United Airlines' Chief Financial Officer Andrew Levy is stepping down, the carrier said on Thursday, in a major management shakeup as the airline's financial performance lags rivals.

Levy will be replaced in the interim by Gerry Laderman, a senior United executive, who had served as acting chief financial officer before Levy's appointment. The carrier said it will immediately begin a search for a permanent replacement.

In a statement, Levy said he resigned on Monday, May 14, after serving less than two years in the post.

"Since my arrival in August 2016, the company has faced several challenges, but we have nevertheless enjoyed success. As satisfying as this job has been, I am considering several exciting opportunities and will choose one in the coming weeks," he said.

Levy said he would continue to serve on the board of Copa Holdings Inc, the parent company of Panama's Copa Airlines, as an independent member. In a separate letter to employees, Levy wrote that the decision to resign had been reached after several months of thought.

United Chief Executive Officer Oscar Munoz said Levy "leaves the company in a stronger financial position and with a clear strategy and framework in place."

Munoz said the move did not affect the carrier's prior financial guidance.

Levy took the reigns of United's finances in August 2016 as part of a management makeover strategy by Munoz. The move was aimed at righting the airline's course in a years-long struggle to match the profit margins and operational performance of larger U.S. rivals American Airlines and Delta Air Lines.

His departure highlights the difficulties United has faced in building a cohesive suite of executive personalities.

Public relations blunders, executive in-fighting and continued operational shortfalls have plagued the airline.

Shares of United Continental Holdings Inc (UAL.N) closed down 0.35 percent. Its stock price is up 3 percent in the year to date.