At 0907 on December 1, 2011, a runway incursion and operational error occurred at MDW when Southwest Airlines flight 844 (SWA844), a Boeing 737-700, was cleared to cross runway 31R immediately after Gama Charters flight 17 (GAJ17), a Learjet 45, was cleared for takeoff on the same runway. After landing on runway 31C, the crew of SWA844 was instructed to cross runway 31R and contact ground control. GAJ17 was departing from runway 31R at the time, and conflicted with SWA844 as the B737 crossed the hold-short line for runway 31R at taxiway N. The first officer of SWA844 saw the Learjet departing runway 31R and warned the captain, who was at the controls, to stop. The captain stopped the B737 short of the runway edge. Air traffic control did not take any actions to resolve the conflict between the two aircraft. After the incident, the captain of SWA844 said that the departing Learjet had overflown his aircraft. Recorded FAA data indicated that the closest proximity as the Learjet passed the B737 was 287 feet laterally and 62 feet vertically. Although MDW is equipped with an Airport Surface Detection Equipment – X (ASDE-X) ground movement safety system that included conflict detection and warning capability, the system did not sound an alarm during the incident. The 0851 weather observation for MDW was wind 180 degrees at 4 knots, visibility 10 statute miles, few clouds at 15,000 feet above ground level (AGL), broken clouds at 20,000 feet AGL, broken clouds at 25,000 feet AGL, temperature 1 degree Celsius, dew point minus 4 degrees Celsius, altimeter 30.26 inches of mercury. For further information, see the Air Traffic Control Group Chairman's Factual Report included in the docket for this incident.