Bart Jansen, USA Today

WASHINGTON -- A government watchdog says much of the jump in air-traffic control mistakes several years ago was caused by actual mistakes rather than just a new reporting system the Federal Aviation Administration adopted.

The FAA had blamed a 53% increase from 2009 to 2010 in planes getting too close together to the new Air Traffic Safety Action Program, which encouraged controllers to report mistakes without fear of punishment. The goal of the new reporting system was to prevent future mistakes.

But Jeffrey Guzzetti, the Department of Transportation's assistant inspector general for aviation, says that the FAA's automated system for detecting operational errors had a 39% increase at that time.

"This suggests that a portion of the overall increase is due to more errors actually occurring, rather than being attributable entirely to improved reporting," Guzzetti says in a report released on Monday.

He says that close encounters "continue to be a major air safety concern, particularly in light of dramatic increases in their occurrence."

Also of concern, the report says, are so-called near misses, including "a near mid-air collision" near New York City in January 2011 involving a jetliner and two military aircraft that flew within a mile of each other.

The jump in air-traffic control errors was startling. The 1,234 events in 2009 rose to 1,887 in 2010. The number remained steady at 1,895 in 2011. The amount reported last year hasn't been released yet.

Among regional control centers, Southern California accounted for 156 of the incidents in the increase from 2009 to 2010. The Dallas region had 59 incidents and the New York region had 35 of the incidents.

The California incidents included 147 landings that FAA reclassified as errors. That's after revoking a waiver that had allowed planes to land at the same time closer than normally allowed, according to the inspector general. Those incidents accounted for 23% of the increase over that time.

The FAA has 16 staffers in investigate the "high number" of mistakes, with plans to hire more, the report says. And that presents "staffing challenges," the report says.

In response, the FAA says it's developed action plans to reduce the number of high-risk events and more steps are planned this year.

FAA has completed the most significant improvements in control safety in 30 years, including the program for voluntary reporting of incidents and electronic detection,according to Clayton Foushee, director of FAA's office of audit and evaluation. More initiatives are planned this year, he wrote in reply to the audit.