WARRENTON, Va. – During a morning meeting in early May, staff at the federal air traffic command center rattle off a few of the day's obstacles: storms near the Florida coast and in Texas, a military aircraft exercise, and a report of a bird strike at Newark Liberty International Airport.

The center, about an hour's drive from Washington, D.C., is responsible for coordinating the complex web of more than 40,000 flights a day over the U.S. Shortly after 7 a.m. ET, there were already 3,500 flights in the air. During peak travel periods, that figure can climb to more than 5,000 flights at once.