The Department of Transportation said it will review the incident, in which a passenger was forcibly removed from the Louisville, Kentucky-bound United flight 3411 at Chicago O'Hare International Airport.
The incident has prompted one security officer's suspension and created a publicity nightmare for United.
Several passengers recorded the incident on their phones and posted video on social media showing three Chicago Department of Aviation security officers dragging the man, who has not been identified, down the aisle by the arms and legs while other passengers shout in protest. He continued to resist after he was removed and ran back onto the airplane, face bloodied from the encounter.
"It was very traumatic," passenger Jade Kelley said. She did not witness the entire event but she said the sound of the screams still haunt her.
"It was horrible. I had trouble sleeping last night and hearing the video again gives me chills."
An 'involuntary de-boarding situation'
The incident sparked criticism of a system that allows airlines to involuntarily boot passengers from flights. United was acting within their rights and following policy. Then, the situation turned physical.
United asked passengers to give up their seats voluntarily for compensation. Four crew members needed to get on the flight in order to work another one in Louisville or else that flight would be canceled, airline spokeswoman Maddie King said.
When no one volunteered, the airline was forced into an "involuntary de-boarding situation," airline spokesman Charlie Hobart said.
United weighs a number of factors to determine which passengers would leave the flight, such as connecting flights and how long the delay will leave the customer at an airport, Hobart said.
United employees explained the situation to the man several times, Hobart said. When he refused they followed Department of Transportation protocol and called local law enforcement to forcibly remove him from the plane.