The chief executive of United Airlines has apologised for the 'truly horrific' removal of a passenger from an overbooked flight.
Oscar Munoz said he "continues to be disturbed" by the incident, during which a passenger was forcibly dragged, screaming, off a plane.
He said the company would "fix what's broken so it never happens again".
United's parent company's share price plummeted after a video of the incident went viral on Twitter.
Stock in United Continental Holdings dropped by more than 4 percent at one point on Tuesday, and at one point nearly $US1 billion was wiped off its value - but prices later recovered partially.
The footage taken inside the airliner showed a man being pulled out of his seat and dragged, screaming, down the aisle. He is later seen with blood on his face.
The flight from Chicago to Louisville, Kentucky, on Sunday evening had been overbooked - a fairly common practice - so the airline wanted to get four passengers to leave the flight to make room for four staff members.
Three passengers - reportedly including the man's wife - agreed and left the plane. But the man said he worked in a hospital, and needed to see his patients the next day, an eyewitness tweeted.
A video that appears to show the man dazed and with blood around his mouth, saying "just kill me", having run back on the plane, has also emerged online.
Earlier on Tuesday Mr Munoz defended employees' conduct and said the passenger had been "disruptive and belligerent". He came under intense criticism online and the incident reached the ears of the White House press secretary, Sean Spicer, who called it "troubling".