During the final holiday weekend of the summer, a record 16.5 million people are expected to fly on U.S. airlines — a 3.5 percent increase over the Labor Day weekend in 2017, according to Airlines for America, the trade group for the nation’s air carriers.The country’s airlines are expected to fly 2.36 million passengers a day over the four-day weekend, an increase of 79,000 travelers a day from the same weekend in 2017, according to the trade group.