Sacrificial Runway Pavers

On December 8, 2005, a Southwest Airlines jet skidded off the end of a snow-covered runway at Chicago’s Midway Airport and onto a road that bordered the

On December 8, 2005, a Southwest Airlines jet skidded off the end of a snow-covered runway at Chicago’s Midway Airport and onto a road that bordered the field, crushing a car and killing a six-year-old boy inside.

With the help of a soft ground arresting system developed and sold exclusively by Logan Township, N.J.-based Engineering Arresting Systems Corp. (ESCO), Midway officials hope to avoid recurrence of such an event. The company’s Engineered Material Arresting System (EMAS) consists of modular, 4- _ 4-ft. low-density, crushable concrete blocks installed at an increasing angle on the runway overrun to decelerate an aircraft in an emergency. Federal Aviation Administration (FAA) Policy Order 5200.9 identifies EMAS as equivalent to a 1,000-ft.-long runway safety area.

When an aircraft is unable to stop on the active runway, it rolls into the EMAS arrestor bed and is decelerated by the loads applied to the aircraft landing gear as the wheels travel through the EMAS. The depth of the EMAS gradually increases as the aircraft travels into the arrestor bed, providing increasing deceleration when required by heavier or faster aircraft.

Although ESCO holds many details regarding its process proprietary, since the EMAS is the only such system approved by the FAA so far, it was revealed that individual panels are prefabricated in the company’s New Jersey plant, near Philadelphia, and shipped to the job site. The exact mix design of the panels is not known, although foam is a major component. To date, the company has installed systems on 25 runways, including the four at Midway (one already completed and three set for completion by the summer 2007) and two at airports outside the United States.

In the early 1990s, the FAA approached ESCO, a 50-year-old company specializing in arresting systems for the military, about developing such a system for commercial use. In 1996, the company unveiled its system and began load and distance testing with the FAA, and installed its first EMAS at New York’s JFK International Airport later that year. Three years later, the installation paid off when a commuter plane landed long and overran the runway at more than 70 knots. The plane stopped safely, protecting those inside, and was extracted within four hours, with the runway reopening immediately. Repairs to the arrestor bed were made in 12 days.

Typically, the arrestor bed runs the full width of the runway and is set back from the end of the runway by about 35 feet, primarily to avoid potential damage from jet blast from planes taking off. A coating is applied to the blocks to protect from jet blast and avoid having to set the arrester bed the standard 75 feet from the runway. Because the arrestor bed is built at an increasing angle, the runway width features stepped sides to provide emergency-vehicle access and passenger egress.

According to a representative from ESCO, the subbase for the bed is 4 to 6 inches of asphalt pavement. Since the distance at the Chicago Midway runways is limited, the total distance of the arresting bed is about 210 feet, although runways handling 747s and larger (such as JFK) would need 400 feet or more. Since Midway is known as a hub for many discount airlines, the most common plane using its runways is a 737.

Every EMAS installation is customized based on several factors, including size of aircraft, level of performance acceptable by the FAA and the airport authorities at a given location, space beyond the runways, and available money. The cost to install one such system ranges from $2 million to $4 million. A typical installation takes four to six weeks just for block placement, not including site preparation time. Although it was considered a smaller job in terms of the number of blocks used, the three-week installation at Midway’s Runway 31 Center was unique since crews could only work four or five hours overnight, so the runway would not need to be shut down. Once the three remaining beds are installed, Midway will have more EMAS beds in place than any other U.S. airport.