Chicago Injury Blog

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.

On January 27, 2006, the Safety Board issued an urgent
Safety Recommendation to the Federal Aviation Administration
(FAA) to prohibit airlines from using credit for the use of
thrust reversers when calculating stopping distances. In
today's report, this recommendation was classified "Closed-
Unacceptable Action/Superceded" by 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 new recommendations to the FAA contained in
the final report include:

* 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.