Chicago ? Another error by controllers at an air traffic center put planes too close to each other over central Illinois, but they were never in danger of colliding, the Federal Aviation Administration said Thursday.

It was the second error by controllers at the FAA’s Chicago Center radar facility in Aurora reported this week.

The Boeing 737 jet came within 3.6 miles horizontally of a Beechcraft Super King Air 200 about 20 miles from Springfield on Wednesday morning, said FAA spokesman Tony Molinaro.

Minimum spacing between planes is 5 miles horizontally or 1,000 feet vertically.

The 737, operated by Southwest Airlines, flew to Chicago from St. Louis, and the other plane traveled to Farmington, N.M., from West Lafayette, Ind., the Chicago Tribune reported Thursday on its Web site.