CBS News has independently confirmed one air traffic controller was doing the job normally handled by two when a passenger jet and a Black Hawk helicopter collided in midair Wednesday night and crashed into the Potomac River near Reagan National Airport and Washington,

Amid increased concerns about aviation safety, here's how many air traffic controllers there are in the U.S., and how the hiring process works.

After a tragic midair collision at Reagan National Airport, air traffic controller staffing and training have come under scrutiny. Here’s what it takes to enter this demanding career.