CHICAGO (CBSNewYork/AP) — United Airlines is pledging to review company policies on the removal of passengers after video of man being dragged off a full flight in Chicago sparked intense backlash.

In an interview with ABC’s “Good Morning America” aired Wednesday, United Airlines CEO Oscar Munoz said he felt “ashamed” watching the video of Dr. David Dao of Elizabethtown, Kentucky being dragged off a United Express flight.

Munoz apologized to Dao, his family and the other passengers who witnessed him being forcibly removed from the plane.

Calling it a “system failure,” he vowed this “will never happen again on a United flight” and that law enforcement won’t be involved in the future.

Munoz said the company would reassess policies for seeking volunteers to give up their seats, for handling oversold situations and for partnering with airport authorities and local law enforcement.

The incident began as United was trying to make room for four employees of a partner airline, meaning four people had to get off.

At first, the airline asked for volunteers, offering $400 and then when that did not work, $800 per passenger to relinquish a seat. When no one voluntarily came forward, United selected four passengers at random.

Three people got off the flight, but the fourth, Dao, said he was a doctor and needed to get home to treat patients on Monday. He refused to leave.

Three Aviation Department police officers got on the plane. Two officers tried to reason with Dao before a third came aboard and pointed at him “basically saying, ‘Sir, you have to get off the plane,'” said Tyler Bridges, a passenger whose wife, Audra D. Bridges, posted a video on Facebook.

One of the officers could be seen grabbing Dao from his window seat, across the armrest and dragging him down the aisle by his arms.

In the video, other passengers are heard saying, “Please, my God,” ”What are you doing?” ”This is wrong,” ”Look at what you did to him” and “Busted his lip.”

After people were horrified by the video, Munoz said the airline was reaching out to Dao to “resolve this situation.” Hours later on Monday, his tone turned defensive. Munoz described the passenger as “disruptive and belligerent.”

By Tuesday, Munoz issued his most contrite apology yet, describing the incident as “truly horrific.”

“No one should ever be mistreated this way,” said Munoz.

Meanwhile, more details have emerged about Dao. He was convicted in 2004 of several counts of obtaining drugs by fraud or deceit and was placed on five years of supervised probation and surrendered his medical license, which he got back in 2015.

But there’s no indication that Dao’s past influenced how he was treated or that the airline or police were aware of his background or would have known anything about him other than basic information such as his name and address, if that.

Screaming can be heard on the videos, but nowhere is Dao seen attacking the officers. In fact, he appears relatively passive both when he was dragged down the aisle of the jet and when he is seen standing in the aisle later saying quietly, “I want to go home, I want to go home.”

Airport officials have said little about Sunday’s events and nothing about Dao’s behavior before he was pulled from the jet that was bound for Louisville, Kentucky. Likewise, the Chicago Aviation Department has said only that one of its employees who removed Dao did not follow proper procedures and has been placed on leave.

No passengers on the plane have mentioned that Dao did anything but refuse to leave the plane when he was ordered to do so.

An attorney who represents Dao said his client was being treated at a Chicago hospital for injuries he sustained on the plane and that the family would not comment.

Leaders of a key Senate committee have asked United Airlines and Chicago airport authorities to explain what led to the incident, saying United’s explanation “has been unsatisfactory, and appears to underestimate the public anger about this incident.”

The four senators wrote letters Tuesday to Munoz and Ginger Evans, commissioner of the Chicago Department of Aviation.

“The last thing a paying airline passenger should expect is a physical altercation with law enforcement personnel after boarding, especially one that could likely have been avoided,” they said.

The senators directed most of their questions at Munoz, including queries about the airline’s policy for bumping passengers off oversold flights, and whether it makes a difference that passengers have already boarded the plane, as happened on the United Express plane in Chicago.

The senators said the incident could have been prevented with better communication or “additional incentives” — an apparent suggestion that United didn’t offer passengers enough compensation to voluntarily give up their seats.

The letter was signed by the four top-ranking members of the Senate commerce committee — the Republican chairman, John Thune, the Republican aviation subcommittee chairman, Roy Blunt, and the two senior Democrats, Bill Nelson of Florida and Maria Cantwell of Washington.

New Jersey Gov. Chris Christie also wants to prevent a similar scene at Newark Airport and is calling for a federal ban on overbooking flights and bumping passengers.

Read Christie’s Letter To Secretary Chao

Christie sent his suggestion to Transportation Secretary Elaine Choa on Tuesday.

“This conduct is abusive and outrageous. The ridiculous statements, now in their third version, of the CEO of United Airlines displays their callousness toward the traveling public with the permission of the federal government,” Christie said in the letter. “I know the Trump administration wants to reform regulations to help the American people. This would be a great place to start.”

United flights amount to 70 percent of the air traffic at Newark.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)

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