Experts say police who dragged passenger had other options

Dubai-based Emirates released an ad after video went viral of a United passenger being forcefully removed that toyed with the Chicago-based carrier's longtime slogan.

When Dao is informed that he will be dragged off the flight, he threatens to sue United Airlines.

But if the passenger posed no threat and was not being disruptive, officers nearly certainly could have tried an approach other than dragging him out of his seat and down the aisle, including simply telling the airline to resolve the situation itself, experts said.

Asked what the company would do in future if a seated passenger refused voluntarily to leave an overbooked plane, Mr Munoz said: "We're not going to put a law enforcement official to take them off".

Lawyers for the passenger dragged from a United Airlines plane in Chicago filed an emergency request with an IL state court on Wednesday to require the carrier to preserve video recordings and other evidence related to the incident.

Three aviation security officers involved in the United flight incident have now been placed on administrative leave the Chicago Department of Aviation said.

The filing with the Cook County Circuit Court likely presages an eventual lawsuit against United for the April 9 incident, where Dao was snatched from the seat he had paid for, and was dragged by his hands on his back off the parked plane, which had been bound for Louisville, Kentucky on Sunday evening (local time).

In images now seen around the world, a passenger was forcefully removed and bloodied in the process - the entire event captured on video by passengers and posted on social media.

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The airline's chief executive, Oscar Munoz, is insisting he will not resign.

Also Tuesday, Chicago Mayor Rahm Emanuel called the way Dao was treated "completely unacceptable" and praised Aviation Commissioner Ginger Evans for taking "swift action".

"No one should ever be mistreated this way", said Munoz, who also pledged to conduct a wide-ranging review of company policies. Two more officers were suspended Wednesday. United was trying to find seats for four employees, meaning four passengers had to deplane.

Meanwhile, details emerged about the passenger, who was identified as 69-year-old Kentucky physician David Dao.

No passengers on the plane have mentioned that Dao did anything but refuse to leave the plane when he was ordered to do so. When no one volunteered, the offer was increased to United States dollars 800. He refused to leave.

The airline offered compensation at first, but when that didn't convince enough passengers to take a later flight, it picked Dao randomly. "But to just randomly say, 'You're getting off the plane, ' that was bad".

One of the officers could be seen grabbing the screaming man from his window seat, across the armrest and dragging him down the aisle by his arms. "This is wrong", "Look at what you did to him" and "Busted his lip".