United Airlines apologises to investors, says no one will be fired over Flight 3411 passenger incident

The CEO of United Airlines says no one will be fired over the dragging of a man off a plane - including himself.

CEO Oscar Munoz said on Tuesday (US time) that he takes full responsibility "for making this right" and he promised more details later this month after United finishes a review of its policies on overbooked flights.

Company executives said it's too soon to know if the incident is hurting ticket sales.

United has been pummelled on social media - BoycottUnited is a popular hashtag - and late-night television. Through Tuesday, its shares have fallen 4.4 per cent since Flight 3411, wiping out nearly $US1 billion ($1.3b) in market value, although some other airline stocks also declined in the same period.

After the market closed on Monday, United reported a $US96 million ($127 million) first-quarter profit, down 69 per cent from a year earlier largely because of higher costs for fuel, labour and maintenance. The revenue picture was looking better - evidence was growing that after two years of falling average fares, United will be able to push prices higher this year.

On a conference call to discuss those results, Munoz started by apologising again for the April 9 scene on a United Express plane at Chicago's O'Hare airport. David Dao, a 69-year-old doctor, was bloodied and dragged off the plane by Chicago airport officers who had been summoned by United employees when Dao wouldn't give up his seat. The three officers have all been suspended.

Munoz and other executives vowed to treat customers with dignity, and said that what happened to Dao will never happen again.

Munoz's early statements on the incident were widely criticised. He initially supported employees and blamed Dao, calling him "disruptive and belligerent." On Tuesday, he was asked if the company ever considered firing anyone, including management.