Ninety percent of airplanes that run off the end of runways are traveling at less than 60 knots when they exit, according to FAA data. Most of these airplanes came to a stop within 1,000 feet of the end.
Although most modern airport designs include a 1,000-foot runway safety area (RSA) for overrun protection, old airport design standards allowed obstacles, such as bodies of water, highways, railroads, populated areas, or even a severe terrain gradient, to be located at the runway end. Because of this, many airports are not able to qualify for the full standard RSA.
Hence, the need for a little help. One solution comes in the form of an engineered materials arresting system (Emas) to provide the safety edge needed to prevent an overrun from becoming a tragedy. Emas is made of high-energy absorbing materials, and is similar in concept to the runaway-truck exit ramps made of sand and gravel that adjoin some steep highway gradients. The system is normally placed in the RSA and varies in size and height based on site-specific requirements.
And Emas works. A 400-foot-long Emas can stop a DC-9 or Gulfstream G550 within the confines of the system, even if the aircraft leaves the runway at 75 knots. What does make some communities catch their breath, however, is the price tag. A typical Emas often costs north of $5 million.