CHICAGO – Federal transportation investigators released a preliminary report Monday about two near midair collisions at Chicago's O'Hare International Airport that raises questions about air-traffic control at one of the world's busiest airports.

The report released by the National Transportation Safety Board doesn't draw conclusions or assess blame for the incidents, which involved landing and departing planes coming within several hundred feet of each other. But it highlights concerns about the configuration of a control tower and two intersecting runways.

A final report isn't expected for several months.