Investigators probing a Southwest Airlines accident in Chicago last month want the Federal Aviation Administration to urgently consider changing the way airlines calculate runway stopping distances.
The National Transportation Safety Board said on Friday the FAA should prohibit airlines from including the effect thrust reversers have on slowing an aircraft when calculating stopping distances on wet or icy runways.
On December 8, a Southwest Airlines Boeing 737 landed at Chicago's Midway Airport during a snow storm, skidded off the runway and rolled through two fences before stopping on a road. The plane struck two vehicles, killing a 6-year-old boy in one of them.
The safety board said the plane's pilots had used a computer before landing to calculate the stopping distance, assuming that thrust reversers would be used on touchdown.
Thrust reversers block or redirect powerful airflow blowing out the back of jet engines to create drag, which helps slow the plane on the runway. Brakes are applied separately.
"Flight data recorder information revealed that the thrust reversers were not deployed until 18 seconds after touchdown, at which point there was only about 1,000 feet of usable runway remaining," the NTSB said in a statement.
If the thrust reverser credit had been taken out of the calculation, the computer would have indicated a safe landing on the runway was not possible, the safety board said.
"We believe this recommendation needs the immediate attention of the FAA since we will be experiencing winter weather conditions in many areas of our nation for several more months to come," said NTSB Acting Chairman Mark Rosenker.
FAA spokeswoman Laura Brown said the agency would look at the recommendation and get back to the board as soon as possible.
