The US National Transportation Safety Board has urged the Federal Aviation Administration to "immediately" mandate a 15% safety margin to be added into distance calculations that airline, air taxi and fractional providers use when calculating whether a landing can be safely accomplished on a particular runway.
The action follows the final hearing on the Southwest Airlines Boeing 737-700 runway overrun accident in a night-time snow storm at Chicago's Midway airport in December 2005.
Probable cause for the accident was the pilots' failure to use thrust reversers "in a timely manner", but Investigators found that the distance calculation the pilots made before arrival on Southwest-provided portable laptop computers did not include actual wind conditions and had already taken into account the use of reverse thrust. The pilots had assumed the calculations did not include reverse thrust.
The NTSB is asking that a 15% safety margin be added to the pre-landing calculations, and that the computations be based on "existing performance data and actual conditions".
The request, which applies to airline, air taxi and fractional operators, is an attempt by the NTSB to better account for unknowns in weather conditions and subjective braking action reports given by pilots.
While the FAA plans to pursue a rulemaking for landing distance margins in the future, the agency in the immediate aftermath of the accident published a safety alert asking operators to voluntarily institute the change.
According to the NTSB, a recent FAA survey showed that of the 65 airlines that responded to a questionnaire, 27 had adopted the 15% safety margin in full and 22 had adopted the changes in part.
Source: FlightGlobal.com
