>> he's real close. >> reporter: the rules of separation in the skies breached. the faa's latest numbers show planes came too close nearly 4,400 times in one year. 41 of them deemed high-risk events. >> they are scary. they're unacceptable. they're worked on. but there's a backup system and people are safe. >> reporter: it's an air traffic system under stress. increasing air traffic and a potential shortage of controllers. thousands more need to be hired and trained over the next seven years. some experts worry the agency's new hiring practices could make matters worse. the agency no longer gives preference to recent graduates from aviation colleges. just last month, a government auditor said he would study controller staffing levels and the impact of retirement. but incidents where planes get too close aren't necessarily controller errors. >> these mistakes can occur through a controller making an