The Federal Aviation Administration is investigating after an air traffic controller was accused of ignoring a request for an emergency landing in Denver after a commercial airline pilot reported smoke in the cabin.

The controller thought the call was a prank. The controller dismissed the emergency call minutes later.

The United Express plane from Peoria, Ill., was evacuated Tuesday after the plane landed at Denver International Airport. 1 of the 21 passengers was taken to the hospital.

According to the recordings, the controller apparently misunderstood the call letters of the airliner.

The National Transportation Safety Board says the investigation has been turned over to the FAA. A spokesman for the FAA says it would comment later Friday.