This is helping to keep ticket prices low, which also drives demand, especially among leisure travelers. According to data from the travel booking platform Hopper, round-trip domestic ticket prices for holiday flights are averaging $304, a drop of nearly 10 percent from last year. (Prices for international flights ticked up a bit, rising $66 on average.)

“If you actually look at the average price of tickets in real terms adjusted for inflation, air traffic continues to be more and more affordable,” Mr. McKone said.

With ticket prices lower, more Americans will be flying, and Hopper estimates that overall spending will be 6 percent higher this holiday season than last. “Having lower prices definitely does drive demand,” Mr. McKone said.

Airlines for America, the industry trade organization, estimates that domestic airlines will add, collectively, 143,000 seats daily to accommodate holiday travelers, and according to Patrick Surry, chief data scientist at Hopper, much of that capacity is being added by the major carriers at large hub airports.

Southwest Airlines, for instance, announced new routes last month in Northern California and the Washington, D.C., area, as well as to popular warm-weather vacation destinations. United Airlines, which expects to transport roughly half a million passengers — a 4 percent increase over 2017 — on its peak holiday travel days, is increasing the frequency of flights to locations like the Caribbean and ski resort areas, and plans to add nearly 20 domestic wide-body aircraft to help manage full flights over the holidays, an airline spokesman, Charlie Hobart, said.