WASHINGTON ( CNN ) -- A Learjet departing Chicago 's Midway airport last month came within about two plane-lengths of striking a taxiing Southwest Airlines Boeing 737 that had been cleared to cross the same runway , according to a preliminary report by the National Transportation Safety Board . The airborne Learjet passed 62 feet above -- and within 287 feet laterally -- of the Southwest passenger plane , according to the NTSB , which is investigating the incident . According to the NTSB , the co-pilot of the taxiing Southwest jet saw the Learjet and shouted `` Stop '' to the plane 's captain , who brought the plane to a halt near the edge of the runway . Air traffic control audio tapes , released by LiveATC.net , a website for aviation enthusiasts , captured conversations between the Southwest crew and controllers in the minutes immediately afterward . `` OK ... You just cleared us onto a runway ( where ) there was a plane taking off , '' one of the pilots said to controllers . `` What technology clears us on the runway when a plane was taking off ? '' a pilot added , sounding exasperated . The Southwest crew then radioed another controller . `` We had to hit our brakes and the thing went right over our head , '' the crew said . According to the NTSB 's preliminary report , the incident occurred about 9 a.m. CT on December 1 , when a Learjet 45 was instructed to line up and wait on runway 31 right . Southwest Flight 844 had landed on a parallel runway -- 31 center . As the Southwest plane was decelerating on the center runway , the Learjet was cleared for takeoff on the right . When an air traffic controller gave the Southwest plane clearance to turn right on a taxiway that crossed the right runway , the two planes came into potential conflict . Kevin Hiatt , a former 737 pilot now with the non-profit Flight Safety Foundation , said it is still unclear what caused the mishap , but credited the Southwest co-pilot for averting potential disaster . `` Fortunately , the first officer was 'heads up ' in that cockpit and basically saw the Learjet coming , and told the captain to stop , which he did just prior to entering into the active runway , '' Hiatt said . `` If that Learjet had had any kind of a problem and not lifted off when it did -- they prevented a very serious accident , '' Hiatt said . Hiatt said Midway airport is one of 35 airports equipped with an surface movement detection system known as ASDE-X to detect potential runway conflicts . `` The investigation will probably look into whether ASDE-X was in operation at the time or ( whether ) the controllers using it or not using it , '' he said . The NTSB said the report is preliminary , and no blame has been assigned in the matter . No one was injured in the event . CNN 's Mary Snow contributed to this report .
The Southwest crew tells the tower , `` The thing went right over our head '' The incident happened on December 1 . A preliminary NTSB report does not assign blame .