WASHINGTON -- United Airlines and the Chicago department of aviation missed a Senate deadline Friday to provide information about the violent removal of a passenger from a flight, but said they would provide details next week.

The top members of the Senate Transportation Committee – Sens. John Thune, R-S.D., and Bill Nelson, D-Fla. – demand information about the incident that created a worldwide firestorm.

The passenger, David Dao, was seated and dragged off flight 3411 at Chicago O’Hare International Airport on April 9 to make room for a crew member on the sold-out flight. Dao suffered a concussion and lost two teeth in the incident, according to this lawyer.

United has apologized, refunded fares to all passengers on the flight and said the airline won’t ask police to remove passengers any more. The three aviation police officers who removed Dao were suspended.

Lawmakers including Thune and Nelson asked for more information April 11 about the incident while considering whether legislation is necessary. The House Transportation and Infrastructure Committee plans a hearing on airline policies, and United is expected to testify. But airlines have argued that overbooking policies should be left to the competitive marketplace.

“Getting answers for the public about what happened and what can be done to prevent such an incident from happening again is a priority for the members of our committee,” Thune and Nelson said in a joint statement. “We find any further delay in getting necessary answers unacceptable.”

United has said its internal investigation would be completed by April 30. United CEO Oscar Munoz sent a letter Thursday to the senators saying he could provide them “a full set of facts about this incident” by April 27.

“This includes examining how we move our crews, incentivize customer volunteers in these situations, handle oversold situations and work with airport authorities and local law enforcement moving forward,” Munoz said in the letter.

Ginger Evans, commissioner of the Chicago aviation department, also said the investigation of the officers was continuing, with results expected by April 26.