CHICAGO - The man dragged off a United Airlines flight, sparking an international uproar, suffered a broken nose and concussion, his lawyer said Thursday, adding that he is planning to sue.

David Dao was released from the hospital overnight and was at a "secure location," attorney Thomas Demetrio said at a news conference during which a member of Dao's family spoke out for the first time.

Meanwhile, United remained under the spotlight as representatives of the carrier faced tough questioning at a city council hearing in Chicago, where the airline is headquartered and where the incident occurred.

Dao's lawyers filed a petition in court requesting that the city, which operates O'Hare International Airport, and United Airlines preserve evidence related to the incident. They also said a lawsuit was forthcoming.

"This lawsuit, among other things, hopefully, will create a not just national discussion, but international discussion, on how we're going to be treated going forward," Demetrio said.

"For a long time, airlines, United in particular, have bullied us."

- Dao 'healing -

Online video of airport security officers dragging Dao off a packed flight Sunday sparked worldwide outrage. He screamed as officers pulled him from his seat, and was bloodied by the altercation.

The 69-year-old doctor's lawyers said he also suffered injury to his sinuses and lost two front teeth.

"My dad is healing right now," said Crystal Dao Pepper, 33, one of Dao's five children.

"We were completely horrified and shocked at what had happened to my father," she said.

In response, United Airlines released a statement reiterating apologies from earlier in the week.

"We continue to express our sincerest apology to Dr. Dao. We cannot stress enough that we remain steadfast in our commitment to make this right," the statement said.

The airline also said that it would no longer ask law enforcement to remove a passenger from a flight unless it is a matter of safety and security.

United's apologies have not quelled a torrent of criticism, especially since those apologies came days after the incident -- and after its initial statements appeared at least in part to blame Dao.

- 'A failure of our system' -

At a sometimes tense hearing Thursday at Chicago's city hall, officials from United and O'Hare said they are conducting investigations to determine what went wrong with their procedures.

United said it will release the results of its review on April 30.

"We commit to you that this type of situation will never happen again aboard our aircraft," Margaret Smith, United's head of corporate affairs, said at the hearing.

Asked why United took days to apologize,Smith said the airline made a mistake.

"We took too long to say anything, and our statement -- when it first came out -- did not show the depth of our concern and regret," Smith said.

"We should have handled it quicker, and we should have been better at expressing how that is something that we just do not want ever to happen again at United."

John Slater, who is in charge of O'Hare's Chicago operations, clarified that the incident had not been the result of overbooking, the practice of selling more tickets than seats on a plane, as the airline had initial claimed.

Instead, it arose because the airline needed four passengers to give up their seats so employees could be repositioned to work a flight the next morning.

"It was a failure of our system," Slater said.

In addition to scrutiny by Chicago officials, and an internal investigation at United, congressional lawmakers in the US capital have signaled a likelihood to take action, as well.

Congresswoman Jan Schakowsky of Illinois said she would author a bill to end the practice of airlines denying boarding to passengers on overbooked flights. Meanwhile, a group of 21 senators said they planned to examine the incident.-AFP