The National Transportation Safety Board (NTSB) on Oct. 2 ruled that the
pilots' failure to use thrust reversers "in a timely manner" was the primary
cause of the Dec. 8, 2005 runway excursion at Chicago's Midway International
The Safety Board said the accident involving Southwest Boeing 737-74H
(N471WN) occurred because the pilots' lack of familiarity with the airplane's
autobrake system distracted them from using the thrust reverser properly during
the challenging landing in a snow storm.
The jetliner traveled 500 feet past the end Runway 31 Center (31C)
through a blast fence and airport perimeter fence, coming to rest on a road
where it hit a car, killing a six-year-old boy who was riding in a car.
Southwest Flight 1248 was inbound from Baltimore, Md.
http://www.nyu.edu/classes/copyXediting/STABBREV.htmlThe crash was the first in
Southwest's 36 years in operation.
The Safety Board said the pilots received mixed braking action reports
for the landing runway. The flight crew used an on-board laptop performance
computer (OPC) 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, the 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 pilots were not aware that the stopping margins computed by the
SWA OPC incorporated the use of thrust reversers for their model aircraft, 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
Contributing to the accident was Southwest Airlines' failure to provide
its pilots with "clear and consistent" guidance and training regarding use of
Also contributing to the fatal accident was the failure to divert to
another airport given the reports that included poor braking action and a
tailwind component greater than five knots.
"The crew knew they were flying on the edge," said NTSB member Deborah
Hersman. "The problem was that they didn't know where the edge was."
Contributing to the severity of the accident was the absence of an
engineering materials arresting system that was needed because of the limited
A Southwest spokesman said the air carrier has implemented fixes to
prevent similar errors.
The NTSB previously advised the Federal Aviation Administration (FAA) to
prohibit airlines from factoring in the use of thrust reversers when calculating
stopping distances. A new safety recommendation 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.
The Safety Board also recommended that all Part 121 and 135 operators be
required 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.