In most aircraft overruns, an aircraft comes to a stop within 1,000 ft (305 m) of the runway threshold. In response, U.S. airfields are required by FAA to have a 1,000-ft runway safety area in addition to the design runway length in case of aircraft overruns. At airfields where space is limited, airport operators need to consider alternative solutions. One solution is for an airport operator to reduce runway length and therefore limit aircraft types landing at their airport. Conversely a more attractive solution is for an airport to implement an engineered material arrestor system (EMAS). An EMAS is a passive system comprising a cementitious type material. Aircraft deceleration occurs because of drag forces that are incurred by the aircraft landing gear as the aircraft passes through and crushes the arrestor material. Parameters significantly influencing a B727 or B747 aircraft's stopping distance as it traverses an EMAS are presented. The computer code, ARRESTOR, developed for FAA, was used to compute the aircraft stopping distances. Five aircraft parameters (mass moment of inertia, weight, wheel friction, reverse thrust, and center of gravity location) for each aircraft type are examined, along with two arrestor material types (low-density concrete and phenolic foam) and three arrestor bed geometries. Each parameter is individually varied to investigate stopping distance sensitivity. Twenty-one overrun simulations were used in the aircraft parameter study, and 100 overrun simulations were used to determine an optimal material compressive strength. Arrestor bed geometry was investigated by using 32 overrun simulations. Study results are summarized in plots and tables.