United Airlines CEO Abruptly Steps Down Amid Internal InvestigationHis replacement has already been named.

United Continental Holdings Inc said Chief Executive Jeff Smisek had stepped down and named CSX Corp (CSX.N) Chief Operating Office Oscar Munoz as his replacement, effective immediately.

United Continental's shares fell 2.8 percent in trading after the bell on Tuesday.

Smisek, who has been the company's CEO since 2010, will also step down as chairman and president, United Continental said in a statement.

Smisek will receive a separation payment of $4.9 million, payable as a lump sum in cash, the company said in a regulatory filing.

United Continental also said its executive vice president of communications and government affairs and its senior vice president of corporate and government affairs were leaving.

The company did not specify why Smisek was leaving.

But, after announcing the departures of the other two executives in the statement, the company said "the departures announced today are in connection with the company's previously disclosed internal investigation related to the federal investigation associated with the Port Authority of New York and New Jersey."

In February, the carrier had opened an internal investigation into its relationship with the former chairman of the Port Authority of New York and New Jersey, following a government probe.

调查正在进行,它的内部probe and the related circumstances do not raise any accounting or financial reporting concerns, United Continental said on Tuesday.

(Reporting by Sweta Singh in Bengaluru; Editing bySavio D'Souza)