posted 30th May
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
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
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.)