But the most acute challenge, The Times found, is that the nation’s air traffic control facilities are chronically understaffed. While the lack of controllers is no secret — the Biden administration is seeking funding to hire and train more — the shortages are more severe and are leading to more dangerous situations than previously known. As of May, only three of the 313 air traffic facilities nationwide had enough controllers to meet targets set by the F.A.A. and the union representing controllers, The Times found. Many controllers are required to work six-day weeks and a schedule so fatiguing that multiple federal agencies have warned that it can impede controllers’ abilities to do their jobs properly.

The roots of the current staffing shortage date to the early 1980s, when the Reagan administration replaced thousands of controllers who were on strike. Since then, there have been waves of departures as controllers become eligible for retirement. The F.A.A. has struggled to keep pace.During the pandemic, many controllers left, and the F.A.A. slowed the pace of training new ones because of health restrictions. The staffing shortage became a crisis.