For four and a half hours, the sky above the United States emptied out.Normally, throughout the day and the night, thousands of planes are taking off, crisscrossing the country, and landing. When the Federal Aviation Administration grounded all U.S. flights around 4:00 p.m. today, because of “extraordinary circumstances and for reasons of safety,” some 4,000 airplanes were in the sky, headed for U.S. airports, according to Flightradar24, an aviation-tracking website. Even if no more flights took off, all of those planes needed to land.For the people below, getting them down…
