Boeing 737-700
Chicago, IL, USA · 2005-12-09·N471WN
What happened
NTSB summary, verbatimThe Safety Board's full report is available at http://www.ntsb.gov/publictn/publictn.htm. The Aircraft Accident Brief number is NTSB/AAR-07/06. On December 8, 2005, about 1914 central standard time, Southwest Airlines (SWA) flight 1248, a Boeing 737-7H4, N471WN, ran off the departure end of runway 31 center (31C) after landing at Chicago Midway Airport (MDW), Chicago, Illinois. The airplane rolled through a blast fence, and airport perimeter fence, and onto an adjacent roadway, where it struck an automobile before coming to a stop. A child in the automobile was killed, one automobile occupant received serious injuries, and three other automobile occupants received minor injuries. Eighteen of the 103 airplane occupants (88 passengers, 3 flight attendants, and 2 pilots) received minor injuries, and the airplane was substantially damaged. The airplane was being operated under the provisions of 14 Code of Federal Regulations (CFR) Part 121 and had departed from Baltimore/Washington International Thurgood Marshall Airport (BWI), Baltimore, Maryland, about 1758 eastern standard time. Instrument meteorological conditions prevailed at the time of the accident flight, which operated on an instrument flight rules flight plan.
Photographs
2the aircraft, and what the investigators foundPhotographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.
Probable cause
the Board's determinationThe pilots' failure to use available reverse thrust in a timely manner to safely slow or stop the airplane after landing, which resulted in a runway overrun. This failure occurred because the pilots' first experience and lack of familiarity with the airplane's autobrake system distracted them from thrust reverser usage during the challenging landing. Contributing to the accident were Southwest Airline's 1) failure to provide its pilots with clear and consistent guidance and training regarding company policies and procedures related to arrival landing distance calculations; 2) programming and design of its onboard performance computer, which did not present inherent assumptions in the program critical to pilot decision making; 3) plan to implement new autobrake procedures without a familiarization period; and 4) failure to include a margin of safety in the arrival assessment to account for operational uncertainties. Also contributing to the accident was the pilots' failure to divert to another airport given reports that included poor braking action and a tailwind component greater than 5 knots. Contributing to the severity of the accident was the absence of an engineering materials arresting system, which was needed because of the limited runway safety area beyond the departure end of runway 31C.
Safety recommendations
9 issuedwhat changed because of this accidentTO THE FEDERAL AVIATION ADMINISTRATION: Immediately prohibit all 14 Code of Federal Regulations Part 121 operators from using the reverse thrust credit in landing performance calculations. (Urgent) (Superseded by A-07-57)
TO THE FEDERAL AVIATION ADMINISTRATION: Immediately require all 14 Code of Federal Regulations Part 121, 135, and 91 subpart K operators to conduct arrival landing distance assessments before every landing based on existing performance data, actual conditions, and incorporating a minimum safety margin of 15 percent. (Urgent) (Supersedes Safety Recommendation A-06-016)
TO THE FEDERAL AVIATION ADMINISTRATION: Require all 14 Code of Federal Regulations Part 121 and 135 operators to ensure that all on board electronic computing devices they use automatically and clearly display critical performance calculation assumptions.
TO THE FEDERAL AVIATION ADMINISTRATION: Require all 14 Code of Federal Regulations Part 121 and 135 operators to provide clear guidance and training to pilots and dispatchers regarding company policy on surface condition and braking action reports and the assumptions affecting landing distance/stopping margin calculations, to include use of airplane ground deceleration devices, wind conditions and limits, air distance, and safety margins.
TO THE FEDERAL AVIATION ADMINISTRATION: Require all 14 Code of Federal Regulations Part 121 and 135 operators of thrust reverser-equipped airplanes to incorporate a procedure requiring the non-flying (monitoring) pilot to check and confirm the thrust reverser status immediately after touchdown on all landings.
TO THE FEDERAL AVIATION ADMINISTRATION: Require all 14 Code of Federal Regulations Part 121, 135, and 91 subpart K operators to accomplish arrival landing distance assessments before every landing based on a standardized methodology involving approved performance data, actual arrival conditions, a means of correlating the airplane’s braking ability with runway surface conditions using the most conservative interpretation available, and including a minimum safety margin of 15 percent.
TO THE FEDERAL AVIATION ADMINISTRATION: Develop and issue formal guidance regarding standards and guidelines for the development, delivery, and interpretation of runway surface condition reports.
TO THE FEDERAL AVIATION ADMINISTRATION: Establish a minimum standard for 14 Code of Federal Regulations Part 121 and 135 operators to use in correlating an airplane’s braking ability to braking action reports and runway contaminant type and depth reports for runway surface conditions worse than bare and dry.
TO THE FEDERAL AVIATION ADMINISTRATION: Demonstrate the technical and operational feasibility of outfitting transport-category airplanes with equipment and procedures required to routinely calculate, record, and convey the airplane braking ability required and/or available to slow or stop the airplane during the landing roll. If feasible, require operators of transport-category airplanes to incorporate use of such equipment and related procedures into their operations. (Safety Recommendation A-07-064 is superseded by Safety Recommendations A-16-023 and A-16-024)
Sequence of events
9 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)- until 13 s before touchdownapproachp.2Glideslope and localizer within 1/2 dot; at 141 ft radio altitude the glideslope deviation reached about 1 dot (fly down) and stayed there until just before touchdown; localizer never exceeded 1/2 dot
- main gear touchdown (19:13:5x local)landingp.2Air/ground transition: airspeed 124 kts, ground speed 131 kts, heading 316 deg, vertical acceleration 1.413 g; wind 5.5 kts from 147.7 deg (tailwind)
- touchdown + 1.25 slanding rollp.2Ground spoilers fully deployed and autobrakes applied as vertical acceleration peaked at 1.74 g; brake pressure rose over 5 s to 2,400 psi (left) and 2,600 psi (right)
- touchdown + 6 slanding rollp.2Peak deceleration -0.26342 g as brake pressure reached the autobrake command; ground speed 113 kts
- touchdown + 10 slanding rollp.2Engine N1 decreased from 32% at touchdown to about 20%, remaining there about 8 s
- touchdown + 12 slanding rollp.2Autobrakes selected off; brake pressure increased to 3,000 psi (manual braking)
- touchdown + 15 to 27 slanding rollp.2First thrust reverser activity at +15 s, fully deployed at +18 s, N1 reached 80% at +27 s as ground speed decreased to 62 kts
- touchdown + 33.8 soverrunp.2Nose gear departed the paved overrun and overrode the blast fence: sharply increased acceleration activity, pitch spiked from -1.9 to 2.6 deg in under a second; ground speed 39.5 kts, reversers still fully deployed, brake pressure 3,000 psi
- touchdown + 41.8 sstoppedp.3Aircraft came to rest 8 s after leaving the paved overrun, nose gear collapsed, heading 336 deg
NTSB analysis
from the final reportThe Safety Board's full report is available at http://www.ntsb.gov/publictn/publictn.htm. The Aircraft Accident Brief number is NTSB/AAR-07/06. On December 8, 2005, about 1914 central standard time, Southwest Airlines (SWA) flight 1248, a Boeing 737-7H4, N471WN, ran off the departure end of runway 31 center (31C) after landing at Chicago Midway Airport (MDW), Chicago, Illinois. The airplane rolled through a blast fence, and airport perimeter fence, and onto an adjacent roadway, where it struck an automobile before coming to a stop. A child in the automobile was killed, one automobile occupant received serious injuries, and three other automobile occupants received minor injuries. Eighteen of the 103 airplane occupants (88 passengers, 3 flight attendants, and 2 pilots) received minor injuries, and the airplane was substantially damaged. The airplane was being operated under the provisions of 14 Code of Federal Regulations (CFR) Part 121 and had departed from Baltimore/Washington International Thurgood Marshall Airport (BWI), Baltimore, Maryland, about 1758 eastern standard time. Instrument meteorological conditions prevailed at the time of the accident flight, which operated on an instrument flight rules flight plan.