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San Francisco Airport uses tech to meet runway safety standards

In order to meet a federal directive, the airport will close two runways this summer to install a special concrete material that will bring runaway aircraft quickly to a stop.

As a departing aircraft lines up on Runway 1 Left at SFO, construction is starting on the Runway Safety Areas. In the background you can see the airport's new control tower, which is scheduled to open in early 2016. Kent German/CNET

For the most part, major airports like San Francisco International avoid closing runways whenever possible. But on May 17, SFO will cut its number of active runways in half just as the summer travel season begins.

The reason isn't the low clouds that often slow air traffic at the Bay Area's largest airport, but rather the last phase of a $214 million project designed to bring SFO's runways up to federal safety standards. Airport officials insist the project will result in only minimal delays, but a looming deadline to complete the work means that the airport has little choice.

Safety first

During the four-month closure, the airport will install new Runway Safety Areas (RSAs) on both ends of Runways 1 Left and 1 Right, which are normally used for domestic departures. Nothing more than bare ground at a runway's threshold, RSAs are designed to give aircraft that overshoot the runway a cushion of space for coming safely to a stop.

The project is the result of legislation passed by Congress in 2005 that requires more than 40 of the country's largest commercial airports to have RSAs by 2015. SFO has already installed the safety zones on its longer pair of runways, 28 Left and 28 Right, which are mainly used for arrivals and long-haul departures to Europe, Asia, and Hawaii.

"Our top criteria is safety first," said Andy Richards, SFO's airport traffic control tower manager. "It's safety first, safety second, and safety third."

A map of of SFO showing runway locations and the new taxiways. The new EMAS materials will be installed in the green areas. San Francisco International Airport

A runway's length and the aircraft using it (the largest airliner to operate here is the Airbus A380) determine the required size for an RSA. At SFO they must be 1,000 long and 500 feet wide, which is a lot of real estate to find at an already-crowded airport.

Looking for elbow room

Indeed, space has always been at a premium at SFO due to its location on San Francisco Bay, but that's especially true for the two runways in question. Not only are 1 Left and 1 Right the airport's two shortest runways (8,646 feet and 7,500 feet respectively), but also they're squashed between the bay and the 101 freeway.

The airport is able to increase each runway's RSA slightly by building new taxiways, but they'll still be short of the 1,000-feet mandate. And because SFO is unable to lengthen the runways beyond the freeway or into the bay, it had to pursue a different solution.

To make up the difference and meet the directive, the airport will install an Engineered Material Arresting System, or EMAS, at the ends of both runways. Similar to a runaway truck ramp at the bottom of a hill, EMAS technology is designed to stop an aircraft quickly without causing significant damage to the landing gear or injuries to passengers and crew.

As an aircraft encounters EMAS material, it sinks into the concrete and comes to a stop. James Martin/CNET

The EMAS being installed in San Francisco consists of a series of pads made of a lightweight porous substance called cellular concrete. It resembles your average airport taxiway on the surface, but a look inside reveals tiny air pockets embedded throughout the material. Think of honeycomb and you'll get the idea, though without the uniform rows of hexagonal cells.

When something as heavy as an airplane passes over the EMAS, its weight compresses the concrete, which causes the plane to sink into it and come to a stop. Walking over it won't cause any harm, but I was able to pick off flecks of a sample of the material with my finger. Emergency vehicles can compress an EMAS, but airport officials said that fire engines and ambulances will still be able to maneuver to provide assistance to an airplane.

In all, 23,000 blocks will go in at the end of each runway. And if the pads are compromised by an accident, the Federal Aviation Administration requires that they be replaced within 40 to 45 days without closing the runways.

The FAA does not mandate a specific formula for an EMAS' material, but the agency has certified only one company, Engineered Arresting Systems Corp., to build it in the United States. Based in Logan Township, NJ, EASC is a division of the French company Zodiac Aerospace.

EMAS technology has successfully stopped aircraft in the United States since it first became available in the late 1990s. In this incident in 2011, it captured a Cessna Citation that had a brake failure after landing in Key West. Key West International Airport

Delays to come

Though the project is already under way, all departing and arriving traffic will need to use 28 Left and 28 Right when the heavy construction begins in May. SFO Public Information Officer Doug Yakel said that after running several scenarios, from closing one runway at a time to shuttering them only part time, the dual closure plan was projected to take the least amount of time and reduce actual capacity by only 15 percent in optimal weather (from a maximum of 100 departures and arrivals an hour to 85).

What's more, Yakel said that the traffic pattern has been used before, including last year when the RSAs were installed on 28 Left and 28 Right. "This is not a new configuration for us -- we actually do this all the time based on wind conditions."

Arriving flights, which are given priority, should not see any delays unless bad weather further impacts operations. Departing flights, however, could see delays between 5 and 15 minutes, especially during the airport's peak period from 10 a.m. to 1 p.m.

A Lufthansa Boeing 747 passes over the RSA at the end of Runway 28 Right just before landing. Kent German/CNET

To help cope with the reduced departure capacity, the airport worked with airlines to develop flight schedules and invested in equipment that will allow for more parallel operations. Because SFO's runways are so close together, simultaneous landings and takeoffs can occur only in good visibility.

Also, the airport will operate a Departures Management System during the closure. Similar to metering lights on a freeway on-ramp, the system will give each flight a specific takeoff time. Yakel said the purpose of the system is to keep aircraft at the gate while they wait, instead of lining up on the taxiways burning fuel and trapping passengers.

"There is a possibility of some departure delays because of this," Yakel said. "Departing aircraft have to wait a bit longer for a queue to take off for their flight."