UPDATED 09/25/12 10:23 a.m.

CHICAGO (CBS) — The number of airline flights has decreased in the past four years, but, the New York Times is reporting the number of potentially catastrophic incidents on the ground has remained steady.

As WBBM Newsradio’s Mike Krauser reports, in one incident on Dec. 11 of last year, Southwest Flight 844 had just arrived at Midway International Airport from Minneapolis with 74 passengers onboard, and the tower cleared the 737 to cross a runway.

LISTEN: WBBM Newsradio’s Mike Krauser reports

But the co-pilot saw a Lear jet and told the pilot to slam on the brakes. The Lear jet flew 62 feet overhead.

Last year, there were also two collisions within months of each other at O’Hare International Airport.

The first incident happened on May 16, 2011, when SkyWest Flight 6958 passed 275 feet above and 480 feet behind ExpressJet Airlines Flight 6075, the NTSB told Bloomberg News.

Then on Aug. 8, 2011, Republic Airways Holdings Inc.’s Chautauqua Airlines Flight 5021 passed 125 feet above and 350 feet in front of Trans States Airlines Inc. Flight 3367, Bloomberg News reported.

LISTEN: WBBM Newsradio’s David Roe reports

Air Traffic Controllers are supposed to monitor flights going through the area to prevent near-collisions. A controller involved in one of the near mishaps told investigators he hadn’t been trained to avoid such problems, Bloomberg reported.

The NTSB opened its public files on the cases Monday, Bloomberg reported.

In four years, the New York Times reported, there have been about three incidents a day in which a plane or a vehicle gets on an active runway by mistake.