HISTORY OF FLIGHT On July 8, 2005, about 0915 central daylight time, a Boeing 737-7H4, N494WN, operated as Southwest Airlines flight 1492 to Tampa, Florida, piloted by an airline transport pilot rated captain and copilot, sustained substantial damage when the airplane impacted a food service truck during the flight's pushback at gate B14 at Chicago Midway International Airport (MDW), Chicago, Illinois. The food service truck tipped on its side after the impact. The 14 Code of Federal Regulations Part 121 scheduled domestic passenger flight was operating on an IFR flight plan. Visual meteorological conditions prevailed at the time of the incident. The 2 flight crewmembers, 3 flight attendants, and 105 passengers were uninjured. The food service truck driver was uninjured. The flight was originating at the time of the accident and was destined for the Tampa International Airport (TPA), near Tampa, Florida. The operator's accident report, in part, stated: Note: MDW has an airport specific regulation that requires the provisioning trucks to be marshaled back from the aircraft. The trucks are not allowed to back up without a marshaler in place to assist. Due to congestion on the ramp it is common for an additional provisioning truck to park behind the aircraft while that driver assists the truck working the flight to back out. Inbound Flight #1745 from RDU arrived and pulled into gate B-14 at MDW. The process of turning the aircraft to depart as Flight #1492 to TPA was normal until pushback. As part of the aircraft turn, the flight was provisioned with drinks/ice/peanuts/etc. An additional provisioning truck parked behind the aircraft so that driver could assist the driver of the provisioning truck working the flight at the rear right side door. The process to finalize the turn was complete except for the provisioning truck. The Captain was informed by the pushback driver of the "provo truck" at the rear galley and told the driver to push at his discretion. The truck servicing the flight completed its service and was marshaled back from the aircraft and departed. The pushback driver, unaware of the second truck behind the aircraft, began to push the aircraft out. During pushback, as the flight crew initiated the #2 engine start and approximately 15 to 25 feet from the jetway, the APU stopped running. The engine start was terminated immediately. The flight crew stated that "Shortly thereafter the push sequence was stopped. We did not feel any jolts or unusual aircraft movement." The pushback driver stated that he experienced "difficulty with going forward" and stopped the push. During the push the area of the aircraft APU door impacted the right side of the parked provisioning truck and pushed it over onto its side. The truck driver had just entered the cab and was inside the truck when the event took place. He suffered no injuries. The pushback driver stated that he "did not see anyone telling me to stop pushing that my zone was not clear." Southwest Airlines has a procedure in place that requires wing walkers during pushback. The wing walker took his position at the taxiway to walk out the flight and was aware of the truck behind the aircraft. He stated that "The next thing I saw was the plane at B-14 being pushed back ..." Additionally he stated that "I put up the stop signal and yelled stop but the plane kept on being pushed." According to the wing walker the "go-ahead and push hand signal was never given." The aircraft was positioned back at the jetway and the passengers were deplaned. There were no injuries. All checklists were run and the aircraft secured. DAMAGE TO AIRCRAFT The operator's damage description, in part, stated: After surveying the [aircraft], it was evident that the [aircraft] was damaged in three major fields in the fuselage. The damage is located approximately at fuselage BS [body station] 930 to BS 1156, and from stringer 22 [left] to stringer 22 [right]. PERSONNEL INFORMATION Captain: The captain held an airline transport pilot (ATP) certificate with an airplane multiengine land rating. The captain additionally had a rating for commercial privileges in single-engine land airplanes. He was type-rated for a Boeing 737 airplane. His last medical examination was completed on April 4, 2005, and he was issued a first-class medical certificate with no limitations. The operator reported the captain as having accumulated a total flight time of approximately 19,300 hours and approximately 12,000 hours in a Boeing 737 airplane. He flew 180 hours during the last 3 months, 120 hours during the previous 30 days, and 14 hours during the prior 24 hours. First Officer: The first officer (FO) held an ATP certificate with an airplane multiengine land rating. The FO additionally had a rating for commercial privileges in single-engine land airplanes. He was type-rated for a Boeing 737 airplane. His last medical examination was completed on December 15, 2005, and he was issued a second-class medical certificate with no limitations. The operator reported the FO as having a total flight time of approximately 7,900 hours, and approximately 720 hours in the Boeing 737 airplane as second-in-command. He flew 270 hours during the last 3 months, 90 hours during the previous 30 days and 7 hours during the prior 24 hours. AIRCRAFT INFORMATION N494WN a Boeing 737-7H4, serial number 33868, was a pressurized, low-wing, narrow-body transport category airplane. The airplane had an all-metal full-cantilevered wing and tail surfaces, a semi-monocoque fuselage, and a fully retractable landing gear. The two wing mounted CFM International CFM56 turbofan engines each produced 24,000 lbs of thrust. The airplane was configured to accommodate 137 passengers and 8 crew members. The airplane had a maximum gross takeoff weight of 154,500 lbs. According to the operator, the airplane had accumulated 2,181 hours total time in service. The airplane was being maintained under the provisions of a FAA approved continuous airworthiness program. The last inspection was completed on July 4, 2005, and the airplane had accumulated 35.3 hours since the inspection. METEOROLOGICAL INFORMATION At 0853, the recorded weather at MDW was: Wind variable at 3 knots; visibility 10 statute miles; sky condition clear; temperature 24 degrees C; dew point 16 degrees C; altimeter 30.13 inches of mercury. AIRPORT INFORMATION MDW was located approximately 9 miles southwest of Chicago, Illinois, and was owned and operated by the city of Chicago, Illinois. MDW was a certificated airport under 14 CFR Part 139. The East Central U.S. Airport/Facility Directory (A/FD) indicated MDW's field elevation was 620 feet above mean sea level (MSL). The A/FD listed five runways: Runway 13C/31C - 6,522 feet by 150 feet, concrete/grooved; runway 4R/22L - 6,446 feet by 150 feet, asphalt/concrete/grooved; runway 4L/22R - 5,507 feet by 150 feet, asphalt/grooved; runway 13L/31R - 5,141 feet by 150 feet, asphalt/grooved; and runway 13R/31L - 3,859 feet by 60 feet, concrete. MEDICAL AND PATHOLOGICAL INFORMATION The operator reported that post accident testing on the push back crew was negative for the tests performed. TESTS AND RESEARCH The operator's ground operations manuals were reviewed. The manual stated that the pushback driver "is ultimately responsible for ensuring that the aircraft has been secured, all personnel involved in the push are in proper position, and the pushback is conducted in a safe manner." The manual did not list, note, caution, or warn the pushback driver to stop the pushback when the driver's visual contact with the guide agent (wing walker) is not maintained. The manual told the guide agent to "always be in visual range of the pushback driver ... ." The operator was asked if there was a back up aural signal to the visual stop signals. The operator indicated that there was none and "since this event we are testing headset communication systems." When asked where the supervisor was, the operator responded that "the supervisor was within visual range but his attempts to stop the push were not heard or seen." ADDITIONAL INFORMATION The parties to the investigation included the FAA, Southwest Airlines Co., and the Southwest Airline Pilot's Association.