Soft Ground Arrestor Systems

Aircraft can and do overrun the ends of runways, sometimes with disastrous consequences. In order to minimize the hazards of overruns the Federal Aviation Administration (FAA) requires a safety area 1000 feet in length beyond the end of the runway. Although this safety area is now an FAA standard, many runways were constructed prior to its adoption. For those locations that do not have the space for full safety area, soft ground arrestors provide an engineered solution to restore a margin of safety. "Soft ground," means any material that will deform readily and reliably under the weight of an aircraft tire. As the tires crush the material, the drag forces decelerate the aircraft. The FAA research program began with the development of a mathematical model of the wheel/ground interface. This model accurately predicts aircraft gear loads, deceleration, and stopping distance within the arrestor bed. A series of field tests in 1991 validated the model. In 1993, a full-scale arrestor bed (680’ long by 48’ wide by 18" deep), constructed with phenolic foam, safely stopped a Boeing 727 aircraft, traveling at 50 knots, 420 feet into the bed. The aircraft was extracted, the bed repaired, and a second demonstration was conducted. The Boeing 727 traveling at 60 knots was safely stopped 540 feet into the bed. Aircraft rescue and firefighting vehicles and personnel maneuvered on the bed without difficulty.

In September 1994, the FAA and Engineered Systems Co. (ESCO) entered into a Cooperative Research and Development Agreement (CRDA) to test new materials and methods related to the practical aspects of soft ground arrestors. By November 1994, an arrestor bed of cast-in-place cellular concrete was constructed and tested at the FAA Technical Center. An instrumented Boeing 727 aircraft (permanently grounded) entered the bed at 35 knots and exited the bed at 15 knots. The energy absorbing quality of the material was excellent but uniformity of strength was unacceptable.

ESCO established a laboratory to produce a cellular concrete material with uniform strength. Lab tests indicated that uniform compressive strengths (± 5 PSI) could be achieved. On June 26, 1995, a second test bed comprised of pre-cast cellular concrete was tested at the FAA Technical Center. The nose gear of the instrumented Boeing 727 taxied through the test bed at 35 knots. Nose gear rut depth and drag shear loads indicated a product with very uniform strength.

A larger test bed of cellular cement (40 feet-wide by 325 feet-long and tapered to a depth of 24") was constructed and tested in May 1996 at the Technical Center. The instrumented B-727 entered the bed at 55 knots weighing 132,000 pounds. The aircraft decelerated evenly and came to a stop in 278 feet. Math modeling predicted a stop at 260 feet into the bed. Approximately 100 feet into the cellular cement bed the nose wheel separated from the aircraft. The drag and vertical loads on the gear did not appear high enough to cause this action. Post-test investigation of the cause for this separation revealed evidence of fatigue and corrosion on the nose gear support members.

Under a separate partnership the FAA and the Port Authority of NY&NJ, initiated a design for the prototype arrestor bed for runway 4R at JFK International Airport. The 400 feet-long by 150 feet-wide arrestor bed was completed in November 1996. Arrestor beds for runways 13 and 22 at New York’s LaGuardia are scheduled for completion in 1999/00.

The Office of Airport Safety and Standards (AAS-1) issued Advisory Circular 150/5220-22
Engineered Materials Arresting Systems (EMAS) for Aircraft Overruns on 8/21/98.

Link for Advisory Circular (pdf.)

http://www2.faa.gov/arp/pdf/5220-22.pdf