A new survey from industry trade organization Airlines for America (A4A) revealed an estimated 51 million passengers are expected to fly globally on U.S. airlines over the winter holiday travel period.The number of travelers flying between December 15 and January 4 will grow by 3.5 percent from the 49.3 million estimated to have flown during the same period last year.To accommodate the 80,000 additional daily passengers expected to travel during the holidays, airlines will offer 91,000 additional seats per day, book additional flights and utilize larger planes.MORE Airlines & AirportsCarriers in the United States are also expected to boost staffing levels throughout the holiday period to accommodate the millions of holiday travelers.In addition, A4A officials revealed 88 percent of passengers traveling in domestic markets last year could choose among carriers other than American, Delta and United, a dramatic increase from just 65 percent in 2000.“With affordable fares and expanded route options, flying to see family, friends and loved ones this holiday season is more accessible than ever before,” A4A Vice President John Heimlich said in a statement. “Intense competition within the airline industry is enabling passengers to choose the flights that most closely match their preferences and budgets.”READ MORE: Where is Everyone Headed for the Holidays?As for which days people should travel, the A4A study found that December 21, 22 and 26 will be the busiest travel days, and December 16, Christmas Eve, Christmas Day and New Year’s Eve will be the lightest travel days.While daily passenger volumes will vary between two million and 2.7 million, U.S. airlines carried an average of 2.25 million passengers per day last year.Follow @Donald_Wood