American strengthens lead as US fortress hubs grow more concentrated

The top ten U.S. fortress hubs this September include:

- Charlotte (American Airlines) – 88%

- Dallas/Fort Worth (American Airlines) – 84%

- Atlanta (Delta Air Lines) – 79%

- Houston Intercontinental (United Airlines) – 79%

- Minneapolis (Delta Air Lines) – 76%

- Philadelphia (American Airlines) – 75%

- Detroit (Delta Air Lines) – 74%

- Salt Lake City (Delta Air Lines) – 73%

- Washington Dulles (United Airlines) – 72%

- Newark (United Airlines) – 72%

These percentages reflect each airline's share of total passenger flights at their respective hubs for September; shares can vary during other months.

Nine out of these ten hubs have increased their level of dominance compared to last year. Only United’s position at Washington Dulles remained unchanged at 72%. No hub saw a decrease in market share by its primary operator over the past year.

Some notable increases include American’s share at Charlotte rising by one percentage point to reach its current high, United gaining a point at Houston Intercontinental, and Delta increasing by one point at Detroit. Larger jumps were seen at Dallas/Fort Worth (+2 points), Atlanta (+2), Salt Lake City (+2), Newark (+2), while Philadelphia and Minneapolis both grew by three points.

At Philadelphia International Airport, American’s share climbed from 72% last September to 75%, totaling an average of 578 daily movements out of the airport’s overall count of 767. The increase was driven partly by new or reinstated routes such as Des Moines, Edinburgh, Milan Malpensa, Norfolk, Northwest Arkansas, and Omaha. However, Cirium data shows that reductions in service from other airlines—especially Frontier (-33%) and Spirit (-30%)—also contributed significantly: “The oneworld member's higher share is largely not of its making. Cirium indicates that movements by all other carriers have fallen by 16% year-on-year, which necessarily pushed up American's share.”

Minneapolis also saw a rise in Delta’s presence—from holding a market share of 73% last year to now controlling about three-fourths of traffic: “Delta's dominance at Minneapolis has increased from 73% to 76%. Compared to last September, movements by all other carriers have fallen by 13%, while Delta's have risen by 3%. The SkyTeam airline has introduced or reintroduced several routes... However, its higher activity is, as usual, mainly from higher frequencies on multiple existing routes.”

Overall trends show that most major U.S. fortress hubs are becoming even more concentrated around their dominant airlines—a development with implications for both passengers and competitors.