Updated 01/10/12 – 9:38 p.m.

CHICAGO (CBS) — The National Transportation Safety Board is investigating a near-collision last month at Midway International Airport, involving a Southwest Airlines jet.

The Southwest flight, a Boeing 737, had just arrived from Minneapolis-St. Paul International Airport on Dec. 1.

A preliminary NTSB report on Tuesday said the pilot was told by an air traffic controller to cross runway 31R on its way to the gate, but another controller had apparently just given a Learjet permission to take off on 31R.

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The NTSB report indicates that the Southwest co-pilot saw the Learjet approach and yelled to the pilot to stop. The 737 halted past the “hold short” line, at the edge of the runway. The Southwest crew told investigators that the Learjet flew directly over it, but NTSB investigators estimate that the Learjet crossed 287 feet overhead and 62 feet in front of the 737.

In a recording of air traffic control communications with the plane, you can hear the Southwest pilot’s frustration.

“What technology clears us on the runway when there’s a plane taking off?” the pilot asks air traffic controllers.

“Contact ground please,” replies a tower controller.

It’s a question the air traffic controllers at Midway did not answer.

No one aboard either plane was hurt. The NTSB indicated in its report that 85 passengers and crew members were aboard the 737.

NTSB investigators have interviewed controllers who were on duty at the time as well as the crews.

“When you look at the size of these planes, anything below three-, four-hundred feet is a very close call,” DePaul University transportation expert Joe Schweiterman told CBS 2’s Dana Kozlov.

He said it appears the mistake came from the control tower; a mistake that could have cost lives.

“No doubt, this requires more vigilance at Midway to make sure we have, you know, the right controllers rested,” Schweiterman said.

Calls to the National Air Traffic Controllers Association, which represents the tower controllers, were not immediately returned.

The FAA referred comment to the NTSB.

Southwest issued a statement in which it said it is “fully cooperating” with the NTSB on the investigation but, because it is an open investigation, said it cannot provide additional comment.

“Safety is our top priority and we will continue to support the NTSB as the investigation process unfolds,” said Southwest spokesperson Brandy King.