History of Flight
On April 26, 2011, at approximately 1333 central daylight time, a Boeing 737-7Q8, registration N799SW, operated by Southwest Airlines as Flight 1919, exited the left side of the pavement near the departure end of runway 13C after landing at Chicago Midway International Airport (MDW), Chicago, Illinois. The flight was a regularly scheduled passenger flight from Denver International Airport, Denver, Colorado, operating under 14 Code of Federal Regulations Part 121. There were no injuries to the 134 passengers, including 5 lap-held children, or the 5 crewmembers. The airplane sustained minor damage to the left and right engines and the inboard aft flaps.
The flight was routine until nearing the Chicago terminal area. At about 1232, Chicago Approach Control advised of delays and that arrivals would use required navigation performance (RNP) approaches. The crew briefed the area navigation (RNAV) GPS Z approach instead and discussed flight management system setup. At 1238, they performed the descent checklist, setting altimeters, bugs, reference and target airspeeds (129 and 145 knots), and autobrakes to “MAX” per the onboard performance computer (OPC) and Southwest Airlines Flight Operations Manual (FOM). At about 1240, the flight was instructed to hold at the SMARS waypoint due to traffic congestion.
About 1256, the crew received ATIS Oscar (observation time 1251 CDT) with wind 190 degrees at 16 knots, gusts to 23 knots, visibility 6 statute miles in light rain and mist, ceiling 1,400 feet broken, and altimeter 29.40 inches of mercury. The recording stated the ILS for runway 13C was in use.
Following the weather update, the crew performed landing distance calculations using the OPC. Initial input: landing weight 127,000 pounds, wet runway with good braking action, thrust reverse at detent 2. The OPC output for maximum braking (autobrake MAX) showed a positive margin of 690 feet. Minimum or medium braking did not provide a positive margin. A second calculation with 126,000 pounds landing weight and maximum braking gave 720 feet.
At 1314, C90 began accepting RNP-capable aircraft for MDW; the incident flight was third in sequence. At 1319, the crew reported level at 6,000 feet, 210 knots, and received information Oscar. The controller advised the RNAV (RNP) Y 13C approach and to slow to 170 knots. The crew was cleared direct to Joliet waypoint and to intercept the final approach course. There was some confusion about the instructions. At 1326:36, the controller cleared the flight for the RNAV RNP Y approach to runway 13C.
At 1329:26, the crew selected landing gear down and flaps 15. The preceding Southwest crew reported the runway wet with fair braking action. The incident crew overheard this report and made new OPC entries: wet runway, fair braking action, 126,000 pounds, maximum reverse and braking, resulting in 210 feet of margin. The crew attempted flaps 25 but airspeed was too high; they then selected flaps 30 and then 40. The before-landing checklist was not heard on the cockpit voice recorder.
At 1330:44, the crew reported passing JUPIR waypoint. At 1331:37, the captain stated the airplane was approaching minimums, and the first officer noted an altimeter discrepancy. At 1333:05, the airplane touched down on runway 13C at 136 knots airspeed, 143 knots groundspeed, within 500 feet of the displaced threshold, leaving about 5,600 feet of runway.
Flight data recorder (FDR) information shows that upon touchdown, autobrakes indicated “applied” and brake pressures increased. After about 1 second, the autobrake parameter indicated “No Auto Brk” as pilot-commanded brake pressure increased to about 3,000 psi. Crews reported applying maximum manual braking shortly after touchdown due to perceived lack of braking effectiveness. High manual brake pressure disarms the autobrake system.
The speedbrake handle remained at 0 degrees (not armed) throughout final approach, touchdown, and initial rollout. The speedbrake “armed” light was not illuminated. The handle remained down for the first 16 seconds of landing rollout. According to the Southwest FOM, braking effectiveness is reduced by as much as 60% without speedbrake deployment.
FDR and video data indicate spoilers did not deploy until about 17 seconds after touchdown, when the airplane was about 4,600 feet beyond the threshold. Between 15 and 20 seconds after touchdown, the reverse thrust levers were moved, causing spoilers to automatically deploy. However, due to a transient left throttle advance, spoilers initially retracted briefly before deploying fully at about 1333:25. At that time, the airplane had traveled about 4,150 feet from touchdown. About 3 seconds later, thrust reversers indicated deployed, with about 1,259 feet of runway remaining. The airplane slowed to 55 knots with 250 feet of runway remaining. The airplane heading diverged left, and the captain attempted to turn onto the last taxiway but was moving too fast. At 1333:35, a rumbling sound was heard as the airplane left the pavement at about 30 knots. The airplane stopped about 180 feet beyond and left of the runway end in a soft grassy area north of the engineered materials arresting system (EMAS).
Passengers and crew exited via airstairs and were bused to the terminal.
Injuries and Damage
There were no injuries to the 134 passengers or 5 crewmembers. The right engine ingested a taxiway light, damaging the thrust reverser and inlet cowls. Two fan blades of the left engine were bent. Left and right inboard aft flaps were damaged. Damage did not meet the definition of “substantial.”
Personnel Information
The captain, age 50, was hired by Southwest Airlines in January 1993 and upgraded to captain about 3 years later, also serving as a check airman. He reported about 10,500 total hours, with 7,000 hours as pilot-in-command and 7,000 hours in the B737. The first officer, also age 50, was hired in July 2002 and reported about 17,000 total hours, including an estimated 7,000 hours of B737 second-in-command time. Both held valid FAA ATP certificates and first-class medical certificates.
Aircraft Information
The incident airplane, N799SW, a Boeing 737-7Q8, had about 45,577 hours total time. Estimated landing weight was 124,665 pounds. The auto speedbrake control system is designed to automatically deploy spoilers upon landing if the speedbrake handle is armed. The autobrake system disarms if manual brake pressure is applied.
Meteorological Information
Weather at 1328 CDT: wind 220° at 10 knots gusting 17 knots, visibility 1.5 miles in moderate rain and mist, ceiling 1,500 feet broken with cumulonimbus. A thunderstorm moved over the site 5-10 minutes before touchdown. SIGMET and CWSU advisories indicated thunderstorms in the area.
Probable Cause
None stated in the source.