Passenger traffic at Des Moines International Airport increased by 4.6 percent in May compared with the year-ago period, which increased year-to-date growth to 6.7 percent. A total of 220,557 passengers departed or arrived at the airport in May. Frontier Airlines had the biggest increase in passengers in May, up 53 percent. United Airlines had the largest number of passengers in May at 60,895, up nearly 20 percent from a year ago.