United Continental Holdings named an acting CEO to replace Oscar Munoz, who is taking medical leave following a heart attack just one month into the job.
Brett Hart, previously United's executive vice president and general counsel, has taken the chief executive appointment effective immediately.
"Brett has taken on increasing responsibility beyond general counsel over the last few years in the operations and customer facing areas of the company," Henry Meyer, non-executive chairman of the board, said in a statement.
"I am confident in his ability to continue to implement the company's strategy and Oscar's mission of bringing United's people together around the shared purpose of becoming the best airline for our customers and employees."
United did not confirm the length of Munoz's medical leave, saying it was "too soon to know the course of treatment and timing of recovery," but confirmed he had suffered a heart attack on Thursday.
Munoz, 56, was named CEO of United Continental on September 8 after the surprise ouster of Jeff Smisek linked to a federal investigation into allegedly inappropriate dealings with the New York regional transportation authority. Two other top executives also resigned.
The company immediately replaced Smisek with Munoz, president and chief operating officer of CSX Corporation, a US rail operator.