How do you stop a 174,000-pound Boeing 737 about to skid into the intersection of Airport and Post Roads, without injuring the passengers or destroying the airplane?

Concrete.

That’s right, concrete. But this is no ordinary concrete, as Brian Bennett, project manager for McFarland Johnson, explained yesterday to a clutch of news reporters and cameramen standing at the end of Runway 16 in the heat of the sun.

Behind Bennett, forklifts maneuvered pre-numbered four-foot square blocks of cement into a grid painted on the black asphalt. The blocks vary in thickness, from 6 to 20 inches, and are positioned to create an incline at the end of the runway. But a lot more than the slope will stop an aircraft from overshooting the runway.

An extension of the runway and grassy areas often make up the safety areas at the end of runways. The Federal Aviation Administration (FAA) standard for a safety area is a minimum of 1,000 feet, but in some cases, like those at Green Airport, there’s not enough space for the conventional 1,000-foot roll-off. That’s where the special concrete called an “engineered materials arrestor system” or EMAS, comes in.

When completed, the layout of 2,646 blocks will extend 255 feet and provide the same stopping power of 1,000 feet of open area. As the opposite end of the runway – Runway 34 for approaching aircraft – backs up to the wetlands of Buckeye Brook, it will also get a layer of EMAS. Once completed by December of 2015, aircraft will be able to use the full 6,081-foot length of the runway and comply with FAA safety standards. As the runway is used primarily during the winter months, when there are greater instances of westerly winds, its closing during the summer is not seen as interrupting airport operations.

So how does EMAS concrete stop an airplane?

Bennett didn’t have the specifications, which are most likely proprietary information anyhow, but generally, the concrete is porous light material that is crushed by the weight of the aircraft. As the landing gear of an aircraft sinks into the material, it slows the craft’s forward momentum without causing a nosedive. ESCO-Zodiac Aerospace is the sole provider of EMAS. The cost of each block is nearly $1,500 but, as Bennett explained, should the system be used, individual blocks can be replaced without having to rebuild the entire system.

Work on the 16 end of the runway is costing $8.4 million.

Safety improvements to Runway 16-34, that also included the demolition of Hangar 1 and the construction of the blast fence on Airport Road, designed to deflect the blast of a jet taking off, is one of several major ongoing projects at Green Airport. As part of the plan to extend the airport’s main runway, from 7,166 to 8,700 feet, Winslow Park playing fields are being relocated to the Lakeshore Drive area at the northeast end of the runway. That area was cleared of houses under the airport’s voluntary land acquisition program. Work on the park, which includes softball and soccer fields, will start next week, Rhode Island Airport Corporation (RIAC) spokeswoman Rebecca Pazienza Bromberg said yesterday. Access to the new ball fields will be from an extension of the service road to the airport maintenance garage.

Relocation of Winslow Park will allow for the realignment of Main Avenue, which must take place to extend Runway 5-23 to 8,700 feet. The longer runway is scheduled for a Dec. 6, 2017 debut, according to the timetable of RIAC president and CEO Kelly Fredericks.