Ms. Syth said Mr. Kirby had led a domestic strengthening for the airline, which focused on its international strengths during and after the Great Recession.

“Scott has really come in and with his team changed that dynamic, where they’re increasingly a much more important domestic player,” she said.

Ms. Syth and Mr. Didora both said they expected little to change under Mr. Kirby, who has led United’s push to further segment its cabins, introducing extra fees such as those that allow passengers to sit closer to the front of planes. He is also leading a multiyear effort to strengthen United’s hubs, particularly in Chicago, Denver and Houston. He has described that move as critical to growth.

In recent years, the United States airline industry has shrunk through mergers and acquisitions to four large carriers: American, Delta, United and Southwest. That has increased the importance of hub airports, where typically one airline is dominant.

United, which also has a major presence at Newark Liberty International and San Francisco International Airports, has done well financially in recent years. The company reported third-quarter earnings in October that topped analyst expectations.

As a result of its success, United has been able to close in on competitors like Delta, and Mr. Kirby is likely to continue to work toward that goal. “They made great strides, but I think they still have their sights on narrowing” the gap, Ms. Syth said.

Despite the airline’s turnaround, Mr. Munoz’s tenure was marred by several controversies. In April 2017, a passenger, Dr. David Dao, was dragged off a United flight at O’Hare International Airport when he objected to giving up his seat for an airline employee. Video of the incident quickly spread on social media and became the subject of days of news coverage and public commentary.