Carroll McCormick looks at a safety feature with an outstanding record.
The Bombardier CL 600 ploughed to a stop in a cloud of cement dust less than 350 feet (106.7 m) from the edge of the 270ft (82.3m) high embankment. It had been saved from certain destruction and loss of its 34 passengers and crew by an Engineered Materials Arresting System (EMAS) designed to safely decelerate aircraft after rejected take-offs and runway overruns.
EMASMAX is made by the New Jersey-based Zodiac Aerospace Engineered Arresting Systems Corporation (ESCO-Zodiac Aerospace). An EMAS is composed of lightweight crushable concrete that: “predictably and reliably crushes under the weight of an aircraft, providing deceleration and a safe stop,” according to ESCO-Zodiac Aerospace.
This incident occurred on January 19, 2010, at the Yeager Airport in Charleston, West Virginia. Pilots rejected take-off on runway 23, braked and overshot the runway. The nose wheel travelled 128ft (39m) into the 405ft (123.4m) long EMAS before stopping. Had this incident occurred just four years before, the aircraft would have skidded across the 120ft (36.6m) Runway Safety Area (RSA) and 50ft (15.2m) of grass that existed at the time and straight down the embankment.
An aerial view shows a hill with its top neatly sliced off to make way for the 767-acre (310.6 hectare) airport and its 6,300ft (1,920.2m) Runway 5/23 and 4,751ft (1,447.8m) runway 15/33. The 120ft (36.6m) RSA for Runway 23 fell well short of the Federal Aviation Administration (FAA) requirement for RSAs established in the FAA Advisory Circular AC 150/5300-13, Airport Design. RSAs for commercial airports must extend 1,000ft (304.8m) beyond the runway ends.
Alternatively, however, the FAA will accept a shorter arrestor bed, or EMAS, which safely slows and stops aircraft in less than 1,000ft (304.8m). “EMAS is thus deployed, on the basis that it can provide a level of safety that is generally equivalent to a standard RSA. [This] may be financially [preferable] to building out an RSA to 1,000ft (304.8m) particularly if constrained by difficult topographic features, sensitive environmental surroundings or man-made structures,” explains David Heald, regional director, ESCO-Zodiac Aerospace.
On November 30, 2005, the United States Congress mandated that all Part 139 Certificated Airports in the United States must bring their RSAs in line with FAA requirements by 2015. After the FAA did a RSA Determination at Yeager Airport in 2000 and identified the need for overrun protection, the airport decided to install an EMAS on the runway 23 departure end.
This project, which began in May, 2005, was unusually complex and time-consuming, because contractors first had to extend the hill beyond the runway end before constructing the EMAS. “Contractors moved more than one million cubic yards (765,000m3) of material to create the 270ft (82.3m) high [hill extension] for the EMAS to sit on,” says Atkinson. The earth work cost US$10 million and the EMAS $6 million, 85% of which the FAA provided.
Each EMAS is custom designed for each airport. “The depth of the EMAS gradually increases as the aircraft travels into the arrestor bed, providing increasing deceleration when required by heavier or faster [moving] aircraft. Aircraft run out distance will be determined by the aircraft size, weight, speed and bed configuration,” according to ESCO-Zodiac Aerospace.
The design aircraft for the Yeager Airport was the ERJ-145 at 80% maximum landing weight. ESCO-Zodiac Aerospace designed the EMAS to achieve 70 knots deceleration performance, that is, stop an aircraft overrunning the runway end at 70kt. ESCO-Zodiac Aerospace also evaluated the CRJ-200, A319, and Dash 8-300, which achieved greater than 70kt predicted performance.
The EMAS at Yeager Airport is 405ft (123.4m) long and 170ft (51.8m) wide, with a 50-ft (15.2m) setback from the runway end. The additional width is for stepped sides that allow access for fire fighting and rescue vehicles and passengers egress. The first 200ft (61m) of the EMAS has a –2% slope, the next 100 feet has a –3% slope and the rest has a slope of –5%. RSA standards allow for negative breaks through runway safety areas, up to -5% being the maximum. Negative slopes can significantly reduce fill (earthworks) when trying to establish an RSA. ESCO-Zodiac Aerospace completed the EMAS in October 2007.
ESCO-Zodiac Aerospace describes a typical install procedure once it has prepared the site: “Blocks that are factory finished with a jet blast-resistant coating are placed using standard forklifts, and then pushed tightly against the neighbouring blocks in the bed. They are then adhered to the underlying pavement using hot asphaltic cement. The block joints are then sealed with tape materials that prevent moisture ingestion.”
According to a preliminary flight data recorder analysis, the Bombardier was travelling 50kt when it entered the EMAS at 4:30 PM. Photographs show the nose wheel completely buried in the EMAS material, but with the belly clear of the EMAS. A shot from the rear show grey, mud-like furrows made by the landing gear.
Airport maintenance crews, assisted by Aircraft Rescue Fire Fighting personnel from the WV Air National Guard 130th Airlift Wing, removed the aircraft, with directions from its owner, PSA Airlines. The airport returned the runway to service at 10:00 PM the same day.
Repairing and returning an EMAS to service usually takes only a few days; for example, after a Saab 340 overrun at the John F Kennedy International airport in 1999, repairs took only 12 working days to complete. Low temperatures, however, delayed repairs to the Yeager Airport EMAS. “We experienced a cold winter and the night time temperatures needed to be above 32° Fahrenheit (0° Centigrade) for the adhesive to properly be applied to the EMAS blocks. But once the temperatures were right for the installation it took three nights of work to repair the EMAS. There was a total of six weeks from the date of the accident until the EMAS was repaired,” Atkinson explains.
“Thirty-one passengers and three crew members are alive today who would not have been, but for the EMAS installation,” Atkinson adds. “Knowing that I was part of the decision-making process for proceeding with the installation, will be the proudest achievement that I will ever have in my career.”
Increasing the Safety Margin
There are currently 55 Engineered Materials Arresting Systems (EMAS), manufactured by New Jersey-based Zodiac Aerospace Engineered Arresting Systems Corporation (ESCO-Zodiac Aerospace) installed in 36 airports in the United States. Madrid’s Barajas International Airport and the Jiuzhai-Huanglong Airport in the Peoples Republic of China each had two systems installed in 2006. ESCO-Zodiac Aerospace is currently installing a 56th EMAS at the Songshan Airport in Taipei City, which will allow the airport to improve safety without having to lengthen its Runway Safety Area (RSA) which would be a difficult and expensive proposition.
Installed off runway ends, EMAS are pads made of pre-cast blocks of lightweight, crushable concrete that entrap and slow down aircraft. They are typically, but not always, about 300-500 feet (91-152m) long and a few feet wider than the runway.
The first EMAS were installed in 1996 at the John F Kennedy International Airport, on runways 4R and 22L. They have stopped three aircraft so far: a SAAB 340 overrun in May, 1999, an MD-11 freighter overrun in May, 2003 and a Boeing 747 freighter overrun in January, 2005. The most recent of the four other overruns EMAS has stopped was a Gulfstream G-IV at Teterboro Airport in October 2010.
The FAA, which assisted ESCO-Zodiac Aerospace in the development of the technology through a Cooperative Research and Development Programme, already accepts EMAS as an shorter alternative to the 1000-ft (304.8m) RSA rule it wants all Part 139 Certificated Airports airports to be in compliance with by 2015.
In April 2008 the Australian Civil Aviation Safety Authority issued a revised Part 139 Aerodrome Standard permitting airports to install an “Engineered Solution” – a reference to EMAS without explicitly referring to the ESCO-Zodiac Aerospace EMASMAX product.
On October 2010, the UK Civil Aviation Authority issued a policy on EMAS with four parts: (1) “permit the installation of EMAS at UK licensed aerodromes as an alternative where a 240m [787.7ft] RESA cannot be achieved”; (2) “accept the FAA performance specification and guidance material as suitable for use in EMAS design in the UK …”; (3) “permit EMAS to be located within the runway strip or RESA as determined by the design assessment” and (4) “permit an increase in runway declared distances that can be achieved from the installation of EMAS …”
According to ESCO-Zodiac Aerospace, Transport Canada, France’s DGAC and the International Civil Aviation Organisation are presently preparing new policies regarding safety areas and arrestor beds.