United Airlines abruptly replaced its CEO as a federal investigation continued into whether the airline gave preferential treatment to the former chairman of the agency that operates the New York-area airports.

United Continental Holdings said Tuesday that Jeffery Smisek and two other senior executives had stepped down. Oscar Munoz, a railroad executive and head of United's audit committee, was named CEO and president.

Federal prosecutors are probing United's ties to David Samson, the former chairman of the Port Authority of New York and New Jersey. United began a direct flight between Newark, N.J., and Columbia, S.C., where Samson has a summer home, while he was chairman and ended it days after he resigned last year. United, the dominant airline at Newark Liberty International Airport, was negotiating with the Port Authority over projects at the airport at the same time.

United said the departures announced Tuesday were the result of the federal probe and its own investigation into the matter.