Planes in U.S. airspace flew too close to each other nearly 4,400 times last year, more than double the number from the previous year, the FAA reported Thursday.
In addition to the close calls, there were 18 near collisions on runways, according to the agency. None of the incidents resulted in a collision.
Of the 4,394 close-call incidents, 1,271 were termed "risk analysis events," serious enough for further review because the planes were more than 34 percent closer together than regulations allow, and 41 were termed “high risk events,” Reuters reported.
But the more than doubling of the close calls, the FAA said, can be largely attributed to a new computer system and enhanced radar that automatically records every time two planes violate the FAA’s flight separation rules.
Those rules require a distance of 3.5 miles or 1,000 vertical feet of separation near airports.
"Some of them are a breach of airspace where there was never really a collision that was imminent," Greg Feith, a former senior NTSB investigator, told NBC News. "It's just that the reporting criteria says if you lose separation the FAA needs to know about it."
The FAA’s new reporting system means it will no longer rely only on controllers and pilots to self-report those mistakes. And the FAA is seeing a drop in the percentage of the serious types of close-calls, according to the agency.
In one very close call on July 31, 2012, at Washington’s Reagan National Airport, three regional jets got far too close to each other as controllers tried to direct them away from thunderstorms.
In a statement, the National Air Traffic Controllers Union said, "maintaining the safety of the world's largest, most efficient national airspace requires constant vigilance and focus."
Federal Aviation Administration controllers handle 133 million takeoffs and landings each year and 99 percent go without incident.
But with the rising number of reports, safety officials now will have even more data to pore over.
"Well, we need to take a look at the fact that the number did rise," said Kevin Hiatt of the Flight Safety Foundation. “And by doing that, we're going to be able to pinpoint more of those areas that we need to work on."