The industry group Airlines for America said the total would eclipse the 24.7 million travelers who took to the skies last year.

The 2.1 million passengers per day during the 12-day holiday period will be about 31,000 higher per day, according to the airlines.

The busiest days will be the Sunday, Dec. 1, followed by Wednesday, Nov. 27 and Monday, Dec. 2. The lightest days will be Thursday, Nov. 28 and Friday, Nov. 29. Planes throughout the holiday period will be more than 85% full.

John Heimlich, chief economist for the airline group, said air travel costs less after inflation than in 2000 and travel continues to rebound from the economic downturn.

"More seats are returning to the marketplace to accommodate growing demand as carriers are increasing the number of available seats for Thanksgiving travel by roughly 2%," Heimlich said.

The airline projections came a day after the Transportation Department reported that the average domestic airline fare fell to $378 during the second three months of the year, down from $392 from a year earlier. The fares didn't include fees, such as for baggage.

The highest average fare of $547 was at Huntsville, Ala., and the lowest of $159 was at Atlantic City, N.J., according to the Bureau of Transportation Statistics.

The average fares were down 18.4% from 1999, when adjusted for inflation, according to the bureau.

Despite fares declining against inflation, Heimlich said the 10 largest U.S. airlines reported combined earnings so far this year of $4.5 billion -- a 4% net profit -- up from $312 million during all of 2012.

Airline investment more than doubled since 2010, to $965 million per month this year, to buy new planes, install Wi-Fi and improve websites, Heimlich said.

"When airlines are profitable, customers, employees and the economy win because airlines are better able to invest in the business and improve the product and travel experience," Heimlich said.