New United Airlines CEO Oscar Munoz admitted to hospital

United Airlines’ new chief executive, Oscar Munoz, has been admitted to a hospital, possibly for a heart attack, raising concerns about the ability of the carrier to improve its performance.

United Continental Holdings Inc. said Friday that Munoz’s family informed the company that he was admitted to a hospital on Thursday. The Chicago company said in a statement that it was continuing to operate normally.

A company spokeswoman would not provide additional information, but the Wall Street Journal reported that Munoz suffered a heart attack, citing people familiar with the matter.

Munoz, 56, was named CEO of United Continental Holdings on Sept. 8 after the company announced that CEO Jeff Smisek had suddenly stepped down. Smisek faced questions about whether United sought favors from the officials who operate the New York-area airports. Federal prosecutors are investigating United’s ties to David Samson, former chairman of the Port Authority of New York and New Jersey and a political ally of New Jersey Gov. Chris Christie.

Munoz was a railroad executive who had spent 11 years on the boards of Continental Airlines and United Continental, which was formed by the 2010 merger of United and Continental.

In a newspaper ad this month, Munoz apologized to customers for problems that have plagued United since the merger, including several technology outages that have caused large-scale flight delays and cancellations. United’s on-time performance has trailed its three biggest peers — American, Delta and Southwest — so far this year. In the ad, Munoz said United had failed to live up to its promises and vowed, “That’s going to change.”

On an introductory conference call with Wall Street analysts last month, Munoz said United must convince customers that it will improve customer service but added, “That is going to take a lot of time and effort.”

Although United was slower to return to profitability after the financial crisis that began in 2008, it has posted record profits recently, helped by cheaper jet fuel. The company earned $1.7 billion in the first six months of 2015, although revenue slipped 2.6%.

S&P Capital IQ analyst Jim Corridore said that until more details are known about Munoz’s health, the situation could cause uneasiness among investors.

Shares of United fell $1.79, or 3.1%, to $55.97 on Friday.