EMAS: Making aviation safer
Why EMAS is better than RESA?
Every year, on average,10 planes overrun a runway while taking off or landing. Over the past 30 years, overruns have caused at least 23 deaths and 300 injuries to passengers and crew at U.S. airports.
While Runway End Safety Area (RESA) was mandated at airports, overruns continued to be fatal for passengers and planes. Engineered Materials Arresting System (EMAS) can complement, and in a few cases, can replace RESA.
RESA and EMAS
RESA is the land adjacent to the runway, at both ends, for helping airplanes that overrun the runway to stop. The present FAA (Federal Aviation Administration) requirement for airports is a 1,000 ft long RESA.
EMAS are crushable concrete cells installed at both ends of the runway that stops overrun planes safely.
But RESA has limitations. Just like seat belt wasn’t enough to prevent deaths/injuries in a car crash and airbags were added to improve passenger’s safety, EMAS are airbags of aviation.
What makes EMAS?
The same asphalt that makes up the runway strip is used for building RESA. Asphalt is not a specially designed material to decelerate airplanes.
In contrast, EMAS uses crushable concrete cells and foam to slow the airplane. The concrete cells are glued to the EMAS bed by hot asphalt, and the seams between cells are caulked to seal the top surface.
When an airplane enters the EMAS bed, the tyres sink as it rolls onto the EMAS bed. The EMAS bed is made up of high absorbing materials that absorb the speed. Think of the EMAS bed as a sponge that absorbs energy.
EMAS takes less area than the RESA. The minimum recommended EMAS length is 180m, whereas the minimum required length for RESA is 305m. Further, an FAA compliant EMAS installation provides equivalent safety to a full-length RESA.
EMAS can be installed at airports where the topography doesn’t permit a full-length RESA. And in ecologically sensitive locations, where airport expansion can cause significant damage to the environment, EMAS can be installed as it requires smaller space.
EMAS more effective than RESA
EMAS are more effective in stopping airplanes than RESA and have been recommended as an alternative to RESA where a full-length RESA can’t stop a high-speed airplane.
Before EMAS, runway excursions had injured several passengers, and in a few cases, runway excursions even caused death.
Airplanes land and take off at high speeds, and even the best pilots can make mistakes, so EMAS accommodates the room for human errors. Further, circumstances like hydroplaning, brake failure, etc. can contribute to a runway excursion.
FAA was aware that it had to look beyond RESA for stopping high-speed planes safely when planes overrun a runway.
In February 1984, a DC-10 overshot the runway at JFK, New York, and the incident galvanised FAA to find an alternative to RESA.
The DC-10 touched down on the runway further than the normal touchdown point at a higher than normal approach speed. The approach speed was 205 knots, 50–45 knots above the normal speed.
FAA developing EMAS
The FAA joined hands with the U.S airforce to develop a soft land arrester system. The earlier experiment used phenolic foam, concrete cells and Boeing 727. The results were encouraging, and it shaped the EMAS development.
While the ICAO hasn’t issued any specification for EMAS, FAA has. EMAS is designed on the following assumptions:
- “Most installations to date have used a maximum 70 knots bed-entry speed.
- an aircraft is still attempting to stop as the runway is exited
- reverse thrust / reverse pitch is not being used as the runway is exited
- the surface area leading to the EMAS bed has poor braking characteristics
- there is minimal or no structural damage to the landing gear
- there is no aircraft braking or use of reverse thrust / reverse pitch once an aircraft enters the EMAS.”
An FAA-approved computer model analyses the wheel and concrete cell interaction before EMAS is laid at the airport. The model considers airplane weight, speed and other factors for designing a suitable EMAS bed.
EMAS has made aviation safer than before, and RESA limitations make EMAS a better choice for stopping planes that have overshot the runway safely.
Click here to see successful arrests using EMAS