CHICAGO (CBS) — Chicago Aviation Commissioner Ginger Evans on Thursday apologized for the role city employees played in dragging a passenger off a United Airlines flight at O’Hare International Airport last month, but told a U.S. Senate subcommittee changes in procedures are underway.

Evans told Aviation Operations, Safety, And Security Subcommittee Chair Roy Blunt (R-Mo.) the Chicago Department of Aviation security officers who dragged Dr. David Dao off Flight 3411 to make way for airline employees should not have carried out United’s request to remove him.

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“Our policy is clear; that force should only be used when absolutely necessary to protect the security and safety of our passengers. Our policy states, and I quote, ‘The safety of innocent persons and bystanders must be given primary consideration whenever the use of force is contemplated,’” she said.

Dao suffered a concussion and a broken nose, and lost two teeth, when three CDA security officers yanked him out of his seat and dragged him down the aisle by his arms, after he refused to get off the plane when the crew decided to bump him and his wife from the flight to make way for a flight crew that needed to get to Louisville.

Evans said the incident was “completely unacceptable,” and offered Dao and his family her “sincerest apologies.”

“That a passenger of one of our airports was injured in this way is deeply saddening and personally offensive to me. This is not how we do business, and these actions will not be tolerated,” she said. “Based on my review, the security officers involved in the incident on United Flight 3411 broke from our standard procedures, and failed to provide Dr. Dao and his family the respect we demand be given to all of the traveling public flying in and out of Chicago.”

The commissioner said new rules dictate only sworn police officers are authorized to remove a passenger from a plane, and then only in a medical emergency or dangerous situation.

With an investigation underway, Evans said she could not explain why the CDA officers agreed to remove Dao from the plane.

“In terms of what they were thinking, or why they did what they did, I have to wait for the findings of that report to know. I honestly don’t know at this point why,” she said.

Pressed on whether there was a lack of proper instruction for the officers, Evans said the department will “enhance our training.”

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Three security officers and one supervisor have been suspended for the incident on Flight 3411.

In his report on the incident, Officer James Long claimed Dao “started swinging his arms up and down fast and violently” and then “started flailing his arms and started to fight.”

Long said Dao was injured when he hit his arm, causing him to lose his grip, and his face smashed against an armrest.

Assisting officer Mauricio Rodriguez stated Long used “minimal but necessary force” to remove Dao.

United Airlines has agreed to a settlement with Dao for an undisclosed amount. As part of the settlement, the city will not be held liable for any damages.

While Thursday’s subcommittee hearing focused largely on the incident on Flight 3411, some senators also complained about other airline issues, such as overbooking and passenger fees.

U.S. Sen. Tammy Duckworth (D-Ill.) told Sharon Pinkerton, an executive with airline industry trade group Airlines 4 America, about problems for passengers with disabilities.

“As someone who travels and has trouble with a wheelchair for over a decade now, I’ve seen no improvement,” Duckworth said. “In the last 24 months, I’ve had two wheelchairs broken, and I don’t see improved training of anyone, especially your baggage handlers.”

Pinkerton apologized and said the airlines “want to fix that,” but Duckworth shot back, “It doesn’t appear that way.”

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The senator also cited problems other wounded veterans have encountered when they fly.