Many older airports squeezed next to dense city neighborhoods, bodies of water or steep drop-offs don't have room to allow the 1,000-foot safety margin at the end of the runway that the federal government considers adequate.

Runway overruns can be extremely dangerous. In June 1999, an American Airlines jetliner slid past the end of the runway in Little Rock, Ark., killing nine passengers and injuring 86. And it was only the remarkable speed of the passengers' evacuation - less than two minutes - that prevented serious injury or death when an Air France Airbus skidded off the runway in Toronto and burst into flames in August.

The Federal Aviation Administration in the 1990s began researching a solution to the problem faced by airports that don't have enough space for their runways: putting down a bed of soft concrete to stop or slow an airplane that overruns a runway.

The agency has found that a certain light, crushable concrete will cause an airplane to decelerate. The soft concrete bed, called EMAS, for engineered material arresting systems, extends about 600 feet from the runway's end.

This technology is in place at the end of 18 runways at 14 airports. It has already prevented dangerous overruns three times since May 1999 at John F. Kennedy International Airport in New York, including a Boeing 747 in January, according to the FAA.

There are plans to install EMAS at four more, according to the FAA's Web site.

But a little-noticed provision in the 2006 transportation spending bill signed by President Bush recently will force airports to deal with the problem sooner than they may have planned.

Sen. Frank Lautenberg, D-N.J., sponsored a measure that will require 284 U.S. airports to have at least 1,000 feet at the end of a runway by 2015. That number is based on an FAA inventory of major commercial airports that don't meet the standard.