The more immediate concern for Mr. Munoz is the current investigation into the company’s relationship with the Port Authority of New York and New Jersey. The United States attorney for New Jersey has been investigating whether United agreed to reinstate money-losing flights to an airport near the weekend home of the Port Authority’s former chairman David Samson in return for improvements the airline wanted at Newark Liberty International Airport, where United is the dominant carrier.

The airline said this year that it had also been conducting its own investigation into the matter. Some analysts speculated that the resignation of Mr. Smisek and two other top officials at the airline might signal that indictments might be issued soon.

United’s recent history is that of a troubled carrier that has faced recurring difficulties following its merger with Continental Airlines in 2010. The company’s financial results have been wildly uneven while customers complain about repeated delays, poor on-time performance and generally poor service.

United’s share price has lagged that of other airlines by about 15 percent in the last 18 months. The reason, according to analysts at Morgan Stanley, is its poor management since the merger, which led to lower unit revenues and profit margins than its rivals.

While Mr. Munoz has no operational experience in the airline business, where executives often like to say that jet fuel runs through their blood, his background does reflect the direction airlines have been taking in recent years, focusing on financial returns, pricing power and capital discipline.

“We believe a leader from a well-established rail company, which is an industry that airline managements aspire to replicate and investors use as a comparison given margins that are twice higher, may be a positive for shares over time given the performance history and the opportunity ahead for United,” Morgan Stanley analysts said in a note to investors on Wednesday.

Others were more skeptical of Mr. Munoz’s ability to bring his financial expertise running a large freight organization to a customer-minded business.