On takeoff and landing, one measure of aviation safety is the usable runway. Addison Airport’s Runway 15/33 is 7,202 feet long, but it has displaced thresholds at both ends that reduce its length in both directions. By adding an Engineered Materials Arresting System (EMAS) to the south end, Runway 15 reclaims 610 feet of useable pavement without increasing the length of the runway.
Displaced thresholds provide an approach path for landing airplanes that is clear of obstacles, such as tall buildings. They also serve as a runway safety area (RSA), should an airplane be unable to stop in the usable distance on takeoff or landing. In the 1980s, the FAA has required 1,000 foot RSAs. If this is unavailable, the FAA determines what portion of the pavement, a “declared distance,” can be used to meet operational requirements, such as accelerate-stop, the distance a jet needs to accelerate to rotation speed, abort its takeoff, and safely stop in the remaining distance.
On Runway 15, the displaced thresholds reduce this distance from 7,202 feet to 6,592 feet. And they reduce the available landing distance from 6,223 feet to just 5,613 feet. EMAS reclaims this distance, effectively making Runway 15 610 feet longer without extending its length. Fully tested its Boeing 727, the FAA deemed a 600-foot EMAS overrun equal to the desired 1,000-foot RSA and found it superior to turf, especially in inclement weather. It also calculated that, at most airports, it costs roughly one-third the amount needed to buy and develop the land needed for a 1,000-foot RSA, which is why it is approved for the Airport Improvement Program, which is providing the federal and state funds that will install EMAS at Addison Airport, once all the final details are worked out this year.