on the boarding priority list, per the CFR, are the time a passenger checked in, whether a passenger had a seat assignment before arriving at the gate, the fare they paid, their frequent-flyer status, and if the passenger is disabled or is traveling as an unaccompanied minor. It gets more complicated from there, but in certain situations, federal regulations state that passengers who are kicked off flights can be entitled to 200%–400% of their fare.

Ellie Hall and Talal Ansari contributed additional reporting to this story.