Pilot error: Southwest runway overrun at Midway in 2005

The National Transportation Board (NTSB) recently concluded its investigation of the Southwest Airlines runway overrun at Chicago Midway Airport in 2005. One person on the ground was killed, and 22 people were injured. The NTSB report cites pilot error as the primary cause of the accident.

The NTSB report specifies "the pilot's failure to use available reverse thrust in a timely manner to safely slow or stop the airplane after landing" as the probable cause. The NTSB goes on to say, "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."

Here is a summary of the NTSB findings, quoted from a press release about the agency's report:

On December 8, 2005, Southwest Airlines (SWA) flight 1248, a Boeing 737-7H4, (N471WN), ran off the departure end of runway 31 center (31C) after landing in a snow storm at Chicago Midway International Airport (MDW), Chicago, Illinois. The airplane rolled through a blast fence, an airport perimeter fence, and onto an adjacent roadway, where it struck an automobile before coming to a stop. One occupant in the automobile was killed, one received serious injuries, and three others received minor injuries. Eighteen of the 103 persons on board the airplane received minor injuries and the airplane was substantially damaged.

As outlined in the Board's report, the investigation revealed that as the crew neared their destination the pilots received mixed braking action reports for the landing runway. The flight crew used an on-board laptop performance computer (OPC) provided in the cockpit of SWA's airplanes to calculate expected landing distance. They entered multiple scenarios including wind speed and direction, airplane gross weight at touchdown and reported runway braking action. Observing OPC indications that they would stop before the end of the runway with either fair or poor braking action, they decided that they could safely land at MDW.

However, as stated in the report, the accident pilots were not aware that stopping margins displayed by the OPC for poor runway conditions were in some cases based on a lower tailwind component than that which was presented. Also, the accident pilots were not aware that the stopping margins computed by the SWA OPC incorporated the use of thrust reversers for their model aircraft, the 737-700, which resulted in more favorable stopping margins. Therefore, the Safety Board concluded in the report that had the pilots known this information, the pilots might have elected to divert to another airport.

Contributing to the accident were Southwest Airlines' failure to provide its pilots with clear and consistent guidance and training regarding company policies and procedures related to arrival landing distance calculations; programming and design of its on board performance computer, which did not present critical assumption information despite inconsistent tailwind and reverse thrust assessment methods; plan to implement new autobrake procedures without a familiarization period; and failure to include a margin of safety in the arrival assessment to account for operational uncertainties.

Contributing to the accident was the pilot's failure to divert to another airport given the reports that included poor braking action and a tailwind component greater than 5 knots.

Also, contributing to the severity of the accident was the absence of an engineering materials arresting system (EMAS), which was needed because of the limited runway safety area beyond the departure end of runway 31C.

Click here to view the NTSB animation of the landing runway overrun accident at Midway Airport, Chicago, Illinois on December 8, 2005.

One outcome of the investigation of this accident is that the NTSB has issued "a new urgent safety recommendation that calls on the FAA to immediately require 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." Additional recommendations to the FAA in the NTSB report include the following:

• Require all Part 121 and 135 operators to ensure that all on board electronic devices they use automatically and clearly display critical performance calculation assumptions.
• Require all 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.
• Establish a minimum standard for 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.
• Develop and issue formal guidance regarding standards and guidelines for the development, delivery, and interpretations of runway surface condition reports.

The Synopsis Report on the Southwest Airlines Flight 1248 accident is available on the NTSB website now. The final report will be posted there in several weeks.