A safety bed: Aircraft overshooting the runway isn’t uncommon but as the Calicut airport accident shows it can have devastating consequences sometimes. To prevent such runway excursions, some of the world’s major airports have a safety mechanism called arrestor beds to slow down or halt a plane if it overshoots the runway. Such arrestors are especially important for airports that cannot afford to have a long safety area beyond the runway either due to lack of space or due to the nature of the airport (table tops for instance).
The idea: The basic idea behind arrestors is that the “soft ground” that they create deforms easily under the weight of the aircraft that has overshot the runway. As the aircraft’s tires crush the material it is made of, the drag slows it down. Aviation regulators have worked with the industry, have come up with engineered solutions for the design of these arrestors as well as the material that goes into them. Mathematical models have helped predict aircraft stopping distances which have been further validated by full-scale aircraft testing.
A tabletop runway
The system: The Engineered Material Arresting System (EMAS) approved by the US Federal Aviation Administration (FAA) is one of the most common safety mechanisms in use around the world. It was an aircraft overrun in New York in 1984 that was the catalyst in the development of EMAS. A program initiated by the FAA in 1989 led to experiments on various soft-ground materials like phenolic foam and cellular cement, as well as designs of the safety beds. Beginning in 1994, a prototype arrestor bed built with precast cellular cement blocks was tested at the JFK airport in New York and the first one installed in 1996. The FAA issued the first broad specifications for EMAS design, installation and maintenance in 1998. Since then, over 100 airports around the world have installed it to prevent runway overruns. A standard EMAS can stop an aircraft from overrunning the runway at approximately 80 miles per hour.
The makers: The FAA defines ‘engineered materials’ as ‘high energy absorbing materials of selected strength which will reliably and predictably crush under the weight of an aircraft’. The actual material, however, varies depending on the manufacturer. For instance, while the US company Zodiac Arresting Systems uses blocks of lightweight, crushable cellular concrete material, the Swedish company Runway Safe AB’s EMAS system has a foamed silica bed made from recycled glass.
EMAS have successfully prevented aircraft from accidents on tabletop runways
The worth: The FAA lists at least 15 incidents in the US where EMAS systems have safely stopped overrunning aircraft, carrying 406 crew and passengers, aboard those flights. One of the first successes of the EMAS came in May 1999 when a Saab 340 commuter aircraft with 30 people on board overran the runway at JFK Airport in New York. In December 2018, the system halted a Boeing 737 with 117 on board that overran the runway at Bob Hope Airport in Burbank, California.
In India: After the Mangalore crash in May 2010, which killed 159 people, a court of inquiry report said table-top runways (like in Calicut and Mangalore) should have arrestor platforms, such as the EMAS, at either end of the runway so that planes come to a halt when the wheels sink on it when the plane rolls off the runway. However, airports have cited the high operational and maintenance cost of the system to not install it in India. A 2018 newspaper report quotes the then Calicut airport director saying: “The EMAS technology was unsuitable for the Calicut airport. How can we bear the cost of Rs 100 crore for an imported technology”. Additionally, once an EMAS has had an aircraft impact, it needs to be replaced as it cannot be repaired, which means another bill of Rs 100 crore or more. The Calicut airport, which is located on a hill with limited space at the end of the runway, too doesn’t have the system and that had prompted several international airlines to stop flying bigger aircraft there due to safety issues.