On October 2, 2017, at about 0840 CDT, Southwest Airlines flight 681, Boeing B737-700, N930WN, was struck by an unmanned tug while boarding was ongoing at Chicago Midway Airport (KMDW), Chicago, Illinois. There were no injuries to the 84 passengers and crew onboard. The airplane received substantial damage to the lower fuselage skin, frames and stringers over an area about 3 feet by 3 feet. The flight was operating under 14 Code of Federal Regulation Part 121 as a scheduled passenger flight from KMDW to Omaha Airport (KOMA), Omaha, Nebraska. A ramp agent was driving a covered baggage tug with two baggage carts in tow between Gates B22 and B24 when the tug made contact with two staged baggage carts. The ramp agent jumped off the tug as the tug continued to accelerate forward. The now unmanned baggage tug struck additional ground support equipment before striking the fuselage of the accident airplane at Gate B22. The ramp agent stated afterwards that he could not get the tug to stop and thought running the tug into the staged baggage carts would stop or at least slow the tug down. Examination of the baggage tug after the event revealed there was a mechanical failure of the fuel governor which resulted in the runaway. The runaway could have been stopped by either turning the ignition key off or using the manual shut down lever on the front cover. There was no guidance in the Ground Operations Training Manual related to how ramp personnel should handle mechanical failures of ground support equipment.