NTSB Wants Airlines to Improve Stopping Distance Assessments

The U.S. National Transportation Safety Board (NTSB) is recommending to the FAA that Part 121, 135, and 91 subpart K operators be required  to conduct arrival landing distance assessments before every landing based on actual conditions existing at the time, and to incorporate a minimum safety margin of 15 percent.

The NTSB's "urgent" recommendation (A-07-57) follows the release of its final report on the Southwest Airlines' fatal runway overrun at Chicago Midway in December 2005.

In its report, the Board determined that the probable cause of the accident was the pilot's failure to use available reverse thrust, which it attributed to the "pilots' first experience and lack of familiarity with the airplane's autobrake system, which distracted them from thrust reverser usage during the challenging landing."

The Safety Board's investigation revealed that as the crew neared their destination, they used a Southwest-provided on-board laptop performance computer (OPC) to calculate their expected landing distance.  Since they received mixed braking action reports for the landing runway, they entered multiple scenarios including wind speed and direction, airplane gross weight at touchdown, and reported runway braking action. The OPC calculations indicated they could stop before the end of the runway with either fair or poor braking action, leading them to decide that they could safely land.

The pilots were not aware, however, that the 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, they weren't aware that the stopping margins computed by the OPC were based on the use of thrust reversers for the B-737-700 they were flying.

The Board concluded that had the pilots known this information, the pilots might have elected to divert to another airport.

Contributing to the accident, according to the Board, 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; implementation of new autobrake procedures without a familiarization period; and failure to include a margin of safety in the arrival assessment to account for operational uncertainties.

Additional new recommendations to the FAA contained in the final report include:

• Requiring all Part 121 and 135 operators to ensure that all on board electronic devices they use automatically and clearly display critical performance calculation assumptions.

• Requiring 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.

• Establishing 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.

• Developing and issuing formal guidance regarding standards and guidelines for the development, delivery, and interpretations of runway surface condition reports.

A synopsis of the Board's report, including the probable cause and recommendations, is available on the NTSB's website, www.ntsb.gov, under "Board Meetings." The Board's full report will be available on its Website in several weeks.  10-09-2007.

Click here to become a registered Flt Tech Online subscriber and receive headlines delivered to your e-mail each week

Click here to go back to the headlines