Chicago aviation officers broke with standard operating procedures when they forcibly removed and dragged a man off a United flight after he refused to give up his seat last month, the head of city’s Department of Aviation told a Senate committee Thursday.

“As someone who has spent more than three decades in the aviation industry, that a passenger at one of our airports was injured in this way is deeply saddening and personally offensive,” said Chicago Aviation Commissioner Ginger Evans, who apologized to the passenger, David Dao, and his family. “This is not how we do business and these actions will not be tolerated.”

Four aviation security officers have been placed on leave in connection with the April 9 incident. The City of Chicago’s Office of the Inspector General is also conducting a separate probe.

Evans’ comments came during testimony before the Senate Subcommittee on Aviation Operations, Safety and Security. It was the second of two Capitol Hill hearings held this week examining the circumstances that led to Dao’s removal of from the Louisville-bound flight.

Video footage of a bloodied Dao, screaming as he was removed from the plane drew international condemnation and calls for a boycott of United. Dao suffered a concussion, broken nose and lost two teeth in the fracas. Late last month, he agreed to a confidential settlement with United.

“What happened to Dr. Dao is just simply unconscionable,” Sen. Bill Nelson, D-Fla., said in his opening statement. “This is a subtext and a foretelling of larger issues – because the airline industry in this country has become anti-competitive and consumers are being hurt in the process.

Evans statements were the strongest to date from the agency that manages Chicago’s two airports.

An incident report released last month in response to a public records request by the conservative watchdog group Judicial Watch, said that the officers used “minimal but necessary force” to remove Dao from the plane. They said Dao “responded repeatedly in an aggressive manner” when asked to leave the plane and swung his arms “up and down, fast and violently.”