EMAS is an acronym
ystem. For once, it's a quite descriptive acronym. The quick expansion: EMAS is a system for safely halting aircraft
which have missed or rolled off their runway
. Not to be confused with EMALS
, whose job is launching
aircraft rather than stopping them.
The United States' FAA has a set of regulations, called Part 139, which prescribes safety rules for airports in the U.S. One of the safety measures it calls for is a 'Runway Safety Area' (RSA) which is a cleared space around active runways. As described by the current regulation, which is around 20 years old, any runway in active use should be in the middle of an RSA which is 500 feet wide (~152 meters). The RSA should extend 1,000 feet (~305 meters) past each end of the runway, to ensure that aircraft which land short or overrun the runway on landing or aborted takeoff have a clear area in which to safely stop.
One problem with this is that many of the U.S.' major (and minor) airports were built before this regulation came into effect, and furthermore are sited in locations where it is impractical to achieve this 1,000 foot distance either due to built-up areas or due to terrain features (such as rivers or dropoffs). The EMAS is a system designed to compensate for the shorter overrun distance by actively stopping (arresting) the aircraft, like the cable-and-barrier systems on CATOBAR and STOBAR aircraft carriers.
The EMAS is simple in design, if a bit more complex in construction. Essentially, it is a paving system - the EMAS area is paved with a special foamed concrete which crushes easily and then is covered over with plastic or paint-based waterproofing. The (tested) theory is that when an airplane overruns the runway and rolls onto an EMAS, the weight of the aircraft will cause it to crush the concrete, and its undercarriage will sink into the soft surface. Once it does so, of course, it will start 'plowing through' the stuff, and the hugely increased resistance of its sunken landing gear will bring it to a stop much more quickly. For an image of a Canadair Regional Jet stopped by EMAS, look here.
As of October 2010 EMAS systems were installed at 51 runway ends at 35 airports in the U.S., according to the FAA. As of that time, seven incidents of EMAS systems halting aircraft have occurred, in all cases with minimal damage to the aircraft or injury to passengers. An FAA manager for airport engineering claims that every aircraft stopped by EMAS has been flown away after inspection and repair. The aircraft saved have ranged in size from a Grumman Gulfstream executive jet (Teterboro airport, NJ, October 2010) to a Boeing 747 (JFK Airport, NY, January 2005).
EMAS is designed, manufactured and installed by Engineered Arresting Systems Corporation (ESCO) of New Jersey, USA.
Iron Noder 2010