Airlines for America expects 51 million passengers will fly globally on U.S. airlines over the 21-day winter holiday travel period beginning today, Dec. 15, and lasting through Jan. 4. The total is a 3.5 percent increase over the 49.3 million passengers traveling last year.

To accommodate the roughly 80,000 additional passengers per day, airlines offer 91,000 additional seats per day by increasing flight frequencies and utilizing larger aircraft.

“With affordable fares and expanded route options, flying to see family, friends and loved ones this holiday season is more accessible than ever before,” said John Heimlich, vice president and chief economist, Airlines for America.“Intense competition within the airline industry is enabling passengers to choose the flights that most closely match their preferences and budgets.”

“In recent months, notwithstanding the impact of severe weather events such as Hurricanes Harvey, Irma and Maria, flight completion and on-time arrival rates remained high, while reports of mishandled baggage and involuntary denied boardings plunged to their lowest ever recorded. These recent developments bode well for the winter holiday flyer,” he added.

Airlines for America projects the busiest holiday travel days, with more than 2.7 million passengers per day, as Dec. 21, 22 and 26. Lightest travel days, with just below 2 million passengers per day, include Dec. 16, 24, 25 and 31.